AU622158B2 - Active sound attenuation system for engine exhaust systems and the like - Google Patents

Description

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1 1 i I: OPI DATE 06/09/89 0 J DP" SW 810/ 8 9 liT NA (51) International Patent Classification 4 F01N 1/06 APPLN. ID 31944 89 PCT NUMBER PCT/US89/00665 TREATY (PCT) (11) International Publication Number: WO 89/ 07701 Al (43) International Publication Date: 24 August 1989 (24.08.89) (21) International Application Number: PCT/US89/00665 (22) International Filing Date: 17 February 1989 (17.02.89) (31) Priority Application Number: 158,883 (32) Priority Date: (33) Priority Country: 19 February 1988 (19.02.88) (72) Inventors; and Inventors/Applicants (for US only) GARDNER, John, W. [US/US]; 3105 Weller Road, Silver Spring, MD 20906 ZIEGLER, Eldon, Jr. [US/US]; 10092 Hatbrin Terrace, Columbia, MD 21046 (US).

(74) Agent: EVENSON, Donald, Barnes Thornburg, 1815 H Street, 8th Floor, Washington, DC 20006 (US).

(81) Designated States: AU, BR, DE (European patent), FR (European patent), GB (European patent), IT (European patent), JP, KR, SE (European patent), SU, US.

Published With international search report.

Parent Application or Grant (63) Related by Continuation

US

Filed on 158,883 (CIP) 19 February 1988 (19.02.88) (71) Applicant (for all designated States except US): NOISE CANCELLATION TECHNOLOGIES, INC. [US/ US]; 10015 Old Columbia Rd., Ste. F100, Columbia, MD 21046 (US).

(54) Title: ACTIVE SOUND ATTENUATION SYSTEM FOR ENGINE EXHAUST SYSTEMS AND THE LIKE 19 8 1 8 9 19 y. 2 DIGITAL POWER CONTROLLER AMPLIFIER (57) Abstract .An active sound attenuation system for combustion engine exhaust systems and the like is disclosed. The system includes counter-noise acoustic wave generators (19) that are protected from the environment of a medium propagating undesireable noise by an acoustically tuned anti-noise chamber 11) interposed between the wave generators (19) and the medium with the undesirable noise. To provide for noise cancellation at an outlet end of an exhaust pipe (10) the antinoise chamber 11) has an annular opening disposed substantially in the plane of the exhaust pipe outlet thereby giving an effective common point source for the propagated undesirable noise and the counter-noise acoustic wave.

i i i I i WO 89/07701 PCT/US89/00665 ACTIVE SOUND ATTENUATION SYSTEM FOR ENGINE EXHAUST SYSTEMS AND THE LIKE of which the following is the specification.

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ACTIVE EXHAUST MUFFLER Backniound and Summary of the Invention The present invention is related to an improved arrangement for reducing intake and/or exhaust noises from combustion engines and the like. More specifically, the present invention relates to a new sound attenuation arrangement for such apparatus which uses anti-noise or counter-noise acoustic wave generators to attenuate the sound generated in such apparatus. Various aspects of the present invention can be utilized in attenuating sound in combustion engine intake and exhaust systems, in compressors, and in pumps and the like.

The preferred embodiment of the invention described refer primarily to combuvtion 1 0 engines, however, it is to be understood that the invention is adaptable to attenuate sound in other arrangements exhibiting similar noise generating configurations such as in the intake and exhaust of certain compressor and pumps and the like.

Numerous passive systems for suppressing noise at the intake and/or exhaust of gas movement systems have been proposed previously. Such passive systems use sound :'15 insulating material and/or baffles to suppress sound waves before they reach the S..surrounding atmosphere. These so-called "passive systems", such as conventional Sautomative gas mufflers, inherently restrict the exhaust gas flow, thereby resulting in i energy losses with reductions in the efficiency of operation of the vehicle contribution engines. It is well known to those skilled in the art of internal combustion engines that 2 0 reduction or removal of the *I ei j r ooooo* •go• •go o^^oo oo0 r

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ooo° I i WOo 89/07701 PCT/US89/00665 exhaust gas restriction back pressure substantially improves the performance of the engine. However, permitting such "straight pipe" operation of automotive vehicles results in sound patterns in public places that are not only unpleasant, they are unhealthy. For these reasons, virtually every industrialized nation has restrictions on the level of noise propagation that can be generdted by automotive vehicles and other machinery operating in public places. To date, in order to satisfy these noise abatement restrictions, virtually all automotive vehicles have relied on the passive muffler systems with consequent reduction in engine efficiency. Coupled with the reduction in engine efficiency there is of course inherent increased pollution due to increased hydrocarbon fuel consumption.

