US 20020040827 A1
Reduced-noise devices or their components, in particular engine or combustion units and their components or fluid-carrying systems and their components, which are constructed, partially or wholly, from thermoplastics and which, at a distance from the surfaces of the devices, have at least one perforated plate, which is firmly connected, rests essentially with a form fit on continuously circumferential attachments on the thermoplastic component and encase the devices, in part or completely.
1. A reduced-noise device or its components which are constructed, partially or wholly, from thermoplastics, wherein at a distance from the surfaces of the device they have at least one perforated plate, which is firmly connected, rests essentially with a form fit on continuously circumferential attachments on the thermoplastic component and encases the device, in part or completely.
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 The present invention relates to reduced-noise devices or their components, in particular reduced-noise engine or combustion units and their components and reduced-noise fluid-carrying systems, which are constructed, partially or wholly, from thermoplastics.
 Internal combustion engines contribute significantly to noise pollution in road traffic. The disturbing engine noise essentially originates from individual sources, such as the exhaust opening, the exhaust wall, the intake system, the combustion operation itself, the tilting of the pistons, the injection pump, the fan and the alternator. In this case, structure-borne sound and also the radiation of airborne sound are responsible for the resulting noise level. In particular, the engine block represents a serious source of structure-borne sound. For this reason, and also necessitated by the large number of individual sound sources reducing the sound radiation at the engine block is particularly difficult. Noise-reducing measures are aimed firstly at optimizing the acoustic behavior of the various individual sources (primary soundproofing) and secondly at the so-called secondary soundproofing measures, such as the tight encapsulation of, for example, internal combustion engines (see also Taschenbuch der Technischen Akustik [Handbook of Technical Acoustics], edited by M. Heckl and H. A. Müller, 2nd Edition, Springer Verlag, Berlin, 1994). For example, in order to reduce the propulsion-unit noise in all motor vehicles with internal combustion engines intake and exhaust-gas silencers are incorporated, and engines and gearboxes are mounted resiliently. In the case of diesel engines, a considerable reduction in the sound level can be achieved only by means of additional encapsulation of engine and gearbox. Encapsulations of this type often have a sound-absorbing material on the inside. The drawback with the encapsulation is that an additional outlay on materials is necessarily required and that, during the production process at least one further operation arises which regularly has a detrimental effect on weight and costs.
 DE 297 12 278 U1 describes underfloor cladding made of a thermoplastic material and having a sealing lip likewise injection-molded on. Shell-like underbody cladding can be stiffened by webs in the hollow area facing the engine. A thin diaphragm in the form of a sheet capable of vibrating can be applied to these webs in order to damp engine noise. In this way, the engine noises are absorbed or reduced only partly, particularly only to the outside, but not at the same time in the direction of the interior. Instead, in the case of non-optimal flexibility of the sheet, that is to say in the case of a vibration of behavior not matched optimally to the engine noise, it can happen that the motor noise is reflected and, as a result, the noise level in the interior is amplified. In order to cover the entire frequency spectrum of an engine effectively to some extent, a large number of diaphragm sheets of different size and formed by webs and diaphragm sheet would be required. The more ribbing webs are used as an underfloor protective cavity, the heavier this component becomes. However the aim of motor vehicle construction is to minimize the vehicle weight, in order to be able to reduce the fuel consumption.
 DE-A 44 04 502 discloses a sound-damping covering hood, in particular a cylinder-head hood for internal combustion engines. The noise source is covered by a surface which is closed on the outside and on the inside has cavities formed by intersecting stiffening ribs. Particularly good noise reduction is achieved if the cavities are sealed off by a closed sheet, so that a large number of closed hollow chambers is obtained. In addition, in a less advantageous embodiment, the sheet covering the hollow chamber can also be provided with a hole.
