EP0274659B1 - Absorption/reflection silencer - Google Patents

Abstract

An absorption silencer, particularly a multi-stage silencer, having a main silencer with a built-in resonator silencer connected upstream of a secondary silencer, the main silencer comprising a directly stressed resonator (8), tuned to low frequencies, with a resonator tube (7) projecting into the exhaust gas flow against the flow direction of the main gas flow. <IMAGE>

Description

The invention relates to an absorption / reflection exhaust gas muffler, in particular in a multi-stage exhaust gas muffler system with a main muffler connected upstream of a rear muffler, with a resonator tube tuned to low frequencies, with a resonator tube arranged in the exhaust gas flow counter to the direction of flow of the main gas stream.

In addition to pure absorption mufflers and correspondingly pure resonator mufflers, combination arrangements have also already been proposed (compare, for example, German Offenlegungsschrift 30 35 332 and FR-A-2131431), in which an exhaust muffler is combined with a resonator within a muffler housing to selectively dampen special frequencies in the resonator. A major problem here is the coupling of the resonator, so that it can actually decouple a significant proportion of the sound frequency range carried in the main gas flow and dampen it accordingly.

The invention is therefore based on the object of designing an absorption / reflection exhaust gas silencer of the type mentioned at the outset in such a way that it ensures, with simple expenditure, a high level of decoupling of the sound component to be damped in the reflector and in particular in this way the so-called start-up hum can be eliminated.

To achieve this object, it is provided according to the invention that the resonator tube projects into the exhaust gas stream, the ratio of the cross section to the cross section of the exhaust gas duct surrounding it being approximately 1: 3 in the mouth region of the resonator tube.

führt.The direct protrusion of the resonator tube into the exhaust gas flow - which is in contrast to the construction of an exhaust gas silencer as described in DE-PS 28 39 756 - also has a number of consequences with regard to sound attenuation, which do not occur in the arrangement according to this patent specification can. The direct protrusion of the resonator tube 7 into the sound-guiding channel 6 results in a cross-sectional constriction, which results in a reflection attenuation according to the formula

leads.

also ca. 8,7 m. Eine Welle dieser Wellenlänge kann aber überhaupt nur über ein Resonatorrohr in einen Resonator eingekuppelt werden, wenn die Schallwelle unmittelbar in das Resonatorrohr hineinläuft. Würde man beispielsweise seitlich ein Querrohr ankoppeln, das quer zum schallführenden Kanal verläuft, so kann man eine Schallwelle mit einer derart großen Wellenlänge überhaupt nicht einkoppeln. Da nun aber bei der Entgegenhaltung 3 das schallführende Gas nicht wirklich an dem Resonatorrohr R vorbeiströmt, so daß die vorstehend genannte direkte Einlaufkopplung stattfinden kann - der Abgasstrom hat sich ja längst vor Beginn des Resonatorrohrs R bereits links und rechts in die Rohre L verzweigt- , wird auch dort nicht die erfindungsgemäß angestrebte starke Einkopplung tiefer Frequenzen überhaupt stattfinden können.A very important special feature of this direct protrusion of the resonator tube, which is not present in DE-PS 28 39 756, also results from the special objective of the present invention, namely the damping of low frequencies. If you assume, for example, a frequency of 60 Hz, the wavelength at an exhaust gas temperature of 400 ° C (calculated from the formula

therefore approx.8.7 m. A wave of this wavelength can only be coupled into a resonator via a resonator tube if the sound wave runs directly into the resonator tube. If, for example, a cross tube were connected to the side, which runs transversely to the sound-conducting channel, a sound wave with such a large wavelength cannot be coupled in at all. However, since document 3, the sound-conducting gas does not really flow past the resonator tube R, so that the above-mentioned direct inlet coupling can take place - the exhaust gas flow has long since left and right in the tubes L before the start of the resonator tube R. branched, the strong coupling of low frequencies sought according to the invention will not be able to take place there either.