So-called "active" noise-cancellation systems have been proposed in the past and adapted to certain environments on a small scale, usually environments involving relatively constant frequency sound generation pattern of the type that might be experienced in a fixed combustion engine constant velocity operating for a generator station or the like. U.S. Patents 4,122,303; 4,489,441; and 4,527,282 to Chaplin et al. disclose various aspects of active noise cancellation systems. French Patent 1,190,317 to Sherrer; U.S. Patents 4,677,676 and 4,677,677 to Eriksson, and U.S. Patent 4,473,906 to Wannaka disclose additional methods for active noise cancellation in building system air ducts or exhaust pipes in which the cancelling noise generator (speaker) is required to be exposed directly to the exhaust gas stream. Those systems requiring placement of the speakers in the exhaust gas stream generating the undesirable

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WO 89/07701 PCT/US89/00665 sound to be cancelled place the speakers in such a harsh chemical and heat environment that they cannot operate over an extended period of time, at least not without inordinate costs for insulating the speaker and/or designing them to withstand the loud environment. Further, such placement restricts the flow of exhaust gases to some extent, thereby resulting in the above-mentioned disadvantages regarding the back pressure on the combustion engine. Furthermore, those prior art systems that have been utilized in exhaust environments do not exhibit the compactness to facilitate commercialization and use on automotive and marine passenger vehicles and also do not have control systems that are responsive to the varying noise spectrum generated during the normal driving of such vehicles, with acceleration and deceleration over a wide range of vehicle engine speeds.

An object of the present invention is to provide an improved active noise cancellation system that is compatible with the operating conditions of motor vehicle combustion engine exhaust systems and the like. Another object of the invention is to provide a system that will suppress noise generated from rapidly changing noise sources such as experienced in motor vehicle exhaust systems during normal driving operations and the like.

Another object of the invention is to provide a compact, economical to manufacture sound cancellation system that can be incorporated into mass production vehicles with a consequent substantial reduction in the overall costs of operating such vehicles as compared with vehicles having conventional passive muffler systems.

WO 89/07701 4 PCT/TJS89/00665 These and other objects are achieved according to the invention by providing a sound attenuation system which exhibits one or more of the following characteristics: an anti-noise chamber is interposed between the anti-noise acoustic wave generators and the fluid guide system for the fluid medium propagating the undesirable noise, thereby protecting the anti-noise acoustic wave generators from any harsh environment of the undesirable noise propagating medium; (ii) the anti-noise acoustic wave generators open into an acoustically tuned anti-noise chamber which in turn opens to the fluid medium propagating the undesirable noise thereby enhancing the effective efficiency of the anti-noise acoustic wave generator; and (iii) the anti-noise acoustic waves are introduced into the medium propagating the undesirable sound at a position so that the effective source of both the undesirable sound and the anti-noise sound is substantially nearly coincidental, thereby enhancing efficient global cancellation of the undesirable sound.

In certain preferred embodiments of the present invention an active noise attenuation system is so constructed as to avoid the placement of the anti-noise acoustic wave generators into the environment of fluid flow propagation the undesirable noise, such as the harsh environment of the exhaust gases of a vehicle exhaust system. In especially preferred embodiments, the attenuation system includes an anti-noise chamber which surrounds over a portion of its length, a centrally disposed engine exhaust pipe, with the anti-noise chamber and exhaust pipe opening to atmosphere I..I 2 w Roe/77fl PrT/~TasO/nhfri in substantially the same plane, and at least within a length corresponding to less than one third of the shortest wave length of the undesirable noise to be attenuated. The anti-noise speakers open into the anti-noise chamber, which is totally isolated from the exhaust pipe and thereby the speakers are not subjected Lo the harsh chemical and heat environment of the exhaust gases.

