US3353627A

US3353627A - Muffler with concentric tubes forming helmholtz chambers

Info

Publication number: US3353627A
Application number: US433225A
Authority: US
Inventors: Robert A Heath
Original assignee: Walker Manufacturing Co
Current assignee: Walker Manufacturing Co
Priority date: 1965-02-16
Filing date: 1965-02-16
Publication date: 1967-11-21
Anticipated expiration: 1984-11-21

Description

R. A. HEATH Nov. 21, 1967 MUFFLER WITH CONCENTRIC TUBES FORMING HELMHOLTZ CHAMBERS 2 Sheets-Sheet l NVENTOR.

P J N Q Filed Feb. 16, 1965 R. A. HEATH 3,353,627

MUFFLER WITH CONCENTRIC TUBES FORMING HELMHOLTZ CHAMBERS Nov. 21, 1967 2 Sheets-Sheet 2 Filed Feb. 16, 1965 INVENTOR. /7. H64 2 BY jam,

w Z an/vzns United States Iatent Gfilice 3,353,627 MUFFLER WITH CONCENTRIC TUBES FORMING HELMHQLTZ CHAMBERS Robert A.'Heatl1, Jackson, Mich, assignor to Walker Manufacturing Company, Racine, Wis., a corporation of Delaware Filed'Feb. 16, 1965, Ser. No. 433,225 13 Claims. (Cl. 181-48) My invention relates to mufilers and is particularly, though not exclusively, concerned with mufiiers of the type that are used in exhaust systems for internal combustion engines such as are found in automobiles and trucks.

It is an object of my invention to provide a muffler structure which incorporates various silencing principles but which is small in diameter, contains a minimum number of parts, and is economical to produce.

The invention accomplishes the foregoing and other objects by means of a construction in which there is a center tube that serves as a gas conveying conduit and it. is surrounded by an outer tube which may also form the outer housing or shell of the muffler. Between the two tubes is an inner shell which is preferably held in place by means of pinched sections formed on either the outer tube togrip the shell or on the shell to grip the center tube. The space between the intermediate shell and either-the outer tube or the center tube, or both, forms a passage which is used as a tuning neck to lead into a chamber formed between the center tube and the outer tube and act with the chamber as a Helmholtz resonator to'attenuate desired frequencies.

The invention is illustrated in the accompanying drawings in which: 1

FIGURE 1 is a longitudinal cross section, partly broken away, through one form of the invention;

FIG. 2 is a cross-sectional along the line 22 of FIG. 1; FIG. 3 is a longitudinal cross-section through another form of the invention;

FIG. 4 is a cross section on the line 4-4 of FIG. 3;

FIG. 5 is a longitudinal section, partly broken away, through another form of the invention;

FIG. 6 is a longitudinal cross section, partly broken away, through a fourth form of the invention; and

FIG. 7 is a cross section along the line 77 of FIG. 6.

The muffler 1 of FIGS. 1 and 2 comprises a center tube 3' which is supported at opposite ends in the reduced diameter portions 5 and 7, which form the inlet and outlet bushings of the muffler 1. The bushings 5 and 7 may be formed by swaging down the ends of the outer tube 9 which forms the outer shell of the housing of the mufiler 1. Adjacent the inlet end of the muffler 1 the tube 3' is preferably providedwith a bank of louvers or perforations ll .whichfopen into the space between the center tube 3 and the outer tube 9. Surrounding the center tube, located at an intermediate point of its length,

is an inner shell 13. At its upstream end the shell is supported by a pinched or rolled-down section formed in the outer tube 9 which provides a gas-tight fit with theperiphery of the shell 13. This, therefore, divides the space within the outer tube 9 into'a first chamber 17 which is in direct communication with the louvers 11, and a second chamber 19 which surrounds and is located downstream of the shell 13. The chamber 19 has communication withthe 'gas in the chamber 17 by means of the pinch-down connection 21 between the downstream end of the shell 13 in the center tube 3, which is of such a nature as to leave open passages 23 which provide a large open area communicating the interior of the shell 13 with the chamber 19. It will be seen that the shell 13 and the center tube 3, in effect, define an annular pas- 3,353,027 Patented Nov. 21, 1967 sage 25 which is open at 23 or its downstream end into the chamber 19 and at 27 or its upstream end into the chamber 17. If desired, the shell 13 may overlap a portion of the bank of louvers 11, as indicated in FIG. 1. It will be seen that that portion of the annular passage 25 between the downstream end of the bank of louvers and the downstream end of the shell 13, i.e., the distance L in the drawings, constitutes a tuning neck or throat which will act in conjunction with the volume of chamber 19 to provide a Helmholtz resonator which will attenuate frequencies to which it is tuned. The natural frequency of this resonator is capable of being calculated by the well-known Helmholtz formula, the frequency being dependent upon the volume of chamber 19, the length of the passage 25, and the area of the passage 25.

