| Catalyst body and an exhaust system for a small-size engine and a method for producing the catalyst body -> Monitor Keywords |
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Catalyst body and an exhaust system for a small-size engine and a method for producing the catalyst bodyRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust Gas, By Means Producing A Chemical Reaction Of A Component Of The Exhaust GasCatalyst body and an exhaust system for a small-size engine and a method for producing the catalyst body description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070113540, Catalyst body and an exhaust system for a small-size engine and a method for producing the catalyst body. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] A catalyst body and an exhaust system for a small-size engine and a method for producing the catalyst body [0002] The invention relates to an annular catalyst body that can be flowed through in a radial manner for installation in a muffler housing, an exhaust system for a small-size engine and a method for producing the catalyst body. [0003] Such small-size engines are used for example in lawnmowers, motor saws, pistol-grip cross-cut saws, power units and in bikes. As a result of increasing awareness for environmental issues, a demand has developed to continually improve exhaust gas cleaning and sound muffling of small-size engines. The increasingly stricter emission regulations demand that components are adjusted continually to changing requirements. [0004] It is known in the exhaust gas treatment in such devices to use catalyst bodies of radial or axial configuration for reducing the pollutants contained in the exhaust gas. The terms of radial and axial shall be understood as the direction of main flow of the exhaust gas in which it flows through the catalyst body. It is further known to provide such catalyst bodies in the form of hollow cylinders. This shape is obtained as a result of production, as a result of flow configuration or as a result of the type of fastening. Especially annular catalyst bodies are used in practice. Such annular bodies currently mostly consist of pressed woven metal wire cloth or bent metal wire cloth. It has been noticed in practical application however that such wire structures have a low mechanical stability, and upsetting and bulging can occur especially when used in a muffler housing as a result of the stresses caused by oscillations and the flow and the elasticity of the wire structure. Additional loads on the catalyst body occur in the case of a catalyst body fixed under pre-tension in the muffler housing. As a result of the elastic and plastic deformations of individual wires and the entire ring body, the catalytic active coating and the washcoat will detach, thus reducing the performance of the catalyst and reducing the efficiency of pollutant reduction. Individual wires may also rub against each other, thus leading to the coating of the wires crumbling away or cracking off. When wire cloth is used, bending and bulging will occur even in the case that the wires are soldered together. Moreover, closed ring structures consisting of wire require a high amount of effort in production. The transport of such prefabricated annular bodies proves to be expensive because a large amount of space is required as a result of the inner cavity. [0005] A muffler unit is built into the muffler housing in addition to the catalyst body as a further component in known exhaust systems of small-size appliances. The muffler unit usually consists of a so-called reflection body. The exhaust gas is introduced into the pipe and the openings situated in the pipe cause a refraction of sound and thus a reduction in noise. Concerning the arrangement of catalyst body and muffler unit, it is common practice to switch them in series, which means that the exhaust gas, after entering the muffler housing, is supplied first to the reflection body and thereafter flows through the catalyst body in an axial or radial manner. When a radial catalyst is used, the same is often arranged about the reflection body coaxially to and spaced from the same. This requires an adjustment of the geometric dimensions of the components to be arranged, a plurality of means for fastening the components and a time-consuming assembly. Moreover, the catalyst bodies and muffler units cannot be used in all types of exhaust systems of a small-size engine as a replacement for used components. [0006] The invention is thus based on the object of providing an annular catalyst body which can be flowed through in a radial manner, is easy to produce, requires little space in transport and simultaneously fulfils the requirements concerning the catalytic effect and sufficient stability, so that it remains dimensionally stable during the use in an exhaust system. It is a further object of the invention to provide an exhaust system which offers a lower complexity in assembly and also offers an improved exchangeability of the components. It is also an object of the present invention to provide a method for producing the catalyst body with which a timely and cost-effective production is possible. [0007] The object is achieved for an annular catalyst body which can be flowed through in a radial manner in such a way that it consists of a perforated metal