In certain especially preferred embodiments for use with automotive exhaust systems, the anti-noise chamber is constructed as an acoustically tuned annular chamber concentric with the exhaust pipe. In especially preferred embodiments, the anti-noise speakers are symmetrically arranged around the axis of the exhaust pipe and anti-noise chamber. The anti-noise chamber is constructed as a first, relatively large diameter section which is closed off at one end by an annular supporting plate that is connected to the exhaust pipe, the speakers being mounted adjacent that end plate. The anti-noise chamber then extends in the downstream direction of the exhaust pipe and opens at the same plane as the atmospheric outlet of the exhaust pipe, thereby providing an effective coincidental sound source for both the anti-noise sound waves and the undesirable sound waves from the exhaust pipe, with consequent "global" noise cancellation.

According to certain preferred embodiments of the invention, the anti-noise acoustic wave generators are controlled by a digital controller which has inputs from a synchronization sensor monitoring the engine rotational speed and a residual sensor microphone which picks up the sound at the outlet of the exhaust pipe. These sync sensor and microphone signals are processed by -x~ "1 o A WO 89/07701 7 PCT/US89/00665 the controller and drive power amplifiers for the anti-noise speakers.

According to other preferred embodiments of the control system for the anti-noise acoustic wave generators, an upstream sensor microphone picks up the sound in the exhaust pipe upstream of the location of the anti-noise chamber and feeds its signal to the digital controller, the other signal to the controller being from a residual sensor microphone at the outlet end of the exhaust pipe. As in the other embodiments referred to in the immediately preceeding paragraph, the digital controller processes this sensed information and accordingly controls and drives the anti-noise acoustic wave generators to cancel the sound.

Although the preferred embodiments descrbied involve vehicle combustion engine exhaust systems, preferred embodiments of the invention are also contemplated for engine intake systems, for compressors and pumps with undesirable sound waves propagated in a pipe exhausting to atmosphere, and the like.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side view of a passenger vehicle d:picting the location of the engine exhaust system and a digital muffler system constructed according to a preferred embodiment of the present invention; t 1 1 1 1 1 1 J 1 1 1 1 1 1 1 WO 89/07701 PCT/US89/00665 Figure 2 is a schematic bottom view of the vehicle of Figure I depicting the vehicle exhaust system and active digital muffler system constructed according to a preferred embodiment of the present invention; Figure 3 is a side schematic view of a motor boat equipped with another preferred embodiment of the present invention; Figure 4 is a schematic view showing the engine, exhaust system and active digital muffler system for use with the boat of Figure 3; Figure 5 is a schematic perspective view of an exhaust muffler arrangement constructed according to a preferred embodiment of the present invention; Figure 6 is a longitudinal section view of the muffler arrangement of Figure Figure 7 is an end view taken from the right side of Figure 6; Figure 8 is a view similar to Figure 6, showing an alternative of the exhaust muffler arrangement of the present invention, having an intermediate exhaust gas low pressure cooling chamber; Figure 9 is an end view from the right side of Figure 8; Figure 10 is a schematic depiction of a complete active digital muffler system constructed according to a preferred Sembodiment of the present invention; Figure 11 is a schematic depiction of a complete active digital muffler system constructed according to another preferred embodiment of the present invention; Figure 12 is a graph comparing test results on a vehicle with a diesel engine, showing the sound spectrum at the exhaust with i/ I, WO 89/07701 PCT/US89/00665 and without noise attenuation using the system of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Figures 1 and 2 schematically depict respective side views and bottom views of a passenger motor vehicle having an active digital muffler system constructed according to preferred embodiments of the present invention. The system depicted in Figures 1 and 2 corresponds to the Figure 10 embodiment of the overall system (described in more detail below). The passenger vehicle 1 includes a multi-cylinder/piston internal combustion engine 2, the exhaust of which is transported by exhaust pipe system 3 to the exhaust outlet 4 at the rear of the vehicle. The rear portion of the exhaust pipe system 3, is depicted as a single exhaust pipe in the following description, although similar duplicate arrangements can be provided for dual exhaust pipe systems, is provided at its rear end with a surrounding anti-noise chamber arrangement 5, which includes anti-noise speakers driven by a power amplifier 6 and digital controller 7. The digital controller 7 has input signals from a residual sensing microphone 8 adjacent the exhaust outlet 4 and a synchronization sensor 9, such as a tachometer at the drive shaft of the engine 2.

