Abstract:
A sound-absorbing cellular component is produced in multiple-chamber array, using a grid of spaced elongate rods, and by engaging to the rods of said grid a foil of deformable sheet material which is then drawn by deformation through spaces between rods, to thereby define adjacent partition walls of adjacent chambers. Various embodiments are described, involving retention and/or removal of the rods, and/or involving application of one or more insulating or finishing materials continuously over outwardly facing bottoms of the chambers of the array.

Description:
This application is a continuation of Ser. No. PCT/EP97/03540 filed Jul. 4, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a process for the production of a sound absorbent component as well as to a sound absorbent component wherein chambers present thin side walls and form acoustic resonators. 
     In the known process (DE-A-195 29 440), a foil is deformed to have cup or chamber-like cavities in such manner that there remain spacings between the side walls of adjacent chambers. 
     In another &#34;sound absorber&#34;, it has already been known (EP O 683 480 A1) to form cylinder-shaped, cup-like cavities in a deep-drawing process from a foil and to cover them with a liquid-tight cover layer on the open side facing the incident sound so that no foreign matter nor impurities may accumulate in the resonator chambers. It is also known to form the chambers from flexible tubes being attached to the underside of such a carrier layer. Such sound absorbers have proven their functional worth, however, the production thereof is relatively expensive. 
     Moreover, it is also known (DE 43 34 984 C1, DE-U 69 48 849 and EP O 214 559 A3) to line chambers formed of plastic foam with thin foils in order to protect the porous chamber side walls from impurities. Production is relatively expensive in this case too. 
     BRIEF STATEMENT OF THE INVENTION 
     It is the object underlying the invention to produce sound-absorbing components of this type even more easily and nevertheless provide for a good sound-absorbing or, respectively, sound-damping effect. 
     In contrast to the above-cited prior art, the thin side walls of adjacent chambers are not disposed at a larger spacing from each other, but they are, in accordance with the invention, placed closely next to each other or preferably integrated to form a partition respectively assigned to more than one chamber. Therefore the chambers form a compartment-like chamber system together with the partitions wherein the chambers forming kind of a duct are delimited from each other by the respective partitions only, i.e., they extend immediately next to each other. 
     According to a special configuration of the invention, the chambers are disposed adjacent to and behind each other such that they form sort of a honeycomb system in the chamber plane although the respective chamber cross-section is, unlike for bee honeycombs, not hexagonal, but quadrangular, more particularly in the shape of a rectangle and a square, above all. 
     The functional advantage consists in that the available space is filled with the optimum number of chambers since the chambers are separated from each other by the thin partitions only which comprise a foil layer thickness or, respectively, a double foil layer thickness preferably in the order of 0.1-5 mm. 
     Although the component according the invention may be cast or, respectively, transfer molded in one piece, where the use of thermosetting or, even better, thermoplastic plastics offers itself, a deep-drawing process is used for the production according to a special development of the invention. In the process, a deep-drawing tool, which is more particularly grid-like, is placed on a foil, providing for that the grid rods draw the respective foil portions, upon which they rest, so far from the foil plane using heat and pressure or, respectively, that the foil is drawn around and away from the grid rods so far that the connecting portions between the portions, upon which the rods rest, and the upwardly drawn foil portions form the partitions; in the process, the foil portions are placed next to each other as the side walls of adjacent chambers; they may even fuse to each other. In one particular configuration of the invention, the grid is formed to be three-dimensional. 
     In addition to the above-mentioned functional advantages and the advantages in process technology described here, expenditure for material is low and the chamber bottoms provide for that no impurities nor humidity may penetrate into the chambers while additional cover foils are not needed. The bottoms formed of foil are so thin that they act like membranes and thus let sound pass into the chambers from outside. Therein, a spring mass system is formed in connection with the partitions and optionally a carrier, upon which the free partition ends are supported, which damps certain frequencies of the sound energy. By selecting the material for the component as well as the size of the chambers and the material thickness for the partitions and bottoms, certain frequency ranges may be damped especially strongly or it becomes possible to damp a relatively broad frequency spectrum of the sound energy. If a specific foil material has proven to be favorable for the bottoms and partitions of the component chambers, it is merely necessary to dimension the spacings between the grid rods used for deep-drawing and the extent by which they deep-draw the respective foil portions from the foil plane, more particularly perpendicularly to the foil plane, in correspondence with the desired frequencies. 
