Patent Application
20090029139
The invention relates to a heat shield for shielding an object against heat and/or noise, which has two metal layers directly adjacent to one another.
Heat shields of this type are used as noise and/or heat protectors for other components. Heat shields are used, for example, in engine compartments of motor vehicles, in particular in the area of the exhaust system, to protect adjacent temperature-sensitive components and assemblies from excessive heating. The heat shields are often used simultaneously as a noise absorber.
To be able to absorb noise and shield heat to a sufficient extent, heat shields of this type frequently have an at least three-layered structure. The two cover layers typically comprise metal, in particular steel, aluminum-plated steel, or aluminum (alloy). A nonmetallic insulation layer is embedded between the cover layers. It comprises, for example, mica or vermiculite, temperature-resistant cardboard, inorganic or organic fiber composite materials, or other suitable insulation materials such as fabrics, knitted fabrics, and/or warp knitted fabrics made of temperature-resistant fibers.
The nonmetallic inlays cause increased effort in regard to the recycling of the heat shields and are therefore often undesirable.
There is therefore a need for an entirely metallic recyclable heat shield, which, at the lowest possible weight and without fiber inlay and/or without porous absorber, is nonetheless as stable as possible and offers good noise and heat protection.
The object of the invention is accordingly to specify a heat shield which does not have the above disadvantages and is producible simply.
The invention thus relates to a heat shield for shielding an object against heat and for absorbing noise, which comprises two metal layers situated directly adjacent to one another. A first of the metal layers has at least one perforated area, and the second of the metal layers is provided with at least one partial area having protrusions pointing in the direction of the first metal layer, whose apices press against the first metal layer.
The invention is explained in greater detail hereafter on the basis of drawings. These drawings are used exclusively to illustrate preferred exemplary embodiments of the invention, without the invention being restricted thereto. Identical parts are provided with identical reference numerals in the drawings.
In the schematic figures:
Besides the two metal layers, the heat shield according to the invention has no further layers, in particular no nonmetallic insulation layer. Surprisingly, it has been established that such an insulation layer is not required at all for good noise and heat absorption if the two metal layers are implemented and oriented to one another in the way described. The first metal layer provided with the perforated area is situated toward the noise source and, through its perforation, allows noise not to be reflected, but rather be able to reach the interior of the heat shield and be absorbed therein. The resonance chambers formed between the protrusions of the second metal layer are used for setting the frequencies to be absorbed. The air cushion in the interior of the heat shield simultaneously forms an outstanding insulation layer against heat.
To ensure the best and most complete possible noise absorption, the perforated area preferably extends over the entire area of the first metal layer. The flow resistance with which noise may penetrate into the interior of the heat shield, and thus the absorption, may be set in a targeted manner via the design of the perforated area. The number, size, and shape of the holes and their distribution in the perforated area may be varied. If the entire first metal layer is not perforated, multiple perforated areas may also be distributed over the first metal layer, the design of the holes—except for a variation within each area—being able to differ from area to area. Perforated areas are expediently situated above all where high noise incidence is to be expected. Non-perforated or only slightly perforated areas may be provided where especially strong three-dimensional deformations of the heat shield are required for the overall shape of the heat shield and otherwise cracking would be a concern due to the weakening of the first metal layer because of the perforation.
In principle, the shape of the holes is arbitrary. Polygonal or rounded external contours and symmetrical or asymmetrical shapes are possible. Circular holes are preferred in regard to simple production. The diameter of the holes typically lies in a range from 0.05 mm to 3 mm, in particular from 0.08 mm to 1 mm. For asymmetrical holes, the largest diameter of the hole is used as the diameter. In general, the perforated area will contain 1 to 200 and in particular 3 to 100 holes per square centimeter. The area occupied by the holes is preferably between 0.1% and 20%, in particular between 0.2% and 10% of the total area of the first metal layer. The perforated metal layer is preferably smooth. If the perforation is generated using piercing or laser cutting, however, an additional surface structure may arise, in which the immediate surroundings of the particular holes may be shaped out of the plane of the metal layer. The structures arising in this way are an immediate continuation of the hole course transversely through the particular sheet. Intentional and/or targeted production of embossments on the perforated metal layer does not occur, however.
