US2191620A

US2191620A - Resonator silencer

Info

Publication number: US2191620A
Application number: US102678A
Authority: US
Inventors: Lloyd E Muller
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1936-09-26
Filing date: 1936-09-26
Publication date: 1940-02-27
Anticipated expiration: 1957-02-27

Description

Feb. 27, 1940.

L. MULLER RESONATOR SILENCER Filed Sept, 26, 1936 faja? WPA/.fiez

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Patented Feb. 27, 1940 PATENT OFFICE RESONATOR Smm Lloyd E. Muller, Flint, Mich., assignor to General Motors Corporation, Detroit. Mich., a corporation of Delaware Application September 25, 1936, Serial No. 102,878 12 Claim. (Cl. 181-48) This invention has to do with resonator silencers and is concerned with the connections of the resonance chambers thereof to the ducts through which the sound waves which are to be attenuated travel. f

The invention is based on the discovery that it is advantageous toemploy relatively small orices to connect chambers of resonators whose natural. frequencies are relatively high and relatively large orifices to connect chambers of resonators whose naturalfrequencies are relatively low to the ducts through which the sound waves which are to be attenuated pass. It may be that orifices graduated in size in accordance with the natural frequencies of the resonators 'whose Achambers they connect to the ducts would be rnost satisfactory but I have found that very satisfactory results can be obtained if only two different sizes of orifices are used.

For resonators whose natural frequencies are relatively high (i. e., higher than about 300 or 400 c. p. s.), I have found that orices equivalent in area to circular orifices about 11;" (onesixteenth of an inch) in diameter are most satisfactory. For resonators whose natural frequencies are relatively low (i. e., lower than about 300 or 400 c. p. s.), I have found that oriiices equivalent in area to circular orifices between about 1A (one-eighth) and about A (one-quarter), preferably between M3 (one-eighth) and 352 (live thirty-seconds), of an inch in diameter are most satisfactory. The difference between the optimum sizes of the orifices for the two typesof resonators may be explained upon the basis of the characteristics of the resonators which it is desirable to accentuate and the limitations on the accentuation of these characteristics.

In the case of resonators whose natural frequencies are relatively high, it is desirable to accentuate-broaden the range of response. This may be done by increasing the acoustical resistance of the orifices which connect the chambers of the resonators to the ducts through which the sound waves which are to be attenuated pass. Therefore, in the case of resonators whose natural frequencies are relatively high, relatively small orifices of which 'relatively high acoustical resistance is characteristic are employed. The limitation, beside the necessity of maintaining satisfactory communication between the chambers of the resonators and the ducts, is the size of the orifice that can be produced commercially iny the material through which the orifice is to be made.

In the case of resonators whose natural irequencies are relatively low, the characteristic which it is desirable to accentuate is the eillciency ot, response at the natural frequency or frequencies of the resonators. This may be done by decreasing the acoustical resistance of the orifices whichwconnect the chambers of the resonators to the ducts through which the sound waves which are to be attenuated pass. Therefore, in

lthe .case of resonators whose natural frequencies are relatively low, relatively large orifices of which relatively `low acoustical resistance is characteristic are employed. There are two limitations on the accentuation of this characteristic. They are that the sizes of the orifices must not be so great that the gases which flow past them will interfere considerably with the natural movement of the gases within the chambers or as to reduce the acoustical inertance of the resonators to too low values.

For a better understanding of my invention, reference is made to the accompanying drawing and the following specification wherein there is shown and described a resonator silencer in Vwhich the invention is embodied.

In the accompanying drawing:

The two parts of Figure 1 constitute a longitudinal section through a resonator silencer in which my invention is embodied;

Figure 2 is an enlarged fragmentary longitudinal section, taken as indicated by the line 2-2 of Figure 3, through the relatively low free quency section of the center tube of the silencer shown in Figure 1;

Figure 3 is a fragmentary section taken as indicated by the line 3-3 of Figure 2;

Figure 4 is a fragmentary longitudinal section on approximately the same scale as Figures 2 and 3, taken as indicated by the line lli--4 of Figure 5, through one of the relatively high frequency sections of the center tube of the silencer shown in Figure 1;

Figure 5 is a fragmentary section taken as indicated by the line 5-5 of Figure 4.

