Muffler for an exhaust system of an internal combustion engine

Abstract

A muffler for an exhaust system of an internal combustion engine includes a housing, a through pipe that conducts exhaust gas during operation of the muffler and is guided through the housing, and a branch pipe fluidically branching off from the through pipe within the housing. The branch pipe has an upstream end at the through pipe and ends freely and open at an end face with a downstream end within the housing. The branch pipe has a length from the upstream to the downstream end or up to a lateral recess which has a cross-sectional area which is greater than half a pipe cross-section of the branch pipe. The branch pipe has downstream perforations in a section from ⅜ of the length as measured from the upstream end A total area of the downstream perforations is smaller than half the pipe cross-section of the branch pipe, and no perforations or upstream perforations have a total area of at most 10% of the pipe cross-section of the branch pipe being present in a section before ⅜ of the length.

Claims

1. A muffler for an exhaust system of an internal combustion engine, for a motor vehicle comprising: a housing; a through pipe which conducts exhaust gas during operation of the muffler and which is guided through the housing; and a branch pipe fluidically branching off from the through pipe within the housing, the branch pipe beginning with an upstream end at the through pipe and ending freely and open at an end face with a downstream end within the housing, the branch pipe having a length from the upstream to the downstream end and having downstream perforations in a section from ⅜ of the length as measured from the upstream end, a total area of the downstream perforations being smaller than half a pipe cross-section of the branch pipe, and no perforations or upstream perforations having a total area of at most 10% of the pipe cross-section of the branch pipe being present in a section before ⅜ of the length.

2. A muffler for an exhaust system of an internal combustion engine for a motor vehicle comprising: a housing; a through pipe which conducts exhaust gas during operation of the muffler and which is guided through the housing; and a branch pipe fluidically branching off from the through pipe within the housing, the branch pipe beginning with an upstream end at the through pipe and ending freely and open at an end face with a downstream end within the housing and having a lateral recess with a cross-sectional area which is greater than half a pipe cross-section of the branch pipe, the branch pipe having a length from the upstream end to the lateral recess, and having downstream perforations in a section from ⅜ of the length as measured from the upstream end, a total area of the downstream perforations being smaller than half the pipe cross-section of the branch pipe, and no perforations or upstream perforations having a total area of at most 10% of the pipe cross-section of the branch pipe being present in a section before ⅜ of the length.

3. The muffler according to claim 1, wherein at least part of the downstream perforations is arranged circumferentially in a ring shape on the branch pipe.

4. The muffler according to claim 1, wherein at least part of the downstream perforations is arranged in a row along a longitudinal extension of the branch pipe.

5. The muffler according to claim 1, wherein the downstream perforations each have a cross-sectional area between 3 mm2 and 13 mm2.

6. The muffler according to claim 1, wherein the total number of the downstream perforations is between four and forty.

7. The muffler according to claim 1, wherein the pipe cross-section of the branch pipe is substantially constant.

8. The muffler according to claim 1, wherein the branch pipe extends substantially parallel to the through pipe at least in the region of the downstream end.

9. The muffler according to claim 1, wherein the housing is at least partially filled with an absorption material, and wherein the absorption material is adjacent to the downstream perforations.

10. The muffler according to claim 1, wherein the housing has at least one partition wall which divides the housing in partial chambers, and in that the branch pipe is mounted on the at least one partition wall.

11. The muffler according to claim 1, wherein the muffler has a Helmholtz resonator or a bypass muffler.

12. The muffler according to claim 1, wherein the branch pipe has a section curved in an arcuate manner which merges into a linear section extending up to the downstream end, the downstream perforations being present exclusively in the linear section.

13. The muffler according to claim 12, wherein the curved section is curved by at least 90°.

14. The muffler according to claim 2, wherein at least part of the downstream perforations is arranged circumferentially in a ring shape on the branch pipe.

15. The muffler according to claim 2, wherein at least part of the downstream perforations is arranged in a row along a longitudinal extension of the branch pipe.

