U.S. patent application number 13/876203 was filed with the patent office on 2014-05-29 for variable capacity compressor with line-start brushless permanent magnet motor.
This patent application is currently assigned to EMERSON CLIMATE TECHNOLOGIES, INC.. The applicant listed for this patent is Pingshan Cao, Vincent Fargo, Xin Li, Qiang Liu. Invention is credited to Pingshan Cao, Vincent Fargo, Xin Li, Qiang Liu.
Application Number | 20140147294 13/876203 |
Document ID | / |
Family ID | 45891982 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140147294 |
Kind Code |
A1 |
Fargo; Vincent ; et
al. |
May 29, 2014 |
VARIABLE CAPACITY COMPRESSOR WITH LINE-START BRUSHLESS PERMANENT
MAGNET MOTOR
Abstract
A variable capacity compressor assembly (20) configured for
variable capacity modulation includes a housing (30), with a
compressing mechanism (22) and a driving mechanism (24) disposed
within the housing. The compressing mechanism includes compressing
members (54, 56) that are shiftable relative to one another between
loaded and unloaded states. The driving mechanism includes a
line-start brushless permanent magnet motor (26). The line-start
brushless permanent magnet motor includes a plurality of permanent
magnets (102) that are mounted on, and extend generally axially
along, a rotor core body (90) of the motor. Using the motor may
reduce manufacture cost, maintain conveniently, and increase
reliability.
Inventors: |
Fargo; Vincent; (St.
Charles, MO) ; Cao; Pingshan; (Suzhou, CN) ;
Li; Xin; (Suzhou, CN) ; Liu; Qiang; (Suzhou,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fargo; Vincent
Cao; Pingshan
Li; Xin
Liu; Qiang |
St. Charles
Suzhou
Suzhou
Suzhou |
MO |
US
CN
CN
CN |
|
|
Assignee: |
EMERSON CLIMATE TECHNOLOGIES,
INC.
Sidney
OH
|
Family ID: |
45891982 |
Appl. No.: |
13/876203 |
Filed: |
September 30, 2011 |
PCT Filed: |
September 30, 2011 |
PCT NO: |
PCT/CN2011/080488 |
371 Date: |
June 10, 2013 |
Current U.S.
Class: |
417/53 ;
417/410.1; 417/410.3; 417/410.5; 417/415 |
Current CPC
Class: |
F04C 29/0085 20130101;
F04C 23/02 20130101; F04C 2240/40 20130101; F04B 35/04 20130101;
F04C 18/0215 20130101; F04C 27/005 20130101; F04C 28/24 20130101;
F04C 23/008 20130101; F04C 18/3564 20130101; F01C 21/0863 20130101;
F04C 11/008 20130101; F04B 17/03 20130101 |
Class at
Publication: |
417/53 ;
417/410.1; 417/410.5; 417/415; 417/410.3 |
International
Class: |
F04C 11/00 20060101
F04C011/00; F04B 17/03 20060101 F04B017/03; F04C 23/00 20060101
F04C023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2010 |
CN |
201010537890.1 |
Claims
1. A variable capacity compressor assembly configured to provide
variable capacity modulation, said compressor assembly comprising:
a housing; a compressing mechanism disposed within the housing and
including first and second mechanical elements, said mechanical
elements being shiftable relative to one another between a loaded
state and an unloaded state; and a driving mechanism disposed
within the housing and drivingly engaging at least one of the
mechanical elements for causing the mechanical elements to move
relative to one another, said driving mechanism including a
line-start brushless permanent magnet motor, said motor including a
stator and a rotor rotatable about an axis and spaced away from the
stator, said rotor including a rotor core body and a plurality of
permanent magnets mounted on the rotor core body, said permanent
magnets extending generally axially along the rotor core body.
2. The variable capacity compressor assembly as claimed in claim 1,
said mechanical elements comprising scroll members.
