EP2581567A1 - Active acoustic baffler - Google Patents

Abstract

The absorber has a connecting pipe (8) for acoustic and fluidic connection of a housing (7) with an exhaust system (1). An active membrane (10) separates front volume (12) from rear volume (13) in the housing, and is connected with the connecting pipe. An actuator stimulates vibration of the active membrane, and a condensation line (14) i.e. pipe, fluidically connects the rear volume with the front volume, in which vapor contained in the exhaust gas is condensed, where the condensated vapor is directed to the front volume.

Description

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

From the DE 10 2009 049 280 A1 An active silencer is known, which has a housing and a connecting tube for acoustically and fluidically connecting the housing to the exhaust system. In the housing, a speaker is arranged, which comprises an active membrane and an actuator for vibrational excitation of the membrane. The membrane separates in the housing a fluidly connected to the connecting tube Vorvolume of a back volume.

Active silencers of this kind are used to influence, preferably to damp, preferably to attenuate a mouth sound of the exhaust system by supplying a calculated sound, in particular counter sound or anti-sound. For this purpose, the pre-volume via the connecting pipe in fluid communication with the exhaust system. The pre-volume typically has no direct connection to the atmosphere outside the exhaust system, ie to the surroundings of the exhaust system. The back volume is limited by the active diaphragm and the muffler body, so that the speaker works on the back of a closed volume and on the front of the exhaust system.

Due to the design of the membrane of such a loudspeaker with electro-dynamic actuator is sensitive to different static or quasi-static pressures in front of and behind the membrane. Depending on the area of the membrane and the rigidity of a membrane suspension, the membrane becomes of the loudspeaker is deflected by a differential pressure from the central position, which reduces the performance of the loudspeaker, through its electro-dynamic drive (actuator) to generate dynamic alternating pressures in front of and behind the membrane. If this deflection from the central position also persists over a longer period of time and additionally under thermal stress on the loudspeaker, the membrane can remain permanently deflected due to the creep behavior of individual components of the loudspeaker, in particular the membrane suspension, even without a pressure difference between the pre-volume and the back volume and acts on the membrane.

The differential pressures between the pre-volume and the return volume occurring in this context can be roughly distinguished from one another as follows. On the one hand, a static pressure difference arises by changing the external air pressure in the atmosphere or environment of the exhaust system as a result of the weather, for example when changing from a low pressure area to an anticyclone area or as a result of a change in altitude above sea level, eg when traveling uphill. These static pressure changes take place relatively slowly, for example with a time constant or period of more than 10 seconds, ie with a frequency of less than 0.1 Hz. Furthermore, a quasi-static pressure difference is created by changing the flow conditions in the exhaust system, in particular by the Bernoulli effect at the junction between the connecting pipe and the exhaust system. The flow conditions in the exhaust system change depending on the respective operating state of the internal combustion engine, for example. When changing from idle mode to higher loads or full load, which is associated with higher mass flows and exhaust gas temperatures. These quasi-static pressure changes take place, for example, with a time constant or period between 0.1 sec. And 10 sec., Ie with a frequency between 0.1 Hz and 10 Hz. Finally, dynamic pressure differences can arise, namely the intended purpose of the speaker generated alternating pressures, so the acoustic signals to influence the sound emission of the exhaust system. These dynamic pressure fluctuations typically have a period or time constant less than 0.1 sec., Ie frequencies greater than 10 Hz.

To ensure the proper functioning of the electro-dynamic loudspeaker, ie the assembly of active membrane and associated electro-dynamic actuator, therefore, all differential pressures with a period greater than 0.1 sec., So the static and quasi-static pressure fluctuations must be compensated , At the same time, it must be ensured that the electro-dynamically generated alternating pressures are not significantly reduced or even acoustically short-circuited in the relevant frequency range above 10 Hz.

Compensation or compensation of the static pressure differences, ie the slow fluctuations of the atmospheric air pressure compared to the closed back volume, can be achieved by providing at least one relatively small pressure equalization opening, which fluidly connects the back volume to the surroundings of the silencer. Under certain circumstances, even a slight leakage of the housing may be sufficient to compensate for the static pressure differences.

A compensation of the quasi-static pressure fluctuations can according to the aforementioned DE 10 2009 049 280 A1 be made possible by at least one pressure equalization opening, which fluidly connects the back volume with the pre-volume. Such a pressure compensation opening is comparatively small dimensioned to avoid an acoustic short circuit between Vorvolumen and back volume.

