EP0683849B1 - Silencieux - Google Patents

Silencieux Download PDF

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Publication number
EP0683849B1
EP0683849B1 EP94906136A EP94906136A EP0683849B1 EP 0683849 B1 EP0683849 B1 EP 0683849B1 EP 94906136 A EP94906136 A EP 94906136A EP 94906136 A EP94906136 A EP 94906136A EP 0683849 B1 EP0683849 B1 EP 0683849B1
Authority
EP
European Patent Office
Prior art keywords
container
discharge opening
silencer
pipe
silencer according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP94906136A
Other languages
German (de)
English (en)
Other versions
EP0683849A1 (fr
Inventor
Eyvind Frederiksen
Svend Frederiksen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Silentor AS
Original Assignee
Silentor AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Silentor AS filed Critical Silentor AS
Publication of EP0683849A1 publication Critical patent/EP0683849A1/fr
Application granted granted Critical
Publication of EP0683849B1 publication Critical patent/EP0683849B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/08—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling
    • F01N1/10—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling in combination with sound-absorbing materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/06—Silencing apparatus characterised by method of silencing by using interference effect
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/08—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling
    • F01N1/085—Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling using a central core throttling gas passage
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00—Silencing apparatus characterised by method of silencing
    • F01N1/24—Silencing apparatus characterised by method of silencing by using sound-absorbing materials