That portion of the passage 25 which overlaps a portion of the louver bank is indicated at 29 and will serve to some eXtent as a high frequency sound attenuating chamber to attenuate spit and scratchiness and high frequency noises, whereas the chamber 17 will also attenuate these sounds as well as lower frequency sounds and roughness. Since the gas and sound in chamber 17 has communication with the chamber 19 only through the annular passage 25, which passage includes the length L which is imperforate, lower-frequency sounds or notes of the frequency to which this structure is tuned will be attenuated.

In the embodiment 101 of FIGS. 3 and 4 there is a center tube 103 which is received in the reduced diameter end sections 105 and 107 of the outer tube 109, the sections 105 and 107 forming inlet and outlet bushings, respectively, for the muflier 101. The center tube 103 is provided with two banks of louvers or perforations 111 and 113. Surrounding the bank 113 is an intermediate shell 115 which has gas-type connections 117 and 119 at opposite ends with the center tube, these being illustrated in FIG. 4 as formed by pinched-down sections 121 in the end of the shell 115. The shell therefore defines a spit chamber 123 with the center tube 103 into which high frequency sounds pass from the louver bank 113 and are attenuated. The outer periphery of the shell 115 defines an annular passage 125 with the outer tube 109. The upstream end of the annular passage 125 is open as seen at 127 to communicate freely with a chamber formed between the center tube 103 and the outer tube 109 and located between the open end 127 and the upstream end of the. mufiier. The downstream end of the annular passage 125 is open, as indicated at 131, and in free communication with a chamber. 133 that is formed in the mufiler between the center tube and the outer tube and located downstream in the open end 131.

The passage 125 is of a length and an area that are selected in relationship withthe volume of chamber 133 to provide a Helmholtz resonator that is-tuned to attenuate a desired frequency.

As already indicated, the spit chamber 123 will at.- tenuate scratchy noises and high frequency hissing sounds.

The chamber 129 will act to eliminate somewhat lower frequencies and roughness and, if desired, the length of the chamber 129 may be selected with respect to the center of the bank of louvers 111 so that it is approximately one-quarter of the wave length of any frequency which itis desired to attenuate.

Thus, the unit 101 with only three parts has at least four different silencing techniques embodied in it, namely: 1) spit chamber for high frequencies, (2) the Helmholtz resonator, (3) the roughness control chamber 129 and (4) a'quarter wave length tuner or quincke tube.

It will be understood that the quarter wave length tuning technique could be applied to other embodiments of the invention, including those illustrated herein if desired.

The mufiler 201 of FIG. 5 has a center tube 203 which is supported in the reduced

diameter sections

205 and 207, which form inlet and outlet bushings, respectively, for the outer tube 209. The center tube 203 has a bank of louvers 211 and a second bank of louvers 213 located downstream of the louvers 211. Surrounding the bank of louvers 213 and extending downstream a substantial distance beyond the end of the bank 213 is a shell 215. The upstream end of the shell 215 is connected to the center tube 203 in a gas-tight joint 217 by necking down, rolling, swaging, or pinching down the upstream end of the shell 215. The downstream end of the shell 215 is open, as indicated at 219, for free communication with a chamber 221 which is formed by the center tube 203 and the outer tube 209 and which extends from the downstream end 223 of the outer tube to the shell 215. While the downstream end of the shell 215 is shown as unsupported on the center tube, it is obvious that it could be supported by the technique shown in FIG. 2 if that is desired. A length L of the center tube inside of the shell 215 is imperforate so that the shell and the center tube define-an annular passage 225 which will serve as a tuning neck of the chamber 221. The annular space 227 between the shell 215 and the center tube 203 located immediately upstream of the passage 225 will form a modified spit chamber, and also serves to deliver gases and sound waves to the passage 225.

