U.S. patent application number 12/307805 was filed with the patent office on 2009-12-17 for screw compressor capacity control.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Bruce A. Fraser, Steven J. Holden, Alexander Lifson.
Application Number | 20090311119 12/307805 |
Document ID | / |
Family ID | 38981804 |
Filed Date | 2009-12-17 |
United States Patent
Application |
20090311119 |
Kind Code |
A1 |
Holden; Steven J. ; et
al. |
December 17, 2009 |
Screw Compressor Capacity Control
Abstract
A screw compressor has a housing (22; 302) having first (53;
330) and second (58; 340) ports along a flowpath. A first rotor
(26; 306) has a lobed body. A second rotor (28; 308, 310) has a
lobed body enmeshed with the first rotor body. The rotors and
housing cooperate to define a compression path between suction (60;
332) and discharge (62; 342) locations along the flowpath. Means
(100, 110, 120; 200, 210, 220; 370, 380, 390) provide relative
longitudinal movement between a blocking portion (57; 352) of the
housing and at least one of the first rotor and second rotor
between: a first condition wherein a pocket of the first and second
rotors is closed by the blocking portion; and a second condition
wherein the blocking portion does not close the pocket. To provide
capacity control, a control system (110; 390) is configured to
provide duty cycle control of the movement.
Inventors: |
Holden; Steven J.; (Manlius,
NY) ; Lifson; Alexander; (Manlius, NY) ;
Fraser; Bruce A.; (Manlius, NY) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C. (UTC)
900 CHAPEL STREET, SUITE 1201
NEW HAVEN
CT
06510-2802
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
38981804 |
Appl. No.: |
12/307805 |
Filed: |
July 27, 2007 |
PCT Filed: |
July 27, 2007 |
PCT NO: |
PCT/US07/74548 |
371 Date: |
January 7, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60820511 |
Jul 27, 2006 |
|
|
|
Current U.S.
Class: |
418/1 ;
418/201.1; 418/27 |
Current CPC
Class: |
F04C 27/006 20130101;
F04C 18/16 20130101; F04C 28/265 20130101 |
Class at
Publication: |
418/1 ;
418/201.1; 418/27 |
International
Class: |
F04C 18/16 20060101
F04C018/16; F04C 28/00 20060101 F04C028/00; F01C 20/18 20060101
F01C020/18 |
Claims
1. A screw compressor comprising: a housing (22; 302) having first
(53; 330) and second (58; 340) ports along a flowpath; a first
rotor (26; 306) having a lobed body (30) and an axis (500) and
mounted to the housing for rotation about said first rotor axis;
and a second rotor (28; 308, 310) having: a lobed body (34)
enmeshed with the first rotor body (30); and an axis (502), the
second rotor mounted to the housing for rotation about said second
rotor axis and cooperating with the first rotor (26; 306) and
housing (22; 302) to define a compression path between suction (60;
332) and discharge (62; 342) locations along the flowpath,
characterized by: means (100, 110, 120; 200, 210, 220; 370, 380,
390) for providing relative longitudinal movement between a
blocking portion (57; 352) of the housing and at least one of the
first rotor and second rotor between: a first condition wherein a
pocket of the first and second rotors is closed by the blocking
portion; and a second condition wherein the blocking portion does
not close the pocket; and a control system (110; 390) configured by
one or both of hardware and software to provide duty cycle control
of the movement.
2. The compressor of claim 1 wherein: the means (380, 390) provides
longitudinal movement of the blocking portion (352) relative to a
remainder of the housing between a first position associated with
the first condition and a second position associated with the
second condition.
3. The compressor of claim 2 wherein the means comprises: a spring
(370) biasing the blocking portion from the second position toward
the first position.
4. The compressor of claim 1 wherein: the means (100, 110, 120;
200, 210, 220) provides longitudinal movement of a single one of
the first rotor and second rotor relative to the blocking portion
(57).
5. The compressor of claim 1 wherein: the means provides
longitudinal movement of at least a movable rotor (28) of the first
and second rotors between first and second positions; and the means
comprises an actuator (100; 200) coupled to at least the movable
rotor of the first and second rotors to shift the movable
rotor.
6. The compressor of claim 5 wherein: a spring (120; 220) biases
the movable rotor from the second position toward the first
position.
7. The compressor of claim 1 wherein: the compressor lacks an
unloading valve.