Such pressure equalization openings between the pre-volume and the rear volume are permeable to gas and open to diffusion, as a result of which exhaust gas, in particular, which enters the pre-volume via the connecting pipe from the exhaust system, can also enter the rear volume. At the same time, a temperature gradient occurs because the exhaust gas in the exhaust system is usually exposed to higher temperatures than in the rear volume. This creates the problem that condenses the moisture bound in the exhaust gas, ie steam, in the cooler rear volume. Depending on the exhaust gas composition, the resulting condensate is relatively aggressive, in particular, the condensate may include sulfuric acid. The aggressive condensate can permanently damage the electro-dynamic actuator and connection cable. Measures for improving the condensate resistance on the loudspeaker as well as the insulation of the cable and the connection between the cables and the actuator are comparatively complicated and increase the production costs. Avoiding these costly measures to improve the condensate resistance, the active silencer can be positioned on the exhaust system only in the area of a tailpipe, which can be ensured by constructive measures at each tailpipe that caused by the flow velocity quasi-static pressure difference between Vorvolumen and Back volume is then as small as possible. As a result, it is possible to dispense with the pressure compensation opening between the pre-volume and the return volume. However, this significantly restricts the design of the active silencer and obstructs or prevents the use of an active silencer at an area remote from the tailpipe upstream of the engine, although the acoustic effectiveness of the active silencer may be better there.

The present invention addresses the problem of providing an improved muffler for an improved embodiment, which is characterized in that on the one hand disadvantages caused by quasi-static differential pressures arise between pre-volume and back volume, reduced or eliminated or avoided, at the same time disadvantages that may be caused by condensation in the back volume, reduced or eliminated or avoided.

This problem is solved in the invention in particular by the subject matters of the independent claims. Advantageous embodiments are the subject of the dependent claims.

According to a first solution, the invention is based on the general idea of fluidically connecting the back volume with the pre-volume via at least one condensation line. In this case, this condensation line is designed so that it condenses contained in the exhaust steam, the condensation line then passes the resulting condensate to the pilot volume. In other words, the respective condensation line supports the condensation in such a way that the condensate is obtained within the condensation line, that is, while the steam moves from the pre-volume in the direction of the rear volume. Since the back volume is closed, there is no flow through the condensation line, but only to diffusion processes or very slow volume shifts by the respective pressure compensation. The long residence time of the steam in the condensation line, which results on the one hand by the slow gas movements and on the other hand can be achieved by a correspondingly dimensioned line length, the condensation can take place substantially already within the condensation line, so that hardly steam enters the back volume. This means that the condensate can not accumulate in the back room, but already on the way there, within the condensation line accumulates. By a suitable arrangement of the condensation line, this can easily lead the condensate accumulating in the pre-volume, where it evaporates again due to the prevailing temperatures there and can be taken from the exhaust stream. By equipping the active silencer with such a condensation line thus the formation of aggressive condensate in the back volume can be significantly reduced or even avoided. As a result, the risk of damage due to aggressive condensate on the actuator is reduced. It is also noteworthy that at the same time the desired pressure equalization between Vorvolumen and back volume can be realized by the created with the help of the condensation line fluidic connection between Vorvolumen and back volume. Overall, the proposed measure opens the possibility to use the active muffler close to the engine, so that virtually any positionings for the active muffler on the exhaust system can be realized. The condensation line replaces that of the prior art, compare the above DE 10 2009 049 280 A1 , known pressure equalization opening between Vorvolumen and back volume.

According to an advantageous embodiment, the condensation line can therefore fluidly connect the back volume for pressure equalization without an acoustic short circuit with the pre-volume. In other words, the condensation line is dimensioned such that it is unsuitable for transmitting dynamic pressure fluctuations between the pilot volume and the return volume, in particular due to the friction occurring in the condensation line. Appropriately, this is the condensation line significantly longer than its inner diameter. In particular, the cable length is at least 10 times greater than the cable diameter, preferably the cable length is at least 100 times larger than the cable diameter. The condensation line can basically be designed in a straight line. Likewise, an embodiment is conceivable in which the Kondesationsleitung is curved, for example, helical and / or helical, to realize a short length a large cable length.

In another advantageous embodiment, the condensation line can be arranged completely inside the housing, so that it is an internal condensation line. This design reduces the risk of leaks.

According to an expedient development, a substantial portion of the condensation line running in the interior of the housing can now be arranged in the back volume. Suitably more than half, that is more than 50% of the length of the condensation line is arranged in the rear volume. In particular, at least 75% of the length of the condensation line are arranged in the back volume. As a result, the temperature prevailing in the rear volume acts on a comparatively large proportion of the condensation line, so that a substantial portion of the condensation line is cool in comparison with the exhaust gas and brings about the desired condensation.

According to another advantageous embodiment, the condensation line may have a portion extending outside the housing. This section may suitably connect an end section of the condensation line connected to the pre-volume to an end section of the condensation line connected to the rear volume. In this way, an at least partially externally extending condensation line is created, which opens up possibilities to support the formation of condensation within the condensation line.

For example. can be cooled according to a development of the arranged outside the housing portion of the condensation line. It is conceivable, for example, a purely passive cooling by the ruling in the environment of the muffler temperatures. Another passive cooling can be achieved by a flow around the muffler and the externally extending portion of the condensation line be caused, for example, by wind of a motor vehicle equipped with the internal combustion engine. Active cooling of the section of the condensation line extending outside the housing is likewise conceivable, for example with the aid of a blower which generates an air flow for acting on the section. The section can be equipped with cooling fins or the like. It is also possible to incorporate said section in a heat exchanger, which is also involved in a cooling circuit, so that with the aid of the heat exchanger heat from the condensation line can be transferred to a coolant of the cooling circuit.

