CA2121908C - Actively sound reduced muffler having a venturi effect configuration - Google Patents

Abstract

In an actively sound dampened muffler, the improvement of a venturi effect area (22) producing means adjacent an aperture (23) in said muffler near which is mounted a loudspeaker (25) in an enclosure (24), the venturi effect area (22) preventing hot exhaust gases from impinging on the loudspeaker (25).

Description

2 1 2 1 9 0 ~ PCr/US91/07831 Actively Sound Red4ced M~ffler havi~ a VPnt--ri ~ ect Confi~-ration In the design of active noise controlled ~urn~ a cC~ on problem is the res~lting lengthy P.xten~inn which protrudes beyond the main enclosure to the end of the vehicle res~lhng in an unattractive "snout". Beyond the physical undesirability of this eYten~ion there is a more serious problem created and that is the large acoustic air mass that resides in the snout. As this air mass is eA~ lcly fliffir,lllt to move to and fro at high frequencies the result is a small amount of anti-sound being g~,ne.~d.
To ovel.;oll.e this problem it is plu~osed to keep thè eYtçn~ion or snout short which reduces the moving m~ss. The solution has typically resulted in a co~fi~ration that has a very short link between the loudspeaker and the pipe and ~h~ the lou~l~pe~k~r is typically placed far from the engine for the benefit of reduced sound pl~,S~ul~ and ~e ..~ ....,. The controller can then cancel the exhaust noise provided only one aCo~stir mode can propagate in the eYhAn~t pipe over the control band vidth. The lûuA~e~kP,r encloslme volume may be reduced SO~ at and the rli~mptpr of the tail-pipe need not be larger than nnrmAl The l,lubl~,~s with this solutiQn were that the loudspeaker is subjected to high ~~ e a~u~s as well as the collo~iv~ effects of eAhaust gases.
To solve these residual l~lubl~,~s the instant invention manipulates the mean flow of the exhaust gases to cool the lo~ c~kPr enrlosllre. Either a full or partial venturi is used to ge ~ an area t_at is below Al...o~he ;c ~ Ul~. A bleed pipe allows ambient air to flow into t_is area thcreby cuu~ g the flow of eYh~nst gases into the speaker area A filtcr can bc provided in the bleed pipe to reducc the radiated noise. ~drlition~lly a heat shield can be employed to protect the lo~ kpr from the e~h~nst pipe or, in~ad a reflective coated layer that con~1uct~ sound. To prevent a sudden reversal of the cooling air the confi~lr~tion is dP~ignP~l to allow the cooling flow to ~..Ainl~h~ the exhaust gas conr~çntration in the front cavity at a re~on~hle level. A difluier section can - Q 2~21~8 be used to accomplish this as well as a contracted section followed immediately by an expansion section. Cooling can also be accomplished by using the cooling fluid of the vehicle or by using separate fans. Both would entail additional expenditures and add a degree of complexity to the configuration.
Therefore, it is an object of this invention to provide an improved muffler thatelimin~tes the long loudspeaker enclosure.
Another object of this invention is to provide an actively controlled noiseless muffler having a short connection between the exhaust pipe and the loudspeaker enclosure.
A further object of this invention is to an active noise cancellation system for an exhaust system wherein the diameter/size of the exhaust pipe can be of standard size.
A still further object of this invention is to provide an actively controlled muffler configuration that prevents ingestion of exhaust gases into the loudspeaker enclosure.
Yet another object of this invention is the provision of a venturi means in an 15 active noise cancellation exhaust system to create a differential pressure adjacent the speaker enclosure.
In accordance with one aspect of the present invention there is provided an actively noise cancelled muffler system comprising: an exhaust pipe having a front end and a rear end, for exhausting exhaust gases; an aperture in the exhaust pipe disposed 20 between said front end and said rear end of said exhaust pipe; an enclosure mounted adjacent said exhaust pipe and over said aperture containing at least one loudspeaker means adapted to produce opposite sound from that emanating from said exhaust pipe through said aperture; a venturi effect means in said exhaust pipe adjacent said aperture for generating a low pressure region in said exhaust pipe, said low pressure region being ~ e~

- 2a 1~ 2 1 2~ ~0 8 ~ below atmospheric pressure; a conduit means having a first end and a second end, said first end being disposed in said enclosure adjacent said low pressure region and said second end being spaced from said rear end of said exhaust pipe, for allowing ambient air to flow to said low pressure region to thereby prevent or inhibit any exhaust gases 5 from coming into contact with said loudspeaker means.
These and other objects of this invention not specifically enumerated herein will become apparent as reference is made to the following detailed discussion and drawings in which FIG. 1 is a diagrammatic view of a standard active noise cancellation muffler, 1 0 and FIG. 2 is a diagrammatic view of an improved configuration of an improved active noise cancellation muffler system and FIG. 3 is a diagrammatic view of an in-pipe or venturi configuration in an improved active noise cancellation muffler, and FIG. 4 is a diagrammatic view of a venturi nozzle configuration in an active noise cancellation muffler to reduce radiation heating, and r''A

