Sound absorbing element with low profile micro-louver slits and muffler assembly using the same
A novel sound absorbing sheet material with a unique combination of micro-louver slit parameters and patterns provides superior noise attenuation and a reduced perforation area (less than 3.5%) to better protect fiberglass insulation when used in a muffler assembly. A muffler assembly is disclosed incorporating the novel sound absorbing sheet as the inner exhaust conduit.
1 . A sound absorbing element comprising:
a metal sheet having a thickness (t) greater than or equal to 0.2 mm and less than or equal to 0.4 mm,
said metal sheet having a plurality of louvered slits formed in a predetermined longitudinally extending pattern,
wherein each of said plurality of louvered slits has a width (w) greater than or equal to 1 mm and less than or equal to 3 mm, a louver height (h) greater than or equal to 0.35 mm and less than or equal to 0.45 mm, and a slit height (x) greater than or equal to 0.03 mm and less than or equal to 0.120 mm,
wherein the metal sheet has a perforation ratio (P) greater than or equal to 1% and less than or equal to 3.5%,
wherein said metal sheet comprises a tube having an inner conduit through which an airflow passes from a first end to a second end; and
at least one layer of fiber insulation extending around said outside of said sheet metal tube,
said slit height and width, said louver height and said perforation ratio being configured to allow acoustic waves through the louvered slits for sound attenuation yet also retain fibers from said fiber insulation from entering the airflow within the inner conduit.
2 . The sound absorbing element of claim 1 wherein the metal sheet is selected from the group consisting of stainless-steel, stainless-steel alloys, aluminum, aluminum alloys, aluminized steel, ferritic alloys, and austenitic alloys.
3 . The sound absorbing element of claim 2 wherein the metal sheet is stainless steel and has a thickness (t) between 0.25 mm and 0.35 mm.
4 . The sound absorbing element of claim 1 wherein said louvered slits are in an in-line pattern.
5 . The sound absorbing element of claim 1 wherein said louvered slits are in a staggered pattern.
6 . The sound absorbing element of claim 1 wherein rows of said louvered slits have an offset (o) of greater than or equal to 0.5 mm and less than or equal to 1.5 mm and a spacing(s) of greater than or equal to 0 and less than or equal to 0.6 mm.
7 . The sound absorbing element of claim 3 wherein said louvered slits are in a staggered pattern.
8 . The sound absorbing element of claim 7 wherein rows of said louvered slits have an offset (o) of greater than or equal to 0.5 mm and less than or equal to 1.5 mm and a spacing(s) of greater than or equal to 0 and less than or equal to 0.6 mm.
9 . The sound absorbing element of claim 1 wherein said louvered slits are in a mirror pattern.
10 . The sound absorbing element of claim 1 wherein said louvered slits are in a nested pattern.
11 . A muffler assembly comprising:
a sound attenuating inner tube;
an outer concentric housing tube;
opposing end caps configured to capture the inner and outer tubes in concentric relation and form input and output ends for exhaust gases; and
at least one layer of fiber insulation disposed between the inner tube and the outer tube,
wherein the sound attenuating inner tube comprises,
a metal sheet having a thickness (t) greater than or equal to 0.2 mm and less than or equal to 0.4 mm,
said metal sheet having a plurality of louvered slits formed in a predetermined longitudinally extending pattern,
wherein each of said plurality of louvered slits has a width (w) greater than or equal to 1 mm and less than or equal to 3 mm, a louver height (h) greater than or equal to 0.35 mm and less than or equal to 0.45 mm, and a slit height (x) greater than or equal to 0.03 mm and less than or equal to 0.120 mm,
wherein the metal sheet has a perforation ratio (P) greater than or equal to 1% and less than or equal to 3.5%,
said slit height and width, said louver height and said perforation ratio being configured to allow acoustic waves through the louvered slits for sound attenuation yet also retain fibers from said fiber insulation from entering the airflow within the inner conduit.
12 . The muffler assembly of claim 11 wherein the metal sheet is selected from the group consisting of stainless-steel, stainless-steel alloys, aluminum, aluminum alloys, aluminized steel, ferritic alloys, and austenitic alloys.
13 . The muffler assembly of claim 12 wherein the metal sheet is stainless steel and has a thickness (t) between 0.25 mm and 0.35 mm.
14 . The muffler assembly of claim 11 wherein said louvered slits are in an in-line pattern.
15 . The muffler assembly of claim 11 wherein said louvered slits are in a staggered pattern.
16 . The muffler assembly of claim 15 wherein rows of said louvered slits have an offset (o) of greater than or equal to 0.5 mm and less than or equal to 1.5 mm and a spacing(s) of greater than or equal to 0 and less than or equal to 0.6 mm.
17 . The muffler assembly of claim 13 wherein said louvered slits are in a staggered pattern.
18 . The muffler assembly of claim 17 wherein rows of said louvered slits have an offset (o) of greater than or equal to 0.5 mm and less than or equal to 1.5 mm and a spacing(s) of greater than or equal to 0 and less than or equal to 0.6 mm.
19 . The muffler assembly of claim 11 wherein said louvered slits are in a mirror pattern.
20 . The muffler assembly of claim 11 wherein said louvered slits are in a nested pattern.
21 . The sound absorbing element of claim 1 , wherein said fiber insulation comprises fiberglass insulation.
22 . The muffler assembly of claim 11 , wherein said fiber insulation comprises fiberglass insulation.