8. The compressor of claim 1 wherein: the compressor lacks variable
speed motor control.
9. The compressor of claim 1 wherein: the control system is
configured to vary a frequency of the duty cycle control responsive
to a condition of a motor of the compressor.
10. The compressor of claim 1 wherein: the control system is
configured to vary a frequency of the duty cycle control responsive
to a condition of a motor of the compressor and a fluctuation in a
sensed temperature in a conditioned environment.
11. A method for operating the compressor of claim 1, the method
comprising: determining a desired loading state; and duty cycle
modulating of the means to provide the desired loading state.
12. The method of claim 11 further comprising: altering a frequency
of the duty cycle modulating responsive to a loading condition of a
motor of the compressor.
13. The method of claim 11 further comprising: altering a frequency
of the duty cycle modulating responsive to a sensed temperature
fluctuation of a conditioned environment.
14. The method of claim 11 further comprising: varying a frequency
of the duty cycle modulating responsive to a sensed temperature of
a motor of the compressor.
15. A screw compressor comprising: a housing (302) having first
(330) and second (340) ports along a flowpath; a first rotor (306)
having a lobed body and an axis (510) and mounted to the housing
for rotation about said first rotor axis; and a second rotor (308;
310) having: a lobed body enmeshed with the first rotor body; and
an axis (512; 514), the second rotor mounted to the housing for
rotation about said second rotor axis and cooperating with the
first rotor (306) and housing (302) to define a compression path
between suction (332) and discharge (342) locations along the
flowpath, wherein: a blocking portion (352) of the housing is
mounted for longitudinal movement of the blocking portion (352)
relative to a remainder of the housing between a first position
engaging the lobed bodies to define at least one compression pocket
and a second position retracted from the first position.
16. The compressor of claim 15 further comprising: an actuator
(380) coupled to blocking portion to shift the blocking portion
between the first and second positions.
17. The compressor of claim 15 further comprising: means (380, 390)
for shifting the blocking portion between the first and second
positions.
18. The compressor of claim 15 wherein: a spring (370) biases the
blocking portion from the second position toward the first
position.
19. The compressor of claim 15 wherein: the first position is
relatively toward a section end of the housing; and a spring (370)
biases the movable rotor from the second position toward the first
position.
20. The compressor of claim 15 wherein: the actuator is
fluid-operated.
21. The compressor of claim 20 wherein: the fluid is
refrigerant.
22. The compressor of claim 15 further comprising: a controller
(390) coupled to the actuator and configured to provide capacity
control of the compressor by modulating the blocking portion
between the first and second positions.
23. The compressor of claim 15 wherein: the compressor lacks an
unloading valve.
24. The compressor of claim 15 wherein: the compressor lacks
variable speed control.
25. A method for operating the compressor of claim 15 comprising:
determining a desired loading state; and duty cycle modulating an
actuator (380) of the movement between the first and second
positions to provide the desired loading state.
26. The method of claim 25 wherein: the duty cycle modulating is
performed while operating a motor of the compressor at an
essentially fixed speed.
27. The method of claim 25 wherein: the duty cycle modulating is
performed via a controller and the actuator fluidically operates to
provide the desired loading state.
28. The method of claim 25 wherein: the modulating of the actuator
(380) operates against a bias spring (370).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Benefit is claimed of U.S. patent application No. 60/820511,
filed Jul. 27, 2006.
BACKGROUND
[0002] The disclosure relates to compressors. More particularly,
the disclosure relates to screw-type refrigerant compressors.
[0003] 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.
[0004] 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 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.
[0005] 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 A1
and U.S. Pat. Nos. 4,249,866 and 6,302,668.
SUMMARY
[0006] One aspect of the disclosure involves a screw compressor
having a housing having first and second ports along a flowpath. A
first rotor has a lobed body and an axis and is mounted to the
housing for rotation about the axis. A second rotor has a lobed
body enmeshed with the first rotor body. The second rotor has an
axis and is mounted to the housing for rotation about that axis.
The rotors and housing cooperate to define a compression path
between suction and discharge locations along the flowpath. Means
provide relative longitudinal movement between a blocking portion
of the housing and at least one of the first rotor and second rotor
between a first condition and a second condition. In the first
condition, a pocket of the first and second rotors is closed by the
blocking portion. In the second condition, the blocking portion
does not close the pocket. To provide capacity control (to achieve
a desired loading condition), a control system is configured to
provide duty cycle control of the movement.
