CA1038770A

CA1038770A - Method and device for silencing the exhaust noise of internal combustion engines

Info

Publication number: CA1038770A
Application number: CA235,004A
Authority: CA
Inventors: Moriyuki Taguchi
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 1974-08-28
Filing date: 1975-08-22
Publication date: 1978-09-19
Also published as: FR2283312B1; FR2283312A1; GB1513473A; DE2537946C2; DE2537946A1

Abstract

METHOD AND DEVICE FOR SILENCING THE EXHAUST
NOISE OF INTERNAL COMBUSTION ENGINES

ABSTRACT OF THE DISCLOSURE
An exhaust gas silencing system wherein standing waves are utilized in a silencing chamber to reduce low frequency compo-nents of noise, and a downstream muffler is utilized to reduce the high frequency components of noise. An expansion chamber can be utilized further to reduce the pressure of the sound waves.

Description

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2 This invention relates ~o siler1cing of the noise in the

3 exhaust streaa1 f'r~m internal cornbustion ~ngine~q. I

4 , The exhaust noise from internal combustion engines is ge I
nerally considered as consisting of (l) sound which is genera~ed when gases of combustion are exhausted rom an exhaust port of the 1~
7 engine where they rapidly expand, and (2) sound generated when the ,8 exhaus~ gas flows thxough an exhaust pipe from the exhaust port. ,~
The first portion is propagated in the form of pulsating pressure , waves, including frequency components which are substantially pro-ll portional to the engine speed. This portion'of the sound there-12 fore includes a relatively,large amount of low freguency compo-nents. The second portion is generally considered as comprising 14 sound generated by eddies and the like in the exhaust gas flow, and has a relatively small amount of 19w frequency components and 16 a;relatively high proportion of high frequency components. ' 17 It is relatively straightforward to muffle high frequeacy 18 components with mufflers o modest siz:e. However~ it has general-ly been necessary to use relatively large muflers or silencLng the low frequency components of the sound, Particularly in'situa~
2l tions where'the available space for t~e muffler is limited, for ¦
22 ~xample on motorcycles,'it has heretoore been impossible to use a i 23 conventional muffler of sufficiently large siæe to absorb substan~ !~
2~ tially all of the low frequency noise components. Therefore, on smalLer vehicles it has been difficult to silence exhaust noises ' 1 26 which include a large amount o~ low frequency components. These I
27 vehicle5 tend sometirne~ to produce an undesirable amount of ex-28 haust noise or this reason, , 29 One objective o the present invention is to provide an , 30 ,ef~ective and improved method and device for silencing exhaust ;

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~ises,especially of the lower frequency components, which is of a relatively small si~e. The me-thod and device of the present in- ;
vention are characterized by the elimination of the lower frequency noise components in a silenciny chamber, and of the higher frequen- -cy noise components in a muffler more suitable for disposing of -the higher frequency noise. -The following United States and foreign patents relate to previous efforts to reduce noise:
Bourne U.S. Patent ~o. 2,017,748 : i.
Leadbetter U. S. Patent No. 2,360,429 i:
~ Hasui U. S. Patent No.3,589,469 .. ~ ..
Tenney U. S~ Patent No.3,665,712 ;i Fichtel & West Germany Sachs Patent No.595,425 (1934) ` ;

Martin West Germany ;~
j Patent No.802,204 (1949) ~
,.;' i ~ ~,. , Anero West Germany s;;
;~ Patent No. 964,915 (1957) ' -, ,. ~, :
`~i Bauer West Germany Pa~
-~ ~ tent No. 1,121,410 (1958) Reference is also made to applicant's co-pending Cana~
dian Patent Application Serial No. 216,854, filed December 23, 1974, relating to exhaust means for attenuating noise producing ~ -pulsating pressure in engine exhaust gas. `
. The invention is carried out by providing a silencing ~
chamber downstream from the exhaust port of the engine, which cham- ~ -ber includes a re~lecting wall. The reflecting wall causes stand-- ing waves to be developed in the silencing chamber. A standing wave ha~ "nodes" of least amplitude linked by "loops". An exit ; port from this silencing chamber is provided at a location axially adjacent to a node. Gases exhausted from this exhaust port will ~ have low frequency noise components. Gases cominy out from the ,r exit port have the lower amplitude of the node, rather than the hiyher amplitude of the loops between the nodes. Accordingly, the low frequency noise will have been reduced.

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Accordiny to another feature of the invention, a muffler ~ -receives the effluent gas stream from the exit por-t and muffles ~:-~, the higher frequency components which were not muffled in the si- '~
`. lencing chamber. The exhaust stream leaving the muffler is there-"~ , .,, "

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l fore substantially devoid of both lo~ and high frequency noise co~-2 ponents. ¦
According to still another preferred but optional feature i of the invention, means is provided for moving the reflecting wall ~ ~ ~ the exit port axially in the silencing chamber or the purpose .~ 6 o relating the relative positions of the node and of the exi~ l~
7 port. This provides for both frequency and temperature compensa-tion, if desired ~
9 According to still another preferred but optional feature I -of the inventisn, a catalytic converter can be placed downstrejam ~ 11 rom the silencing chamber so as to per~orm its catalytic function 1 ., 12 on the exhaust stream without exposure to the damaging ef~ects of ¦-13 the low frequency vibrations. Catalytic elements have frequently been rapidly destroyed in motorcycle muflers, for example, by the I-~y 15 low frequency noises. -16 The above and other features of this invention will befully understood from the following detailed description and the 18 accompanying drawings, in which:
19 Fig. 1 illustrates a prior art first expansion chamber; I
Fig. 2 is an axial cross-section showing the present~y 21 pxeferred embodiment of a silencing chamber for use in this inven~ ~:
22 tion;
Figs. 3, 4 and 5 are graphs illustrating certain opera-~;' 24 tive features of this invention;
~5 Fig 6 is an axial cross~section showing a modification 26 of the device of Fig. 2 together with a muf~ler; l~
: 27 FLgs, 7 and 8 are cross-sections taken at lines 7-7 and ~ 8-8, respectively, oi Fig. 6, f~,~, 29 Fig 9 is a cross-section taken at line 9-9 oE Fig. 8;
~ 30 Fig. lO is an axial section o~ yet another embodiment of v the invention;

