WO 2006/096178 PCT/US2005/007595
COMPRESSOR SOUND SUPPRESSION
BACKGROUND OF THE INVENTION
[0001] The invention relates to compressors. More
particularly, the invention relates to compressors having
check valves.
[0002] Screw-type compressors are commonly used in air
conditioning and refrigeration applications. In such a
compressor, intermeshed male and female lobed rotors or screws
are rotated about their axes to pump the working fluid
(refrigerant) from a low pressure inlet end to a high pressure
outlet end. During rotation, sequential lobes of the male
rotor serve as pistons driving refrigerant downstream and
compressing it within the space between an adjacent pair of
female rotor lobes and the housing. Likewise sequential lobes
of the female rotor produce compression of refrigerant within
a space between an adjacent pair of male rotor lobes and the
housing. The interlobe spaces of the male and female rotors in
which compression occurs form compression pockets
(alternatively described as male and female portions of a
common compression pocket joined at a mesh zone). In one
implementation, the male rotor is coaxial with an electric
driving motor and is supported by bearings on inlet and outlet
sides of its lobed working portion. There may be multiple
female rotors engaged to a given male rotor.
[0003] When one of the interlobe spaces is exposed to an inlet
port, the refrigerant enters the space essentially at suction
pressure. As the rotors continue to rotate, at some point
during the rotation the space is no longer in communication
with the inlet port and the flow of refrigerant to the space
is cut off. After the inlet port is closed, the refrigerant is
compressed as the rotors continue to rotate. At some point
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during the rotation, each space intersects the associated
outlet port and the closed compression process terminates. The
inlet port and the outlet port may each be radial, axial, or a
hybrid combination of an axial port and a radial port. The
compression pocket opening and closing (particularly discharge
port opening) are associated with pressure pulsations and
resulting sound. Sound suppression has thus been an important
consideration in compressor design. Many forms of compressor
mufflers have been proposed.
[0004] Additionally, various transient conditions may tend to
cause reverse flow through the compressor. For example, upon a
power failure or other uncontrolled shutdown high pressure
refrigerant will be left in the discharge plenum and
downstream thereof in the refrigerant flowpath (e.g., in the
muffler, oil separator, condenser, and the like). Such high
pressure refrigerant will tend to flow backward through the
rotors, reversing their direction of rotation. If rotation
speed in the reverse direction is substantial, undesirable
sound is generated. For some screw compressors, damage to
mechanical components or internal housing surfaces can also
occur. Accordingly, a one-way valve (a check valve) may be
positioned along the flowpath to prevent the reverse flow.
Other forms of compressor (e.g., scroll and reciprocating
compressors) may include similar check valves.
SUMMARY OF THE INVENTION
[0005] A compressor apparatus has a housing having first and
second ports along a flowpath. One or more working elements
cooperate with the housing to define a compression path
between suction and discharge locations along the flowpath. A
check valve has a valve element having a first condition
permitting downstream flow along the flowpath and a second
condition blocking a reverse flow. Sound suppressing means at
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least partially surround the flowpath upstream of the valve
element.
[0006] 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
[0007] FIG. 1 is a longitudinal sectional view of a
compressor.
[0008] FIG. 2 is a partial sectional view of a discharge
housing of the compressor of FIG. 1 including a first sound
suppressing means.
[0009] FIG. 3 is a partial sectional view of a discharge
housing of the compressor of FIG. 1 including a second sound
suppressing means.
[0010] FIG. 4 is a partial sectional view of a discharge
housing of the compressor of FIG. 1 including a third sound
suppressing means.
[0011] Like reference numbers and designations in the various
drawings indicate like elements.
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DETAILED DESCRIPTION
[0012] FIG. 1 shows a compressor 2 0 having a housing assembly
22 containing a motor 24 driving rotors 26 and 28 having
respective central longitudinal axes 500 and 502. In the
exemplary embodiment, the rotor 26 has a male lobed body or
working portion 30 extending between a first end 31 and a
second end 32. The working portion 30 is enmeshed with a
female lobed body or working portion 34 of the female rotor
28. The working portion 34 has a first end 35 and a second end
36. Each rotor includes shaft portions (e.g., stubs 39, 40,
41, and 42 unitarily formed with the associated working
portion) extending from the first and second ends of the
associated working portion. Each of these shaft stubs is
mounted to the housing by one or more bearing assemblies 44
for rotation about the associated rotor axis.
