Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-1- 724-1502E
This invention relates to sirens. In particular, the
invention is directed to a siren for circumferentially radial dis-
tribution of acoustic output for alerting communities, for
instance, in emergencies at nuclear power stations or in events
of o-ther calamity. This invention is divided from Canadian Patent
Application Serial No. 448,657, filed March 1, 1984.
Sirens can be of an integral blower-type siren where
the sound generation includes an internal air compressor-rotary
valve combination, and this inherently of low efficiency. The
alternative siren design employs an axial flow which includes an
external compressor. Although it incorporates efficient compres-
sion, it is only unidirectional, and the bending of sound into the
radial horizontal plane creates inefficiencies such that the hori-
zontal plane acoustic power generation is reduced. Turbulence of
air in such a siren acts as a pneumatic or acous-tic resistance to
the siren.
As such therefore known sirens for warning and alerting
opera-te a-t a relatively low acoustical efficiency. The eEficiency
is a measure of the acoustical output, usually in the horizontal
plane, relative -to the electrical or mechanical input power. In
the Applicant's experience, this efficiency varies between 3
to 10% for commercially
167/221 DIV II
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available sirensO In the known sirens where the acoustical
output is generated in an axial direction, usually upwardly,
a horn or the like is provided for turning the acoustical
output to radiate in a horizontal direction. For a siren
to be heard over a wider geographical area, it is desirable
to radiate the acoustical output horizontally, and many of
the commercially available sirens do not provide an
internal mechanism for inherently creating such horizontal
radiation. It is only by the provision of the append-
aged horn that this horizontal radiation is achieved.
The redirecting of this radiation pattern, eitherthrough the use of deflectors or bent tubes or horns,
or by some similar guiding, reflecting or defracting
mechanism, all resul-t in a loss of available sound energy
in the horizontal plane, compared to an inherently radially-
radiating siren. This redirection of acoustical output
impairs the acou~tic efficiency of the siren performance.
A further problem which is encountered in known
sirens is that the mechanism within the sirens generating
the sound is of a nature which causes excessive turbulence
of the compressed gas or air passing through the siren
mechanism, such that the acoustical output and the effi-
ciency is further reduced.
Furthermore, known sirens do not provide an efficient
or adequate degree of a sealing action between moving
parts such that leakage of compressed air between moving
parts further impairs the output efficiency and causes
turbulence within the acoustical generating mechanism.
When the relatively rotational ports are not in
alignment, namely, the ports are closed, ideally no air
should flow outwardly to the siren horn. In actual fact,
there is always some air flow or lea]cage, and this leakage
is a significant source of lost siren efficiency. The
space between the inside wall of a stator member and out-
side wall of a rotGr member is often only a few thousandths
of an inch or less, but even with such close spacing the
loss of efficiency is significant. Where in commercial,
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community-type warning sirens such close clearances are
impractical, the losses are even higher. The seal for an
application to a siren where there is relatively high
speed between the inside face and the ouside wall of the
stator and rotor, respectively, such speed being in the
order of 10,000 feet per minute, or greater, presents a
difficulty since this generates unacceptable heat and/or
friction where the seal comes into contact with the
stationary face of the stator. This heat and/or friction
tends to destroy the seal and/or the rotor or stator, or
to increase the torque requirements to unacceptable
levels.
Another problem with sirens arises in the desirabi-
lity to radiate the sound uniformly in the horizontal
plane. This is often accomplished by employing four or
more horns to distribute the sound as uniformly as possible
in the circumferential horizontal plane.
Where there are spaced ports for outlets for horns
circumferentially around the location of the siren the
acoustical output generated from the one horn e~fectively
diminishes or cancels the acoustical output from adjacent
horns so that at locations remote from the siren the
acoustical output is consequently diminished and the
efficiency of the reception is reduced~
At any given observation point, the sound field will
originate not only from the horn pointing most directly
towards the observer, but also from al] the other horns.
Since the effective sources of sound are near the mouths
of the horns, the sound from each horn will travel a
distance dependent upon the relationship between the
observation point and the horn geometry. With the obser-
vation point directly in line with one horn, there will be
a series of siren-to-observer distances at which the sound
from the two horns adjacent to the centrally positioned
horn will travel exactly one-half of the acoustic wave-
length, for the particular siren frequency, farther than
the sound from the central horn.