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l Fig. ll is a cross-section taken at line 11-11 of Fig. 10;
2 Figs. 12-18 are axial cross-sections showing other e~bodi 3 ments of the invention;
4 Figs~ 19 and 20 are cross~sections taken at lines 19-19 and 20-20 in Fi8~ 18;
Fig. 21 is a top view of a motorcycle incorpora~ing ano ther embodiment o the inven-tion;
8 ~ Fig. 22 is a showing of a portion of Fig. 21 with t~e g chassis o the motorcycle removed; and 1~' Figs. 23 and 24 are axial cross-sections of othe'r embodi~
11 ments of the invention incorpo~ating catalysts. l 12 Figs.'l and 2 illustrate, respectively, a conventional I
13 first expansion chamber and a silencing chamber according ~o the 1~ invention. In Fig. 1 a conventional exhaust pipe~l is connected 1~ at la to an exhaust' port 2a of an internal combustion engine, or ~- ;
16 example a single-cylinder, two-stLoke engine. Pipe l includes a 1~ ' 17 cylindrical ~ront portion 3 (whose end at point B constit~utes an ,`~
18 "entrance port") having a relatively small diameter. ~The~first`ex 19 pansion chamber 4 comprises a cylindrical rear portion S having a I -larger diameter than that of the entrance port. A conical portion 2~- 6 is placed between portions 3 and 5.~ Chamber 4 is comprised of 22 portions 5 and 6. An exhaust gas outlet 7 is formed at the rear 23 end of the irst expansion chamber.
24 In the presently preferred embodiment of the invention 2~ as shown in Fig, 2, por~ions which correspond to portions of Fig ¦~
26 1 are given corresponding numbers. These two dévices differ in that chamber 4 is denoted as a silencing chamber in Fig. 2, and i 28 has a reflecting wall 5a without a port, and an exhaust gas outlet 1, port 17 exhaus'ting through the sidewall of the silencing cha~ er , 30 at a location y~ ~o be discussed In Fig 1 the end wall is , 31 // l 32 /l , ~, I . .
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1 ported and the sidewall is imperforate. ~
Z ¦ In accordance with known theory, lower frequencies ~ say .
¦ on the order of between about 300 and 1,000 cycle~ per second, will 4 ¦ tend, in a chamber such as shown in Fig. 2, ~o ~orm standing ~aves ~ I for example, standlng wave lO. Such a wave has portions o~ loop l 6 L of pressure and nodes l2 oE pressure. As schematically sho~m in , IN -th6 L~P
~ig. 2, the amplitude is greatest ~-J4Y~ r~ ll and least at node 12. The objective of the invention is to exhaust the gases throug 9 an exit port 17 from a region as near as possible to a node so 10 tha-t-only reduced low frequency comporlents o~ the noise accompany l~ -..- 11 the stream. The axial location Qf khe nodes varies with the re-12 quency and with the ~emperatureO Also ~ while the most frequent 13 nodal-positions occur at odd whole multiples of one-quarter wave ilength, they are also formed at other fract1ons and, of course, there will be standing waves of many diferen~ frequencies. In ad 16 dition, the wave length of a given frequency varies wLth the tempe 17 rature. Accordingly, some empirical adjustment of the location 18 must be made after the best theoretical location is calculated~ in ' lg order to be certain tha~ the most troublesome components of the - 20 particu1ar sound are silenced. Also9 ~he temperature is not even-~- 21 ly distributed, and thereore some emp~irlcal adjustment will be 22 ~leeded 23 Ordinarily, the frequency of most concern will be dete~
~,~ 24 mined by measuring and observing the characteristics of the-ex-' 25 haust stream from a particular engine whose exhaust stream is to ,i, 26 be quieted. The best theoretical locakion for low frequency silen 27 cing is one~quarter wave length from ~he reflecting wall at warm- l ,28 en~ine, warm-silencer condi-tions I
s 29 When ~he relative locations of the node and oE the ex-.5 ~ 30 h~L~t port are not adjustable, there will be some theoretical :.; 31 I/
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1 ~ssening of silencing e~ficiency at different temperatures. Ho~7- ¦
2 ever, in a practical silencer on a typical engine, nodes from othe 3 standing waves of nearby frequencies, and nodes formed at differen 4 fractions of a wave leng~h, will usually cause a diminished output , of the low frequency noise components, even iE silencing of the 6 frequency of greatest interest is somewhat less effectively re- I
; 7 duced.
8 ~ It will be found that there is a band of axial length "L"
~-; 9 along the axis 13 within which the node for the ~requency of most 10 interest will customarily stand ~or most operative temperatures.
11 The location o such a node can be approxiMately determined theo-12 retically, and ultimately must be adjusted experimentaily, but thi 13 requires little effort As heretofore stated, the adjustment seek ~-~
14 the most effective nodal position, and also compensates for the 15 effect of unequal temperature distribution. The objective of the 16 invention, th~refore, is to provide an exit port of adequate capa-- 17 city to pass the exhaust gases at a region within the band. One 18 or more exit ports may be provided~, but one will usually be suffi-cientS When more than one is provided, all will lie within the 20 said band, Some theoretical studies have shown that the exit port 21 unctions most effectively to remove about 94% o a low frequency 22 of interest when its axial length is less than about 4 cm. and pre ¦~
23 ~erably less than about 2 cmn The smaller the length of the exit port, the sharper the cutoff. There is a surprisingly broad~band 25 "L", which can be as great as abou~ 10 cm The above criteria are 26 respective to ~requencies of about 500 Hertz, the wave length of ~ 27 which, at ahou~ ~C, is about 1 meter. The exit port is conven-f 2~ iently located about 0.25 meter fro~ the reflecting wall, i.e., 29 about ~ eeione-quarter lc~ th~ It is often important to elimi-30 n~te 500 Hertz noi9e.
31 ~ligher ~requency components (i.e., above about 1000 Hertz 32 o~ the noi~e do rlot ~end to ~r~