In a further development of the invention, particularly advantageous damping is achieved if the distance between the resonator tube and the exhaust duct inlet cross section is approximately equal to its diameter.

In order to avoid radiation through the absorption muffler part, the perforated exhaust pipe passing through the absorber part should be designed as curved as possible, it has also proven to be advantageous if the exhaust pipe has a counter-cone downstream of the mouth of the resonator pipe.

Very favorable conditions, especially as far as the structure is concerned, since in this case the cover between the resonator and the absorber part can be simply inserted without threading the resonator tube, are obtained in a further embodiment of the invention in that the resonator tube, bent at approximately 180 ° C., with its Middle section runs directly adjacent to a narrow side wall of the flat muffler housing, the muffler housing preferably being constructed in a manner known per se from drawn half-shells, which allows a particularly favorable adaptation to the underbody of the vehicle and thus a reduction in the CW value.

Although the above-described absorption exhaust muffler with an additional built-in special resonator can also be used on its own, it has proven to be particularly effective to use it as part of a multi-stage exhaust muffler system, and because of its very favorable damping properties it is sufficient to have a rear muffler connected downstream to be designed as a simple Helmholtz resonator, whereas in the case of previous multi-stage exhaust silencers it was usually necessary to design the rear silencer in a very complex manner in order to achieve the desired damping values. It is up to the particular engine conditions whether a front silencer is used or not, the structure of the front silencer being relatively uncritical with regard to the damping properties of the main silencer.

Fig. 1

einen Schnitt durch einen erfindungsgemäßen Absorptions-Schalldämpfer mit angekoppeltem Resonator,

Fig. 2

einen Querschnitt längs der Linie II-II in Fig. 1, und

Fig. 3

einen Längsschnitt durch einen Nachschalldämpfer, wie er bevorzugt in Verbindung mit einem Schalldämpfer nach den Figuren 1 und 2 bei mehrstufigen Abgasschalldämpferanlagen Verwendung finden kann.

Further advantages, features and details of the invention result from the following description of an exemplary embodiment and from the drawing. Show:

Fig. 1

3 shows a section through an absorption silencer according to the invention with a coupled resonator,

Fig. 2

a cross-section along the line II-II in Fig. 1, and

Fig. 3

a longitudinal section through a rear silencer, as it can preferably be used in connection with a silencer according to Figures 1 and 2 in multi-stage exhaust silencer systems.

The muffler shown in FIGS. 1 and 2, particularly suitable as a center muffler in multi-stage exhaust gas muffler systems, comprises a preferably made of drawn Half-shell muffler housing 1, in which a first absorber-muffler chamber 2 is arranged, which is penetrated by a curved exhaust pipe 3 provided with gas outlet bores 4, which are only indicated in the illustration. From the inlet pipe 5, which can be coupled, for example, to the outlet of a pre-silencer, the exhaust pipe initially widens to a nominal exhaust duct inlet cross section D. Approximately in this area, a resonator pipe 7, which is essentially U-shaped, opens into the exhaust duct counter to the gas flow direction bent into a resonator chamber 8 with the volume V opens. To facilitate assembly, the arrangement is chosen such that the central section 9 of the U-shaped resonator tube runs essentially closely adjacent to one of the narrow sides of the flat muffler housing 1, so that it lies between this narrow side and a corresponding indentation 10 between the absorber section 2 and the Resonator space 8 arranged lid 11 can be inserted. A counter cone 12 is provided downstream of the mouth of the resonator tube 7, the distance of which from the point 6, at which the nominal exhaust gas duct cross section D is reached, should correspond approximately to this diameter D.

