WO 2006/085863 PCT/US2005/003813
COMPRESSOR UNLOADING VALVE
BACKGROUND OF THE INVENTION
[0001] The invention relates to compressors. More
particularly, the invention relates to refrigerant
compressors.
[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 or vice versa.
[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.
[0004] It is often desirable to temporarily reduce the
refrigerant mass flow through the compressor by delaying the
closing off of the inlet port (with or without a reduction in
the compressor volume index) when full capacity operation is
not required. Such unloading is often provided by a slide
valve having a valve element with one or more portions whose
positions (as the valve is translated) control the respective
suction side closing and discharge side opening of the
compression pockets. The primary effect of an unloading shift
of the slide valve is to reduce the initial trapped suction
volume (and hence compressor capacity); a reduction in volume
index is a typical side effect. Exemplary slide valves are
disclosed in U.S. Patent Application Publication No.
20040109782 Al and U.S. Patent Nos. 4,249,866 and 6,302,668.
SUMMARY OF THE INVENTION
[0005] According to one aspect of the invention, a compressor
has an unloading slide valve. The valve has a valve element
having a range between a first condition and a second
condition, the second condition being unloaded relative to the
first condition. A piston is in a cylinder and mechanically
coupled to the valve element. A control valve is coupled to a
headspace of the cylinder to selectively expose the headspace
to a fluid source, pressure of fluid in the headspace
producing a force on the piston and valve element in a
direction from the second condition toward the first
condition. The compressor includes means for relieving excess
pressure in the headspace.
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[0006] In various implementations, the means may include a
passageway through or around the piston. The means may include
a pressure relief valve. The means may be provided in a
remanufacturing of a compressor or the reengineering of a
compressor configuration from an initial baseline
configuration.
[0007] 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
[0008] FIG. 1 is a longitudinal sectional view of a
compressor.
[0009] FIG. 2 is a transverse sectional view of a discharge
plenum of the compressor of FIG. 1, taken along line 2-2.
[0010] FIG. 3 is a sectional view of a slide valve assembly of
the discharge plenum of FIG. 2 in a fully loaded condition,
taken along line 3-3.
[0011] FIG. 4 is a view of the slide valve of FIG. 3 in a
relatively unloaded condition.
[0012] FIG. 5 is a longitudinal sectional view of a piston and
cylinder of the valve of FIG. 3.
[0013] FIG. 6 is a partial longitudinal sectional view of a
first alternative piston and cylinder.
[0014] FIG. 7 is a partial longitudinal sectional view of a
second alternative piston and cylinder.
[0015] Like reference numbers and designations in the various
drawings indicate like elements.
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DETAILED DESCRIPTION
[0016] FIG. 1 shows a compressor 20 having a housing assembly
22 containing a motor 24 driving rotors 2 6 and 2 8 having
respective central longitudinal axes 500 and 502. In the
exemplary embodiment, the rotor 26 has a male lobed body or
working portion 3 0 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.
[0017] 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 4 8 having an upstream/inlet end face 4 9 approximately
midway along the motor length and a downstream/discharge end
face 50 essentially coplanar with the rotor body ends 32 and
36. Many other configurations are possible.
[0018] 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/discharge housing 56 having an upstream face 57 mounted
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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.
[0019] 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 (FIG.2). A series of pairs of
male and female compression pockets are formed by the housing
assembly 22, male rotor body 30 and female rotor body 34. Each
compression pocket is bounded by external surfaces of enmeshed
rotors, by portions of cylindrical surfaces of male and female
rotor bore surfaces in the rotor case and continuations
thereof along a slide valve, and portions of face 57.
[0020] 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. 2. The
spring 82 biases the element 72 upstream toward the upstream
position of the closed condition. In the closed condition, an
annular peripheral seating portion 90 of the head upstream
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surface seats against an annular seat 92 at a downstream end
of a port 94 from the discharge plenum.
[0021] 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 the rotors
(i.e., along the high pressure cusp). The exemplary valve
element has a first portion 106 (FIG. 3) at the discharge
plenum and a second portion 108 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.
