Noise attenuation device for air induction system for internal combustion engine

A pressure actuated noise attenuation device for an air induction system of an internal combustion engine is disclosed, comprising a quarter-wave tube and a tuning body movably mounted within the quarter-wave tube. The quarter-wave tube has an open first end in fluid communication with an air intake passage of the air induction system. The tuning body is movable by vacuum developed within the air induction system during operation of the internal combustion engine. The tuning body is also optionally acted upon by a biasing force and/or gravity. The tuning body is movable between at least a first position establishing a first operative length for the quarter-wave tube for attenuating air induction system noise at a frequency which is significant for a first engine operating level, to a second position corresponding to a second engine operating level. In its second position, the tuning body may either establish a second operative length for the quarter-wave tube for attenuating noise at a second frequency, or may substantially close the quarter-wave tube to deactivate the noise attenuation device.

TECHNICAL FIELD 
The present invention is directed to a noise attenuation device for an air 
induction system of an internal combustion engine. More particularly, the 
invention is directed to a noise attenuation device having variable 
frequency noise reduction. 
BACKGROUND OF THE INVENTION 
It is well known to employ silencers, such as quarter-wave tuners and other 
resonators, to reduce air induction noise created by the air induction 
system of an internal combustion engine. Such air induction systems 
generally comprise an air cleaner and prior approaches have often employed 
a resonator or the like incorporated into the air cleaner or communicating 
with an air intake passage downstream thereof. Typically, such noise 
reduction systems attenuate noise at only a fixed narrow frequency range. 
The dominant noise frequency produced by an air induction system (or, in 
any event, the frequency most desirably attenuated) is different, however, 
at different engine operating levels. Such prior, fixed narrow frequency 
range noise reduction devices tuned for a first engine operating level may 
be substantially ineffective, or even counter-effective, at other 
significant frequencies, most notably at a dominant noise frequency 
produced by the air induction system at a second engine operating level. 
Attempts to overcome the problem of fixed narrow frequency range noise 
reduction devices have included proposals for use of electronically 
actuated controls, for example, electronically actuated valves to turn a 
resonator on and off. A noise reduction device is shown in U.S. Pat. No. 
4,538,556 to Takeda, wherein a tank communicates at two spaced ports with 
an air intake tube of an air induction system. One port is opened and 
closed by a vacuum actuated valve. The vacuum is supplied to the valve 
from a vacuum tank through a solenoid valve. An electronic signal, based 
on engine speed or other engine operating condition, actuates the solenoid 
valve to open or close fluid communication between the vacuum tank and the 
vacuum actuated valve. Electronic controls add expense and complexity to 
noise reduction devices for air induction systems. 
A noise reduction device for the air induction system of an internal 
combustion engine is disclosed in Ojala et al There, a noise reduction 
side-branch reactive silencer is formed within a sub-frame interposed 
between the engine and a vehicle body. The sub-frame forms the reactive 
cavity and has a connector for communicating the reactive cavity with the 
air induction system. The connector is positioned along the sub-frame in 
accordance with the desired attenuation frequency. This system, while 
innovative and effective, is not directed to providing variable frequency 
noise reduction. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a noise attenuation device is 
provided for an air induction system of an internal combustion engine. The 
noise attenuation device comprises a quarter-wave tube having an open 
first end for fluid communication with an air intake passage of the air 
induction system. A tuning body is movably mounted within the quarter-wave 
tube. Specifically, the tuning body is movable within the tube by vacuum 
developed within the air induction system during operation of the engine. 
More specifically, the tuning body is movable from a first position within 
the quarter-wave tube to at least one other position. In the first 
position, the tuning body establishes a first operative length for the 
quarter-wave tube effective to attenuate noise at a first frequency which 
is significant at a given engine operating level. The second position of 
the tuning body within the quarter-wave tube corresponds to a second 
operating level of the engine. 
