EP2195512A1

EP2195512A1 - Sound-absorbing arrangement

Info

Publication number: EP2195512A1
Application number: EP08834479A
Authority: EP
Inventors: Ragnar Glav; Mikael Karlsson
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2007-09-25
Filing date: 2008-09-18
Publication date: 2010-06-16
Anticipated expiration: 2028-09-18
Also published as: SE0702130L; AU2008305782B2; CN101802352B; KR20100061568A; EP2195512B1; WO2009041892A1; EP2195512A4; KR101648526B1; AU2008305782A1; BRPI0816220A2; CN101802352A; SE531516C2

Abstract

The present invention relates to a sound-damping arrangement. The sound-damping arrangement comprises a sound-damping container (3) with an internal space (3a), an inlet line (2) adapted to leading a fluid to the container (3) from a machine (1) which generates during operation a dominant noise with a frequency which is related to the speed of the machine, and an outlet line (4) adapted to leading the fluid out from the container (3). The arrangement comprises also a line element (5) which has an internal passage which connects the inlet line (2) and the outlet line (4) at a position in the vicinity of the sound-damping container (3), and an adjusting device (5a-d, 6- 9) adapted to adjusting the configuration of the passage and hence the acoustic characteristics of the sound-damping container so that the latter continuously assumes a natural frequency corresponding to the dominant sound frequency generated by the machine at its current speed.

Description

Sound-absorbing arrangement

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The present invention relates to a sound-damping arrangement according to the preamble of claim 1.

A problem in the dimensioning of exhaust systems and silencers of vehicles is the difficulty of damping the dominant low- frequency noise generated during the combustion processes in diesel and Otto engines. The frequency of this noise varies with the speed of the combustion engine.

Exhaust systems of vehicles usually comprise a silencer which contains a more or less curved flow passage for the exhaust gases. In such cases the sound led into the silencer is reflected a number of times by the walls of the silencer before it can proceed further. For such a silencer to be able to damp low-frequency noise effectively without much pressure drop, it needs to have very large dimensions. Silencers of a resonance type can effect good damping of low- frequency noise, but such silencers are only effective within a narrow frequency range and are therefore usable with advantage for damping noise from engines run at constant speed. Another sound-damping technique is to actively generate a counternoise which cancels out unwanted noise. This technique works well in, for example, the interior of vehicles but is difficult to implement in the harsh environment which prevails in an exhaust system.

JP 2001-140627 refers to a silencer for an exhaust system in a vehicle. The silencer comprises a inlet line which leads exhaust gases into the silencer and a outlet line which leads exhaust gases out from the silencer. A bypass line extends between two different portions of the silencer. The bypass line comprises a control valve and a chamber. The chamber serves as an expansion space in the silencer when the control valve is open and as a resonance chamber when the control valve is closed. US 6,494,290 refers to a silencer arranged in a line which leads air to a combustion engine. The silencer comprises a resonance chamber connected to the air line. One embodiment involves the use of an adjustable wall which can give the resonance chamber a variable volume.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a sound-damping arrangement of relatively small dimensions which has high capacity for damping low- frequency noise generated at variable frequency.

This object is achieved with the sound-damping arrangement of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. Conventional sound-damping containers usually have a natural frequency considerably higher than the low- frequency noise generated by machines run at variable speed. Conventional sound-damping containers therefore do not normally have the ability to damp low-frequency noise if they are not made large enough. Arranging a line element between an inlet line and an outlet line close to a sound-damping container makes it possible for the natural frequency of the sound- damping container to be lowered markedly. A relatively small sound-damping container may thus have a natural frequency which corresponds to the frequency of the low-frequency noise generated by a machine run at variable speed. By suitably altering the configuration of the internal passage of such a line element it is possible to vary the acoustic characteristics of the line element and hence the natural frequency of the sound-damping container. By means of an adjusting device which actively and steplessly adjusts the characteristics of the line element, such as the latter' s geometry and material, the sound-damping container can be given a variable natural frequency which corresponds at each time to the frequency of the noise which the machine generates at different speeds. Such a sound-damping arrangement damps very effectively the dominant low-frequency noise generated by the machine irrespective of how the speed of the machine changes during operation. According to a preferred embodiment of the present invention, the adjusting device comprises a control unit adapted to substantially continuously receiving information about the machine's current speed, and an actuator adapted to receiving control signals from the control unit and adjusting the configuration of the passage on the basis of that information. The control unit may be a computer unit with suitable software. The control unit may contain stored information about how the actuator should be controlled to give the passage a configuration such that the sound-damping container has a natural frequency corresponding to the frequency of the dominant noise generated by the machine at its current speed.