16. The muffler according to claim 2, wherein the pipe cross-section of the branch pipe is substantially constant.

17. The muffler according to claim 2, wherein the housing is at least partially filled with an absorption material, and wherein the absorption material is adjacent to the downstream perforations.

18. The muffler according to claim 2, wherein the housing has at least one partition wall which divides the housing in partial chambers, and in that the branch pipe is mounted on the at least one partition wall.

19. The muffler according to claim 2, wherein the muffler has a Helmholtz resonator or a bypass muffler.

20. The muffler according to claim 2, wherein the branch pipe has a section curved in an arcuate manner which merges into a linear section extending up to the downstream end, the downstream perforations being present exclusively in the linear section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the present invention will become apparent from the description below and from the drawings below to which reference is made and which show:

(2) FIG. 1a schematically illustrates a longitudinal section through an exemplary muffler,

(3) FIG. 1b is a diagram for illustrating the possible sound absorption using the muffler of FIG. 1a,

(4) FIGS. 2a to 8a each schematically illustrate a longitudinal section through a muffler according to the invention,

(5) FIGS. 2b to 8b are each a diagram for illustrating the sound absorption using the respective muffler according to the invention,

(6) FIGS. 9, 10 and 11 each schematically illustrate a longitudinal section through a further embodiment of a muffler according to the invention, and

(7) FIG. 12 schematically illustrates a longitudinal section through a muffler according to the invention in an alternative embodiment according to the invention.

DETAILED DESCRIPTION

(8) FIG. 1a schematically shows a longitudinal section of an exemplary muffler 10. The basic structure and the operating principle of a muffler 10 is to be explained on the basis of FIG. 1a.

(9) The muffler 10 is suitable for an exhaust system of an internal combustion engine, in particular for a motor vehicle. The muffler 10 includes a housing 12 having a through pipe 14 which conducts exhaust gas during operation of the muffler 10 and which is guided through the housing 12, the exhaust gas flowing through the through pipe 14 in the direction of the arrow.

(10) A branch pipe 16 fluidically branches off within the housing 12. The branch pipe 16 begins at the through pipe 14 with its upstream end and ends freely and open at the end face with a downstream end within the housing. A length L of the branch pipe 16 is measured from the upstream end to the downstream end at a center line of the branch pipe 16. This is illustrated in FIG. 1 by a dashed line L.

(11) The branch pipe 16 runs substantially parallel to the through pipe 14 at least in the region of its downstream end. In particular, the branch pipe 16 has a section 17 curved in an arcuate manner which merges into a linear section 19 extending up to the downstream end. In the example embodiments shown, the curved section 17 is curved by 90°, but the curved section 17 can also be more or less curved, for example by 110°.

(12) If the curvature of the curved section 17 essentially deviates from 90°, the branch pipe 16 extends inclined to the through pipe 14 at least in the region of its downstream end.

(13) The pipe cross-section of the branch pipe 16 is substantially constant over the length L of the branch pipe 16.

(14) The housing 12, for example, has a length of 400 mm and a volume of 5 liters. The through pipe 14, for example, has a diameter of 152 mm. The branch pipe 16, for example, has a length of 330 mm and a diameter of 35 mm. However, these values are only exemplary and can be varied as needed.

(15) The muffler 10 includes a Helmholtz resonator. However, a valve can additionally be arranged in the through pipe 14, which can selectively close or open a flow path through the through pipe 14. In addition, a second outlet pipe can permit the escape of the exhaust gases out of the muffler when the valve is closed. This is referred to as a bypass muffler. If the valve of the bypass muffler is open to a maximum extent, the flow situation is the same as in a Helmholtz resonator. For the sake of simplicity, the sound situation in connection with a Helmholtz resonator is described below, the sound situation in a bypass muffler being however also meant here.