 Precisely for reasons of weight reduction, very many internal combustion engines have already been equipped for some time with intake modules made of thermoplastics (e.g. in the Mercedes 2.8 l and 3.2 l in-line six-cylinder engine from Daimler-Benz (1992), or in the 2.0 l four-cylinder direct injection diesel engine from BMW (1999)). As compared with conventional metal systems—it is usual for aluminum to be used in such intake systems—these plastic intake modules have, as a further advantage, a better ecological balance, that is to say they can be manufactured and recycled in a more environmentally friendly manner, require a lower outlay on materials because of lower component thicknesses, and as a whole can be manufactured more simply and more cost-effectively. However, the noise-damping properties of components made of thermoplastics are disadvantageous, as a result of their lower density as compared with metal components. Without having to carry out encapsulation immediately, the noise behavior of plastic intake systems can often be improved by one or more webs being fitted and firmly connected to the outside of these intake modules. However, natural limits are set on ribbing of this type of components, for example for design technical reasons. In addition, ribbing does not always supply the desired result so that, for reasons of reducing noise whilst accepting the aforementioned disadvantages, again only an aluminum component would be considered.
 In the case of carrying systems for liquids or gases, considerable noise pollution regularly originates from flow noise. In order to reduce noise a remedy is often provided by the entire carrying system being encased positively with a metal plate and the intermediate layer produced being filled with insulating material. However, these measures require a great deal of work and expenditure on material and costs.
 The present invention was therefore based on the object of being able to fall back on constructive components made of thermoplastics, for example for any noise-intensive engine or combustion unit in order with said thermoplastics to achieve a sustained reduction in noise and no longer to be dependent on metal components, in particular aluminum components.
 Accordingly, reduced-noise devices and their components, in particular reduced-noise engine or combustion units and their components have been developed, which are constructed, partially or wholly, from thermoplastics and, at a distance from the engine or combustion units or components, in particular made of thermoplastics, have at least one perforated plate, which is firmly connected, rests essentially with a form fit on continuously circumferential attachments on the thermoplastic component and encases the engine or combustion unit, in part or completely.
 In addition, reduced-noise fluid-carrying systems have been developed which are constructed, partially or wholly, from thermoplastics and, at a distance from the fluid-carrying system, in particular of thermoplastics, have at least one perforated plate, which is firmly connected, rests essentially with a form fit on continuously circumferential attachments on the thermoplastic component and encases the fluid-carrying system components, in part or completely.
 One aspect of the present invention is a noise reduction structure for devices having an outer housing and an inner mechanism. During the operation of the devices, vibrations are transmitted through the housing to an outer surface of the housing. These vibrations are perceived as audible noise. The noise reduction structure consists of at least one web of predetermined height. The web has an upper edge and a lower edge, which is matched to the outer surface of the device and fixed to it. The noise reduction structure also contains at least one plate with a plurality of perforations and a lower face fixed to the upper edge of the web. The web holds the plate at a predetermined distance from the lower adaptable edge, by which means at least part of a chamber is formed. The plate is substantially sealed off at the web and the housing around the circumference of the plate and encloses part of the outer surface of the housing.
 A further aspect of the present invention is a housing structure for the external damping of noise which is produced in the housing and is transmitted to the outer surface of the housing as perceivable audible noise. The housing structure comprises a housing with an outer surface, at least one web of predetermined height extending outward from the outer surface of the housing and ending at an upper edge. The web also has a lower edge, which is matched to the housing and fixed to the outer surface. At least one plate has a plurality of perforations and a lower face fixed to the upper edge of the web. The web holds the plate at a predefined height from the housing outer surface. The plate, the housing outer surface and the web form a chamber.
 In a preferred embodiment, the noise reduction structure or the housing structure comprises a plurality of webs and a plurality of plates, these webs and plates being arranged beside one another and, in this way, defining a plurality of adjacent chamber parts. The chamber parts defined by the webs can have a polygonal wall configuration.
 The reduced-noise engine or combustion units and their components which are constructed, partially or wholly, from thermoplastics and which are considered include intake pipes, intake modules, air filters, cylinder-head hoods, alternators or fans. Engine and combustion units in the sense of the invention also include, for example, gearbox systems and electric motors and hybrid drives, if these are equipped with thermoplastic components.