The pressure difference between atmospheric and the vacuum created in the 
air induction system is used to move the tuning body, for example, a 
sphere or piston disc, within the quarter-wave tube to perform such 
functions. Typically, the pressure drop or vacuum created within an 
engine's air induction system is different at different engine operating 
levels. Typically, also, the dominant noise frequency generated by the air 
induction system differs at different engine operating levels. It is a 
novel and significant advantageous feature of the present invention that 
it takes advantage of such different vacuum levels to control a movable 
tuning body within a quarter-wave tube to provide variable noise reduction 
at different engine operating levels. 
In accordance with certain preferred embodiments of the invention, the 
position of the tuning body is continuously variable between two positions 
to establish a correspondingly continuously variable operative length for 
the quarter-wave tube effective to attenuate noise at a corresponding 
continuum of frequencies. In accordance with certain preferred 
embodiments, the tuning body is movable to a position which effectively 
closes the quarter-wave tube to deactivate the noise attenuation device. 
Thus, the present invention uses pressure drop or vacuum created in the 
air induction system to move a tuning body within a quarter-wave tube to 
change the attenuating frequency of the quarter-wave tube, to 
active/deactivate the quarter-wave tube, or to provide both these 
features. 
Additional features and advantages of certain preferred embodiments of the 
invention will be apparent to those skilled in the art from the following 
more detailed description.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS 
The general operation of a quarter-wave tube for noise attenuation is known 
to those skilled in the art. A quarter-wave tube of given dimensions, 
having a first open end in fluid communication with an air intake passage 
or the like, will attenuate noise at a given frequency range. Holding 
other dimensions constant, lengthening or shortening the tube will cause 
it to attenuate noise at a lower or higher frequency range, respectively. 
In accordance with the present invention, a quarter-wave tube employed in 
a noise attenuation device for an air induction system, although having 
fixed dimensions including length, is provided multiple "effective 
lengths" by virtue of a moveable tuning body mounted within the 
quarter-wave tube. The effective length is the length of the quarter-wave 
tube between the open first end and the movable tuning body. As discussed 
further below, in certain preferred embodiments at least one effective 
length of the quarter-wave tube is a zero length to substantially 
deactivate the noise attenuation. Those skilled in the art will recognize 
that the moveable tuning body should generally have a cross-sectional 
shape and dimension substantially the same as the inside shape and 
dimension of the quarter-wave tube, allowing clearance for free axial 
movement of the tuning body within the quarter-wave tube. 
The second end of the quarter-wave tube, that is, the distal end (opposite 
the open first end), preferably is in direct fluid communication with the 
atmosphere, meaning communication without intervening valves or 
passageways or the like. Typically, such direct fluid communication is 
provided by a simple hole in an end wall otherwise closing such distal end 
of the quarter-wave tube. Advantageously, such fluid communication hole 
may double as a drain hole, particularly for quarter-wave tubes extending 
downwardly from an air intake passage. In certain preferred embodiments, 
the drain hole may be centrally located in the distal end wall and serve 
as a seat to receive a spherical tuning body, thus establishing one 
position of the tuning body within the quarter-wave tube. 
In the case of a noise attenuation device for an air induction system of an 
internal combustion engine of a motor vehicle, a "significant frequency" 
typically is a noise frequency readily perceptible to the motor vehicle 
operator under normal operating conditions at a certain engine operating 
level. Such significant frequency may be undesirable, at least under a 
particular range of operating conditions, in view of its tonal quality, 
sound pressure level or both. The term engine operating level is not 
necessarily limited to engine speed. Various atmospheric conditions, such 
as barometric pressure, may impact the functioning of the noise 
attenuation device. 