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form standing ~laves in the manner indica-ted in Fig. 2, and these components will generally leave the sllencing chamber along with the gas, and must be silenced by means located downstream from ~, , the silencing chamber.
n the operation of the engine, pulsating pressure waves " . ~,:
;~ in the exhaust gas enter the exhaust pipe 1. In Figs. 1 and 2, ;~
' the maximum values of the pulsating pressuresat the points A, B, ,; ,. , C, D, and E are as shown in Fig. 3. In Fig. 3, the curved dashed line "a" shows the variation of the maximum value of the pulsating pressure in the exhaust pipe at the various points along axis 13 ., ~ ;- . .
~; in the device of Fig. 1. The curved solid line "h" shows the variation of the maximum value of the pulsating pressure in the exhaust pipe of the construction shown in Fig.
As is apparent from Fig. 3, the maximum value of the ex-haust pressure is high at both ends of the exhaust pipe in both -: -constructions, and is lower at an intermediate portion thereof.
~'~ This tendency can be calculated theoretically and observed experi-; mentally. In the exhaust pipe of Fig. 2, the exhaust gases are :.
: removed from an axial location where the maximum value of the ~
` 20 pulsating pressure wave is relatively low, and in that of Fig. 1, -,i where they are relatively high. The axial pulsating pressure in ,, . ;
~'~ the chamber of Fig. 2 is hlgher at every compared point than in ,~ the chamber o~ Fig~ 1, but in the chamber of Fig. 1, the gas -. .; , - stream exits where the pressures are highest, and in the device of Fig. 2, it exits where they are lower, and this lower pres- -- sure is less than the exit pressure of Fig. 1. Therefore, the actually exiting noise pre~sures are significantly lower with ; the device o Fig. 2 than with -the device of Fig. 1.
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~ Fiy. 4 shows the variation of pressure for one cycle , ~ .
o~ a two-stroke engine at the exhaust gas outlet ports 7 and 17 vf the first expansion chamber and the silencing chamber, which , are respectively shown in Figs. land 2. Again, the dashed line ,, ,, ' ' .
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curv~d-solid line "b" is that o the construction o Fig 2 As 31 will be apparent from the drawing, in the exhaust pipe of Fig. 1 I after the maximum pressurec~ , a few peaks appear in the pulsatin_ 51 pressure, as shown by the symbols ~ , and ~ . In the exhaust pipe 61 o~ Fig. 2, peaks c~ ' and c~ nd ~ ' and ~ " appear in the 7¦ pulsating pressure to correspond ~o the pul~ating pressure peaks~
81 ~ , and ~ in the first expansion chamber of Fig. 1. Consequently 91 the number of the pulsating pressure waves having relative large 10 ¦ amplitudes, and appearing fo~ one cycle of the eng;ne, is in- l ll ¦ creased However, the peak value of each pulsating pressure wave 12 ¦ is very small compared with that of the peaks c~, t~ and ~ in the 13 ¦ exhaust pipe in Fig. 1, because the pulsating pressure waves 6~, ll 14 ¦ pand ~ are divided into the pulsat~ng pressure wavesc~ ' and I
15 ~ ' and ~ ", and ~ ' and ~ respectively. This means that ¦
~16 ¦ the low frequency components of the exhaust pulsating pressure wav 17 ¦are relatively decreased, and at ~he same time that the peak value ¦ of the pulsating pressure is los~eredO This situation is experimen 19 ¦~tally observed and can be derived theoretical~y by gas dynamics 20 ¦ analysis. The improved results are evident. Adjusting the distanc -21 ¦ between the re1ecting wall end and the exhaust gas outlet port ap 22 ¦ pears to a~ect the eficiency o~ the silencer, as previously dis-23 ¦ cussed. In conven~ional internal cornbustion engines, i~ is suit-24 able to determine ~he position of the exhaust gas outlet port so j25 that it is effective against the pressure wavecX o~ about 300 to l 26 1,000 Hz, and such a construction appears to be generally useful, I
27 whatever the speed of the engine 28 An internal combustion engine used for testing was a two-cylinder, two-cycle engine having a displacement of 350 cc and a maximum power outpu~ o~ 38 ps/7500 rprn. The engine was run in the 31 /l -32 ll .
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test at 25C and at the speed of 7000 rpm. The dirnensions of the l~ ' 2 silencer used in the test are shown in the upper portion of Fig 4 , ~ -3 ;n millimeters, ~ogether with the wave forms ~lready described 4 This construction was varied to make the test corresponding to a device according to Fig. l by placing the exit port in the ref~ect 6 ing wall to form the construction oE Fig l and closing the exit l -7 port in the sidewall.
8 ~ - Fig. S shows the frequency distribution of noise measured 9 in the test of Fig. 4, in which the broken line "a" shows the nois l~
in decibels (A scale) from the exhaust pipe shown in Fig. l~ and !~"' 11 the broken line "b" shows the noise in decibels from the exhaust l~
12 pipe of Fig. 2. Noise was measured at a location spaced from the I ~
respective exhaust'outlet port by one meter. As shown in Fig. 5, l ~ ;
14 in th'e exhaust pipe of the construction shown in Fig 2, the low l ' frequency components of the noise were substantially decreased. I
16 F'igs.- 6-9 show another embodLment of the present inven~ ~-17 tion in which an exhaust pipe portion 21 is connected to an exhaus 18 port 22a of a two-cycle internal combustion engine 22. The system 21 comprises a front portion 23 (entrance port) having a relativel small cross-sectional area, a cylind~ical rear poxtion 25 having a 21 lax~er diameter, and a coni~al portio~ 26 connecting them. In thi ''' -22 embodiment, as in the others, the conical portion and rear portion 23 comprise an "expansion chamber",in the sense of having an enlarged cross~section compared to portion 23, and also ~orm the silen~ing cham'ber. The rear end is closed by reElecting wall 25a. An ex-26 haust gas exit port 27 is provided near a boundary portion between 27 the conical portion 26 and the rear portion 25 and is located in 2g the band where the node o~ the standing wave having the frequency 29 in question will'be formed in accordance with the previously-de-30 scribed criteria l-31 1/ ~
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~ 11 , , ~3~7~70 l A muffler portion 28 is formed integral with the cylindri : 2 cal rear portion 25 of ~he exhaust pipe portiorl 21, and has an in- ~
. 3 let port 29 connected to the outlet p~rt 27 of ~he exhaust pipe I
portion 21 through an exhaust gas pas,sagc-~ 30, The passage may con veniently be formed by a pla~e welded to the side of the device, t ' . 6 The muffler portion 28 is divided into chambexs 38, 39, 7 -40, 41, 42, 43~ and ~4 by partitions 31, 32, 33, 3'~ 35, 36, and 37 . ~ The . chambers 38, 39, 40 and 41 communicate with one another ¦
.,. 9 through holes in the partitions 31, 32 and 33, The chambers 41 and 44 are adapted to communicate with each other through a pipe I
~`, ll -$5, and the chambers 42 and 44 are al.s~ adapted to communicate I .' 12 witk each other through a p;pe 460 Chamber 42 is opened to atmos- t .~' 13 phere through a plpe 470 The pipes 455 '~6 and $7 have a number of ~:~
"i"' 14 perforations through the sidewall thereof within the chamber 43.