Figures 3 and 4 schematically depict a preferred embodiment of an active digital muffler system according to the invention installed on a motor boat 1A, which, in a similar manner as the passenger motor vehicle of Figures 1 and 2, includes a reciprocating piston multi-cylinder internal combustion engine 2A, I I o 1 L- -il :I 1 WO 89/07701 /d PCT/US89/00665 an exhaust pipe system 3A with an outlet 4A. An anti-noise chamber arrangement 5A is provided adjacent the downstream end of the exhaust pipe system 3 and includes speakers driven by a power amplifier 6A and controlled by a digital controller 7A. The digital controller 7A is in turn supplied with input signals from a residual sensor microphone 8A, the exhaust outlet of the boat motor and a synchronization sensor 9A of the output drive shaft of the boat motor engine 2. Certain embodiments for use with boats will include water supplied exhaust system cooling arrangements, such as water flow directly into the exhaust pipe and water flow in an annular jacket surrounding the exhaust such cooling arrangement being well known in the motor boat industry.

The following description of the details of the anti-noise chamber arrangement surrounding the exhaust pipe and the controller circuit for controlling the same is similar for the embodiments for both the over the road passenger motor vehicles of Figures 1 and 2 and the motor boat of Figures 3 and 4. It will be understood by those skilled in the art that certain components in the motor boat environment need to be "marine" qualified to withstand salt sea air and the like.

Figures 5-7 schematically depict a first preferred embodiment of an anti-noise chamber arrangement 5 and exhaust pipe. Chamber of Figures 6-7 is constructed as an intregal sheet metal structure and includes a centrally disposed cylindrical exhaust pipe 10 which is connected to the exhaust pipe system 3, 3A (compare Figures 1 to The left hand end of the exhaust pipe section 10 is preferably configured so as to be insertable into an existing exhaust pipe of an engine exhaust system 3,3A, with an appropriate sealing clamping connection being provided. WO 89/07701 j/ PCT/US89/00665 An anti-noise chamber 11 is provided in annular surrounding relationship to the exhaust pipe 10. The anti-noise chamber 11 is defined by first cylindrical section 12 of a large diameter and an adjoining smaller diameter section 13. The left hand end of the large diameter section 12 is closed off by an annular end plate 13 which is supported at the outer surface of the exhaust pipe 10 by welding connection 14. The opposite end of the anti-noise chamber 11 is supported by radially extending support plates 15 attached by welding 16 at the exhaust pipe 2 and by welding 17 at the anti-noise chamber 13. A pair of cylindrical speaker support sections 17 are connected by a welding connection 18 to the cylindrical section 12 at a position adjacent the end cap 13. In the illustrated embodiment the cylindrical speaker support sections 17 have a slightly smaller diameter than the diameter of the section 12 of the anti-noise chamber and are there joined by welding seams 18. These anti-noise speaker support cylinder sections 17 are disposed symmetrically with respect to the longitudinal axis of the exhaust pipe 10 and anti-noise chamber 11. Anti-noise speakers 19 are mounted in each of the respective support section 17 and are disposed to generate sound waves emenating into the anti-noise chamber 11. The anti-noise chamber 11 is concentric and to separate from the exhaust pipe 10, with S the anti-noise sound waves generated by the speaker 19 and propagated along the length of the member 11 opening into the atmosphere at the same exit plane 4 as the exhaust gases from the exhaust pipe By arranging the speakers 19 to be symmetrical with the longitudinal axis of the exhaust pipe 10 and by providing the 1 I WO 89/07701 PCT/US89100665 anti-noise chamber 11 as an annular chamber surrounding the pipe the manufacture of the anti-noise muffler chamber arrangement is quite simple and it can be constructed as a unit that can be added on to an existing exhaust system 3 merely by connecting the left hand end of the pipe section 10 to the exhaust pipe of a vehicle. In especially preferred embodiments, the exhaust pipe 2 and the cylindrical sections 12, 13 making up the anti-noise chamber 11 and the speaker supports 17 are all constructed of metal that can be easily welded together, thus further simplifying the manufacturing operation. Embodiments are also contemplated with a heat insulating connection at the exhaust pipe 10 such as an annular heat insulating material ring surrounding the pipe which limits the transfer of heat to the components. Since the speakers 19 are disposed symmetrically with respect to the noise generating exhaust pipe 10, an especially efficient utilization of space and cancellation of noise is provided since ther is symmetrical disposition-of the anti-noise waves around the annular space at the outlet end 4 of the muffler pipe arrangement. Since the noise cancelling sound waves emanate in substantially the same plane or the exhaust gases, the anti-sound wave propagation is symmetrical with the sound wave propagation from the exhaust pipe outlet, thereby simplifying the construction and operation. The speakers 19 are also isolated by chamber 11 from the exhaust g. ases and thereby do not have to withstand the highly corrosive hotgases in the exhaust stream.