The resonator silencer which is. hown in the drawing includes an imperforate cylindrical shell IU over whose ends there are secured heads ii and i2. Through the heads ii and I2 extend cen'tral orices which are encircled by outwardly extending collars I3 and it and connected by a center tube i5 whose ends extend into the collars.

Between portions of the shell Il) and center tube l5 near the head i2 extend imperiorate annular partitions I6 and l1. The partitions I6 and I1 are separated from each other lengthwise of the shell and the center tube and with the latter and the head I2 define the chambers Il and I 9 of two simple resonators with relatively high natural frequencies.

The portion of the center tube I5 between the head II and the partition I6 is encircled by an imperforate tubular shell 20. 'I'he shell 20 is of larger diameter than the center tube and of smaller diameter than the cylindrical shell I0 and is coaxial with both and terminates short of the head II and the partition I6. Between portions of the tubular shell 20 and the center tube I5 about midway between the ends of the silencer extend three imperforate annular partitions 2|, 22 and 23. The partitions 2|, 22 and 23 are separated from each other lengthwise of the tubular shell and the center tube and with the latter define' the

chambers

24 and 25 of two simple resonators with relatively high natural frequen-l cies and two open-ended annular apertures 26 and 21.

Between portions of the cylindrical shell III and the tubular shell 20 somewhat farther from the head than from the head I2 extend

annular partitions

28 and 29 which are separated from each other lengthwise of the cylindrical and tubular shells. The partition 29 is imperforate and with the partition I 6 and the cylindrical andl tubular shells defines the chamber 3|)v of a resonator with a relatively high natural frequency. The partition 28, through which extend one`or more orifices in each of which there is secured a tube 3|, defines with the partition 29 and the cylindrical and tubular shells the secondary chamber 32 and with the head II and the cylindrical and tubular shells the primary chamber 33 of a compound resonator with relatively low natural frequencies.

The portions of the center tube I5 which are encircled by the chambers I8, I9, 2.4 and are riddled with orifices 34 aboutv 0.003 (three thousandths) of a square inch in area which connect the chambers to the center tube. The portion of the center tube Abetween the partitions I 6 and 23 is imperforate from the partition I6 to a point about midway between the ends of the annular aperture 21 but the remainder of it is riddled with orifices 34 of the same size as the orifices 34 mentioned above. 'I'he aperture between the end of the tubular shell 20 and the partition I6, the annular aperture 21 and these orices connect the chamber to the center tube.

The portionvof the center tube I5 between the head II and the partition 2| is imperforate from the 'head to a point well within the annular aperture 26 but the remainderof it is riddled with orifices 35 about 0.015 (fifteen-thousandths) of a square inch in area. The aperture between the end of the tubular shell 20 and the head II, the annular aperture 25 and the orifices 35 connect the chamber 33 to the center tube.

As the drawing indicates, the orifices 34 may be formed in pairs by making in the material of which the center tube is to be formed pairs of short slits which extend lengthwise and are separated circumferentially of the tube and pressing the material between each pair of slits out of the plane of the material without breaking it away therefrom at the ends of the slits so as to form shields 38 which bridge the' space between the slits from end to end and are elevated above the plane of the material. As the drawing also indicates, the orifices 35 may be similarly formed but to make them larger than the orifices 34 the slits are made longer andthe shields 31 pressed farther outv of the plane of the material from which the center tube is to be made.

'I'he silencer shown in the drawing was designed i'or installation in the exhaust system of an internal combustion engine with the collar I 3 connected to the exhaust pipe and the collar I4 to the tail pipe of the engine so that the exhaust gases of the engine pass through its center tube I5 in the course of their passage to the atmosphere. The resonator 32--3I-33-26-35 and the resonators 244-34, 25-34, 30'-21-34,' I8-34 and |1--34 are, of course, so tuned in the manner set forth in the Wilson application Serial No. 470,700, filed July 25, 1930, and the corresponding foreign patents, vi z., Canadian Patent'No. 348,037, British Patent No. 391,180, French Patent No. '720,611 and Italian Patent No. 300,037, that they respond to and attenuate by resonance, respectively, sound waves of relatively low frequencies and sound waves of relatively high frequencies which occurin the exhaust gases of the engine.