 Suitable intake pipes are, for example, those having resonance switching, oscillating-pipe switching or channel disconnection. Intake modules made of thermoplastics are generally of more complex construction and, for example, can include the cylinder-head hood with the integrated or connected components, the connecting bend for the swirl ducts, the lower part of the air-filter housing, the hot-film air mass meter, the oil separator system for the blow-by gases, including the pressure valve, and the air-filter cover and, if appropriate, a covering.
 The noise-radiating devices whose noise level is reduced are composed, partially or wholly, from thermoplastics. In principle, all types of plastic and mixtures of these polymer classes are considered. Suitable materials are, for example, polyesters such as polybutylene terephthalate (PBT), for example the commercial product Ultradur®, and polyethylene terephthalate (PET), polyamides such as polyamide 6 or polyamide 66, for example available under the trademark Ultramid®, polyether sulfones such as the commercial product Ultrason®E, polysulfones such as the commercial product Ultrason®S, polyoxymethylenes, for example the commercial product Ultraform®, polyetherimides, polyether ketones, polyphenylene sulfides, polyphenylene ethers (PPE), PPE/HIPS blends (HIPS=high impact polystyrene) such as the commercial product Luranyl®, styrene (co)polymers such as ASA, ABS and SAN polymers (also available under the trademarks Luran®S, Terluran®/Ronfalin® and Luran®), polymethyl methacrylates such as Lucryl®, polyketones, syndiotactic polystyrene, MABS polymers such as the commercial product Terlux® or polycarbonates (PC) and mixtures thereof (all the aforementioned commercial products: BASF AG). Examples of mixtures which may be mentioned are PBT/ASA, ASA/PC and PBT/PC blends. The aforementioned thermoplastics can also be used in fiber-reinforced form, for example using glass, carbon or aramide fibers. In addition, rubber-modified thermoplastics are also considered. For applications as components of internal combustion engines, it is recommended to select materials which can withstand continuous thermal and mechanical loads. In this case, for intake pipes and intake modules, recourse is preferably made to polyamides, in particular polyamide 6 and polyamide 66, which are preferably present in fiber-reinforced form.
 The thermoplastics and their mixtures which are considered, and their manufacture are well known to those skilled in the art and generally constitute commercially available products. Suitable fiber-reinforced polyamides are, for example, commercially available under the trademarks Ultramid® B3WG7 and Ultramid® A3HG7.
 According to the invention, at a distance from the surfaces of the components made of thermoplastics, there is fitted at least one perforated plate, which is firmly connected, rests essentially with a form fit on continuously circumferential attachments on the thermoplastic component and encases the engine or combustion unit or component, in part or completely. The perforated plates can be produced, for example, from the aforementioned thermoplastics or mixtures thereof, including in fiber-reinforced form. The perforated plate is often made of the same material as the thermoplastic component. Perforated plates made of other plastics, for example from polypropylene, polyethylene or their copolymers, from polystyrene, from thermosetting plastics such as polyurethanes or even of metallic materials, for example from iron, steel or aluminum, are possible. In general, the perforated plates form a defined volume with the side walls resting on the outside of the thermoplastic component. The side walls constitute continuously circumferential attachments and advantageously end in a form-fitting manner both with the surface to which they are fitted or on which they rest and with the perforated plate resting on them, so that no openings remain at these connecting seams or joins. The perforated plates are firmly connected to the side walls. This connection can be produced by means of adhesive bonding, welding, for example vibration welding, or screwing. In addition, so-called clip connections or snap attachments are possible, such as are already used nowadays for fastening components to the engine block. An adhesive connection can be produced using, for example, commercially available silicon adhesives which are known to the person skilled in the art.
 In a preferred embodiment, a resilient intermediate layer is fitted between the surface of the components and the side walls of the perforated plates. Suitable intermediate layer materials are, for example, natural or synthetic rubber, thermoplastic elastomers such as styrene copolymers, for example SBS or SEBS types, as they are known (Kraton® D or Kraton® G, Shell), or elastomer alloys, for example those of EPDM and polypropylene, or thermosetting plastics such as polyurethane foams.
