RELATED APPLICATION

[0001] This application claims priority to United States Provisional Application No. 61/303,408, which was filed February 11, 2010.

TECHNICAL FIELD

[0002] This invention generally relates to a plastic muffler that includes a Helmholtz chamber.

BACKGROUND OF THE INVENTION

[0003] Conventional plastic mufflers include an outer plastic shell with a metal pipe located within an internal cavity to extend from an inlet to an outlet. These conventional plastic mufflers include packing material that completely fills the internal cavity formed between the metal pipe and the outer plastic shell to provide a fully packed configuration. Packing the internal cavity reduces heat transfer from the internal metal pipe to the outer plastic shell.

[0004] While this fully packed configuration provides broadband noise attenuation, it is often desirable to attenuate a specific frequency and/or a limited range of frequencies. Incorporating structure to provide specific noise attenuation characteristics has proved challenging in plastic mufflers.

SUMMARY OF THE INVENTION

[0005] A muffler for a vehicle exhaust system includes a plastic outer shell defining an internal cavity with an inlet and an outlet. An inner metal pipe extends from the inlet to the outlet. A Helmholtz chamber is located within the plastic outer shell for noise attenuation purposes.

[0006] In one example, the muffler includes a Helmholtz neck that is associated with one of the inner metal pipe or the plastic outer shell.

[0007] In on example, the muffler is not fully packed such that at least a portion of the internal cavity is free from packing material. [0008] In one example, the muffler includes a shielding cartridge. The shielding cartridge comprises at least a metal outer pipe that surrounds a portion of an axial length of the metal inner pipe within the internal cavity, and includes packing material positioned within a gap formed between the inner and outer metal pipes.

[0009] In one example, a thermally insulating end plate is mounted between the metal inner pipe and the plastic outer shell at each of the inlet and outlet to thermally decouple the metal inner pipe from the plastic outer shell.

[0010] In one example, a baffle is used to separate the internal cavity into first and second chambers. One of the first and second chambers forms the Helmholtz chamber and the other of the first and second chambers forms an expansion chamber.

[0011] These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic view of one example of a plastic muffler with a Helmholtz chamber.

[0013] Figure 2 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0014] Figure 3 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0015] Figure 4 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0016] Figure 5 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0017] Figure 6 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0018] Figure 7 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0019] Figure 8 is a schematic view of another example of a plastic muffler with a Helmholtz chamber. [0020] Figure 9 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0021] Figure 10 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0022] Figure 11 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0023] Figure 12A is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0024] Figure 12B is a cross-section taken of inner and outer metal pipes as shown at 12B-12B of Figure 12A.

[0025] Figure 12C is a perspective view of the inner and outer metal pipes from Figure 12A.

[0026] Figure 13 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0027] Figure 14 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

[0028] Figure 15 is a schematic view of another example of a plastic muffler with a Helmholtz chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] A muffler for a vehicle exhaust system is shown generally at 10 in Figure 1. The muffler 10 includes a plastic outer shell 12 that defines an internal cavity 14, and which extends from an inlet 16 to an outlet 18. A metal inner pipe 20 is positioned within the internal cavity 14 and extends along a central axis A from the inlet 16 to the outlet 18. The metal inner pipe 20 directs heated exhaust gases through the muffler 10 from an upstream engine to a downstream exhaust component. Thermally insulating end plates 22 extend between the metal inner pipe 20 and the plastic outer shell 12 at each of the inlet 16 and outlet 18. The plates 22 serve to thermally decouple the metal inner pipe 20 from the plastic outer shell 12.

[0030] The muffler 10 includes a Helmholtz resonator defining a Helmholtz chamber 24 that is used to attenuate a desired frequency and/or limited range of frequencies during operating of the vehicle exhaust system. The Helmholtz chamber 24 can be provided in various manners within the plastic outer shell 12. In general, Helmholtz resonators include a chamber defining a main volume that is in fluid communication with a reduced volume portion or neck. The volume within the neck comprises an acoustic mass that rests on an acoustic spring formed by the main volume. Together they provide an oscillating system that can be used to absorb a desired frequency. Figures 1-15 show different examples of how the Helmholtz chamber 24 is incorporated within the plastic outer shell 12.

[0031] Figure 1 shows a configuration that includes a shielding cartridge 30 that is positioned radially between the plastic outer shell 12 and the metal inner pipe 20. The shielding cartridge 30 includes an outer metal pipe 32 that is spaced radially from the metal inner pipe 20 by a gap 34. Packing material 36 fills the gap 34. In the example of Figure 1, the metal outer pipe 32 extends along the entire length of the metal inner pipe 20 within the internal cavity 14 and has ends 38 that are connected to the metal inner pipe 20 outside of the muffler 10. In this type of configuration, the thermally insulating end plates 22 extend from the metal outer pipe 32 to the plastic outer shell 12.

