EP1627996B1 - Active exhaust silencer - Google Patents

Description

The present invention relates to an active silencer for an exhaust system of an internal combustion engine, in particular in a motor vehicle having the features of the preamble of claim 1.

Such a silencer is known for example from EP 1 055 804 B1 and has a housing through which a tube is passed. This tube is made permeable in a first room for airborne sound by having a perforated pipe section in the first space. Furthermore, the known muffler comprises an anti-sound generator in the form of a loudspeaker, which is arranged in a second space. During operation of the muffler, the anti-sound generator acts through a wall opening through a third room with anti-sound. In this case, said wall opening is formed in a partition which separates the second space from the third space. Furthermore, the first room communicates through a sound outlet with the third room for the transmission of airborne sound.

Further active silencers are described in EP 0 373 188 B1, US 5,233,137, US 4,177,874, US 5,229,556, US 5,336,856, US 5,319,165, US 5,432,857, EP 0 674 097 A1, US 5,619,020, US 5,600,106, EP 0 916 817 and DE 197 51 596 known.

During operation of such an active silencer, the airborne sound to be damped is decoupled from the pipe in the first space and introduced into the third space through the sound outlet. At the same time, with the aid of the loudspeaker, anti-sound, that is to say sound with a reciprocal pressure level profile which is to be damped, is generated and likewise fed to the third space. In the third room, sound and anti-sound cancel each other out, thereby characterizing an active silencer of the present type.

In theory, with the help of such active muffler effective sound attenuation can be achieved. In practice, however, occur due to the high temperatures prevailing in the exhaust gases on strong problems, since speakers available so far do not have sufficient life at such high operating temperatures. In addition, the loudspeakers required in active exhaust silencers must be very powerful in order to be able to react appropriately to the extremely large sound pressure levels occurring in the exhaust gas and to achieve the desired damping effect. However, a high power leads to a high additional heat development in the speaker.

The present invention is concerned with the problem of providing for an active exhaust muffler of the type mentioned in an improved embodiment, which is characterized in particular by an increased life and better acoustic efficiency.

This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject of dependent claims 2-16.

The present invention is based on the general idea of avoiding a direct loading of the loudspeaker with the sound to be damped by blocking the direct path between sound outlet and wall opening for the sound transmission and instead providing at least one detour over which the airborne sound is only indirect can get from the sound outlet to the wall opening. This then applies accordingly also for the hot exhaust gases. Thus, since direct loading of the loudspeaker with the sound to be damped and thereby also with the hot exhaust gases is ruled out, the temperature load of the loudspeaker or of the respectively used anti-noise generator can be reduced at the same time. For a direct thermal load, for example by heat radiation from the sound outlet to the wall opening is automatically prevented by the blocking of the direct path between the sound outlet and wall opening. With a reduced thermal load of the anti-noise generator is extended life for the anti-sound generator and thus for the active silencer.

The blocking of the direct path between sound outlet and wall opening is realized in the invention by means of a labyrinth, which is designed for this purpose in the third room. In doing so, the labyrinth obstructs the aforementioned direct path and at the same time creates at least an indirect detour. At the same time, the labyrinth is expediently designed to be thermally insulating in a suitable manner and, at the same time, acoustically designed so transparent that substantially no sound attenuation occurs on the way from the wall opening to the sound outlet. As a result, almost the entire sound power of the anti-noise generator is available for damping or extinguishing the sound transported in the exhaust gas.

Preferably, the labyrinth is equipped with at least one insulating wall which completely covers or shades both the sound outlet and the wall opening and thereby enables airborne sound transmission between a first side of the insulation wall facing the sound outlet and a second side of the insulation wall facing the wall opening on at least one edge. In other words, the airborne sound is guided around the isolation wall along the respective detour. During operation, the insulating wall can thus insulate the heat emitted at the sound outlet, as a result of which it is arranged beyond the insulation wall Wall opening and thus the anti-ballistic agent is protected against direct heat.

According to a particularly advantageous embodiment, at least one further or fourth space can be formed in the housing, which is designed as a Helmholtz resonator, to which the pipe system is connected upstream of the first space. The integration of the Helmholtz resonator in the housing of the muffler results in a particularly compact design. Due to the arrangement of the Helmholtz resonator upstream of the first space, the sound pressure levels in the sound supplied to the muffler in the resonant frequency range of the Helmholtz resonator can be significantly attenuated, whereby critical acoustic loads of the anti-sound generator can be avoided in this resonant frequency range, which also with an increased life for the anti-noise generator and thus for the silencer goes along.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawing and from the associated description of the figures with reference to the drawing.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

A preferred embodiment of the invention is illustrated in the drawing and will be explained in more detail in the following description.

