Field of Invention

The present invention relates to the field of mufflers, specifically to mufflers for internal combustion engines.

Background Art

Until today the interior of mufflers having metallic sound-deadening enclosures, with either single or multiple, e.g. double, triple or quadruple ducts, has been filled with sound-deadening materials by means of classical pre-moulding or blowing methods. These already known methods can be carried out by employing several techniques that can be globally subdivided into two different groups. The first amounts to blowing-in a sound-deadening mass, usually formed of a thread of glass fibre, through a hole obtained on the external housing (or enclosure) of the muffler. The sound-deadening material is blown-in through the hole and fills the whole space between the individual ducts and the external metallic housing that encloses them. The second method consists in the application of a semi-rigid, sound absorbing, and adequately pre-moulded mass, within the muffler, before the latter is hermetically closed. However, both techniques have some drawbacks. The first one is not easily carried out due to the complexity of the blowing operation and to the time required for filling the body of the muffler. On the other hand, the second technique is decisively more expensive and therefore it is economically disadvantageous.

Disclosure of Invention

The object of the present invention is to propose a method of introducing a glass fibre inside a muffler of an internal combustion engine whose muffler has an internal structure defined as "multiple duct structure".

The inventive concept at the origin of the present invention is based on the principle of combining the advantages of the aforementioned techniques, without, however, be forced to accept their burdensome drawbacks. Therefore, the present invention intends to completely change the known techniques by providing a cheap product, that can be produced in large amounts with appropriate equipments and machines, and which further can be pre-packaged and is extremely easy to insert into the muffler before the latter is definitively closed. The sound absorbing material, i.e. the glass fibre, instead of being slowly blown into the muffler, will be directly and rapidly prepared in the factory in accordance with the technique of the present invention. A first phase of the method consists in winding, around a rotating tube or a reel-winder with a specific shape, the thread of glass fibre which will form the final hank (skein) 1 to be introduced into the muffler. Said tube or reel-winder, set in rotation around its axis by an electric motor, will give rise to a reel of glass fibre thread, and the diameter of this reel will be correlated to the distance between the internal baffles of the muffler that contain the discharge gas ducts. On the other hand, the length of the tube or reel-winder will be similar to the circumference of the total number of said (gas discharge) ducts to be soundproofed. Once a structure made of glass fibre has been obtained in accordance with the desired type of muffler, said structure or mass is simply taken manually from the tube or reel- winder on which it was wound, and then it is squeezed.

According to a first embodiment of the invention, said squeezing of the sound- deadening mass is performed in order to allow an industrial sewing machine, of a type similar to the one used by shoemakers, to sew it in one or more parts, so that said mass will finally assume a substantially prismatic shape. The object of this central sewing (central seam) is to permit the handling of the glass fibre, by preventing the individual threads from falling down or getting entangled in an irregular manner before their introduction into the muffler and after their extraction from the tube on which they have been wound. The product, sewed in this manner, is

ready to be introduced manually within the muffler, and it has a width and a length which are perfectly adapted to the space existing within the muffler to be soundproofed. After the product has been put in place, by simply winding it around the ducts located between the two baffles, the muffler can be simply closed and this can be done indifferently using a covering or an embedding technique, both for moulded or rolled muffler types. This can be done because the sound absorbing material processed according to the present invention does not at all protrude from the outer contour of the baffles. Moreover, according to a second embodiment, the present invention has the object to indicate a new, extremely practical, cheap and quick method of filling the mufflers of internal combustion engines with the sound deadening material. Said sound- deadening material is formed exclusively of glass fibre, without any addition of adhesives, additives, or other polymers used for welding or sewing purposes, or for gluing purposes, in order to facilitate the handling of the material before its insertion in place. These substances could in fact possibly give rise to toxic fumes at the elevated operation temperatures of the mufflers, or could require more complex manual operations in order to obtain a mattress-like structure of glass fibre to be introduced into the muffler. The present invention, in the form of its second embodiment, further improves the first embodiment by allowing the realisation of manufactured articles made of glass fibre, which are rapidly obtained and do not require any addition of other polymers or adhesives to render them handy before their introduction inside the muffler to be soundproofed. This new result is achieved by performing a movement with a compressed air jet, both in the vertical and the horizontal - or diagonal - direction, to obtain a continuous or discontinuous "seam" ("sewing line") produced in the latter case by an intermittent air jet, this seam being obtained on the product after its extraction from the tube or reel-winder on which it was previously wound. Also this second embodiment of the present invention consists in a new method of manufacture of sound-absorbing mattress-like structures

