EP1540148B1 - Silencer and method for designing the same - Google Patents

Abstract

The sound damper is contained in a housing (1) the surface (2) of which has one or more flanges (5,6,7). and at least one inlet (3) and outlet (4) for exhaust gas. The flanges are shaped and or arranged unevenly in order to reduce noise radiation. The irregularities concern the shape or symmetry of the flanges; the size-distribution of the flanges' surfaces in relation to the housing's surface; and the curvature distribution of he flanges' peripheral curves.

Description

The invention relates to a silencer and a method for its interpretation according to the preamble of the independent claims.

It is known to provide mufflers in exhaust systems of vehicles. The combustion gas exiting the internal combustion engine is discharged from the exhaust system into the free atmosphere. This should, in addition to avoiding nuisance caused by gaseous and solid pollutants, also take place as quietly as possible. Due to legislative measures, the permissible noise emission is increasingly restricted for environmental reasons.

Another important economic goal for an exhaust system is besides a favorable price. Low weight and compact dimensions, which are important for integration into the vehicle, are becoming increasingly important. Depending on the vehicle and engine size, a complete exhaust system from the exhaust manifold to the tailpipe can weigh between 20 and 45 kg. All components affect the acoustics of the exhaust system, but in very different ways. Both the objective assessment of the noise emission of the mouth and the surface of the exhaust system, which is known to be important for the noise emission in the accelerated passage, and the subjective perception of the sound to the sound plays an important role.

The acoustics of the exhaust system depend, in addition to the charge cycle noise of the engine, to a considerable degree on the structural design of the exhaust system. In this case, in particular the symmetry of the trouser pipe, the number and position of the silencer and the diameter of the connecting pipes play a dominant role. With unfavorable design, the exhaust system can produce amplifying noise. The today increasingly common multi-valve technology of the drive leads to a significant increase in the entering the exhaust system sound level. However, the future further reduction of the noise limit of the accelerated passage requires a significant reduction of the Mouth noise. This required level reduction was previously achieved essentially by an increase in volume of the muffler, but this pushes quickly to the limits of the available space. For optimal use of the space available in the sub-floor space, therefore, mufflers in shell construction are also increasingly used in vehicles of medium size. These shell silencers usually have a large and flat surface, which favors the sound radiation. Such a shell-type silencer is eg in the MTZ Motortechnische periodical, year 62, 2001, vol. 3, p. 3 et seq.

For these reasons, the surface of the exhaust system as a sound source has gained significantly in importance in the design of exhaust systems in recent years. For engines of high specific power and unfavorable muffler geometries, the surface sound radiation may even be dominant. The noise emission and thus the layout of the exhaust system must be evaluated and optimized. If this is not the case, the danger is great that an unfavorable division of the silencer volume and arrangement of the silencer will install significantly more volume than necessary, or that concessions with regard to the exhaust backpressure and thus the power loss of the internal combustion engine of the vehicle will be required.

The increase in volume also leads to further unwanted weight gain. Furthermore, the layout of the exhaust system on the volume distribution and length of the connecting pipes not only significantly affects the noise emission, but also the self-resonance behavior of mechanical vibrations via the associated mass distribution and total mass, which affects both the fatigue strength of the system and the noise level in the passenger compartment. Furthermore, the trend is more due to the increasing space restrictions to reduce the ratio of surface area to volume of the muffler.

Both structure-borne noise and sound radiation depend on the physical parameters of the silencer component. Such parameters are the bending stiffness and the mass density of the component, which are determined by the component geometry. Likewise have material properties such as the modulus of elasticity and the density, which are predetermined by the material used and therefore not significantly variable. The damping of the component is an essential parameter, but difficult to quantify. The change of certain sizes may have different impact on structure-borne noise and radiation. So causes an increase in the Flexural rigidity generally means a reduction of the structure-borne sound mass, but generally an increase in the emission mass, with the influence of the structure-borne sound usually being dominant. Even for simple geometries, it is difficult to model and predict the properties of the later component because the parameters interact very complexly.

To increase the flexural rigidity, it is known to introduce so-called beads in the surface of the muffler. There are known beads with various shapes, such as earthworm beads or golf balls. Earthworm beads are elongated shapes shaped like an earthworm, while golf ball beads are concave or convex hemispherical shapes in the nature of golf balls. Such golf ball beads are e.g. from the magazine Automobilindustrie 6/2002 known.

