Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
2000-07-10
2002-10-01
Donels, Jeffrey (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S294000, C181S284000
Reexamination Certificate
active
06457555
ABSTRACT:
The present invention relates to a sound muffling material. The material is intended particularly although not exclusively for use in mufflers and silencers fitted to internal combustion engine exhausts.
Exhaust mufflers generally include a sound muffling material, usually glass fibers. This material acts to attenuate sounds transmitted through the exhaust system. The fibers are usually disposed in at least a part of the muffler. The fibers generally fill a part of the muffler to a certain density to achieve an effective muffling effect. The fibers are usually in a volumized form.
In one existing arrangement an exhaust muffler includes a cylindrical steel body, usually referred to as a box, in which there is disposed coaxially a perforated steel tube. The perforated steel tube is mounted on annular end caps which are affixed to opposite ends respectively of the cylindrical body by welding or crimping. A muffling material, usually glass fibers, is disposed in the annular region between the perforated steel tube and the muffler body. In use exhaust gases are directed through one end cap, along the perforated tube, and out the opposite end cap.
Mufflers of this type are assembled in one of two common ways. Generally the muffler is assembled by attaching one end cap to support the perforated tube. In one method volumized continuous filament glass fibers are injected, through the open end of the muffler body, into the annular region between the perforated tube and muffler body using specialist equipment. In another method a glass fiber needlefelt fabric is provided wrapped around a cardboard tube, or former, of a similar diameter to the perforated metal tube in the muffler. The cardboard tube is positioned above the perforated tube and the cylinder of needlefelt fabric slid off the cardboard tube and onto the perforated tube.
There are a number of problems associated with both the above described methods. The equipment used to inject continuous filament fibers is expensive and therefore limits the number of mufflers that can be produced simultaneously at reasonable cost. When fibers are provided in the form of a needlefelt they are not necessarily continuous filament fibers. As such, when the muffler is used some fibers may pass through the perforated tube and into the flow of exhaust gases. This is undesirable as the effect of the muffler will be diminished and the escaping fibers may cause problems in the remainder of the exhaust system. Also, sliding a cylinder of needlefelt fabric onto a perforated tube is also inconvenient as the fabric tends to snag on the cut end of the perforated tube. Further, the cardboard tubes present a waste management problem. Often, the tubes are re-used which necessitates returning the tubes to the supplier, increasing transport costs.
By far the most significant drawback with conventional methods of filling mufflers with fibers is that where the fibers are loose, especially in the case of the preferred continuous filament fibers, and the muffler is filled with the required density of fibers this presents problems when the end cap is attached to the muffler. Where fibers stray out of the muffler body they may become trapped between the muffler body and the end cap. This adversely affects the quality of the join between the end cap and muffler body both when the end cap is attached by welding and crimping. It is therefore essential that before the end cap is attached to a muffler body the fibers disposed in the body are carefully moved from the region of the join. This is tedious and time consuming.
Another type of muffler is the clam shell type, which includes two portions which are crimped or welded together to form a complete unit. Mufflers of this type are produced in a variety of shapes and sizes, in general, however, each half is relatively shallow. The clam shell type of muffler cannot be easily filled with fibers using the above described methods as the fibers easily escape. Instead, short fibers are provided packed in, or continuous filaments injected into, perforated polythene bags. A bag of fibers is placed into one half of a clam shell muffler and the second half is welded or crimped to the first half. In use, high temperature exhaust gases cause the polythene bags to disintegrate, releasing the fibers. Again, there are problems associated with this technique. Firstly, the bags tend to be bulky in order to provide the correct density of fibers to fill the muffler. This makes joining the two halves of the muffler difficult. Secondly, where the bag is filled with short filament fibers problems are experienced with the fibers escaping from the muffler in use, as described above.
EP 0434895A discloses a silencer for an internal combustion engine comprising a hollow housing containing a web of fibers and a pipe extending therethrough. The web of fibers is confined by a plastics film and there is a substantial clearance space between the film and the housing. When the silencer has been connected with an internal combustion engine and is subjected to flow of hot exhaust gases from the engine the plastics film inside the silencer is destroyed so that it no longer confines the web of fibers.
DE 3827863A discloses an exhaust gas purification device which includes a resilient support mat. The resilient support mat is surrounded by a covering sheet such that it is compressed. In one arrangement overlapping marginal areas of the covering sheet are fixed together with blobs of adhesive which melts on heating to permit separation of the edges and expansion of the support mat.
WO 91/19082 discloses a protective material for a catalytic convertor block comprising a pad of fibrous material in an envelope of non-woven textile material. The envelope has its depth reduced in at least localized areas or positions by drawing together of opposing faces by stitching.
It is an object of the present invention to provide a convenient method of filling a muffler with fibers, particularly to enable continuous filament fibers to be easily used in clam shell type mufflers.
According to a first aspect of the present invention there is provided a sound muffling material comprising volumised continuous filament fibers retained in a compressed state in the form of a knitted or woven fabric with a density of at least 200 kg/m
3
by a material of lower softening temperature than the fibers, arranged so that the material of lower softening temperature will release the fibers when heated.
According to a second aspect of the present invention there is provided a sound muffling material comprising volumised continuous filament fibers retained in a compressed state in the form of a knitted or woven fabric with a density of at least 200 kg/m
3
by a material which breaks down at a lower temperature than the fibers, arranged so that the material of lower softening temperature will release the fibers when heated.
According to a third aspect of the present invention there is provided a method of making a sound muffling material comprising the steps of providing continuous filament fibers, volumising the fibers, providing a material with a lower softening temperature than the fibers, compressing the volumised fibers and retaining the volumized in a compressed state by means of the material of lower softening temperature by forming the volumized fibers into a knitted or woven fabric with a density of at least 200 kg/m
3
.
According to a fourth aspect of the present invention there is provided a method of making a sound muffling material including the steps of providing continuous filament fibers, volumising the fibers, providing a material with a lower breakdown temperature than the fibers, compressing the volumized fibers and retaining the volumized in a compressed state by means of the material of lower breakdown temperature by forming the volumised fibers into a knitted or woven fabric with a density of at least 200 kg/m
3
.
According to a fifth aspect of the present invention there is provided a method of filling an exhaust muffler with fibers including the steps of placing a mater
Acousta-Fil Limited
Donels Jeffrey
Lockett Kim
Salter & Michaelson
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