I claim:

1. In a, silencer, a tube which is riddled throughout a portion `of its length with orifices equivalent in area to circular orifices about onesixteenth of an inch in diameter and throughout another portion of its length with orifices equivalent -in area to circular orifices between about one-eighth and about five thirty-seconds of an inch in diameter, a shell which encircles and isv equivalent in area to circular orifices between about one-eighth and about one-quarter of an inch in diameter and throughout another portion of its length with smaller orifices, a shell which encircles and is radially spaced from the riddled portion of the tube, heads which with the tube and the shell define a compartment which encircles the riddled portion of the tube, and a partition which subdivides the compartment into chambers of resonators of relatively low frequency and relatively high frequency which are connected to the tube by the larger orifices' and the smaller orifices, respectively.-

3. In a silencer, a tube which is riddled throughout a portion of its length with orifices of relatively small size and throughout another portion of its length with orifices of relatively large size, a shell which encircles and is radially spaced from the riddled portion of. the tube, heads which with the tube and the shell define a compartment which encircles the riddled portion of the tube, and a partition which subdivides the compartment into chambers of resonators of relatively high frequency and relatively low frequency which are connected to the tube by the smaller orifices and the larger orifices, respectively.

4. In a silencer, a tube which isV riddled throughout Aa portion of its length with orifices with relatively high acoustical resistance and 'throughout another portion of its length with oriencircles the riddled portion of the tube, and a partition which subdivides the compartment into chambers of resonators of relatively high frequency and relatively low frequency which are connected to the tube by the orifices of relatively high acoustical resistance and the orifices of relatively low acoustical resistance, respectively.

5. In a silencer, a tube which is riddled throughout a portion of its length with relatively small orices and throughout another portion of its length ywith relatively large orifices, a shell which encircles and is radially spaced from the riddled portion of the tube, heads which with the tube and the shell define a compartment which encircles the riddled portion of the tube, and a partition which subdivides the compartment into chambers of relatively small and relatively large size which are connected to the tube by the smalle er orifices and the larger orifices, respectively.

6. In a silencer, a duct, and means which defines chambers of resonators with natural frequencies above and below about 300 or 400 cycles per second connected to the duct by orifices equivalent in size to circular orifices about onesixteenth of an inch and between about oneeighth and about five thirty-seconds of an inch in diameter, respectively.

7. In a silencer, a duct, and means which deiines chambers of resonators of relatively low frequency and relatively high frequency connected to the duct by oriiices equivalent in size to a circular orifice between about one-eighth and about one-quarter of an inch in diameter and a smaller orifice, respectively.

8. In a silencer, a duct, and means which denes chambers of resonators of relatively high frequency and relatively low frequency connected to the duct by orifices with relatively high acous tical resistance and relatively low acoustical resistance, respectively.

9. In a silencer, a duct, and means which defines chambers of resonators of relatively high frequency and relatively low frequency connected to the duct by orifices of relatively small and relatively large size, respectively.

l0. In a silencer, a duct, and means which de fines chambers of relatively small and relatively large size connected to the duct by orifices of relatively small and relatively large size, respectively.

ll. In a silencer, c. duct, and means which denes chambers of relatively small and relatively large size connected to the duct by orices with relatively high acoustical resistance and relatively low acoustical resistance, respectively.

12. In a silencer, a tube which is riddled throughout a portion of its length with oriiices with relatively high acoustical resistance and throughout another portion o its length with orices with relatively low acoustical resistance, a shell which encircles and is radially spaced from the riddled portion of the tube, heads which with the tube and the shell define a compartment which encircles the riddled portion of the tube,

and a partition which subdivides the compartment into chambers of relatively small and r/elatively large size which are connected to the tube by the orifices of relatively high acoustical resistance and the orifices of relatively low acoustical resistance, respectively.

LLOYD E. MULLER.