FR2604747A1 - MUFFLER FOR GAS STREAMS - Google Patents

Abstract

A DISSIPATIVE SILENCER 1 FOR GASEOUS FLOWS, OF THE TYPE IN WHICH A PIPE 3 CROSSES THE GAS FLOW IS PROVIDED WITH A PLURALITY OF RADIAL HOLES 8 AND IS CONTAINED IN A CASE 2 FILLED WITH SOUND ABSORBING MATERIAL 6; PIPE 3 HAS A CENTRAL PART 10 OF ELLIPTICAL SECTION WITH A CONSTANT PROFILE AND TWO OPPOSED CONNECTION SECTIONS 11, 12 OF CONTINUOUS VARIABLE ELLIPTICAL SECTION, CONNECTING THE CENTRAL PART TO THE RESPECTIVE CIRCULAR SECTIONS 4, 5 OF INLET AND OUTLET OF THE PIPE AVERAGE OF CONVERGENT-DIVERGENT AND RECIPROCALLY VENTURI PROFILES.

Description

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  The present invention relates to a dissipative muffler

  tif of improved type for gas flow which can, in particular, be mounted along the exhaust manifold

of an internal combustion engine.

  The known dissipative silencers, which are constituted

  of one or more circular cross-section tubes, drilled

  dialing and arranged inside a sheet metal envelope

  full of sound absorbing material, present the inconvenience

  deny not being able to simultaneously ensure good acoustic damping performance and good fluidodynamic performance, such as a low pressure drop for example; in the case of use on the pipe

  combustion engine exhaust, this drawback

  due in particular to a net loss of engine power,

  with obvious drawbacks such as lower performance

  mances and increased consumption.

  The object of the invention is that of making a silen-

  dissipative heavens free from these drawbacks, capable of ensuring acoustic damping equal to or greater than

  that of known shock absorbers, but with loss of

  ge limited in the gas flow through the muffler, so as not to produce a significant loss of power in the case of application on internal combustion engines of vehicles. Said object is achieved in the invention in that it relates to a dissipative silencer for gas flow, provided in

  particular to be incorporated along the exhaust manifold

  of the internal combustion engine of a vehicle, of the compression type

  a carcass filled with a sound absorbing material

  and a pipe passing through said carcass, immersed in the ma-

  sound absorbing material and provided with a plurality of orifices

  these radials connecting the interior of said pipe to the interior of

  said carcass, characterized in that said pipe is con-

  formed along its own longitudinal axis, in the direction of

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  the advancement of said gas flow, according to cross sections

  dirty elliptical geometry, having a ratio between the length of its own main axes, large and small respectively, continuously variable between a maximum equal to the unit, corresponding to the inlet and outlet sections

  respective circular of this pipe and a minimum corresponding

  in a central part of constant section of the latter

  deny; this central part of constant section of the pipe being connected without continuity to said inlet section by a first section of said delimited pipe, in the plane passing through the major axis of the section of said central part thereof, by a consistent profile in the

  longitudinal direction in Venturi divergent and, in the plane not

  by the minor axis of the section of said central part

  the latter, by a profile shaped in the longitudinal direction

  tubinal in converging Venturi; said central sec-

  constant tion of the hose being additionally connected without solu-

  tion of continuity to said outlet section by means of a second section of said delimited pipe, in the plane passing through the major axis of the section of this central part thereof, by a profile shaped in the longitudinal direction in converging Venturi and, in the plane passing through the minor axis of the section of said central part thereof by

  a profile shaped in the longitudinal direction in Venturi di-

vergent.

  For a better understanding of the invention, it

  will now be given a non-limiting description of a

  of its examples of implementation with reference to the

  attached sins in which: Fig.l illustrates a transverse view in median section of a silencer produced according to the invention, Fig.2 illustrates a longitudinal sectional view along a plane II-I'I of the silencer of Fig. l, and Fig.3 illustrates a longitudinal sectional view along

  a layout plan III-III of the silencer in Fig.l.

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  Referring to Figs. 1, 2 and 3, there is generally designated by 1 a silencer of the dissipative type, capable of being traversed longitudinally in the direction of the arrows by a gas flow to absorb and ( or) damping the sound waves generated by this flow and particularly suitable for being mounted in series along the exhaust pipe of a combustion engine of a vehicle of any known type and not shown for simplicity;

  the silencer 1 comprises a carcass 2, preferably cylindrical

  drique and built in sheet metal, piping rec-

  coil 3 arranged through the carcass 2, coaxial thereto and provided with sections, respectively, of inlet 4 and outlet 5, capable of being connected in a known manner to said

  engine exhaust pipe not shown by

  corresponding edges 4a and 5a, and a lining of material

  absorbing sounds 6, 'represented schematically by ti-

  rets, which completely fills the carcass 2 and in which the pipe 3 is immersed; sound-absorbing material 6