It is especially preferable if the implementation of the at least one perforated area, both in regard to its location and also the design of the perforation, is adapted to the implementation of the second metal layer. The adaptation is performed in particular in regard to optimized noise and heat absorption by the two-layer heat shield. The design of the resonance chamber, which lies behind the at least one perforated area of the first metal layer viewed from the noise source, bears special significance. The size and shape of the resonance chamber enclosed between first and second metal layers is important above all. It is designed in such a way that the noise oscillates in the perforation of the first metal layer and more or less “dies out” in the spring volume standing on this resonance chamber. The resonance chambers are used simultaneously as an insulation layer against heat, the heat source fundamentally being able to be located on either the side of the first or the second metal layer. The second metal layer is used as a noise and heat barrier and does not have any openings at least in those areas which are opposite to the perforated areas. The second metal layer is preferably entirely free of perforations except for those openings which are used for the passage of fasteners or components such as probes or the like. These openings—which are also significantly larger than the microperforations of the first metal layer—pass through both metal layers as a whole, however, and the metal layers are typically sealed to one another in the area around these openings, so that noise and heat may not penetrate to the outside unobstructed here.
According to the invention, the resonance chambers between the first and second metal layers of the heat shield are generated in that protrusions are shaped into the second metal layer. 10 to 100%, but preferably approximately 45 to 55% of the protrusions point in the direction toward the first metal layer, against which the apices of the protrusions press. The resonance chambers, whose configuration, size, and shape is a function of the location, size, and shape of the protrusions, arise around the protrusions.
The protrusions are typically shaped into a planar blank of the second metal layer which has not yet been three-dimensionally deformed, by embossing, for example. The second metal layer is subsequently connected to the first metal layer, which is also not yet three-dimensionally deformed. The connection between both metal layers may be performed in ways typical per se, for example, in that the edge of one metal layer is flanged at least sectionally around the edge of the other. Subsequently, both metal layers are jointly deformed three-dimensionally into the final shape of the heat shield. The shape and the volume of the resonance chambers located between both layers may alter during this deformation. These alterations are to be considered beforehand in the design of the protrusions, so that the resonance chambers in the finished heat shield have the desired form. In specific applications, it may be advisable to connect the two metal layers to one another not only at their edges, but rather also in the area of their surfaces, so that the metal layers do not unintentionally move away from one another during the deformation. For this purpose, for example, spot welds may be placed in critical areas to connect both metal layers. However, this is not preferable due to the additional effort.
The shape and size of the protrusions is selected in consideration of the above aspects. In addition, the intended three-dimensional deformation of the heat shield plays a further role in the design of the protrusions. The protrusions are expediently placed in such a way that they do not obstruct the desired shaping. Except for this, the shape of the protrusions may be selected freely and is not especially restricted. For example, the protrusions may have the shape of round or oval embossments which at least sectionally laterally delimit the resonance chambers. It is not fundamentally necessary for the resonance chambers to be completely separated from one another. Rather, they may also pass into one another and be largely open to one another. In a preferred embodiment of the invention, for example, the protrusions are implemented as embossments. Resonance chambers which are largely open to one another result between the first and second metal layers, similar to a column-supported vault.
The volume between first and second metal layers is preferably primarily predefined via the height of the protrusions and especially the embossments. The height may be and is generally varied over the area of the first and second metal layers. The cross-section of the embossments may also vary within an embossment and/or from embossment to embossment. The embossments preferably have a round or oval cross-section. For oval shapes, the maximum cross-section is not to be more than three times, preferably not more than twice, especially preferably not more than 1.5 times the maximum extension in the direction perpendicular thereto. For example, the following dimensions may be mentioned for the embossments: a diameter of 2 mm to 20 mm, in particular 3 mm to 8 mm, and a height of 1 mm to 20 mm, in particular 1.5 mm to 6 mm. The diameter is determined as the maximum diameter between the base points of the embossment. Base points are those points at which the slope of the embossment flanks passes through zero or its sign changes. The height of the embossments is measured as the maximum height between a base point and the embossment apex point or the embossment apex face.
