The invention relates to an acoustically effective heat shield, particularly for motor vehicles, having at least two metal foils, preferably made from aluminium, each of which has a plurality of knob-like embossed points, wherein at least one of the metal foils is perforated.
A sound absorbing heat shield that is made from at least two aluminium foils bonded with one another, and of which at least one foil has a plurality of knobs and fissures is known from European Patent No. EP 1 149 233 B1. The fissures are created by exceeding the elasticity threshold of the aluminium foil when the knobs are embossed, so that fissures are formed. To bond the aluminium foils to one another, the edges thereof are cold welded together. However, the structural strength of this foil bond would seem to warrant improvement, since it is suggested in European Patent No. EP 1 149 233 B1to supplement the foil bond with a supporting metal sheet.
A heat shield is also known from German Patent application No. DE 198 25 762 A1that includes a three-dimensional press-formed, multilayer metal foil structure. The heat shield is made from at least three superimposed aluminium foils. At(least two of the aluminium foils have a thickness of no more than 0.15 mm. The aluminium foils have a plurality of knob-like embossments to ensure that a space remains between superimposed aluminium foils. This heat shield is intended for use as an acoustic screen as well. However, its sound absorption capability is rather unsatisfactory.
The object underlying the present invention is to produce a heat shield for use in high-temperature zones of motor vehicles that possesses improved sound absorption capabilities and that has high structural strength even without the use of a supporting metal sheet.
This object is solved by a heat shield having the features of claim 1 as well as by a heat shield having the features of claim 7.
The heat shield according to the invention is constructed from at least two metal foils, preferably aluminium foils, each of which has a plurality of knob-like embossed points, wherein at least one of the metal foils is perforated. The perforated metal foil has a plurality of holes that have an average hole diameter in the range from 0.05 to 0.9 mm. The holes are formed in the metal foil in a density of at least 15 holes per cm2, the perforated metal foil being provided on one side, preferably over the entire surface thereof, with an adhesive layer that is activated above 120° C., and which is correspondingly perforated. The metal foils, which have a thickness in a range from 50 to 200 μm, form a self-supporting composite.
This self-supporting composite can be formed particularly from not more than three adhesive coated metal foils.
In an equally advantageous variant, it is provided that at least one layer made from sound absorbing material is arranged between at least two of the metal foils, wherein said layer forms a self-supporting composite with the metal foils.
The invention provides a heat shield for high-temperature zones of a motor vehicle that demonstrates significantly improved sound absorption capability compared with conventional motor vehicle heat shields. Even without the otherwise standard use of a supporting metal sheet, the heat shield according to the invention has high structural strength.
Further preferred and advantageous embodiments of the heat shield according to the invention are described in the subordinate claims.
In the following, the invention will be explained in greater detail with reference to drawing showing several embodiments thereof. In the drawing:
The microperforation in the metal foils is made up of a plurality of holes having an average hole diameter in the range from 0.05 to 0.9 mm. The holes are arranged in a density of at least 15 holes per cm2 in the metal foil. The hole density is preferably at least 20 holes per cm2.
The perforation of the metal foil coated with the adhesive layer is performed from the uncoated side of the metal foil, so that the shoulder of material surrounding each of the recess craters, raised away from the metal foil, is on the side of the adhesive layer.
The three metal foils are arranged in such manner that two metal foils each are bonded together by material means by at least one adhesive layer 4, 5 or 6. At least one of the two outer sides of the heat shield, preferably both outer sides, are not provided with an adhesive layer. The thickness of adhesive layer 4, 5, 6 is approx. 20 to 30 μm, so that the total thickness of the metal foil coated with the adhesive layer is for example 110 to 120 μm. After hardening, adhesive layer 4, 5, 6 may be exposed to high temperatures. It is preferably made from polyester adhesive and/or polyurethane adhesive.
The metal foils are embossed and each have a plurality of knob-like embossed points 7, 8. In the embodiment shown in
Embossed points or knobs 7, 8 have several functions. Firstly, they serve as spacing elements to create an air gap 9, 10 between two adjacent metal foils. Air gap 9, 10 in particular has a heat insulating effect. Secondly, embossed points or knobs 7, 8 serve to increase the surface of the respective metal film, which is advantageous for the purposes of the desired sound absorption. At moderately high sound frequencies, air gap 9 or 10 between the metal foils functions as the elastic spring in an acoustical spring-mass system. The sound absorbing effect of the heat shield is also enhanced by the microperforation of its metal foils. Noise is damped particularly via the effects of friction in the small holes in the metal foils. Thirdly embossed points or knobs 7, 8 increase the flexural rigidity and thus also the structural strength of the metal foil. The flexural stiffness of the metal foil and thus also the structural strength of the heat shield is particularly increased by the respective adhesive layer 4, 5, 6.