From the generic document DE 198 49 118 A1 discloses an exhaust muffler is known, which is made of half-shells having a substantially flat bottom. In the bottom of the upper shell several outward elongated bulges or beads are provided. The beads stiffen the case on the one hand and contribute, as mentioned above, to reduce the sound excitation due to vibrations. On the other hand, the beads in the interior of the muffler housing form corresponding bulges, which create additional volumes beyond the plane of the floor in the interior of the muffler housing.

The object of the invention is to provide a muffler with further improved damping properties, and a method for its interpretation.

The object is achieved in each case by the features of the independent claims.

According to the invention, an optimized housing surface is provided with beads, wherein the shape and / or the arrangement of the beads is characterized by a suitable irregularity for reducing the sound radiation of the muffler.

The targeted irregularities relate to the curvature distribution of the circumferential curves of the beads.

Preferably, beads according to the invention generally have no line of symmetry in the cross-sectional area parallel to the housing surface of the silencer. Further preferably, the area ratio of the individual beads in relation to the total area of the muffler on a wide distribution. Furthermore, it is favorable to provide a broad, preferably continuous distribution of the curvatures of boundary curves of the beads.

Further advantages and favorable embodiments of the invention are also independent of the formulation of the claims, the description and the drawings refer to.

Fig. 1

eine Sicht von schräg oben auf einen Schalldämpfer mit bevorzugten Sicken, die durch lsolinien dargestellt sind,

Fig. 2

eine Draufsicht von schräg unten auf den Schalldämpfer aus Fig. 1 mit bevorzugten Sicken,

Fig. 3

eine Ansicht des Inneren eines Schalldämpfers mit Funktionsflächen, welche den Schalldämpfer in Segmente aufteilen,

Fig. 4

einen Schnitt durch eine klassische Regenwurmsicke,

Fig. 5

eine bevorzugte Größenverteilung von bevorzugten Sicken als Funktion der Sickenzahl,

Fig. 6

eine bevorzugte Größenverteilung von bevorzugten Sicken bezogen auf die Gesamtoberfläche eines Schalldämpfers als Funktion der Sickenzahl,

Fig. 7

eine bevorzugte Verteilung von bevorzugten Sicken bezogen auf den Flächenanteil der Sicken,

Fig. 8

den Vergleich der Schallpegel bei klassischen Sicken (a₀, b₀, c₀) und Sicken gemäß der Erfindung (a₁, b₁, c₁).

The invention is described in more detail with reference to drawings, wherein the figures show:

Fig. 1

a view obliquely from above of a silencer with preferred beads, which are represented by Isolinien,

Fig. 2

a top view obliquely from below of the muffler of Figure 1 with preferred beads,

Fig. 3

a view of the interior of a muffler with functional surfaces, which divide the muffler into segments,

Fig. 4

a section through a classic earthworm bead,

Fig. 5

a preferred size distribution of preferred beads as a function of the number of beads,

Fig. 6

a preferred size distribution of preferred beads relative to the overall surface of a muffler as a function of the number of beads,

Fig. 7

a preferred distribution of preferred beads based on the area ratio of the beads,

Fig. 8

the comparison of the sound levels in classical beads (a ₀ , b ₀ , c ₀ ) and beads according to the invention (a ₁ , b ₁ , c ₁ ).

The function of known beads in a muffler housing is primarily in increasing the flexural rigidity of the housing and the flow guide. Usually surfaces of the muffler housing are further subdivided by functional surfaces. These portions of the housing surface generally serve as a seat for floors. The subregions each act as reflection chambers in the interior of the muffler, in which the sound is to be damped, whereby there is usually parallelism between the sill seats. In order to increase the bending stiffness, a minimum number of floors must be provided in which corrugations are regularly embedded. In contrast, the inventive Shape and / or arrangement of the beads are determined in a preferably numerical optimization process, which results in the lowest possible sound radiation of the muffler.