According to another advantageous embodiment, the condensation line may be a tube, which is in particular made of a metallic material and is characterized by a particularly high thermal conductivity.

According to a preferred embodiment, the back volume may be hermetically sealed from an environment of the muffler. This means that the housing of the muffler in the region of the rear volume has no opening through which a fluid can enter the back volume or escape therefrom. In other words, the back volume is completely encapsulated except for the fluidic connection with the pre-volume created by the condensation line. In particular, in this case neither a pressure equalization opening is present, which fluidly connects the back volume with the environment, nor a sontiger connection provided via which a fluid can be supplied to the back volume or discharged therefrom.

According to a second solution, the present invention is based on the general idea to provide at least one pressure compensation chamber. Such a pressure compensation chamber encloses a compensating volume, which is fluidically connected to the pre-volume via at least one connecting line is. Thus prevails in the compensation volume of the pressure of the Vorvolumens. Furthermore, at least one passive membrane is provided, which is positioned such that it is exposed on the one hand to the pressure prevailing in the compensating volume and, on the other hand, to the pressure prevailing in the rear volume. In other words, the passive membrane deforms depending on the pressure difference acting thereon, which ultimately corresponds to the pressure difference between the pre-volume and the return volume due to the fluidic coupling between the equalization volume and the pre-volume. Thus, depending on its rigidity, the passive membrane can transmit the pressure prevailing in the pre-volume to the back volume, whereby the desired pressure compensation is more or less realized. It is noteworthy that the connection of the passive membrane gas exchange between Vorvolume and back volume is no longer possible. In other words, in the second solution presented here, the pre-volume and the return volume are fluidically separated from one another. As a result, no condensate can accumulate in the back volume. Overall, the proposed measure opens the possibility to use the active muffler close to the engine, so that virtually any positionings for the active muffler on the exhaust system can be realized. If condensate accumulates in the compensation volume, this can be passed through the connecting line to the pilot volume.

To increase the efficiency of the pressure compensation chamber, the passive membrane is designed to be softer than the active membrane of the loudspeaker. In particular, the passive membrane is at least twice as elastic as the active membrane.

In a particularly advantageous embodiment, the pressure compensation chamber may have a chamber arranged in the rear volume chamber housing, in which case the passive membrane forms at least a part of the chamber housing. In other words, the passive membrane separates the equalization volume from the back volume within the housing of the muffler. This can reduce leakage problems.

According to an advantageous development, the passive membrane can form the entire chamber housing. In other words, the passive membrane is shaped so that it forms the chamber housing and encloses the compensation volume. In particular, the housing may be configured as an elastic balloon or as an elastic bellows. In this case, the passive membrane defines the elastic skin of the balloon or the elastic bellows body. If the passive membrane forms the entire chamber housing, depending on the pressure difference between the equalizing volume and the back volume, the chamber housing may expand or shrink to equalize the pressures between the equalizing volume and the back volume. A complete pressure equalization is not possible due to the internal tension of the passive membrane. The softer the passive membrane is, the closer the pressures between equalization volume and back volume can be.

In an alternative embodiment, the pressure compensation chamber can have a chamber housing arranged outside the return volume or outside the housing, in which case the passive membrane in the chamber housing separates the compensation volume from a coupling volume. A coupling line then provides a fluidic connection between the coupling volume and the back volume. Thus prevails in the coupling volume of the pressure of the return volume. A pressure difference between the pre-volume and the back volume thus leads to a corresponding pressure difference between the compensating volume and the coupling volume, which can be more or less compensated by a corresponding deformation of the passive membrane. Again, that is true desired pressure equalization the better, the softer the passive membrane is.

According to a further alternative embodiment, the pressure compensation chamber may be formed in the housing, in which case the passive membrane in the housing separates the compensation volume from the rear volume. This internal design also reduces leakage problems.

In an expedient development, the connecting line can be arranged in the housing and extend through the rear volume. Additionally or alternatively it can be provided that due to a correspondingly selected positioning of the passive membrane within the housing, the compensation volume is distal to the pre-volume, so that in particular the back volume between the compensation volume and the pre-volume is arranged. Furthermore, the compensation volume within the housing is expediently arranged so that the passive membrane has no contact with the pre-volume.

In another embodiment, the connecting line may be arranged so that it leads condensate possibly accumulating condensate to the pre-volume. In other words, the connecting line is adapted to the intended installation situation so that it has a slope in the direction of the front volume.