and it provides for various simple fabrication steps. The first of these steps is analogous to the corresponding one of the first embodiment and consists in winding a desired amount of glass fibre around a tube, or reel- winder, having a diameter equal to the distance between the baffles to be soundproofed. The aforesaid tube, or reel- winder, which will be completely wrapped by the glass fibre mass, due to the rotation imparted to it in a conventional manner by any kind of motor (not shown), will have a length equal to the total circumference of the ducts to be soundproofed. The extraction ("unthreading") of the glass fibre mass thus wound around the tube or reel-winder, will be facilitated by providing one or more slits on the tube, or by a superposition of lamellae or annular elements modifying (increasing) the diameter of the original tube. The extraction operation could also be facilitated by realizing the reel-winder with a slight taper. The second, innovative processing step, which characterises the second embodiment and thereby renders it different from the first embodiment, consists in squeezing (compressing) the so obtained article of glass fibre while forcing the same to pass beneath one or more compressed air jets whose air pressure is within the region from 1 to 12 atmospheres (atm); the appropriate, selected value of pressure, depends on the Tex of the glass fibre which is comprised between 200 and 9600 Tex, and on the density of the fibre, all of which may vary according to the values specified by the customer. These focalised (concentrated) compressed air jets cause a mutual entanglement between the individual threads of glass fibre, thereby rendering extremely handy the so obtained mattress-like structure of glass fibre. This new method according to the second embodiment, due to the velocity with which the glass fibre can be made to slide beneath the compressed air jet(s), further reduces the manpower required for the job. This reduction allows to save one half of the required production time and it also increases safety on the production site, since the simple use of compressed air - acting as "glue" - in place of needles and adhesives makes the whole production extremely rapid, harmless, and cheap, due to the fact that no additional material is

directly utilised in the product, apart from the glass fibre and compressed air. The number of compressed air jets and their position is directly related to the size of the "small mattress" to be packaged, and as a general rule it may be stated that the greater its size, the greater will be the number of air jets required. The complete absence of seams (sewing lines) and of gluing operations, in this second embodiment, allows the mattress-like structure of glass fibre to be extended - by applying a simple traction thereto - to an additional length of about one third of its initial total length, thereby increasing the efficiency and standardisation of the product. A further advantage of the present invention consists in providing industry with a "small mattress" of sound absorbing material which is realized, in a proportion of 100%, of glass fibre alone. This is advantageous both under the ecological and the bureaucratic viewpoint, since it avoids to be forced to provide the technical specific parameters required by the rigorous European anti-pollution regulations with respect to the materials added to the glass fibre roving (= continuous thread of glass fibre).

Brief Description of DrawinRS

The present invention will now be explained with reference to the drawings, which show two embodiments thereof, wherein:

Fig. 1 shows a small mattress or mattress-like structure consisting of a glass fibre, processed according to the method corresponding to the first embodiment of the present invention, before its winding around the ducts of a muffler of an internal combustion engine;

Fig. 2 shows a muffler with three ducts, of an internal combustion engine, wherein the glass fibre sewed according to the first embodiment of the invention is wound between the two baffles; the mass of glass fibre (small mattress) is first fitted in the

space between the individual ducts and then it is wound around them;

Fig. 3 shows a muffler of an internal combustion engine, on whose ducts there has been applied - so as to perfectly occupy the space between the two baffles - the glass fibre (small glass fibre mattress) processed according to the first embodiment of the present invention;

Fig. 4 shows a small, sound-absorbing mattress, or mattress-like structure, made of glass fibre, processed according to the method of the second embodiment of the present invention (which does not include a sewing step), that is, subjecting the small mattress to the action of compressed air;

Fig. 5 is a perspective view of the muffler surrounded by the sound-deadening material (small mattress of glass fibre) which is wound around the muffler and is processed according to the second embodiment of the present invention; the figure shows the glass fibre and the ducts, besides the baffles between which the glass fibre is wound, the latter having a "welding line formed by compressed air".

Description of Preferred Embodiments of the Invention The objects, the features, and the advantages of the present invention have already been illustrated in detail above.

In substance, in the first embodiment of the invention, a glass fibre is wound around a tube or reel- winder (not shown) of adequate diameter; this manufacturing step does not differ from the corresponding one of the second embodiment of the invention. Therefore, the glass fibre (which then forms a "tube of glass fibre") is taken

(extracted or "unthreaded") from the respective tube or reel-winder, and the "tube of glass fibre" is subsequently squeezed (flattened).

From now on, the two embodiments (methods) according to the present invention

differ from each other, because in one case (first embodiment), depending on the size of the squeezed small mattress of glass fibre, one or more seams (sewing lines) 4 (cf. Fig. 1-3, in which a single sewing line is present) will be provided on the small mattress 1, while in the other case (i.e. the second embodiment; cf. Figs. 4 and 5), the small mattress 1 ' will be "welded" by means of compressed air (causing mutual entanglement between individual threads of the fibre along the line indicated by 4'). Thus, the small mattress or structure 1 or 1 ' can in both cases be easily handled by an operator, in order to realise a muffler for a vehicle with internal combustion engine, by winding the mattress on the ducts 2 (the latter are three in the illustrative drawings of Figs. 1-3 and 5). Notice that the space between the baffles 3 is entirely filled up by the glass fibre 1 or 1 ' :

Although the second embodiment further speeds up and facilitates the manufacturing process with respect to the background art, a particular advantage, shared by both embodiments, is that the mass of glass fibre (1 or 1') does not include additional materials other than a glass fibre. In fact, preferably, the sewing 4 of the first embodiment is entirely performed with glass fibre threads.