US1720507A - Silencer - Google Patents

Description

July 9; 1929.

R. B. BOURNE S ILENCER Filed May 16, 1928 /0 [Q] j I INVENTOR.

Patented July 9, 1929.

,UNITED STATES PATENT OFFICE.

ROLAND B. BOURNE, OF HARTFORD, CONNECTICUT, ASS IGNOR, I BY IMESNIE ASSIGN- MENTS, TO THE MAXIM SILENCER COMPANY, OF HARTFORD, CONNECTICUT, A. COR

1 PORATION OF CONNECTICUT.

SILENCE-R.

Application filed May 16, 1928. Serial No. 278,224.

This invention relates to devices for silencing the exhaust of internal combustion engines, the intake of air compressors, or the like. The term silencing is used in a broad significance, having relation to the reduction to an unofl'ensive amplitude of sound waves Whether of audible or of subaudible frequencies. The object of the invention is to provide a simple and compact device presenting a minimum of resistance to gas flow which will be effective in silencing the noise source to which it is attached.

Sound waves of the lower frequencies, either audible or subaudible, predominate in certain types of noise creating apparatus to such an extent that if they are removed the frequencies remaining are unobjectionable. The apparatus herein described is of the filter type, blocking the passage of certain low frequency sound waves while permitting the transmission of those of certain higher frequencies. Low frequency sound waves may present their disagreeable, effects directly to the ear, in case they are above the limit of audibility; or, while themselves inaudible, may create disturbances by shaking buildings, rattling windows, or the like.

For attenuating such low frequency sound waves, I make use of the principles of the acoustic wave filter, a device capable of attenuating sound waves of certain. frequencies and depending, for itsaction, not upon friction (or bafiiing) but upon acOustic'reac tion between suitably disposed series and shunt elements comprising the acoustic network. In general, the series elements are formed by the main acoustic channel through the device, While the shunt elements comprise chambers or other cavities suitably coupled to the main acoustic channel. Various arrangements are possible, giving correspondingly different attenuation versus frequency characteristics. The simplest of acoustic wave filters consists of a main acoustic channel having laterally disposed side branches suitably coupled, as by holes,

to the main or series passageway, at intervals along the length thereof. The side branches may be tubes or chambers, or combinations thereof.

Every acoustic wave filter has more than one pass band of frequencies and more than one attenuation band. It is obvious, where the filter is primarily intended as a silencer,

that the attenuation bands should be as broad as possible. Recourse is made, therefore, in the present invention, to a disposition wherein the attenuation versus frequency characteristics of more than one acoustic system are superimposed in such a way that there results a wide band of sound frequencies which sufier attenuation.

Referring to the drawings:

Fig. 1 is a diagrammatic View illustrating the principle of my invention;

Fig. 2 is a longitudinal section through one form of apparatus embodying my invention;

Fig. 3 1s a section'through the apparatus in the drawings as 20, 21, 22 and 23, enter the common outlet acoustic channel 24 at intervals along the length thereof. It is to be noted that, in all the dispositions shown in the drawings, the first cross branch encountered upon entering the device communicates with the outlet channel at a point farthest removed from the final outlet, whereas the last cross branch leaving the inlet passageway communicates with the outlet channel at a point nearest the final outlet; the intermediate cross branches being correspondingly disposed.

The arrangement shown in Fig. 1, while primarily intended as a schematic representation of my invention, may form a practical embodiment, the side branches 11, 12, etc. being formed as pipes and the side chambers 16, 17, 18, 19, as cylinders surrounding the pipes and communicating therewith 'by means of coupling holes, slots or the like. Such an embodiment of the invention is, however, unwieldly, and the more compact arrangement of Fig. 2 is preferred;

of sheet metal secured together by welding at-their lines of contact, and hence no rivets or bolts have been shown in the drawing. The structure is cnifined .within a cylindrical casing 30 having headers 31 and 32 at its ends. Pipes 33 and 34 leading out of these headers may be of such length as desired for attachment to the structure to be silenced, the apparatus functioning when connected in either direction.

' lVithin the cylinder 30 is a second shell 35 secured at one end to the header 32 and spaced from the casing 30 so as to form an annular acoustic channel 36. The other end of the inner shell is closed by a header 37 spaced from the header 31 to form a chamber 38 connecting with passageway 36. Between the header 37 and the header 32 are three partitions 39, 40 and 41, serving to divide the inner easing into four spaced compartments 42, 43, 44 and 45. The number of these compartments may be changed as desired, although in general the mathematical ideal will be approached more closely the higher the number. For practical purposes, however, four will usually be found suflicient.