In the optimization process according to the invention, first of all, a numerical determination of the gas pulsation in the muffler takes place. H. a pressure field p (x, t, u (x)). Here, x indicates a location on the inner surface of a muffler housing. Since the wall thickness of the muffler is small compared to characteristic measures such as length and width and height, preferably the difference between inner and outer surface is negligible for the value of x. Furthermore, t denotes the time and u (x) a displacement vector of the outer surface of a beaded silencer to the outer surface of an untwisted silencer. The size u (x) therefore defines the beads. Empirically, it has been found that the dependence on the displacement vector u (x) is often negligible for the pressure signal. The pressure field p (x, t, u) results in a velocity field v (x, t, u (x)) on the outer surface of the muffler. This velocity field v (x, t, u (x)) leads to the emission of sound. An optimized housing surface is now characterized by the fact that the acoustic emission is reduced or limited to a permissible value.

In Fig. 1 is an oblique top view of an inventive silencer with a known body of two half-shells and a number of beads shown, while Fig. 2 shows a view of the underside of the muffler of FIG. 1. The beads may extend both into the interior of the muffler and out of the muffler. The half-shells of the preferably predetermined basic body can be configured as single-walled or double-walled.

The silencer comprises a silencer housing 1 with at least one inlet 3 and an outlet 4 for an exhaust gas, to which one or more customary openings and pipes extending inside the silencer can be assigned. In the housing surface 2, one or more functional surfaces 8 and one or more beads 5, 6, 7 are embedded. For clarity, not all existing beads are marked, which are easily recognizable in the figures due to their irregular shapes.

The functional surfaces 8 divide the muffler into three inner segments 9, to which the ends of the muffler housing 1 still adjoin on both sides, the are also provided with beads 5, 7. The functional surfaces 8 are formed like a sickle, but their task is primarily to ensure a bottom seat of the muffler.

In Fig. 3, the interior view of a muffler 1 is shown without housing 2, so that only the inner tubes 11 are visible to the exhaust system and frame for floors 10. The trays 10 correlate with the location of the functional surfaces 8 and define segments 9 therebetween. The exhaust gas pulsations in the tubes 11 are a source of radiated sound. Depending on the housing, which encloses the arrangement, it comes to more or less sound radiation.

From the prior art known conventional beads are characterized by a shape with contours with high symmetry, such. As the trapezoidal bead whose cross-section is trapezoidal or the earthworm bead. In the classical earthworm bead a continuous line of symmetry can be easily found, the distance from the bead edge is characterized in that at one point on the symmetry line two opposite edge points can be found whose normal distance to this point on the line of symmetry is substantially equal, each surface are considered parallel to the housing surface 1.

In the earthworm bead illustrated in FIG. 4a, the connecting line between the two boundary points R ₁ and R ₂ and the point P on the line of symmetry Sp generates, with the tangents T ₁ , T _{2 of} the edge curves of the beads in the two edge points, two angles α ₁ and β ₁ , and α ₂ and β ₂ . These angles α, β generally have the property that α ≤ 90 ° (± 0.5 °) and β≥90 ° (± 0.5 °), and α + β = 180 ° (± 1 °). The known beads also have mostly the property that α ₁ = α ₂ (± 0.5 °), while this is generally not the case with optimized beads 5, 6, 7 according to the invention. Rather, in the case of earthworm beads according to the invention, the angles α, β fluctuate, so that α1 is not equal to α2 with a deviation of at least ± 1 °, preferably ± 10 °. Alternatively or additionally, the angles α ₁ and α _{2 may be} unequal with a deviation of ± 5 °, preferably ± 10 °.

FIG. 4 b shows a cross-sectional view along a sectional plane A - A 'of the earthworm bead 4 a. The inner contour IK of the earthworm bead has an approximately circular shape, but is also triangular or the like formed in the prior art. According to the invention, the inner contour of a bead is fluctuating. For example, a varying radius of curvature may be provided. In particular, the inner contour of the cross section can fluctuate along a longitudinal line L, wherein the longitudinal line L is a curve along a longitudinal extent of the bead is generally not symmetrical to the edge curves of the bead lying characterizing the length of the bead. Empirically, it has been found that in general a certain minimum proportion of the irregularities having beads are required in order to achieve an effective reduction of the sound radiation, so that, for example, beads with an irregularity in an end region, for example in Fig. 4a, the end region E is not the desired Achieve damping effect.

