Note: Descriptions are shown in the official language in which they were submitted.
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~ACKGROUND AND S~MMARY OF THE INVENTION
The present invention is related to an improved arrangement
for reducing intake and/or e~haust 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 e~haust systems, in compressors, and
in pumps and the like. The preferred embodiment of the invention
described refer primarily to combustion engines, however, it is to
be understood that the invention is adaptable to attenuate sound
in other arrangements e~hibiting similar noise generating
configurations such as in the intake and e~haust of certain
- compressor and pumps and the like.
Numsrous passive systems for suppressing noise at the intake
, andfor e~haust of gas movement systems have been proposed
I previously. Such passive systems use sound insulating material
and/or baffles to suppress sound waves before they reach the
surrounding atmosphere. These so~called "passive systems", such
as conventional automotive e~haust gas mufflars, inherently
restrict the e~haust gas flow, thereby resulting in energy losses
with reductions in the efficiency of operation of the vehicle
combustion engines. It is well known to those skilled in the art
of internal combustion engines that reduction or removal of the
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e~haust gas restriction back pressure substantially improves the
perormance 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 generated 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 o course inherent increased pollution ~ue to
increased hydrocarbon fuel consumption.
So-called "active" noise-cancellation ~ystems 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 fi~ed 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 ~riksson, and U.S. Patent 4,473,906 to Wannaka disclose
ad~itional methods for active noise cancellation in building
system air ducts or e~haust 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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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
e~haust gas~s 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 e~haust environments do not e~hibit the
compactn~ss to facilitate commercialization and use on automotive
and marine p~ssenger vehicles and also do not have control systems
that are responsive to the varying noise spectrum generated during
the normal driving of such vehicleR, 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 e2haust
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.
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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:
(i) an anti-noise chamber is interposed between the
anti-noise acoustic wave gen~rators 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 und~sirable noise propagating mcdium;
(ii) the anti-noise acoustic ~ave generators open into
an acoustically tuned anti-noise chamber which in turn opens to
the ,luid 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
More particularly, according to one aspect of the
invention there is provided 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 exhaus-t gas to the
ambient atmosphere; an anti-noise chamber, annularly surround-
ing 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
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an-ti-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; separation means for isolating said anti-noise
chamber from exhaust gas.
According to another aspect of the invention there is
provided an active noise cancelling arrangement for cancelling
original noise emanating from a substantially concentric opening
comprising: anti-noise chamber means surrounding the concentric
opening and opening adjacent to the concentric opening via anti-
noise chamber opening means concentric to said concentric opening
for said original noise, and anti-noise speaker means faing into
the anti-noise chamber means for generating anti-noise pressure
waves in the anti~noise chamber means such that the anti-noise
pressure waves and original noise pressure waves cancel the
effect of one another at the region of the concentric opening to
reduce the overall noise level of the arrangement.
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 e~haust 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 e~haust pipe opening to atmosphere
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in substantially the same plane, and at least within a length
corresponding to less than one third o 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 e~haust pipe and thereby the speakers are not
subjected to the harsh chemical and heat environment of the
e~haust 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 e~haust pipe, the speakers being mounted adjacent
that end plate. The anti-noise chamber then extends in the
downstream direction of the e~haust pipe and opens at the same
plane as the atmospheric outlet of the e2haust 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 ea~haust
pipe. These sync sensor and microphone signals are processed by
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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 o~ the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE ~RAWINGS
Figure 1 is a schematic side view of a passenger vehicle
depicting the location of the engine e~haust system and a digital
muffler system constructed according to a preferred embodiment of
the present invention;
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Figure 2 is a schematic bottom view of the vehicle of Figure
1 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 usle with the boat of
Figure 3;
Figure S 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 5;
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
chambeT;
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
embodiment 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
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and without noise attenuation using the system of the present
invention.
DETAILED DESCRIPTION OF THE DRAWIN~S
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 eghaust pipe system 3, is depicted as a single
exhaust pipe in the following description, although similar
duplicate arrangements can be provided for dual e~haust 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 e~haust outlet 4 and a synchronization sen~or 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 lA, which, in a similar manner as the
passenger motor vehicle of Figuxes 1 and 2, includes a
reciprocating piston multi-cylinder internal combustion engine 2A,
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an e~haust 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 s~illed 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-~oise chamber arrangement 5 and exhaust pipe. Chamber
5 of Figures 6-7 is constructed as an intregal sheet metal
structure and includes a centrally disposed cylindrical e~haust
pipe 10 which is connected to the exhaust pipe system 3, 3A
(compare Figures 1 to 4~. The left hand end of the exhaust pipe
, section 10 is preferably configured so as to be insertable into an
i existing exhaust pipe of an engine exhaust system 3,3A, with an
appropriate sealing clamping connection being provided.