[0007] In various implementations, at least a movable rotor of the
first and second rotors may be mounted for translation between
first and second positions along its axis. An actuator may be
coupled to at least the movable rotor to shift the movable rotor.
Alternatively, the means may provide longitudinal movement of the
blocking portion relative to a remainder of the housing between a
first position associated with the first condition and a second
position associated with the second condition.
[0008] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a longitudinal sectional view of a baseline
compressor.
[0010] FIG. 2 is a partial, partially schematic, view of a
reengineered compressor in a loaded condition.
[0011] FIG. 3 is a view of the compressor of FIG. 2 in an unloaded
condition.
[0012] FIG. 4 is a partial, partially schematic, view of a second
reengineered compressor in a loaded condition.
[0013] FIG. 5 is a view of the compressor of FIG. 4 in an unloaded
condition.
[0014] FIG. 6 is a longitudinal sectional view of a second
reengineered compressor in a loaded condition.
[0015] FIG. 7 is a transverse sectional view of the compressor of
FIG. 6 taken along line 7-7.
[0016] FIG. 8 is a longitudinal sectional view of the compressor of
FIG. 6 taken along line 8-8.
[0017] FIG. 9 is a longitudinal sectional view of the compressor of
FIG. 6 in an unloaded condition.
[0018] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0019] FIG. 1 shows a baseline compressor 20 having a housing
assembly 22 containing a motor 24 driving rotors 26 and 28 having
respective central longitudinal axes 500 and 502. For purposes of
illustration, the basic structure of the compressor is taken from
one existing compressor. However, other existing or yet developed
compressor configurations are possible.
[0020] 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.
[0021] In the exemplary embodiment, the motor is an electric motor
having a rotor 45 and a stator 46. 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. Many other configurations are
possible.
[0022] 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 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.
[0023] 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 series of pairs of male compression pockets 66 and female
compression pockets 68 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 portions of face 57. The pockets sequentially form,
close, compress, and then open to a discharge port in the face 57
along a mesh of the associated rotor pair.
[0024] In the prior art, various mechanisms are used for screw
compressor unloading. Poppet and slide valves are used for
mechanical unloading whereas variable speed drives are used for
unloading via modulation of shaft speed. Slide valves offer
improved part load efficiency over poppet valves by providing
continuous modulation (vs. step changes in capacity). Variable
speed drives provide further improvement over slide valves by
extending the range of continuous modulation. The cost of these
unloading systems increase along with the improved performance
(poppets being lowest cost, then slide valves, then variable speed
drives being the highest cost). The exemplary baseline compressor
has a slide valve system 70 having a slide valve element 72 driven
by a fluidic (e.g. refrigerant) actuator 74.
[0025] FIGS. 2 and 3 show an actuator 100 coupled to the second
rotor 28 to provide relative longitudinal movement between the
second rotor and a blocking portion of the housing (e.g., the
upstream face 57). The exemplary relative movement comprises
shifting the second rotor between first and second positions. In
the first position/condition (FIG. 2), the normal sealing clearance
is provided between the body end/face 36 and discharge housing
upstream face 57 so that the face blocks/closes the compression
pocket(s). In the second position/condition (FIG. 3), the second
rotor 28 is shifted relatively away from the discharge housing to
open up a non-sealing clearance gap of thickness T between the body
end/face 36 and discharge housing upstream face 57. This unloads
opens the compression pocket(s) so that the compressor (e.g., fully
unloads).
[0026] Intermediate capacities may be achieved by bistatic
modulating between the two positions (e.g., changing the duty cycle
under a pulse width modulation type control). The exemplary
controller 110 is a microcontroller or computer configured by one
or both of hardware and software to provide the duty cycle control
to achieve a target capacity. The controller could be specific to
the compressor or of a broader system. The controller may determine
the target/desired capacity (e.g., as a fraction of full capacity)
responsive to sensed parameters (e.g., temperatures at various
locations in a refrigeration/cooling system) and/or programmed or
user entered parameters (e.g., thermostat settings).
[0027] A basic example is a fixed frequency system wherein the duty
cycle is controlled. With an exemplary frequency of 0.05 Hz, the
cycle period/(time) is twenty seconds. The duty cycle may be
determined as the fraction of the cycle period which the rotor body
end is in the engaged second position (or alternatively the
disengaged first position).