The microperforated metal foil or foils are embossed via at least one pair of embossing rollers (not shown), which has a plurality of knob-shaped embossing elevations on the mantle surface thereof. These embossing elevations are preferably arranged in a grid on the mantle surfaces of the embossing rollers, the distance between two embossing elevations on the respective roller being selected such that an embossing elevation can be immersed in the corresponding gap (clearance) on the paired counter roller without allowing the embossing elevations on the embossing rollers to come into contact with each other. The width of the die gap between the paired embossing rollers is selected such that the tips of the embossing elevations on the one embossing roller do not touch the roller surface of the respective counter roller. In this way, it is assured that the paired embossing rollers do not come into contact with each other and the small holes of the microperforation created previously in the metal foil are not compressed and closed up again when the embossed points or knobs 7, 8 are produced.
In the embodiment shown in
In order to ensure that the embossed points of the respective metal foil do not engage the corresponding embossed points in the adjacent metal foil, which would prevent the formation of the desired air gap 9 or 10 between the immediately adjacent metal foils, according to a variant of the heat shield according to the invention that is not shown, two neighbouring metal foils may have a differing embossing pattern, in such manner that the one metal foil has a different embossing pattern than the other metal foil. In particular, to neighbouring metal foils may be differently embossed so that at least some of the knob-like embossed points in the one metal foil each have a larger diameter than the knob-like embossed points in the other metal foil.
In the following, the production of a heat shield according to the invention will be explained with reference to FIGS. 3 to 5.
Three plies 1, 2, 3 of microperforated, embossed aluminium foil, which is provided on one side with a layer of thermally activatable adhesive, or two plies 1, 3 of a similar aluminium foil and an intermediate ply 2′ of fine-pored, sound absorbing material are unrolled from a supply rolls. Aluminium foils 1, 2, 3 or 1, 3 and intermediate ply 2′ of fine-pored, sound absorbing material where appropriate are fed to the material transport device and clamped at the edges between the endless chains of endless belts and/or are affixed to the edges thereof by fixing means (not shown).
A preheating and laminating station 15 is assigned to a first section of the material transport device, and is equipped with heating devices 16, 17, for example in the form of radiant heaters arranged above and below the endless conveyor. In preheating and laminating station 15, the heat-activated adhesive layer of the respective aluminium foils 1, 2, 3, or 1, 3, and where applicable hotmelt adhesive fibres contained in intermediate ply 2′ are activated or melted, with the result that the three plies 1, 2, 3 or 1, 2′, 3 are bonded together by material means.
Preheating and laminating station 15 is arranged downstream of a crosscutting device 18, which makes pre-cut parts adapted as far as possible to the dimensions of the heat shield to be manufactured from the supplied material strips. Several forming tools that are movable towards and away from each other, and which include at least a first forming tool 19 for forming a three-dimensionally shaped heat shield and at least a second forming tool 20 for trimming the edges of the heat shield and for producing fixing holes by corresponding punching are arranged after the preheating and laminating station 15 in the direction of feed. In addition, a further forming tool 21 is preferably provided to flange the edge of the heat shield. The flanging results in a smooth edge of the heat shield. Sharp edges that are likely to cause injury are thus avoided. In addition, the flanged edge increases the flexural stiffness of the heat shield.
The forming tools 19, 20., 21 that are shown schematically in
A protrusion 25 is conformed on each upper tool 22 and effects a relatively strong embossment of a partial area of the heat shield. The knob-like embossed points in the metal or aluminium foils are pressed flat in this partial area, which is used for the provision of a fixing hole or fixing member. After embossing, the metal or aluminium foils in this partial area are pressed flush against one another or flush against intermediate ply 2′ of fine-pored, sound absorbing material with no space.
Outer peripheral area 26, 27 of the cavity defined by upper tool 22 and lower tool 23 is conformed such that here the edge of the heat shield is either punched out (shown at right in
The use and configuration of the heat shield according to the invention is not limited to its installation in the area of the exhaust system. In particular, the heat shield may also be arranged on a dash panel separating the engine compartment from the passenger cabin and may be shaped in a manner corresponding to the dash panel area to be covered.
Number | Date | Country | Kind |
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203 19 319.9 | Dec 2003 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP04/12345 | 10/30/2004 | WO | 4/5/2006 |