The outer periphery of the shell 215 and the inner periphery of the tube 209- define an annular passage 229 which is substantially longer than the passage 225 as well as being of larger cross-sectional area in the particular embodiment shown since it is of larger diameter and approximately the same width. The passage 229 will communicate the chamber 231 which is formed between the center tube 203 and the outer tube 209 and located upstream of the shell 215 with the chamber 221, and sound waves being delivered to the chamber 231 by the bank of louvers 211. Thus, in this embodiment the chamber 221 is connected through two different tuning necks to the gas flowing through the center tube 203, that is, the tuning neck provided by annular passage 225 and the tuning neck provided by the annular passage 229, both of which are formed by the inner shell 215'. Assuming the areas of the passages 225 and 229 are the same, it will be seen that the passage 229 acting in conjunction. with the chamber 221, will form a Helmholtz resonator having a fundamental frequency which is substantially higher than that formed by the passage 225 in the chamber 221 inasmuch as the frequency is inversely proportional to the square root of the length of the tuning passage.

The chamber 231 will act to attenuate roughness and spit noises as well as serve as a feeder chamber, or collection chamber, for furnishing pressure to the annular passage 229, all as in the preceding embodiments.

Additionally, the length of the outer tube 209 downstream from about the midpoint of the bank of louvers 211 may be such as to serve as a quarter wave length tuning chamber for an objectionable frequency. In this case, the chamber 221 would serve as a portion of two different Helmholtz resonators and also as a portion of a quincke or quarter wave length tuning chamber.

The muffler 301 of FIGS. 6 and 7 has a center tube 303 which is supported in reduced diameter sections 305 and 307 which form inlet and outlet bushings, respectively, for the outer tube 309. The center tube has three banks of perforations .or louvers 311-, 3:13, and 315, respectively,

formed in it. Surrounding the upstream and the downstream bank of louvers are'inner shells 317 and 3159, respectively, which have the opposite. ends pinched down, as indicated at 321, by pinches 323, into gas tight connections at opposite ends with the center tube 303. Thus, there is a spit chamber 325 formed by the shell 317 and ,a spit chamber 327 formed by the shell 319. The

shells

317 and 3 19 may, of course, .be of .dilferent lengths to form chambers of different volumes, if desired. It is clear that the louvers 311 and 315 opening into the chambers 325 and 327 act to attenuate high frequency noises and spit.

The outer diameter of the shells 317 and 319 define

annular passages

329 and 331, respectively, with the er ube 0.9 whi h are in op n ommunic tion at the upstream end 333 of the passage 3.29 and the downstream end 335 of the passage 331 with the chambers 337 and 339, respectively. The downstream end 3.41 of the passage 329 and the upstream end 343 of the annular passage 331 are in open communication with a chamber 345 which is defined by the center tube 303 and the outer tube 309 into which the bank of louvers 313 opens. The chamber 345 will attenuate roughness and serve as a collection or feeder chamber for the

passages

329 and 331. It is clear that by making the volumes of chambers 337 and339- of such size in relation to the respective lengths and areas of the

passages

329 and 331 that two substantially differently tuned Helmholtz resonators can be obtained in the muffler 301.

It will now be recognized that by the use of a center tube, an outer tube, and an intermediate shell the invention provides various possible muffler constructions capable of silencing sounds of high, low, and intermediate frequencies by means of various silencing techniques. Modifications in the specific structures shown may be made without departing from the spirit and scope of the invention.

I claim:

7 1. A gas mufiler for attenuating sound of a predetermined frequency comprising an outer tube, an inner center tube, and an intermediate shell telescoped between said tubes, at least part of the space between said tubes form-mg a chamber of predetermined volume having a major portion located out of radial alignment with said shell, at least one cross section of said shell being connected in a gas tight joint to one of said tubes, said shell forming with the other of said tubes an annular passage of predetermined length and area and having first and second ends and both said ends being open, the first end of said passage opening to said predetermined volume chamber, said center tube forming the gas flow passage for saidmufilenthe length and area of said annular passage and the volume of said chamber being interrelated and selected to form a Helmholtz sound attenuating chamber for-said predetermined frequency, and means forming a flow connection of said gas flow passage with the second end of said annular passage.

2,. A rnufiler as defined in claim 1 wherein said gas tight joint is between said outer tube and said shell whereby said annular passage is formed by said shell and said center tube, said joint subdividing the space between said tubes into said chamber of predetermined volume and into a second chamber, said means and said second end .both opening into said second chamber.

3. A muffler as, defined in claim 2 wherein said means comprises perforations in the center tube and said second chamber acts to attenuate roughness sound in the gas.

4. A mufller as defined in claim '1 wherein said gas tight joint is between said center tube and said shell whereby said annular passage is formed by said shell and said outer tube.

