EP0781372B1 - Internal combustion engine silencer device - Google Patents

Abstract

PCT No. PCT/FR96/01098 Sec. 371 Date Apr. 17, 1997 Sec. 102(e) Date Apr. 17, 1997 PCT Filed Jul. 16, 1996 PCT Pub. No. WO97/04220 PCT Pub. Date Feb. 6, 1997A muffler device for the exhaust of an internal combustion engine comprising a tube (1) formed of at least a cone and a cylinder of a single piece of perforated sheet metal with alternating holes of varying diameters distributed over its length, the tube (1) being surrounded with a coaxial envelope formed of a cylindrical and/or conical front portion (2) and a back portion (3) with a conical nozzle terminating in an exhaust pipe at an angle to permit exhaustion of gas, the exhaust gases passing through an annular space between the tube and envelope through outlet parts or walls whose form and geometry prevent the formation of a turbulence generating back pressure.

Description

The present invention relates to an exhaust silencer for internal combustion engine, particularly for aircraft.

There are currently several muffler systems in baffles, by absorption by relaxation, which attenuate the level noise emitted to bring it back to the standards in force.

We notably know the document FR 1 041 034, which describes a silencer device for exhaust of motor vehicles with internal combustion. This device includes a cylindrical envelope comprising frustoconical elements pierced with holes and arranged for forming baffles one behind the other in said envelope.

These systems have the disadvantages of creating overheating and pressure disruptive contra-guidelines.

To overcome these drawbacks, the invention provides a device simple using a particular geometry and secondarily elements in austenitic stainless steel. Besides a significant reduction the noise level emitted compared to existing systems, like this will be described later in an example of application, the proposed device is easy to install and remove, its maintenance is easy and its maintenance over time improved.

It was not obvious that the proposed geometry and the selection of austenitic stainless steel provides the benefits important of the invention, and in particular a gain greater than 5 db minimum compared to the prior art mufflers. He was not no more obvious to forgo the often used baffle devices in many types of mufflers, in different types industries.

The silencer according to the invention is described in claim 1.

Secondarily, according to a preferred embodiment, the silencer is made of austenitic stainless steel. The space between the nozzle and the envelope is filled with a straw also made of steel austenitic stainless.

An important advantage of the invention is to authorize the processing a larger volume of gas, with a larger area of contact, the whole reducing the noise significantly, while allowing, surprisingly, the rapid evacuation of this larger volume without generating the foreseeable major drawback of back pressures.

The geometry of the invention will be understood by those skilled in the art at reading the attached drawings, without it being necessary to explain it more in detail. The skilled person will also be able to contemplate without difficulties of variants and derivatives of this geometry, respecting the general concept above.

It is also surprising to find that the unpleasant noise well known to professionals using stainless steel (caused by frequencies) is not produced by the device according to the invention. We know that for example the use of copper gives a sound "felted" but copper is naturally very heavy. He's surprising obtain a pleasant sound with a material sought after for its qualities but also known for its unpleasant noise.

• figure 1 : une coupe longitudinale d'un dispositif qui n'est pas selon l'invention,
• figure 2 : une coupe longitudinale du dispositif selon l'invention.
• figures 3 et 4 : coupes longitudinales de variantes du dispositif selon l'invention,
• figures 5 et 6 : coupes transversales respectives des figures 3 et 4 selon A - A ( représentant les cloisons perforées (6 BIS) ),
• figure 7 : détail d'un dispositif représenté en figure 2,
• figures 8 et 9 : détails d'un dispositif représenté en figure 3 ou 4.

Other features and advantages of the invention will appear clearly in the following description given by way of nonlimiting example with reference to the appended figures which represent:

• FIG. 1: a longitudinal section of a device which is not according to the invention,
• Figure 2: a longitudinal section of the device according to the invention.
• FIGS. 3 and 4: longitudinal sections of variants of the device according to the invention,
• Figures 5 and 6: respective cross sections of Figures 3 and 4 along A - A (representing the perforated partitions (6 BIS)),
• FIG. 7: detail of a device shown in FIG. 2,
• Figures 8 and 9: details of a device shown in Figure 3 or 4.

Referring to Figure 1, the device comprises a nozzle (1) formed of a cone and a cylinder in one piece made of perforated sheet metal, holes alternate and of different diameters from one row to another, over the whole length of the silencer. The outer envelope is formed by a part front (2), cylindrical and conical, and a conical end piece (3) forming the rear part and ending with a biased leak tube allowing gas evacuation down. The front part of the envelope outer (2) is here conical to facilitate penetration into the air. The edges of these two parts (2) and (3) intended to be assembled are machined by molding to form two circular grooves in a known technique. According to a preferred characteristic, the three elements (1), (2) and (3) are made of austenitic stainless steel (we recalls that austenite is a component of steel made up of a solid solution of iron and carbon), as well as the straw filling (4).

• soudage de la tuyère sur la partie avant au niveau du col (6),
• remplissage de l'espace entre la tuyère et l'enveloppe avec de la paille en acier inoxydable austénitique (4),
• mise en place de l'embout arrière (3) par emboítement et vissage.

