US3493076A - Apparatus for smoothing pressure variations in gaseous flow - Google Patents

Description

R. MARDUEL Feb. 3, 1970 APPARATUS FOR smoo'mnm'e PRES-SURE VARIATIONS IN eAsEous FLOW Filed Nbv. 21. 19 68 Inventor Raga Mm Attorncy:

United States Patent 129,061 Int. Cl. F01n l/08, 7/18, 1/16 US. Cl. 181-57 Claims ABSTRACT OF THE DISCLOSURE The invention provides apparatus, e.g., a silencer for an engine or compressor, for smoothing pressure variations in gaseous flow, in which a tubular body is provided with a portion, e. g., a bellows portion, which is elastically deformable under the influence of pressure pulses in the gas, bafiles extending inwardly from the walls of the body.

The present invention relates to an apparatus for smoothing pressure variations in gaseous fiow. It is particularly suitable for smoothing variations in pressure in the exhaust of gases from internal combustion engines, i.e., it is suitable as a silencer.

It is known that the gaseous flows can show sudden variations, for example, because of the abrupt opening of cocks, poppet valves or valves, and certain gaseous streams can have a pulsatory character, for example in a conduit in which pulsatory flow conditions are established or in gaseous streams leaving apparatus which themselves set up pulsating streams, such as piston-type compressors or internal combustion engines.

Attempts have been made to smooth these flows, particularly by introducing into the conduits in which such flows exist, devices which carry baflie members or similar devices which introduce fairly high pressure drops and throttling effects which regulate the rate of flow. Expansion chamber systems have also been combined with batfle-type or similar devices. Very generally, all these arrangements or of a rigid construction.

When a gaseous stream under pulsating conditions exists in a conduit, this pulsation (or its harmonics) are transmitted to the conduit itself, exerting on the latter mechanical stresses which can be prejudicial thereto. In order to avoid this phenomenon, metal bellows are used which give a certain flexibility to the conduits.

All these solutions have disadvantages: a considerable pressure drop, a large volume and insufiicient action, so that the choice of the most suitable apparatus is always rather difficult. The problem is complicated if the gases concerned are hot gases capable of exerting a corrosive action on the metals of which such apparatus are generally formed. It is especially diflicult to resolve the problem in the case of the exhaust gases from internal combustion engines. The arrangements which are used and which are called at the present time silencers are very generally formed of rigid elements; nevertheless, a few embodiments thereof are known which have attempted to make use of the elastic deformation of their components. Thus, United States patent specifications Nos. 2,859,830 and 2,877,860 describe silencers which comprise elements of elastomeric material. All the known arrangements cause the gases to traverse complicated paths or to pass through narrow slots, so that the pressure drop of these arrangements always remains very high.

Additionally it is necessary for silencers for automobile vehicles, to be as light as possible and to be able to with- "ice stand unfavourable weather conditions. According to the present invention, there is provided apparatus for smoothing pressure variations in gaseous flow, such apparatus comprising a tubular wall, having an inlet and an outlet, at least a portion of said wall being elastically deformable under the influence of variations in dynamic pressure, substantially proportionally to such variations, and axially spaced apart baflies extending inwardly from the deformable portions of the wall, said baflies leaving a free passage for the flow of gas having an area equal to at least half of the cross-sectional area of the deformable portion of the tubular wall at the location of such baflie. The deformable portion may, for example, be formed of an elastomeric plastics material and this provides a very light arrangement which will smooth the variations in pressure in the gaseous flow and which can be used for gases up to a temperature capable of reaching 300 C., of which the chemical inertia eliminates almost completely the dangers of corrosion and introducing only a pressure drop which can be ignored under existing practical conditions.

The most important application of the apparatus according to the invention is a silencer for an internal combustion engine and more especially a silencer for automobile vehicles.

In order that the invention may more readily be understood, the following description is given, merely by Way of example, reference being made to the accompanying drawing, in which the sole figure is a schematic cross section through one embodiment of apparatus, in the form of a silencer, according to the invention.

As shown in the figure, the silencer includes a tubular body or wall comprising a substantially cylindrical inlet part 1 adapted to be fitted over an engine exhaust manifold M, the inlet part being joined to a portion 2 of which the wall is deformable, the latter part being itself joined to a rigid portion including a substantially cylindrical part 3, which is followed by a shaped part 4 and a substantially cylindrical outlet part 5 adapted to be fitted over a gas exhaust pipe E.