The vacuum controlled noise attenuation device of the invention can be 
implemented in an air induction system of an internal combustion engine as 
an effective and cost efficient means for variable noise reduction. It can 
provide air induction noise attenuation at more than one frequency range 
with a single quarter-wave tube, which is particularly useful for air 
induction systems having an undesirable tonal quality or like noise 
problem at two (or more) distinct frequency ranges generated at two (or 
more) corresponding different engine operating levels. In addition, the 
movable tuning body within the quarter-wave tube can be implemented in 
certain preferred embodiments to enable the quarter-wave tuner to be 
turned on and off at particular engine operating levels. This may be 
particularly beneficial in applications where the noise attenuation 
device, although effective to attenuate a dominant noise frequency at one 
engine operating level, is ineffective or counter-effective at other 
engine operating levels. 
The vacuum or pressure drop created between a first point ("P1") and a 
second point ("P2") within an air intake passage of an air induction 
system can be estimated to a first approximation from the one dimensional 
energy equation: 
##EQU1## 
Assuming that friction and potential energy losses near the air inlet are 
negligible, rearranging the energy equation yields the following equation: 
EQU P.sub.2 -P.sub.1 =p(V.sub.1.sup.2 -V.sub.2.sup.2)/2 
If the second point ("P2") is taken to be outside the air induction system 
air inlet, then it may be assumed to be at atmospheric pressure and zero 
velocity. The energy equation above will then approximate the pressure 
difference existing between the atmosphere and the air intake passage of 
the air induction system. It is this pressure difference which is employed 
in the present invention, optionally in conjunction with gravity and/or 
biasing force, as discussed further below, to move a tuning body within a 
quarter-wave tube of a noise attenuation devices to change the frequency 
range at which the noise attenuation device operates and/or to deactivate 
the device. 
A light sphere, for example, an optionally hollow plastic ball, forming a 
sliding fit within a quarter-wave tube (see, e.g., FIG. 1, discussed 
further below) will be at equilibrium at the bottom of a quarter-wave tube 
extending downwardly from an air intake passage if its weight exceeds the 
net pressure differential between atmosphere and the air intake tube. When 
the pressure differential is sufficient to overcome the weight of the 
ball, the ball will move upwardly until it encounters a stop or seat. This 
will tune the quarter-wave tube to a higher frequency. In this regard, it 
will be understood by those skilled in the art that the average velocity 
of air within an air intake passage is a function of engine speed, 
generally in accordance with the following equation: V=[n.multidot.e.sub.v 
.multidot.d]/2A where: V=average velocity; n=engine speed; e.sub.v 
=volumetric efficiency; d=engine displacement; and A=cross-sectional area 
of the air intake passage at the velocity measurement point. This velocity 
equation may be used with the aforesaid energy equation to estimate the 
pressure differential acting on a moveable tuning body within a 
quarter-wave tube in fluid communication with the air intake passage. The 
pressure force exerted on the tuning body will be equal to the pressure 
difference multiplied by the cross-sectional area of the tuning body 
measured in a plane normal to the longitudinal axis of the quarter-wave 
tube. Thus, the engine operating level needed to lift a tuning body of a 
given weight and cross-section can be determined. Therefore, the weight of 
the tuning body can be readily calibrated by those skilled in the art, 
such that it will move at a preselected engine operating level to perform 
the desired on/off function or the desired change of attenuation frequency 
function. 
Referring now to FIG. 1, an internal combustion engine 10 and its 
associated air induction system 12 are illustrated. The air induction 
system 12 comprises air cleaner 14 in fluid communication with the 
atmosphere via air intake passage 16. Air intake passage 18 extends 
between air cleaner 14 and engine intake manifold 20. A noise attenuation 
device for the air induction system comprises quarter-wave tube 22 
extending downwardly from air intake passage 18 mediate the air cleaner 14 
and air intake manifold 20. The device also can be located upstream of the 
air cleaner to prevent introduction of moisture, etc., into intake passage 
18. Quarter-wave tube 22 has an open first end 24 in fluid communication 
with air intake passage 18. A spherical tuning body 26 is movably mounted 
within the quarter-wave tube 22. With the engine either not operating or 
at a low operating condition, the weight of tuning body 26 causes it to be 
seated in axially centered, circular hole 28 in distal end wall 30 of 
quarter-wave tube 22. This establishes a first effective length for the 
quarter-wave tube, at which the noise attenuation device will attenuate 
air induction noise at a certain frequency range. It will be quite 
apparent to those skilled in the art that the effective length of the 
quarter-wave tube can be readily determined for attenuating a particular 
frequency range which is significant at such first engine operating level. 