Other preferred embodiments are contemplated which utilize S only a single speaker opening into the acoustically tuned chamber 11, the annular outlet at plane 4 effectively providing an Z tS !i .WO 89/07701 PCT/US89/00665 appropriate effective common point source for the cancelling and undesired sound. The additional speakers of the preferred embodiments illustrated facilitate the use of smaller speakers for the same output, thus economizing space. Also embodiments are contemplated where the speakers are remote from the chamber 11, with the sound waves transmitted by ducting 'o open into chamber 11, such arrangements being practical where space considerations are important such as in passenger automobiles, and the like.

In an especially preferred practical embodiment, the dimensions are as follows referring to Figure 6: diameter 10 of the exhaust pipe 10 is 2.250 inches inside diameter, the length 13 between end plate 13 and the left end of the pipe 10 is 2 inches, the radial width 12R of the chamber section 12 outside of the pipe 10 is 1.75 inches, the radial width 13R between the outside of the pipe and the outer wall of cylindrical section 12 is .75 inches, the radial length of the speaker support sections 17, 17R is 2.5 inches, the diameter of the cylindrical sections 17, 17D is inches, the distance between the edge of the sections 17 and the end chamber section 12, 12L is 4.75 inch.es, and the length 13L of the section 13 is 5 inches.

The embodiment of Figures 8 and 9 is the same as the embodiment of Figures 5 through 7 described above, except for the IIIi~ PCT/US89/00665 WO 89/07701 1 WO 89/07701 PCT/US89/00665 addition of an intermediate low pressure cooling exhaust gas chamber 20 between the anti-noise chamber 11A and the exhaust pipe. In Figures 8 and 9, like reference numerals with a suffix A will be included to designate corresponding structure from the embodiment of Figures 5 through 8. These structures are described only to the extent that they function differently from the corresponding structure embodiment of Figures 5 and 8. The annular intermediate chamber 20 is communicated with the exhaust pipe 10A by eight radially extending 1/8 inch diameter holes 21 in the pipe 10A. The holes 21 are disposed at the upstream end of the anti-noise chamber 11 and allow a small amount of cooling air to be sucked in by the exhaust gas flow through the opening at end plane 4A so cooling air flows in chamber 20 counter to the direction of flow of the exhaust gases and then into the exhaust pipe. The radially ex.tending reinforcing plates 15 extend also through the end portion of this chamber 20 and support the respective concentric pipes forming same. The cooling air flow communicated to the exhaust pipe through openings 21 also aid in reducing the turbulence of the exhaust gases that exit from the exhaust pipe 10A and thereby further reduce over all noise levels.

Figure 10 schematically depicts a first embodiment of a control system for the active digital muffler system of the present invention. A synchronization sensor such as an engine tachometer 9 provides'synchronization signal inputs to a digital controller 7 which is also supplied by a residual sensor microphone 8 which picks up the actual sound wave pattern downstream of the outlet 4 of the exhaust pipe 10 and the anti-noise chamber 11 the controller 7 controls power amplifier 6 *7 1 i 1 1 *N 1 1 11 1 1 1 1 1 WO 89/07701 PCT/US89/00665 which in turn drives the speakers 19 to generate the noise-cancelling waves in the chamber 11, which then travel to the outlet plane 4 of the exhaust pipe 10 and effect cancellation of the sound waves amenating from the pipe outlet. In especially preferred embodiments, the audio power amplifier 6 is integrated with the digital elec--onic controller 7. The digital controller can utilize a frequency domain alogorithm as described in U.S.