[0032] A baffle 40 is positioned within the internal cavity 14 and supports a Helmholtz neck 42 that extends in a direction that is common with the central axis A. The neck 42 comprises a ring-shaped member that is spaced radially outwardly of the metal outer pipe 32. The baffle 40 extends in a direction transverse to the central axis A from an outer surface of the neck 42 to an inner surface 44 of the plastic shell 12. The baffle 40 and neck 42 cooperate to form first 14a and second 14b chambers within the internal cavity 14. In the example shown, the first chamber 14a comprises an expansion chamber and the second chamber 14b comprises the Helmholtz chamber 24.

[0033] The metal inner pipe 20 includes a perforated portion 20a that extends through both the first 14a and second 14b chambers from the inlet 16 to the outlet 18. The metal outer pipe 32 includes a perforated portion 32a that is located within the first chamber 14a and a non-perforated portion 32b that is positioned to extend from a beginning of the neck 42, through the second chamber 14b, and to the outlet 18.

[0034] The configuration of Figure 2 is similar to that of Figure 1 in that the muffler 10 includes a shielding cartridge 30, but this configuration does not include a baffle with a neck. Instead, the muffler 10 includes an overlap tube 50 that is spaced radially outwardly from the metal outer pipe 32 by an air gap 52. One end 54 of the overlap tube is fixed to the metal outer pipe 32 and the opposite end 56 is spaced from the metal outer tube 32 by the gap 52. The overlap tube 50 only extends along a portion of the overall length of the metal outer tube 32 and forms a Helmholtz neck. The length of the overlap tube 50 can be varied as needed to attenuate a desired frequency. As such, in this configuration, the entire internal cavity comprises the Helmholtz chamber 24.

[0035] In the example of Figure 2, the shielding cartridge 30 extends along the entire length of the metal inner pipe 20 within the internal cavity 14 with the ends 38 being connected to the metal inner pipe 20 outside of the muffler 10. The metal inner pipe 20 includes a perforated portion 20a that extends from the inlet 16 to the outlet 18. The metal outer pipe 32 includes a perforated portion 32a that is spaced axially from the overlap tube 50, i.e. that overlap tube 50 does not overlap the perforated portion 32a. The metal outer pipe includes a non-perforated portion 32b positioned radially inward of the overlap pipe 50. The non-perforated portion 32b includes one or more discrete openings 32c to provide an acoustical connection to the Helmholtz chamber 24.

[0036] The configuration of Figure 3 is similar to that of Figure 1 in that the muffler 10 includes a shielding cartridge 30 and baffle 40, but in this configuration the baffle does not include a Helmholtz neck. In this example, the shielding cartridge 30 does not extend along the entire length of the metal inner tube 20 and instead extends only from the inlet 16, through the first chamber 14b, and to a location just past the baffle 40. Thus, one end 38 of the cartridge 30 is connected to the metal inner pipe 20 outside of the muffler 10 and the opposite end 38 is attached to the metal inner pipe 20 within the second chamber 14b.

[0037] A Helmholtz neck 60 extends radially outwardly from the metal inner pipe 20 within the second chamber 14b. The neck 60 is axially spaced from the shielding cartridge 30. Thus, the second chamber 14b comprises the Helmholtz chamber 24 and the first chamber 14a comprises an expansion chamber. The inner metal pipe 20 includes a perforated portion 20a that is located within the first chamber 14b and a non-perforated portion 20b that extends from the baffle 40, through the second chamber 14b, and to the outlet 18. The metal outer pipe 32 includes a perforated portion 32a that is located within the first chamber 14a and includes non-perforated portions 32b at the inlet 16 and at the baffle 40. A gasket 62 is installed between the baffle 40 and the metal outer pipe 32 to thermally decouple the metal outer pipe 32 from the baffle 40 and associated plastic outer shell 12.

[0038] Figure 4 is similar to Figure 3 but includes packing material 64 in the Helmholtz chamber 24. Filling the Helmholtz chamber 24 with packing material 64 broadens out the response and lowers the peak frequency.

