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COMPRESSOR MUFFLER
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Benefit is claimed of U.S. Patent Application Ser. No.
60/670,499, filed April 11, 2005, and entitled "Compressor
Muffler", the disclosure of which is incorporated by reference
herein as if set forth at length.
BACKGROUND OF THE INVENTION
[0002] The invention relates to compressors. More
particularly, the invention relates to sound and vibration
suppression in screw-type compressors.
[0003] In positive displacement compressors, discrete volumes
of gas are: trapped at a suction pressure; compressed; and
discharged at a discharge pressure. The trapping and discharge
each may produce pressure pulsations and related noise
generation. Accordingly, a well developed field exists in
compressor sound suppression.
[0004] One class of absorptive mufflers involves passing the
refrigerant flow discharged from the compressor working
elements through an annular space between inner and outer
annular layers of sound-absorptive material (e.g., fiber
batting). US Patent Application Pub. No. 2004/0065504 Al
discloses a basic such muffler and then improved versions
having integral Helmholtz resonators formed within the inner
layer. The disclosure of this '504 publication is incorporated
by reference herein as if set forth at length.
[0005] International Applications PCT/US04/34946 and
PCT/US05/03403 disclose further muffler configurations.
Exemplary embodiments of these mufflers use inner and outer
stacked rings of sound absorbing material. Exemplary ring
material is expanded polypropylene beads (e.g., material known
as porous expanded polypropylene (PEPP)). The disclosures of
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these applications are incorporated by reference herein as if
set forth at length.
SUMMARY OF THE INVENTION
[0006] Accordingly, one aspect of the invention involves a
compressor having first and second enmeshed rotors rotating
about first and second axes to pump refrigerant to a discharge
plenum. The compressor includes a muffler system comprising a
sound absorbing first element and a sound absorbing second
element. The second element at least partially surrounds the
first element and defines a generally annular flow path
portion between the first element and the second element. A
wall at least partially surrounds the second element. A
sound-absorbing third element at least partially surrounds the
wall within a muffler case.
[0007] In various implementations, the wall may be essentially
imperforate. The wall may have a thickness in excess of 0.5cm.
The thickness may be 0.8-1.2cm. The wall may consist
essentially of steel. The case may consist essentially of
steel or cast iron. At least one of the first, second, and
third elements may comprise a number of rings of porous
expanded polypropylene. Along majorities of total longitudinal
spans of the first and second elements, the first and second
elements may have inboard and outboard surfaces that are
essentially non-convergent and non-divergent. At least one
foraminate metallic element may be between the first and
second elements. A first such foraminate metallic element may
be at an inboard boundary of the generally annular flowpath
portion and a second may be at an outboard boundary. The third
element may have a median thickness of 0.5-2.0cm (more
narrowly 1.0-1.5cm). The second element may have a median
thickness of 3.0-8.0cm (more narrowly 4.0-6.0cm).
[0008] Such a muffler may be provided in a remanufacturing of
an existing compressor or a reengineering of an existing
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configuration of the compressor. The initial/baseline
compressor or configuration may lack at least one of the wall
and the third element.
[0009] The details of one or more embodiments of the invention
are set forth in the accompanying drawings and the description
below. Other features, objects, and advantages of the
invention will be apparent from the description and drawings,
and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a longitudinal sectional view of a
compressor.
[0011] FIG. 2 is a view of a case and muffler assembly for
installation on the compressor of FIG. 1.
[0012] FIG. 3 is an upstream end view of the assembly of FIG.
2.
[0013] FIG. 4 is a downstream end view of the assembly of FIG.
2.
[0014] FIG. 5 is a longitudinal sectional view of the muffler
of the assembly of FIG. 2.
[0015] FIG. 6 is a partially exploded view of the muffler of
FIG. 5.
[0016] Like reference numbers and designations in the various
drawings indicate like elements.
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DETAILED DESCRIPTION
[0017] FIG. 1 shows a compressor 20 as in PCT/US05/03403
having a housing or case assembly 22. The exemplary compressor
is a three-rotor, screw-type, hermetic compressor having
rotors 26, 28, and 30 with respective central longitudinal
axes 500, 502, and 504. In the exemplary embodiment, the first
rotor 26 is a male-lobed rotor driven by a coaxial electric
motor 32 and, in turn, enmeshed with and driving the
female-lobed rotors 28 and 30. In the exemplary embodiment,
the male rotor axis 500 also forms a central longitudinal axis
of the compressor 20 as a whole. The rotor working portions
are located within a rotor case segment 34 of the case
assembly 22 and may be supported by bearings 36 and sealed by
seals 38 engaging rotor shafts at each end of the associated
rotor working portion. When driven by the motor 32, the rotors
pump and compress a working fluid (e.g., a refrigerant) along
a flowpath from a suction plenum 40 to a discharge plenum 42.
