FR2466613A1 - Engine exhaust noise silencer - has casing with cells temporarily storing gas under pressure released when pressure falls - Google Patents

Abstract

The silencer reduces the exhaust noise from an internal-combustion engine, the gases under pressure being temporarily stored, and released when pressures subsequently fall. Thus pressure is regularised at the core of an acoustic attenuator, the latter operating particularly by reflection, absorption, interference and/or resonance. The silencer used for this system can have a casing containing a large number of interconnected acoustic attenuation sections. These each consist of a chamber incorporating a perforated tube between inlet and outlet. There is also a dead-ended pressure regulation chamber (C4) with no tube, forming a temporary reservoir for gas under pressure, and connected to the casing between two of the sections.

Description

 The present invention relates to the internal combustion engine industry. It specifically targets the exhaust muffler industry for automobile and other vehicle engines.

 Internal combustion engines and more particularly internal combustion engines are extremely noisy.

Regulations impose the attenuation of these noises in significant proportions.

 There are many conventional systems for reducing noise in well-known devices called silencers.

 These conventional systems essentially call upon phenomena of reflection, absorption, interference and / or resonance.

 To attenuate the noises by reflection, there are on the path of the engine exhaust gases, in the silencer, acoustic obstacles or baffles which cause a reflection of the sound waves.

 Attenuation of noise by absorption is carried out during the passage of gases through a fibrous material.

 To obtain interference which attenuates noise, we divide part of the exhaust gas stream into several secondary streams which are reintroduced into the main stream in places where the time difference in noise created by the difference in length of the main stream and sub stream creates interference which decreases noise. In practice, this result is obtained by passing the chambers through a plurality of perforated tubes or having a continuity solution.

 Noise attenuation is also obtained according to a principle analogous to that of interference by means of resonance chambers which phase the noises and cause their interference.

 These conventional devices give almost satisfactory results under normal operating conditions of internal combustion engines. However, this is not the case when there are sudden changes in the pressure of the gas flow, as is the case in the rapid acceleration or deceleration phases of the engine.

 I1 indeed seems that the optimal conditions for attenuation of noise by conventional devices are only achieved in a relatively limited range of average engine operation, which results in an almost constant pressure inside the silencer. .

 Some conventional silencers include, before the entry of gases, into the noise attenuation system of the silencer or even at the exit thereof, chambers which can ensure a certain regulation of the pressure of the gases.

 However, these conventional devices do not provide pressure regulation at the most critical location, that is to say at the heart of the muffler.

 The invention aims to overcome the drawbacks of conventional silencers.

 It relates to a method for attenuating the noise of the exhaust of the burnt gases from an internal combustion engine. This process consists of temporarily storing said gases during overpressures in order to restore them during subsequent pressure drops and thus regulate the pressure of said gases at the heart of an acoustic attenuation assembly, in particular by reflection, absorption, interference and / or resonance. .

 A silencer for exhausting cross-linked gas from an internal combustion engine according to the invention comprises at least one enclosure containing an acoustic attenuation assembly constituted by a plurality of intercommunicating sections, each composed of at least one chamber containing at least one tube in perforated part, arranged between an inlet and an outlet of said gases from said enclosure. This silencer further comprises at least one dead end pressure regulating chamber, devoid of tube, forming a temporary reservoir of gas under pressure, and opening into said enclosure between two of said sections.

In such a silencer, the pressure regulation chamber can be constituted by a blind tube arranged
outside and along the enclosure.

 Such a blind tube can advantageously be fixed by its two ends, respectively to two end faces of the enclosure.

The invention will be better understood on reading the detailed description which follows and on examining the appended drawings which represent, by way of nonlimiting examples, several embodiments of the invention. On these drawings
- Figure 1 schematically shows a conventional type silencer
- Figure 2 shows schematically the silencer of Figure 1 improved following the invention;
- Figure 3 is a schematic view of another embodiment of the silencer according to the invention.