~ .15 ~hamber 43 is filled with sound absorbing tnateri~l, such as glass t~
.,j~ .16 wool. This is a muffler construction especiaIly well suited to .' ~- . 17 the reduction of high frequency noise components. ,:~
~ 18 ~ Exhaust gas flows from the front: portion 23 (entrance . --'.'' . l9 port)' ~f the ~exhaus~ pipe por~ion 21~ and into the silencing cha~-- :
ber 24, where the gas expands and foxms a sta~ldi.ng wave respec~ive ~ ' 21 to the engine speed, The wave, wherever sho~n, is respective to'a .
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~r ~g~e frequency generated by some spec~fic engirlQ speed. T~e ex- ' c panded gas 10ws through the exit port 27, th~ough t.he exhaus~ gas ~' y:l 24 'passage 30 and the inlet port 29g and ente~s into the chamber 38 $ ~ ~5 of the muf~'ler portio~ 28, ' ~ l;~
,. 26 The'maximum value o the exhaus~ pulsating pressure wave ¦~
' 27 has been lowered i.n -the expansion charnbe~ by expanding ~he gas, an t . . low frequency components have been speci.fically reduced, The high ~' 29 frequency components remain to be muffled, The exhaust gas flows ~
~' 30 f~om chamber 38, through chambers 39, 40 and 41 and the pipe 45, ! ' ~'' 31 /J ' i ~' 32 // ' ~ l ,; . t ,~_ ~,,' _~ ~03~77~ ~:
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and enters into the chamber 44, and thereafter flows back to the ~;
chamber 42 through pipe 46, and is finally exhausted throuyh the pipe 47. Pipe 47 is some-times called the muffler outlet port.
During this process, the high frequency pulsating pressure of the exhaus-t gas is attenuated, and consequently the higher `~ frequency noise level is lowered. The cons-truction to the right of wall 25a is sometimes called a "muffler", and any suitable muf-fler may be used provided it is effective to muffle higher fre-quencies. This term is used in like manner in the other embodi-ments. The combination of muffler and silencing chamber reduces both low and high frequency components, and the expansion chamber (this feature being optional) reduces the total pressure. An opti-mally quieted stream is emitted from this structure.
Figs. 10 and 11 show another example of a silencing de- -vice according to the present invention~ This example was espe-~- cially designed for a four cycle internal combustion engine. In - ~ Figs. 10 and 11, an exhaust pipe 51 is connected to an exhaust port of a four-cycle internal combustion engine (not shown). The ex-?"~ haust pipe 51 has a un1form diameter along its entire length, and ~i 20 is closed at one end thereof by a silencing wall 55a to form a si-~, :-?~ lencing chamber 55b. An exhaust gas exit port 57 is provided at a location of the exhaust pipe forwardly (to the left in Fig. 10, re-presenting a vehicle's forward direction of motion) from the re-flecting wall, and will be located where the node of a standing wave will exist at common vehicle engine speeds as described above. ; ~-~
An expansion chamber 60 is formed downstream from the exit port and illu~trate~ that expansion is unnecessary to the feature of -. .,,?
withdrawing gases near a node. Expansion can be eliminated or, as shown can follow after the standing wave "treatment".
A muffler 58 is placed rearwardly from the expansion cham-ber. Chambers 68,69,70,71,7~, and 73 are defined by partitions ,~ , ~ - 12 -h'~
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-- 1 , - ~0;~3~377a 61, 62, 63, 6~, 65, and 66. Expansion chamber 60 and chamber 68 !
¦ are connected to each o~her through a passage 59. 1.
A pipe 75 with a number of perfora~ions throllg~ its sid~-~: 41 wall is Mounted to extend through the partitions 61, 62, 63 and 6~, and has a front end protruding into ~he charnber 68. Pipe 75 has a 6 partition 75a between partitions 61 and 63. Par~itions 62 and 64 l ~ have through-holes 62a and 6'~a provided at the peripheral portion I .' .- thereof outside the pipe 75. Thus, a zig-zag passage is for~ed l:~
9 which extends from'chamber 68 to the chamber 72, as shown by the I
~:' 10 arrows in Fig. 10. A pipe 76, having a numSer of per~orations 1',-11 through the sidewall thereo~, is placed ~etween the partitions 65 12 and 66. Chamber 73 is filled with sound-abso~bing material~ such , .,.,'~ 13 as glass wool. ~ ~' :~. 14 Exhaust gas from the .internal combustion engine flows ' fro~ exhaust pipe 51 and leaves the silencing chamber through the 16 exhaust gas outlet port 57, into the expansion char.lber 60. Ihe . ~
17 amplitude of the low frequency po~tions has been attenuated, The . ~:
18 noise in the gas stream emitted from exit port 57 has a smaller ., 19 amount of low frequency cornponents than entered the silencing cham-20 b er .
21 Exhaust gas flows ~rom the expansion cha~ber 60~ whexe ., '22 the total pressure value is lowered~ then through the passage 59, .
,, 23 and into the chamber 68. While the exhaust gas 10ws through ~he .
,,,,,: '24 ..mufler 58, much of ~he energy o~ the high frequency noi.se ~o~p~--., 25 nent is absorbed~ and then the stream is exhausted to atmosphere, :
~, 26 , Fi~, 12 shows another silencing system according to the ~ ;
~', 27 in~en~iob, wherein an exhaust pipe 100 has a conical portion 101 28¦ expanding ~o an enlarged c~lindrical portion 102. A silencin~
~9 charnber 107 is~ormed whieh is bounded in part by reflecting wall .',' 3~ 113 and by portions 101 and 102. This wall is Eormed on a piston~ ,, 31 1 ke body 114 in the cylindrical portion and is rnovable back and . .