foil. A catalyst body with high mechanical stability is thus created which is also easy to produce in a cost-effective manner. Moreover, the metal foil has a low volume prior to mounting and can thus be transported in a compact manner. The stability of the metal foil also contributes to the fact that consumed catalytic coatings will hold permanently. [0008] The perforations of the perforated metal foil are adjusted in a preferred embodiment for sound reduction in such a way that the metal foil simultaneously fulfils the function of a conventional reflection body. The metal foil which is adjusted for sound reduction as a replacement for a conventional muffling unit also comprises favorable stability properties in addition to the catalytic effect. Because the perforations are adjusted for reduction of pollutants and sound, the reflection body can be omitted, as a result of which one component of the exhaust system can be omitted. [0009] The term "metal foil" shall be understood as any metallic layer which is configured in such a way that the intended perforations can be introduced and the same can be shaped into a ring. The term "metal foil" shall also include sheet metal. All these materials can also be provided with a catalytic coating. A strip of a certain dimension is obtained from metallic base material and is brought into the form of a closed circle. [0010] The term "perforation" relating to the invention shall designate any type of opening in the metal foil. It can have a round, angular, circular, elliptic, slotted and further linear or non-linear shapes and can be introduced in the known manner into the metal foil. [0011] The thickness of the metal foil can be adjusted according to the requirements concerning pollutant treatment, noise reduction and the stresses resulting from the gas pressure and the fastening in the muffler housing. [0012] The metal foil in accordance with the invention provides a catalyst body which is easy to produce and can also be used as a replacement for a conventional reflection body and also allows easy handling during mounting. The metal foil, which is plane at first, enables easy transport with little need for space. Sufficient stability for use in a muffler housing is achieved after the final shaping into a closed circle. [0013] A further preferred embodiment is that webs are arranged between the perforations for stiffening the metal foil. They are adapted in such a way that they prevent any bulging of the metal foil in the built-in state. These connecting webs or material bridges are thus obtained in combination with the arrangement of the perforations and are directly dependent upon the same. The dimensions and thicknesses of the webs are dimensioned in such a way that they can permanently withstand all stresses occurring after the installation in the muffler housing, i.e. both in the idle state as well as in operation of the device. Such webs ensure the dimensional stability of the catalyst body. In a further preferred embodiment this is achieved in such a way that the webs are aligned according to the forces acting upon the catalyst body. Pressure forces usually occur in the direction of the longitudinal axis of the annular catalyst body, especially when the same is fastened in the muffler housing by being subjected to a pre-tension, whereas tensile forces can occur perpendicular to the same. The webs can also extend in an oblique manner over the circumference of the annular catalyst body. The thus formed grating-like bracing stabilizes the catalyst body and prevents squashing or barrel-like bulging. In a further appropriate embodiment, the webs are aligned coaxially to the longitudinal axis and/or in the circumferential direction of the catalyst body. Optimal bracing is achieved especially in the case of directions of the webs standing perpendicular with respect to each other. [0014] Certain requirements placed on the thickness of the metal foil will arise from the aforementioned requirements concerning the occurring loads and with respect to exhaust gas treatment and assembly. 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 inside hollow cross section of the ring or according to the desired inside diameter in the case of circular configuration. It should be chosen on the one hand in such a way that the metal foil is still sufficiently pliant so as to form the circular shape on the one hand and also still has a sufficient dimensional stability on the other hand. The metal foil should further be configured in a heat-resistant manner and can comprise shares of chromium or aluminum for example for this purpose. [0015] The metal foil is appropriately provided with a helical, star-like, trapezoid or wave-like shape for optimizing the catalytic and/or muffling effect. Such shapes can be punched into the originally planar metal foil by means of the respective tools. The eddies formed on the leading edges increase the contact of the exhaust gas with the catalytic layer and contribute to the refraction of sound. [0016] For simplifying the assembly and reducing the apparatuses necessary for this purpose, it is provided for in a further embodiment of the invention that the ends of the metal foil are joined with a detachable interlocking connection. It is advantageous in this respect when the ends of the metal foil are provided