     The rods used for deep-drawing may be removed from the partition ends, which are thickened in particular, by undoing said ends. However, it is recommended for some applications to use so-called &#34;lost grids&#34; as deep-drawing tools so the rods remain in the partition ends. This results in an improved stability of the entire component, which is for instance required for an application as a bonnet absorber, i.e., a sound-deadening lining for an automobile hood. In this case it is recommended that the rod material consist of the same or similar material as the foil or plate from which the deep-drawing process originates. The invention is not limited to the use of thin foils, but plates being thicker than foils may be used too. 
     In case the sound-absorbing or, respectively, damping effect is to be improved even more for special cases, it is recommended according to a further development of the invention to put the chamber bottoms on sound-absorbing layers like damping webs, in particular. Further, the foil might be put on an aluminum ribbon coated with polypropylene, for instance, which acts as a heat shield. In order to reinforce the sound-absorbing component, it may also be useful to attach reinforcing members like, for instance, reinforcing grids on the bottoms of the chambers and optionally insert the reinforcing grids between the bottoms and the additional sound-absorbing and/or heat-deflecting layer. Such reinforcing members may be formed by a fabric and it is recommended to use a reinforcing mat, for instance, if thermoplastically bonded fibers are used for the reinforcing members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, preferred embodiments of the invention will be explained in detail in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic partial cross-section through a sound-absorbing component 1 according to the invention; 
     FIG. 2 is an enlarged partial section through a further embodiment of the invention; 
     FIG. 3 is a schematic cross-section through a component according to the invention connected with a carrier 2, wherein the carrier 2 is in a single plane, and wherein the exterior side of the component (a) faces incident sound and (b) is not confined to a single plane; 
     FIG. 4 is a cross-section corresponding to that of FIG. 3 wherein the carrier 2 is situated in different planes; 
     FIGS. 4a, 4b, and 4c show different deforming stages during the process for manufacture of the component according to the invention; 
     FIG. 5 is another schematic cross-section of a component according to the invention, in illustration of a further process stage; and; 
     FIG. 6 is an isometric view of a cut-through portion of the component. 
    
    
     DETAILED DESCRIPTION 
     According to FIG. 1, component 1 is formed of a plurality of chambers 14 which are disposed adjacent to and, optionally, behind each other (not represented in FIG. 1). Chambers 14 are respectively separated from each other by partitions 4. At its outer edge, component 1 is terminated by flange 6 which extends into the plane of the thickened partition ends 5 and which may serve as a fastening means for a carrier 2, as for instance, shown in FIG. 3. Bottoms 13 of chambers 14 face the incident sound; they are produced from foil 3 in a deep-drawing process just like partitions 4. The incident sound is indicated by arrows provided with the letter &#34;S&#34;. 
     According to FIG. 2, bottoms 13 are covered with a web 12 additionally damping sound waves on the side facing the incident sound. A reinforcing grid 15 inserted between bottoms 13 or, respectively, foil 3 and web 12, which may be thermally sealed to web 12 and foil 3. In this embodiment, the thickened partition edge 5 is cut by a slot 8 leading to the interior region 7 wherefrom rods, which are no longer shown here and form portions of a deep-drawing tool, have been removed via slot 8. 
     In the embodiment of FIG. 3, chambers 14 do not have the same size, but chamber bottoms 13a are situated at a smaller spacing from carrier 2 than other chamber bottoms 13. The sectional width of chambers 14 is selected in different sizes so that different sound frequencies are &#34;damped&#34; due to the spring mass effects. 