  is of known type and, in the case where the. muffler 1 is used

  read on internal combustion engines, it must also be

  heat resistant and, for this purpose, it is preferred to use

  this mineral wool retained, in accordance with the invention,

  by a fine mesh metal mesh 6a, of the con- type

  any nude, in order to prevent the phenomena of depression due to the gas flow. The pipe 3 is preferably also made of sheet metal and is provided along the entire lateral surface itself with a plurality of radial through holes 8 connecting the inside of the pipe 3 to the inside of the carcass 2, so placing the sound absorbing material 6 in communication with the passage section at the disposal of the gas flow and the inlet and outlet sides of which are indicated diagrammatically by arrows opposite sections 4 and (Fig.2); according to the invention, the pipe 3, instead of being cy-

  lindrique as in known silencers, presents a geo-

  a very peculiar metric which has proved surprisingly

  capable of providing extremely high sound absorption, both normal and tangential, as well

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  that a high absorption also in the field of low frequency noise. In particular, the pipe 3 is shaped,

  along its own longitudinal axis, in the direction of advance-

  ment of the gas flow indicated by the arrows, according to sec-

  transverse positions (Fig. 1) of variable geometry, given

  that it comprises a central portion 10 having a section-ellip-

  tick of constant profile, the length of which is not critical in order to meet the aims of the invention and which can therefore

  be sized by a technician of the trade following pa-

  known rameters (obviously, the longer the length of the pipe 3

  the greater the absorption and the pressure drop of the gas flow) and two opposite connection sections 11 and 12, of continuously variable elliptical section, connecting the central part 10, respectively to the inlet section 4 and to the section outlet 5 of the pipe 3 which reciprocally, according to the invention, a circular shape and can thus be easily connected without any problem, for example by means of said fittings 4a and 5a, to an exhaust pipe which

  existing conch shell, which is known to be circular in shape.

  Since, from a strictly geometric point of view, the circular profile is a special case of an elliptical profile

  (in fact, as we know, a circumference is nothing

  tre an ellipse whose main axes are of equal length or whose reciprocal ratio is equal to 1), the pipe 3 is characterized, according to the invention, by the fact that it is shaped in the direction of advancement of the gas flow, according to

  cross sections all having an elliptical geometry

  that but having a relationship between the length of its pro-

  near main axes, small and large respectively (designated respectively by the letters X and Y in Fig. 1)), variable

  continuously between a maximum equal to unity with regard to sec-

  tions 4 and 5 which, in fact, are circular, and a minimum of

  look of the central part 10, of constant section; that-

  ci therefore being connected, according to the invention, without continuity with the inlet and outlet sections 4 and 5, by connection sections 11 and 12 which, according to the invention,

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  have sections narrowed in opposite directions, along the X and Y axes; in particular, as shown in Fig.2, the pipe section ll is delimited, in the plane passing through the major axis X of the elliptical section of part 10, by a symmetrical profile 14, shaped in the longitudinal direction in Venturi diverge and, in the plane passing through the small Y axis

  of the elliptical section of part 10, by a profile 15 sy-

  metric, shaped longitudinally in Venturi con-

  vergent. Conversely, as well shown in Fig.3, the pipe section 12 is delimited, in the plane passing through the major axis X, by a symmetrical profile 16 shaped, in the longitudinal direction, in converging Venturi and, in the plane

  passing through the small Y axis, through a symmetrical profile 18, coLfor-

  mé in the longitudinal direction in divergent Venturi.

  There is therefore in fact, in pipe 3, parts of

  converging and diverging parts along the plane of the longitudinal section considered, parts which, belonging to the lateral surface of the pipe 3, are obviously provided with holes 8 and which,

  consequently, allow to define portions of surface area

  cée arranged in such a way that the absorbent material

  sounds 6 is struck simultaneously by the wave front

  ticks that propagate with the long traversing gas flow

  tudinally the silencer 1, both normally, facing the inlet and outlet sections 4 and 5, and tangentially, facing the connection cross-sections 11 and 12, so as to achieve, in accordance with the invention, the absorption

  acoustic waves with variable angle of incidence, compared

  port in the axial position of the front of the gas flow, along the longitudinal axis of the silencer 1; next to the sections

  4 and 5 and successive narrowed sections 11 and 12, the ab-

  sorption will be performed both in the normal direction, in parallel

  to the axis of the pipe 3, that in the tangential direction, perpendicular to

  along the axis of the pipe 3, while along the elliptical section of the constant-section portion 10 of the pipe 3, the absorption will only be in the tangential direction, according to known methods, but through sections passage of the gas flow de'ipt elliptical strongly narrowed, at

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  by means of which the maximum possible profile is obtained between the perimeter of the transverse profile of the pipe 3 and the section of

  passage to the disposition of the gas flow, delimited by it

  this; however, even in this central area, according to the experimental tests carried out by the applicants, a

  high sound absorption, higher than that obtained

fits in known silencers.