Patent 4,490,841 by Chaplin. Alternatively, the digital controller can utilize a time domain alogorithm as described in co-inventor Eldon Ziegler, Jr.'s pending U.S. Patent Application Serial No. 238,188 filed on August 30, 1988.

A practical speaker and microphone usal e with a configuration as in Figures 5-7 or 8 and 9 has the following characteristics.

MAGNET FLUX DENSITY 11,000 GAUSS TOTAL FLUX 58,000 MAXWELLS SENSITIVITY 96dB spc@ Im, 11.2 v RMS THEIL-SMALL PARAMETERS 2 SD 92 cm

M

D 9.8 gm XD 6 mm peak to peak f 37 HZ s Rms 1 l -3 Cms 1.8 x 10 3

M/N

S' VAS 23.6 liters QM =2.44 QE 0.38 QT 0.33 11 i 1 1 1 1 1 1 1 1 i 11 i WO 89/07701 PCT/US89/00665 IMPEDANCE 8 RANGE 55 H Z to 3,500 H

Z

NET WEIGHT 1.13 kg.

MICROPHONE

FREQ. RESPONSE 20 13,000 HZ IMPEDANCE 600 SENSITIVITY -71dB 1 (REF OJB Iv//bar, 1KHZ) POWER 1.5 VDC to 20 VDC- A second control system for the active digital muffler system is schematically depicted in Figure 11. Since the Figure 11 system only differs from the Figure 10 system in the utilization of an upstream sensor microphone 22, in lieu of the tachometer synchronizing sensor 9, the remaining structure is depicted by similar reference numerals as in Figure 10. Similarly to the Figure 10 embodiment, either of a frequency domain alogorithm controller or a time domain alogorithm controller can be utilized. The difference between the Figure 10 and 11 S embodiment being that the input from microphone 22 is utilized instead of the input from a tachometer sensor 9 as in Figure It is further noted that a controller corresponding to the NCT 20CO controller marketed by Noise Cancellation Technologies Inc., can be used to serve as controller 7.

1 1 1 1 1 f WO 89/07701 PCT/US89/00665 Figure 12 is a graphical comparison showing a dramatic reduction in noise levels utilizing the active digital muffler system on a diesel engine, as compared with operating the same diesel engine without cancellation. In Figure 12 the upper graph shows the noise levels without cancellation and the lower graph shows the noise levels with cancellation. The following is a Table of the experimental results shown on the Figure 12 graph.

MARK

0 1 2 3 4 6 7 8 9 LIST X 90.000 104.99 120.00 135.00 150.00 165.00 180.00 240.00 270.00 360.00

Y(U)

-18.0 -45.3 -45.9 -41.8 -38.3 -45.9 -24.8 -36.1 -40.8 -46.1

Y(L)

-44.5 -51.8 -53.4 -59.7 -60.3 -56.0 -49.4 -58.2 -58.2 -52.2 From the Table and the graph, one can see substantial noise level reductions, e.g. 26 decibels at mark 0 at 90 HZ frequency with the engine exhaust noise silenced by the sound attenuation system by the present invention, the passive muffler can be deleted from the vehicle exhaust pipe system. Deletion of the passive muffler (so-called "straight pipe" operations) results in remarkable increases in engine efficiency and power, as is known to those skilled in the art of automotive internal combustion engines.

wo 89/07701 PCT/US89/00665 Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.

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Claims (21)

1. An active noise suppression system for exhaust of a combustion engine comprising: an exhaust transfer pipe coupled to the combustion engine and having first and second ends for transferring exhaust gas in a first direction from the combustion engine to ambient atmosphere, said first end receiving the exhaust gas from the combustion engine and said second end emitting the exhaust gas to the ambient atmosphere; an anti-noise chamber annularly surrounding an outer periphery of said exhaust transfer pipe and having an outlet open to the ambient atmosphere adjacent said second end of said exhaust transfer pipe for projecting anti-noise sound waves through said outlet to the ambient atmosphere; an anti-noise speaker, mounted to said anti-noise chamber for communication therewith, for generating and projecting said anti-noise sound waves into said anti-noise chamber to cancel noise generated by the combustion engine exhaust; and separation means for isolating said anti-noise chamber from exhaust gas.