The flowpath is divided along distinct compression pockets or
compression paths defined by associated pairs of the rotors
between the suction and discharge plenums. Thus, the flow
splits in the suction plenum and merges in the discharge
plenum.
[0018] In the exemplary embodiment, the suction plenum 40 is
located within an upstream end of the rotor case 34 and the
discharge plenum is located generally within a discharge case
46 separated from the rotor case by a bearing case 48 and
having a generally downstream-convergent interior surface 49.
In the exemplary embodiment, a bearing cover/retainer plate 50
is mounted to a downstream end of the bearing case 48 to
retain the bearing stacks. Downstream of the discharge case 46
is a muffler 52 in a muffler case 54. Downstream of the
muffler 52 is an oil separator unit 60 having a case 62
containing a separator mesh 64. An oil return conduit 66
extends from the housing 62 to return oil stopped by the mesh
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64 to a lubrication system (not shown). An outlet plenum 68
having an outlet port 69 is downstream of the mesh 64.
[0019] The exemplary main muffler 52 includes annular inner
and outer elements 70 and 72 separated by a generally annular
space 74. These elements may be formed of sound absorption
material. In the exemplary embodiment, the inner element 70 is
retained and separated from the space 74 by an inner
foraminate sleeve 76 (e.g., wire mesh or perforated/expanded
metal sheeting) and the outer element 72 is similarly
separated and retained by an outer foraminate sleeve 78. In
the exemplary embodiment, the outer element 72 is encased
within an outer sleeve 80 telescopically received within the
housing 54. The sleeves 80 and 78 are joined at upstream and
downstream ends by annular plates 82 and 84. In the exemplary
embodiment, the upstream end of the sleeve 7 6 is closed by a
circular plate 86 and the downstream end closed by an annular
plate 90. In the exemplary embodiment, a non-foraminate
central core 94 (e.g., steel pipe) extends through the inner
element 70 and protrudes beyond a downstream end thereof. At
the upstream end of the main muffler, radially-extending
connectors 96 join the circular plate 86 to the annular plate
82. At the downstream end, radially-extending connectors 98
connect the annular plates 84 and 90 to hold the inner and
outer elements concentrically spaced apart to maintain the
annular space 74.
[0020] In operation, compressed gas flow exits the compression
pockets of the screw rotors 26, 28, 30 and flows into the
discharge plenum 42. Upon exiting the compressor discharge
plenum, the gas flows down the annular space 74. Upon exiting
the muffler, the gas flow, which typically has entrained oil
droplets, flows through the oil separating mesh 64. The mesh
64 captures any oil entrained in the gas and returns it to the
oil management system by means of the conduit 66. The gas
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leaves the oil separating mesh and enters the plenum 68 and
exits the outlet 69 toward the condenser (not shown).
[0021] It may be desirable to further limit the sound
transmitted by the muffler case. One method is to thicken the
muffler case. PCT/US04/34946 shows a relatively thick combined
discharge and muffler case. Yet further sound limitation may
be desired. According to the present invention further means
are used to isolate the muffler case from the refrigerant
flow. FIG. 2 shows an improved case and muffler assembly 200.
The assembly 200 uses a case 202 that serves as a combined
muffler case and discharge case (e.g., as in PCT/US04/34946),
although muffler case-only implementations are also possible.
[0022] The exemplary case 202 has an upstream mounting flange
204 (also in FIG. 3) for bolting to the bearing case. A
generally circular cylindrical body or sidewall 206 is welded
to and extends downstream from the flange 204. A downstream
end plate 208 (also in FIG. 4) is welded to a downstream end
of the body 206. A periphery of the end plate includes an
array of threaded holes for bolting to an upstream flange of
the separator case/housing 62.
[0023] A muffler unit 210 (FIG. 6) may be installed to the
case 202 through the open upstream end of the body 206. A
structural core assembly 212 of the muffler includes an
upstream metal end member 214. The exemplary member 214 is
approximately bat-or butterfly-shaped, having a central hub
area 216 positioned to cover the male rotor bearing
compartment and two wings 218 positioned to cover the female
rotor bearing compartments while leaving the discharge ports
open.
[0024] FIG. 5 shows a central core pipe 220 having an upstream
end welded to a downstream face of the member 214. A
foraminate centerbody sleeve 222 (e.g., metallic mesh or
perforated sheet metal) has an upstream end welded to a
downstream face of the member 214 at the periphery of the hub
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216. A metal frustoconical discharge plenum wall member 224
has a large upstream end welded to a downstream face of the
member 214 slightly inboard of the wing periphery. A
foraminate outer element liner 226 (e.g., metallic mesh or
perforated sheet metal) has an upstream end welded to a small
downstream end of the wall member 224.
