Patent Application
20240175381
This application is a U.S. non-provisional application claiming the benefit of German Application No. 10 2022 131 738.2, filed on Nov. 30, 2022, which is incorporated herein by reference in its entirety.
The disclosure relates to a muffler for an exhaust system.
Mufflers in exhaust systems, for example in exhaust systems of vehicles or stationary systems, serve to minimize the sound emissions emanating from the respective vehicle or from the stationary system. Mufflers are known in different embodiments with different operating principles, for example in the form of reflection, absorption or resonance mufflers.
Depending on the design of the components used in the exhaust system, for example the pipe courses and/or pipe cross-sections used, certain sound frequencies are of particular interest in order to be able to achieve an optimal noise reduction in the muffler, i.e., an optimal reduction of the sound pressure level.
However, the tuning to the relevant sound frequencies can necessitate complex structural configurations of a given muffler. In particular, it is not readily possible in many cases to align the muffler to certain sound frequencies without increasing the installation space or space requirement of the muffler.
The subject disclosure provides a muffler for an exhaust system, the noise dampening effect of which is flexibly adaptable. In particular, the muffler should have a small space requirement.
In one example, a muffler for an exhaust system includes a muffler housing with an inlet chamber that is fluidically connected to an outlet chamber. The inlet chamber has an inlet pipe for supplying an exhaust gas stream into the inlet chamber, and the outlet chamber has an outlet pipe for discharging the exhaust gas stream from the outlet chamber, wherein the inlet pipe and the outlet pipe each have a first pipe portion and a second pipe portion. The inlet pipe and the outlet pipe in the respective first pipe portions are circumferentially impermeable to the exhaust gas stream and in the respective second pipe portions are circumferentially porous, wherein the first pipe portions each have a predetermined length, such that a λ/4 resonator is formed between each respective first pipe portion and an inner wall of the muffler housing associated with the respective first pipe portion.
The sound-reducing effect of a λ/4 resonator is due to the fact that the λ/4 resonator provides a branch of finite length in the sound chamber, wherein the finite length is selected such that a damping maximum occurs at a wavelength corresponding to four times the finite length. In other words, the choice of the finite length makes it possible to tune to a sound frequency that is particularly relevant for the reduction of the sound level.
The disclosure is based on the basic idea of configuring the achievable noise reduction of the muffler to be adaptable via a coordinated design of the inlet pipe and the outlet pipe. According to the disclosure, the lengths of the first pipe portions of the inlet and outlet pipe are selected such that the λ/4 resonator formed between the respective first pipe portion and the inner wall associated with the respective first pipe portion is tuned to a specific sound frequency that is particularly relevant for the respective application. At the same time, the noise can be minimized via the porosity of the second portions of the inlet and outlet pipe, or an additional broad-spectrum reduction of the sound pressure level can be performed, and an optimal compromise between reduction of the sound level and increase of the backpressure in the exhaust system can be found. An adaptation to changing relevant sound frequencies and requirements can thus be accomplished via an adaptation of the inlet and outlet pipes used, in particular without the dimensions of the muffler housing having to be changed.
The predetermined length of the first pipe portion of the inlet pipe and the predetermined length of the second pipe portion of the outlet pipe can be the same or different. In this way, optimal tuning to the relevant sound frequencies is possible, the sound levels of which are reduced at least via the λ/4 resonators that are formed. In particular, identical or different sound frequencies in the inlet chamber and the outlet chamber can thus be effectively suppressed. In this way, an additional broad-spectrum reduction of the sound pressure level can also be set in a targeted manner.
According to the disclosure, the design of the muffler housing is not further limited as long as the inlet and outlet chambers can be formed within the muffler housing. For example, the muffler housing is box-shaped or cylindrical.
The exhaust system can be an exhaust system of a vehicle or an exhaust system of a stationary motor. The vehicle can be a land vehicle or a watercraft, for example a motor vehicle or a ship. The stationary motor can be a stationary motor in a power generating device.
The ratio of the porosity in the second pipe portion of the inlet pipe is preferably three to six times the porosity in the second pipe portion of the outlet pipe. In other words, the second pipe portion of the inlet pipe preferably has a significantly higher porosity than is the case for the second pipe portion of the outlet pipe. It has been found that such a porosity ratio provides an even better compromise between the desired reduction of the sound level, on the one hand, and a generally undesirable increase in the backpressure in the exhaust gas stream of the exhaust system, on the other hand.