A third solution of the invention is based on the general idea of compensating for the static deflection of the active membrane formed by a corresponding actuation of the actuator due to a pressure difference between the pre-volume and the back volume. For this purpose, the active silencer with a sensor for measuring a pressure difference between Vorvolumen and back volume fitted. This sensor system may, for example, include a differential pressure sensor which directly measures the pressure difference between the pre-volume and the back volume. Likewise, the use of two absolute pressure sensors is conceivable, one of which measures the absolute pressure in the pre-volume, while the other measures the absolute pressure in the back volume. The difference between the two absolute pressures then gives the desired differential pressure. The sensor is further coupled to a controller which serves to drive the actuator. This control is now programmed or designed so that it controls the actuator depending on the measured pressure difference so that it deflects the active membrane against the deflection caused by the pressure difference, whereby the deflection caused by the pressure difference of the active membrane more or less compensated can be. Since a control for actuating the actuator in the active speaker is present anyway, the solution presented here only requires a sensor suitable for measuring differential pressure and a corresponding coupling in conjunction with a suitable programming. Thus, this embodiment can be comparatively inexpensive and realize almost no design effort. In particular, such an embodiment comes without pressure equalization between Vorvolumen and back volume. In particular, this design can therefore be characterized in that the pre-volume and the back volume are fluidly separated from each other. Due to the fluidic separation of the return volume from the pre-volume, there is also the risk of condensate formation in the return volume. Overall, the proposed measure opens the possibility to use the active muffler close to the engine, so that virtually any positionings for the active muffler on the exhaust system can be realized.

According to an advantageous embodiment, the controller may superimpose a static control signal dependent on the measured pressure difference on dynamic control signals with which the controller drives the actuator activates the active membrane so that this counter-noise to influence, in particular for the damping of entrained in the exhaust air generated airborne. In other words, the static control signal generated to compensate for the deflection of the active membrane caused by the pressure differential is modulated onto the dynamic control signals with which the controller drives the actuator to drive the active diaphragm to provide the desired pressure pulsations into the exhaust system can initiate.

A fourth solution of the invention is also based on the general idea of compensating for the static deflection of the active membrane formed by a corresponding actuation of the actuator due to a pressure difference between the pre-volume and the back volume. Notwithstanding the above-described third solution, the pressure difference is not measured in the fourth solution, but the resulting deflection of the active membrane is determined from its central position to use the deflection directly as a basis for the control of the actuator. For this purpose, the silencer comprises a device for determining a deflection of the active membrane from its central position. A control provided for driving the actuator is coupled to said device and controls the actuator depending on the determined diaphragm deflection for compensating the diaphragm deflection. In this way can be dispensed with a complex pressure measurement.

The determination of the diaphragm deflection can be carried out in different ways. For example, the device may have a sensor for measuring the diaphragm deflection. Alternatively, the device can evaluate the current consumption of the actuator when it is actuated and determine the diaphragm deflection as a function of this. This purely electronic measure does not require additional sensors. In particular, the usual, occurring during the silencing operation current consumption of the actuator be evaluated. This measure is based on the consideration that the current consumption of the actuator changes depending on a deflection of the membrane, since the actuator optionally works with or against a bias of the membrane. Alternatively, it is likewise conceivable that the device evaluates a microphone signal of a microphone which detects the sound emitted by the active membrane and determines the diaphragm deflection as a function of this. This measure is based on the consideration that the sound emitted by the active membrane changes as a function of the prestressing of the membrane. Such a microphone is already present in a conventional active sound damping system, so that even with this solution can be dispensed with an additional sensor. It is clear that, in principle, other measures are conceivable in order to determine the actual diaphragm deflection.

According to a fifth solution, the present invention is based on the general idea of equalizing the pressure difference between the pre-volume and the back volume by means of a delivery device, which for this purpose is fluidically connected to the return volume. If the pressure in the back volume is higher than the pressure in the pre-volume, gas or air can be sucked out of the back volume and conveyed into the environment or into the pre-volume, for example, with the delivery device in order to bring about the pressure compensation. If, on the other hand, the pressure in the rear volume is lower than in the pre-volume, gas or air, for example from the environment or from the pre-volume, can be sucked in by means of the delivery device and supplied to the return volume in order to effect the pressure equalization. As an output signal for driving the conveyor can thereby serve a correlated with the pressure difference signal or correlated with the deflection of the diaphragm from the central position signal. The corresponding devices are already described above.

According to a particularly advantageous embodiment, which is applicable in particular for all solutions and embodiments mentioned above, at least one pressure equalization opening can be provided, which fluidly connects the back volume to an environment of the housing of the muffler. With the help of such a pressure equalization opening, which can be designed with suitable measures, for example. By means of a gas-permeable and liquid impermeable membrane, gas permeable and liquid-tight, the static pressure differences between the back volume and the atmospheric environment described above can be compensated. The above-described first solution, in which the pre-volume and the back volume are fluidly connected to one another by the condensation line, as well as the associated embodiments, can be configured such that the back volume is fluidically separated from the environment of the housing of the muffler. In these cases, it is thus possible to dispense with such a pressure compensation opening between the rear volume and the environment. In contrast, it seems to be useful in the other solutions described above, including the associated embodiments, to provide such a pressure compensation opening.