[0025] An annular flow passageway 230 is defined between the
liner 226 and the sleeve 222. To form the inner element 232, a
stack of PEPP rings 234 is received in the annular space
between the pipe 220 and sleeve 222. To form the outer element
236, a stack of PEPP rings 238, 240, and 242 is accommodated
over the liner 226. The upstream ring 238 has a frustoconical
upstream surface for engaging a downstream surface of the
member 224 via a neoprene seal 244. A plurality of rectangular
sectioned rings 240 follow to a downstreammost ring 242.
[0026] An additional annular wall 250 may be placed over the
outer element rings 238, 240, and 242. The exemplary wall 250
is a continuous, imperforate metallic (e.g., steel) tube/pipe
intended to acoustically float relative to the case 202 (e.g.,
not being rigidly structurally connected to the case 202. The
exemplary floating is accommodated by allowing the upstream
end 252 to rest against the seal 244. An inboard surface 254
rests against the outer surface 256 of the outer muffler
element. In the exemplary embodiment, the upstream end 252 is
beveled to minimize contact pressure against the downstream
surface of the seal 244.
[0027] The annular space 259 between the wall outboard surface
258 and the inboard surface 260 of the body may be filled by
further sound-absorbing material 261 such as a stack of PEPP
rings 262, 264, and 266. The upstreammost ring 262 may be
rebated to accommodate the wings 218. An isolation seal 270
may engage the downstream rim area 272 of the wall 250 and may
have a portion extending outward between the downsteammost
ring 266 and a downstreammost one of the rings 264 to prevent
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infiltration of refrigerant pulsations into the space 259.
Thermal isolation gaskets 274 and 276 (FIG. 6) are inserted
between the downstream ends of the inner and outer
polypropylene rings, respectively, and the end plate 208 to
protect the polypropylene material from heat caused by welding
operations during final muffler assembly.
[0028] When assembled, the muffler may be inserted into the
case 202. When fully inserted, an end portion of the pipe 220
is received in a central aperture 280 in the end plate 208.
The end plate further includes outlet apertures 282 aligned
with the passageway to pass the refrigerant to the separator.
[0029] The combined effect of the case sidewall 206 and the
floating wall 250 is greater sound reduction than a single
wall of the same mass or combined thickness (although not
necessarily greater than a much more massive wall - e.g.,
whose thickness equals the combined wall thickness plus the
thickness of the space 259). The particular relative
dimensions may be engineered to provide maximal or other
desired degree of sound/vibration suppression at one or more
frequencies (e.g., the frequencies of compression pocket
opening/closing at nominal operating speed or a range
thereof).
[0030] The floating wall may operate to keep noise from
reaching the outer case and then propagating downstream
through piping to the condenser (not shown, which may act as
an acoustical radiator). Sound propagating radially outward
through the outer element 236 is deflected by the floating
wall 250 back toward the center of the muffler where it can be
further attenuated.
[0031] In the absence of the floating wall 250, the sound
would travel directly to the outer muffler case 54. The sound
would then either radiate into the room or travel downstream
along the housing and discharge the pipe (not shown) to the
condenser (not shown) and then radiate into the room.
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[0032] In alternative embodiments, the floating wall can be of
a non-steel or non-metal heavy/dense material which can exist
in a refrigerant environment. The floating wall may have
multiple layers (e.g., as multiple floating walls). Other
materials may be used for the inner, outer and exterior
elements (e.g., glass fiber batting).
[0033] The inventive system may be implemented in a
remanufacturing of a given compressor system or a
reengineering of a configuration thereof. One area of
possibilities involve preserving an existing case. This may
involve a new muffler whose annular flow space is shifted
inward to provide room for the floating wall. Another area
involves preserving an existing basic muffler element while
expanding the case to accommodate the floating wall. In the
reengineering of a baseline system having a thick-walled case,
the case could be thinned with the floating wall making up for
the thinning (e.g., to maintain or reduce an overall weight
while not adversely affecting noise control).
[0034] One or more embodiments of the present invention have
been described. Nevertheless, it will be understood that
various modifications may be made without departing from the
spirit and scope of the invention. For example, in a
reengineering or remanufacturing situation, details of the
existing compressor may particularly influence or dictate
details of the implementation. Accordingly, other embodiments
are within the scope of the following claims.
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CLAIMS
What is claimed is:
1. A compressor comprising:
a first rotor (26) having a first rotational axis (500);
a second rotor (28; 30) having a second rotational axis
(502; 504) and enmeshed with the first rotor;
a discharge plenum (42); and
a muffler system (200) comprising:
a case (202);
a sound-absorbing first element (232);
a sound-absorbing second element (236) at least
partially surrounding the first element and defining a
generally annular flow path portion (230) between the
first element and second element;
a wall (250) at least partially surrounding the
second element; and
a sound-absorbing third element (261) at least
partially surrounding the wall within the case.