The size and weight of the spherical tuning body 26 can also be readily 
determined, such that it will rise within quarter-wave tube 22 at a 
preselected higher engine operating level at which the pressure 
differential acting on the tuning body, that is, the difference between 
atmospheric pressure and the sub-atmospheric pressure within the air 
intake passage 18, overcomes the weight of the tuning body. In the 
embodiment of FIG. 1, the tuning body will rise until it is seated in 
axially centered, circular hole 32 formed by annular wall 34 extending 
radially inward from the inside surface of quarter-wave tube 22. The axial 
position of annular wall 34 can be readily determined by those skilled in 
the art in view of the present disclosure to establish a second operative 
or effective length for the quarter-wave tube to attenuate noise at a 
second frequency which is significant at such second, higher operating 
level. Tuning body 26 will simply fall of its own weight back to the first 
position at end wall 30 when the engine operating level falls back again 
below such second, higher operating level. 
A second preferred embodiment of a noise attenuation device for an air 
induction system of an internal combustion system is illustrated in FIG. 
2. The noise attenuation device comprises a quarter-wave tube 122 
extending downwardly from air intake passageway 118. Air flow in air 
intake passageway 118 is in the direction of arrow 119. End wall 130 is 
seen to have a drain hole 128. A radially centered annular wall 134, 
defines circular hole 135 in open fluid communication with air intake 
passage 118 which forms a seat to receive spherical tuning body 126 (shown 
in phantom at such first position). A side branch air passage 123 extends 
from the open first end of the quarter-wave tube to open fluid 
communication with the main body of the quarter-wave tube 122. 
Specifically, passage 123 intersects the quarter-wave tube mediate the 
first position of tuning body 126 at radial wall 134 and a second position 
of the tuning body. When the tuning body is in the aforesaid first 
position, the quarter-wave tube operates to attenuate noise at a 
preselected frequency, via air passageway 123. 
The second position of the tuning body is defined by a second radially 
centered annular wall 138 extending radially inward from the inside 
surface of the quarter-wave tube in a plane normal to the axis of the 
tube. Annular wall 138 defines circular opening 139 which forms a second 
seat for tuning body 126. Such second position is proximate the open first 
end of the quarter-wave tube. That is, with the tuning body seated in such 
second position the quarter-wave tube is substantially deactivated. 
In accordance with the principals of the invention previously discussed, 
those skilled in the art will recognize that at a sufficiently high engine 
operating level the pressure differential acting on tuning body 126 will 
lift it to its first position at radial wall 134. At lower engine 
operating levels, tuning body 126 will be seated in its second position at 
radial wall 138, thereby substantially deactivating noise attenuation by 
the quarter-wave tube. Annular wall 138, forming a seat for the spherical 
tuning body 126, should have sufficiently small radial dimension to avoid 
undue interference with the operation of the quarter-wave tube at its full 
operative length. 
Another preferred embodiment of the invention is illustrated in FIG. 3 
wherein, as in the embodiment of FIG. 2, the tuning body operates as an 
on/off switch for noise attenuation by the quarter-wave tube of the noise 
attenuation device. In contrast to the embodiment of FIG. 2, in the 
embodiment of FIG. 3 the quarter-wave tube is deactivated at a higher, 
rather than lower engine operating level. In the embodiment of FIG. 3, 
quarter-wave tube 222 is seen to intersect air intake passageway 218 of an 
air induction system. Air intake is in the direction of arrow 219. Annular 
wall 234 defines radially centered, circular hole 235, forming a seat at 
the open first end of quarter-wave tube 222 for tuning body 226. With the 
tuning body in this position, it will be readily seen that the 
quarter-wave tube is substantially deactivated. A preselected engine 
operating level must be maintained to lift tuning body 226 into such 
position against the force of gravity. Below such engine operating level, 
tuning body 226 will fall to side branch 224, which forms a well 223 to 
receive the tuning body. Well 223 is seen to have drain hole 227 which 
serves also to provide direct fluid communication to atmosphere. 