Definitions

  • the present invention concerns silencers to reduce noise in flowing gas media, preferably for incorporation into exhaust pipes from internal combustion engines.
  • Silencers for such uses are frequently either of the reflection silencer type, absorption silencer type or a combination of these two types. Both are characterized by giving a wideband damping in the acoustic frequency spectrum. Such a wideband damping is generally needed, since the unsilenced spectrum from the engine, although it may contain peaks, also contains a considerable share of all frequencies within the audible range.
  • Both reflection and absorption silencers are based on silencing mechanisms in connection with one or more chambers, typically in a container having an admission pipe and an exhaust pipe.
  • the silencing effect is obtained in the reflection silencer in that sound energy is reflected at cross-sectional transitions between pipes and chambers.
  • the effect of the absorption silencer is obtained in that sound energy is transmitted to a sound absorbing material, e.g. mineral wool, in which oscillatory energy is dissipated by internal friction in the gas and by interaction between the gas and the fibres of the absorbent.
  • the damping range in the frequency spectrum is different for the two silencer types. Since the effect of the absorption silencer requires standing waves in the absorbent, this gives a downward limitation in the spectrum. Also the effect of the reflection silencer is limited downwardly in the spectrum, viz. by the filter natural-frequency. This, however, is generally considerably lower. Thus, in many uses for internal combustion engines it is difficult to obtain sufficient low frequency damping with absorption silencer alone. This is of importance, since precisely the most powerful frequency in the unsilenced spectrum, generally the ignition frequency of the engine (attributable to the cyclic process of the engine) is relatively low. A pure reflection silencer, or a combined reflection and absorption silencer is thus generally necessary.
  • the pure reflection silencer has the weakness that interfering passage frequencies occur in its damping spectrum, i.e. declines in the damping spectrum. These declines can be attributed to standing gas oscillations in the chambers. In some cases a decline may be so pronounced that it actually involves negative damping at the characteristic frequency, i.e. this frequency is amplified.
  • Incorporation of a sound absorbent in a reflection silencer can reduce the detrimental effect of passage frequencies to some degree, since standing oscillations in the chambers can be reduced by dissipation of oscillatory energy in the absorbent.
  • the basic natural frequency of a chamber can still occur with a considerable decline in the damping spectrum.
  • the basic natural frequency of the chamber is frequently somewhat higher in the frequency spectrum than the filter natural frequency.
  • a known method of counteracting this decline comprises extending the admission pipe to the center of the first chamber.
  • Such a geometry is expedient, because the basic natural frequency of a chamber has a pressure node precisely at the center. This means that oscillatory energy emitted here can excite the basic natural oscillation in the chamber only to a limited degree. Furthermore, this avoids excitation of all higher order natural frequencies which also have a pressure node in the center of the chamber.
  • the change in direction, from axial to radial flow, involved by the radial diffuser does not necessarily entail significant irreversibility in the flow. If the geometry of the diffuser is appropriate, flow separation can be avoided.
  • a further advantage of using radial diffusers in reflection silencers according to DK patent No. 128427 is that the transverse plate of the diffuser reflects sound. This provides a sound reducing effect which is added to the initially mentioned reflection effect caused by the cross-sectional transition (from pipe to chamber), and to the above-mentioned effect that can be obtained by pressure node positioning.
  • the present invention is based on the finding that reflection silencers having radial diffusers enable almost complete elimination of passage frequencies corresponding to standing gas oscillations axially in the chambers, but not standing gas oscillations transversely thereto. In some uses this is not considered to be a serious drawback, viz. when the mounting conditions make it natural to make the silencer elongated, so that the standing transverse waves correspond to relatively high frequencies that can be reduced relatively efficiently by means of the sound absorbent incorporated in the chambers.
  • silencers e.g. where the mounting conditions make it necessary or expedient to select a shorter embodiment with a container diameter which is large with respect to the pipe diameter.
  • the use of a radial diffuser involves reflection of sound at the transverse wall in the diffuser and pressure recovery, two of the properties which are advantageous, as described above.
  • positioning to the chamber center in an axial direction while being expedient in principle, is of less importance because of the disadvantage that exact positioning to the node of the basic natural frequency, which is more serious in this case owing to lower frequency, of standing waves transversely in the chamber is not possible.
  • Transverse oscillations of passage frequencies are therefore of greater importance in short silencers. But this may also be important in those cases where the length of the silencer is somewhat greater than the diameter, viz. in the event that the silencer contains several chambers, one or more of which being shorter than the diameter.
  • French patent No. 800850 discloses a silencer of the type stated in the introductory portion of claim 1.
  • This silencer is provided with a slot outlet along the shell walls in the silencer, which causes the gas flow to be conveyed into the chamber in the form of a thin veil. Since all rotation-symmetrical transverse oscillations have their pressure maximum on the inner side of the shell, they will hereby be excited. Of this basically infinite amount of oscillation modes, it is in practice primarily the lower order modes, and in particular the basic oscillation in the transverse direction which may give rise to interfering passage frequencies.
  • the object of the invention is to provide a silencer which exhibits improved properties with respect to damping of transverse oscillations in the chamber. This is achieved by the features defined in the charactering portion of claim 1.
  • the exhaust gas discharge opening is thus positioned radially substantially symmetrically about the pressure node of a transverse oscillation in the container, and so that the outer plate or the discharge opening is spaced from the shell, it is possible to construct a silencer which exhibits improved properties with respect to damping of transverse oscillations in the chamber, in particular as regards lower order transverse oscillations.
  • the subject-matter of claim 4 provides damping of transverse oscillations together with a reasonable damping of axial oscillations in the container.
  • the subject-matter defined in claim 5 provides a diffuser effect of the medium flow and thus a lower back-pressure for the silencer.
  • claim 7 or claim 8 provides an embodiment of the invention which is particularly easy to manufacture and thus inexpensive.
  • Fig. 1 shows an axial section of a rotation-symmetrical embodiment of the invention.
  • the silencer is here defined by a cylindrical shell 1 and by end bottoms 2 and 3.