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

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.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

Figur 1

eine teilweise geschnittene isometrische Ansicht einer Abgasanlage im Bereich eines aktiven Schalldämpfers,

Figuren 2 bis 10

stark vereinfachte Prinzipdarstellungen des aktiven Schalldämpfers bei verschiedenen Ausführungsformen.

Show, in each case schematically,

FIG. 1

a partially sectioned isometric view of an exhaust system in the region of an active muffler,

FIGS. 2 to 10

highly simplified schematic diagrams of the active silencer in various embodiments.

Corresponding FIG. 1 an exhaust system 1 of an internal combustion engine, not shown here, an exhaust line 2 and at least one active muffler 3, which is connected to the exhaust line 2 and thus to the exhaust system 1. In the example, the silencer 3 is connected to a in the operation of the internal combustion engine in FIG. 1 connected by an arrow indicated exhaust gas flow leading exhaust pipe 5, wherein in this example a Y-shaped connector 6 is used, the in FIG. 1 only half is shown. It is clear that the muffler 3 can in principle be connected to any component of the exhaust system 1, that is not necessarily to an exhaust pipe 5. The active muffler 3 serves to dampen airborne sound that is carried in the exhaust gas flow 4 or in the Exhaust line 2 spreads.

The muffler 3 comprises a housing 7 and a connecting tube 8 for fluidically connecting the housing 7 with the exhaust system 1. Through this connecting tube 8 through the acoustic coupling between the Muffler 3 and the rest of the exhaust system 1. The connecting pipe 8 is not traversed by the exhaust gas. However, the exhaust gas may enter the connection pipe 8.

According to the FIGS. 2 to 10 For example, the active muffler 3 includes a speaker 9 that includes an active diaphragm 10 and an actuator 11. The active membrane 10 separates in the housing 7 a fluidly connected to the connecting tube 8 Vorvolumes 12 from a back volume 13, which is shown in the illustrations of FIGS. 2 to 8 is located on a side facing away from the connecting tube 8 side of the speaker 9. Accordingly, the pre-volume 11 faces the connecting pipe 8, while the rear volume 13 faces away from the connecting pipe 8. The actuator 11 operates electromagnetically and serves for the vibration excitation of the active membrane 10.

In the in the FIGS. 2 and 3 In embodiments shown, the muffler 3 is also equipped with at least one condensation line 14, which is preferably formed from a metallic tubular body. In principle, the condensation line 14 can also be designed as an elastic hose, in particular made of plastic. The condensation line 14 leads to a fluidic connection of the rear volume 13 with the pre-volume 12, which results in a pressure equalization between the pre-volume 12 and the rear volume 13. So that this pressure compensation takes place only for static or quasi-static pressure differences and not for dynamic pressure differences, the condensation line 14 is designed so that it fluidly connects the back volume 13 with the pre-volume 12 without acoustic short circuit. This is achieved, for example, by a corresponding throttle effect, in particular by friction within the condensation line 14. For example. is a length 15 of the condensation line 14 significantly larger than a diameter 16 of the condensation line 14. Suitable conditions are, for example, at least 10: 1 or at least 100: 1.

The condensation line 14 is also designed so that vapor, which is contained in the exhaust gas, which penetrates in particular by diffusion processes in the condensation line 14, condenses in the condensation line 14. In addition, the condensation line 14 is arranged so that the condensate accumulating in it can flow to the pre-volume 12. Accordingly, in the installed state of the muffler 3, the condensation line 14 has a gradient in the direction of the front volume 12.

Thus, the condensation effect occurs in the condensation line 14 to the desired extent, according to the in FIG. 2 In the embodiment shown, the condensation line 14 can be arranged completely inside the housing 7. In this case, a substantial section 17, which extends over at least 50% of the total condensation line length 15, is expediently arranged in the rear volume 13. As a result, a large part of the condensation line 14, namely the essential portion 17, is exposed to the temperatures prevailing in the rear volume 13, which are significantly lower than the temperatures of the exhaust gas entering the condensation line 14. As a result, the desired condensation of steam in the condensation line 14 can be realized.

At the in FIG. 3 In the embodiment shown, the condensation line 14 is arranged such that it has a section 18 extending outside the housing 7. This outer section 18 connects a first end section 19 of the condensation line 14 connected to the pre-volume 12 to a second end section 20 of the condensation line 14, which is connected to the rear volume 13. The outer portion 18 may, for example, be cooled by means of a cooling gas flow 21, which in FIG. 3 indicated by an arrow. This can be the driving wind that arises during operation of a vehicle that is equipped with the internal combustion engine whose exhaust gases be discharged with the help of the exhaust system 1 presented here. Alternatively, the cooling gas flow 21 can be realized, for example, with the aid of a blower 22. To improve the heat transfer between the outer portion 18 and the cooling gas flow 21, the condensation line 14 in the outer portion 18 may have cooling fins 23. Additionally or alternatively, the condensation line 14 may be integrated in the outer portion 18 in a heat exchanger 24, which in turn is integrated into a cooling circuit 25, wherein a media separation between the cooling medium in the cooling circuit 25 and the exhaust gas is provided in the condensation line 14.

