AU2679992A - Fishbone standardised silencers for (internal) combustion engines - Google Patents

Abstract

This patent application is for a new silencer design with the following features: free (exhaust) gas flow through, which means close to zero back pressure, or head loss; superior acoustic performance, especially in the high- and mid frequency ranges; increased engine net performance and efficiency; identical accoustical performance throughout its service life; simple, light, modular configuration, prone to: cheap industrial automatic production; reusing (cartridge type), and/or recycling, thus avoiding pollutant waste; standardising and uniformising of silencers throughout the (automotive) industry; constructed from the suitable material, can provide a really unlimited lifetime. Although this design is particularly suitable for (internal) combustion engine exhaust and induction mufflers, it can be applied advantageously to other silencers in- and outside the industry and, in general, our living environment (gas flow duct silencers, airco-, venting-, etc...).

Description

FISHBONE STANDARDISED SILENCERS FOR (INTERNAL) COMBUSTION ENGINES

DESCRIPTION

See fig. 1 to 7, pages 9 to 12.

The silencer is composed by a cylindrical enclosure (1) - wi preferably a near circular or elliptic cross section-, closed both ends by end caps (2), through which the up- (3) and do stream pipes (4) pass.

This enclosure is subdivided longitudinally into a high numb of shallow cells, by transversal diaphragms (5).

The (exhaust) gas flows through (circular) holes in t diaphragms, approx. the same diameter as the up- a downstream pipe diameter, and aligned with these.

A high passage rate perforated pipe or mesh (6) may or may n be running through the diaphragm holes (fig. 1 & 2). T perforated pipe would facilitate the assembly and impro further the gas flow, and heat exchange.

Alternatively, the fishbone subdivision may be obtained by t introduction of a cartridge (ceramic, sintered, etc.) (fig 5 p. 1 or the silencer might be produced as a monolithic constructi

(ceramic, sintered, casting, extrusion, etc.) (fig. 6 p. 11).

The shallowness of the cells can be defined by the ratios ai and ai which should be d t respectively < ι.o and < o.5 where t is the mean enclosure transversal dimension and d t diaphragm aperture (fig 1-6, p. 9-11); ai, the axial dimension the respective cells, can be choosen constant or varia optimising the silencer acoustic performance for its specific ta (noise reduction for particular frequency ranges). See Fig. 3 p. 10.

Silencer design is still largely empirical, due to its diffic mathematical analysis. For silencers of this new configurati tests can easily be set up to find out the optimum design. T comes down to determining ai, for given overall dimensions. DESCRIPTION

In conventional silencers with reflection, expansion, absorption cavities & resonator chambers, cross flow and perforated pipe throughflow configurations, the gas flow did expand into the spacious cavities, and gas flow velocity and - pressure did fluctuate heavily - see fig. 7 p.12. Turbulence was generated at the flow variation locations, causing the build-up of high back pressure (as much as o.25 bar) or head loss.

(Expensive) stuffings did improve this situation slightly, but whatever the (expensive) precautions taken (fine mesh fleece), they did get blown - and sucked out soon, melted, burned or got clogged up, with decline of the acoustic performance, and causing pollution.

Contrary to the former belief, the contribution of the stuffings was not direct sound absorbing, but braking down the gas velocity through the cavities, thus reducing the gas flow expansion into - and contraction out of the cavities, which, in itself generated new noise.

In this new design, on the contrary, the gas flow does not expand into the shallow cells, due to their sheer shape. Gas flow velocity stays constant, and little turbulence occurs at the diaphragm hole edges (depending on the ratio of flow and hole & pipe diameter "d"). Back pressure or head loss build up is close to zero.

The sound waves, however, do move into each of the numerou shallow cells, and are damped by the standing waves. Compared to conventional design, noise reduction is intensifie for the same overall silencer dimensions. DESCRD7TION

Constructively, the new silencer is made of one single materi (fig. 1-4, p. 9-10; fig. 6, p. 11) or, alternatively, is fitted with ( cartridge(s), which is (are) easily introduced or exchanged f overhaul (Fig. 5 p. 11).

