EP0337877B1 - Silencer for internal-combustion engines - Google Patents

Description

The present invention relates to a silencer for an internal combustion engine consisting of an internal gas channeling circuit housed in an outer casing.

To reduce the noise produced by internal combustion engines, particularly those of motor vehicles, it is common practice to place silencers in the exhaust gas circuits.

These silencers are made of sheet steel and undergo internal (acid condensates) and external (water, mud and salt spray) corrosion.

The solution consisting in replacing all or part of the ordinary steel by stainless steel is expensive.

Document GB-A-2.129.490 describes a silencer using an outer casing of composite material. However, the thermoplastics used such as nylon with mineral fillers such as mika do not ensure good resistance of the envelope to corrosions both internal, by acidic condensations, and external and do not allow good resistance to temperature. . In addition, the assembly of the exhaust line inside said envelope appears complicated and costly.

The present invention aims to overcome these drawbacks by referring to a new design of exhaust silencers and the development of new composite materials having good heat resistance. The design of the silencer provides good thermal insulation so that the temperature of the enclosure remains limited. The design of the enclosure provides good thermal insulation which allows the internal circuit to rise faster and higher in temperature (therefore less condensate) and good soundproofing.

The silencer according to the invention is characterized in that the gas pipe is integral on the one hand with two insulating flanges made of refractory material placed at the two ends of the pipe, said flanges being intended to engage directly in defined suitable grooves in the half-shells and on the other hand of vertical partitions which rest on the half-shells with the interposition of insulating glues made of refractory material. In addition, the half-shells may have cooling ribs on the outside.

• la figure 1 représente une vue éclatée d'un silencieux selon l'invention,
• la figure 2 est une demi-coupe longitudinale d'un silencieux assemblé,
• La figure 3 est une demi-coupe transversale du même silencieux,
• La figure 4 est une vue de détail d'une demi-coquille,
• La figure 5 est une variante de montage des collerettes.

The invention will now be described in more detail with reference to an embodiment given by way of example and represented by the appended drawings in which:

• FIG. 1 represents an exploded view of a silencer according to the invention,
• FIG. 2 is a longitudinal half-section of an assembled silencer,
• FIG. 3 is a half cross-section of the same silencer,
• FIG. 4 is a detailed view of a half-shell,
• Figure 5 is an alternative mounting flanges.

Referring to Figure 1, the silencer has an internal gas circuit consisting of a metal tube 1 forming a baffle and two partitions 2. This circuit is made of steel protected against internal corrosion. It is integral with two insulating flanges 3 made of refractory material placed on the two ends of the tube 1.

This circuit is wrapped in an external envelope formed by two half-shells 4 of composite material in the form of glass-polyester prepreg or glass-phenolic prepreg. Insulating shims 5 made of refractory cardboard are placed in the half-shells 4 in line with the partitions 2.

The assembly is carried out in such a way that the half-shells 4 are not in direct contact with the metallic central circuit, as indicated in FIG. 2 which is a longitudinal half-section of the assembled silencer.

Two metal rings 6 fixed to the tube 1 (by welding, soldering or crimping) make it possible to correctly position the insulating washers 3. The flanges 3 engage in grooves housed in the caps 41 of the half-shells. In the variant of FIG. 5, the flanges 3 have an outwardly curved shape, which makes it possible to lengthen the distance between the connections on the hot tube 1 (inlet and outlet) which are outside the envelope. Washers 9 made of refractory fibers can be placed inside the steel flanges 3 so as to reduce heat exchanges with the hot gases circulating inside the silencer.

The two half-shells are assembled together by screws, collars or rivets 7 with the interposition of a silicone seal 8 as shown in Figure 3 which is a half cross-section in the assembly area. The assembly elements of the two half-shells can come from molding. For example, these assembly elements can act by clipping.

The half-shells 4 can be compression molded, by placing on the press punch a cloth of verranne and a blank of prepreg.

Closing the press ensures complete filling of the mold, including the imprints of the ribs arranged in the die.

The molds are heated to a constant temperature between 100 and 200 ° C (150 ° C in the present example), the polymerization is thus carried out between one and two minutes depending on the thickness of the part to be molded and the reactivity of the resin used.

The half-shells thus molded have the particularity of presenting on their internal face a layer of unimpregnated verranne fabric 14 (see FIG. 4) forming a certain thermal insulation, and of presenting on their external face cooling ribs 42 obtained from molding .

The insulation of the internal face can be increased by the presence of a layer of glass wool or rock as it already exists in many metallic silencers to attenuate the sound emission.

The internal insulation layer may be missing. The polyester resin constituting most of the matrix is calcined on a small thickness of the internal face of the envelope. The glass fiber thus exposed remains in place, thus forming an insulating layer which stops the progression of the calcination of the matrix. It is therefore sufficient to provide the ablative allowance at the time of design.

The shell is made with a composite material comprising glass fibers, pulverulent fillers and an organic matrix. The arrangement and distribution of the constituents is such that heat exchanges are favored towards the outside and reduced towards the inside so that the temperature of the shell does not exceed 200 ° C.

It is then possible to use certain unsaturated polyester resins or phenolic resins.

As an indication, the prepreg is made with an impregnation paste and it comprises 27% glass by weight in the form of rovings cut to 25 and / or 50 mm in length, and this prepreg can be easily manufactured using the machine described in patent FR-A-2 266 595 of the applicant.

The presence of extra-conductive carbon black increases the thermal and electrical conductivities, but it gives the paste a thixotropy which hinders the impregnation of the glass fibers during the preparation of the prepreg.

According to a variant, the prepreg intended for molding the half-shells is manufactured on the same machine as previously but by incorporating hollow glass microspheres in the impregnation paste supplying the upper coating, while the lower coating is supplied with a dough without microspheres.

These microspheres, for example those corresponding to the reference B37 / 2000 of the company 3M, have a particle size greater than 50 μm and are thus filtered by the sheet of cut glass fibers.

In addition, they have an apparent density lower than that of the resin.

These microspheres therefore form an insulating layer on top of the prepreg.

The molding of the half-shells is thus carried out by placing the face of the prepreg filled with hollow microspheres on the punch side, with or without the interposition of verranne fabric.

Claims (5)

1. A silencer for an internal combustion engine comprising a gas conduit (1) housed in a casing formed by two half-shells (4) of composite material characterised in that the gas conduit (1) is fixed on the one hand with respect to two insulating collars (3) of refractory material which are placed at the two ends of the conduit, said collars (3) being intended to engage directly into suitable grooves defined in the half-shells and on the other hand vertical partitions (2) which bears against the half-shells (4) with the interposition of insulating fitting pieces (5) of refractory material.

2. A silencer according to claim 1 characterised in that the half-shells (4) have cooling ribs (42) on the outside.

3. A silencer according to either one of the preceding claims characterised in that the composite material is formed by glass fibres, powder fillers and an organic matrix.

4. A silencer according to any one of the preceding claims characterised in that the composite material comprises glass microballs.

5. A silencer according to any one of the preceding claims characterised in that the collars (3) are curved outwardly.

Images