(Zylinderanzahl), was für einen 4-Zylindermotor eine Frequenz von etwa 50 Hz und für einen 6-Zylindermotor eine Frequenz von 75 Hz bedeutet. Auf diesen entsprechenden Frequenzwert legt man die Frequenz des durch das Resonatorrohr 7 und den Resonanzraum 8 gebildeten Resonators, wobei sich diese Frequenz ergibt zu

wobei V das Resonatorvolumen, A die Querschnittsfläche des Resonatorrohrs und 1 dessen Länge ist. Andeutungsweise ist im Ausführungsbeispiel nach den Figuren 1 und 2 auch das Flächenverhältnis des Resonatorrohrquerschnitts zum Abgaskanaleintrittsquerschnitt D zu etwa 1:3 gewählt, wodurch sich - wie durch umfangreiche Versuche nachgewiesen werden konnte - besonders gute Dämpfungseigenschaften ergeben. In Fig. 3 ist ein einfacher Helmholtzresonator dargestellt, wie er in Verbindung mit einem Schalldämpfer nach den Figuren 1 und 2 als Nachschalldämpfer verwendet werden kann. Durch die besonders vorteilhaften Dämpfungseigenschaften des Resonators nach den Figuren 1 und 2 bedarf es keines komplizierten Nachschalldämpfers, sondern es genügt für praktisch alle Anwendungsfälle ein derart einfacher Nachschalldämpfer, wie er in Fig. 3 gezeigt ist.The frequency F at which the start-up hum occurs is determined by the basic motor frequency at the corresponding speed n and results in

(Number of cylinders), which means a frequency of about 50 Hz for a 4-cylinder engine and a frequency of 75 Hz for a 6-cylinder engine. The frequency of the resonator formed by the resonator tube 7 and the resonance chamber 8 is placed on this corresponding frequency value, this frequency resulting

where V is the resonator volume, A is the cross-sectional area of the resonator tube and 1 is its length. This is also indicated in the exemplary embodiment according to FIGS. 1 and 2 The area ratio of the resonator tube cross-section to the exhaust duct inlet cross-section D was chosen to be about 1: 3, which - as was proven by extensive tests - results in particularly good damping properties. In Fig. 3 a simple Helmholtz resonator is shown as it can be used in connection with a silencer according to Figures 1 and 2 as a rear silencer. Due to the particularly advantageous damping properties of the resonator according to FIGS. 1 and 2, no complicated rear silencer is required, but a simple rear silencer such as that shown in FIG. 3 is sufficient for practically all applications.

Claims (8)

1. Absorption/reflexion silencer, in particular in a multiple-stage silencer device with a main silencer connected upstream of a reverberation damper, with a directly actuated resonator tuned to low frequencies, with a resonator tube mounted in the exhaust stream counter to the direction of flow of the main gas stream, characterised in that the resonator tube (7) projects into the exhaust stream, the ratio of the cross-section (A_r) of the resonator tube (7) to the cross-section (A_AK) of the exhaust channel surrounding it being approximately 1:3 in the region of the mouth of the resonator tube (7).
2. Silencer according to claim 1, characterised in that the natural frequency

   

   of the resonator is tuned to the frequency of the starting hum

   

   where V represents the volume of the resonator, 1 the length and A the cross-section of the resonator tube, n the speed of the engine and z the number of cylinders.
3. Silencer according to claim 1 or 2, characterised in that the distance between the resonator tube (7) and the exhaust channel inlet cross-section (6) is approximately equal to its diameter (D).
4. Silencer according to one of claims 1 to 3, characterised in that the perforated exhaust pipe (3) penetrating the absorber part is curved.
5. Silencer according to one of claims 1 to 4, characterised in that the exhaust pipe (3) has a countercone (12) upstream of the mouth of the resonator tube (7).
6. Silencer according to one of claims 1 to 5, characterised in that the central section of the resonator tube, which is bent through approximately 180°, runs directly adjacent to the one narrow side wall of the flat silencer housing (1).
7. Silencer according to one of claims 1 to 6, characterised in that the silencer housing (1) is composed of drawn half-shells.
8. Silencer according to one of claims 1 to 7, characterised in that a reverberation damper constructed as a simple Helmholtz resonator is connected in series thereto.

Images