with a hook-like configuration and can thus be brought into engagement with a few manipulations. The ends of the metal foil can be bent over in opposite directions for forming the hooks. [0017] It is also appropriate as a detachable interlocking connection that the one end of the metal foil comprises a recess and the other end of the metal foil comprises a counterpart for the engagement in the recess. The counterpart can have a larger extension than the recess once it has been introduced into the recess and is in engagement with the same, so that the connection is no longer able to detach or open by itself. Especially in the case of a configuration of the ends of the metal foil with a recess or a counterpart, they can be easily integrated in the same during the punching or cutting of the metal strip. The recess and the counterpart can have a shape of any linear or non-linear type which are adjusted to each other, e.g. they can have rectangular, oval or bent shapes. The said interlocking connections can also be secured by joining measures if necessary, such that one or several spot welds are made in the corner regions of the one end for permanent fixing with the other end of the metal foil. [0018] Concerning the configuration of the perforations, they are formed in a further preferred embodiment by bending away the metal foil. At least a part of the contour outline of the later perforation is predetermined at first by punching or cutting on the metal foil which is plane at first. Thereafter the material of the perforation to be produced at the respective location is bent away in such a way that the bent portion of the metal foil still has a connection with the metal foil or the adjacent web. The bending away can occur in different directions. For the purpose of forming the spacers simultaneously, the bending away occurs in one direction, e.g. to the outside. As an alternative it is possible to produce the perforations also in such a way that the material still present at the location is fully removed by punching for example. A symmetrical pattern in the form of rows with or without offset extending parallel in the circumferential direction of the ring is chosen with respect to the arrangement pattern of the perforations. An asymmetric or irregular distribution of the perforations is also possible. [0019] The object in accordance with the invention is achieved for an exhaust system in such a way that the catalyst body consists of a perforated metal foil. The catalyst body can thus be produced more easily and cost-effectively and can be installed better in the exhaust system. [0020] In a preferred embodiment the catalyst body consists of a perforated metal foil, with the perforations of the perforated metal foil being adjusted for sound reduction in such a way that the metal foil simultaneously assumes the function of a conventional muffling unit. The number of components for exhaust treatment thus required in an exhaust system of a small-size engine is reduced. This leads to a reduction of the production costs and the required assembly work and to a better exchangeability of the components. Reference is hereby also made to the information provided with respect to the first mentioned solution for configuring the catalyst body in accordance with the invention. [0021] Preferably, the catalyst body is arranged coaxially to the inflow direction of the exhaust gas into the muffler housing about an inlet of the muffler housing. Suitable flow conditions are created within the muffler housing and especially with respect to the radial flow against the metal foil from the inside, thus leading to favorable results with respect to silencing and pollutant reduction. [0022] In a further preferred embodiment of the invention, the catalyst body is tensioned with a pretension against the muffler housing. For fixing the position of the catalyst body before and after bracing, embossed portions shaped according to the ends of the catalyst body are provided in the respective parts of the muffler housing and/or additional parts such as holding rings or holding plates. The fastening means used for bracing such as screws for example can be used at the same time to fasten the muffler housing on or close to the small-size engine or on the respective device. By bracing the catalyst body between the housing parts or additional parts of the muffler housing, complex fastening measures within the muffler housing can be avoided. [0023] The object in accordance with the invention is achieved for the production of the catalyst body in accordance with the invention in such a way that the catalyst body is bent in a ring-like manner from a perforated metal foil strip and the ends of the strip are joined by means of an interlocking connection. [0024] In a preferred production method, the perforated metal foil strip is cut prior to this from a continuous product, punched or broken from previously applied perforation points. The production from a continuous product also allows a continuous coating process and especially considerable cost savings. The foils or strips of sheet metal can also be produced individual in sections. Continue reading about Catalyst body and an exhaust system for a small-size engine and a method for producing the catalyst body... 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