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The sound from the central horn would be exactly 180
degrees out of phase with the sound from the adjacent
horns. Thus, if the siren has only three horns and the
level from each off-axis horn was 3 dB less than that from
the central horn at the observation point, complete
cancellation would result and the sound level would be
zero. At some other observation distance, the path length
difference would be 1 wavelength, and the sound level
would be 3 dB greater than if only one horn were radiating.
Thus, the level would fluctuate from zero to 3 dB more
than that from one horn alone. Similarly, if the observer
traveled in a circle about the siren, the level would
fluctuate as the relationship between the path length
changed due to the changing geometry. A similar or
somewhat more complex effect occurs when the siren has
more than three horns. At a constant measurement distance
from the siren, the level may fluctuate several d~ above
and below the median value~
The result is tha~ the alerting effectiveness is less
at some locations that at others the same distance from
the sirens. With the horn arrangement of the invention,
these undesirable acoustic characteristics are reduced,
not by rotating the horns, which would result in undesir-
able mechanic'al reliability problems, but through internal
design.
Accordingly, the distance from which a siren may
effectively be heard will be markedly affected and reduced
by these inefficient operating characteristics in known
sirens.
There is accordingly a need to provide a siren
which minimizes the above problems and provides a more
eEficient acoustical output, and, for this purpose, to
minimize the air turbulence generation within the siren,
and to insure that leakage of compressed air between
moving parts is minimized. Furthermore, it is desirable
to provide a siren where the acoustical outputs generated
by different output ports of the stator are in a phase
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relationship relative to each other so that they complement
each other, that in a spatial distribution at a removed
distance from the siren the effective sound generation is
additive and hence more efficient and more uniform.
Summary of the Invention
A siren comprises a compressed gas supply means
with a guide for directing the gas supply in a first flow
direction. Stationary deflector means changes the gas
flow direction substantially transversely to the first
flow direction. Stator means is in substantial alignment
with a rotor means and includes spaced stator port means.
The rotor means with spaced rotor port means is mounted
for rotation about an axis substantially parallel to the
first gas flow direction, and stationary vane means with
the deflector means and the stator means form plenums.
On rotor rotation the rotor ports move periodically
into and out of alignment with the stator ports, thereby
to permit the periodic egress of air from the plenums.
By having stationary deflector means to change
the air flow direction from an axial direction to a radial
direction smoothly, turbulence generation is minimized and
the air flow is retained substantially laminar. With the
stationary vahes spaced circumferentially about the axis,
likewise no turbulence is created by a rotating vane
action moving across the air flow. The air compression
can then take place in the plenum defined between the
deElector plates, vanes and stator, while there is
a separate chopper or valvin~ efficiency created by the
rotating ported rotor. With the first Elow direction
being vertical and the transverse air flow direction being
horizontal, a more efficient acoustical horizontal output
is attained within the siren mechanism.
The number of ports in the rotor is fewer than the
number of ports in the stator. The stator ports are
substantially rectangular-type slots or slits, while the
ports in the rotor are larger and rectangular, and more
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nearly of square dimensions. sy havlng this ratio equal
to 2:1 between the stator and rotor ports, as in one
embodiment, adjacent ports are alternately simultaneously
opened and closed. This generates a square wave acoustic
output with omitted alternating pulses~ The fundamental
frequency is half that of one where the rotor ports and
stator ports are equal in number. The second harmonic of
the output is approximately the same amplitude as the
fundamental frequency, and the acoustic combination
o adjacent horns is a resultant double-frequency siren.
Since the ports on either side of an open port are
closed and these ports would be the major source of the
spatial fluctuation, with the remaining ports about the
circumference contributing less acoustic energy in this
direction, and the adjacent horns are no longer emitting
sound simultaneously, the spatial fluctuation is substan-
tially reduced at any remote location from the siren. In
fact, pulse from adjacent ports combine acoustically in
the far field to form an acoustic square wave from the
constituent pulse trains.