The porosity of the second pipe portions is defined here as the ratio of the sum of the area of all openings in the circumferential surface of the particular pipe portion to the total surface of the circumferential surface of the particular pipe portion. Accordingly, an opening of an axial end of the inlet or outlet pipe possibly adjacent to the second pipe portion remains disregarded when calculating the porosity.
The ratio of the length of the second pipe portion of the inlet pipe to the length of the second pipe portion of the outlet pipe is preferably in the range from 1 to 2. In this way, the λ/4 resonator which is formed in the output chamber is tuned to an acoustic frequency which is equal to or higher than the sound frequency to which the λ/4 resonator implemented in the inlet chamber is tuned.
In order to achieve a particularly outstanding compromise between reduction of the sound level and the backpressure occurring in the exhaust gas stream, the ratio of the porosity in the second pipe portion of the inlet pipe is particularly preferably three to six times the porosity in the second pipe portion of the outlet pipe, and the ratio of the length of the second pipe portion of the inlet pipe to the length of the second pipe portion of the outlet pipe is in the range from 1 to 2.
In one embodiment, the inlet pipe and/or the outlet pipe have an axial end associated, respectively, with the inlet chamber and the outlet chamber, which end is at least partially sealed. In this way, the achievable noise reduction is further increased.
The more the axial end of the respective pipe is sealed, the greater the influence of the corresponding porous second pipe portion on the flow behavior of the exhaust gas stream through the muffler.
The axial end of the inlet pipe and/or of the outlet pipe can be completely sealed off. In this variant, the exhaust gas flows from the inlet pipe or into the outlet pipe only over or through the respective second pipe portion.
For example, the inlet pipe and/or the outlet pipe can extend into the inlet chamber or, respectively, the outlet chamber in such a way that each axial end of the inlet pipe or of the outlet pipe is sealed off by the inner wall.
An exhaust gas aftertreatment element for treating at least one pollutant contained in the exhaust gas stream can be arranged between the inlet chamber and the outlet chamber. In this way, the muffler according to the disclosure is a combined muffler/exhaust gas aftertreatment device so that in particular a separate exhaust gas aftertreatment device can be dispensed with. This simplifies the design of the exhaust system and minimizes its installation space requirement. The flexible design of the inlet and outlet pipe makes it possible, in particular, to realize such a dual function without the muffler housing having a space requirement which is higher than that of a muffler without an exhaust gas treatment function and/or of an exhaust gas aftertreatment device without a muffler function.
In this embodiment, the inlet pipe can be a mixing pipe for mixing the exhaust gas stream with a treatment chemical. For example, the inlet pipe can be designed to be used as a mixing pipe for injecting a urea solution, which serves in the exhaust gas aftertreatment element for catalytic conversion of nitrogen oxides contained in the exhaust gas stream.
In yet another variant, the inlet chamber and/or the outlet chamber have multiple partial chambers, which are delimited from one another by a partition wall through which the exhaust gas stream can flow.
The partition wall is designed such that the exhaust gas stream can flow through it, for example by the partition wall being porous.
It is also possible for the partition wall to be porous only in one sub-portion which is associated with the second pipe portion of the inlet pipe or of the outlet pipe. In this way, a λ/4 resonator can also be formed between the partition wall and the first pipe portion of the inlet pipe or the outlet pipe.
The partition can additionally or alternatively have one or more connecting pipes which fluidically connect the partial chambers to one another.
Overall, the use of one or more partition walls, can adapt the acoustic behavior in the inlet chamber and/or the outlet chamber in a targeted manner in order to achieve an optimal reduction of the sound level.
In order to prevent the additional generation of high-frequency components of the noise spectrum, the axial end of the outlet pipe associated with the outlet chamber can be tulip-shaped.
“High-frequency” is understood here to mean, in particular, sound frequencies which correspond in the upper third of the entire frequency distribution of the noise spectrum.
In particular, the term “high-frequency” denotes a frequency of more than 500 Hz. Such frequencies are caused, for example, by flow noises which are to be avoided or at least reduced.