2. An active noise suppression system according to claim 1, further comprising S another anti-noise speaker, said anti-noise speakers being disposed on said anti-noise chamber at opposed axial positions with respect to said exhaust transfer pipe upstream of said second end of said exhaust transfer pipe. S 3. An active noise suppression system according to claim 2, wherein said anti- noise chamber is acoustically tuned and has a large diameter section joined to a smaller diameter section, said anti-noise speakers being mounted to said large diameter section, said smaller diameter section extending along said exhaust transfer pipe to said second end.

4. An active noise suppression system according to claim 3 wherein a front end of j said large diameter section is closed off by an annular plate connected to an outer portion of said exhaust transfer pipe, an outlet end of said smaller diameter section serving as said outlet of said anti-noise chamber which is supported from said exhaust transfer pipe by radially extending support plates. IT oI Y! :iI~ i An active noise suppression system according to claim 1 wherein said anti- noise chamber is symmetrically configured with respect to a longitudinal axis t! rough a center of said exhaust transfer pipe.

6. An active noise suppression system according to claim 5, wherein said exhaust transfer pipe and said anti-noise chamber are cylindrical and concentric with respect to said longitudinal axis.

7. An active noise suppression system according to claim 1, further comprising a cooling chamber, disposed annularly between said exhaust transfer pipe and said anti-noise chamber, for drawing cooling air from the ambient atmosphere into said exhaust transfer pipe to cool said exhaust gas within said exhaust transfer pipe, said separation means comprising an outer wall of said cooling chamber.

8. The active noise suppression system according to Jlaim 7, wherein said cooling chamber draws cooling air inward from adjacent said second end of said exhaust transfer pipe to flow n a second direction opposite the flow of exhaust gas through said exhaust transfer pipe in said first direction.

9. An active noise suppression system according to claim 8, wherein said exhaust transfer pipe has air flow openings for passing said cooling air from said cooling chamber into said exhaust transfer pipe, said air flow openings being symmetrically disposed about a circumference of said exhaust transfer pipe. An active noise suppression system according to claim 9, whereinjair flow openings are comprised of at least four separate radial openings. S11. An active noise suppression system according to claim 9, wherein said air flow openings are comprised of eight separate radial openings.

12. The active noise suppression system according to claim 1, wherein the combustion engine is an internal combustion engine. I i i,;

13. An active noise suppression system according to claim 12, wherein the combustion engine is a driving engine for a motor boat.

14. An active noise suppression system according to claim 12, wherein the combustion engine is a driving engine for a motorized road passenger vehicle. An active noise suppression system according to claim 1, wherein the combustion engine has an exhaust pipe for delivering the exhaust gas to said first end of said exhaust transfer pipe, said first end of said exhaust transfer pipe being insertable into said exhaust pipe and permanently affixable thereto by clamping seal means.

16. An active noise suppression system according to claim 15, wherein said exhaust transfer pipe, said anti-noise chamber and said anti-noise speakers are integrally constructed within a unitary sheet metal housing. o o

17. An active noise suppression system for exhaust of a combustion engine oooo -I comprising: ~an exhaust transfer pipe coupled to the combustion engine and having first and S second ends for transferring exhaust gas in a first direction from the combustion engine to ambient atmosphere, said first end receiving exhaust gas from the combustion engine and said S" second end emitting the exhaust gas to the ambient atmosphere; passive noise reduction means surrounding an outer periphery of said exhaust transfer pipe, for reducing noise generated by the combustion engine and exhaust gas turbulence by cooling the exhaust gas within said exhaust transfer pipe; active noise reduction means for attenuating noise generated by the combustion engine and exhaust, said active noise reduction means comprising: an anti-noise chamber surrounding an outer periphery of said passive noise reduction means, having an outlet portion open to tho ambient atmosphere adjacent said second end of said exhaust transfer pipe for projecting anti-noise sound waves through said outlet port to the ambient atmosphere, W O an anti-noise speaker mounted to said anti-noise chamber for generating and projecting said anti-noise sound waves into said anti-noise chamber to further reduce noise generated by the combustion engine and exhaust; and separation means for isolating said anti-noise chamber from exhaust gas.

