1 Field of the Invention
The present invention relates to sound absorbing components that are useful in reducing sound perception in automotive applications.
2. Background Art
There is an increasing demand for the reduction of sound levels to improve speech perception in 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 increased sensitivity of vehicle passengers in that range for speech intelligibility and speech clarity.
Concurrent with these sound reduction demands, economic factors provide pressure to reduce the weight of all automobile components including sound absorbing components. Lighter weight components lower the cost of manufacturing by reducing the amount of materials used, and generally lower the operating expense of the vehicle by contributing toward improving the gas mileage. On the other hand, the benefits of lighter weight sound absorbing components must be balanced with a competing issue of strength. For example, if a sound absorbing pad is too thin, it may not be sufficiently rigid to be positioned without extra support.
The attenuation of sound waves present in automobile passenger compartments is accomplished by a number of components. For example, dash and floor panels have been designed to include sound absorbing or attenuating material. However, success using sound attenuating dash and floor panels have 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 cost of such systems and the added burden of incorporation in an aesthetically pleasing manner.
Accordingly, their exists a need in the prior art for more economical and efficient systems for reducing noise in an automobile.
The present invention solves one or more problems of the prior art by providing in at least one embodiment a sound absorber suitable in automotive applications. The sound absorber of the present invention comprises a molded sheet having a first side and a second side. The first side of the molded sheet is substantially non-planar while the second side is such that the molded sheet can be placed proximate to an automobile component surface with the second surface adjacent to or opposing the automobile component surface. In order to absorb sound efficiently, the first side has a surface area that is greater than an equivalent surface area of a planar surface. Advantageously, the sound absorber of the invention is useful for sound insulation in a vehicle engine compartment. An example of the position at which the sound absorber of the invention can be placed include, under the vehicle hood, along the fire wall, around the shock tower, and the like.
In another embodiment of the present invention, a method of molding the sound absorber described above is provided. The method of this embodiment comprises introducing a molding material into a mold cavity. The molding cavity has a surface that is the inverse of the first surface. Next, sufficient heat or pressure to form the sound absorber is applied.
Reference will now be made in detail to presently preferred compositions or embodiments and methods of the invention, which constitute the best modes of practicing the invention presently known to the inventors.
In an embodiment of the present invention, a sound absorber suitable for providing sound insulation in automotive applications is provided. The sound absorber of the present invention comprises a molded sheet having a first side and a second side. The first side of the molded sheet is substantially non-planar while the second side is such that the molded sheet can be placed proximate to an automobile component surface with the second surface adjacent to or opposing the automobile component surface. In order to absorb sound efficiently, the first side has a surface area that is greater than an equivalent surface area of a planar surface. This greater surface area is achieved by the first side having corrugations. In one variation, the first side comprises corrugations along a single direction. In another variation, the first side has corrugations along two distinct directions. In a variation, the higher surface area is obtained constructing the molded sheet to have a cross section that is at least partially curved. In another variation of the present embodiment, the first side has a surface area that is from about 1.1 to about 4 times greater then a corresponding planar surface. In yet another variation, the first side has a surface area that is from about 1.2 to about 3.0 times greater then a corresponding planar surface. In still another variation, the first side has a surface area that is from about 1.3 to about 2.0 times greater then a corresponding planar surface. The first side of the present embodiment includes virtually any shape that is non-planar. For example, the first surface may have a substantially egg-crate pattern having a plurality of peaks and valleys (corrugations in two directions), a sawtooth pattern, or a curved pattern. Optionally, the sound absorber further comprises a scrim layer over the first side. Typically, such a scrim layer is for aesthetic purposes having less air flow resistance than the molded sheet.
With reference to
Table 1 provides combinations of parameters for the sawtooth variation. In general, more acute values of the interior angle A1 for a given height provide a greater increase in surface area than for less acute angles.
Table 2 provides combinations of parameters for the semi-circular variation. In general, more acute values of the arc angle A2 for a given height provide a greater increase in surface area than for less acute angles.
In addition to providing sound absorption when applied to automobile component surfaces, variations of the sound absorber of the prevention invention allows lower density materials to be used for the molded sheet. The corrugations, peaks, and valleys that characterize the present embodiment provide rigidity allowing thinner and less dense materials to be used to form the molded sheet. For example, in a variation of the invention, the molded sheet has a density of about 20 to about 150 grams per square foot. Although any moldable material may be used to form the molded sheet of the invention, thermoplastic resins or thermosetting resins are particularly useful. Useful resins include polyesters (polyethylene terephthalate) and polyolefins (e.g., polypropylene). Typically, useful materials are also fibrous. Such fibrous components include polyester (e.g., polyethylene terephthalate) and polyolefin (e.g., polypropylene) fibers. In yet another refinement, the molded sheet comprises a foam resin (e.g., melamine foam). Moreover, the molded sheet of the present embodiment optionally further comprises an additive selected from the group consisting of glass fibers, cotton (e.g., cotton shoddy), fire retardants, and combinations thereof.
In another embodiment of the present invention, a method of molding the sound absorber described above by a compression molding process is provided. The method of this embodiment comprises introducing a molding material into a heated mold cavity. The molding cavity has a surface that is the inverse of the first surface. Next, sufficient heat or pressure to cure the molding material is applied thereby forming the sound absorber.
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.