According to the FIGS. 4 to 7 For example, the silencer 3 may be equipped with at least one pressure compensation chamber 26, which encloses a compensation volume 27. Furthermore, at least one connecting line 28 is present, which connects the compensating volume 27 fluidically with the pre-volume 12. In addition, at least one passive membrane 29 is provided which is exposed on the one hand to the pressure prevailing in the compensating volume 27 and on the other hand to the pressure prevailing in the rear volume 13. Accordingly, the passive diaphragm 29 deforms depending on the pressure difference between the compensating volume 27 and the rear volume 13. Since the compensating volume 27 communicates with the pre-volume 12 through the connecting line 28, the pressure prevailing in the compensating volume 27 corresponds to the pressure prevailing in the pre-volume 12. Thus, the passive membrane 29 deforms depending on the pressure difference between the back volume 13 and Vorvolumen 12. In the FIGS. 4 to 7 is shown for the passive membrane 29 with a solid line an initial state, while at the same time is shown with a broken line, a state in which the passive membrane 29 is deformed due to the pressure difference between the pre-volume 12 and back volume 13.

In the embodiments of the FIGS. 4 and 5 the pressure compensation chamber 26 comprises a chamber housing 30, which is arranged in the rear volume 13 in the interior of the housing 7. The passive membrane 29 forms at least a part of the chamber housing 30. As a result, the passive membrane 29 separates the compensation volume 27 from the rear volume 13 in the interior of the housing 7, so that it is indirectly exposed to the pressure of the return volume 13. In the examples shown, the entire chamber housing 30 is formed by the passive membrane 29. At the in FIG. 4 In the embodiment shown, the chamber housing 30 is designed as an elastic balloon 30 '. This balloon 30 'or its skin or sheath is formed by the passive membrane 29. At the in FIG. 5 In the embodiment shown, the chamber housing 30 is designed as a bellows 30 ", whereby the bellows body is formed by the elastic passive membrane 29.

At the in FIG. 6 In the embodiment shown, the pressure compensation chamber 26 is arranged outside the housing 7. In addition, the chamber housing 30 is disposed outside of the housing 7. In this embodiment, the passive membrane 29 in the chamber housing 30 separates the equalizing volume 27 from a coupling volume 31. A coupling line 32 provides a fluidic connection of the coupling volume 31 with the back volume 13. In the example of FIG. 6 the chamber housing 30 is arranged by the connecting line 28 and the coupling line 32 spaced from the housing 7 of the muffler 3. Likewise, it is conceivable to grow the chamber housing 30 directly to the housing 7, in which case the coupling line 32 and the connecting line 28 are reduced to a connection opening or a coupling opening. The respective opening then penetrates either a wall of the housing 7 and a wall of the chamber housing 30 or a common wall of the housing 7 and the chamber housing 30. The connection opening then provides for the fluidic coupling between the compensation volume 27 and Vorvolumen 12. Die Coupling opening then provides for the fluidic coupling between coupling volume 31 and back volume 13.

At the in FIG. 7 In the embodiment shown, the pressure compensation chamber 26 is again formed in the interior of the housing 7, in which case the passive diaphragm 29 in the housing 7 separates the compensation volume 27 from the back volume 13. In the example of FIG. 7 reduces the structural complexity of the chamber housing 30 on a partition, which in FIG. 7 is also designated 30, which separates within the housing 7 a region containing the back volume 13 of an area containing the compensating volume 27. At this partition 30, the passive membrane 29 is mounted or suspended. The connecting line 28 is also disposed within the housing 7, wherein it extends through the rear volume 13 to connect the compensating volume 27 with the Vorvolumen 12 can.

In the in the FIGS. 4 to 7 In the embodiments shown, the connecting line 28 is in each case arranged in such a way that it conducts condensate, which may occur in the connecting line 28 or in the compensating volume 27, to the pilot volume 12. For this purpose, the respective connecting line 28 in the installed state have a corresponding gradient in the direction of the pre-volume 12.

Corresponding FIG. 8 In principle, the silencer 3 may in all embodiments be equipped with a controller 33 which can actuate the actuator 11 via a corresponding control line 34. The actuator 11 then drives the active membrane 10 to generate pressure waves, in particular sound waves, depending on its activation.