     In the sound-absorbing component according to FIG. 4, carrier 2 is not situated in a flat plane; rather, the outer surface of carrier 2, which faces the sound absorbent component, extends in different planes which are partially inclined towards each other. The thickened partition ends 5 are supported by corresponding surface portions of carrier 2 according to FIG. 4. Partitions 4 extend between such partition edges 5 and bottoms 13 of the &#34;membrane absorber&#34;, which face the incident sound, the chambers 14 being formed between bottoms 13, partitions 4 and the surface of carrier 2. This means that the thickened partition ends or, respectively, partition edges 5 are not situated in a flat plane, but are adapted to the outer contour of carrier 2, which is already taken account for in the production process for the component. 
     A particularly simple production process will be demonstrated from FIGS. 4a and 4c as follows: 
     According to FIG. 4a, a thin film 3 of PP (polypropylene) having a thickness of 1-5 mm is pressed against rods 9 from below, which are combined with grid rods lying perpendicularly to each other in the form of a grid. In this &#34;initial stage&#34; of the production process according to FIG. 4a, the foil 3 is situated in a single flat plane. 
     According to FIG. 4b, the heated foil 3 is subsequently drawn upwardly from these rods 9 in the direction of the arrows with rods 9 or, respectively, the grid being fixed, whereby portions of the plastically deformable foil 3 form grooves or, respectively, folds 3a in the region of the rods 9. 
     According to FIG. 4c, the final &#34;deep-drawing stage&#34; is schematically represented, wherein foil 3 is drawn out of the original plane A of FIG. 4a into final plane E at an offset spacing from plane A. Rods 9 are situated inside the thickened edge 5 of partitions 4 which are formed by a double layer of the foil portions drawn out of foil plane E, at right angles in this case. Folds 3a of FIG. 4b are drawn substantially farther and have been placed next to each other to form partitions 4 between chambers 14 formed thereby. 
     Rods 9 may remain in partition ends 5. In this embodiment, the &#34;deep-drawing grid&#34; formed of rods 9 is provided in the form of a &#34;lost grid&#34;, which on the one hand renders superfluous the application of another process step, but also contributes to the reinforcement of the edge regions 5 and chamber 14. 
     If said reinforcements and &#34;lost grids&#34; are not desired, the embodiment according to FIG. 5 may also provide for that the thickened partition ends 5 are undone and the rods 9 are taken out with a tool 11. In the embodiment of FIG. 5, the foil plane E is situated below so that the tool 11 would have to carry out an upward movement in the direction of arrows O. The grid formed of rods 9 may either be cut out of partition ends 5 with a punching knife located in the counterdie of the deep-drawing machine or it may be fused out by heating of the partition edges. According to one embodiment of the production process, the foil 3 is drawn by a counterdie over the grid onto the above-mentioned sound-insulating web 12 and, together with same, onto kind of a &#34;deep-drawing bed&#34;. Foil 3, which is held by a frame not shown here, is moved downwardly from the top over the grid towards the &#34;deep-drawing bed&#34;. Foil portions for the formation of partitions 4 are thereby also drawn downwardly and the chambers 14 are formed simultaneously. The thickened partition edges 5 are then situated above so that, according to FIG. 5 for instance, a counterdie moves downwardly, cuts the portions of the partition ends which are situated above and penetrates up to the rods 9. When the counterdie is moved back upwardly, the grid rods 9 are drawn upwardly too and removed from component 1. 
     FIG. 6 shows a schematic oblique plan view of a component 1 composed of such a chamber system. 
     The material for the component is not limited to plastics nor to thermoplastic plastics. A thin aluminum foil may be used as well for configuring a corresponding chamber system by deep-drawing. 
     Preferred applications of the invention lie within the scope of engines, automotive engines in particular. Therein, the engine enclosure or the bonnet sheet (hood panel) may serve as a carrier onto which the component with the free partition ends is put and connected therewith via welding, gluing, clipping or the like.