[0013] In the exemplary embodiment, the motor is an electric
motor having a rotor and a stator. One of the shaft stubs of
one of the rotors 26 and 28 may be coupled to the motor's
rotor so as to permit the motor to drive that rotor about its
axis. When so driven in an operative first direction about the
axis, the rotor drives the other rotor in an opposite second
direction. The exemplary housing assembly 22 includes a rotor
housing 48 having an upstream/inlet end face 49 approximately
midway along the motor length and a downstream/discharge end
face 50 essentially coplanar with the rotor body ends 32 and
36.
[0014] The exemplary housing assembly 22 further comprises a
motor/inlet housing 52 having a compressor inlet/suction port
53 at an upstream end and having a downstream face 54 mounted
to the rotor housing downstream face (e.g., by bolts through
both housing pieces). The assembly 22 further includes an
outlet housing 56 (shown as an assembly) having an upstream
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face 57 mounted to the rotor housing downstream face and
having an outlet/discharge port 58. The exemplary rotor
housing, motor/inlet housing, and outlet housing 56 may each
be formed as castings subject to further finish machining.
[0015] Surfaces of the housing assembly 22 combine with the
enmeshed rotor bodies 30 and 34 to define inlet and outlet
ports to compression pockets compressing and driving a
refrigerant flow 504 from a suction (inlet) plenum 60 to a
discharge (outlet) plenum 62. A pair of male and female
compression pockets is formed by the housing assembly 22, male
rotor body 30, and female rotor body 34. In the pair, one such
pocket is located between a pair of adjacent lobes of each
associated rotor.
[0016] FIG. 2 shows further details of the exemplary flowpath
at the outlet/discharge port 58. A check valve 70 is provided
having a valve element 72 mounted within a boss portion 74 of
the outlet housing 56. The exemplary valve element 72 is a
front sealing poppet having a stem/shaft 76 unitarily formed
with and extending downstream from a head 78 along a valve
axis 520. The head has a back/underside surface 80 engaging an
upstream end of a compression bias spring 82 (e.g., a metallic
coil). The downstream end of the spring engages an
upstream-facing shoulder 84 of a bushing/guide 86. The
bushing/guide 86 may be unitarily formed with or mounted
relative to the housing and has a central bore 88 slidingly
accommodating the stem for reciprocal movement between an open
condition (not shown) and a closed condition of FIG. 3. The
spring 82 biases the element 72 upstream toward the closed
condition. In the closed condition, an annular peripheral
seating portion 90 of the head upstream surface seats against
an annular seat 92 at a downstream end of a port 94 from the
discharge plenum.
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[0017] For capacity control/unloading, the compressor has a
slide valve 100 having a valve element 102. The valve element
102 has a portion 104 along the mesh zone between rotors. The
exemplary valve element has a first portion at the discharge
plenum and a second portion at the suction plenum. The valve
element is shiftable to control compressor capacity to provide
unloading. The exemplary valve is shifted via linear
translation parallel to the rotor axes.
[0018] The opening and closing of the compression pockets at
suction and discharge ports produce pressure pulsations. As
the pulsations propagate into the gas in the discharge plenum
and downstream thereof, they cause vibration and associated
radiated sound which are undesirable. This pulsation may be at
least partially addressed by modifications involving the
discharge plenum upstream of the check valve. Exemplary
modifications involve modifications to the discharge plenum at
the port 94 to incorporate one or more resonators tuned to
suppress/attenuate one or more sound/vibration frequencies at
one or more conditions. An exemplary frequency is that of the
compression pockets opening/closing at the designed compressor
operating speed and at the designed refrigeration system
operating condition. Thus examples of otherwise identical
compressors may feature differently-tuned resonators for use
in different systems or conditions thereof. Exemplary
modifications make use of existing manufacturing techniques
and their artifacts. Exemplary modifications may be made in a
remanufacturing of an existing compressor or a reengineering
of an existing compressor configuration. An iterative
optimization process may be used to tune the resonator(s).
[0019] FIG. 2 shows one exemplary modification of a basic
compressor. This modification involves providing an outlet
conduit 120 having a distal/upstream protruding portion 122
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exemplary implementation, the outlet conduit is separately-
formed, from the remainder of the outlet housing (e.g., as a
steel cylindrical tube having a proximal/downstream portion
127 press-fit into a cast iron housing member 56 within 2cm of
the head 78 in the second (closed) condition). An annular
channel 128 is defined in the discharge plenum surrounding the
protruding portion 122 to form an annular resonance cavity
that functions as a side branch resonator. The exemplary
cavity has an annular opening/port 130;. When implemented in a
remanufacturing of an existing compressor or a reengineering
of an existing configuration, the cavity may be associated
with a change in the local discharge plenum surface 132 (e.g.,
from an initial/baseline surface 132'). In the exemplary
implementation, the surface is relieved so as to deepen and
broaden the cavity. The cavity is shown having a length L, an
inner radius R, and a radial span R. These parameters may be
selected to provide desired tuning. The annular base portion
of the surface 132 forms a back wall of the cavity, off which
pressure waves reflect. The length L may thus be chosen to
provide an out-of-phase cancellation effect relative to
incident pulsations at the plane of the port 130 and rim 126.