According to a preferred embodiment of the present invention, the adjusting device is adapted to adjusting the configuration of the passage by varying the material which defines the wall of the passage. Passages defined by different materials have different acoustic characteristics. In this case the configuration of the passage may be such that by suitable measures it is possible for the adjusting device to have two different materials for defining the walls of the passage in variable proportions. Alternatively or in combination, the adjusting device may be adapted to adjusting the configuration of the passage by varying the geometry of the passage. Varying the geometry of the passage will alter its acoustic characteristics and hence the natural frequency of the sound-damping container. The adjusting device may be adapted to varying the geometry of the passage by steplessly adjusting the length of the passage. If the adjusting device increases the length of the passage, the sound-damping container assumes a higher natural frequency. If instead the adjusting device reduces the length of the passage, the sound-damping container assumes a lower natural frequency. Alternatively or in combination, the adjusting device may be adapted to steplessly adjusting the cross-sectional area of the passage in at least one region. Such variation of the cross-sectional area may be effected by means of a valve or other constricting mechanism which steplessly varies the cross-sectional area in a limited region of the passage or throughout the passage. If the adjusting device increases the cross-sectional area of the passage, the sound-damping container assumes a lower natural frequency. If instead the adjusting device reduces the cross-sectional area of the passage, the sound-damping container assumes a higher natural frequency. Relatively small changes to the geometry of the passage may result in large changes in the natural frequency of the sound-damping container.

According to another preferred embodiment of the present invention, the line element comprises at least two line portions arranged for movement relative to one another. The line portions may be made of different materials. The different materials of the line portions may therefore define wall surfaces in the passage with a varying size when the line portions are placed in different linear positions relative to one another. By means of a plurality of movable line portions the length of the passage may also be steplessly varied. If the adjusting device increases the length of the passage, the sound-damping container assumes a higher natural frequency. If instead the adjusting device reduces the length of the passage, the sound-damping container assumes a lower natural frequency.

According to another preferred embodiment of the present invention, the inlet line and the outlet line have apertures within the sound-damping container which are so oriented relative to one another that sound led into the container from the aperture of the inlet line cannot be led out through the aperture of the outlet line without first having been reflected at least once by an internal surface in the container. Such a sound-damping container also provides effective damping of higher- frequency noise. With advantage, the inlet line and the outlet line are arranged in parallel close to the sound-damping container. This makes it easier to apply the line element between the inlet line and the outlet line. Such a sound-damping container may be called a turning chamber.

According to another preferred embodiment of the present invention, the arrangement is part of a exhaust system for leading exhaust gases out from a combustion engine. Otto engines and diesel engines generate during operation a dominant low- frequency noise which arises from their combustion processes. The frequency of the noise thus varies with the speed of the combustion engine. This low- frequency noise which is difficult to damp with conventional silencers can with advantage be damped with the sound-damping arrangement according to the invention. The sound-damping arrangement is usable in line systems for both gaseous and liquid fluids in cases where a machine generates low-frequency noise at variable frequency. The arrangement may for example be part of a line system for leading compressed air from a compressor. The arrangement may also be part of a line system for leading a liquid fluid with a machine which generates during operation a dominant noise with a frequency which is related to the speed of the machine. In such cases the arrangement may be part of a hydraulic system in which a machine, e.g. an oil pump, generates low- frequency noise with variable frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below by way of examples with respect to the attached drawings, in which:

Fig. 1 depicts a sound-damping arrangement according to a first embodiment of the invention and

Fig. 2 depicts a sound-damping arrangement according to a second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 depicts a sound-damping arrangement adapted to being applied in an exhaust system for a combustion engine 1. The combustion engine 1 may be a diesel engine or an Otto engine run at variable speed. The combustion engine may power a vehicle which may be a heavy vehicle. The exhaust gases in the exhaust system are led via an inlet line 2 to an internal space 3 a in a sound-damping container 3. The inlet line 2 has an aperture 2a situated at a distance from an interior wall surface in the container 3. The exhaust gases are intended to be led out from the sound-damping container 3 via an outlet line 4. The outlet line 4 has an aperture 4a which is likewise situated at a distance from an interior wall surface in the container 3. The inlet line 2 and the outlet line 4 have a substantially parallel extent close to the sound-damping container 3. The aperture 2a of the inlet line and the aperture 4a of the outlet line are so arranged relative to one another that sound led into the sound-damping container 3 has to be reflected at least once by an internal surface before it can be led out through the outlet aperture 4a. The sound-damping container 3 constitutes here a so-called turning chamber. A line element 5 which has an internal passage connects the inlet line 2 and the outlet line 4 close to the sound-damping container 3. The internal passage of the line element 5 is considerably narrower than the internal passages of the inlet line 2 and the outlet line.