[0039] Figure 5 is similar to Figure 2 but has a shorter shielding cartridge 30 and does not include an overlap tube. In the example of Figure 5, one end 38 of the shielding cartridge 30 is secured to the inner metal pipe 20 within the internal cavity 14 and the other end 38 is secured to the metal inner pipe 20 outside of the muffler 10. This leaves a portion of the inner metal pipe 20 exposed within the internal cavity 14. This portion of the metal inner pipe 20 comprises a non-perforated portion 20b and includes a Helmholtz neck 66 that extends radially outwardly from the metal inner pipe 20 in a direction toward the plastic outer shell 12. The metal inner pipe 20 also includes a perforated portion 20a that is located within the shielding cartridge 30. The metal outer pipe 32 is non-perforated in this example.

[0040] Figure 6 shows a configuration where the shielding cartridge 30 is similar to that of Figure 1 ; however, the metal outer tube 32 includes a perforated portion 32a that extends substantially across the internal cavity 14 from the inlet 16 to the outlet 18. The metal inner pipe 20 also has a perforated portion 20a that extends from the inlet 16 to the outlet 18.

[0041] A baffle 70 positioned within the outer shell 12 extends from one end wall 72 at the inlet 16 to an opposite end wall 74 at the outlet 18. As such, the baffle 70 extends in a direction that is generally parallel to the axis A. The baffle 70 can be formed as one-piece with the plastic outer shell 12.

[0042] The baffle 70 separates the internal cavity into first 14a and second 14b chambers. A Helmholtz neck 76 extends radially outwardly from the baffle 70 toward the central axis A. The length of the neck 76 can be varied as needed to attenuate a specific frequency. The first chamber 14a forms an expansion chamber and the second, side chamber 14b forms the Helmholtz chamber 24.

[0043] Figure 7 is similar to Figure 6 but does not include a shielding cartridge 30. Instead, in this configuration, the metal inner pipe 20 is the only pipe extending between the inlet 16 and the outlet 18. The metal inner pipe 20 includes a perforated portion 20a that extends from the inlet 16 to the outlet 18. Packing material 78 fills the entire first chamber 14a (expansion chamber) and is positioned between the metal inner pipe 20 and the baffle 70 and between the metal inner pipe 20 and the outer shell 12. The second chamber 14b (Helmholtz chamber) remains free of packing material.

[0044] Figure 8 shows a configuration where a metal baffle plate 80 is used to separate the internal cavity into first 14a and second 14b chambers. The baffle plate 80 extends radially outwardly from the metal inner pipe 20 toward the outer shell 12. A thermal seal 82 is positioned between the inner wall 44 of the outer shell 12 and an outermost edge 84 of the baffle plate 80. The metal inner pipe 20 is the only pipe that extends from the inlet 16 to the outlet 18. The metal inner pipe 20 includes a perforated portion 20a that is located within the first chamber 14a and a non-perforated portion 20b that is located within the second chamber 14b. The first chamber 14a forms an expansion chamber and the second chamber 14b forms the Helmholtz chamber 24. A Helmholtz neck 86 extends radially outwardly from the metal inner pipe 20 toward the outer shell 12. Packing material 88 is optionally included within the expansion chamber; however, packing material could also be utilized in the Helmholtz chamber.

[0045] Figure 9 is similar to Figure 8 but includes an overlap tube 50' similar to that shown in Figure 2. The metal baffle plate 80 separates the internal cavity into first 14a and second 14b chambers. The metal inner pipe 20 extends from the inlet 16 to the outlet 18 and includes a first perforated portion 20a located within the first chamber 14a and a non- perforated portion 20b that is located in the second chamber 14b. In this example, one end 54' of the overlap tube 50' is secured to the metal inner pipe 20 in the first chamber 14a and an opposite end 56' of the overlap tube 50' is radially spaced from the metal inner tube 20 by a gap 52' . The opposite end 56' of the overlap tube 50' is located within the second chamber 14b, and thus forms a Helmholtz neck, making the second chamber 14b a Helmholtz chamber.

[0046] The overlap tube 50' is supported within the baffle 80 such that an outer surface of the overlap tube 50' is received within an opening in the baffle 80. The outermost edge 84 of the baffle 80 is supported within the outer shell 12 by the thermal seal 82. The metal inner pipe 20 includes at least two discrete openings 20c in the non-perforated portion 32b. These openings 20c in the inner pipe 20 are located inside of the overlap tube 50' . [0047] Figure 10 discloses an outer shell 12 with a reduced portion 12a that separates the outer shell 12 into first and second chambers 12b and 12c. The metal inner pipe 20 is the only pipe that extends from the inlet 16, through the reduced portion 12a, to the outlet 18. A thermal gasket or seal 90 supports the metal inner pipe 20 within the reduced portion 12a. The metal inner pipe 20 includes a perforated portion 20a located within the first chamber 12b and a non-perforated portion 20b that is located within the second chamber 12c.