The cancellation effect reduces pulsation magnitude at the
conduit mouth and, in turn, downstream through the conduit. By
changing the curved section of the baseline surface 132' to
the more right angle section of the surface 132, a flat radial
back wall/base is formed that provides a more coherent
reflection, permitting advantageous cancellation properties.
[0020] FIG. 3 shows an alternative modification wherein the
outlet conduit 22 0 has an upstream end wall 222 and a sidewall
224. The end wall 222 includes an array of apertures 226. The
sidewall 224 includes an array of apertures 228. The apertures
226 and 228 serve to break-up the discharge flow into many
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substreams passing through the apertures and recombining in
the interior of the conduit 220. This helps attenuate the
downstream impact of upstream pulsations. The sizes,
densities, and distributions of the apertures may be selected
to provide a desired degree of attenuation. Optionally, there
may be some tuning of the plenum volume surrounding the
conduit 220 to also provide additional pulsation reduction
within the conduit 220.
[0021] FIG. 4 shows another alternative modification wherein
an outlet conduit assembly 320 has a main conduit 322
extending downstream from a rim 324. Although optionally
similarly constructed to the conduit 12 0, the conduit 322 has
an array of apertures 326 similar to the apertures 228 of the
conduit 220. However, rather than passing a net flow, the
apertures 326 serve as ports to a resonator volume 33 0
surrounding the conduit. The volume 330 is otherwise sealed
and longitudinally and laterally bounded by an inwardly-open
C-sectioned member 332 (e.g., having a pair of upstream and
downstream collars 333 and 334 welded to the outboard surface
of the conduit 322). Thus, although similarly located to the
resonator volume 128, the resonator volume 33 0 has a
longitudinal and circumferential array of discrete radial
ports provided by the apertures 326 raither than a single
annular longitudinal port 130. Optionally, the volume 330 may
be filled with a sound dissipating material. The presence of
that dissipative material may reduce cancellation
effectiveness at a single target frequency but compensate by
providing some cancellation over a wider frequency range,
making tuning accuracy less critical.
[0022] The relative proximity of the resonator (s) to the
discharge plenum is believed advantageous for several reasons.
First, flow turbulence may tend to increase downstream.
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Turbulent conditions make tuning difficult. The relatively low
turbulence of an upstream location (e.g., within the
compressor housing), helps facilitate proper tuning. Second,
the proximity to the pulsation source may maximize the
sound/vibration cancellation effect.
[0023] Many known or yet-developed resonator configurations
and optimization techniques may be applied. The former
include, for example, Helmholtz resonators.
[0024] 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. Implementations may involve
check valves used in other locations in the fluid circuit. The
principles may be applied to compressors having working
elements other than screw-type rotors (e.g., reciprocating and
scroll compressors). Accordingly, other embodiments are within
the scope of the following claims.
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CLAIMS
What is claimed is:
1. A compressor apparatus, (20) comprising:
a housing (22) assembly having first (53) and second (58)
ports along a flow path and; including a cast discharge case
(56) ;
one or more working elements (26; 28) cooperating with
the housing (22) to define a compression path between a
suction (60) plenum and a discharge (62) plenum along the flow
path, wherein the one or more working elements include:
a screw-type male-lobed rotor (26) having a first
rotational axis (500); and
a screw-type female-lobed rotor (28) having a second
rotational axis (502) and enmeshed with the male-lobed
rotor;
a check valve (70) in the discharge case and having a
valve element (72) having a first condition permitting
downstream flow along the flow path and a second condition
blocking a reverse flow; and
sound suppressing means (120; 220; 320) at least
partially surrounding the flow path upstream of the valve
element.
2. The compressor of claim 1 wherein:
the sound suppressing means comprises a rigid conduit
(120; 220; 322) having a first portion (127) secured to the
discharge case and a second portion (122) extending away from
the check valve.
3. The compressor of claim 2 wherein:
the conduit (120; 322) has a completely open upstream
end.
4. The compressor of claim 2 wherein:
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the conduit (220) nas:
a partially closed upstream end (222) having a
plurality of ports (226); and
a sidewall (224) having a plurality of
longitudinally and circumferentially spaced ports (228).