 In the silencer of FIG. 1, gases penetrate via the tube T1 through the wall P1, then, through perforations, into two absorption chambers CA1, CA2 where they undergo sound attenuation by interference.

 They undergo additional sound attenuation by reflection in a C2 room. The gases then pass through the tubing T2 where perforations create interference when passing through the chamber C5.

 Additional attenuations by reflection occur in the chamber C3, then by interference in the chamber C5, again through the perforations in the tube T3, at the end of which the gases are evacuated outside.

 Additional attenuation can be obtained conventionally by the provision of baffles or padding in one or more of the aforementioned chambers.

 Such a conventional device is clearly improved according to the invention as indicated in FIG. 2 by adding a chamber C4 at a dead end, devoid of tubes and ensuring pressure regulation in the chamber C3, that is to say at the heart even of the noise attenuation device.

 A similar result could be obtained by opening the chamber C4 or another similar pressure regulation chamber in the chambers C1, C2 or C5.

 It is only imperative that a pressure regulation chamber according to the invention, which constitutes a temporary reservoir of overpressure gas, communicate with the silencer between any two conventional noise attenuation devices.

 Such a pressure regulating chamber according to the invention must not be traversed by the gases which must enter and leave it through a single opening.

 In some cases, experience shows that it may be useful to have inside a pressure regulating chamber according to the invention a lining slowing the outlet of the gases stored in overpressure.

 In the embodiment shown in FIG. 3, the regulation chamber C4 is produced in the form of a blind tube opening out inside the chamber C3 and fixed by its blind end to the opposite face of the silencer. This arrangement in which the tube C4 is held by its two ends avoids untimely vibrations which are difficult to avoid in a cantilever mounting, such as that of FIG. 2.

 The improved silencers according to the invention do not make it possible to obtain, under normal engine conditions, noise levels lower than those of the conventional devices to which they are adapted.

 The invention on the other hand makes it possible to eliminate unpleasant noises during the rapid acceleration and deceleration phases which are well known to motorists.

 These parasitic noises are eliminated or at least reduced in large proportions with the creation of a gas reserve according to the invention.

 The normal operation of the muffler under normal engine conditions is not changed.

 The damping capacity of sudden overpressures during the acceleration phase and the reestablishment of a normal gas pressure recovery during the deceleration phase are linked to the volume of the regulation chamber according to the invention. Its shape has practically no influence on its effectiveness. Its volume must be determined empirically according to the type of engine and the type of muffler to which the invention is applied.

 For a practical realization, it is obviously necessary to take into account, moreover, the manufacturing facilities and, in the case of automobiles, the location available under the vehicle.

 Of course, the invention is in no way limited to the embodiments described and shown, it is capable of numerous variants accessible to those skilled in the art, depending on the applications envisaged and without departing from the scope of the invention. 'invention.

Claims (4)

 1. Method for attenuating the noise of the exhaust of the burnt gases of an internal combustion engine, characterized in that the said gases are temporarily stored during  overpressures to restore them during subsequent pressure drops and thereby regulate the pressure of said gases at the heart of an acoustic attenuation assembly, in particular by reflection, absorption, interference and / or resonance.  2. Muffler for exhaust of burnt gases from an internal combustion engine according to the method of claim 1, comprising at least one enclosure containing an acoustic attenuation assembly constituted by a plurality of intercommunicating sections, each composed of at least one chamber containing at least one partially perforated tube, disposed between an inlet and an outlet of said gases from said  enclosure, said silencer being characterized in that it comprises at least one dead end pressure regulation chamber, devoid of tube, forming temporary reservoir  gas overpressure, and opening into said enclosure  between two of said sections.  of the enclosure.  stuck by a blind tube-placed outside and along  -3. Silencer according to claim 2, characterized in that the pressure regulation chamber is cons  4. Silencer according to claim 3, characterized in that the blind tube is fixed by its two ends respectively to two end faces of the enclosure.