Furthermore, at least one inner wall of the muffler housing can be lined at least partially with a sound-absorbing material in order to further improve the achievable noise reduction, in particular with regard to high-frequency components of the noise spectrum. Sound-absorbing materials are known from the prior art. For example, the sound-absorbing material can comprise or be mineral wool.
In particular, an inner wall of the muffler housing associated with the outlet chamber is at least partially lined with the sound-absorbing material, preferably that inner wall which is arranged furthest downstream in the exhaust gas flow.
The sound-absorbing material can be fastened via a perforated holding element, in particular via a micro-perforated holding element.
Further features and properties of the disclosure result from the following description of exemplary embodiments, which are not to be understood in a limiting sense, and from the drawings. In the figures:
The muffler 10 can also be used in principle for other devices. For example, the muffler 10 can be a component of an exhaust system of a stationary motor (not shown), for example a stationary motor of a power generating device.
The muffler 10 has a gas-tight muffler housing 12 which is formed by a jacket 14 comprising an upper side 16 and an underside 18 and a first end floor 20, e.g. first end cap, and a second end floor 22, e.g. second end cap.
The muffler housing 12 shown in
In the interior of the muffler housing 12, said housing has an inlet chamber 24 and an outlet chamber 26, which are in fluid communication with one another, i.e., are fluidically connected. Both the inlet chamber 24 and the outlet chamber 26 comprise multiple partial chambers 28 and 30 or 32 and 34, which are each delimited from one another by a partition wall 36.
The inlet chamber 24 has an associated inlet pipe 38 which is configured to conduct the exhaust gas stream of the exhaust system into the interior of the muffler housing 12, as indicated by the arrow P1
Analogously thereto, the outlet chamber 26 has an associated outlet pipe 40 which is configured to divert the exhaust gas flow from the interior of the muffler housing 12, as indicated by the arrow P2 in
The inlet pipe 38 comprises a first pipe portion 42 and a second pipe portion 44 along its axial extension direction, wherein the first pipe portion 42 extends from an inner wall 46 associated with the upper side 16 of the muffler housing 12 up to the second pipe portion 44. The second pipe portion 44 in turn runs from the connection point at the first pipe portion 42 up to an axial end 48 of the inlet pipe 38.
The first pipe portion 42 of the inlet pipe 38 has a length L1 in the axial direction of the inlet pipe 38 and the second pipe portion 44 of the inlet pipe 38 has a length I1 in the axial direction of the inlet pipe 38. The total length of the inlet pipe 38 thus results from the sum of the lengths L1 and I1.
Thus, the total length means only that length of the inlet pipe 38 with which the inlet pipe 38 extends into the muffler housing 12. It goes without saying that the inlet pipe 38 can additionally extend further from the muffler housing 12 to the outside.
In the first pipe portion 42, the inlet pipe 38 is designed to be solid, i.e., impermeable to the exhaust gas stream. In contrast, in the second pipe portion 44, the inlet pipe 38 has a plurality of openings 50 on the circumference side, so that the inlet pipe 38 is porous on the circumference. The porosity of the second pipe portion 44 is also designated as porosity x1 and is determined via the ratio of the sum of the area of all openings 50 in the circumferential surface of the second pipe portion 44 to the total surface of the circumferential surface of the second pipe portion 44.
Accordingly, in the embodiment shown, the exhaust gas stream can flow from the inlet pipe 38 into the inlet chamber 24, namely into the partial chamber 28, via the axial end 48 and via the openings 50.
A λ/4 resonator 54 is formed between the inner wall 46, an inner wall 52 associated with the first end floor 20, and the first pipe portion 42, wherein the frequency at which the λ/4 resonator 54 has a damping maximum is defined by the length L1.
Accordingly, by selecting the inlet pipe 38 used, the damping behavior of the muffler 10 can be adapted in a targeted manner.
Similarly to the inlet pipe 38, the outlet pipe 40 comprises a first pipe portion 56 and a second pipe portion 58 along its axial extension direction, wherein the first pipe portion 56 extends from an inner wall 60 associated with the underside 18 of the muffler housing 12 up to the second pipe portion 58. The second pipe portion 58 in turn runs from the connection point for the first pipe portion 56 up to an axial end 62 of the outlet pipe 40.