5. The compressor of claim 2 wherein:
the conduit (120; 220; 322) has a right circular
cylindrical sidewall (120; 224; 322).
6. The compressor of claim 2 wherein:
a volume (128; 330) encircling the conduit (120; 220,-
322) forms a resonator.
7. The compressor of claim 6 wherein:
the resonator has a port (130) surrounding a distal end
of the conduit.
8. The compressor of claim 6 wherein:
the resonator has a plurality of ports, longitudinally
and circumferentially spaced along the conduit.
9. The compressor of claim 1 wherein:
the valve element (72) has an upstream head (78) and a
downstream stem (76).
10. The compressor of claim 9 wherein:
the sound suppressing means comprises a conduit (120;
220; 322) interference fit in the discharge case (56) within
2cm of the head (78) in the second condition.
11. The compressor of claim 1 wherein:
the sound suppression means comprises a branch resonator.
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12. A compressor comprising:
a housing having first and second ports along a flow
path; and
a sound suppressing element having a conduit {120; 220;
322) having a first portion interference fit in a discharge
case member of the housing and a second portion extending
upstream from the first portion.
13. The compressor of claim 12 wherein the conduit comprises
a metallic right circular cylindrical tube.
14. The compressor of claim 12 wherein the conduit cooperates
with a portion of the discharge case member to define a
resonator.
15. The compressor of claim 12 being a screw compressor.
16. A method for remanufacturing a compressor or
reengineering a configuration of the compressor comprising:
providing an initial such compressor or configuration
having:
a housing having a flow path batween first and
second ports; and
one or more working elements cooperating with the
housing to define a compression path between a suction
plenum and a discharge plenum along the flowpath;
a check valve along the flow path and having a valve
element; and
adding sound suppressing means in the discharge plenum
including a rigid conduit extending upstream from a portion
mounted to the housing.
17. The method of claim 16 further comprising:
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selecting at least one geometric parameter of the conduit
to provide a desired control of a pressure pulsation
parameter.
18. The method of claim 17 wherein:
the selecting comprises tuning a resonator.
19. The method of claim 17 wherein the selecting comprises an
iterative:
varying of said at least one geometric parameter; and
determining the pressure pulsation parameter.
20. The method of claim 19 wherein:
the determining comprises measuring a sound intensity at
a target frequency for pulsation.
21. The method of claim 16 wherein:
the initial such compressor or configuration lacks such a
conduit.
22. The method of claim 16 applied in the remanufacturing of
a screw-type compressor or reengineering of a configuration of
a screw-type compressor.
23. A compressor apparatus (20) comprising:
a housing (22) assembly having first (53) and second (58)
ports along a flow path and including a cast discharge case;
one or more working elements (26; 28) cooperating with
the housing (22) to define a compression path between a
suction (60) plenum and a discharge (62) plenum along the flow
path; and
a check valve (70) in the discharge case and having a
valve element (72) having a first condition permitting
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downstream flow along the flow path and a second condition
blocking a reverse flow; and
sound suppressing means (120; 220; 220) at least
partially surrounding the flow path upstream of the valve
element wherein a volume (128; 33 0) encircling the conduit
(120; 220; 322) forms a resonator having a plurality of ports
(228, 326), longitudinally and circumferentially spaced along
the conduit.
24. A compressor apparatus (20) comprising:
a housing (22) assembly having first (53) and second (58)
ports along a flow path and including a cast discharge case;
one or more working elements (26; 28) cooperating with
the housing (22) to define a compression path between a
suction (60) plenum and a discharge (6.2) plenum along the flov;
path; and
a check valve (70) in the discharge case and having a
valve element (72) , the valve element having, an upstream head
(78) and a downstream stem (76) andhaving a first condition
permitting downstream flow along the flow path and a second
condition blocking a reverse flow; and
sound suppressing means (120; 220i; 320) at least
partially surrounding the flow path upstream of the valve
element.
25. The compressor of claim 24 wherein:
the sound suppressing means comprises a conduit (120;
220; 322) interference fit in the discharge case within 2cm of
the head (78) in the second condition.
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A compressor apparatus has a housing (22) having first (53) and second (58) ports along a flowpath. One or more
working elements (26, 28) cooperate with the housing to define a compression path between suction and discharge locations along
the flowpath. A check valve (70) has a valve element having a first condition permitting downstream flow along the flowpath and a
second condition blocking a reverse flow. Sound suppressing means (120,220,320) at least partially surround the flowpath upstream
of the valve element (70).