The only Fig. 1 shows a highly simplified, schematic longitudinal section through an active silencer according to the invention.

1, an active silencer 1 comprises a housing 2 with which the silencer 1 can be integrated into an exhaust system 3 of an otherwise not shown internal combustion engine, which is arranged in particular in a motor vehicle. In this case, an inlet pipe 4 in the installed state leads from the internal combustion engine to an exhaust gas inlet 5 of the housing 2. Accordingly, an outlet pipe 6 leads from an exhaust gas outlet 7 of the housing 2 into the surroundings of the internal combustion engine.

Through the housing 2, a pipe system 8 is passed through which the exhaust gas inlet 5 communicates with the exhaust gas outlet 7 without appreciable flow resistance. In the preferred embodiment shown here, the pipe system 8 is formed by a single tube, which connects the exhaust gas inlet 5 directly and in particular rectilinearly with the exhaust gas outlet 7.

In the housing 2, a first space 9 is formed, through which the pipe or pipe system 8 is passed. In the first room 9, the pipe system 8 is made permeable to airborne sound, which is expediently achieved by means of a corresponding perforation 10 of a pipe section 11 of the pipe system 8 extending in the first space 9.

Furthermore, the housing 2 includes a second space 12 in which an anti-sound generator 13 is arranged. The anti-sound generator 13 has a gas-tight membrane 14 and a exciter or motor 15, which can excite the membrane 14 to vibrate to generate anti-sound. Usually, the anti-sound generator 13 is constructed like a loudspeaker. A partition wall 16 separates the second space 12 from a third space 17 and includes a wall opening 18 through which the anti-sound generator 13 can radiate anti-sound into the third space 17. Suitably, the anti-sound generator 13 is positioned in the second space 12 so that it closes the wall opening 18 gas-tight.

The third space 17 is bounded, in addition to the dividing wall 16, by a boundary wall 19, which preferably extends parallel to the dividing wall 16. In this boundary wall 19, a sound outlet 20 is formed which is permeable to airborne sound and through which the first space 9 communicates with the third space 17 for airborne sound transmission. For example, the airborne sound outlet 20 may be formed by a perforated portion of the boundary wall 19 or by a vibratable membrane.

According to the invention, a labyrinth 21 is now formed in the third space 17. This labyrinth 21 is designed in this way that it blocks a direction indicated by a broken line direct path 22 for airborne sound propagation between the sound outlet 20 and wall opening 18. At the same time, the labyrinth 21 forms at least one, here two, detours 23, which allow an indirect airborne sound propagation between sound exit 20 and wall opening 18.

By blocking the direct path 22 and by creating the detours 23, a thermal load on the anti-sound generator 13 is simultaneously significantly reduced, since this can no longer be done on the direct path 22. Suitably, the labyrinth 21 is designed at least in the region of the direct path 22 as a thermal insulator.

In the preferred embodiment shown here, the labyrinth 21 has at least one insulation wall 24, which is arranged and dimensioned in the third space 17 in such a way that it completely covers both the sound outlet 20 and the wall opening 18. In this case, the insulation wall 24 has a first side 25, which faces the sound outlet 20, and a second side 26, which faces the wall opening 18. The arrangement and dimensioning of the insulation wall 24 in the third space 17 also takes place in such a way that an airborne sound transmission between the first side 25 and the second side 26 can take place at least at an edge region 27 of the insulation wall 24. That is, the respective detours 23 lead through the respective edge region 27 of the insulation wall 24 or at the respective edge regions 27 around the insulation wall 24 around.

The isolation wall 24 may be spaced apart from an outer wall 28 with its respective edge region 27 in order to realize the detours 23. In Fig. 1, an alternative embodiment is also shown, in which the insulation wall 24 is designed permeable in the edge region 27 for airborne sound, which can be realized for example by means of a corresponding perforation 29.