W O 93/09334 2 ~ O ~ PC~r/US91/07831 Fig S is another dia~"..~ view of an in-pipe or venturi configllration in an o~ed active noise cQnrÇllQtion muffler showing a SC~)~alc~ heat shield, and Fig 6 is a ~liQe.~...,.AI;c view of a partial venturi nozzle configl--ation in an active noise c~ncell-A~tis)n muffler.
RPferring to the figures, Fig 1 shows a state-of-the-art active noise cAncellQtion muffler having an eYh~n~t pipe 1, a speaker enclosure 2 conlA;ni~g a loud~aker 3 and having an extPnC-ion which is co-axial and larger than pipe 1 and which also extends back beyond fender 5 and tçrminAtes in the same plane as pipe 1.
Demands on the pel~ol ~ nce of the llwrn~r suggest that the loudspc~kers must function up to 500Hz and this causes conci(1erable l foblc lls in the design of the lou~cpeQkPr units for the following reasons:
(a) The current design of the active muffler re 4Uil~S the lolldcpeQkPr units to be positionPA in front of the rear fender, and yet the exit ~om the loudcpeQker çnClosllre must be at the end of the muffler pipe which is behind the fender.
(b) Inevitably, this leads to a "snout" on the e~ G~ , that is several inches long, and the acoustic mass of the air in the snout is cQnci~pr-Qble (c) At high LAluellcies it is ~lifficult to move the slug of air in the snout bs~kw~ ls and forwards sllffiriçntly to ~,e,n~,~dlc; much anti-sound. This ,cquil~s a very small volume t~ . ~n the loudspea_er and the snout, and results in a a very large magnet QcsPmhly for the lou-lcpeQkPr unit.
In order to avoid the large moving mass of the snout, it is essçntiQl to keep the snout very short indeed, and this precludes the use of the culTent design.
Fig 2 shows an i~lo~ed system wherein the noise is cQnr~Pllpll directly in the muffler pipe. FYhQllCt pipe 11 is directly open to enrlQsllre 12 co~ g lo~ cpeQkPr 13. There is no long ex~P~ nci~n or snout and the advantages of this cQnfi~lrdtion are (a) the link bet~. ~n the loudspeaker and the pipe can he very short, ~ Çor red-lcing the moving mass;

W O 93/09334 2 1 2 1 ~ 0 8 PC~r/US91/07831 (b) The active system can be placed at any c~n~ ~nt loc~tinn in the muffler pipe (~lthough far ~om the engine has the b.,ll~,rlla of reduced sound ~l~,sa~uc and L~ a~u~c);
(c) provided only one acoustic mode can propagate in the exhaust pipe over the control bandwidth, the controller can in principle "cancel" the exhaust noise perfectly; this is not the case with the state of the art configuration because the source and anti-source are not quite coinridrnt (d) the .li~ te. of the tail-pipe on the muffler need be little, if any, larger than it would be on a passive system;
(e) overall loudspeaker enrlosnre volume is reduced so~ a~.
The main disadvantages of this improved confi~ A~ , ho.._~,r are:
(a) the _igh t~,~p~a~ that the lo~lflcpç~ker unit might be subject to;
(b) ingestiQn of eYh~ t gases into the front cavity or the lo~ld~c~k~r enclosure and consequent corrosion.
In order to circumvent these problems, the present invention manipulates the mean flow of the exhaust gases to force a clean, cooling airflow through the front (and/or back) cavities of the lo~lds~aker enclrsll.e. One confi~lration is shown in figure 3.
An exhaust pipe 21 has a ,c.luced section as at 22 so as to ~lo luce a low plessulc region at opening 23 into enrlos~lre 24. Loudspeaker 25 is ...b~ A in enrlos~e 24 so as to cancel, by counter-sound, noise ~,...~nz.~;ng at the exit 28.
The smooth c~n~ clior/e~r~n~ion (a "venturi") 22 is used to g~ e locally in the pipe a region that is below atmospheric l~lesa~c. A bleed pipe 26 in the ~ont cavity of the lo ~ er enclos~l~e 24 pennits air from outside to flow ~ ds the low pl~,SaUlc region, thereby l~ cing ingestion of exhaust gases into the ~ ker e"-~lGs~c, and also providing cooling.

