1. Field of the Invention
The present invention relates to automobile interior trim sound absorbing components.
2. Background Art
There is an increasing demand for the reduction of sound levels to improve perception in the passenger compartments of automobiles. Development of methods and systems that accomplish such reductions require an understanding of the potential internal and external noise sources in an automobile as well as the effect of various automobile components in masking or attenuating such noise. Moreover, reduction of noise in the 1 KHZ to 5 KHz frequency range is particularly desirable due to the increase sensitivity of vehicle passengers in that range for speech intelligibility and speech clarity.
The attenuation of sound waves present in automobile passenger compartments is accomplished by a number of components. For example, headliners have been designed to include sound absorbing or attenuating material. However, success using sound attenuating headliners has been limited by material properties and design restraints. Moreover, incorporation of complicated sound absorbing systems and components into an automobile are undesirable because of the additional costs of such systems and the added burden of incorporation in an aesthetically pleasing manner.
Various strategies for reducing passenger compartment noise using perforated structures. For example, EP1202874B1 discloses a perforated structure for a headliner. Similarly, M. van Ruiten et al disclose a perforated panels for vehicle interiors that operate at least to some degree as Helmholtz resonators. (M. van Ruiten et al, Improved Acoustics Through Perforated Plastic Panels, 2003 SAE Noise & Vibration Conference Proceedings, May 5th-8th 2003, Traverse City, Mich.) Although these perforated structures work reasonably well, these prior are structures tend to utilize rather large perforations that may interfere with the aesthetics of the passenger compartment and degrade the integrity of structural components. Moreover, additional sound reduction is still desired.
Accordingly, their exists a need in the prior art for more economical and efficient systems for reducing noise in an automobile passenger compartment.
The present invention overcomes one or more problems of the prior art by providing in one embodiment a perforated hard trim construction for incorporation into a an automobile interior with sound absorbing properties. The perforated hard trim construction includes a non-perforated metal component and a perforated hard trim component having a plurality of openings and connected to the non-perforated metal component. The plurality of openings have a sufficient total area such that the random incidence absorption coefficient is greater than about 0.1 for one-third octave center frequencies from about 1000 to about 10000 Hz. The perforated hard trim construction also include an external absorbing material covering the perforated hard trim component and a fabric layer covering the first absorbing layer.
In another embodiment of the invention, a perforated hard trim construction is provided. The perforated hard trim construction of this embodiment includes a non-perforated metal component and a perforated hard trim component. The perforated hard trim component has a plurality of openings and is connected to the non-perforated metal component. The construction of this embodiment is distinguished from the first embodiment in that it further includes an porous sound absorbing material interposed between the non-perforated hard trim component and the perforated hard trim component.
Reference will now be made in detail to the presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventors.
“Random-incidence sound absorption” as used herein is the difference of the Sabine absorption of a reverberation chamber with and without the sample under test present. The sound absorption coefficient of the sample is calculated by dividing the Sabine absorption of the sample by the surface area of the sample.
“Sabine absorption” as used herein refers to the sum of absorptions due to objects and surfaces in a room, and due to dissipation of energy in the medium within the room.
“Reverberation chamber” as used herein means a specially designed acoustic room to approximate a diffuse field by minimizing the sound absorption of all surfaces.
“Third-octave band” as used herein means a band of frequencies extending one-third of an octave from 0.891 f0 to 1.122 f0, where f0 is the band-center frequency. The band-center frequency is also referred to herein as the one-third octave center frequency.
In an embodiment of the invention, a perforated hard trim construction for incorporation into a an automobile interior with sound absorbing properties. The perforated hard trim construction includes a non-perforated metal component and a perforated hard trim component having a plurality of openings and connected to the non-perforated sheet metal component. The present invention represents an improvement over the typical hard trim constructions currently used in many automobiles. With reference to
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Perforated hard trim component includes a plurality of openings 36 that have a sufficient total area to significantly absorb sound present in an automobile passenger compartment when the automobile is operated. Typically, the total area will be such that the random incidence absorption coefficient is greater than about 0.1 for one-third octave center frequencies from about 1000 to about 10000 Hz. In a variation of the present invention, the plurality of openings have a sufficient total area such that the random incidence absorption coefficient is greater than about 0.2 for one-third octave center frequencies from about 2000 to about 10000 Hz. The sound absorption properties of the perforated hard trim construction of the invention which depend on the spacing and area of the plurality of opening. Typically, the plurality of openings have a total surface area that is less than about 12% of the surface area of perforated hard trim component 32. Moreover, the average opening area of the plurality of openings 36 is less than about 30 mm2. When a substantially circular hole is used as the opening, this area corresponds to a hole with a radium less than about 3.1 mm. In some variations of the invention, the plurality of openings have a total surface area from about 5% to about 10% of the surface area of the perforated hard trim component. In another variation of the invention, the average opening area in the plurality of openings is from about 0.10 to about 20 mm2 (for substantially circular holes, this is a radius from about 0.18 mm to about 2.52 mm). In still other variations of the invention, the average opening area in the plurality of openings is from about 0.22 to about 10 mm2 (for substantially circular holes, this is a radius from about 0.18 mm to about 1.78 mm). Although the openings of the plurality of openings may be of arbitrary shape, substantially circular holes are particularly useful because of their simplicity of manufacture (i.e., injection molding with pins, drilling). It is significant that the plurality openings use openings with a smaller area and have a lower total area than typically used in the prior art. The lower areas do not significantly interfere with the strength and structural integrity of parts into which the perforated hard trim construction of the invention is incorporated.
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In a particularly useful variation of the invention, perforated hard trim construction 30 includes interior porous absorber 42 interposed between perforated hard trim component 32 and non-perforated metal component 34. The presence of interior porous absorber 42 significantly increases the sound absorbing properties of the invention. Although any porous material may be used for interior porous absorber 42, absorbers made from PET or cotton shoddy are particularly useful. In this variation, the plurality of openings have a sufficient total area such that the random incidence absorption coefficient is typically greater than about 0.2 for one-third octave center frequencies from about 1000 to about 10000 Hz. In yet another variation of the present invention in which interior porous absorber 42 is used, the plurality of openings have a sufficient total area such that the random incidence absorption coefficient is greater than about 0.2 for one-third octave center frequencies from about 2000 to about 10000 Hz.
The porosity of interior porous absorber 42 is at least partially characterized by its density which is typically from about 10 kg/m3 to about 50 kg/m3. In other variations of the invention, interior porous absorber 42 has a density from about 20 kg/m3 to about 30 kg/m3. In yet other variations of the invention, interior porous absorber 42 has a density of about 26.5 kg/m3.
Finally, although placement of the perforated hard trim construction of the invention at any location in an automobile passenger compartment. Placement at positions close to the height of passengers heads is desirable. Such positions include locations on the A, B, C, or D pillars above the midline of the care (above the bottom of the vehicle windows.) The following examples illustrate the various embodiments of the present invention. Those skilled in the art will recognize many variations that are within the spirit of the present invention and scope of the claims.
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While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.