The portion 2 with a deformable wall is provided with batfles 6, 7 and 8 which are rigidly fixed and which close off a part of the passage for the gases. At least the deformable part is made of an elastic material preferably based on a silicone elastomer and which is resistant to the action of the exhaust gases.

The bafiies can be made of any material which is resistant to the action of the gases and capable of being secured to the deformable wall portion, and are preferably made of a material based on a silicone elastomer, which may or may not be reinforced.

The entire assembly is preferably made of silicone elastomer, it being possible for each part to be reinforced by any constructional elements for giving thermal and mechanical resistance and an elasticity which are appropriate to the function required of this part.

The dimensions of each part are not critical and they are to be determined in accordance with the usual rules in connection with the mechanical construction, depending on the number of cylinders and the rating of the engine to be equipped.

Preferably, the baffles are of such dimensions and number that, when they are dispensed substantially perpendicular to the general direction of the flow, none of them forms an aerodynamic screen for the following baflie. The bafiies can be annular, with the internal diameter decreasing in the general direction of flow of the gases. Preferably, the bafiies are simple circular segments which close off at a maximum half of the flow section for the gases and are disposed alternately on each side of the axis of the apparatus. Thus, a deformable compartment is provided by the space defined by the various baffles.

When a pressure pulse of gas originating from the exhaust of a cylinder flows through inlet part 1 and encounters the baflle 6 the dynamic pressure of the gas exerts a force on the bafile 6 which tends to drive it in the direction of flow, but as this bafile is secured to the deformable wall 2, it effects a deformation of the latter, which absorbs a part of the energy of the pulse and thus tends to reduce the initial pressure shock. This energy iS restored to the gaseous mass when the maximum pressure of the pulse has gone beyond the bafile and tends to increase the pressure of the last part of the pulse. There is thus obtained a smoothing or flattening of the pressure curve of the gas, and a similar phenomenon is produced between the baffles 6 and 7 and then between the baffles 7 and 8, and so on, depending on the number of baffles provided.

The pressure differences between the peak and the trough and the pulse are reduced on passing each of the bafiles, and after passing through a suflicient number of baffles an equalisation of the pressure and a nearly constant flow rate is obtained.

It is seen from the foregoing that the dimension of the battles, the dimensions of the deformable portion and the possibility of elastic movement of the assembly must be connected with the volume of the gaseous pulse and its extreme pressure differences. The adjustment to the operating conditions of a specified engine is thus a simple matter of practical experience. It appears that the best functioning is obtained when one compartment can move elastically at the same rate as that of the pulses of gas.

From the foregoing explanations, it is clear that the shape of the deformable wall is not critical, but nevertheless it has appeared in practice that the most advantageous form is a bellows form, either with annular or helical corrugations.

The inherent elasticity of the material which forms the wall can be utilised, but it is possible easily to have an influence on the elastic deformation of each compartment by making the deformable wall in the form of a bellows having helical corrugations and by embedding in these corrugations one or more helically wound elastic metal wires, for example, by incorporating therein one or more steel wires which are helically wound.

It has likewise been found that a conical bellows of which the diameter increases regularly in the direction of flow gives particularly satisfactory results.

If the walls are in bellows form they are easily deformed and this permits the dimensions of the baffles to be reduced. In many cases, the bafiies can be a simple prolongation of the edges of certain internal corrugations and can frequently coincide with the actual edge of these corrugations, this being particularly the case with conical bellows.

The cylindrical part 3 can optionally be separately made and a different material can be employed if desired. By way of example, it is possible to use a metal sleeve.

The dimensions of these parts are not critical, but it has been observed that the part-cylindrical and part-profiled or shaped assembly provides a steadying chamber and the adoption of profiles of double curvature which are conventional in connection with combustion chambers of rockets contributes to providing a regular flow of the discharging gases with high ejection velocities. The adoption for this part of the same formative material as that of the elastically deformable part, but duly reinforced so as to ensure the preservation of the shape, permits a slight elasticity for the assembly, which contributes to the damping of vibrations at sonic frequency, which could exist in the flow.