[0022] FIG. 3 shows the valve element at an upstream-most
position in its range of motion In this position, the
compression pockets close relatively upstream and capacity is
a relative maximum (e.g., at least 90% of a maximum
displacement volume for the rotors, and often about 99%). FIG.
4 shows the valve element shifted to a downstream-most
position. Capacity is reduced in this unloaded condition
(e.g., to a displacement volume less than 40% of the FIG. 3
displacement volume or the maximum displacement volume, and
often less than 30%). In the exemplary slide valve, shifts
between the two positions are driven by a combination of
spring force and fluid pressure. A main spring 120 biases the
valve element from the loaded to the unloaded positions-. In
the exemplary valve, the spring 12 0 is a metal coil spring
surrounding a shaft 122 coupling the valve element to a piston
124. The piston is mounted within a bore (interior) 126 of a
cylinder 128 formed in a slide case element 130 attached to
the outlet case. The shaft passes through an aperture 132 in
the outlet case. The spring is compressed between an underside
134 of the piston and the outlet case. A proximal portion 136
of the cylinder interior is in pressure-balancing fluid
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communication with the discharge plenum via clearance between
the aperture and shaft. A headspace 138 is coupled via
electronically-controlled solenoid valves 140 and 142 (shown
schematically) to a high pressure fluid source 144 at or near
discharge conditions (e.g., to an oil separator). A port 146
is schematically shown in the cylinder at the headspace at the
end of a conduit network connecting the valves 140 and 142. In
an exemplary implementation, the portions of the conduit
network may be formed within the castings of the housing
components.
[0023] The loaded position/condition of FIG. 3 can be achieved
by coupling the headspace 138 to the source 144 and isolating
it from drain/sink 150 by appropriate control of valves 140
and 142. The unloaded position/condition of FIG. 4 can be
achieved by coupling the headspace 13 8 to the drain/sink 150
and isolating it from source 144 by appropriate control of
valves 140 and 142. Intermediate (partly loaded) positions,
not shown, can be achieved by alternating connection of
headspace 138 to either the source 144 or the drain/sink 150
using appropriately chosen spans of time for connection to
each, possibly in combination with isolating the headspace 138
from both source 144 and drain/sink 150 for an appropriately
chosen span of time (e.g., via appropriate modulation
techniques).
[0024] Low-friction guidance and sealing is advantageously
provided between the piston 124 and the bore surface 160. For
low-friction guidance, a longitudinally split plastic guide
ring 162 of generally longitudinally elongate section is
partially accommodated within an annular channel/groove in the
outer surface 164 of the piston. The exemplary ring 162 is
circumferentially energized by a coil spring 166 inboard
thereof in an annular countersunk channel/groove. The
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exemplary sealing is provided by an annular C-sectioned
polymeric sealing ring 170 (e.g., of PTFE) in an annular
channel 172 proximally of the ring 162. The seal 170 is
energized by a spring 174. For ease of installation, a
proximal rim 176 of the channel 172 is slightly radially
rebated. This rebating creates a local gap 178 between the
piston and wall substantially greater than gaps immediately
proximally and distally of the ring 162. The section of the
exemplary seal 170 is open longitudinally proximally (i.e.,
away from the headspace 13 8 and toward the proximal portion
13 6 of the bore).
[0025] With such a sealing arrangement, potential damage may
be caused by excessive pressure in the headspace. For example,
such pressure may tend to unwrap and extrude the seal 170
through the gap 178. In normal operation, the headspace is at
most at a pressure very close to that of the proximal volume
136. In unloading, it will be substantially less. In loading,
it will typically be slightly below or equal. Under certain
aberrant conditions, pressure in the headspace may become
excessive. Accordingly, some means for pressure relief is
advantageously provided. FIG. 5 shows one such means in the
form of a pressure relief valve 190 mounted in a passageway
192 through the piston between distal (face) and proximal
(underside) surfaces of the piston. The exemplary valve 190 is
a one-way spring-loaded pressure relief valve having a
predetermined threshold or pop-off pressure. The exemplary
valve 190 is normally closed, when the pressure in the
headspace exceeds that in the volume 136 by the threshold,
this pressure difference will shift the relief valve element
against its spring force to open the valve and permit oil to
pass from the headspace to the volume 13 6 until the
overpressure is relieved. Reverse flow is not permitted by the
exemplary valve 190. Exemplary threshold pressures are ten psi
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or less (e.g., an exemplary three psi) but may be tailored to
address the strength of a given seal. Properties of the valve
190 and the other components of the slide valve may be
selected in view of compressor operating conditions so that
the valve 190 is only likely to open when the slide valve has
reached the fully loaded condition (e.g., bottomed). The
spring rate of the main spring 12 0 may be relevant to this
condition.