In addition to beads with longitudinal symmetry, there are in the prior art also beads with rotational symmetry, such as the mentioned golf ball bead. In this case, symmetry elements are brought to coincidence by rotation about an axis of symmetry. According to the invention, an increased sound attenuation is achieved if such corrugations are deliberately subjected to increased irregularity by fluctuations in the symmetry angles. Depending on the type of bead, for example in the case of the golf ball bead, the symmetry line of known beads can also degenerate to a point of symmetry since a golf ball bead can have any number of symmetry surfaces.

Furthermore, bilaterally symmetric beads are known, which can be divided by a plane into two mirror-inverted halves. Corresponding beads according to the invention are characterized at least by fluctuations of the symmetrical elements of such classic beads.

Furthermore, in the case of the known beads, the normal distance between the two edge points including the point on the line of symmetry differs by at most ± 10%, preferably ± 5%, particularly preferably ± 1% from the characteristic bead width. Such deviations can z. B. resulting from manufacturing tolerances and are not specifically introduced within the meaning of the invention.

The known beads are further distinguished by the fact that their borders are formed by straight sections and substantially uniformly curved areas, wherein in this characterization, the curvature of the body is not taken into account. The radii of the border are therefore such that they assume practically only a few discrete values.

In contrast, the shape and / or arrangement of the beads 5, 6, 7 according to the invention have specific irregularities.

The curvature of the border curves of the beads 5, 6, 7 is according to the invention a broad distribution and is not characterized by a few discrete values. Furthermore, preferably about 30% of the beads 5, 6, 7 with a surface> 1.5 cm ^{2 in} this case radii of curvature with the ratio> 1.5.

• die Gestalt der Sicke 5, 6, 7 weist eine verminderte Symmetrie auf. Insbesondere sind die Sicken 5, 6, 7 in Schnittebenen parallel zur Gehäuseoberfläche 2 bezogen auf ihre in der Schnittebene liegende Umrandungskurve im wesentlichen symmetrielinienfrei. Vorzugsweise weisen zwischen 10% und 90% der Sicken 5, 6, 7 keine Symmetrieachse oder Symmetrielinie auf. Dabei sollte zweckmäßigerweise auf Planarität normiert werden, da Sicken Raumgebilde sind und Symmetrielinien nach dem Stand der Technik aus Punkten lokaler Symmetrie gebildet sind.
• Flächenanteile der einzelnen Sicken 5, 6, 7 weisen bezogen auf die Fläche der Gehäuseoberfläche 2 eine Verteilung mit einer nichtlinearen Hüllkurve auf, wie etwa eine Gaussverteilung, eine Poissonverteilung oder dergleichen.
• Umfangskurven der Sicken 5, 6, 7 weisen Krümmungen mit im wesentlichen kontinuierlicher Verteilung auf. Dabei beträgt der gekrümmte Kurvenanteil der Umlaufkante von Sicken 5, 6, 7 bezogen auf eine einzelne Sicke vorzugsweise mindestens 30%. Der gerade Anteil der Umfangskurven ist vorzugsweise minimal 10%, wobei unter "gerade" vorzugsweise mindestens 1 cm Länge verstanden wird und wobei auf 1 cm höchstens 1 mm Abweichung zu beobachten ist. Die Wölbung des Grundkörpers des Schalldämpfergehäuses 1 wird dabei sinnvollerweise herausgenommen.
• Die Einpresstiefe der Sicken 5, 6, 7 relativ zur Gehäuseoberfläche fluktuiert; insbesondere hat 80% der im Boden der Sicke liegenden Fläche eine Höhenveränderung von 30%, 40%, 50 % oder 60 % der tiefsten Einpresstiefe. Die Sicken 5, 6, 7 sind keine geraden Streifensicken; insbesondere weisen sie keine Symmetrielinie auf.

The targeted irregularities of the beads 5, 6, 7 may further comprise one or more of the group of the following properties:

• the shape of the bead 5, 6, 7 has a reduced symmetry. In particular, the beads 5, 6, 7 are in section planes parallel to the housing surface 2 relative to their lying in the cutting plane bordering curve substantially symmetrielinienfrei. Preferably, between 10% and 90% of the beads 5, 6, 7 have no axis of symmetry or symmetry line. It should be expediently normalized to planarity, since beads are spatial structures and symmetry lines are formed according to the prior art of points of local symmetry.
• Surface portions of the individual beads 5, 6, 7 have a distribution with a non-linear envelope, such as a Gaussian distribution, a Poisson distribution or the like, based on the area of the housing surface 2.
• Circumferential curves of the beads 5, 6, 7 have curvatures of substantially continuous distribution. In this case, the curved curve portion of the peripheral edge of beads 5, 6, 7 with respect to a single bead is preferably at least 30%. The straight portion of the circumferential curves is preferably at least 10%, wherein "straight" is preferably understood to be at least 1 cm in length, and at most 1 mm deviation can be observed at 1 cm. The curvature of the main body of the muffler housing 1 is usefully taken out.
• The Einpresstiefe the beads 5, 6, 7 fluctuates relative to the housing surface; In particular, 80% of the area lying in the bottom of the bead has a change in height of 30%, 40%, 50% or 60% of the deepest Einpresstiefe. The beads 5, 6, 7 are not straight strip beads; In particular, they have no symmetry line.

Preferably, the beads are arranged with a targeted disorder to reduce the sound radiation in the housing surface. The arrangement can take place along a longitudinal or transverse direction of the muffler housing (1). Dependent on from the position of the beads on the housing surface, in particular, the flexural rigidity changes even with otherwise unchanged component geometry.

In addition to corrugations, which in a sectional plane parallel to the housing surface have a simply connected surface with an irregular contour, other corrugations according to the invention have a topology with a higher correlation. In Fig. 1, Sk is a bead with enclave designated, in which a beaded island is arranged in the interior of a bead. Here, areas of the surface which are associated with the original surface of the silencer housing 1 are referred to as being unextended. In the simplest case, this may result in circular structures, but irregularities occur through the outer contour of the bead or the inner contour of the bead or the contour of the enclave or island or by both. Furthermore, even more complicated shapes may be provided with more than one unencrypted enclave.

In a preferred embodiment of the invention, the surface portion of individual beads 5, 6, 7 in relation to the total area of all beads 5, 6, 7, in particular there are individual beads 5, 6, 7, which in their area clearly from the surfaces of other beads 5, 6, 7 take off. This is shown in FIG. 5. Thus, a plurality of the beads 5, 6, 7 has a relatively small area. In this example, 25 out of 28 beads have an area below 100 cm ² , while a few beads have significantly larger areas up to 250 cm ² .

The surface portion of all beads 5, 6, 7 in relation to the total surface area of the muffler 1 is preferably at most 50%, particularly preferably at most 30%. In this case, the bead area fraction at the individual floors 9 defined by functional surfaces 8 can be between about 3% and about 70%, preferably between 5% and about 60%, of the respective outer surface of the housing 1.

Based on the total surface of the muffler, the area of the individual beads 5, 6, 7 is between 0.05% and 10% of the total surface, preferably between 0.1% and 5%. This is shown in Fig. 4. A plurality of beads, in the example about 25 out of 30 beads, has an area fraction of at most 2% of the total surface, while a few beads take up much larger areas of up to 5%. Of course, the absolute number of beads can be different for different silencers and individually adjusted.

In Fig. 5, a preferred distribution of beads according to the invention based on the area ratio of the beads is illustrated. The abscissa shows the relative number of beads S and the ordinate the corresponding relative area. The totality of all beads is characterized by the point S / F = 1 with an area ratio of 1. For beads of the same size results in the distribution of a straight line. However, a sub-linear distribution of the areas over the number of beads is preferred, as can be seen on the curve below the straight line. At a ratio of 0.4, the area ratio is 0.1. This means that 25% of the beads according to the invention occupy an area fraction of less than 0.1 of the total bead area of the beads according to the invention. With a value of F / S = 0.85, the area ratio is 0.6. This means that almost 75% of the beads occupy an area of 0.6.

It is favorable if surfaces of individual beads 5, 6, 7 have deviations of more than 50% from an average, based on the total area of all beads 5, 6, 7.

Furthermore, it is favorable if the percentage distribution of the areas of individual beads 5, 6, 7 relative to the total area of the housing surface 2 is non-linear.

In an expedient arrangement of the beads 5, 6, 7, these are arranged asymmetrically on two opposite upper and lower shells of the housing surface 2, as can be seen clearly in the comparison of the views of Fig. 1 and Fig. 2.