The insulation wall 24 is expediently designed at least partially as a thermal insulator. Preferably, it can - as here - be formed as a hollow wall and accordingly contain a cavity 30 in its interior. This cavity 30 may suitably be provided with a thermally insulating material, e.g. Stone or glass wool, to be filled. It is likewise expedient to produce the insulation wall 24 itself from a thermally insulating material. Advantageously, the insulation wall 24 is arranged in the third space 17 so that it extends parallel to the partition 16 and parallel to the boundary wall 19. The insulating wall 24 can also - as in this case - be arranged symmetrically in the third space 17.

Another feature of the embodiment shown here is the measure that the wall opening 18 is arranged offset with respect to the sound outlet 20. That is wall opening 18 and sound outlet 20 are arranged so that they are not aligned with each other and also have no or only the smallest possible coverage. By this offset, the thermal load of the partition 16 is also carried out offset to the wall opening 18 and thus offset to the anti-sound generator 13th

In the embodiment shown here, the anti-sound generator 13 is attached to the partition wall 16, such that it is spaced apart from a wall 31 which limits the second space 12. In other words, the anti-sound generator 13 is on the one hand completely disposed within the housing 2 and on the other hand with this not directly, but only indirectly via the partition wall 16 thermally connected. Expediently, the second space 12 is made gas-tight to the outside.

According to a further development, a further space 32 can be formed in the housing 2, which is also referred to below as the fourth space 32. This fourth space 32 is designed as a Helmholtz resonator, to which the pipe system 8 is connected, upstream of the first space 9. The connection of the pipe system 8 to the fourth space 32 takes place via a neck 33. The pipe system 8 is expedient with a pipe section 34 passed through the fourth space 32. Incidentally, the fourth space 32 is made gas-tight to the outside. The attenuation of the sound already upstream of the first space 9 can reduce the pressure level amplitudes in a critical oscillation range to such an extent that the load on the downstream antinoise generator 13 is considerably reduced. The Helmholtz resonator in the fourth space 32 is suitably tuned such that: $${\mathrm{f}}_{\mathrm{res}}\mathrm{=}{\mathrm{C}}_{\mathrm{T}\mathrm{.}\mathrm{p}}\mathrm{/}\mathrm{4}{\mathrm{L}}_{\mathrm{ZR}}$$

• f_res = Resonanzfrequenz des Helmholtz-Resonators,
• C_T,p = Schallgeschwindigkeit im Einlassrohr 4 stromauf des Schalldämpfers 1,
• L_ZR = akustisch wirksame Länge des Einlassrohrs 4 vom Schalldämpfer 1 bis zum nächsten, stromauf in Richtung Brennkraftmaschine liegenden Schalldämpfer oder allgemein Volumenelement, wie z.B. ein Mittel-Schalldämpfer.

Here are:

• f _res = resonance frequency of the Helmholtz resonator,
• C _{T, p} = speed of sound in the inlet pipe 4 upstream of the muffler 1,
• L _ZR = acoustically effective length of the inlet pipe 4 from the muffler 1 to the next, upstream in the direction of the internal combustion engine muffler or generally volume element, such as a central muffler.

In the embodiment shown here, a further space 35 can be formed in the housing 2, which is referred to below as the fifth space 35. The fifth space 35 is expediently designed as an absorption chamber, to which the pipe system 8 is connected, downstream of the first space 9. In this case, the pipe system 8 is expediently passed through a pipe section 36 through the fifth space 35. For the acoustic connection of the pipe system 8 to the absorption chamber of the pipe section 36 is designed to be permeable to airborne sound, which can be conveniently achieved by means of a perforation 37. The fifth space 35 is advantageously filled with a sound-absorbing material, preferably with stone or glass wool. Incidentally, the fifth space can be made gas-tight to the outside.

The outlet pipe 6 may, for acoustic reasons, a selectively selected length of z. B. 100 to 1000 mm, preferably from 200 to 500 mm, in order to reduce by the reflection at the pipe end the sound in the first space 9. In other words, the outlet tube 6 is expediently designed as a λ / 4 tube, which can be tuned in particular to disturbing residual frequencies, which still occur despite the effective extinction by the antinoise generator 13 in the first space 9.

Due to the integration of the Helmholtz resonator (fourth space 32) and / or the absorption chamber (fifth space 35), the active muffler 1 according to the invention builds extremely compactly.