Within the compartments are side branches 46, 47, 48 and 49, each conveniently formed by a piece of sheet metal bent in circular form 50 at its center, and having its sides 51 converging as is clearly shown in Fig. 3. The partitions 39, 40 and 41 and the header 32 are provided with central holes in alignment with the circular portions 50 of the side branches, so that the composite structure constitutes a central circular acoustic channel 52 closed at one end by header 37 and opening out through pipe 34 at the other, and having side branches 46, 47, 48 and 49.

These side branches are preferably angularly arranged with respect to each other, each ofthem being advanced at a right angle from the preceding one. The walls 51 terminate short of the inner wall of the casing 35, leaving coupling openings 53 corresponding to the coupling openings 15 in Fig. 1, where the side branches are coupled to the otherwise closed acoustic side chamhers. Opposite the end of each side branch the casing 35 is slotted at 54 to provide a short passage connecting the annular acoustic channel 36 .with the side branches, and, through the openings 53, with the closed side chambers 42, 43, 44 and 45.

It will be apparent that the structure of Figs. 2 and 3 corresponds to the idealized case of Fig. 1 ifthe coupling openings 15 in the latter be shifted to one end of the side branches instead of being located centrally. If it is desired to vary the position of the coupling opening to correspond with the nication to the side chambers being had through coupling holes 66 That I claim is:

1. A silencer comprising an annular acoustic channel, a central acoustic channel, a plurality of connecting side branches, and side chambers communicating imlividually with the side branches but otherwise closed.

v2. A silencer comprising a pair of main acoustic channels, a plurality of side branches joining the main acoustic channels, and side chambers communicating individually with the side branches but otherwise closed.

3. A silencer comprising an annular acoustic channel, a central acoustic channel, a plurality of side branches longitudinally and angularly spaced from each other, and side chambers communicating individually with the side branches but otherwise closed.

4. A silencer comprising a pair of cas ings, one within the other, presenting an annular acoustic channel between them, a plurality of partitions within the inner casing dividing itinto separate compartments, a central acoustic channel through all of said compartments, walls within each of said compartments dividing, it into a side branch and a side chamber, and coupling openings from each compartment to the annular acoustic channel and from each side branch to its contiguous side chamber.

5. A silencer comprising apair-of casings, one within the other, to present an annular acoustic channel between them, a plurality of partitions within the inner casing dividing it into separate compartments, a sheet of converging U-form extending between each of said partitions and terminating short of the inner casing, slots in the inner casing opposite theconverging portions of said sheets, and central openings through the partitions forming with the sheets a central acoustic channel.

6. A silencer comprising a pair of acous tic channels, a plurality of side branches extending therebetween and connecting to said acoustic channels at intervals along the lengths thereof, and side chambers communicating individually with said side branches.

7. A'silencer comprising a pair of acoustic channels, a plurality of side branches extending therebetween and connecting to said acoustic channels at intervals along the lengths thereof, and side chambers communin the wa lls.

icating individually with said side branches but otherwise closed.

8. A silencer comprising an inlet acoustic channel, an outlet acoustic channel, a plurality of side branches extending therebetween and connecting with said inlet and outlet channels at intervals along the lengths thereof, the side branch communicating with the inlet channel at the point nearest the inlet to the silencer opening into the outlet channel at a point farthest removed from the outlet of the silencer, and side chambers communicating individually with said side branches.

9. A silencer comprising an inlet acoustic channel, an outlet acoustic channel, a

plurality of side branches extending therebetween and connecting with said inlet and outlet channels at intervals along the lengths thereof, so disposed that, starting from the inlet of the silencer, the side branches '1, 2, n,, open into the outlet channel in the order n,2, 1, viewed from the outlet'end of the outlet channel, and side chambers communicating individually with said side branches. R 10. A silencer comprising a pair of main acoustic channels, a plurality of side branches joining the main passages, said side branches varying in cross-sectional area along their lengths, and side chambers coupled acoustically to the side branches but otherwise closed. e

In testimony whereof I have affixed my signature.

ROLAND B. BOURNE. I

Images