  • the gas flow is conveyed into the silencer from the inlet pipe 4 and is discharged from the silencer by the discharge pipe 5.
  • the double-deflecting element is composed of an outer plate 6, which forms an abrupt bend at the contour K to form the cover plate 7, and of the curved inner plate 8 and of a plurality of radial ribs 9, which are welded to both the cover plate 7 and the inner plate 8 to retain the latter.
  • Sound absorbents 10 and 11, respectively, protected by perforated plates 12 and 13, are arranged around the inlet pipe 4 and behind the inner plate 8.
  • Pressure oscillation modes of basic natural frequencies in the longitudinal direction as well as in the transverse direction are plotted in the figure. The positioning of the gas flow to the pressure node will appear from this.
  • the node occurs approximately at two thirds of the radius, calculated from the center axis toward the inner contour of the shell. More precisely, the position can be calculated to 0.63 times radius. This result occurs by the solution of the partial differential equation called wave equation, which describes the rotation-symmetrical, three-dimensional gas oscillation field in the chamber.
  • the double-deflection involves considerable irreversibility, i.e. contributes significantly to increasing the overall flow resistance of the silencer.
  • a close analysis of the field of flow in the flow element shows that the double-deflection can be realized with a remarkably low loss.
  • This advantageous property can be ascribed both to the rotation-symmetry of the flow element and to the fact that the center C of the transverse plate as well as the contour K constitute stagnation singularities in the field of flow. This can be explained as follows:
  • deflection of the flow involves a considerable friction loss. This is the case e.g. with a 90° pipe bend, even if it has an arc-shaped center line, e.g. without sharp bends.
  • the flow will be turbulent in most cases, i.e. the smooth flow along flow lines will be superimposed by random particle movements in all directions.
  • the average travel of such movements characterizes the degree of turbulence in the flow.
  • This degree of turbulence is somewhat greater in the double-deflecting element than in a straight pipe flow, which involves a somewhat greater friction loss.
  • this loss is useful in the sense that it contributes to the resistive acoustic resistance of the element, i.e. is associated with a silencing effect.
  • the double-deflecting element has a controlled turbulence degree.
  • Fig. 2 shows another, distinctly flat embodiment of the invention.
  • the outer plate is omitted here, the inlet end bottom 2 serving the dual function of forming part of the silencer boundary toward the surroundings and of forming the flow directing outer plate.
  • the discharge pipe 5 is shown to be laterally directed with respect to the longitudinal axis of the otherwise rotation-symmetrical silencer.
  • An embodiment according to fig. 2 may e.g. be expedient in case of a silencer which is positioned below the engine of a truck with a downwardly directed admission pipe from the engine, the extension of the exhaust pipe being horizontal along the undercarriage.
  • the embodiment may e.g. be combined with an elongate silencer of a known type.
  • Fig. 3 shows a third, likewise distincly flat embodiment of the invention.
  • the inner plate coincides with the other end bottom 3 in such a manner that the double directional change of the gas flow results in a veil-like inflow to the chamber directly against the flow direction in the admission pipe.
  • Directional changes will here involve a particularly efficient sound reflection in the double-deflecting flow element.
  • the embodiment according to fig. 3 is almost rotation-symmetrical; the only deviation from rotation-symmetry is that the discharge pipe 5 is secured to the end bottom 2 on a certain radius.
  • the embodiment according to fig. 3 may e.g. be expedient in the positioning of a silencer below a truck engine like in fig. 2, but where the extension of the exhaust system is upward e.g. to a mouth at the level of the roof of the driver's cab.
  • an elongate silencer of a known type may be incorporated in the upwardly directed discharge pipe.
  • Fig. 4 shows a fourth embodiment of the invention.
  • This embodiment differs from those described above in that the cover plate forms an extension of the outer plate 6 without sharp bends, so that the contour K is omitted. This reduces the sound-reflecting effect of the double-deflecting pipe element to some degree. But e.g. in case of gas flows having a great content of soot, this embodiment may be appropriate in order to prevent accumulation of soot in the corner which is included in the double-deflecting flow element embodied with the contour K.
  • Figs. 5 and 5a show an embodiment of the invention in which the double-deflecting flow element is fork-shaped, enabling a split tangential flow veil into a silencer chamber.
  • the veil flow is axial.
  • An embodiment with a tangential veil may be expedient in those cases where the mounting conditions make it advisable to mount the admission pipe transversely to the shell 1, and not via the end bottom 2.
  • the tangential veil flow in the embodiment according to fig. 5 involves a slightly reduced possibility of positioning at the pressure node of transverse oscillations in the chamber in comparison with embodiments having an axial veil.
  • the reason is that on an average the veil flow, which has a length of the order of some times the veil width, follows a cylinder face having a somewhat varying radius, seen in relation to a cylinder face concentric with the shell. When the shell diameter is not too small, this deterioration of the positioning is not of great importance however. It may moreover be reduced if the veil-like tangential flow to the chamber is withdrawn slightly (as shown in fig. 5), so that the center of the veil (seen in the axial direction of the admission pipe) is on the cylinder face of the pressure node in the chamber.
  • Fig. 6 shows an example of a two-chamber embodiment.
  • the last one of the chambers here utilizes a flow element of the same type as in fig. 3, while a variant of a flow element according to the invention is additionally provided in the first chamber.
  • a ring channel 15 is interposed between the admission pipe 4 and the discharge opening 14.
  • This variant enables an axial veil flow to the first chamber, even though the axial direction of the admission pipe is transverse to the axis of the container (like in fig. 5).
  • Peripheral flow takes place in the ring channel, so that the exhaust gas, without a major loss of total pressure, can be distributed evenly along the periphery before flowing axially into the slot at the discharge opening.
  • the examples of embodiments of the invention shown above are built with a circular cylindrical shell and with a considerable degree of rotation symmetry.
  • the basic ideas of the invention are not bound to the circular cylinder shape.
  • the shell may e.g. be conical or elliptic. This may e.g. be of interest in uses where the mounting conditions make it advisable for the silencer to have a flat shape.
  • a catalyst or a heat exchanger such that these are positioned between the discharge opening 14 and the discharge pipe 5.
  • the geometry of the discharge opening 15 will ensure a particularly good efficiency of the catalyst or the heat exchanger, since these are supplied with an even flow of exhaust gases over the entire active surface.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust Silencers (AREA)
  • Surgical Instruments (AREA)
  • Portable Nailing Machines And Staplers (AREA)

