Abstract:
A shielding device includes a perforated inner sheet metal layer; an outer sheet metal layer and a hollow space delimited by the perforated inner sheet metal layer and the outer sheet metal layer. A plurality of metallic hollow bodies are provided in the hollow space, wherein the minimum diameter of the hollow bodies is greater than the perforation of the inner sheet metal layer.

Description:
[0001]    The present invention relates to a device for shielding temperature-sensitive components vis-à-vis heat sources, for example in the engine compartment of a motor vehicle, in particular vis-à-vis considerable radiated heat as a result of exhaust-carrying components. Furthermore, the device comprises a sound-deadening and sound-insulating design. In particular, the invention relates to a device that can be re-used without additional expenditure, and that can be used as encapsulation or as partial shielding. 
         [0002]    In the automotive industry, predominantly heat-shielding plates are used to carry out the task of temperature shielding. Said heat-shielding plates protect vehicle components from heat emanating from the engine, catalytic converter, muffler, exhaust train or other hot components. The components to be protected are predominantly located in the engine. compartment or in the subfloor. This includes, for example, plastic components, electronic components or fluid-carrying lines in the engine compartment, cables, the fuel tank, suspension devices of the exhaust system, and the body floor in the subfloor region. 
         [0003]    Heat-shielding plates have been used for a long time in the automotive industry. These plates can be designed as simple single-layer plates, as insulated plates, or in so-called sandwich construction. Insulated plates comprise a single-sheet carrier plate, a heat-resistant insulation layer and a cover layer. 
         [0004]    A heat-shielding plate in sandwich construction can be made from two structural plates that prior to being joined have been three-dimensionally deformed independently of each other with the use of deep-drawing techniques. In addition, an insulation layer can be placed between the two structural plates. Furthermore, heat-shielding plates can also be used as sound-insulating devices if the structural plate exposed to the sound source is perforated in the insulated region. The heat-shielding plate can thus also act as a sound absorber. 
         [0005]    Heat-shielding plates are often designed as self-supporting constructions, and among other things have to meet the following criteria: they need to keep away sufficient heat; in the case of an impact they must provide safety insulation between hot components and sensitive parts; they must withstand the vibrations experienced during the life cycle of the vehicle; and they must be economical to produce. Acoustic efficiency is an additional positive characteristic of a heat-shielding plate. 
         [0006]    Generally-speaking, a heat-shielding plate in sandwich construction, in other words a two-layer heat-shielding plate, is generally stiffer and more vibration resistant than a single-layer heat-shielding plate. However, the cost is higher, because for each structural plate a tool needs to be made, and because in principle at least three process steps are necessary in order to deform the two shells and to join them. 
         [0007]    Other heat-shielding plates merely comprise two plates joined by clinching, which plates have essentially no space between each other. The insulation property of such heat-shielding plates is not very good because no insulation material can be put in place. Furthermore, when exposed to continuous vibration loads, the connections established by toxing, clinching, spot welding or roll seam welding can become loose or even detached. Rattling noises can thus arise that are undesirable in a vehicle. Furthermore, there may be a danger of injury as a result of sharp edges. Various motor vehicle manufacturers require the use of heat-shielding plates with flanged edges, at least in those regions in which the heat-shielding plate needs to be handled by a mechanic. 
         [0008]    In heat-shielding plates in sandwich construction with an inner insulating layer between the two outer plates, for example rock wool, recycling is rendered more difficult when compared to heat-shielding plates made from a uniform material, because the insulating material needs to be separated from the material of the plates. 
         [0009]    According to a first aspect of the invention, shielding is provided comprising:
       a perforated inner sheet metal layer;   an outer sheet metal layer, wherein a hollow space delimited by the perforated inner sheet metal layer and by the outer sheet metal layer is defined; and   a plurality of metallic hollow bodies in the hollow space, wherein the minimum diameter of the hollow bodies is greater than the perforation of the inner sheet metal layer.       
 
         [0013]    In this arrangement the metallic hollow bodies are arranged as a type of bulk material comprising, for example, hollow spheres between two plates. In order to achieve favourable sound absorption with such a material construction, the inner sheet metal layer, which faces the heat source and/or sound source, comprises perforation in order to let the sound reach the open-pore structure of the hollow bodies. At this location, as a result of friction, the sound waves are then converted to heat. The outer sheet metal layer of the above-mentioned material construction is used to receive the fill comprising hollow bodies, thus circumferentially enclosing it by means of a flanged edge around the inner layer. Further connection methods include toxing, clinching, spot welding or roll seam welding. 
         [0014]    In this manner a corrosion-resistant durable component without settling behaviour in the region of the mounting points is provided, which component provides good thermal absorption and/or sound absorption. A purely metallic material construction results that can be easily recycled without any need for separating the layers. 