By keeping the e.,L,~ce 27 to the bleed pipe a little away ~om the çxh~n~t exit 28, a cleaner flow will result, and help to reduce corrosion. On the other hand, some W O 93/09334 21219 0 ~ PC~r/US91/07831 sound will escape from the bleed pipe, and it is adv~nt~geous to position the en~lce of the bleed pipe close to the residual error microphone 29 so that the control system will "cancel" the co .hine~ sound of the exhaust and bleed pipe noises. If pipe 26 is quite long, and not too large in ~i~mçter~ r~i~tion will not be very strong and will be very frequency selective. The ~rlition of a filter in the bleed pipe could also help to reduce the radiated noise. When r~di~tion from the bleed pipe is not a ~lublem, its entrance can be placed WLe~ iS convenient.
Bleed-pipe routing should avoid water traps ("sumps"), and it may be possible for the bleed pipe to drain the loudspeaker enclosure in the event of flooding.
To avoid having the lollA~pe~kt~r unit(s) face directly into the hole in the muffler pipe since r~ tiQn of heat from the hot gasses could then directly heat the loudspe~ker diaphragms (this may not be a serious ~luble~ as the e~si~ily of the gas is likely to be much lower than that of the pipe), the hole 42 in the l~luf~r pipe 41 is arranged so that the loudspea_er is ~hirlrlç~ by the muffler pipe itself. See figure 4. A bleed pipe 45 conduct~ a cooling flow into speaker enclos~lre 44.
As shown in Fig S a sep~r~t~ heat shield 52 can be used in colljullc~ion with exhaust pipe 51 with its ope.ning 53 across from lou~1~pePk~r 54 in speaker enclosllre 55.
A cooling flow is brought in through cooling bleed pipe 56.
The heat shield can be a reflective coated subi~l.alulll that is aco~l~tir~lly transparent (e.g. a coated "foam"; overlapping, s~a~a~d grids etc.) and span most or all of the width of the front cavity, or it can be a solid shield just large enough to "shadow"
the ~ rhr~rn from the hot co.-ll,ollellt~ without i~ c;.~g sig,~;r~anl ~~ousl;c blocl~e It can be ~d~ just to have a reflective coating on h~st-sellsili~ parts such as the ~ phr~grn The crucial aspects of this design are:
(a) ~n~,la~ing the cooling flow with the ~--;n;-------- ba~ ;,sul~ for the e~rh~nct flow; and WO 93/09334 ~1219 0 8 6 PCI'/US91/07831 (b) the de.t~ fluid ,..f~h~ s of the flow through the section in order to ~~
reduce turbulence, in~stinn of gases into the lou~ kPr enc10s11re (despite the cooling flow), flow-excited instabilities and flow noise.
Although on average the cooling flow will be flowing into the muffler pipe, the strong osc~ tory COlllpollCl~L in the muffler flow and the anti-sound may cause the flow to reverse inct~n~ ously and ingest exhaust gases into the lou~l~pe~k~P çn~ 1os11re. This is not a problem provided that on average the cooling flow keeps the exhaust gascol~r,e ntl aLion in the front cavity at a rea~sn~ble level.
The cl~ c~l venturi arrAngempnt of a smooth conL.~Lion followed by a dirruser section is not the only way of pro~ucing a low p,~su ~ region in the muffler flow (although it is a good one), for eYAnlrlP a cont~tion followed by an abrupt e~l.Ancinn will also work, but with potP-nti~11y higher back~ u~ pe~nnltiçs~ One PY~mr1e of an ~lte n~tive to the full venturi is ~1" tch~A in figure 6. The ~.. ;n~ ,le of the idea is that the mean flow of the eYhAll~t gasses is manipulated in such a way that an auxiliary cooling flow can be ~e~ t~yl An eYhaust pipe 61 is shown to have a partial venturi effect pl~luced by split ope-ning 62 which opens the pipe to speaker en~1os~1re 63 co~l~;..;ng 1ou~<-Al~P~r 64 and bleed pipe 65.
Forced cooling of the ~ c-~AlrPrs by e.g. fans can obviously be done, but this would inG~P~e the corr~lie~tion and cost of the system. It is also possih1e to use the car's f~ l motion to drive a cooling flow over the 1~vA~ but this would not work with the car st~tinn~ry. Cooling with fluid (e.g. by tapping into the engine-cooling circuit) will also work, again at the cost of comr1PYity~ but it might be ~lim( 111t to get suffirient cooling on moving parts such as the diaphragms.
Having clescrihell several aspects of the in~e..Lion it is ~ntirir~ted that other v3ri~tinn~ will occur to those of or~ ~y skill in the art without d~,p~ling from the scope of the appended claims.

Claims (4)

Claims:

1. An actively noise cancelled muffler system comprising:
an exhaust pipe having a front end and a rear end, for exhausting exhaust gases;
an aperture in the exhaust pipe disposed between said front end and said rear end of said exhaust pipe;
an enclosure mounted adjacent said exhaust pipe and over said aperture containing at least one loudspeaker means adapted to produce opposite sound from that emanating from said exhaust pipe through said aperture;
a venturi effect means in said exhaust pipe adjacent said aperture for generating a low pressure region in said exhaust pipe, said low pressure region being below atmospheric pressure;
a conduit means having a first end and a second end, said first end being disposed in said enclosure adjacent said low pressure region and said second end being spaced from said rear end of said exhaust pipe, for allowing ambient air to flow to said low pressure region to thereby prevent or inhibit any exhaust gases from coming into contact with said loudspeaker means.

2. A system as in claim 1, further comprising a depressed cross-sectional area in said exhaust pipe, said aperture contained in a section of said exhaust pipe opposite said depressed cross-sectional area.

3. A system as in claim 1, wherein said venturi effect means is a reduced cross-sectional area of said exhaust pipe.

4. A system as in claim 1, wherein said conduit means is a bleed pipe.