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forth in the cylindrical portion~ A tension cable 118 can pull it to the left in Fig. 12 against the resistance of tension springs 116 which are fixed to wall 108. When the cable is released, the springs tend to return body 114 to -the right in Fig. 12. Movement of body 114 adjusts the position of the reflect-ing wall so that the node is optimally disposed axially adjacent to exit port 109. rrhe body can be moved manually or automatically to compensate for the movement of the node with temperature changes, or can be moved t,o seek a more agreeable or efficient setting for Y 10 removing other frequencies, for example at different speeds. ~ore precisely stated, movement of wall 113 serves to keep the node of the pressure wave having the frequency in question located more nearly adjacent to the exit port. Exit port 109 communi-: ~ .
-,, cates via passage 110 to the inlet port 112 of a muffler 111, ;~
all as heretofore described. Partition 108 separates the muf-fler from the silencing section. The embodiment of Fig. 12 pro-vides means for adjusting the posit:ion of the node of the pres-sure wave having the frequency in question relative to the inlet port for optimum advantage. The term "frequency in question"
is used herein to describe a frequency whoseelimination is most ;
sought after. In any practical engine installation there will be ~1 a certain lower frequency or group of frequencies preferentially ,:, : -to be attenuated. I'his i8 the "frequency in question". ~

~,~ Fig. 13 shows a device with a similar objective to that ~ , "~ of Fig. 12, except in this case it adjusts the position of the ex- ` ~-, ~, "
it port relative to a fixed reflec-ting wall, ra-ther than adjusting -khe posi,tion of the wall. The frequency desired to be ~silenced might be different, and the location of the most useful node might be at a different distance from the reflecting wall than would be the situation for the rnost useful node of another frequency.
, For example, at hiyher speeds, the frequency to be silenced might ... .
,~ be higher, and the node would be closer to the wall. Then it is , .....
~, useful to be able to move the exit port (or the re~lectiny walL) so that this node i~ axially adjacent to the exik port.
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; '' ' : ' ' , ~3~77~) In the embodimen-t of Fi g o 13 ~ exhaust gas is received from the engine through exhaust pipe 120, passes -throuyh a coni-; cal portion 121, and enters a cylindrical enlarged portion 122.
This portion i~ bounded by a fixed reflecting wall 123, which wall has a hole 124 which slidingly accommodates a slidable tube 125 which is axially slidable along axis 126. A push-pull cable 127 is connected to the throttle and also to tube 125 for shifting ;
the same in response to changes in engine speed.
,~ Exit port 128 is formed in the wall of the tube 125, l 10 instead of in the outer wall of the chamber, and exit gases flow :, - :
f through passage 129 in the tube 125 and pass into muffler 130, ; which includes a plurality of baffles 131 and conventional pack-. . .
ing 132. The tube 125 forms an internal wall of the silencing chamber.
The embodiment of Fig. 14 is intended to provide a .,, : .
series of standing waves with the objective of increasing the ~; likelihood of establishing a node adjacent to the exit port for - , ,, a wider range of frequencies. For this purpose, the exhaust ,~ pipe 150 discharges into conical portion 151 which in turn dis-charges into a cylindrical enlarged portion 152. An exit port 153 is formed in the wall of cylindrical portion 1S2, and a pas- -' sage 154 connects the exit port of the silencer section with the inlet port 155 of a muffler 156. The silencing chamber 157 is , defined by an imperforate partition 158 and two perforated partitions 159, 160, which have respective holes 161,162 there-, in. Hole 161 is larger than hole 162. It will thereby be seen "~ that three standing waves will be formed, and, depending on the ,; frequency, at least one of them, and probably more, iB likely ',~ to establish a node axially adjacent to the exit port.
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~' 30 Because the ~lowable length of a silencer and muffler combination is likely to be limited, especially on motor bikes, ~,~