The line element 5 comprises a first line portion 5a fastened in the inlet line 2 and a second line portion 5b fastened in the second exhaust line 4. A third line portion 5c is arranged for movement relative to the first line portion 5 a and the second line portion 5b. The third line portion 5c is arranged radially outside the first line portion 5a and radially inside the second line portion 5b. The third line portion 5c is made of different material from the first and second line portions 5a, b. A first actuator 6 is adapted to steplessly moving the third line portion 5c relative to the first and second line portions 5a, b. When the third line portion 5c is moved downwards in Fig. 1, the material of the third line portion 5c defines a larger proportion of the wall surface of the passage than when it is moved upwards to a higher position. A schematically depicted second actuator 7 is adapted to steplessly varying the cross-sectional area of the passage in a region of the second line portion 5b by placing a valve body 8 in a variable rotational position. A control unit 9 is adapted to substantially continuously receiving information concerning the speed of the combustion engine 1 and to controlling the actuators 6, 7 on the basis of that information. The control unit 9 may be a computer unit with suitable software for this purpose.

During operation, the combustion engine generates noise which is propagated by the exhaust flow. This noise is composed of various frequencies, but the low- frequency noise generated during the combustion processes of the combustion engine 1 is the clearly dominant noise. This noise, the frequency of which varies with the speed of the combustion engine, is difficult to damp with conventional silencers. Every sound- damping container has a natural frequency which is related to the configuration of the container with regard to material and geometry. Effective damping of a low- frequency noise involves using a very large conventional sound-damping container. However, arranging the line element 5 between the inlet line 2 and the outlet line 4 makes it possible for a sound-damping container 3 with a relatively small size to assume a natural frequency which is level with the dominant low-frequency noise generated by a combustion engine 1. The stepless linear movement of the third line portion 5c to different positions, effected by the first actuator 6, makes it possible for the internal wall surface of the passage to be defined by different materials in varying proportions. The acoustic characteristics of the line element 5 and the natural frequency of the sound-damping container can thus be varied. The stepless positioning of the valve 8 at different angles of rotation, effected by the second actuator 7, makes it possible for the internal passage of the line element 5 to assume a steplessly variable cross-sectional area in the region where the valve 8 is arranged. By varying the cross-sectional area of the passage, the acoustic characteristics of the line element 5 and the natural frequency of the sound-damping container 3 can also be varied. An advantage of such a line element 5 is that quite small changes to the configuration of the internal passage result in a relatively large difference in the natural frequency of the sound-damping container 3. The sound-damping arrangement may therefore have relatively small dimensions.

Operation of the combustion engine 1 results in the generation of exhaust gases which flow through the inlet line 2 to the sound-damping container 3. The exhaust gases are led from the sound-damping container to the outlet line 4. A small proportion of the exhaust gases is led from the inlet line 2 to the outlet line 4 via the passage in the line element 5. The control unit 9 substantially continuously receives information about the current speed of the combustion engine 1. On the basis of that information, the control unit 9 substantially continuously estimates the frequency of the dominant noise of the combustion engine 1. The control unit 9 contains stored information about how the actuator 6 should position the third line portion 5c and about how the actuator 7 should position the valve 8 if the sound-damping container 3 is to assume a natural frequency which corresponds to the dominant sound frequency of the combustion engine. As soon as the speed of the combustion engine changes, the control unit 9 activates the actuators 6, 7 so that the sound-damping container 3 continuously assumes a natural frequency which corresponds to the dominant sound frequency of the combustion engine. In this way the sound-damping arrangement can damp the dominant low-frequency noise from a combustion engine very effectively irrespective of the speed of the combustion engine.

Fig. 2 depicts an alternative version of a sound-damping arrangement. In this case the arrangement is part of a line system for leading compressed air from a compressor 11. A sound-damping container 3 is here viewed from outside and an inlet line 2 and an outlet line 4 are depicted in a transverse section. The compressed air from the compressor 11 is led via the inlet line 2 to an internal space in the sound-damping container 3. The air is intended to be led out from the sound-damping container 3 via the outlet line 4. The inlet line 2 and the outlet line 4 have a substantially parallel extent close to the sound-damping container 3. A tubular line element 5 with an internal passage connects the parallel lines 2, 4 close to the sound-damping container 3. The line element 5 comprises a first line portion 5a fastened on the inlet line 2, and a second line portion 5b fastened on the outlet line 4. The line element 5 comprises a third line portion 5d which connects the first line portion 5a and the second line portion 5b. The third line portion 5d comprises a first tubular connecting portion 5d] connected movably to the first line portion 5a, and a second tubular connecting portion 5d₂ connected movably to the second line portion 5b. The third portion 5d also comprises a base portion 5d₃ which constitutes a transverse connection between the tubular connecting portions 5di, 5d₂.