Claims (12)

  1. Silencieux, de préférence pour les gaz d'échappement de moteurs à combustion interne, constitué par un récipient possédant une coque (1) formée essentiellement d'une surface de cylindre et de deux fonds d'extrémités (2, 3) ainsi qu'au moins un tube d'admission (4) et un tube d'échappement (5) pour les gaz d'échappement, dans lequel avant d'entrer dans le volume intérieur du récipient, l'écoulement est transformé en un écoulement de fente entre une plaque extérieure (6) et une plaque intérieure (8), lesdites plaques (6, 8) étant conformées au niveau de leur périphérie de manière à former une ouverture (14) de sortie des gaz d'échappement, lesdites plaques ayant une direction de profil qui est sensiblement perpendiculaire à la direction radiale, caractérisé en ce que considérée dans un plan radial, l'ouverture de sortie (14) est positionnée, sensiblement symétriquement autour de noeud de pression d'une oscillation transversale à l'intérieur du récipient, et de manière que la plaque extérieure (6) prévue à l'ouverture de sortie (14) soit espacée de la coque (1).
  2. Silencieux selon la revendication 1, caractérisé en ce que, considérée dans un plan radial, l'ouverture de sortie (14) est placée sensiblement symétriquement autour de noeuds de pression de l'oscillation de base existant dans le récipient.
  3. Silencieux selon la revendication 1, caractérisé en ce que, considérée dans un plan radial, l'ouverture de sortie (14) est positionnée sensiblement symétriquement autour de noeuds de pression de la première harmonique supérieure dans la direction transversale.
  4. Silencieux selon une des revendications 1 à 3, caractérisé en ce que, considérée dans la direction axiale, l'ouverture de sortie (14) est positionnée autour du noeud de pression d'une oscillation axiale à l'intérieur du récipient.
  5. Silencieux selon une des revendications 1 à 4, caractérisé en ce que l'aire de section transversale totale de l'ouverture de sortie est plus grande que l'aire de section du tube d'admission.
  6. Silencieux selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'en un point situé entre le tube d'admission (4) et l'ouverture de sortie (14), la plaque extérieure (6) présente un changement brusque de direction dans le profil de la plaque (6), pour former la plaque couvercle (7).
  7. Silencieux selon une ou plusieurs des revendications précédentes, caractérisé en ce que la plaque extérieure est formée entièrement ou partiellement par le fond d'extrémité du récipient au droit du tube d'admission.
  8. Silencieux selon une ou plusieurs des revendications 1 à 6, caractérisé en ce que la plaque intérieure est formée partiellement ou entièrement par le fond d'extrémité du récipient qui est à l'opposé du tube d'admission.
  9. Silencieux selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'un canal annulaire (15), auquel le tube d'admission (4) est raccordé, est interposé entre le tube d'admission (4) et l'ouverture de sortie (14).
  10. Silencieux selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'un élément catalytique est incorporé dans le récipient entre l'ouverture de sortie et le tube d'échappement.
  11. Silencieux selon une ou plusieurs des revendications précédentes, caractérisé en ce que la coque (1) du récipient est formée par un tube cylindrique à base circulaire.
  12. Silencieux selon une ou plusieurs des revendications 1-10, caractérisé en ce que la coque (1) du récipient est formée par un tube elliptique.
EP94906136A 1993-02-01 1994-01-31 Silencieux Expired - Lifetime EP0683849B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DK011293A DK169823B1 (da) 1993-02-01 1993-02-01 Lyddæmper
DK112/93 1993-02-01
PCT/DK1994/000049 WO1994018438A1 (fr) 1993-02-01 1994-01-31 Silencieux