Claims (16)

1. An active exhaust muffler for an exhaust system (3) of an internal combustion engine, in particular in a motor vehicle,

   - having a housing (2) through which passes a pipe system (8), which is designed to be permeable for airborne sound in a first space (9),

   - having an antisound generator (13) which is situated in a second space (12) and acts upon a third space (17) with antisound through a wall opening (18) during operation,

   - wherein the wall opening (18) is provided in a partition (16) separating the second space (12) from the third space (17),

   - wherein the first space (9) communicates with the third space (17) through a sound outlet (20) to transmit airborne sound,

   characterized in that
   a labyrinth (21) which is provided in the third space (17) blocks a direct path (22) between the sound outlet (20) and the wall opening (18) for the propagation of airborne sound and supplies at least one indirect bypass (23) for the propagation of airborne sound between the sound outlet (20) and the wall opening (18).
2. The exhaust muffler according to Claim 1,
   characterized in that
   the labyrinth (21) has at least one insulation wall (24) which completely covers both the sound outlet (20) and the wall opening (18) and permits transmission of airborne sound between a first side (25) facing the sound outlet (20) and a second side (26) facing the wall opening (18) along at least one edge (27).
3. The exhaust muffler according to Claim 2,
   characterized in that
   the insulation wall (24) is designed to be permeable for airborne sound at its edge (27) or is arranged at a distance from an outside wall (28) that encompasses the third space (17).
4. The exhaust muffler according to Claim 2 or 3,
   characterized in that

   - the insulation wall (24) is designed at least partially as thermal insulation and/or

   - the insulation wall (24) is designed at least partially as a hollow wall and/or

   - the insulation wall (24) is filled at least partially with a thermal insulation material, and/or is made of a thermal insulation material.
5. The exhaust muffler according to any one of Claims 2 through 4,
   characterized in that
   the insulation wall (24) runs parallel to a bordering wall (19) that contains the sound outlet (20) and borders the third space (17) and/or runs parallel to the partition (16).
6. The exhaust muffler according to any one of Claims 1 through 5,
   characterized in that
   the labyrinth (21) provides at least two bypasses (23) for indirect transmission of the airborne sound between the sound outlet (20) and the wall opening (18).
7. The exhaust muffler according to any one of Claims 1 through 6,
   characterized in that
   the sound outlet (20) is arranged in a bordering wall (19) that borders the third space (17) and extends parallel to the partition (16).
8. The exhaust muffler according to Claim 7,
   characterized in that
   the wall opening (18) and the sound outlet (20) are arranged offset to one another in the respective wall (16, 19).
9. The exhaust muffler according to any one of Claims 1 through 8,
   characterized in that

   - the antisound generator (13) is mounted on the partition (16) and is arranged at a distance from the wall (31) otherwise bordering the second space (12) and/or

   - the second space (12) is designed with an airtight seal with respect to the outside.
10. The exhaust muffler according to any one of Claims 1 through 9,
    characterized in that
    another space or a fourth space (32) is provided in the housing (2) and is designed as a Helmholtz resonator to which the pipe system (8) is connected upstream from the first space (9).
11. The exhaust muffler according to Claim 10,
    characterized in that

    - the pipe system (8) passes through the fourth space (32) with a pipe section (34) and/or

    - the fourth space (32) is designed to be airtight.
12. The exhaust muffler according to any one of Claims 1 through 11,
    characterized in that
    another space or a fifth space (35) is provided in the housing (2) and is designed as an absorption chamber to which the pipe system (8) is connected downstream from the first space (9).
13. The exhaust muffler according to Claim 12,
    characterized in that

    - the fifth space (35) is filled with a sound-absorbing material and/or

    - the pipe system (8) passes through the fifth space (35) with a pipe section (36) which is permeable for airborne sound and/or

    - the fifth space (35) is designed with an airtight seal to the outside.
14. The exhaust muffler according to any one of Claims 1 through 13,
    characterized in that

    - the first space (9) is separated from the third space (17) by a wall section,

    - the wall section is designed to be permeable for airborne sound to form the sound outlet (20).
15. The exhaust muffler according to any one of Claims 1 through 14,
    characterized in that
    the pipe system (8) connects an exhaust inlet (5) of the housing (2) directly to an exhaust outlet (7) of the housing (2).
16. The exhaust muffler according to any one of Claims 1 through 15,
    characterized in that

    - the pipe system (8) has a perforated pipe section (11) in the first space (9) and/or

    - the pipe system (18) has a perforated pipe section (36) in the fifth space (35) and/or

    - the wall section separating the first space (9) from the third space (17) is perforated and/or

    - the insulation wall (24) has at least one perforated section on its edge (27), which is connected to the outside wall (28) bordering the third space (17).

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