The muffler is installed as follows:

• welding of the nozzle on the front part at the neck (6),
• filling the space between the nozzle and the casing with austenitic stainless steel straw (4),
• establishment of the rear end piece (3) by fitting and screwing.

The number and size of the perforations of the nozzle are adapted depending on the engine displacement. The muffler is connected to the exhaust manifold by an expansion bellows which is itself held by two clamps with braked screws.

FIG. 2 represents a variant of the device in which the nozzle has different counter cones (5), intended according to the applications to improve the relaxation of gases in the straw (4).

FIG. 7 represents the rear part of a device described in Figure 1 or 2, on which is shown the socket (9) of the tip conical (3) on the nozzle (4).

Figures 3 and 4 show other variants of the device according to the invention.

In these variants, a perforated partition (6 BIS) in the form of disc, is placed perpendicular to the axis of the nozzle to maintain the stainless steel straw in place and especially facilitate the evacuation of gas, hence the result of a reduction in back pressures. The straw is preferably held at the rear by this plate or partition perforated (6 BIS) giving passage to gases at its periphery and, in its center, at the nozzle outlet.

In these variants, the nozzle is welded to the perforated partition rear (6 BIS) which is itself screwed onto the rear part of the outer casing (2) and the conical end piece (3), and fitted into the front part of the outer casing (2) at the neck (6).

FIG. 8 represents the front part of a device described in Figure 3 or 4, on which is shown the socket (9) of the nozzle (1) on the outer casing (2) at the neck (6).

FIG. 9 represents the rear part of a device described in Figure 3 or 4, on which is shown the weld (8) of the nozzle (1) on the perforated partition (6 BIS), and the screwing (7) of the enclosure outside (2), the conical end piece (3) and the perforated partition (6 BIS).

Example of realization:

• Point fixe - puissance maximum pour une vitesse affichée de 2350 tr/mm   64 db
• Lâcher des freins - 2500 tr/mn pour une vitesse affichée au lâcher de 2300 tr/mn   74 db
• Passage 300 ft stabilisé - 2500 tr/mn   73 db
• Passage 1000 ft stabilisé - 2500 tr/mn   67 db
• Vitesse au cabrage 60 kn pour temps de roulage obtenu en 20 sec    71 db
• Passage 300 ft stabilisé - 2500 tr/mn pour vitesse affichée au passage de 120 km   70 db
• Passage 1000 ft stabilisé - 2500 tr/mn pour vitesse affichée au passage de 112 kn   68 db
• Montée initiale 80 kn pour une vitesse affichée de 2500 tr/mn   70 db
• Passage 300 ft stabilisé - 2500 tr/mn   70 db
• Passage 1000 ft stabilisé - 2500 tr/mn   65 db
• Verticale montée initiale 80 kn pour une hauteur obtenue au passage de 500 ft   89 db
• Passage 300 ft stabilisé - 2500 tr/mn   87 db
• Passage 1000 ft stabilisé - 2500 tr/mn   78 db

According to an example, a silencer was produced as described here with a nozzle of thickness 10 / 10th and an envelope of thickness 8 / 10th, the perforations have diameters varying between 8 mm and 10 mm. The test protocol provided the following results:

• Fixed point - maximum power for a displayed speed of 2350 rpm 64 db
• Release brakes - 2500 rpm for a release speed of 2300 rpm 74 db
• Passage 300 ft stabilized - 2500 rpm 73 db
• Passage 1000 ft stabilized - 2500 rpm 67 db
• Rise speed 60 kn for rolling time obtained in 20 sec 71 db
• Passage 300 ft stabilized - 2500 rpm for speed displayed at the passage of 120 km 70 db
• Passage 1000 ft stabilized - 2500 rpm for speed displayed at the passage of 112 kn 68 db
• Initial ascent 80 kn for a displayed speed of 2500 rpm 70 db
• Passage 300 ft stabilized - 2500 rpm 70 db
• Passage 1000 ft stabilized - 2500 rpm 65 db
• Vertical initial climb 80 kn for a height obtained at the passage of 500 ft 89 db
• Passage 300 ft stabilized - 2500 rpm 87 db
• Passage 1000 ft stabilized - 2500 rpm 78 db

On average, the level is equal to 72.8 db.