This means a tremendous simplification of production, and t advent of the possibility of easy overhaul.

On the other hand, this concept implies a generally cylindric shape.

Cross sections should be near circular or elliptic, while they a acoustically the stiffest, and allow the thinnest mantle materi thickness, avoiding shell noise.

Multiple layer mantles should be avoided, because they redu the silencers' cooling (in case of use for hot (exhaust) gases).

The diaphragms should be stiff enough and well clamped, not transmit noise to the next cell by vibrating themselves. They c be doubly curved (stamped) for maximum stiffness and lightnes See fig. 2 p. 9.

Their clamping can be by heat-shrinking of the mantle arou them (either of a complete cylinder which is heated, or by t shrinkage of 1 or 2 longitudinal welds, (1 open shell or 2 pa shells) f.i.

The gas flow channel can be concentric but may be eccentr (fig. 3 & 4 p. 10). DESCRIPTION

The author proposes thus an inversion of the (car) muffler design and selection procedure : instead of filling up available space under the car with custom designed volumes of mufflers, the car designers would accept from the start that they be cylindrical, with a limited but handsome number of standardised cross-sections and pipe eccentricities to choose from, and provide space for these under the body.

Claims (16)

1. This new silencer design produces minimum back pressure head loss.

2. This new silencer design has superior acoustic performances f given overall dimensions.

3. Following claim 1, this new design raises net engi performance, efficiency, and service life.

It reduces unwanted exhaust gas remaining in the combusti space, and allows thus a more precise control of exhaust g recirculation.

4. This silencer design is of advanced simplicity and modulari necessitating very few different operations for its productio This makes it prone to cheap industrial production. Investment needed to produce this type of silencer is much le than for conventional silencers.

5. Silencers of this design are made of only one material, or of o material and a cartridge.

6. Metallic silencers of this design have a minimum amount joints. The few welds to be made can shrink freely, witho leaving any residual stress.

7. Metallic silencers of this design have their structure so w cooled that they act as heat exchangers. Due to the temperatu drop of the exhaust gas, this silencer acts as an extractor, whi improves further the engine's performance and efficiency.

8. The high number of diaphragms stiffens the outer shell a eliminates shell noise. CLAIMS

9. Following claim 7, silencers of this design can be built from alu- alloy, which provides :

improved exhaust gas cooling, and thus engine performance and efficiency. weight - reduction. high corrosion - resistance.

Traditional belief that alu-alloy mufflers would melt proved wrong, also because the alu-oxide layer that forms spontaneously at every free surface resists temperatures beyond 2000°C.

10. With silencers of this design, stuffings are useless and thus needless.

11. Silencers of this design with fishbone cartridge(s) can easily be overhauled, exchanging the cartridge(s).

12. Silencers of this design are suitable for monolithic constructio (ceramic, sintered, cast, extruded, etc.).

13. Silencers of this design can be made for unlimited life time, which was not the case with the former designs, whateve materials they were built from.

14. The availability of this design stimulates car designers o different automotive corporations to uniformise in space and i time their demand on silencer manufacturers. CLAIMS

15. Silencers of this design are a solution to the growing pollutan waste pile.

16. Although this design was particularly developed for (exhaust engine mufflers, it can be applied for other silencing purposes.

AMENDED CLAIMS

[received, by the International Bureau on 20 August 1993 (20.08.93⁾ ; original claims 1-16 replaced- by amended claims 1-5 (3 pages) ]

1. This new silencer design is characterised by «straight», unobstructed (exhaust) gas flow through closely spaced diaphragms ((5), fig. 1,2), which form characteristically a high number of shallow cells, within the overall silencer dimensions (fig. 1-6, 8).

These characteristic shallow cells repeatedly split up the sound wave energy, delay, dephase, and smooth out the wave pressure variations, without causing turbulence, back pressure or head loss.