This rotor and stator port relationship between the
rotor and stator improves the acoustic reception at points
remotely located from the siren.
Between the rotor and stator there is provided a
seal to minimize air leakage between the two relatively
spaced and moving components. The seal is of a material
having a low coefficient of friction, ability to cold
flow, a hardness less than the material of the stator
against which it contacts, and a coefficient of thermal
expansion greater than that of the stator and rotor.
The seal is run-in by operating it initially at a
temperature higher than the normal operating temperature,
and thereafter removing the heat such that a minimal
spacing is obtained between the seal and stator during
normal rotation of the rotor relative the stator. The
seal is mounted about the ports of the rotor and includes
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a lip directed towards the stator for forming -the seal with -the
stator componen-t.
Thus there is provided an acoustic generator appara-tus
cornprising a sound generating means, multiple acoustic output
means circumferentially located about an axis around which the
outpu-t is to be generated, means for periodically activating
different output means of the multiple acoustic output means there-
b~ to permit the perlodic output of generated sound from each out-
pwt means, whereby a substantially spatially and circumferentially
regularized sound pattern is remotely generated.
As well, this invention provides a method of generating
an acoustic output comprising sound outpu-t providing multiple
acoustic outputs circumferentially about an axis around which the
output is to be generated, periodically activating different out-
puts of the multiple acoustic outputs thereby permitting the
periodic output of generated sound from each output as a square
wave with missing alternative pulses, transmitting said missing
pulses through adjacent outpu-ts, and being out of phase and where-
by the fundamental frequency is substan-tially half of a frequency
without missing pulses, and the second harmonic being substantially
the same amplitude as the fundamental, thereby to produce an
eEfective double frequency sound output.
This characteristic reduces the abili-ty of air to leak
between the s-tator and the rotor, and hence the efficiency of
acoustic genera-tion is improved.
Figure 1 is a sec-tional eleva-tional view of one embodi-
men-t oE this inven-tion.
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Figure 2 is a sectional plan view along lines 2-2 of
Figure 1 illustrating the deflector, vanes, rotor and stator, with
the horns shownin phantom.
Figure 3 is a detailed partial sectional side view illus-
trating the deflector plate, rotor, stator and seal means.
Figure 4 is a view along lines 4-4 of Figure 3 illustrat-
ing a rotor port with the vanes to either side of the stator port,
-the base of the deflector plate being omitted from view.
Figure 5 is a plan diagrammatic view illustrating the
location of the siren and a remote spatial point in a horizontal
plane, the horns of the siren being shown about the siren-generat-
ing mechanism.
Description of Preferred Embodiments
The siren comprises means for receiving a compressed
gas supply means 10 which is diagrammatically illustrated in
Figure 1. This compressed gas supply, which is conventionally
an air supply generated by a motor and compressor, is connected
with a duct 11 which directs the air supply in a first air flow
direction indica-ted by arrow 12. The duct 11 is connected through
an expanding -tube extension 18 at the end 13 remote from the com-
pressor 10 wi-th a collar 1~ of housing 15. The collar 1~ provides
apertures through which bolts 16 in a mating collar 17 are passed.
The duct 11 itself is connected wi-th an expanding -tube 18 to -the
collar 1~ of the housing 15.
A deflector element 19 of housing 15 includes a central
hub or cup with a smoothly shaped outer faced head 20 which smoo-thly
blends into the curved deflec-tor elements 21 joined wi-th the outer
faced head 20 of the hub. The
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effect of the deflector 21 is to change the air flow
direction 12 to a transverse air flow direction 22, which
direction is radially outward from the axis defined by the
first flow direction 12. The vertical elements 24 prevent
rotational flow of air about the axis 53 of the siren. By
having the cup outer face 20 smooth and a curved connection
area 19 and 23 between the end face 20 of the cup and the
deflectors 21, the change in air flow direction is effective
with a minimum of turbulence.
Spaced circumferentially around the vertical axis 53
of the siren are vanes 24 which are affixed to the outside
face 25 of the deflector element 19. The vanes 24,
together with the deflector 19, act to sectionalize the
air flow into the housing 15 of the siren into compartments
26. The deflector element 19 and vanes 24 are stationary,
thus minimizing turbulent effects caused to the incoming
air 12.