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it is advantageous to attempt to increase the path length with-` in a construction of a given total length. For example, in ?
Fig. 15 the exhaust pipe 170 enters the silencing chamber 17L and strikes a reentrant, circularly grooved, reflecting wall 172 which returns the standing wave, not only into the reverse ~ direction, but also outwardly lnto an annular region 173 where -~ reflecting wall 174 is located. A standing wave is ormed by wall 174 and is reflected back into chamber 171 to form a node.
: Exit port 175 is formed at the desired location. The path to and from the reflecting wall is therefore "folded". Exit 175 discharges to a passage 176 which might be formed by a welded plate spaced from the outer wall of the construction that in .,:
turn communicates through an inlet port 177 to a muffler 178 that includes baffles 179 and packing 180a.
Fig. 16 shows another device according to the invention, ~ ~;
wherein an exhaust pipe 180 discharges through a conical portion m~ ~ 181 to a silencer chamber 182 with a flrst leg 183 and a second leg 184. The legs are partially bounded by a deflector plate l85, ~ ;~
which is disposed at about a45angle to the axis 186 of the de~
vice so as to deflect the gases and waves sidewardly into the ~-second leg toward a re~lecting wall 187, which wall forms the ; ;
standing~wave. A node is ormed adjacent to exit port 188. The ';~
exit port in turn communicates with an inlet port 189 of a ~;
muffler 190 comprising baffles 191 and a packing 192. This con-struction has the advantage of shortening the axial length of ;
the device by providing a side leg. ;
Figs. 17 and 18 show concentric alignments of the silenc-ing chan~er and the muffler. In Fig. 17 the entry port 195 en- -ters a conical portion 196, and gases flow to a cylindrical portion 196a. These portions form silencing chamber 197. A plurality of . .

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exit ports 1~8 are placed relative to a reflecting wall l9g in accordance with -the principLes already discussed. This shows that a plurality of exit ports can be used so long as they are in a zone defined by the dimension "L", as previously discussed.
A muffler 200 lies concentrically around the silencing chamber and shares a common wall with it, which constitutes substantial economic advantaye. An expansion chamber 201 is formed to the -left of a plurality of baffles 202 and a packing 203. Gases exit from the righthand end of the device in Fig. 17.
;; 10 Fig. 18 is a re~ersal of parts of Fig. 17. It includes an exhaust pipe 205 from the exhaust system. A conical .~
~i~ portion 206 extends to a cylindrical portion 206a forming a ;
cylindrical annular silencing chamber 207 around wall 206b. `-A reflecting wall 208 closes the right-hand end of the annular ,.-,-, . . .
silencing chamber. A muffler 209 is surrounded by the silencing chamber. It shares wall 206b with a silencing chamber. Muffler 209 includes a pointed end 210 to deflect the gases into the :
annular silencing chamber, and an exlt port 211 in its wall, located where the node is to be expected, to admit -the gases to the muffler. The muffler comprises a plurality of baffles 212 and a packing 213, all for muffling the high frequency components.
Fig. 21 shows an embodiment for still ~urther reducing the length required for the device, wherein a motor bike 220 has a chassis 221 to receive a silencing chamber 222 and a muffler 223. The silencing chamber and muffler are made in accordance with any of the foregoing constructions. For example, a conven-ient pair of devices would be the silencing chamber of E`ig. 2 ";, i ,: , ~, and the muffler of Fig. 6. They are connected by a tube 224 which extends from the exit port of the ~ilencing chamber to the inlet port of the muffler. In this manner these devices may placed side by side on opposite sides of the motor bike, and the weight rnore e~enly distributed. The right-hand rear end of silencing ch~mber 222 is clo3ed, and the right-hand rear end of the mu~ler , . . .. .. .
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is open, all exhuast gases departing from the muffler. The devices are made to look alike for cosmetic purposes.
It is known that much of the damage to catalytic ~ -elements is caused by vibration induced by the low fre~uency elements. It i,s also known that some catalytic elements operate : i ,, : .
best at low temperatures, and others at high temperatures. It is therefore a convenience of this invention that the catalytic ~:
element can be placed quite close to the hottest portions of the gas; that is, near the silencing chamber, or downstream where cooler, if desired. They have a substantially increased life because they operate in the presence of markedly diminished low frequency sound components.
Fig. 23, for example, shows a construction analogous ~-~ to that of Fig. 6, and bears like numbers. The dif~erence -~ ;
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between the devices of Figs. 23 and of Fig. 6 is the interposi~
tion of a catalytic element 230 inside the casing, directly s~ between the muffler and the silencing chamber. It is held be~
tween two perforated plates 231 and~232, and acts on the gases at ,~
~; ~ that point. The catalytic e1ement is cocled by external radiation ~20 and tends to run cool. It can be put further downstream, if .-;: ~ . .
'~l desired.
Fig. 24 shows the construction o~ Fig. 17 with a ~,,:, , : , ~
~ catalytic elemènt 235 held between two perforated plates 236 and .,,.~ - .. ' 237. Catalytic element 235 is active at cold temperatures and s treats the exhaust stream when cold to remove excess hydrocar- -~
i bons from it. After the engine is warmed up, catalyst 235 is no ~, longer ei~ective, but catalyst 238 downstream can be provided i,~i which isactive at hiyher temperatures. It can also be provided ~i; in combination with a muffler structure.
In all embodiments of the invention, the silencing ~, chamber has an ~'entrace port". It enters on the axis of the silencing chamber and faces the reflecting wall. In Fig. 6, i,,",, , - 18 -~'' 'i; ~,~, ~, ,",. " .... . .