         [0015]    According to one embodiment the plurality of metallic hollow bodies comprises at least two different external diameters and/or at least two different wall thicknesses. 
         [0016]    With the use of hollow bodies of different external diameters the hollow space is better filled, because the spaces between larger hollow bodies can be filled by smaller hollow bodies. 
         [0017]    As an alternative or in addition to the aforesaid, the wall thickness of the hollow bodies can be varied. Walls that are less thick result in a more lightweight shielding device and improve the thermal insulation and sound absorption, but on the other hand also result in easier compressibility of the device, which compressibility may at times even be desirable. By means of walls that are less thick it is also possible to compensate for the greater rigidity of smaller hollow bodies relative to larger hollow bodies with otherwise identical wall thicknesses. 
         [0018]    By means of this embodiment, different densities that are to be adapted to a particular application can be created. A further variation option relates to the degree of filling of the hollow bodies between the two pieces of sheet metal and the option of being able to press the compound structure of layers to different overall thicknesses. By pressing the layers to different overall thicknesses it is also possible to deform individual hollow bodies so that other body geometries can also result. Furthermore, it is possible for the component in the region of attachment by screwing to be pressed to such an extent that the material no longer displays any settling behaviour in this region. 
         [0019]    According to one embodiment the outer sheet metal layer at its edge is flanged over the perforated inner sheet metal layer. 
         [0020]    This results in stable shielding and in a reduction of the risk of injury or damage to other components during installation. In particular, the edge of the perforated sheet metal layer, which edge may be sharp, is covered as a result of this. In this embodiment the use of sheet metal layers that can be produced economically but that comprise sharp edges is thus possible without the need for any reworking of the edge of the perforated sheet metal layer, without this resulting in an increased danger of injury or damage. 
         [0021]    According to one embodiment the maximum diameter of the metallic hollow bodies does not exceed ¼ of the maximum height of the hollow space. 
         [0022]    This results on the one hand in good filling of the hollow space, while on the other hand also preventing relatively short sound bridges or thermal bridges from arising, for example as is the case with hollow bodies of diameters of the height of the hollow space. In this arrangement any contact between the sheet metal layers is only across several hollow body walls. 
         [0023]    It should be noted that the maximum diameter in the case of non-spherical hollow bodies is the respective maximum external diameter of all the possible diameters. The height of the hollow space is the perpendicular space between the perforated inner and outer sheet metal layers. 
         [0024]    According to one embodiment the metallic hollow bodies are arranged loosely in the hollow space. 
         [0025]    Consequently, good thermal insulation is achieved, and furthermore the shielding remains more flexible. As an alternative, the hollow bodies can also be fixed, for example by means of suitable adhesives. It is also possible to bind the hollow bodies more firmly to each other by means of at least partial elastic deformation, for example by pressing the sheet metal layers together. A rough surface design or a corresponding coating of the hollow bodies may also be considered in order to keep the relative movements among hollow bodies at least small as a result of high friction. Coating the metallic hollow bodies can also improve the thermal insulation and/or sound absorption. 
         [0026]    According to one embodiment the metallic hollow bodies comprise high-temperature-resistant stainless steel. As an alternative other materials can also be used, wherein in this case the temperature resistance and if applicable the necessary corrosion resistance can be ensured, for example with the use of a coating process. 
         [0027]    According to one embodiment the metallic hollow bodies are essentially spherical in shape. The spherical shape represents a simple and expedient shape on the one hand to fill the hollow space well, while on the other hand to maintain the porosity required for thermal insulation and sound absorption. The spherical shape ensures good mechanical stability also of a collection of only loosely bulked hollow bodies. However, other shapes are also possible, provided an adequate degree of filling with the necessary porosity can be achieved by them, and provided mechanical stability is ensured. The hollow bodies can be closed per se or can comprise openings, for example small holes, wherein the variant without openings or holes is preferred because the outer wall of the hollow bodies is preferably porous. 
         [0028]    According to a first aspect of the invention, a machine component is provided, comprising:
       a three-dimensional section to be encapsulated; and   a plurality of metallic hollow bodies that form an encapsulation that conforms to the shape of the three-dimensional section;
 
wherein the metallic hollow bodies are sintered to each other.
       
 
         [0031]    In this component encapsulation, metallic hollow bodies in a shape matching the shape of the hot component to be encapsulated are produced as a type of envelope of the component. By means of a process of sintering the metallic hollow spheres said hollow spheres are interconnected, thus forming a self-supporting encapsulation that does not require the use of self-supporting sheet metal layers. No outer sheet metal layer is provided. By means of a structural density (porosity) of up to 97% such encapsulation that matches the application provides excellent muffling characteristics and low thermal conductivity while at the same time providing excellent sound absorption. 