In addition, the in FIG. 8 shown embodiment of the muffler 3 have a sensor 35, with the help of a pressure difference between Pre-volume 12 and back volume 13 can be measured. In the example of FIG. 8 The sensor system 35 includes a differential pressure sensor 36, which is coupled on the one hand in a suitable manner, for example via a first sensor line 37, with the pre-volume 12 and on the other hand in a suitable manner, for example via a second sensor line 38, is coupled to the rear volume 13. Via a signal line 39, the sensor 35 is coupled to the controller 33, so that the controller 33 knows the pressure difference between the pre-volume 12 and back volume 13. The controller 33 is now configured or programmed so that it controls the actuator 11 depending on the measured pressure difference. The targeted control of the actuator 11 can now more or less compensated by the prevailing between the pre-volume 12 and back volume 13 pressure difference deflection of the active membrane 10. For example. causes an overpressure in the Vorvolumen 12 a deflection of the active membrane 10 in the direction of rear volume 13. By appropriate driving of the actuator 11, this can drive the active membrane 10 statically in the direction of Vorvolumen 12 and in particular zurückverstellen back to the starting position. Thus, the deflection of the active membrane 10 caused by the pressure difference between the pilot volume 12 and the back volume 13 is substantially neutralized or compensated.

The controller 33 is expediently configured so that it generates a dependent of the measured pressure difference static control signal to produce the desired static adjustment of the active membrane 10 to compensate for the pressure difference caused by the deflection of the active membrane 10. In contrast, the controller generates 33 for generating pressure oscillations, which are to be transmitted via the connecting pipe 8 in the exhaust line 2, dynamic control signals with which the controller 33, the actuator 11 for driving the active diaphragm 10 drives. Depending on this activation, the active membrane 10 can now achieve the desired pressure oscillations produce. In particular, it is counter-noise to combat entrained in the exhaust airborne sound. The static control signals, which are provided to compensate for the deflection caused by the pressure difference of the active membrane 10, are now superimposed on the dynamic control signals which are provided for generating the pressure oscillations or the counter-noise.

FIG. 9 shows an embodiment in which instead of a pressure difference, which has a deflection of the active membrane 10 from the center position result, the diaphragm deflection is determined directly and is used as input to the static control signal for compensation. So according to FIG. 9 a device 42 may be provided, with the aid of which the diaphragm deflection can be determined. The deflection of the active membrane 10 is determined from its central position, which it assumes when the pressures in the pre-volume 12 and in the rear volume 13 are the same. In the example of FIG. 9 The device 42 comprises a microphone 43, which can detect and measure the airborne sound emitted by the active membrane 10. The microphone signals are supplied via a corresponding signal line 44 to the controller 33 in order to evaluate them. Since the sound radiation of the diaphragm 10 changes from its bias or from its deflection, the diaphragm deflection can be determined by a desired-actual comparison. Alternatively, the device 42 according to FIG. 10 have a sensor 45, by means of which the deflection of the membrane 10 can be measured. A corresponding signal can then be returned to the controller 33 via a signal line 46.

FIG. 10 now shows an embodiment in which a conveyor 47 is provided which is fluidly connected to the rear volume 13. A control line 48 connects the controller 33 with the conveyor 47. The conveyor 47, for example, a pump can as over- or vacuum generator serve to be able to pressurize the back volume 13 with overpressure or negative pressure as needed, in such a way that the unwanted static diaphragm deflection is compensated in whole or in part. As the base signal for the actuation of the conveyor 47 can serve directly the diaphragm deflection, which can be determined again with the aid of the device 42. Alternatively, the pressure difference between pre-volume 12 and back volume 13 can be used to control the conveyor 47, since the pressure difference correlates with the diaphragm displacement. To determine the pressure difference, the sensor 35 can be used again. In the example, the conveyor 47 is arranged on the outside of the housing 7. It is clear that the conveyor can also be arranged in the interior of the housing 7. Furthermore, the conveyor 47 in the example conveys into the environment 41 or sucks from the environment 41 in order to adjust the pressure in the back volume 13 to the pressure prevailing in the pilot volume 12.

In the in the FIGS. 4 to 10 In embodiments shown, the muffler 3 is also equipped with at least one pressure equalization opening 40 which is formed in the housing 7 or in a wall of the housing 7 and which connects the back volume 13 fluidly with an environment 41 of the muffler 3. In this case, the pressure compensation opening 40 may well be designed so that it is permeable to gas, but impermeable to liquid. For example. For this purpose, the pressure compensation opening 40 can be closed with a gas-permeable membrane, which is not shown here. In the in the FIGS. 2 and 3 In principle, such a pressure equalization opening 40 may also be present. However, an embodiment in which such a pressure compensation opening 40 is dispensed with is preferred. In particular, therefore, in the embodiments of the FIGS. 2 and 3 the back volume 13 is decoupled from the environment 41.

Although not shown here, it will be understood that features shown only in one embodiment may be practiced in the other embodiments, as appropriate.