3. The variable capacity compressor assembly as claimed in claim 2,
said driving mechanism further including a drive shaft configured
to rotate with the rotor, said drive shaft being operably coupled
with one of the scroll members for causing the one of the scroll
members to move in a generally orbital relationship relative to the
other of the scroll members.
4. The variable capacity compressor assembly as claimed in claim 3,
said scroll members being shiftable generally axially relative to
one another between the loaded and unloaded states.
5. The variable capacity compressor assembly as claimed in claim 4,
said housing comprising a hermetic shell defining a substantially
enclosed space.
6. The variable capacity compressor assembly as claimed in claim 1,
said permanent magnets being received within the rotor core body,
said rotor core body comprising a plurality of axially stacked
rotor laminations, at least one of said rotor laminations being
disposed in contact with the plurality of permanent magnets to
retain the same in place.
7. The variable capacity compressor assembly as claimed in claim 6,
said permanent magnets being disposed generally parallel to the
axis, said permanent magnets being disposed substantially adjacent
a radially outer periphery of the rotor core body.
8. The variable capacity compressor assembly as claimed in claim 7,
said rotor assembly further including a plurality of
circumferentially spaced axial bars disposed adjacent the radially
outer periphery of the rotor core body to cooperatively define at
least a portion thereof.
9. The variable capacity compressor assembly as claimed in claim 8,
said rotor assembly including four substantially equally-sized
permanent magnets, said permanent magnets being arranged in two
pairs, with each of the pairs of magnets being symmetrical to the
other of the pairs of magnets with respect to the axis.
10. The variable capacity compressor assembly as claimed in claim
9, said mechanical elements comprising scroll members shiftable
generally axially relative to one another between the loaded and
unloaded states, said motor assembly defining a single-speed,
three-phase motor.
11. The variable capacity compressor assembly as claimed in claim
1, said motor assembly defining a single-speed motor.
12. The variable capacity compressor assembly as claimed in claim
11, said motor assembly defining a three-phase motor.
13. The variable capacity compressor assembly as claimed in claim
1, said stator including a stator core body presenting a plurality
of circumferentially spaced axial slots and defining a central bore
for receiving the rotor, said stator further including electrically
conductive winding coils received within and distributed generally
across multiple ones of the axial slots of the stator core body,
said winding coils comprising aluminum.
14. The variable capacity compressor assembly as claimed in claim
1, said permanent magnets comprising neodymium.
15. The variable capacity compressor assembly as claimed in claim
1, said compressing mechanism comprising a piston and cylinder
assembly, and said mechanical elements including a valve to block
suction gas to said piston and cylinder assembly.
16. The variable capacity compressor assembly as claimed in claim
1, said compressing mechanism comprising scroll members and said
mechanical elements including a valve to release gas from an
intermediate chamber of said scroll members to a suction chamber
within said housing.
17. The variable capacity compressor assembly as claimed in claim
1, said compressing mechanism comprising a rotary vane and a
compression rotor and said mechanical elements including a
three-way valve to alternately apply suction gas and discharge gas
to said rotary vane to bias said rotary vane against and away from
said compression rotor.
18. In a variable capacity compressor assembly configured to
provide variable capacity modulation including a compressing
mechanism disposed within a housing with first and second
mechanical elements shiftable relative to one another between a
loaded state and an unloaded state, and a driving mechanism
disposed within the housing for drivingly engaging one of the
mechanical elements to cause the mechanical elements to move
relative to one another, wherein the improvement comprises
combining the shiftable mechanical elements with a single-speed,
line-start brushless permanent magnet motor operable to drive the
one of the mechanical elements, said motor including a stator and a
rotor rotatable about an axis and spaced away from the stator, said
rotor including a rotor core body and a plurality of permanent
magnets mounted on the rotor core body, said permanent magnets
extending generally axially along the rotor core body.
19. In the variable capacity compressor assembly configured to
provide variable capacity modulation as claimed in claim 18, said
mechanical elements comprising scroll members, said driving
mechanism further including a drive shaft configured to rotate with
the rotor, said drive shaft being operably coupled with one of the
scroll members for causing the one of the scroll members to move in
a generally orbital relationship relative to the other of the
scroll members.