 This resilient intermediate layer, on which the side walls stand or rest, can also wholly or partially cover the component surface beyond these contact areas, that is to say the surface of the noise-reduced device or components.
 In addition, for the purpose of fastening, the perforated plate walls may have holes, notches or cutouts in the contact area, for example rails fitted at right angles to the wall, into which elevations, for example in bolt form, formed on the surface of the device can be introduced. If these elevations, for example, are likewise produced from a thermoplastic, they can be fused on, inter alia by means of a heating device, ultrasound or laser light. If the melt is permitted to spread beyond the edge regions of the holes, notches or cutouts, then after it has cooled down, an intimate connection is obtained between the perforated plate and the surface of the noise-reduced device, in particular also when the edge region of the holes, notches or cutouts is likewise softened or fused on and mixes with the melt of the elevation. In this case, the edge region can be heated specifically or can soften or melt via the contact with the melt of the elevation. Such types of connection are known to the person skilled in the art as heat, ultrasonic or laser stakings.
 In a preferred embodiment, hole openings are provided only in the perforated plate itself. The total area of the holes in a perforated plate preferably assumes a value over all the holes in the range from 0.5 to 40, preferably 3 to 30%, based on the area of the perforated plate. Considerable reductions in noise are regularly already obtained with a total hole area of about 20%. The thickness of the perforated plate can vary over wide ranges and also depends, inter alia, on the size of the perforated plate itself, the material of the perforated plate, the size of the sound-radiating device or the sound intensity radiated. It is usually in the range from 0.3 to 6 mm, preferably in the range from 1 to 4 mm. The holes in the perforated plate can have any desired form, that is to say regular or irregular. The diameter or the side length of the holes is regularly in the range from 0.3 to 10 mm, preferably from 0.8 to 6 mm. A large number of holes are preferably applied regularly or in a random distribution to a perforated plate or a perforated-plate segment. A perforated plate usually has at least three holes. The holes in the perforated plate can be obtained by known methods, for example by means of stamping or drilling. It is also possible to manufacture the perforated plate in one production operation, for example by means of injection molding.
 The area which can be covered by the perforated plate depends firstly on the constructional conditions of the sound source, secondly also on the fact that, in specific cases, complete encasing is no longer associated with any significant advantages as compared with encasing a selected area. The spacing of the perforated plate from the device underneath it is defined, inter alia, by the height of the side walls on which the perforated plate rests, the shape of the perforated plate and the shape of the device underneath it. In the case of conventional components such as intake pipes or intake modules, the distance to components of engine and combustion units is generally in the range from 1 to 50 mm, preferably from 3 to 25 mm.
 The perforated plate applied or fitted to the side walls can encase the entire noise source or only part thereof. In addition, it is possible to arrange a number of perforated-plate segments, connected to each other or unconnected, to the device that produces the noise, so that either in turn the entire noise source or only part thereof is present in encased form. In this way, the encasing can be adapted to design requirements.
 In a further embodiment, the circumferential side walls are likewise provided with holes, partially or wholly, as previously described for the perforated plate.
 In a preferred embodiment, one or more webs are fitted to the outer surfaces of the thermoplastic components. These webs can be arranged in any desired manner on the thermoplastic components, as long as they are connected to the component surface with a form fit. A number of webs can run parallel or virtually parallel, but can also cross and in this way form, for example, a large number of geometric patterns. It is possible, for example, for only square, rectangular, triangular or trapezoidal segments to be applied to the surface and to form a regular or any desired pattern. In addition, these geometric figures can also be combined with one another as desired. This ribbing serves to stiffen the component and has, in particular, the purpose of suppressing the production of structure-borne sound, above all at those points which are shown to emit a great deal of sound. The webs themselves are generally composed of the aforementioned thermoplastic materials. They are preferably made of the same material as the plastic component to which they are fitted. The webs or ribs can be fixed to the thermoplastic surface with a form fit by current methods, by means of adhesive bonding or welding, for example vibration welding. In the case of injection-molded components, in particular, the casing and the webs are advantageously produced directly during the manufacturing process by means of a suitable design of the injection mold. In terms of their cross section, the webs can be, for example, arcuate, that is to say designed as a bead, triangular, square or rectangular. For reasons of simple manufacture, the webs generally have a more or less standard height. In the case of intake pipes or modules, this is generally in the range from 1 to 50 mm, preferably from 3 to 40 mm.