Publications (2)

Publication Number Publication Date
EP0683849A1 EP0683849A1 (fr) 1995-11-29
EP0683849B1 true EP0683849B1 (fr) 1996-12-27

Family

ID=8089886

Family Applications (1)

Application Number Title Priority Date Filing Date
EP94906136A Expired - Lifetime EP0683849B1 (fr) 1993-02-01 1994-01-31 Silencieux

Country Status (7)

Country Link
EP (1) EP0683849B1 (fr)
AT (1) ATE146850T1 (fr)
AU (1) AU5998594A (fr)
DE (1) DE69401264T2 (fr)
DK (2) DK169823B1 (fr)
ES (1) ES2095745T3 (fr)
WO (1) WO1994018438A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998014693A1 (fr) * 1996-09-30 1998-04-09 Silentor Notox A/S Silencieux pour flux de gaz
US6220021B1 (en) 1995-05-19 2001-04-24 Silentor Notox A/S Silencer with incorporated catalyst
US6520286B1 (en) 1996-09-30 2003-02-18 Silentor Holding A/S Silencer and a method of operating a vehicle

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DK57996A (da) 1996-05-15 1997-11-16 Silentor As Lyddæmper
WO1999050539A2 (fr) 1998-03-30 1999-10-07 Silentor Notox A/S Silencieux et procede de mise en fonctionnement d'un vehicule
ATE242659T1 (de) 1997-11-13 2003-06-15 Haldor Topsoe As Mischvorrichtung und mit dieser ausgestatteter abgaskanal
JP4468513B2 (ja) * 1998-05-11 2010-05-26 ハルドール・トプサー・アクチエゼルスカベット 混合装置及びそれが装備された燃料ガス流路
WO2002036944A1 (fr) * 2000-11-02 2002-05-10 Rouse Gregory C Silencieux de turbogenerateur
FR2854427A1 (fr) * 2003-04-29 2004-11-05 Mig Production Silencieux pour gaz d'echappement de moteurs a combustion interne.

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2990906A (en) * 1958-10-08 1961-07-04 Koppers Co Inc Acoustic absorber
FR1226438A (fr) * 1958-10-09 1960-07-11 Silencieux pour l'écoulement des fluides
EP0020823A1 (fr) * 1979-04-10 1981-01-07 Lionel Fothergill Silencieux d'échappement pour moteur

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6220021B1 (en) 1995-05-19 2001-04-24 Silentor Notox A/S Silencer with incorporated catalyst
WO1998014693A1 (fr) * 1996-09-30 1998-04-09 Silentor Notox A/S Silencieux pour flux de gaz
US6332510B1 (en) 1996-09-30 2001-12-25 Silentor Holding A/S Gas flow silencer
US6520286B1 (en) 1996-09-30 2003-02-18 Silentor Holding A/S Silencer and a method of operating a vehicle
EP1403476A2 (fr) * 1996-09-30 2004-03-31 Silentor Notox A/S Silencieux pour courant gazeux
EP1403476A3 (fr) * 1996-09-30 2004-04-28 Silentor Notox A/S Silencieux pour courant gazeux

Also Published As

Publication number Publication date
DK0683849T3 (fr) 1997-03-10
WO1994018438A1 (fr) 1994-08-18
DK11293A (da) 1994-08-02
DK169823B1 (da) 1995-03-06
DE69401264D1 (de) 1997-02-06
AU5998594A (en) 1994-08-29
EP0683849A1 (fr) 1995-11-29
DK11293D0 (da) 1993-02-01
ES2095745T3 (es) 1997-02-16
DE69401264T2 (de) 1997-05-15
ATE146850T1 (de) 1997-01-15

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