20. In the variable capacity compressor assembly configured to
provide variable capacity modulation as claimed in claim 19, said
permanent magnets being received within the rotor core body, said
rotor core body comprising a plurality of axially stacked rotor
laminations, at least one of said rotor laminations being disposed
in contact with the plurality of permanent magnets to retain the
same in place.
21. In the variable capacity compressor assembly as claimed in
claim 18, said compressing mechanism comprising a piston and
cylinder assembly, and said mechanical elements including a valve
to block suction gas to said piston and cylinder assembly.
22. The variable capacity compressor assembly as claimed in claim
18, said compressing mechanism comprising scroll members and said
mechanical elements including a valve to release gas from an
intermediate chamber of said scroll members to a suction chamber
within said housing.
23. The variable capacity compressor assembly as claimed in claim
18, said compressing mechanism comprising a rotary vane and a
compression rotor and said mechanical elements including a
three-way valve to alternately apply suction gas and discharge gas
to said rotary vane to bias said rotary vane against and away from
said compression rotor.
24. A method of delivering increased compressor efficiency at lower
incremental cost within a variable capacity compressor assembly
configured to provide variable capacity modulation, wherein the
compressor includes first and second scroll members generally
axially shiftable relative to one another between a loaded state
and an unloaded state, said method comprising: driving one of the
scroll members with a single-speed, line-start brushless permanent
magnet motor, such that the driven scroll member moves in a
generally orbital relationship relative to the other scroll member
to thereby compress a working fluid when the scrolls are in the
loaded state; and shifting the scroll members into the unloaded
state during continuous operation of the single-speed motor to
thereby efficiently modulate capacity of the compressor without the
expense of a complex drive unit to vary motor speed.
25. The increased compressor efficiency delivering method of claim
24, said motor including a stator and a rotor rotatable about an
axis and spaced away from the stator, said rotor including a rotor
core body and a plurality of permanent magnets mounted on the rotor
core body, said permanent magnets extending generally axially along
the rotor core body.
26. The increased compressor efficiency delivering method of claim
25, said scroll members and said single-speed motor being disposed
within a hermetic shell defining a substantially enclosed space.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit and priority of Chinese
Patent Application for Invention No. 201010537890.1, filed on Sep.
30, 2010. The entire disclosure of the above application is
incorporated herein by reference.
FIELD
[0002] The present disclosure relates generally to a variable
capacity compressor assembly configured to provide variable
capacity modulation. More specifically, the present disclosure
relates to a variable capacity compressor including a compressing
mechanism with mechanical elements shiftable between loaded and
unloaded states, wherein the compressing mechanism is driven by a
driving mechanism including a line-start brushless permanent magnet
motor.
BACKGROUND
[0003] Compressors are commonly used in a variety of industrial and
residential applications to circulate refrigerant within a
refrigeration, heat pump, HVAC, or chiller system to provide a
desired heating or cooling effect. For example, some traditional
air conditioning systems often use a compressor that is either
working at maximum capacity, or is switched off, in order to
regulate the temperature of the room. A thermostat can be used to
measure the ambient air temperature and switch the compressor on
when the ambient air temperature is too far from the desired
temperature.
[0004] One way to meet the varying cooling demand is to vary (or
modulate) the capacity of the compressor. A particular type of
compressor that has been generally effective in this area is the
scroll compressor, in which a pair of scroll members cooperate to
compress a working fluid (e.g., coolant in liquid or gas phase). A
scroll compressor typically includes two main groups of components:
a mechanical compressing device including the scrolls, and an
electrical motor driving device to move at least one of the
scrolls. Either of these components, the compressing device or the
driving device, may be manipulated to modulate the capacity of the
compressor.