In the transition region between the beads and the housing surface (2) stages are provided in the beads according to the invention, which may have irregularities to reduce the sound radiation. Preferably, beads with a housing surface (2) substantially parallel bottom, when the bead reaches or exceeds a certain predetermined depth. However, beads, in particular less deep beads, with a sloping bottom, are provided.

8 shows by way of example the sound emission of a silencer according to the invention as a function of an engine speed. Functional surfaces 8 divide the muffler housing 1 in three areas, which each have beads. The curves a ₀ , a _{1 give} the Sound radiation of the left, b ₀ , b _1, the sound radiation of the right area and c ₀ , c _1, the sound radiation of the central region of the muffler housing 1 again. The sound radiation was determined at a distance from the muffler housing 1, which is still sufficient to distinguish acoustically different areas of the muffler, with a sound radiation was generated with a frequency mixture in the range of 250 Hz. The family of curves a ₀ , b ₀ , c ₀ was obtained a muffler, which is provided with conventional, classic beads. All three curves increase monotonically with increasing engine speed on average, eg a ₀ , b ₀ in this example between 1000 and 5000 1 / min from about 70 to a maximum of 100 dB, with the middle range generates about 5 dB lower sound emission than the two end areas whose sound radiation is approximately the same size.

However, if a similar muffler housing configuration provided with beads 5, 6, 7 according to the invention, so there is a significant reduction in the sound radiation. According to the family of curves a ₁ , b ₁ , c _1, the sound radiation is on average about 10 dB lower than the values of the family of curves a ₀ , b ₀ , c ₀ with the known beads. In order to produce a comparable attenuation of the level of sound radiation, a silencer according to the invention can manage with a smaller number of floors than a silencer in a classic design. This allows a simplified production with the corresponding saving potential of manufacturing costs, processing time and tools. Preferably, the number of trays 9 may be reduced by at least one tray 9 as compared to an array with regular beads. On the other hand, with the same number of floors by means of the beads 5, 6, 7 according to the invention a significantly lower level of sound radiation can be achieved.

Claims (12)

1. Silencer with a silencer housing (1) and with at least one inlet (3) and at least one outlet (4) for an exhaust gas, the housing surface (2) having one or more beads (5, 6, 7), and the configuration and/or arrangement of the beads (5, 6, 7) having directed irregularities for the reduction of sound radiation, characterized in that the directed irregularities relate to the distribution in the curvature of the circumferential curves of the beads (5, 6, 7).
2. Silencer according to Claim 1, characterized in that between 5% and 100% of the beads (5, 6, 7) are essentially free of a bisecting line or free of a point of symmetry in sectional planes parallel to the housing surface (2) with respect to their boundary curve lying in the sectional plane.
3. Silencer according to at least one of Claims 1 and 2, characterized in that between 5% and 100% of the beads (5, 6, 7) have a curvature of the boundary curves with an essentially continuous distribution.
4. Silencer according to at least one of the preceding claims, characterized in that the arrangement of the beads (5, 6, 7) is different on the upper and lower housing surfaces (2).
5. Silencer according to at least one of the preceding claims, characterized in that areas of individual beads (5, 6, 7) have deviations of more than 50% from an average value with respect to the overall area of all the beads (5, 6, 7).
6. Silencer according to at least one of the preceding claims, characterized in that the percentage distribution of the areas of individual beads (5, 6, 7) with respect to the overall area of the housing surface (2) is non-linear.
7. Silencer according to at least one of the preceding claims, characterized in that the overall area of the beads (5, 6, 7) occupies a fraction of the housing surface (2) of at most 30%, 40% or 50%.
8. Silencer according to at least one of the preceding claims, characterized in that functional areas (8) defining bottoms (10) are provided in the housing surface (2).
9. Silencer according to Claim 8, characterized in that, in bottoms (10) of the housing surface (2) which are delimited by functional areas (8), the fraction of the bead areas amounts to between 5% and 60% of the respective area.
10. Silencer according to at least one of the preceding claims, characterized in that the area of individual beads (5, 6, 7) has values of between 0.05% and 10% of the housing surface (2).
11. Silencer according to Claim 10, characterized in that the area of individual beads (5, 6, 7) has values of between 0.1% and 5% of the housing surface (2).
12. Method for designing a silencer according to one of the preceding claims, characterized in that the configuration and/or arrangement of the beads (5, 6, 7) are/is determined as a function of the sound radiation of the silencer by means of a numerical optimization method.

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