GB1565517A - Muffler element - Google Patents

Description

(54) MUFFLER ELEMENT (71) We, BBC BROWN BOVERI & COM PANY LIMITED of Baden, Switzerland, a Swiss company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a muffler element comprising sound-suppressing material retained by grids in a support member.

Exhaust gas turbochargers are frequently equipped with an inlet muffler which is mounted on the compressor casing. The purpose of the said muffler is to suppress sound waves which occur in operation of the compressor and to this end the muffler is provided with a plurality of muffler elements which are situated in the interior of the muffler at distances from each other. Such a muffler element generally comprises a support member, which can be a sheet metal pressing, and muffler parts which are fixedly joined to the support member and are constructed of sound-suppressing material, for example, felt or mineral wool. The air flows past the muffler parts to the compressor from which sound waves emerge in the direction opposite to the flow direction so that pressure peaks and troughs occur.Sound suppression is achieved by the air being forced into the sound-absorbing material when pressure peaks arise and being drawn out from the material when pressure troughs occur. The muffler parts therefore function as a buffer which equalizes the pressure difference between the pressure peaks and the pressure troughs to a certain degree and thus reduces the amplitudes of the sound waves. The thickness of the muffler parts depends on the lowest frequency to be suppressedcorres- ponding to the longest wavelength-and the effectiveness of sound suppresion depends on the flow resistance of the muffler parts.

The shape and dimensions of the muffler parts of different mufflers differ in accordance with requirements. In known mufflers with annular muffler elements the latter are cylindrical, disc-shaped or conical or have a combination of such shapes. In all these cases felt layers which function as muffler parts are attached by adhesive bonding and riveting to a support member of solid cross-section which is constructed in accordance with the requirements.

These constructions suffer from certain disadvantages. Owing to the need for adhesive bonding and riveting and because of the different kinds of surfaces which require covering, the manufacture of a muffler element is awkward and costly. The muffler parts can become detached and loosen owing to pressure and heat surges if the compressor performs a "pumping" action. The muffler surface required for compressors operating at high speeds become very large, which results in cost increases. Furthermore, suppression of the low sound frequencies is possible only to a limited degree.

It is the object of the invention to provide a muffler element which offers satisfactory sound suppression with low air flow losses in the light of present day compressor speeds and noise regulation and permits trouble-free operation and economical manufacture.

According to the invention, we provide a muffler element comprising muffler parts of sound-suppressing material retained in a support member by means of grids, characterised in that the support member is a plate perforated by apertures the total area of which amounts to at least 25 % of the total support member surface area, in which apertures the muffler parts are accommodated, one edge of the plate is provided with a rounded nose, an the opposite edge of the plate is provided with a deflector vane.

Compared with known constructions, a muffler element of this kind achieves suppression of the same frequencies with substantially thinner muffler parts and therefore with a reduced expenditure in terms of material; alternatively, lower frequencies can be suppressed with the same thickness. Adhesive bonding and riveting of the muffler parts is obviated, a feature which simplifies manufacture and improves efficiency. The deflector vane results in improved flow conditions with insignificant additional expenditure.

The muffler element can comprise massproduced identical segments, thus achieving an additional increase of efficiency and further facilitating manipulation in the course of installation and transportation.

One embodiment of the invention is explained by reference to the accompanying drawing, in which: Fig. 1 is a part-view of a muffler element, and Fig. 2 is a section through the muffler element according to Fig. 1 along the line IV-IV.

The muffler element shown is annular and comprises a perforated support member 1 with approximately rectangular apertures of relatively large area in which the muffler parts 2 are situated. The said muffler parts, which consist of a sound-suppressing material, are retained on both sides by grids 3 which are secured on the support member by means of rivets (not shown). Holes 7 are provided for attachment of the rivets. The support member also has bores 8 which are intended for receiving tie-rods (not shown) which fix the muffler elements parallel to each other by means of spacer sleeves and retain them in a muffler casing.

The convex external peripheral edge of the support member, which in use is the leading edge relative to the air flow, in constructed as a rounded nose 9; at the concave trailing edge on the internal side is a deflecting vane 10 in order to improve the flow conditions. The total area of the apertures should be at least 25 %, preferably more than 30% of the total support member surface.

The thickness of the muffler parts is such that they completely fill the apertures. The air flows past the said elements but if pressure differences occur it can flow through the muffler parts from one air flow duct into an adjacent duct. The grids 3 practically do not influence the noise-suppressing action, but protect the muffler parts against damage, more particularly if the compressor commences pumping action.