[0005] Conventionally, the electrical motor driving device has been
manipulated to modulate the capacity of the compressor. For
example, inverter technology operates on the principle of variable
compressor motor speed, wherein an electrical signal is given to
the compressor motor to make it rotate faster or slower, depending
on the load. If the load is high, the compressor motor rotates at a
faster speed and delivers higher capacity; conversely, if the load
is low, the compressor motor rotates at a lower speed to deliver
lower output.
[0006] Traditional variation of compressor motor speed, therefore,
has incorporated within the compressor assembly either a two-speed
motor, or a full variable speed motor. Both of these known motors
have been satisfactory in some respects, but also present
drawbacks. For example, the two-speed motor is very complicated to
manufacture and often produces merely adequate performance results.
The full variable speed motor often achieves increased system
performance over a two-speed motor, but requires a complex and
expensive drive unit to continuously vary the motor speed. The
complexity of these prior art systems to vary compressor motor
speed not only require additional manufacturing costs, but can also
lead to maintenance and/or reliability issues.
SUMMARY
[0007] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0008] A variable capacity compressor assembly is configured to
provide variable capacity modulation. The compressor assembly
includes a housing, a compressing mechanism disposed within the
housing and including first and second mechanical elements. The
mechanical elements are shiftable relative to one another between a
loaded state and an unloaded state. The driving mechanism is
disposed within the housing and drivingly engages at least one of
the mechanical elements for causing the mechanical elements to move
relative to one another. The driving mechanism includes a
line-start brushless permanent magnet motor. The motor including a
stator and a rotor rotatable about an axis and spaced away from the
stator. The rotor includes a rotor core body and a plurality of
permanent magnets mounted on the rotor core body. The permanent
magnets extend generally axially along the rotor core body.
[0009] A variable capacity compressor assembly is configured to
provide variable capacity modulation including a compressing
mechanism disposed within a housing with first and second
mechanical elements shiftable relative to one another between a
loaded state and an unloaded state, and a driving mechanism
disposed within the housing for drivingly engaging one of the
mechanical elements to cause the mechanical elements to move
relative to one another. The improvement comprises combining the
shiftable mechanical elements with a single-speed, line-start
brushless permanent magnet motor operable to drive the one of the
mechanical elements. The motor includes a stator and a rotor
rotatable about an axis and spaced away from the stator. The rotor
includes a rotor core body and a plurality of permanent magnets
mounted on the rotor core body. The permanent magnets extend
generally axially along the rotor core body.
[0010] A method of delivering increased compressor efficiency at
lower incremental cost within a variable capacity compressor
assembly configured to provide variable capacity modulation,
wherein the compressor includes first and second scroll members
generally axially shiftable relative to one another between a
loaded state and an unloaded state, said method includes driving
one of the scroll members with a single-speed, line-start brushless
permanent magnet motor, such that the driven scroll member moves in
a generally orbital relationship relative to the other scroll
member to thereby compress a working fluid when the scrolls are in
the loaded state, and shifting the scroll members into the unloaded
state during continuous operation of the single-speed motor to
thereby efficiently modulate capacity of the compressor without the
expense of a complex drive unit to vary motor speed.
[0011] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0012] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0013] FIG. 1 is an isometric view of a variable capacity
compressor assembly configured to provide variable capacity
modulation constructed, with a compressing mechanism and a driving
mechanism including a line-start brushless permanent magnet motor
assembly disposed therein, in accordance with the present
disclosure;
[0014] FIG. 2 is a sectional view of the variable capacity
compressor assembly, taken approximately through the middle of the
compressor assembly of FIG. 1, depicting internal details of
construction of the compressing mechanism including first and
second mechanical elements, and of the driving mechanism including
rotor and stator assemblies of the line-start brushless permanent
magnet motor, in accordance with the present disclosure;
[0015] FIG. 3 is an isometric view of the line-start brushless
permanent magnet motor assembly included in the driving mechanism
of the variable capacity compressor assembly shown in FIGS. 1-2,
illustrating the rotor and stator assemblies, in accordance with
the present disclosure;
[0016] FIG. 4 is a sectional view of the line-start brushless
permanent magnet motor assembly, taken approximately through the
middle of the motor assembly of FIG. 2, depicting internal details
of construction of the rotor assembly, including a plurality of
permanent magnets disposed therein, in accordance with the present
disclosure;
[0017] FIG. 5 is a sectional view of another variable capacity
compressor assembly, in accordance with the present disclosure;
[0018] FIG. 6 is a sectional view of another variable capacity
compressor assembly, in accordance with the present disclosure;
[0019] FIG. 7 is a sectional view of another variable capacity
compressor assembly, in accordance with the present disclosure;
and
[0020] FIG. 8 is a sectional view of another variable capacity
compressor assembly, in accordance with the present disclosure.