[0028] More complex modulations may be provided. For example, the
modulation frequency may be controlled dynamically ("on the fly")
for various performance results. For example, a low frequency may
be advantageous to minimize wear and energy consumption of the
actuator 100. However, a higher frequency may provide smoother
overall refrigerant flow and may reduce variations in motor loading
and associated motor wear. To control motor wear, a motor
temperature may be directly measured or indirectly measured via a
discharge temperature. In such a situation, the control system may
be configured to operate at an initial frequency and, thereafter,
increase the frequency if motor temperature or other motor loading
indication exceeds a desired value. For example, the frequency
might be incrementally increased up to a maximum value. For
example, starting at an initial value of 0.05 Hz, the frequency
could be incrementally increased up to an upper limit (e.g., a
value of 0.4 Hz). Feedback control may reduce the frequency back
toward or all the way to the initial low value.
[0029] Also, frequency could be similarly increased if sensed
temperature variations (e.g., in the conditioned environment such
as a refrigerated compartment or climate controlled room) exceed a
desired threshold (.DELTA.T). As with motor load, feedback can
decrease the frequency responsive to subsequent decreases in
temperature fluctuations.
[0030] Thus, the controller may be configured to modulate the rotor
position to provide the target capacity (subject to acceptable
deviation) while balancing attributes of low modulation frequency
(e.g., actuator wear and energy consumption) against attributes of
higher frequency (e.g., motor wear and energy consumption and
tolerance of fluctuations).
[0031] In various implementations, a spring 120 may bias the second
rotor 28 from the unloaded condition to the loaded condition.
Alternatively, the bias (and associated normal/default position)
may be reversed. The exemplary spring 120 is a metal tension coil
spring located at the discharge end/side.
[0032] Similarly, FIGS. 4 and 5 show first and second
positions/conditions of a compressor wherein an actuator 200 and
metal compression coil spring 220 are located at the suction
end/side. The exemplary spring 220 biases the rotor 28 toward the
loaded first position (FIG. 4) from the unloaded second position
(FIG. 5). The actuator 200 may pull against the spring bias to
shift from the first position/condition to the second
position/condition. Modulated operation may be similar to that of
the actuator 100 discussed above. Yet alternative push-pull
actuators may eliminate a spring bias or supplement the force of a
spring bias in the corresponding direction.
[0033] In various implementations, the actuator may be fluidic
(e.g. operating using fluid pressure such as from the compressor's
lubricant oil recovery system or refrigerant gas from sources at
the low and high pressure (suction and discharge) sides of the
refrigeration system). Alternative actuators may be
electromechanical or electromagnetic. The actuator and spring may
cooperate with the rotor via one or more of the bearing systems
supporting the rotor.
[0034] In alternative implementations, the actuator may be
positioned to shift both rotors (e.g., of a two-rotor compressor).
In a three-rotor compressor, the actuator may be positioned to
shift the central rotor, the other two rotors, or all three.
Depending upon implementation, the actuator may be positioned at
either end of the associated rotor(s).
[0035] FIGS. 6-9 show an alternate reengineered compressor 300. The
compressor 300 is reengineered from a slightly different baseline
compressor than the compressor of FIG. 1. Rather than a shifting of
a rotor while the housing remains stationary, the exemplary
compressor 300 shifts a blocking portion of the housing while the
axial/longitudinal positions of the rotors remain unchanged.
[0036] The compressor 300 has a housing assembly 302 containing a
motor 304 driving a male lobed rotor 306 and female lobed rotors
308 and 310 (FIG. 8) having respective central longitudinal axes
510, 512, and 514. The male rotor working portion has a first
(upstream/suction) end 320 and a second (downstream/discharge) end
322. Each of the female rotor working portions has a first end 324
and a second end 326. Other details may be similar to that of the
compressor 20. The exemplary housing assembly 302 has an inlet port
330 to a suction plenum 332. The housing assembly includes an
outlet port 340 from a discharge plenum 342. A check valve 344 may
be proximate the outlet port.