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for example, i-t is at the termination of the cylindrical exhaust pipe and at the start of the conical section 26. It is simi-larly located in the other embodiments, the conical portion, when used, being regarded as a portion of the expansion chamber~ ~
The high frequency muf~ler means in every embodi- -ment has a muffler inlet port and a muffler outlet port. In Fig. 6 the muffler inlet port is port 29. Its outlet port is pipe 47. In every embodiment, the muffler includes a sound-absorbing packiny through which the entire exhaust stream passes while flowing from the muffler inlet port to the muffler out-Iet port. ~ ~;
In all embodiments of the invention (except for the embodiments of Figs. 16, 2~ and 22), the silencing chamber and the muffler means are coaxial in the sense that they are aligned with one another. The term "aligned with one another" incIudes the situation where they are next to one another, and also when one surrounds the other. Also, the .silencing chamber and the ; ~muffler means are contained within a "single wall". In Fig. 6 the "single wall" forms the peripheral wall 25 of the silencing chamber and also an outer boundaryof the muffler means. This is also the arrangement in Figs. 12, 13, 14, 15,23 and 24. In Fig. 10, where the expansion chamber is separate from the sil~
encing chamber, it is wall 60 within which the silencing chamber ~ is separately contained. The "single wall' in Fig. 17 is ,~ wall 196. It forms an outside boundaryof the muffler. There is a wall 196 between the muffler and the silencing charnber which forms a boundary of both the silencing chamber and of the muffler means.
In Fiy. 1~3 the "single wall" is wall 206a which forms an outer boundary of the silencing charnber. There ls a wall 206b which forms an inner wall of the silencing chamber and an outer boundary o~ the muffler means. It will be noted that in both -the er~odiments o~ Fiys. 17 and 18 the rnuffler means and silenciny ,. ,. . . :
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chamber are coaxial with one another, although one surrounds the other instead of being axially spaced-apart as in the other embodiments o~ the invention (excepting Figs. 16, 21 and 22, of course). ~-To summarize, this invention provides an exceptionally useful means and method to eliminate both low and high frequencies from exhaust stream, especially in small devices where a compact . . .
size and minimum length ~re needed. It provides a means for dis~
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posing of low frequency components, for example on motorcycles, ~
which heretofore have been unable to utilize the long mufflers re- ; ;
quired by the prior art, because of size limitations. The method -of this invention is first to elimi.nate the low frequency compo-nents in a silencing chamber of the type described, and then to i eliminate the high frequency components in a muffler.
It has been found that, if the total volume of the sys-i::
tem downstream from the~entrance port to the silencer exceeds the total displacement of the engine by a factor of between about 6 ;~ ~ to about 12, and preferably about 8, improved silencing is attained by virtue of the resulting expansion of the gases.
~20 Thls device provides a remarkably quiet exhaust stream, ~ using a minimum amount of material of its construction, and - occupying a minimum volume.
This invention is not to be limited by the embodi- ~;
ments s~hown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. Apparatus for silencing noise in the exhaust stream emitted from an internal combustion engine, said apparatus hav-ing an axis and comprising: a silencing chamber comprising an axially-extending peripheral wall and a reflecting wall normal to said axis forming a silencing chamber, said silencing cham-ber having an entry port substantially on said axis and spaced from and facing toward said reflecting wall for entry of exhaust gas from the engine into the silencing chamber, whereby to form a reflected standing wave in said silencing chamber having a node whose distance from said reflecting wall is a function of its temperature and frequency and is located between the entry port and the reflecting wall, an exit port passing through the peripheral wall, said exit port lying axially substantially en-tirely within a band having an axial length within which said node is located when its standing wave is formed by a frequency and at a temperature respective to an exhaust stream to be silenced, exhaust gases discharging from the silencing cham-ber solely through said exit port; high frequency muffler means having an axial dimension of length coaxial with the silencing chamber, a muffler inlet port, a muffler outlet port, and a sound-attenuating packing, through which packing the entire exhaust stream passes while flowing from muffler inlet port to muffler outlet port; and passage means interconnecting the exit port to said muffler inlet port.

2. Apparatus according to claim 1 in which the silenc-ing chamber and the muffler means are contained within a single wall.

3. Apparatus according to claim 2 in which the said single wall forms said peripheral wall and also forms the outer boundary of said muffler means.