  The said experimental tests also revealed

  only to obtain the best absorption results

  acoustics with minimal pressure drop in the flow ga-

  zeux, it is good that not only the connecting sections

  narrowed are delimited by Venturi profiles

  which, as we know, are profiles which allow

  minimize the pressure drops but also that the section 11 of the pipe 3 has a length greater than that of the section 12 and, in particular, that it is such that the connection profiles 14 and 16 have a development in length approximately 50% higher than that of connection profiles and 18. It is known in fact that sound absorption, in

  particularly in the low frequency domain, is pro-

  portable to the length of the connecting sections 11 and 12 and, obviously, to the thickness of the coating of sound absorbing material 6, contained in the casing 2. The latter, although it is preferably made in a section of circular shape, can also be constructed according to a possible variant not illustrated for simplicity, in a shape of also elliptical section, having its main axes arranged in any way with respect to the main axes X and Y of the elliptical section of the part 10; this makes it possible to carry out the absorption preferably in the domain of certain medium and low frequencies and to obtain

  also advantages in terms of external dimensions

  laughing at muffler 1, as a whole. Finally, the pipe 3 is produced, according to the invention, so as to have cross sections which all have the same passage surface for the gas flow or which have surfaces

  constant although having a variable profile and, in order to

  put in a quick and economical construction of the silencer 1,

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  the casing 2 as well as the pipe 3 are produced by stapling of the corresponding specular half-elements 22, 23

in jail.

  The advantages inherent in the invention result from fa-

  obvious lesson from the above description; thanks to geo-

  metry described, an optimal relationship between the peri

  meter of the sound absorbing section and the pass area

  ge of the gas front causing the sound waves to be absorbed and, consequently, a maximum sound absorption compatible with a minimum pressure drop; in addition, the muffler described is easy and economical to produce and has a higher sound absorption efficiency in the direction of low frequencies, absorption which is comparatively reduced in the case of dissipative mufflers

  currently existing on the market.

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Claims (7)

  1. Dissipative silencer (1) for a gas flow, in particular for incorporation along the exhaust pipe of a combustion engine of a vehicle, of the type comprising a carcass (2) filled with sound absorbing material (6 ) and one   pipe (3) passing through said carcass (2) immersed in the ma-   sound absorbing material and provided with a plurality of radial holes (8) connecting the inside of said pipe to the inside of said carcass, characterized in that said pipe (3) is shaped along its own longitudinal axis, in the   direction of advancement of said gas flow, according to cross sections   versals of elliptical geometry presenting a ratio between the length of their own main axes, respectively large (X) and small (Y) continuously variable between a maximum equal to the unit opposite the respective input sections   (4) and outlet (5), circular, of said pipe (3) and a half   minimum opposite a central part (10-) of constant cross-section   te of the latter; this central section (10) of cross section   hose aunt being connected, without continuity solution; to said inlet section (4) by a first section (11) of said delimited pipe, in the plane passing through the major axis (X) of the section of said central part thereof, by a shaped profile (14) in the longitudinal direction in divergent Venturi and, in the plane passing through the minor axis (Y) of the section of said central part thereof by a profile (15) shaped in the longitudinal direction in convergent Venturi; said central portion (10) of constant cross section of the pipe being further connected, without a solution of continuity, to said   outlet section (5) by a second section (12) of said tu-   yau delimited in the plane passing through the major axis (X) of the section of said central part thereof by a profile   (16) shaped longitudinally in converging Venturi   gent and, in the plane passing through the minor axis (Y) of the section of said central part thereof by a profile   (18) shaped in the longitudinal direction in Venturi conver- nice. 9 2 6 42 604 747   * 2. Silencer (1) according to claim 1, character-   rised in that said first section (11) of the pipe (3) has a length greater than that of said second section (12) of the pipe and is such that the connection profiles (14, 16) between said inlet section ( 4), circular, and said par-   central tie (10), elliptical, of the pipe (3) have a   development in length approximately 50% greater than that of the connection profiles (15, 18) between the elliptical central part (10) and said circular outlet section (5), of the hose (3).   3. Muffler (1) according to claim 2, character-   laughed in that it presents, opposite the inlet (4) and outlet (5) sections of the pipe, an acoustic absorption of   normal type as well as tangential type.   4. Silencer (1) according to claim 2 or 3, ca-   characterized in that the sound absorption in the low frequency field is proportional to the length of said   first (11) and second (12) connecting sections.   5. Silencer (1) according to any one of the preceding   your claims, characterized in that the sections   transverse of said pipe (3) are shaped so as to   present a passage surface for said essential gas flow so constant.   6. Silencer (1) according to any one of the preceding   dentes claims, characterized in that said ma-   sohs absorbent material (6) which fills the envelope (2) comprises mineral wool retained in position by a   corresponding wire mesh (6a) with fine mesh.   7.- Silencer (1) according to any one of the preceding   said claims, characterized in that said envelope   pe (2) and the pipe (3) are made by stapling the half   corresponding elements (22, 23), in sheet metal.