It is obvious that this part could be provided with an absorbent lining, such as silicone foams or various forms of roughening in order to provide the maintenance of an appropriate boundary layer or vibration damping zones, but this is generally unnecessary, as it is preferred to keep a smooth internal wall with a curvature providing a regular flow.

With other irregular and particularly pulsatory gaseous flows, it will be possible to use appropriate similar arrangements. For example, in a piping system leading from a compressor, it will be possible to employ an arrangement constituted only by a deformable part in the form of a cylindrical bellows consisting of an elastic material reinforced so as to resist the static pressure, of which the dimensions of the chambers will be adapted to the pulsation of the gaseous current. If the internal pressure becomes too large for the bellows to be able simultaneously to have a resistance sufiicient for resisting the static pressure of the gas and to offer a sufficient elasticity so as to be able to provide an acceptable damping of the pulsations, the damping arrangement may be enclosed in a tight metal tube in which will be set up a pressure of the same order of magnitude as that existing in the piping system, and this will enable a sufiicient thinness and flexibility to be retained for the deformable wall.

The arrangement according to the invention can be constructed in monobloc form or in several parts which are assembled in the manner which is judged to be most suitable. In particular, it can be constructed in the form of longitudinally assembled half shells. The apparatus can be constructed in accordance with the techniques which are usual for the material being employed, such as molding, coating, shaping under vacuum or under pressure.

The only important point is that the design details of the embodiment chosen and the material as it is formed because of its nature and the method of manufacture being used, are such that they permit the visualised deformation of the part of the elastic deformable wall.

As material capable of being used for the construction of apparatus according to the invention, it is possible to employ any material which is resistant to the action of the gases and which offers a sufficient mechanical resistance and elasticity. In some cases, metals can be used and in some other cases elastomers, such as natural or synthetic rubbers, which are possibly cloth-covered or reinforced.

Especially suitable are the fluorinated elastomers and more particularly the fiuorinated silicone elastomers or pure silicone elastomers or the conventional silicone elastomers which are prepared from resins having linear chains of structure:

the free valencies of the silicone atoms being satisfied with organic radicals such as methyl, vinyl and phenyl radicals. The linear chain can also be formed from siliconearylene linkages, which are known to provide temperature resistance, for example, chains of structure:

the organic radicals saturating the other free valencies of silicone atoms being satisfied with the above organic radicals.

The compositions of the elastomers which use these resins are well-known. The compositions which are preferred are those which withstand the highest temperatures, and vulcanise either under heat or at ambient temperature.

As cold self-vulcanising elastomers, those described in French Patents 1,198,749 and 1,266,528 are suitable, these elastomers being well-known and marketed on a Wide scale.

For example, the silicone elastomers which are particularly suitable are those comprising an organopolysiloxane resin of an average molecular weight of the order of 450,000 and of the general formula in which the radicals R to R represent straight or branched alkyl radicals comprising 1 to 4 carbon atoms, alkenyl radicals with 2 to 4 carbon atoms, an aromatic radical or a cycloalkyl radical comprising 3 to 6 carbon atoms, it being possible for these radicals to be substituted with one or more alkyl groupings comprising from 1 to 4 carbon atoms or one or more halogen atoms such as fluorine and an organophilic silicic filler such as silica of combustion, these resins being crosslinked by a vulcanising agent of the benzoyl peroxide type.

As reinforcing material designed to provide the desired mechanical resistance or elasticity for a particular part of the arrangement according to the invention, it is possible to employ any material which is usual in the manufacture of objects which are based on elastomers, such as fabrics, glass fabrics, metal cloths or others. It is also possible to employ local reinforcing elements, such as metal plates, steel wires or the like.

As regards the choice of the materials which form the first baflie it is necessary to pay particular attention to the physical and chemical conditions of the gases, since this first partition directly receives the gas of which the rate of flow is to be smoothed.

In a silencer, for example, it is necessary to take into account the fact that the temperature of the gases can be fairly high, that material particles can be entrained and that liquid combustion residues can be in the gaseous stream. The adaptation of this baffie to the composition of the exhaust gases and to the nature thereof is thus important. A very satisfactory material baflle is a silicone elastomer which is resistant to high temperatures, is reinforced with a metal cloth embedded in the mass or even in the form of a metal plate adhesively bonded to the elastic wall consisting of silicone resin by means of a silicone resin vulcanised in position.