An actuator 6, exemplified here as a cylinder, is adapted to steplessly moving the third line portion 5d relative to the fixed first and second line portions 5a, b. When the third line portion 5d moves downwards in Fig. 1, the internal passage of the line element 5 becomes shorter, and when the third line portion 5d moves upwards in Fig. 1 the passage of the line element 5 becomes longer. By such linear movements the internal passage of the line element 5 can be provided with a steplessly variable length. The acoustic characteristics of the passage and the natural frequency of the sound-damping container 3 can thus be varied. A control unit 9 is adapted to substantially continuously receiving information concerning the speed of the compressor 11 and to controlling the actuator 6 on the basis of that information. The control unit 9 may be a computer unit with suitable software for the purpose.

During operation of the compressor 11, the control unit 9 substantially continuously receives information concerning the speed of the compressor 11 and determines the dominant low-frequency noise emitted by the compressor 11. Alternatively, the control unit 9 may receive information from a sonic sensor which detects the noise generated by the compressor. On the basis of that information, the control unit controls the actuator 6 so that the line element 5 assumes a length which gives the sound-damping container 3 a natural frequency which continuously corresponds to the dominant low-frequency noise of the compressor 11. The dominant low-frequency noise of the compressor 11 can thus be effectively damped in the sound-damping device.

The invention is in no way limited to the embodiment illustrated in the drawings but may be varied freely within the scopes of the claims. The sound-damping arrangement may be arranged in any desired line system which leads a fluid from a machine which produces a noise with a variable frequency. Such a fluid may be gaseous or liquid. The adjusting device may of course comprise other components than those exemplified in the embodiments for varying the natural frequency of the sound-damping container. It is also possible to arrange different types of sound-damping material within the sound-damping container 3 and/or within the line element 5.

Claims

1. A sound-damping arrangement which comprises a sound-damping container (3) with an internal space (3a), an inlet line (2) adapted to leading a fluid to the container (3) from a machine (1) which generates during operation a dominant noise with a frequency which is related to the speed of the machine, and an outlet line (4) adapted to leading the fluid out from the container (3), characterised in that the arrangement comprises a line element (5) which has an internal passage which connects the inlet line (2) and the outlet line (4) at a position in the vicinity of the sound-damping container (3), and an adjusting device (5a-d, 6- 9) adapted to adjusting the configuration of said passage and hence the acoustic characteristics of the sound- damping container so that the latter continuously assumes a natural frequency corresponding to the dominant sound frequency generated by the machine at its current speed.

2. A sound-damping arrangement according to claim 1, characterised in that the adjusting device comprises a control unit (9) adapted to substantially continuously receiving information about the current speed of the machine (1), and an actuator (6, 7) adapted to receiving control signals from the control unit (9) and to adjusting the configuration of the passage on the basis of that information.

3. A sound-damping arrangement according to claim 1 or 2, characterised in that the adjusting device (5a-c, 6, 9) is adapted to adjusting the configuration of the passage by varying the material (5a-c) which defines the walls of the passage.

4. A sound-damping arrangement according to any one of the foregoing claims, characterised in that the adjusting device (5a, b, d, 6- 9) is adapted to adjusting the configuration of the passage by varying the geometry of the passage.

5. A sound-damping arrangement according to claim 4, characterised in that the adjusting device (5a, b, d, 6, 9) is adapted to varying the geometry of the passage by steplessly adjusting the length of the passage.

6. A sound-damping arrangement according to any one of the foregoing claims, characterised in that the adjusting device (7, 8, 9) is adapted to varying the geometry of the passage by steplessly adjusting the cross-sectional area of the passage in at least one region.

7. A sound-damping arrangement according to any one of the foregoing claims, characterised in that the line element (5) comprises at least two line portions (5a-d) arranged for movement relative to one another.

8. A sound-damping arrangement according to any one of the foregoing claims, characterised in that the inlet line (2) and the outlet line (4) have apertures (2a, 4a) within the sound-damping container (3) which are so oriented relative to one another that sound led into the container (3) from the inlet line's aperture (2a) cannot be led out through the outlet line's aperture (4a) without first having been reflected at least once by an internal surface in the container (3).

9. A sound-damping arrangement according to any one of the foregoing claims, characterised in that the arrangement is part of an exhaust system for leading exhaust gases out from a combustion engine (1).

10. A sound-damping arrangement according to any one of claims 1 to 8, characterised in that the arrangement is part of a line system for leading compressed air from a compressor (11).

11. A sound-damping arrangement according to any one of the foregoing claims, characterised in that the arrangement is part of a line system for leading a liquid fluid with a machine which generates during operation a dominant noise with a frequency which is related to the speed of the machine.