Claims (25)

Active silencer for an exhaust system (1) of an internal combustion engine, preferably of a motor vehicle, - with a housing (7) - With a connecting tube (8) for the acoustic and fluidic connection of the housing (7) with the exhaust system (1) - With an active membrane (10) in the housing (7) a fluidly connected to the connecting tube (8) Vorvolumes (12) from a rear volume (13), - With an actuator (11) for vibrational excitation of the active membrane (10), characterized by at least one condensation line (14) which fluidly connects the back volume (13) with the pre-volume (12), condenses in the vapor contained in the exhaust gas and the accumulating condensate to the pre-volume (12) passes. Silencer according to claim 1,
characterized,
in that the condensation line (14) fluidly connects the rear volume (13) for pressure compensation without an acoustic short circuit to the pre-volume (12). Silencer according to claim 1 or 2,
characterized,
that the condensation conduit (14) inside the housing (7) is arranged. Silencer according to claim 3,
characterized,
that a significant portion (17) of said condensing duct (14) in the back volume (13). Silencer according to claim 1 or 2,
characterized,
in that the condensation line (14) has a section (18) extending outside the housing (7), which has an end section (19) of the condensation line (14) connected to the pilot volume (12) with an end section (20) connected to the rear volume (13) ) connects the condensation line (14). Silencer according to claim 5,
characterized,
that the outside of the housing (7) disposed portion (18) of the condensation duct (14) is actively or passively cooled. Silencer according to one of claims 1 to 6,
characterized,
that the condensation conduit (14) is a tube. Silencer according to one of claims 1 to 7,
characterized,
that the condensation line (14) in the installed state of the muffler (3) has a slope in the direction of the pre-volume (12). Silencer according to one of claims 1 to 8,
characterized,
that the back volume (13) to an environment (41) of the muffler (3) is hermetically sealed. Active silencer according to the preamble of claim 1, characterized by at least one pressure compensation chamber (26) enclosing a compensation volume (27), wherein at least one connecting line (28) fluidly connects the compensation volume (27) with the pre-volume (12), wherein at least one passive diaphragm (29) is provided which is exposed on the one hand to the pressure prevailing in the compensating volume (27) and on the other hand to the pressure prevailing in the rear volume (13). Silencer according to claim 10,
characterized, in that the pressure compensation chamber (26) has a chamber housing (30) arranged in the rear volume (13), - That the passive membrane (29) forms at least a part of the chamber housing (30). Silencer according to claim 11,
characterized,
that the passive membrane (29) forms the entire chamber housing (30). Silencer according to claim 11 or 12,
characterized,
in that the chamber housing (30) is designed as an elastic balloon (30 ') or as an elastic bellows (30') '. Silencer according to claim 10,
characterized, - that the pressure balancing chamber (26) outside the reserve volume and / or outside the housing (7) has arranged chamber housing (30), in that the passive membrane (29) in the chamber housing (30) separates the equalizing volume (27) from a coupling volume (31), - That a coupling line (32) fluidly connects the coupling volume (31) with the rear volume (13). Silencer according to claim 10,
characterized, - That the pressure compensation chamber (26) in the housing (7) is formed, - That the passive membrane (29) in the housing (7) the compensating volume (27) from the rear volume (13) separates. Silencer according to claim 15,
characterized,
in that the connecting line (28) is arranged in the housing (7) and extends through the rear volume (13). Silencer according to one of claims 10 to 16,
characterized,
in that the connecting line (28) is arranged so that it leads condensate accumulating in the compensating volume (27) to the pre-volume (12). Active silencer according to the preamble of claim 1, characterized by a sensor system (35) for measuring a pressure difference between pre-volume (12) and return volume (13), wherein a control (33) provided for driving the actuator (11) is connected to the sensor system (35 ) and the actuator (11) depending on the measured pressure difference for compensating a caused by the pressure difference deflection of the active membrane (10) drives. Silencer according to claim 18,
characterized,
in that the controller (33) superimposes a static control signal, dependent on the measured pressure difference, on dynamic control signals with which the controller (33) activates the actuator (11) for driving the active diaphragm (10) so as to counteract this by damping airborne noise entrained in the exhaust gas generated. Active silencer according to the preamble of claim 1, characterized by a device (42) for determining a deflection of the active diaphragm (10) from its central position, wherein a control (33) provided for driving the actuator (11) is provided with the device (42). is coupled and the actuator (11) depending on the determined diaphragm deflection for compensating the diaphragm deflection drives. Silencer according to claim 20,
characterized,
in that the device (42) has a sensor for measuring the diaphragm deflection. Silencer according to claim 20,
characterized,
in that the device (42) evaluates the current consumption of the actuator (11) when it is actuated and determines the diaphragm deflection as a function of this. Silencer according to claim 20,
characterized,
in that the device (42) evaluates a microphone signal of a microphone which detects the sound emitted by the active membrane and determines the diaphragm deflection in dependence thereon. Active silencer according to the preamble of claim 1, characterized by a conveyor (47) fluidly connected to the rear volume (13), wherein a control (33) coupled to the conveyor (47) controls the conveyor (47) depending on a pressure difference between the preliminary volume (47). 12) and rear volume (13) or depending on a deflection of the active membrane (19) from its central position for reducing the pressure difference and the diaphragm deflection for sucking from the back volume (13) or for conveying in the back volume (13) drives. Silencer according to one of Claims 1 to 8 and 10 to 24, characterized by at least one pressure compensation opening (40) which fluidly connects the rear volume (13) to an environment (41) of the housing (7) of the silencer (3).

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