Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
1999-07-26
2001-10-23
Dang, Khanh (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
Reexamination Certificate
active
06305494
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for absorbing and/or attenuating sound waves with a sound wave absorbing and/or attenuating system using a thin vibratable layer on the side facing the incident sound waves.
Such a device is known in the art (DE-OS 33 13 001). This device is formed by a porous base provided with projecting areas so as to create hollow chambers, which are covered by a foil having a layer thickness of preferably 30 &mgr;m, which is placed over the projecting areas. The porous base acts as a sound absorber for the higher frequencies while the foil is a membrane absorber for the lower frequencies.
Other devices with sound wave absorbing and/or attenuating systems are known (EP-0 454 949 A2, DE Utility Model 92 15 132). In these devices, porous nonwovens or open-cell foam, particularly made of polypropylene, are formed so as to create so-called Helmholtz resonators together with a substrate or the engine hood. In one of these embodiments, a polyurethane foil covers the chamber system extending, respectively, along the foam walls forming the chambers.
DE-OS 36 01 204 furthermore discloses a method for forming packing units made of plastic fiber material and highly heat resistant inorganic fiber material, for example basalt fibers, to be used as a sound attenuating lining for the engine compartment of motor vehicles and partly laminating these packing units with a heat reflecting aluminum foil on the side facing the engine.
Finally, it is known in the art (EP-0 439 046 A2, GB Patent 482 747) to arrange aluminum sheets along the exterior of packing units, which are made of corrugated metal layers, to create reflecting heat shields for components that are exposed to flames.
BRIEF STATEMENT OF THE INVENTION
The object of the invention is to improve the devices of the initially cited generic class by simple means so that they can be easily manufactured and can be placed as closely as possible to noise sources and, where appropriate, heat sources while nevertheless providing good long-term sound absorbing and attenuating properties. In addition, the material used for the device should be readily recyclable or disposable without harm to the environment.
The invention is a sound wave absorbing and/or attenuating system comprising a system of resonance chambers for the sound waves, and a thin variable layer of aluminum or aluminum alloy covering the system of resonance chamber, the vibratable layer having a thickness ranging between 0.004 and 0.35 mm on the side facing the incident sound waves. Advantageous embodiments of the invention result from the following description of the figures and the referenced drawings.
According to the invention, the thin vibratable layer is made of aluminum or an aluminum alloy with a layer thickness ranging from 0.004 to 0.35 mm, preferably 0.0045 to 0.020 mm. Experience has shown that despite the use of a significantly more rigid material compared to many plastics, in this case aluminum, such a thin aluminum layer attains the aforementioned object if it is made and arranged so that it can vibrate. “Vibratability” is to be understood as the capability, on impact of the sound waves, of executing oscillations whose amplitude also depends on the degree of the aluminum foil's freedom of oscillation between the parts supporting it. The “thin vibratable foil” transmits airborne sound waves striking it on one side to the air space on the other side even if the “acoustic pressure” is thereby reduced, which is of course also advantageous for acoustic absorption.
The thin vibratable aluminum layer preferably covers a system of resonance chambers according to the so-called Helmholtz principle. For special sound wave frequency spectrums, the aluminum foil may also be at least partially perforated.
In accordance with a preferred embodiment of the invention, the thin vibratable aluminum layer itself is formed into a chamber system by deep drawing. In this as well as in other embodiments of the invention it is recommended to cover the aluminum foil on one side with a thermoplastic layer, for example by lamination. This thermoplastic layer should be made of polypropylene (PP) (polyester, polyethylene or the like are also suitable). The layer thickness should be on the same order as that of the thin aluminum layer. Such an aluminum-thermoplastic composite layer is easily deep-drawn, while nevertheless retaining adequate vibratability on impact of the sound waves.
The aluminum foil can also cover a porous aluminum body, for example a non-woven aluminum fabric. The important thing is that the thin aluminum layer does not lose its ability to vibrate even though this ability is somewhat reduced if non-woven aluminum fabrics are used. This “all aluminum technology” is advantageous with respect to disposal.
The thermoplastic layer is preferably arranged on the side of the aluminum foil facing away from the incident sound waves. The thermoplastic material of this layer can also serve as a coupling agent to a substrate made, in particular, of GMT (glass mat thermoplastics) with which the device is fused together to form a unit.
The inventive vibratable aluminum-thermoplastic composite layer has also proven to be advantageous when it is bonded to the surface of an engine hood facing the engine compartment, e.g., of a motor vehicle. Sound waves produced particularly by the engine frequently cause such engine hoods to vibrate so that the engine hood itself becomes a sound source. By bonding the vibratable aluminum foil via the thermoplastic layer to the engine hood, which is made, in particular, of metal, the vibratable aluminum layer via the thermoplastic layer also becomes an absorbing element for the vibrations of the engine hood. Since the oscillation frequencies of the extremely thin aluminum layer on the one hand and the sheet metal of the engine hood on the other hand differ markedly, the inventive device can also perform its task as sound attenuating and at the same time sound absorbing component.
REFERENCES:
patent: 4425981 (1984-01-01), Klesewetter et al.
patent: 5750944 (1998-05-01), Fuchs
Kock Gerhard
Lahner Stefan
Pfaffelhuber Klaus
Ruhe Thomas
Dang Khanh
Faist Automotive GmbH & Co. KG
Hopgood, Calimafde, Judlowe & Mondolino LLP
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