 The height of the webs or ribs, if these are likewise encased by the perforated plate, is limited by the distance between the perforated plate and the component surface underneath it. In one embodiment, the perforated plate rests on the upper edges of individual webs or all the webs. The perforated plate can likewise be adhesively bonded, welded or fixed in any other way, for example with the aid of screws or clips, to the webs on which it rests, partially or completely. In this case, the perforated plates form perforated-plate segments, which themselves have a self-contained volume. The webs can be covered only by the perforated-plate encasing or can be arranged completely outside the area encased by the perforated plate, or can be located both underneath and beside the encasing.
 In addition, it has been found that, even in the case of fluid-carrying systems, that is to say, for example, pipelines for carrying gases and liquids, the noise level can be reduced in a sustained way by, in particular, such systems, which are constructed, partially or wholly, from thermoplastics, being encased by at least one perforated plate, as already described above, in part or completely. In this case, the perforated plate can cover, for example, only a specific portion of a pipe or can encase the pipe over its entire extent. In addition, the general and specific statements made previously apply appropriately to this embodiment.
 In addition, the reduced-noise devices can contain sound-damping or noise-reducing materials, for example porous sound absorbers such as fibers or open-pore foams, in the space between the perforated plate and the noise-emitting surface located underneath it, that is to say in the chamber part. Suitable absorbers used are felts, glass or mineral fibers, organic fibers such as groundwood and cocoa fibers, and open-pore foams, preferably made of polyurethane. As a rule, glass and/or mineral fibers with fiber diameters in the range from 2 to 20 μm are used. At the crossing points, the fibers are generally connected to one another by synthetic resins, for example phenolic resins.
 The reduced-noise engine and combustion units according to the invention, and their components, as well as the reduced-noise fluid-carrying systems can be used, inter alia, in passenger cars or goods vehicles, here for example in the alternator casing, in the casing for the gearbox or the injection pump, in marine propulsion units, domestic and electrical applicances, tools or burners.
 The devices according to the invention are distinguished by the fact that they effect a considerable reduction in the sound and permit sound-reducing measures such as the encapsulation to be dispensed with. They are simple to produce and to mount and can be adapted simply and effectively to the respective noise problem to be solved. For example, it is possible, even in the case of initially high-noise intake modules made of plastic, to reduce the noise level effectively in such a way that a changeover to intake modules made of aluminum can be dispensed with.
 The above description is seen as a description only of the preferred embodiment. Modifications of the invention will follow to the person skilled in the art and those who utilize the invention. It therefore goes without saying that the embodiment shown in the drawings and described above is used merely for illustration and is not intended to restrict the area of protection of the invention.
 The present invention is explained in more detail with reference to figures and examples.
FIG. 1 is a perspective view of a plastic intake module (1) which, partly sectioned, shows a perforated plate (3) which is fitted to a rib structure (2) formed by a plurality of external, intersecting webs.
FIG. 2 represents a cross section along the section plane A.
 An intake module made of polyamide 6 (Ultramid® B3WG7) was irradiated with white noise from the inside via a loudspeaker. The noise level measurements were performed with the B&K 2260 sound intensity measuring system from Brüel & Kjäer. The intake module for the comparative measurement (intake module V) had ribbing as indicated in FIG. 1, and the intake module according to the invention (intake module 1) was also equipped with a perforated plate, which was adhesively bonded to the webs serving as side walls and on which the perforated plate rested.
 Intake module 1: 50.17 dB(A)
 Intake module V: 55.22 dB(A)