(16) FIG. 1b shows a diagram for illustrating the possible sound absorption using the muffler 10 of FIG. 1a, a transmission loss in dB being plotted against the frequency in Hz.

(17) A Helmholtz resonance f.sub.HH occurs in the range between 0 and 100 Hz. This resonance is advantageous in terms of sound absorption and should be as high as possible. Helmholtz resonance f.sub.HH is calculated according to the following formula:

(18) $f_{\mathrm{HH}}=\frac{c}{2\pi }*\sqrt{\frac{A}{\mathrm{LV}}}$

(19) c standing for the speed of sound, A for the cross-section of the branch pipe 16, L for the length of the branch pipe 16 and V for the volume of the housing 12.

(20) Pipe resonances Fp1, Fp2 and Fp3 as well as housing resonances Fc1, Fc2 and Fc3 occur in addition to the Helmholtz resonance f.sub.HH. The pipe resonances Fp1, Fp2, Fp3 and the housing resonances Fc1, Fc2, Fc3 cause interfering noises, in particular whistling noises, the pipe resonances being particularly disadvantageous with regard to noise development.

(21) It is therefore an object of the invention to provide a muffler in which the disturbing resonances are damped, while the Helmholtz resonance f.sub.HH should remain as unaffected as possible.

(22) For identical structures having identical functions which are known from the above embodiment, the same reference numbers are used in the following, and reference is made in this respect to the previous explanations, wherein the differences of the respective embodiments are discussed in the following to avoid repetitions.

(23) FIG. 2a schematically shows a longitudinal section through a first muffler 10 according to the invention. This muffler 10 differs from the muffler 10 in FIG. 1a in that the branch pipe has 16 perforations 18. Ten perforations 18 are, for example, provided. The number of perforations 18 drawn in the figures is for illustrative purposes only and does not necessarily correspond to the actual number of perforations 18.

(24) The perforations 18 are arranged at a position of ⅜L and circumferentially in a ring shape on the branch pipe 16, more specifically as measured from the upstream end of the branch pipe 16, and are called downstream perforations.

(25) The individual downstream perforations 18, for example, have a cross-sectional area between 3 mm.sup.2 and 13 mm.sup.2, particularly preferably of 9.6 mm.sup.2. In particular, the cross-sectional area of the individual perforations 18 is small in comparison with a cross-sectional area of the branch pipe 18. The perforations 18 may be circular, slit-shaped, elliptical, rectangular or otherwise shaped. The perforations 18 are, for example, circular with a diameter of 3.5 mm.

(26) As can be seen from the corresponding diagram in FIG. 2a, especially the pipe length resonance Fp1 is damped by such an arrangement of perforations 18. This can be explained by the fact that at position ⅜L, an increased pressure pulsation of a first vibrational mode occurs. The housing resonance at Fc1 is almost completely damped.

(27) The damping of the resonances Fp1 and Fc1 results in significantly less disturbing noise occurring during operation of the muffler 10.

(28) The Helmholtz resonance f.sub.HH is slightly damped, but is still within the acceptable range. The further pipe length resonances Fp2, Fp3 and the housing resonances Fc2, Fc3 are only slightly affected. The housing resonance Fc3, however, is very low anyway.

(29) The initial values from the diagram according to FIG. 1b are plotted in FIG. 2b with a dashed line for better illustration. The optimized results obtained with a muffler 10 according to the invention as shown in FIG. 2a are marked with a solid line. In addition, the damping of the different resonances is illustrated by arrows. This also applies to the following FIGS. 3b to 8b.

(30) If a change or damping of the resonances is mentioned below, this always refers to a change or damping with respect to the initial values according to FIG. 1b, unless otherwise described.

(31) FIG. 3a schematically shows a longitudinal section through a further muffler 10 according to the invention. The muffler 10 according to FIG. 3a differs from the muffler 10 according to FIG. 2a in the position of the perforations 18. In particular, ten perforations are arranged at L/2, i.e. in the middle of the branch pipe 16.