Parallel and in line with the central axis of the
in-flowing air 12, there is mounted a stator 27 with
circumferentially spaced ports 28 around the stator. The
stator includes of a cylindrical housing 29 with collar
means through which bolts 30 pass to affix the cylindrical
housing 29 to the base portion of the housing 15 to which
the expander 'tube 18 is connected on the incoming side.
The opposite side of the cylindrical tube contains a
foundation plate 31 affixed to the cylinder 29 and the
remote side 32 of the plate 31 contains an upstanding
housing 33 for shaft means 34 and coupling sleeve 35 for
rotatably driving a rotor 36 by means of a motor 37.
The rotor 36 contains a base plate 38 and a cylindi-
cal sleeve 39 with ports 40 in the circumferential sleeve
39 and spaced about the sleeve 39. The base 41 of the
plate 38 is anchored through stud means 42 to a plate 43
affixed to the one portion of the shaft means 34, namely
35 34a from the rotor 36 connected with the coupling 35.
Through the motor 37, shaft means 34a and 34b from the
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motor 37 and coupling 35, effective rotation of the rotor
36 can thereby be obtained.
Within the central portion of plate 38 is an upstand-
ing central sleeve 43 in which is mounted a sslaft 44. The
end 45 of the shaft 44 is lockingly energized in the
inside of the deflector element 19, which is hollowed.
About the shaft 44 there are spaced bearings 46 and 47 on
which the rotor 36 is arranged to rotate. The bearings 46
and 47 are located substantially at either end wall 48 and
49, respectively, of the ports 40 of the rotor and also of
the ports 28 of the stator. This provides stabilized
location of the rotor 36 about the bearings 46 and 47 in
relation to the ports 28 and 40 and insures a minimum
movement of the rotor 36 at this critical position. Hence
turbulence at the location of the ports 28 and 40 is
further minimized. The plate 43 cooperates with the
plate 38 at the one end to close effectively the central
sleeve 43 in which the shaft 44 is housed.
~ach compartment 26 constituted by the wall 49 of the
stator 27, the adjacent vanes 24 and the deflector element
19 forms a plenum, the outlet of which is the stator port
28. The stator port outlets 28 are connected with horns
50 effectively to spread the acoustical output as desired
in the radiated spatial horizontal direction. Between the
radial ends 51 of the vanes 24 and the inside face 52 of
the stator 49 rotates the rotor 36 with its ports 40. As
the rotor 36 rotates, a chopper or valving function takes
place whereby the plenums are opened to or closed from the
stator port 28, such that as the ports 28 and 40 move into
and out of alignment so the egress of compressed air from
the plenum is regulated as acoustic output.
In the illustrated embodiment, there are eight com-
partments circumferesltially spaced about the central
axis 53, and there are eight stator ports 28 centrally
located between adjacent vanes 24 forming the walls for
each of these compartments. The rotor 36 contains a
lesser number f namely four ports 40, thereby establishing
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a 2:1 ratio between the stator ports 28 and the rotor
ports 28. This ratio can have other valves such as 8:7 or
8:5 or 7:5, for example.
The width of the rotor ports 40 in the direction of
rotation, namely between side walls 54 and 55, is substan-
tially yreater than the length between the side walls 56
and 57 of the stator ports 28. The length of the rotor
ports 40 between the end walls 58 and 59 are somewhat
laryer than the length of the stator ports 28 between the
end walls 60 and 61 of the stator. The stator ports 28
represent substantially slits or slots relative to the
substantially square ports 40 in the rotor 36. Thus, in
the direction of rotation, there is periodic alignment
between the rotor ports 40 and stator ports 28 such that
air can pass from the plenums outwardly to the horns 50.
Between the rotor 36 and the stator 27 are seals 62
which minimize the leakage of air into the space 63
between the wall 52 on the inside of the stator 27 and the
outside wall 64 of the rotor 36. The seals 62 are in the
shape of a frame about the rotor port 40 and are shaped
with an extending lip 65 extending towards the inside wall
52.