• Point fixe - puissance maximum pour une vitesse affichée de 2350tr/mn   77db
• Lâcher des freins - 2500 tr/mn pour une vitesse affichée au lâcher de 2300 tr/mn   74 db
• Passage 300 ft stabilisé - 2500 tr/mn   80 db
• Passage 1000 ft stabilisé - 2500 tr/mn   71 db
• Vitesse au cabrage 60 kn pour temps de roulage obtenu en 20 sec    73db
• Passage 300 ft stabilisé - 2500 tr/mn pour vitesse affichée au passage de 120 kn   75 db
• Passage 1000 ft stabilisé - 2500 tr/mn pour vitesse affichée au passage de 112 kn   73db
• Montée initiale 80 kn pour une vitesse affichée de 2500 tr/mn   77 db
• Passage 300 ft stabilité - 2500 tr/mn   73 db
• Passage 1000 ft stabilisé - 2500 tr/mn   70 db
• Verticale montée initiale 80 kn pour une hauteur obtenue au passage de 500 ft   92 db
• Passage 300 ft stabilisé - 2500 tr/mn   96 db
• Passage 1000 ft stabilisé - 2500 tr/mn   86 db

For comparison, the same measurements obtained with a conventional silencer are as follows:

• Fixed point - maximum power for a displayed speed of 2350rpm 77db
• Release brakes - 2500 rpm for a release speed of 2300 rpm 74 db
• Passage 300 ft stabilized - 2500 rpm 80 db
• Passage 1000 ft stabilized - 2500 rpm 71 db
• Rise speed 60 kn for rolling time obtained in 20 sec 73db
• Passage 300 ft stabilized - 2500 rpm for speed displayed at the passage of 120 kn 75 db
• Passage 1000 ft stabilized - 2500 rpm for speed displayed at the passage of 112 kn 73db
• Initial ascent 80 kn for a displayed speed of 2500 rpm 77 db
• Passage 300 ft stability - 2500 rpm 73 db
• Passage 1000 ft stabilized - 2500 rpm 70 db
• Vertical initial climb 80 kn for a height obtained at the passage of 500 ft 92 db
• Passage 300 ft stabilized - 2500 rpm 96 db
• Passage 1000 ft stabilized - 2500 rpm 86 db

On average, the level is equal to 78.2 db.
Notes: kn = knot 1 ft # 33 cm

The device according to the invention makes it possible today to obtain a gain greater than 5 db minimum compared to current conventional silencers. This device is particularly intended for equipping aircraft with a displacement of 4000 to 8000 m ³ , and more particularly the Piper PA 28.

Other embodiments will become apparent to humans and are part of the invention. In particular, the shape and dimension of the constituents may be adapted provided that the general concept of the invention is respected, i.e. the choice of forms creating at least one Venturi to accelerate the gases on at least one part of their path, and of forms generating the least possible of turbulence at the exit of the Venturi. In particular, the cones may be "rounded" and the Venturi replaced by an accelerator device similarly function. The only limits in this area will be cost and requirements assembly and maintenance. Similarly, the straw (4) can be replaced by any structural material fulfilling a function equivalent. Finally, the austenitic stainless steel can be replaced by any material capable of fulfilling the same function.

Claims (11)

1. A muffler device for the exhaust of an internal combustion engine comprising a perforated tube (1) over its total length, the tube (1) being surrounded with a coaxial envelope formed of a front portion (2) and a conical back portion (3), characterized in that the tube forms a geometry with several cones, the function of which is to form a large space, to create at least a system to accelerate the flow of exhaust gases at least over a section of their passage, the front portion (2) of the outside envelope is cylindrical or conical and that the tube (1) and the envelope (2), (3) form a continuous annular space from the neck (6) as far as the back portion (3) and through which pass the gases, which escape through an exhaust pipe permitting exhaustion of the gases and preventing the formation of turbulences generating back pressure.
2. A muffler device for the exhaust of an internal combustion engine according to claim 1, characterized in that it has no baffle plates and that the space between the tube and the envelope is filled with a steel wool (4) held at the back portion by a perforated partition or plate (6a) releasing passage of the gas at its periphery through the perforations and, at its centre, to the tube's outlet.
3. A device according to claim 1 or 2, characterized in that the tube is formed of one or several cones, counter-cones (5) and a cylinder, all in one piece.
4. A device according to claims 1, 2 or 3, characterized in that the system to accelerate the exhaust gas flow is a "Venturi" type system.
5. A device according to any one of claims 1 to 4, characterized in that the tube's perforations are comprised of alternating holes of different diameters from one row to another, the number and size of the perforations according to the displacement of the internal combustion engine.
6. A device according to any one of claims 1 to 5, characterized in that the envelope is formed of a front part welded to the tube at its neck (6), a non movable conical back part, the two edges joining these two parts being crimped into two throats to permit rapid disassembly and reassembly.
7. A device according to any one of claims 1 to 5, characterized in that the tube is inserted into the outside envelope in front (2) at the neck (6) and welded on a perforated partition (6a) itself being screwed onto the front portion (2) of the outside envelope and onto the back portion (3) of the outside envelope.
8. A device according to any one of claims 1 to 7, characterized in that the back portion (3) of the coaxial envelope terminates in an exhaust pipe at an angle to permit exhaustion of the gas downwards,
9. A device according to any one of claims 1 to 8, characterized in that it is fitted to the exhaust of an aircraft engine or another type of internal combustion engine.
10. A device according to any one of claims 1 to 9, characterized in that the tube-envelope unit is made of austenite stainless steel.
11. A device according to any one of claims 1 to 10, characterized in that the space between the tube and the envelope is filled with steel wool made of austenite stainless steel.

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