(32) As can be seen from FIG. 3b, a very good damping of the pipe length resonance Fp1 is also achieved in this embodiment, while the Helmholtz resonance F.sub.HH is hardly influenced. Furthermore, a significant damping of the pipe length resonance Fp3 is achieved. The housing resonance Fc1 is also well damped.

(33) FIG. 4a schematically shows a longitudinal section through a further muffler 10 according to the invention. The muffler 10 according to FIG. 4a differs from the muffler 10 according to FIG. 2a in the position of the downstream perforations 18. In particular ten perforations are arranged at ⅝L.

(34) As shown in FIG. 4b, a very good damping of the pipe length resonance Fp1 is also achieved in this embodiment, while the Helmholtz resonance F.sub.HH is hardly influenced. The pipe length resonance Fp3 and the housing resonance Fc1 are damped less than in the embodiment according to FIG. 3, they are however still well damped.

(35) FIG. 5a schematically shows a longitudinal section through a further muffler 10 according to the invention. The muffler 10 according to FIG. 5a differs from the muffler 10 according to FIG. 2a also in the position of the downstream perforations 18. In particular ten perforations are arranged at 6/8L.

(36) The diagram shown in FIG. 5b shows that the damping of the pipe length resonance Fp1 is somewhat worse than in the previous embodiments according to FIGS. 2a to 4a. However, the pipe length resonance Fp2, which remained almost unchanged in the previous embodiments compared to the initial situation, is significantly better damped. The Helmholtz resonance F.sub.HH is hardly influenced.

(37) FIG. 6a schematically shows a longitudinal section through a further muffler 10 according to the invention. The muffler 10 according to this embodiment has two subgroups 20a and 20b of perforations 18. A first subgroup 20a of perforations 18 is arranged at L/2, and a further subgroup 18b of perforations 18 is arranged at 6/8L. The subgroups 20a, 20b each include ten perforations 18. The embodiment according to FIG. 6a is thus so to speak a combination of the embodiments according to FIGS. 3a and 5a. The position of subgroups 20a, 20b to each other can be varied as required.

(38) The corresponding diagram of FIG. 6a shows that a very good damping of the resonances Fp1 and Fc1 is achieved in this embodiment. In addition, the pipe length resonances Fp2 and Fp3 are also significantly damped. The Helmholtz resonance F.sub.HH is hardly influenced.

(39) In a further modification of the embodiment shown in FIG. 6a, more than two subgroups 20a, 20b may be provided, which may be arranged at equal distances or at distances of different size to each other. The subgroups may also have a different number of downstream perforations. A subgroup can, for example, have twenty perforations and another subgroup ten perforations.

(40) FIG. 7a schematically shows a longitudinal section through a further muffler 10 according to the invention. In this embodiment, the perforations 18 are not each arranged circumferentially in a ring shape as in the previous embodiments, but are arranged in a row along the longitudinal direction of the branch pipe 16, twenty perforations 18 being for example present.

(41) The downstream perforations 18 are arranged in a region between L/2 and ⅞L.

(42) The diagram in FIG. 7b shows that in this embodiment, all pipe length resonances Fp1, Fp2 and Fp3 and also the housing resonances Fc1 and Fc2 are well damped. The Helmholtz resonance F.sub.HH is hardly influenced.

(43) FIG. 8a schematically shows a longitudinal section through a further muffler 10 according to the invention. The embodiment according to FIG. 8a is similar to the embodiment according to FIG. 7a, but an additional row of perforations 18 is provided.

(44) In particular, the perforations 18 extend in two rows along the longitudinal direction of the branch pipe 16, the rows being arranged side by side in the circumferential direction.

(45) Each row has, for example, twenty downstream perforations 18, so that a total of forty perforations of 18 is provided.

(46) It results from the diagram shown in FIG. 8b that the pipe length resonances Fp1, Fp2 and Fp3 in a muffler 10 according to FIG. 8a, taken as a whole, are very well damped.