The first pipe portion 56 of the outlet pipe 40 has a length L2 in the axial direction of the outlet pipe 40, and the second pipe portion 58 of the outlet pipe 40 has a length l2 in the axial direction of the outlet pipe 40. The total length of the outlet pipe 40 thus results from the sum of the lengths L2 and l2.
Thus, the total length of the outlet pipe 40 means only that length of the outlet pipe 40 with which the outlet pipe 40 extends into the muffler housing 12. It goes without saying that the outlet pipe 40, analogously to the inlet pipe 38, can additionally extend from the muffler housing 12 further to the outside.
In the first pipe portion 56, the outlet pipe 40 is solid, i.e., impermeable to the exhaust gas stream. By contrast, in the second pipe portion 58, the outlet pipe 40 has a plurality of openings 64 on the circumferential side, so that the outlet pipe 40 is porous on the circumferential side. The porosity of the second pipe portion 58 is also referred to as porosity x2 and is determined via the ratio of the sum of the surface of all openings 64 in the circumferential surface of the second pipe portion 58 to the total surface of the circumferential surface of the second pipe portion 58.
Accordingly, in the embodiment shown, the exhaust gas stream can flow into the outlet pipe 40 both via the axial end 62 and via the openings 64 from the outlet chamber 26, namely the partial chamber 32.
A λ/4 resonator 68 is formed between the inner wall 60, an inner wall 66 associated with the second end floor 22, and the first pipe portion 56, wherein the frequency at which the λ/4 resonator 68 has a damping maximum is defined by the length L2.
The lengths L1 and L2 can be the same or different. Preferably, the ratio L1/L2 is in a range from 1 to 2.
The porosity x1 is preferably three to six times the porosity x2. That is to say, the inlet pipe 38 preferably has a higher porosity than the outlet pipe 40, as shown schematically in
The tuning of the lengths L1 and L2 to particularly relevant sound frequencies in the inlet chamber 24 or the outlet chamber 26, the use of an inlet pipe 38 and outlet pipe 40 which are porous only over a partial region, and the selected ratio of the porosities x1 and x2 provide an ideal compromise between the achieved noise dampening effect and the backpressure generated in the exhaust gas stream.
In addition, the resonance behavior of sound waves in the inlet chamber 24 and the outlet chamber 26 can be influenced via the positioning of the partition walls 36 along the upper side 14 and underside 16 and via their porosity.
The partition walls 36 also have connecting pipes 70 which fluidically connect each of the partial chambers 28 and 30 or 34 and 32 to one another. The flow and damping behavior of the muffler 10 can further be adapted to the intended application scenario via the positioning of the connecting pipes 70 relative to the inlet pipe 38 or to the outlet pipe 40 and via the length of the connecting pipes 70.
In the embodiment shown in
The type of exhaust gas aftertreatment element 72 is not further limited and is only to be tuned to the intended place of use and the expected composition of the exhaust gas stream. For example, the exhaust gas aftertreatment element 72 is or comprises an active or passive SCR (selective catalytic reduction) catalytic converter, a filter element, and/or an oxidation catalytic converter.
A sound-absorbing material 74, which in particular serves to damp high-frequency components of the noise spectrum, is also attached to the inner wall 66 of the outlet chamber 26 associated with the end floor 22. The sound-absorbing material 74 is fixed to the inner wall 66 by a perforated retaining element 76, in particular by a micro-perforated retaining element 76.
It is also conceivable that the (micro-)perforated retaining element 76 is used without the sound-absorbing material 74 being present. In this case, the acoustic damping is accomplished by friction in the (micro-)perforation and by the volume situated between the respective inner wall and the holding element 76, which volume is selected via the distance between the respective inner wall and the holding element 76.
The second embodiment substantially corresponds to the first embodiment so that only differences will be discussed below. Identical reference signs designate identical or functionally identical components, and reference can be made to the explanations provided above.
In the second embodiment, the inlet pipe 38 runs completely through the muffler housing 12, so that the inlet pipe 38 extends from the inner wall 46 associated with the upper side 16 up to the inner wall 60 associated with the underside 18.