2. The compressor of claim 1 wherein:
the wall (250) is essentially imperforate.
3. The compressor of claim 1 wherein:
the wall (250) has a thickness in excess of 0.5cm.
4. The compressor of claim 1 wherein:
the wall (250) has a thickness 0.8-1.2cm.
5. The compressor of claim 1 wherein:
the wall (250) consists essentially of steel.
6. The compressor of claim 1 wherein:
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the case consists essentially of steel or cast iron.
7. The compressor of claim 1 wherein:
at least one of the first (232), second (236), and third
(261) elements comprises a plurality of rings (234; 238, 240,
242; 262, 264, 266) of porous expanded polypropylene.
8. The compressor of claim 1 wherein:
along a majority of a total longitudinal span of the
first element (232), the first element has inboard and
outboard surfaces that are essentially non-convergent and
non-divergent; and
along a majority of a total longitudinal span of the
second element (236), the second element has inboard and
outboard surfaces that are essentially non-convergent and
non-divergent.
9. The compressor of claim 1 wherein:
the muffler system includes at least one foraminate
metallic element (222, 226) between the first and second
elements.
10. The compressor of claim 1 wherein:
a first foraminate metallic element (222) is at an
inboard boundary of the generally annular flow path portion
(230); and
a second foraminate metallic element (226) is at an
outboard boundary of the generally annular flow path portion
(230).
11. The compressor of claim 1 wherein:
the third element (261) has a median thickness of
0.5-2.0cm; and
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the second element (236) has a median thickness of
3.0-8.Ocm.
12. The compressor of claim 1 wherein:
the third element (261) has a median thickness of
1.0-1.5cm; and
the second element (236) has a median thickness of
4.0-6.Ocm.
13. A compressor comprising:
a first rotor (26) having a first rotational axis (500);
a second rotor (28; 30) having a second rotational axis
(502; 504) and enmeshed with the first rotor;
a discharge plenum (42); and
a muffler system (200) comprising:
a case (202);
a sound-absorbing first element (232);
a sound-absorbing second element (236) at least
partially surrounding the first element and defining a
generally annular flow path portion (230) between the
first element and second element; and
means (259, 261) for isolating the second element
relative to the case.
14. The compressor of claim 13 wherein:
the case (202) is a portion of a compressor housing
assembly (22).
15. A method for remanufacturing a compressor or
reengineering a configuration of the compressor comprising:
providing an initial such compressor or configuration
having:
a housing (22) having a flow path between first and
second ports;
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one or more working elements (26, 28, 30)
cooperating with the housing to define a compression path
between a suction plenum (40) and a discharge plenum (42)
along the flowpath; and
a first muffler (52) comprising:
a muffler case (80), optionally a portion of
the housing;
a first sound absorptive element (70);
a second sound absorptive element (72); and
a flow space (74) between the first and second
sound absorptive elements; and
providing the remanufactured compressor or reengineered
configuration with:
a housing having a flow path between first and
second ports;
one or more working elements cooperating with the
housing to define a compression path between a suction
plenum and a discharge plenum (42) along the flowpath;
and
a muffler comprising:
a muffler case (202);
a first sound absorptive element (232);
a second sound absorptive element (236); and
a flow space (230) between the first and second
sound absorptive elements;
a wall (250) at least partially surrounding the
second sound absorptive element; and
a third sound absorptive element (261) at least
partially surrounding the wall within the case, the
initial compressor or configuration lacking at least
one of the wall and the third sound absorptive
element.
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16. The method of claim 15 wherein:
a noise output characteristic of the remanufactured
compressor or reengineered configuration is reduced relative
to the initial compressor or configuration.
17. The method of claim 16 wherein:
the noise output characteristic is a radiated sound
intensity.
18. The method of claim 15 wherein:
the flow space (230) of the remanufactured compressor or
reengineered configuration is at least partially shifted
radially inward relative to the flow space (74) initial
compressor or configuration.
19. The method of claim 15 wherein:
the case of the remanufactured compressor or reengineered
configuration is at least partially thinned relative to the
initial compressor or configuration.
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A compressor has first (26) and second (28; 30) enmeshed
rotors rotating about first (500) and second (502; 504) axes
to pump refrigerant to a discharge plenum (42). The compressor
includes a muffler system (200) comprising a sound absorbing
first element (232) and a sound absorbing second element
(236). The second element at least partially surrounds the
first element and defines a generally annular flow path
portion (230) between the first element and the second
element. A wall (250) at least partially surrounds the second
element. A space (259) optionally containing a sound absorbing
third element (261) surrounds the wall.