[0037] In the exemplary compressor 300, the modification from a
baseline condition differs from the FIG. 2-5 modification of the
compressor 20. Whereas the FIG. 2-5 modification of compressor 20
adds means for longitudinally shifting one or more rotors, the
compressor 300 reflects a reengineering wherein the discharge
housing is modified to include a shiftable plate 350. The plate 350
normally seals with the downstream ends of the rotor working
portions to define the associated compression pockets. The plate
350 has an upstream face 352 and a downstream face 354. A periphery
356 joins the upstream face 352 and the downstream face 354. The
plate 350 and its upstream face 352 serve as the housing blocking
portion normally blocking/closing the compression pockets. The
plate has a plurality of through apertures. FIG. 7 shows the plate
350 having through apertures 358, 359, and 360 accommodating the
downstream/discharge end shaft stubs of the rotors. FIG. 7 further
shows the plate as having apertures defining a first discharge port
362 and a second discharge port 364. The first discharge port is
positioned to discharge from the compression pocket between the
male rotor 306 and the first female rotor 308. The discharge port
364 is positioned to discharge refrigerant from the compression
pocket of the male rotor 306 and second female rotor 310.
[0038] The plate 350 may be disengaged from sealing the compression
pockets by a longitudinal translation away from the rotors (e.g.,
to a second (unloading) condition of FIG. 9). A spring 370 within
the discharge housing may bias the plate 350 to the
first/sealed/loaded condition from the second/unsealed/unloaded
condition. Movement beyond the second condition may be restricted
such as by a shoulder 372 of the housing. In the reengineering to
the configuration of the compressor 300, the discharge housing may
be extended along with the discharge end shaft stubs.
[0039] Capacity may be controlled by a modulated shifting of the
plate 350 (e.g., between the first (FIG. 6) and second (FIG. 9)
conditions (positions)). An exemplary modulation is
fluid-controlled. FIG. 6 shows a fluid-actuated shifting mechanism
380 for shifting the valve. The mechanism may be driven by a
controller 390 (e.g., similar to controller 110). FIG. 6 further
shows a motor temperature sensor 392 and a discharge temperature
sensor 394 which may be used by the controller 390 to provide the
feedback control over modulation frequency discussed above. The
shifting mechanism 380 includes a three-way valve 382. The
three-way valve is coupled by a first line (conduit) 384 to a
suction condition/location (e.g., to a port 385 at the suction
plenum 332). A second line 386 is coupled to a high pressure
location (e.g., to ports 387) positioned to intersect the
compression pockets right before the compression pockets normally
open to the discharge plenum 342. A third line 388 communicates
with the discharge plenum 342 (e.g., via a port 389 downstream of
the plate downstream face 354).
[0040] To unload the compressor, the valve 382 may be actuated to
place the lines 384 and 388 in communication with each other. This
communication drops the pressure along the downstream face 354
toward the suction pressure. Meanwhile, the upstream face 352 is
still exposed to higher pressure compressed refrigerant in the
compression pockets. The pressure differential across the plate 350
will shift the plate 350 from the first condition (FIG. 6) toward
the second (FIG. 9) condition (e.g., and compress the spring
370).
[0041] To reload the compressor, the valve 382 is actuated to
establish communication between the lines 386 and 388. This more
closely balances the pressure forces across the plate 350. This
force balance, combined with the bias force of the spring 370, will
shift the plate 50 back to the first condition maintain sealing of
the plate 350 to the rotors and maintain compression pocket
integrity. The spring 370 may also preload the plate 350 and
prevent vibration of the plate 350 from partially unloading the
compressor when a fully loaded condition is desired. Furthermore,
additional damping means may be provided (e.g., a viscous or
hydraulic damper (now shown)).
[0042] Various implementations may have one or more of several
advantages. For example, there may be an advantageous balance of
cost and performance. Continuous control similar to relatively
expensive systems (e.g., slide valve or variable speed systems)
could be provided at cost similar to relatively inexpensive systems
(e.g., poppet valve systems). For example, in a reengineering
situation, the reengineered compressor configuration could be less
expensive to manufacture than the baseline compressor. Such a
reengineering may involve eliminating an unloading valve (e.g., a
slide valve) and its associated actuation hardware. Such a
reengineering may eliminate variable speed motor control (e.g., by
eliminating a variable frequency drive (VFD) also known as a
variable speed drive (VSD)). However, although some systems may
thus lack an unloading valve and/or lack variable speed motor
control, the present features may also be implemented in
compressors having one or both of unloading valves and variable
speed motor control.
[0043] One or more embodiments have been described. Nevertheless,
it will be understood that various modifications may be made. 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.
* * * * *