4. Apparatus according to claim 2 in which the said single wall is said peripheral wall of the silencing chamber, and in which the muffler means is located coaxially inside an inner wall of the silencing chamber, the said inner wall there-by forming a boundary both of the silencing chamber and of the muffler means.

5. Apparatus according to claim 2 in which the said sin-gle wall forms the outer boundary of said muffler means, in which the muffler means concentrically surrounds said silencing chamber, the said peripheral wall thereby forming an inner boundary of said muffler means.

6. Apparatus according to claim 1, in which the muffler inlet is at a side thereof, said passage extending laterally alongside the apparatus, and in which the outer wall of the silencing chamber and the muffler means are continuous with one another.

7. Apparatus according to claim 6 in which said passage is formed by a plate attached to said peripheral wall.

8. Apparatus according to claim 1 in which the muffler means further includes baffles.

9. Apparatus according to claim 1 in which the silencing chamber includes an enlarging portion extending from the entrance port to a cylindrical portion.

10. Apparatus according to claim 1 in which high fre-quency muffler means is provided having an inlet communicating to the exit port and an outlet communicating with the atmosphere for muffling high frequency noise components passed by the silencing chamber.

11. Apparatus according to claim 10 in which the silencing chamber and the muffler are coaxial, a passage interconnecting the silencing chamber and the muffler entering both through a side thereof, the muffler comprising baffles and a packing, and the outer wall of the silencing chamber and the muffler being continuous with one another.

12. Apparatus according to claim 1 in which the exit port discharges exhaust gases into an expansion chamber, the gases from the expansion chamber then passing through the muffler means.

13. Apparatus according to claim 12 in which the silencing chamber is elongated, and in which the expansion cham-ber surrounds and extends along a major portion of the length of the silencing chamber.

14. Apparatus according to claim 1 in which the reflect-ing wall is movably mounted in the silencing chamber, and in which means is provided to move the reflecting wall axially in accordance with changes in engine speed, whereby to tend to maintain said node in axial alignment with the exit port.

15. Apparatus according to claim 14 in which the reflect-ing wall forms a portion of a piston construction and in which the portion of the silencing chamber in which it fits is cylindrical.

16. Apparatus according to claim 1 in which the silen-cing chamber includes a sliding tube axially slidable inside the external peripheral wall, said tube forming an interior per-ipheral wall of the silencing chamber, the exit port passing through said interior peripheral wall, and means for axially mov-ing said tube to locate the exit port axially adjacent to the node.

17. Apparatus according to claim 1 in which a plurality of said relfecting wall is provided, one of said walls being imperforate, and the other of said walls being annular, where-by to form a plurality of standing waves.

18. Apparatus according to claim 1 in which the silencing chamber includes an entrance tube projecting thereinto so as to form an annular region surrounding the same, the reflecting wall reflecting the low frequency waves into the annular region and also back into the entrance tube, the entrance tube forming part of the peripheral wall, and the exit port opening through the wall of the entrance tube.

19. Apparatus according to claim 18 in which the relecting wall is formed to deflect the stream annularly.

20. Apparatus according to claim 1 in which the silenc-ing chamber includes a pair of legs, and in which a deflector plates deflects the stream from one leg to another, the exit port being formed in the wall of one of the legs.

21. Apparatus according to claim 20 in which high fre-quency muffler means is provided having an inlet communicating to the exit port and an outlet communicating with the atmosphere for muffling high frequency noise components passed by the silencing chamber.

22. Apparatus according to claim 1 in which the muffler concentrically surrounds the silencing chamber.

23. Apparatus according to claim 22 in which the muffler and silencing chamber share a common wall.

24. Apparatus according to claim 1 in which the silenc-ing chamber concentrically surrounds the muffler.

25. Apparatus according to claim 24 in which the muffler and silencing chamber share a common wall.

26. Apparatus according to claim 1 in which the silenc-ing chamber and the muffler are substantially parallel and spaced apart from one another, and in which a tube interconnects the exit port of the silencing chamber to an inlet port of the muffler whereby the silencing chamber and the muffler can be placed on opposite sides of a chassis.

27. Apparatus according to claim 26 in which high fre-quency muffler means is provided having an inlet communicating to the exit port and an outlet communicating with the atmosphere for muffling high frequency noise components passed by the silencing chamber.

28. Apparatus according to claim 1 in which a catalytic element is placed in the exhaust stream downstream from the silencing chamber and upstream from the muffler means.

29. Apparatus according to claim 1 in which a cataly-tic element is incorporated in the muffler means.

30. Apparatus according to claim 29 in which a catalytic element is placed in the exhaust stream downstream from the silencing chamber and upstream from the muffler means.

31. Apparatus according to claim 27 in which the silenc-ing chamber, the catalytic element and the muffler means are axially aligned.

32. Apparatus according to claim 27 in which the cata-lytic element concentrically surrounds the silencing chamber.

33. Apparatus according to claim 27 in which the catalytic element and the muffler means concentrically surround the silencing chamber.

34. Apparatus according to claim 1 in which the silenc-ing chamber has a cross-sectional area greater than the entry port, whereby gas expansion occurs therein.

35. Apparatus according to claim 1 in which an expansion chamber is formed downstream from said exit port.

36. Apparatus according to claim 26 further including a motorcycle chassis, said silencing chamber and muffler means being mounted thereto and on opposite sides thereof.

37. Apparatus according to claim 36 in which high frequen-cy muffler means is provided having an inlet communicating to the exit port and an outlet communicating with the atmosphere for muffling high frequency noise components passed by the silencing chamber.