[0048] An overlap tube 50" is mounted to the metal inner pipe 20 solely within the second chamber 12c. The overlap tube 50" is similar to that of Figure 9 and forms the second chamber 12c as the Helmholtz chamber 24. The first chamber 12b comprises an expansion chamber.

[0049] Figure 11 discloses a configuration where the metal inner pipe 20 includes a non-perforated portion that extends from the inlet 16 to the outlet 18. A Helmholtz neck 92 extends outwardly from the metal inner pipe 20 toward the plastic outer shell. In the example shown, the neck 92 extends rearwardly at an angle relative to the central axis A. This angle could be increased to be up to ninety degrees. In this configuration, the entire internal cavity 14 comprises the Helmholtz chamber 24.

[0050] Figures 12A-12C show a configuration where the metal inner pipe 20 includes window cut-outs 100 at a location between the inlet 16 and the outlet 18. A metal outer pipe 102 surrounds the metal inner pipe 20 and includes ends 104 that are connected by sizing for example, at a location outside of the outer shell 12. The metal outer pipe 102 includes window cut-outs 106 that are orientated such that they are axially aligned with the cut-outs 100 of the metal inner pipe 20, but are not radially aligned with the cut-outs 100. In other words, the cut-outs 100 of the metal inner pipe 20 face a solid wall of the metal outer pipe 102 and the cut-outs 106 of the metal outer pipe 102 face a solid wall of the metal inner pipe 20 as shown in Figure 12C.

[0051] The inner 20 and outer 102 pipes are separated by an air gap 108. Exhaust gas flows through the metal inner pipe 20 and out of the cut-outs 100 into the air gap 108. The exhaust gas then flows out of the cut-outs 106 into the internal cavity 14 which forms the Helmholtz chamber 24. The cut-outs 100, 106 and gap 108 cooperate to form the Helmholtz neck. The size and number of cut-outs in the inner and outer pipes can be varied as needed to attenuate a desired frequency.

[0052] Figure 13 shows a configuration that includes a stamped muffler inner shell 110. The inner shell 110 is positioned within the internal cavity 14 and extends from the inlet 16 to the outlet 18. The inner shell 110 is spaced radially inwardly from the outer shell 12 to form a chamber 112. The metal inner pipe 20 is spaced radially inwardly of the inner shell 110 and extends through the center of the inner shell 110 from the inlet 16 to the outlet 18. The end plates 22 thermally seal off the radial area between the metal inner pipe 20 and the inner shell 110. A Helmholtz neck 114 is formed within the inner shell 110 that extends outwardly from the inner shell 110 toward the outer shell 12. The metal inner pipe 20 includes a perforated portion 20a along a substantial length of the pipe such that exhaust gas can flow out of the metal inner pipe 20 into the inner shell 110. The chamber 112 thus forms the Helmholtz chamber 24.

[0053] Figure 14 shows an outer shell 12 with a reduced portion 12a similar to that of Figure 10, which separates the outer shell 12 into first 12b and second 12c chambers. However, instead of including an overlap tube, this configuration uses a layer of packing material 120 that is wrapped around the metal inner pipe 20. The metal inner pipe 20 extends from the inlet 16, through the first 12 chamber, through the reduced portion 12a, and through the second chamber 12c to the outlet 118. The metal inner pipe 20 includes a perforated portion 20a that is located in the first chamber 12b, the reduced portion 12a, and the second chamber 12c.

[0054] The layer of packing material 120 is wrapped around the length of metal inner pipe 20 that is located within the first chamber 12b, the reduced portion 12a, and the second chamber 12c. The first and second chambers 12b, 12c are substantially empty as the layer of packing material is localized along the inner pipe 20. The layer of packing material 120 fills any open area in the reduced portion 12a.

[0055] Figure 15 is similar to Figure 14 except in the configuration of Figure 15 the metal inner pipe 20 includes a non-perforated portion located within the reduced portion 12a. In either configuration, a Helmholtz neck could be added in one of the chambers.

[0056] The subject muffler comprises a hybrid muffler configuration where a plastic outer shell with an inner metal tube extending from an inlet to an outlet also includes a Helmholtz resonator in a reduced pack configuration. Reducing the amount of packing material reduces the weight of the plastic muffler as compared to a traditional packed configuration. Further, using a combination of reduced pack and the Helmholtz resonator provides a plastic muffler configuration that is capable of attenuating specific frequencies.

[0057] It should be understood that in any of the various embodiments shown above, packing material may be included within any chamber and/or removed from any chamber in any combination as needed to achieve a desired noise attenuation characteristic.

[0058] Although a preferred 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 invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.