The axial end 48 is thus completely sealed off by the inner wall 60, so that an exhaust gas stream flowing through the inlet pipe 38 can only pass into the inlet chamber 24 through the openings 50 in the second pipe portion 44 of the inlet pipe 38.
In addition, in the second embodiment the inlet pipe 38 is designed as a mixing pipe. This means that at least one treatment chemical 78 which mixes with the exhaust gas stream is supplied to the exhaust gas stream and is transported together with the exhaust gas stream into the inlet chamber 24 and from there to the exhaust gas aftertreatment element 72. The treatment chemical 78 is, for example, a urea solution which is converted with nitrogen oxides contained in the exhaust gas stream in the exhaust gas aftertreatment element 72.
Furthermore, in the second embodiment, the partition walls 36 have a first sub-region 80 and a second sub-region 82, wherein the partition wall 36 is gas-impermeable in the first sub-region 80 and is porous in the second sub-region 82 and thus the exhaust gas stream can flow through it.
A further λ/4 resonator 84 is formed between the first pipe portion 42, the inner wall 46, and the first subregion 80 of the partition wall 36 arranged in the inlet chamber 24, the resonant frequency of such resonator, analogously to the λ/4 resonator 54, depending on the length L1 of the first pipe portion 42.
Analogously, a further λ/4 resonator 84 is formed between the first pipe portion 56, the inner wall 60, and the first subregion 80 of the partition wall 36 arranged in the outlet chamber 26.
It goes without saying that in all embodiments the partition walls 36 of the inlet chamber 24 and the outlet chamber 26 can also be designed differently.
In the second embodiment, the outlet pipe 40 has a tulip-shaped axial end 62 in order to even better prevent additional flow noises.
In the second embodiment, the sound-absorbing material 74 is likewise attached to the inner wall 66. However, the sound-absorbing material 74 does not completely cover the inner wall 66 as in the first embodiment, but only partially and exclusively in the region of the inner wall 66 which is at the height of the second partial region 82 of the partition wall 36 associated with the outlet chamber 26.
The third embodiment substantially corresponds to the first and second embodiments, so that only differences will be discussed below. Identical reference signs designate identical or functionally identical components, and reference can be made to the explanations provided above.
In the third embodiment, the inlet pipe 38 is not routed through the upper side 16 but through the first end floor 20 into the inlet chamber 24 and extends parallel to the upper side 16 and to the underside 18, i.e., in the direction of the outlet chamber 26.
Likewise, the outlet pipe 40 is not routed through the underside 18, but through the second end floor 22 out of the outlet chamber 26 and extends parallel to the upper side 16 and to the underside 18.
It is clear that a combination of the orientations of inlet pipe 38 and outlet pipe 40 according to the designs shown in the first to third embodiments is also possible.
The orientations of the inlet pipe 38 and the outlet pipe 40, which are changed compared to the first and second embodiment, also change the point at which the λ/4 resonators are formed. Specifically, in the third embodiment, the λ/4 resonators 54 and 68 are formed between the inner walls 46, 52 and 60 and the first pipe portion 42 of the inlet pipe 38 or between the inner walls 46, 66 and 60 and the first pipe portion 56 of the outlet pipe 40.
In the third embodiment, the sound-absorbing material 74 is additionally attached to the inner walls 46 or 60 associated with the upper side 16 and the underside 18.
Furthermore, the outlet pipe 40 has at its axial end 62 a gas-impermeable cap element 86 which completely closes the axial end 62. The exhaust gas stream from the outlet chamber 26 can thus only pass through the openings 64 in the second pipe portion 58 into the outlet pipe 40. Of course, the inlet pipe 38 can also have such a cap element 86.
It is clear that the features and embodiments described only in connection with one of the embodiments can also be used in further embodiments, as long as this does not contradict the basic mode of operation of the muffler 10 according to the disclosure.
Overall, the muffler 10 is characterized by the possibility of being able to be optimally tuned to the relevant frequency ranges in the noise spectrum without adaptations relating to the required installation space becoming necessary. In addition, an optimal compromise between the damping effect and the backpressure that occurs can be found.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 131 738.2 | Nov 2022 | DE | national |