As the exhaust gases generally leave the engine at a temperature in the region of 800 C. it is obviously necessary only to arrange the silencer at the end of a metal pipe which permits the temperature of the gases to be lowered to the region of 300 C., as is the procedure in normal automobile construction. The following example illustrates one practical form of the invention.

EXAMPLE An automobile vehicle having a 4-cy1inder engine with a cylinder capacity of 1468 cc. is used, the engine under normal running conditions turning between 1000 rpm. and 5000 r.p.m

A silencer as illustrated in the figure is disposed between the pipe leading from the engine exhaust manifold and the exhaust pipe.

The elastically deformable part is a bellows made from a silicone elastomer with a molecular weight of 450,000 and of the formula:

containing 30% of silica of combustion and vulcanised with 2,4-dichlorobenzoyl peroxide.

The bellows has annular corrugations, the depth of the folds of the corrugations being 10 mm.; the bellows has 20 corrugations, its minimum diameter, at the entry end for the gases, being 80 mm. and its maximum diameter is 130 mm., while the total length is 300 mm. It is connected by a cylindrical part to pipe M with a diameter of 30 mm.

This bellows is followed by a cylindrical part with a diameter of 130 mm. and a length of 50 mm., which is followed by a part having a double curvature and a length of 500 mm., which is terminated by a cylindrical part with a diameter of 40 mm. and a length of 50 mm., which is connected to the exhaust pipe E of the vehicle.

The part having double curvature consists of an identical silicone elastomer reinforced with glass fabric and made rigid by a helical steel wire of 0.5 mm., diameter of which the turns are spaced at 10 mm. The silencer assembly has a total length of 800 mm., without the short connecting pipes.

The bellows 2 carries three regularly spaced alternate semi-circular batfies consisting of a silicone elastomer of a similar general formula, but carrying phenyl radicals in place of the methyl radicals. These partitions are adhesively bonded to the bellows by a cold-vulcanising silicone elastomer.

It is found that the gases have the following temperatures; discharge temperature of the gases at the exhaust pipe when the motor is running extremely slowly is 38 C., after acceleration for 10 minutes it is 131 C.

It is found that the silencer gives a practically regular flow and that the noise of the explosions is very correctly damped. It is observed that the deformable part beats' according to the pulsations of the gaseous stream leaving the engine. The assembly behaves very satisfactorily mechanically and as regards withstanding the products of combustion. The assembly is very light weighing only 600 g. and it does not require any mechanical fixing to the bodywork. It withstands perfectly the external climatic conditions.

A metal silencer of conventional type for a vehicle of this type weighs 5 kg.

*1 claim:

1. Apparatus for smoothing pressure variations in gaseous flow, said apparatus comprising, in combination:

(a) a tubular wall defining at each location of its length an area for gaseous fiow;

(b) an inlet and an outlet to said tubular wall;

(0) at least a portion of said wall which is elastically deformable under the influence of variations in dynamic pressure, substantially proportionally to such variations; and

(d) axially spaced apart baffles extending inwardly from said deformable portion of said wall, and defining with said portion a reduced area for gaseous flow, said reduced area being at least half the area defined by said tubular wall at the location of each 'bafile.

2. Apparatus as claimed in claim 1, wherein the area defined by said deformable portion of said tubular wall increases from the inlet towards the outlet thereof.

3. Apparatus as claimed in claim 2 and further comprising a shaped rigid portion to said tubular wall between said deformable portion and said outlet, the area defined by said deformable portion decreasing towards the outlet.

4. Apparatus as claimed in claim 1, wherein said deformable portion of said tubular wall is of a bellows construction.

5. Apparatus as claimed in claim 1, wherein said de formable portion comprises a wall of elastomeric plastics material.

References Cited UNITED STATES PATENTS 781,939 2/1905 Fulton. 2,233,804 3/ 1941 Bourne. 3,061,039 10/1962 Peters. 3,187,837 6/1965 Beeching.

FOREIGN PATENTS 357,377 3/1938 Italy.

ROBERT S. WARD, JR., Primary Examiner U.S. C1. X.R. 181-58, 61, 65, 69

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