In the embodiment of FIG. 4, a noise attenuation device in accordance with 
the principles of the present invention employs a piston 326 as the tuning 
body. Piston 326 has a fluid-tight sliding fit within quarter-wave tube 
322. Above piston 326, the quarter-wave tube is in open fluid 
communication with air intake passageway 318. Air flow within passageway 
318 is in direction of arrow 319. Below piston 326, the quarter-wave tube 
is filled with fluid 340 exposed to the pressure differential between the 
atmosphere and the air intake passage, supplied via conduit 342 from a 
reservoir 344. Reservoir 344 comprises a fluid holding tank in which the 
space 345 over the fluid 340 is in direct fluid communication with the 
atmosphere via vent 346. In this embodiment of the invention, the height 
of piston 326 within the quarter-wave tube can vary continuously as a 
function of vacuum or pressure drop established by the air induction 
system. As discussed above, the pressure drop within the air induction 
system is a function of engine operating level. Movement of the piston 
within the quarter-wave tube will establish a continuously variable 
operative length for the quarter-wave tube over a range of positions. 
Hence, the noise attenuation device of FIG. 4 functions to attenuate air 
induction noise at a frequency which varies continuously with engine 
operating level. 
Another preferred embodiment of the invention is illustrated in FIG. 5, 
wherein the tuning body again comprises a piston slidably mounted for 
axial movement within the quarter-wave tube. Biasing means are provided 
for applying an axially directed force to the tuning body. The magnitude 
of the axially directed force varies substantially continuously over an 
operative range of axial position of the piston. More specifically, piston 
426 is seen to be slidably mounted within quarter-wave tube 422 extending 
downwardly from air intake passageway 418. Quarter-wave tube 422 has an 
open first end 424 in fluid communication with air passageway 418. The 
distal end 425 of quarter-wave tube 422, opposite the open first end 424, 
is substantially closed by end wall 430. A drain hole 428 is provided in 
end wall 430, which also ensures substantially atmospheric pressure acting 
on the downward side 427 of piston 426. A first end 447 of a helical 
spring 448 is attached to the bottom face 427 of piston 426. The opposite 
end 449 of helical spring 448 is attached to end wall 430 of quarter-wave 
tube 422. The biasing force applied to piston 426 will be understood from 
this arrangement to vary continuously with axial position of the piston 
within the quarter-wave tube, as the helical spring is increasingly 
stretched or compressed. Thus, as in the embodiment of FIG. 4, the 
effective or operative length of the quarter-wave tube 442 will vary 
continuously with the pressure drop in the air induction system. In 
accordance with the general principals of the invention set forth above, 
those skilled in the art will understand that a noise attenuation device 
in accordance with the embodiment of the invention illustrated in FIG. 5 
will attenuate noise at a frequency which varies continuously with the 
engine operating level over a range of such operating levels. With the aid 
of the present disclosure, it is well within the ability of those skilled 
in the art to configure and dimension the quarter-wave tube and the other 
components of the noise attenuation device to attenuate undesirable noise 
at different significant frequencies at various corresponding engine 
operating levels. 
The exemplary and preferred embodiments of the invention described above 
are intended to illustrate and not limit the invention which is defined by 
the appended claims. It will be apparent to those familiar with the 
technology to which this invention relates, in light of this disclosure, 
that variations and modifications can be made without departing from the 
true spirit of the invention. All such variations and modifications are 
intended to be included within the scope of the appended claims.