18. The active noise suppression system of claim 17, further comprising plural anti-noise speakers mounted to said anti-noise chamber.

19. The active noise suppression system of claim 17, wherein said passive noise reduction means comprises a cooling chamber having an outlet end open to the ambient atmosphere for drawing inward cooling air from the ambient atmosphere. The active noise suppression system of claim 19, wherein said exhaust transfer pipe has air flow openings arranged around an outer periphery thereof near said first end for drawing said cooling air from said cooling chamber into said exhaust transfer pipe to reduce turbulence of the exhaust gas to reduce noise.

21. The active noise suppression system of claim 17, wherein said exhaust transfer pipe is provided with air flow openings communicating with said passive noise reduction means.

22. The active noise suppression system of claim 20, wherein said exhaust Stransfer pipe; cooling chamber, anti-noise chamber and anti-noise speakers are integrally constructed within a unitary sheet metal housing. I 23. The active noise suppression system of claim 22, wherein said combustion engine has an exhaust pipe for delivering the exhaust gas to said first end of said exhaust transfer pipe, said first end being insertable into said exhaust pipe and affixable thereto permanently by sealing clamp means. T• 71 0~ I

24. The active noise suppression system of claim 17, wherein said anti-noise chamber is acoustically tuned and comprises a first section of large diameter coupled to a second section of smaller diameter, said anti-noise speakers comprising two speakers mounted to an outer periphery of said first section 1800 apart from each other. The active noise suppression system of claim 17, wherein said exhaust transfer pipe, passive noise reducing means, active noise reduction means and anti-noise speakers are integrally constructed within a unitary sheet metal housing.

26. An integrally housed anti-noise suppression system comprising: an exhaust transfer pipe having first and second ends for transferring exhaust gas in a first direction from a combustion engine to ambient atmosphere, said first end receiving exhaust gas from an exhaust pipe of the combustion engine, and said second end emitting the exhaust gas to the ambient atmosphere; o an anti-noise chamber, surrounding an outer periphery of said exhaust transfer pipe and having an outlet port open to the ambient atmosphere adjacent said second 0000 end of said exhaust transfer pipe for projecting anti-noise sound waves through said outlet to the ambient atmosphere; an anti-noise speaker, mounted to an outer periphery of said anti-noise S chamber, for generating and propagating said anti-noise sound waves into said anti-noise chamber to cancel noise generated by said combustion engine and said exhaust pipe and separation means for isolating said anti-noise chamber from exhaust gas, said 00 00"0 exhaust transfer pipe, anti-noise chamber and anti-noise speakers being constructed and integrally housed within a sheet metal ar structure. 00 00 0 s 27. The integrally housed anti-noise suppression system of claim 26, wherein said first end of said exhaust transfer pipe is insertable and permanently affixable by clamp sealing means to said exhaust pipe. <:NT O-

28. The integrally housed anti-noise suppression system of claim 27, further comprising: a cooling chamber disposed annularly between said exhaust transfer pipe and said anti-noise chamber and having an outlet end open to the ambient atmosphere, for drawing cooling air inward from the ambient atmosphere, said separation means comprising an outer wall of said cooling chamber.

29. The integrally housed anti-noise suppression system of claim 28, wherein said cooling air is drawn into said cooling chamber in a seccnd direction opposite to said first direction of exhaust gas flow within said exhaust transfer pipe. The integrally housed anti-noise suppression sytem of claim 26, further comprising an additional anti-noise speaker mounted to an outer periphery of said anti-noise chamber, wherein said anti-noise chamber is acoustically tuned and has a first section of large diameter coupled to a second section of smaller diameter, said anti-noise speakers being operatively coupled to an outer periphery of said first section 1800 apart from each S other. *31. The active noise suppression system of claim 1, wherein said separation means comprises an outer wall of said exhaust transfer pipe. S. 32. The active noise suppression system of claim 17, wherein said separation means comprises an outer wall of said passive noise reduction means. se e

33. The integrally housed anti-noise suppression system of claim 26, wherein said separation means comprises an outer wall of said exhaust transfer pipe. DATED this 10th day of December, 1991. NOISE CANCELLATION TECHNOLOGIES. INC. WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRAUA t-