[0026] FIG. 6 shows an alternate pressure relief means. This
means comprises a channel 210 in the surface 160 extending
between a distal end 212 and a proximal end 214. The channel
is positioned so that in the fully loaded condition the seal
170 falls somewhere between the distal and proximal ends 212
and 214. Thus in the loaded condition, the channel 210 may
accommodate a pressure relief flow. If, however, the piston is
shifted substantially distally, the sealing ring will fall
outside of the channel (e.g., by more than an exemplary 5% of
the piston stroke/range).Once the sealing ring is no longer
spanned by the channel (e.g., when shifted beyond the channel
toward the unloaded condition), the channel will not provide
pressure relief and the slide valve will operate otherwise
normally. The degree of relief provided may be determined by
the size of the channel (e.g., its transverse sectional area).
The channel has a longitudinal component and may be exactly
longitudinal or may have a tangential component. By having a
tangential component (e.g., a helix angle of 10-30°) the
interaction between the seal and slide on the one hand and the
channel edges on the other hand is eased during movement of
the piston.
[0027] FIG. 7 shows yet another alternative pressure relief
means wherein a passageway 22 0 is not an open channel but
rather has first and second ports 222 and 224 joined by a
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trunk 226. The ports may be similarly longitudinally
positioned to the ends of the channel 210 of FIG. 6.
[0028] 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 configuration may particularly influence
or dictate details of the implementation. Accordingly, other
embodiments are within the scope of the following claims.
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What is claimed is:
1. A compressor apparatus (20) comprising:
a housing (22) having first (53) and second (58) ports
along a flow path;
one or more working elements (26; 28) cooperating with
the housing (22) to define a compression path between suction
(60) and discharge (62) locations along the flow path; and
an unloading slide valve (100) having:
a valve element (102) having a range between a first
condition and a second condition, the second condition
being unloaded relative to the first condition;
a cylinder (128);
a piston (124) in the cylinder and mechanically
coupled to the valve element and including a body and at
least one seal (170) surrounding and carried by the body;
a control valve (140; 142) coupled to a headspace
(138)of the cylinder to selectively expose the headspace
to a fluid source (144), pressure of fluid in the
headspace producing a force on the piston and valve
element in a direction from the second condition toward
the first condition; and
means (190, 192; 210; 220) for relieving excess
pressure in the headspace sufficiently to avoid damage to
and dislocation of the seal.
2. The apparatus of claim 1 wherein:
the range is a range of linear translation; and
the means comprises a pressure relief valve (190) carried
by the piston.
3. The apparatus of claim 2 wherein the pressure relief
valve is a spring-loaded one-way valve.
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AMENDED SHEET

4. The apparatus of claim 1 wherein:
the means is effective to limit a pressure difference
across the piston to less than ten psi.
5. The apparatus of claim 1 further comprising:
a spring (120) biasing the valve element from the first
condition toward the third condition.
6. The apparatus of claim 5 wherein:
the spring is under compression when the valve element is
along an entirety of said range.
7. The apparatus of claim 5 wherein:
the spring is a metallic coil spring.
8. The compressor of claim 1 wherein the one or more working
elements include:
a. male-lobed rotor (26) having a first rotational axis
(500); and
a female-lobed rotor (28) having a second rotational axis
(502) and enmeshed with the male-lobed rotor.