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An anti-noise chamber 11 is provided in annular surrounding
relationship to the e~haust pipe 10. The anti-noise chamber 11 is
defined by first cylindrical section 12 of a large diameter and an
adjoining smaller diameter sPction 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 e~haust 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 a~is 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 e~haust pipe 10, with
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 e~haust gases from the
exhaust pipe 10.
By arranging the speakers 19 to be symmetrical with the
longitudinal a~is of the exhaust pipe 10 and by providing the
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anti-noise chambsr 11 as an annular chamber surrounding the pipe
10, 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 e~haust pipe 2
and the cylindrical sections 12, 13 making up the anti-noise
chamber ll 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 hsat insulating connection at the exhaust pipe 10 such as
an annular heat insulating material ring surrounding the pipe 10
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 l9 are also isolated by chamber ll from the exhaust
gases and thereby do not have to withstand the highly corrosive
hot gases in the exhaust stream.
Other preferred embodiments are contemplated which utilize
only a sinyle speaker opening into the acoustically tuned chamber
ll, the annular outlet at plane 4 effectively providing an
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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 to 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 10
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 5
inches,
the distance between the edge of the sections 17 and the
end chamber section 12, lZL is 4.75 inches,
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
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addition of an intermediate low pressure cooling exhaust gas
chamber 20 betwe~n the anti-noise chamber llA 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. Thess 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 lOA by eight radially extending 1/8 inch diameter holes 21 in
the pipe lOA. 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 extending 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 lOA 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 ll the controller 7 controls power amplifier 6
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~hich 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 emanating from the pipe outlet. In
especially preferred embodiments, the audio power amplifier 6
is integrated with the digital electronic controller 7. The
digital controller can utilize a frequsncy domain alogorithm
as described in U.S. Patent 4,490,841 by Chaplin.
Alternatively, the digital controller can utilize a time
domain alogorithm.
A practical speak~r and microphone usable with a
configuration as in Figures 5-7 or 8 and 9 has the following
characteristics.
SPEAKER
MAGNET FLUX DENSITY 11,000 GAUSS
TOTAL FLUX - 58,000 MAXWELLS
SENSITIVITY 96dB spc@ lm, 11.2 v RMS
THEIL-SMALL PARAMETERS
SD = 92 cm2
~b = 9.8 gm
XD = 6 mm peak to peak
fs = 37 HZ
Rms = 1 n
Cms = 1.8 x 103 M/N
VAS = 23.6 liters
QM = 2.44
QE = 0.38
QT = 0.33
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IMPEDANCE 8 Q
RANGE 55 Hz to 3,500 Hz
NET WEIGHT 1.13 kg.
MI CROPHONE
FREQ. RESPONSE 20 - 13,000 HZ
IMPEDANCE 600
SENSITIVITY -71dB ~ 5dB
(REF OJB = lv/~ bar, lKHZ)
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 o 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 o~ a frequency dom~in
alogorithm controller or a time domain alogorithm controller can
be utilized. The difference between the Figure 10 and 11
embodimert being that the input from microphone 22 is utilized
instead of the input from a tachometer sensor 9 as in Figure 10.
It is further noted that a controller corresponding to the
NCT 20C0 controller marketed by Noise Cancellation Technologies
Inc., can be used to serve as controller 7.
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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 Eollowing is a
Table of the experimental results shown on the Figure 12 graph.
MARK LIST X Y(U) Y(L)
o 90.000 -18.0 -44.5
1 104.99 -45.3 -51.8
2 120.00 -~5.9 -53.4
3 135.00 -41.8 -59.7
150.00 -38.3 -60.3
165.00 -~5.9 -56.0
6 180.00 -24.8 -49.4
7 24~.0~ -36.1 -58.2
8 270.00 -40.8 -58.2
9 360.00 -46.1 -52.2
From the Table and the graph, one can see substantial noise
level reductions, e.g. 2S 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.
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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
clai.ms.
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