The bead or window-frame-like seal insert 62 around
the periphery of the port 40 is run-in under controlled
conditions to achieve the desired geometry under actual
operating conditions. Initially the seal 62 starts with
zero clearance, and although the seal 62 in the embodiment
is located on the rotor 36, which revolves inside the
stator 27, other permutations of seal 62 and rotor-stator
location are possible. The seal material is Teflon (a
~uPont Trademark for tetrafluoroethylene, polytetraEluoro-
ethylene or fluoronated ethylene propylene, generally
referred to as fluorocarbons) or a Teflon with added
graphites, melybdium disulphide or other material, or
other non-tnetallic material. The necessary characteris-
tics of the seal material are a low coefficient of fric-
tion against the working surface, the inside face 52 of
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the stator 27, the tendency to "cold flow", namely per-
manently to form under the application of pressure which
property is accentuated in the presence of heat; machin-
ability; a hardness less than that of the material against
which it works, a coefficient of thermal expansion greater
than that of the rotor and stator material.
The seal materlal 62 is machine molded or otherwise
formed into the desired shape and attached to the rotor
around each port 40 or in some other appropriate location.
The rotor seal mechanism is then machined to the same or a
slightly larger outer diameter as the stator bore diameter,
namely a dia~eter greater than that determined by the
inside walls 52. The seal 62 protrudes outwardly from the
rotor face 64, thereby forming the raised lip 65, typically
from 10- to 30-thousandths of an inch. The width of the
seal is narrow, typically l/8 inch or less, and may be
beveled so that only a chisel-like edge 66 is in contact
with the stator face 52 when the rotor-seal assembly is
inserted in the stator 27.
Starting at a temperature below the-operating tempera-
ture, the rotor 36 is turned in the stator 27, beginning
at a low speed and working up to the operating speed.
Upon reaching operating speed, heated air, warmer than the
operating air temperature, is injected into the siren air
inlet through duct 11. Operation is continued under these
conditions until the torque required to drive the rotor 36
stabilizes. At this time, first the warm air is shut off,
then after the torque has dropped, the rotor drive motor
37 is turned off.
This process or its equivalent accomplishes two
objectives. First, the seal 62 has "cold flowed" so the
detailed seal profile conforms very closely to the stator
profile defined on the inside wall 52. Second, the seal
62 has "cold flowed" so that the seal 62 to stator clear-
ance is finite at ambient, quiescent condi-tions, and near
zero or minimal under operating conditions. Due to the
difference in thermal expansion coefficients, the seal 62
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contracts at ambient temperature to leave a Einite clear
ance between the seal 62 and the stator face 62. This
minimizes the starting torque required to bring the rotor
36 up to operating speed, and it allows dust or foreign
matter which would accumulate during non-operating periods
to be blown and wiped out of the space 63 between the
rotor 36 and stator 27, thereby minimizing abrasion.
Since the air emitted by the compressor 10 through
the duct 11 is warmer than the ambient air, the seal will
expand as operation commences, closing the clearance gap
due to its higher thermal expansion and its intimate
contact with the warm air. However, since the initial
"cold flowing" operation was performed at a temperature
higher than the operating temperature, a small, substan-
tially minimal seal-stator clearance exists at the oper-
ating conditions.
This circumvents one of the major reasons it has not
been possible to use seals 62 of this or other materials
for high-surface-speed applications in the past, namely a
build up of heat due to rubbing friction, it results in
temperatures beyond the limits of the seals 62 and/or the
material of which the stator 27 is made. At the same
time, if a small area of contact does occur between the
edge 66 of the seal and the inside face 52 oE the stator
27, the use of a soft and "cold flowable" seal material
tends to exhibit a self-healing characteristic as opposed
to an avalanche~type degeneration to catastrophic failure
characteristic of other material combinations.
The seal material characteristics described herein
permit operation with near-zero or substantially minimal
clearance seal conditions, and the resultant application
to the siren is of substantially increased efficiency.
Other applications of the seal formation and estab-
lishment technique exist particularly when there is a
relatively high speed interaction between two components
which move relative to each other, for instance in applica-
tion of pumping gas.
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~ ~urther ~eature of the siren which provides for
increased efficiency of the acoustic sound source arises
from the phase cancellation reduction characteristic of
the siren.