The design of the support members (which can advantageously be constructed of cast light alloy and can comprise a plurality of segments arranged serially in the circumferential direction), the muffler parts and the grids is in practice selected in accordance with the appropriate conditions and the special requirements regarding shape and dimensions of the muffler and of the frequencies to be suppressed. A substantial saving of space and material is achieved together with effective sound suppression, and the manufacture of the muffler elements is simple and economical.

WHAT WE CLAIM IS:- 1. A muffler element comprising muffler parts of sound-suppressing material retained in a support member by means of grids, characterised in that the support member is a plate perforated by apertures the total area of which amounts to at least 25 % of the total support member surface area, in which apertures the muffler parts are accommodated, one edge of the plate is provided with a rounded nose, and the opposite edge of the plate is provided with a deflector vane.

2. A muffler element according to claim 1, characterised in that the support member consists of a cast light alloy.

3. A muffler element according to claim 1 or 2 characterised in that the support member is provided with a plurality of bores adapted to receive tie-rods.

4. A muffler element as claimed in any of claims 1 to 3 in which the said edges of the plate are arcuate, the said one edge being convex and the opposite edge being concave.

5. A muffler element as claimed in claim 4 which is annular.

6. A muffler element as claimed in claim 4 or 5 in which the support member comprises a plurality of segments disposed serially in the circumferential direction of the arcuate edges.

7. A muffler element substantially as herein described with reference to the accompanying drawings.

8. A muffler comprising muffler elements as claimed in any of claims 1 to 6 disposed in an air flow path with the said noses being the leading edges and the deflector vanes being the trailing edges relative to the air flow.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. an additional increase of efficiency and further facilitating manipulation in the course of installation and transportation. One embodiment of the invention is explained by reference to the accompanying drawing, in which: Fig. 1 is a part-view of a muffler element, and Fig. 2 is a section through the muffler element according to Fig. 1 along the line IV-IV. The muffler element shown is annular and comprises a perforated support member 1 with approximately rectangular apertures of relatively large area in which the muffler parts 2 are situated. The said muffler parts, which consist of a sound-suppressing material, are retained on both sides by grids 3 which are secured on the support member by means of rivets (not shown). Holes 7 are provided for attachment of the rivets. The support member also has bores 8 which are intended for receiving tie-rods (not shown) which fix the muffler elements parallel to each other by means of spacer sleeves and retain them in a muffler casing. The convex external peripheral edge of the support member, which in use is the leading edge relative to the air flow, in constructed as a rounded nose 9; at the concave trailing edge on the internal side is a deflecting vane 10 in order to improve the flow conditions. The total area of the apertures should be at least 25 %, preferably more than 30% of the total support member surface. The thickness of the muffler parts is such that they completely fill the apertures. The air flows past the said elements but if pressure differences occur it can flow through the muffler parts from one air flow duct into an adjacent duct. The grids 3 practically do not influence the noise-suppressing action, but protect the muffler parts against damage, more particularly if the compressor commences pumping action. The design of the support members (which can advantageously be constructed of cast light alloy and can comprise a plurality of segments arranged serially in the circumferential direction), the muffler parts and the grids is in practice selected in accordance with the appropriate conditions and the special requirements regarding shape and dimensions of the muffler and of the frequencies to be suppressed. A substantial saving of space and material is achieved together with effective sound suppression, and the manufacture of the muffler elements is simple and economical. WHAT WE CLAIM IS:-

1. A muffler element comprising muffler parts of sound-suppressing material retained in a support member by means of grids, characterised in that the support member is a plate perforated by apertures the total area of which amounts to at least 25 % of the total support member surface area, in which apertures the muffler parts are accommodated, one edge of the plate is provided with a rounded nose, and the opposite edge of the plate is provided with a deflector vane.

2. A muffler element according to claim 1, characterised in that the support member consists of a cast light alloy.

3. A muffler element according to claim 1 or 2 characterised in that the support member is provided with a plurality of bores adapted to receive tie-rods.

4. A muffler element as claimed in any of claims 1 to 3 in which the said edges of the plate are arcuate, the said one edge being convex and the opposite edge being concave.

5. A muffler element as claimed in claim 4 which is annular.

6. A muffler element as claimed in claim 4 or 5 in which the support member comprises a plurality of segments disposed serially in the circumferential direction of the arcuate edges.

7. A muffler element substantially as herein described with reference to the accompanying drawings.

8. A muffler comprising muffler elements as claimed in any of claims 1 to 6 disposed in an air flow path with the said noses being the leading edges and the deflector vanes being the trailing edges relative to the air flow.