9. The compressor of claim 8 wherein:
in the first condition, the compressor is at least at 90%
of a maximum displacement volume; and
in the second condition, compressor is at less than 10%
of the first condition displacement volume.
10. The apparatus of claim 1 wherein:
the range is a range of linear translation; and
the compressor is configured so that the means provides
the pressure relief only when the valve element is proximate
the first condition.
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11. The apparatus of claim 1 wherein:
the range is a range of linear translation,- and
the compressor is configured so that the means provides
the pressure relief only when the valve element is essentially
in the first condition.
12. The apparatus of claim 1 wherein:
the means comprises a channel (200; 220) in the cylinder.
13. The apparatus of claim 12 wherein:
the channel is an open channel (200) in an interior
surface of the cylinder.
14. The apparatus of claim 12 wherein:
the channel is a passageway (220) having first (222) and
second ports (224) in an interior surface of the cylinder.
15. A compressor apparatus comprising:
a housing having first and second ports along a flow
path;
one or more working elements cooperating with the housing
to define a compression path between suction and discharge
locations along the flow path; and
an unloading slide valve having:
a valve element having a range between a first
condition and a second condition, the second condition
being unloaded relative to the first condition;
a cylinder;
a piston in the cylinder and mechanically coupled to
the valve element and including a body and at least one
seal (170) surrounding and carried by the body
a control valve coupled to a headspace of the
cylinder to selectively expose the headspace to a fluid
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AMENDED SHEET

source, pressure of luid in the headspace producing a
force on the piston and valve element in a direction from
the second condition toward the first condition; and
a passageway {192; 200; 220) positioned to relieve
excess pressure in the headspace sufficiently to avoid
damage to and dislocation of the seal.
16. The apparatus of claim 15 wherein:
the passageway (192) is through the piston; and
a pressure relief valve (190) is carried by the piston
along the passageway.
17. The apparatus of claim 15 wherein a spring-loaded one-way
valve (190) is along the passageway (192).
18. The apparatus of claim 15 wherein:
the passageway is an open channel (200) in an interior
surface of the cylinder.
19. A method for remanufacturing a compressor (20) or
reengineering a configuration of the compressor comprising:
providing an initial such compressor or configuration
having:
a housing (22);
one or more working elements (26; 28) cooperating
with the housing to define a compression path between
suction (60) and discharge (62) locations; and
an unloading slide valve (100)having:
a valve element (102) having a range between a
first condition and a second condition, the second
condition being unloaded relative to the first
condition;
a cylinder (128);
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AMENDED SHEET

a person (10) and the cylender and mechanically
coupled to the valve element and including a body
and at least one seal (170) surrounding and carried
by the body; and
5 a fluid in a headspace (138) of the cylinder,
pressure of the fluid in the headspace producing a
force on the piston and valve element in a direction
from the second condition toward the first
condition; and
10 adapting such compressor or configuration to include
means (190, 192; 210; 220) for relieving excess pressure in
the headspace effective to relieve the excess pressure
sufficiently to avoid damage to and dislocation of the seal.
15 20. The method of claim 19 wherein:
the adapting includes selecting at least one parameter of
the means to provide a desired limit on said excess pressure.
21. The method of claim 20 wherein the selecting comprises an
20 iterative:
varying of said at least one parameter; and
directly or indirectly determining a level of excess
pressure permitted by the means.
25 22. The method of claim 21 wherein:
the varying comprises varying a cross-sectional area of a
passageway (200; 220) in the cylinder.
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AMENDED SHEET

A compressor (20) has an unloading slide valve
(100). The valve has a valve element (102) having a range between
a first condition and a second condition, the second condition
being unloaded relative to the first condition. A piston (124) is in
a cylinder (128) and mechanically coupled to the valve element.
A control valve (40; 42) is coupled to a headspace (138) of the
cylinder to selectively expose the headspace to a fluid source (144),
pressure of fluid in the headspace producing a force on the piston
and valve element in a direction from the second condition toward
the first condition. The compressor includes means (190, 192; 210;
220) for relieving excess pressure in the headspace.