Utilization of the unequal number of rotor ports 40
and stator ports 28 effectively provides a precession by
introducing a phase vector about the vertical axis of the
siren. The rate is sufficiently great so as to be unde-
tectable to the ear. This is achieved since the stator
ports are non-aligned at all times with the rotor ports so
that the ports are not opened and closed simultaneously.
The unequal combinations will have an effect where
one port 28 is fully open, while other ports 28 are partly
open, and other ports 28 are less fully open, and o-ther
ports 28 are in various stages of being opened or closed.
Thereby, the phase relationship between the acoustic
output from the different horns 50 is changed, and this
phase rotation or precession has the effect oE performing
a spatial averaging of the sound level at the observation
point 100, since two horns that are out of phase (cancelling)
at one instance of time are in phase (enhancing) at a
subsequent instance of time. Thus, the resultant sound
field is more spatially uniform.
~y having the ports 28 and 40 square or rectangular,
the resultant abrupt chopping of the air flow results in
basically a square wave sound generator. Special port
shapes would be required to generate a sine wave. This
square wave generator of the embodiment capitalizes on the
inherent square wave generation by utilizing twice the
number of stator ports 28 (and horns 50) as rotor ports
40, namely a ratio of 2:1.
In this embodiment there are eight stator ports 27,
and four rotor ports 40. In this case, any given horn 50
does not emit a square wave, because every other pulse
comprising the square wave is missing. Rather, each horn
50 emits a pulse train of 50~ duty cycle. The horn 50 on
either side of this horn 50 emits the missing part of the
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square wave. These acoustic pulse trains combine in the
radiated sound field to produce the resultant opposite
sound wave at the observation point 100.
The fundamental frequency is one-half that of the
eight-port rotor, namely, with a ratio 1:1 relative to the
stator ports, with the same rate of rotation, but due to
the acoustic combination of the output of adjacent horns
50, the second harmonic is of approximately the same
amplitude as the fundamental. The result is thus a
douhle frequency siren.
Since the horns 50 on either side of a given central
horn 50 are the ma~or source of the aforementioned spatial
fluctuation, with the remaining horns contributing less
acoustic energy in this direction, and since adjacent
horns 50 no longer emit sound simultaneously, the spatial
fluctuation is greatly reduced by this method. The cir-
cumferential sound level fluctuations at observations
points 100 circumferentially about the siren are in the
order of 2 dB, whereas in the prior art this variation is
in the range of 4 to 6 dB.
The characteristics of phase cancellation and reduc-
tion are not limited to siren embodiments and could
equally be applied to mechanical sirens and electronically,
and to electronic sirens or other arrays or distributions
of loud spea~ersO Furthermore, the shape of the ports and
the ratio of stator ports to rotor ports could be different
for different applicatlons. Embodiments employing 8 stator
ports and 7 rotor ports, and other combinations of port
numbers have been evaluated and are practical.
The stator port to rotor port ratio in the range of
8:7, or 8:5 or 7:5 is a non-integral multiple of the other
and this provides a smooth spatial distribution of sound
in the horizontal plane at a distant point. There can
also be a substantially continuously varying port to port
relationship of the acoustic output. The port arrangement
and geometry is such that at various times all the ports
are closed.
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This unique combination of an external air source
which has been employed with axial flow siren designs of
the prior art with a circumferentially distributed radial
flow of air and sound markedly improves the desirable
operational characteristics of the previous siren designs.
Incorporating the improvements of the characteristic of
non-turbulent radial air flow; air compression function
separated from the chopper or valving function of the
rotor; an improved sealing quality between the rotor and
stator space, and the rotor port and stator port dimensions
and relative number ratio, the obtained siren is one which
is a substantial improvement over existing sirens~
The unique combination of design features disclosed
result in a horizontal-plane siren efficiency typically 4
to 20 times that of existing commercial designsO
Having described the invention with particular refer-
ence to the preferred em,bodiments thereof, it will be
obvious to those skilled in the art to which the invention
pertains after understanding the invention, that various
changes and modifications may be made therein without
departing from the spirit and scope of the invention as
defined by the claims appended hereto.