(47) In a further embodiment that is not represented, a muffler 10 may have at least one subgroup of downstream perforations 18 extending in a row along the branch pipe 16, as shown in FIGS. 7a and 8a, and additionally at least one subgroup of downstream perforations 18 arranged circumferentially in a ring shape on the branch pipe 16, as shown in FIGS. 2a to 6a.

(48) FIG. 9 shows a further embodiment according to the invention of a muffler 10 having two subgroups 20a, 20b of perforations 18. The perforations 18 of a subgroup 20a, 20b are each arranged in the form of a matrix, the downstream perforations 18 of a subgroup 20a, 20b forming in particular a rectangle.

(49) In order to achieve an even stronger damping of the various resonances, the housing 12 can be at least partially filled with an absorption material 22, in particular with the absorption material 22 adjoining the perforations 18. This is illustrated in FIG. 10.

(50) Furthermore, as shown in FIG. 11, the housing 12 may have at least one partition wall 24 dividing the housing 12 into partial chambers 26a, 26b, the branch pipe 16 being mounted on the partition wall 24.

(51) All embodiments according to the invention of the muffler 10 have in common that a total area of the downstream perforations 18 is smaller than half the largest pipe cross-section of the branch pipe 16, the latter being measured in a radial plane to the center line of the branch pipe 16.

(52) In addition, in all embodiments according to the invention of the muffler 10, the downstream perforations 18 are arranged in a section starting from ⅜L as measured from the upstream end of the branch pipe 16, in particular in the linear section 19 of the branch pipe 16. The number of the downstream perforations 18 is preferably between four and forty.

(53) It is also conceivable that a few further perforations are arranged in a section before, i.e. upstream of ⅜L (see FIG. 11). These perforations are called upstream perforations 40 and can be present in all embodiments. However, the total area of these additional upstream perforations shall be so small that it has no appreciable effect on the acoustic behavior of the muffler 10. Therefore, the total area of the upstream perforations in the section before ⅜L must be less than 10% of the pipe cross-section of the branch pipe 16, preferably less than 5% of the pipe cross-section of the branch pipe 16. The total area of the perforations in the section before ⅜L is, for example, less than 50 mm.sup.2.

(54) FIG. 12 schematically shows a longitudinal section through an alternative muffler 10 according to the invention. The muffler 10 according to FIG. 12 differs from the mufflers 10 according to FIGS. 2 to 11 in the presence of a large lateral recess 28. The recess 28 has a cross-sectional area which is greater than half the pipe cross-section of the branch pipe 16, in particular greater than 75% of the pipe cross-section of the branch pipe 16. The lateral recess 28 thus forms a main outlet opening of the branch pipe 16 opening into the housing 12.

(55) In this case, instead of the length L up to the downstream end of the branch pipe 16, the length L.sub.1 up to the lateral recess 28 is measured along the pipe center line to determine a position of the perforations 18. This is illustrated by the dashed line in FIG. 12.

(56) The perforations 18 can in particular be arranged in a section from ⅜L.sub.1. In the embodiment shown, the perforations are arranged as an example at L.sub.1/2, i.e. from this distance from the upstream end of the branch pipe 16.

(57) The arrangement and number of downstream perforations 18 described in connection with FIGS. 2 to 9 can be transferred to the embodiment according to the invention of FIG. 12, wherein only the length L.sub.1 has to be taken into account instead of the length L. However, for the sake of simplicity, these embodiments are not presented and described individually.

(58) Furthermore, analogously to FIG. 10, the housing 12 of the muffler according to FIG. 12 may also be at least partially filled with an absorption material 22, in particular the absorption material 22 adjoining the perforations 18.

(59) In addition, analogously to FIG. 11, the housing 12 may have at least one partition wall 24 which divides the housing 12 into partial chambers 26a, 26b, the branch pipe 16 being mounted on the partition wall 24.

(60) Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.