5. A muffier as defined in claim 4 wherein a chamber is formed between said tubes adjacent the second end of said annular passage, said means comprising perforations in said center tube opening into said just-mentioned chamber. j

6. A mufiler as defined in claim 5 wherein longitudinally spaced gas tight joints are formed between. said shell and center tube to provide a chamber between the cen er tube and shell, said center tube. being perforated within said last-mentioned chamber. 7

7. A mufiler as defined in claim 1 wherein longitudi nally spaced gas tight joints are formed between said shell and center tube to provide a chamber between the center tube and shell, said center tube being perforated within said last-mentioned chamber.

8. A mufiier as defined in claim 1 wherein said gas tight joint is between said center tube and said shell whereby said annular passage is formed by said shell and said outer tube, said shell and said center tube defining an annular passage opening at one end of the shell into the space between the tubes, a portion of said tube located inwardly of the open end of the annular passage formed between said shell and center tube being perforate, the area of said last-mentioned annular passage and the imperforate length thereof and the volume of the space into which it opens being selected to form a Helmholtz sound attenuating chamber for a desired frequency.

9. A mufi ler as defined in claim 8 wherein said two annular passages both open into the same chamber and are tuned to attenuate two different frequencies.

10. A mufiler as defined in claim 9 wherein the center tube in the space between said tubes adjacent the second end of said annular passage is perforated whereby such space acts as a roughness sound attenuating chamberv 11. A mufiler as claimed in claim'l including a second intermediate shell telescoped between said tubes and spaced longitudinally of the other shell, a pair of gas tight joints connecting each shell to the center tube to form a spit chamber between each shell and the center tube, said center tube being perforated in each spit chamber and also being perforated between the two shells to open into the space between the tubes intermediate the two shells, said two shells and said outer tube defining two annular passages having second ends opening into said intermediate space, the two spaces between the tubes adjacent the two first ends of the annular passages being of predetermined volumes and respectively related to the lengths and areas of the annular passages to act as tuning chambers.

12. A mufiler as claimed in claim 11 wherein said two annular passages and the two spaces are tuned to attenuate two ditferent frequencies.

13. A mufiier as claimed in claim 1 wherein the length of the space between said tubes communicating with said means is substantially one quarter the Wave length of a selected frequency to be attenuated.

References Cited UNITED STATES PATENTS 2,124,933 7/1938 Starkweather 18148 2,139,151 12/1938 Deremer 18148 2,297,046 9/1942 Bourne 181-48 2,331,344 10/1943 Powers 181-48 X 2,367,753 1/1945 Buck. 2,580,564 1/1952 Ludlow l814-8 2,899,007 8/1959 Morrish et a1. 18154 2,930,440 3/1950 Fetzer et al. 181-54 3,263,772 8/1966 Irwin et al. 18l-59 FOREIGN PATENTS 450,398 7/ 1936 Great Britain. 258,890 6/1928 Italy.

RICHARD B. WILKINSON, Primary Examiner. ROBERT S. WARD, JR., Assistant Examiner.

Claims

1. A GAS MUFFLER FOR ATTENUATING SOUND OF A PREDETERMINED FREQUENCY COMPRISING AN OUTER TUBE, AN INNER CENTER TUBE, AND AN INTERMEDIATE SHELL TELESCOPED BETWEEN SAID TUBES, AT LEAST PART OF THE SPACE BETWEEN SAID TUBES FORMING A CHAMBER OF PREDETERMINED VOLUME HAVING A MAJOR PORTION LOCATED OUT OF RADIAL ALIGNMENT WITH SAID SHELL, AT LEAST ONE CROSS SECTION OF SAID SHELL BEING CONNECTED IN A GAS TIGHT JOINT TO ONE OF SAID TUBES, SAID SHELL FORMING WITH THE OTHER OF SAID TUBES AN ANNULAR PASSAGE OF PREDETERMINED LENGTH AND AREA AND HAVING FIRST AND SECOND ENDS AND BOTH SAID ENDS BEING OPEN, THE FIRST END OF SAID PASSAGE OPENING TO SAID PREDETERMINED VOLUME CHAMBER, SAID CENTER TUBE FOR FORMING THE GAS FLOW PASSAGE FOR SAID MUFFLER, THE LENGTH AND AREA OF SAID ANNULAR PASSAGE AND THE VOLUME OF SAID CHAMBER BEING INTERRELATED AND SELECTED TO FORM A HELMHOLTZ SOUND ATTENUATING CHAMBER FOR SAID PREDETERMINED FREQUENCY, AND MEANS FORMING A FLOW CONNECTION OF SAID GAS PASSAGE WITH THE SECOND END OF SAID ANNULAR PASSAGE.