Additionally, dissipation occurs at the far end of the cells (fig. 8), and absorption into the cell walls for the versions with porous (ceramic, sintered) cartridge(s) (fig. 5, 6) (hence the advantage of increasing their surface by raising the number of diaphragms).

Said shallow cells characteristically avoid self-generated noise, because their said shallow shape keeps the (exhaust) gases from flowing into and out of them (cf. fig. 7 with fig. 1-6, 8).

In said silencers, stuffings are unnecessary, and are dispensed with.

Acoustic performance of said silencers stays identical throughout service life.

The characteristic diaphragms may be flat (fig. 1, 3, 6), or simply (fig. 8a), or doubly curved (fig. 2, 5, 8b), for maximum acoustic performance, and minimum weight-

The height «a» of the shallow cells (fig. 1, 2, 3, 5, 6) may be constant (fig. 1, 2, 5, 6, 8) or variable (fig. 3), optimising the silencer acoustic performance for it's specific task (frequency spectrum of the noise to be attenuated).

The characteristic high number of said diaphragms stiffens the outer shell and eliminates shell noise (fig. 1, 2, 3, 8).

The overall shape of said silencers is preferably cylindrical, (for simplified and standardised construction), with a near circular or elliptic cross section, because these are the stiffest acoustically, and, conversely, allow the thinnest mantle material thickness. This is desirable for better cooling and less weight and cost. Said silencers may (fig. 1, 3, 8b) or may not (fig. 2, 5, 6, 8a) be fitted with ( perforated pipe(s) ((6) fig. 1), with an open rate of at least 20 % (= acousticall transparent). Adding them improves the (exhaust) gas flow.

The (exhaust) gas flow may be central (fig. 1, 2, 5, 6) or eccentric (fig. 3, 4) wit respect to the silencer.

One silencer may carry one (fig. 1-3, 5, 6, 8) or several (fig. 4) parallel (exhaus gas flows.

2. Said silencers according to claim 1 produce characteristically close to zero, an adjustable back pressure or head loss.

They thus raise engine efficiency, output, and service life.

They allow greater overlap of intake and exhaust cycles, and impro scavenging, raising again engine performance.

Metallic silencers according to claim 1. have their structure so well cooled that th act as heat exchangers.

Due to the (adjustable) temperature drop of the (exhaust) gas, said silencers act extractors, which improves further the engine's performance and efficiency.

With said silencers, multiple layer mantles are preferably avoided for norm applications, as they impair the silencer's cooling.

Following claim 3, silencers according to claim 1 can be built from Aluminium-all (Al Mg3 - Al Mg5 f.i.), which provides : improved exhaust gas cooling, and thus raised engine perfor-mance a efficiency. weight reduction. improved corrosion resistance. This is thanks to the fact that the (exhaust) gas does not flow through the characteristic shallow cells, and to the characteristic superior, adjustable, cooling capacity of the configuration accor-ding to claim 1.

Also, the alu-oxide layer that forms spontaneously at every free surface resists temperatures beyond 2000 °C.

Said silencers according to claim 1 are made of only one material, or of one material and a cartridge.

Metallic silencers of said design have a amount of joints. The few welds to be made can shrink freely, without leaving any residual stress.

To preserve their stress-free state, said silencers will preferably be suspended by bolted-on straps.

Silencers of said design with fishbone cartridge(s) can easily be overhauled, exchanging the cartridge(s).

Silencers of said design according to claim 1 are suitable for monolithic construction (fig. 6) (ceramic, sintered, cast, extruded, etc.).

Silencers of said design can last an unlimited life time, which was not the case with prior art designs, whatever materials they were built from.

Silencers of said design are of advanced simplicity and modularity, necessitating few operations for their production. This makes them prone to cheap industrial manufacturing.

The availability of said design stimulates car designers of different automotive corporations to standardise in space and in time their demand on silencer manufacturers.