Like the holes in the first metal layer, the distribution of the embossments over the area of the second metal layer may also change. 1 to 10, in particular 1 to 5 embossments are typically provided per square centimeter of the second metal layer. At least one of the two layers, but preferably both, does not have a pattern relationship in relation to the entire heat shield in regard to its embossments and/or holes. It may also be advantageous if the configuration of the embossments changes independently of the configuration of the holes in the adjacent layer. By targeted variation of dimensions and/or distribution of holes and/or embossments over the area occupied thereby and adaptation of these features to one another, a heat shield may be obtained which displays outstanding noise damping and heat protection effects, although it only comprises two layers and does not have a nonmetallic insulation layer.
The materials typical up to this point in the prior art may be used as materials for the metallic layers. For example, they comprise steel, aluminum-plated steel, or aluminum (alloys). Hot-dip aluminized steel is especially widely distributed. Stainless steels are preferred for fields of use having a high risk of corrosion and increased temperature strain, nickel-rich steels for high temperature applications. Aluminum-plated steel has special reflection properties. Because of the lack of the insulation layer, the two metallic layers may be formed comparatively thick, if the same thickness as for a three-layer heat shield is to be achieved. The danger of cracking during the three-dimensional deformation is thus reduced. Vice versa, in comparison to a three-layer heat shield, the total thickness of the heat shield or at least its weight may be reduced while maintaining the thickness of the metal layers. The metal layers of the heat shield typically have a thickness of 0.15 to 0.6 mm, preferably 0.25 to 0.4 mm. It is a function of the particular application whether equal sheet thicknesses or different sheet thicknesses are selected for both layers. The individual sheet thicknesses are selected as a function of the elasticity required for the three-dimensional deformation and the rigidity required for the deformed component in such a way that cracking is avoided in the finished part under usage conditions, but the most regular and reproducible possible pleating is made possible. The processing is performed in the way typical up to this point using tools typical up to this point. The protrusions are expediently embossed, the holes are preferably needled or stamped.
The heat shield according to the invention is typically used in the area of the internal combustion engine and exhaust system in motor vehicles. The heat shield may be used for shielding the exhaust manifold, the turbocharger, and add-on parts such as catalytic converter, precatalytic converter, particulate filter, or other components.
To be able to absorb the noise of a noise source situated in front of the heat shield 1 in the direction toward the observer, such as an exhaust pipe, the first metal layer 2 facing toward the noise source has a perforated area 4. In the case shown, holes 7 are provided distributed essentially uniformly over the entire area of the metal layer 2. The entering noise is absorbed by the holes 7 of the heat shield. The cavity 9, which forms a resonance chamber for absorbing the noise, is obtained in that a plurality of protrusions 5 is embossed in the second metal layer 3, which comprises a metal sheet which is not provided with holes (except for the fastener openings 8). The protrusions 5 have the shape of round embossments here. The circles only indicate the location of the embossments 5, but not their precise size. The embossments 5 were already embossed in a planar blank of the metal layer 3 before the three-dimensional deformation of the heat shield 1 into its final saddle-like shape. In the example shown, the embossments 5 all have identical sizes and shapes and are distributed essentially uniformly over the area of the metal layer 3. Only in the area of the outside edges of the heat shield 1, directly adjoining the fastener openings 8, and in the areas which are three-dimensionally deformed especially strongly (indicated in
The apices 6 of the embossments 5 point in the direction toward the first metal layer 2 and press against it. If necessary, both metal layers 2 and 3 may be fastened to one another at individual points over their surface. This is advisable above all in those areas which are three-dimensionally deformed especially strongly and in which the danger exists that the metal layers 2 and 3 will move away from one another upon deformation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07014702.0 | Jul 2007 | EP | regional |