         [0032]    An encapsulation produced in this manner makes it possible to achieve direct installation (without spaces) on the respective hot component and is thus more space-saving when compared to shielding that is mounted on the hot component so as to be spaced apart from said component. Such space-saving encapsulation is thus particularly advantageous in so-called downsizing engine projects with installation spaces that are becoming ever smaller. In these applications so-called compact exhaust gas systems in which all the functional units or components of an exhaust gas system are bundled without connecting pipes can be shielded. 
         [0033]    According to one embodiment the plurality of metallic hollow bodies comprises at least two different external diameters and/or at least two different wall thicknesses. 
         [0034]    According to one embodiment the maximum diameter of the metallic hollow bodies does not exceed ¼ of the maximum height of the encapsulation. According to the requirements and the component thickness, the diameter of the hollow bodies is selected so as to be between 1.5 mm and 10 mm. 
         [0035]    Half-shells can preferably be sintered separately as 3-D shells without a hot component in the tool. In this process, two half-shells are then mounted around the hot component as an enclosed encapsulation. 
         [0036]    According to one embodiment the machine component comprises an outer enclosure of the encapsulation in the form of a sheet metal layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0037]      FIG. 1  shows a cross section of an embodiment of a heat-shielding plate according to the invention; and 
           [0038]      FIG. 2  shows a cross section of an embodiment of an encapsulation according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]      FIG. 1  shows a cross section of a heat-shielding plate according to a first embodiment of the invention. In this embodiment the heat-shielding plate is used to shield a hot component  1  that emits heat in the form of radiation heat. The heat-shielding plate comprises an inner sheet metal layer  3  with through-holes  2  that form perforations. An outer sheet metal layer  4  is flanged around the perforated sheet metal layer  2  in such a manner that in-between a hollow space is defined. According to the invention this hollow space is filled with metallic hollow bodies  5  that in the example shown comprise, for example, a spherical or elliptical shape. 
         [0040]    As a result of the high percentage of gas or air in the hollow bodies  5  themselves and in the spaces between said hollow bodies  5 , the plurality of hollow bodies  5  provides low thermal conductivity or good insulation characteristics while at the same time providing a low overall weight of the heat-shielding plate. The thinnest possible wall thicknesses of the hollow bodies  5  are preferred, on the one hand to keep the weight to a minimum, and on the other hand to keep the formation of thermal bridges to a minimum. 
         [0041]    As a result of the spaces remaining between the hollow bodies  5 , furthermore, good sound absorption results. As a result of the holes  3  in the inner sheet metal layer  2 , sound waves emanating from the component  1  can enter the hollow space comprising the hollow bodies  5 . As a result of friction in the air-filled spaces, in that location the energy of the sound waves is converted to heat and is thus absorbed. 
         [0042]    The hollow bodies  5  can be filled in the heat-shielding plate essentially in the form of loose bulk fill, i.e. without being interconnected by means of bonding, welding or similar. It is possible to achieve relative firm cohesion by compressing the inner and outer sheet metal layers, and consequently the hollow space is compressed in height, and the hollow bodies  5  are pressed against each other. In this process at least partial plastic deformation of the hollow bodies  5  can be desirable. 
         [0043]    Preferably, the plurality of hollow bodies  5  comprises at least two different diameters. In this manner a greater degree of filling of the hollow space is achieved. Furthermore, in this manner the effective surface area can be increased in order to absorb heat. An essentially circular or elliptical shape of the hollow bodies  5  is preferred in order to be able to keep the surface of the contact points between hollow bodies or between hollow bodies and sheet metal layers to a minimum. In this manner the insulation effect is improved because the heat is impeded in its ability to penetrate the shielding plate in the direction of the outer sheet metal layer  4 . Furthermore, in this manner the transmission of vibrations and sound to the outer sheet metal layer  4  is impeded. 
         [0044]      FIG. 2  shows a cross-sectional view of an encapsulation according to a further embodiment of the invention. In this embodiment a component  10 , for example part of an exhaust gas system, is encapsulated. Encapsulation comprises a plurality of hollow bodies  15  and has been placed without a space or clearance onto the component to be encapsulated. In contrast to the loose bulk fill of hollow bodies  5  from  FIG. 1 , the hollow bodies  15  are interconnected by means of sintering. In this manner a rigid self-supporting structure is formed that conforms to the three-dimensional shape of the component  10 , which shape can also be very complex. Consequently, in terms of thermal insulation, weight and sound absorption similar advantages are achieved as is the case with the shielding plate of  FIG. 1 , wherein if applicable the thickness of the encapsulation could be increased in order to compensate for diminished shielding. Encapsulation is associated with an advantage in that the heat is kept in the hot component and is transmitted onwards in order to achieve a faster rise in the temperature of the exhaust gas pipe during the cold start phase. This also contributes to reducing CO 2  emissions and prolongs the service life of the engine. Furthermore, the exhaust gas energy is increased, e.g. for heating various systems (catalytic converter). Electricity generation would also be imaginable.