[0021] The drawings are not necessarily to scale, emphasis instead
being placed upon clearly illustrating the principles of the
preferred embodiments.
[0022] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0023] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0024] The present disclosure is susceptible of embodiment in many
different forms. While the drawings illustrate, and the
specification describes, certain preferred embodiments of the
disclosure, it is to be understood that such disclosure is by way
of example only. There is no intent to limit the principles of the
present disclosure to the particular disclosed embodiments.
[0025] The present disclosure provides a variable capacity
compressor assembly configured for variable capacity modulation,
wherein a mechanical compressing device is manipulated to modulate
the capacity of the compressor. For example, in a variable
capacity, pulse width modulated (loaded and unloaded) scroll
compressor, the mechanical scrolls of the compressing mechanism are
moved relative to one another to modulate the capacity of the
compressor, while the electrical motor driving the compressing
device is run at a generally constant speed.
[0026] Variable capacity, pulse width modulated scroll compressor
technology operates on the principle of loading and unloading of
the scrolls. While the motor runs at a generally constant speed,
the scrolls are engaged and disengaged periodically in order to
provide durations of "full capacity" and "no capacity" of the
compressing device. Time averaging of the loading and unloading
states results in an effectively infinitely variable capacity
output. Other mechanical compressor capacity modulation
technologies may also be used to vary the capacity of the
compressor while the electric motor driving the compressing device
is operated at a generally constant speed. Additional examples of
mechanical compressor capacity modulation technology, as described
in further detail below, include: delayed suction devices, blocked
suction devices, pulse width modulation of delayed suction devices,
and pulse width modulation of blocked suction devices. Further,
these compressor capacity modulation technologies may be utilized
with scroll compressors, reciprocating compressors, rotary vane
compressors, and the like.
[0027] Eliminating some of the complexity of prior art modulating
systems that rely upon traditional variation of compressor motor
speed, such as via a two-speed motor, or a full variable speed
motor, may reduce manufacturing and/or maintenance costs and
provide enhanced reliability. Furthermore, manipulation of the
mechanical compressing device can lead to quicker and more
efficient transitions between capacity loading states. Embodiments
of the present disclosure improve overall system efficiency by
driving the mechanical compressing device at a generally constant
speed with a line-start brushless permanent magnet motor.
[0028] Improving the efficiency of the electric motor driving the
mechanical compressing device, often one of the highest
power-consuming components of a compressor assembly, can improve
overall compressor system efficiency. It is believed that a
refrigeration system incorporating the variable capacity compressor
assembly with the line-start brushless permanent magnet motor of
the present disclosure provides improved overall system performance
to meet high efficiency standards (e.g., seasonal efficiency energy
rating). Moreover, it is believed that the variable capacity
compressor incorporating the line-start brushless permanent magnet
motor of the present disclosure can achieve new Chinese Level 1
efficiencies.
[0029] Some embodiments of the present disclosure may even offset a
considerable portion of material cost incurred by incorporating
permanent magnets in a rotor assembly of the line-start brushless
permanent magnet motor by using a stator assembly with a winding
formed of aluminum. It has been unexpectedly determined that such a
construction of a line-start brushless permanent magnet motor with
windings formed of aluminum (a material not ordinarily used in
windings for high-performance motors) exhibited only a slight
performance difference compared to a line-start brushless permanent
magnet motor with traditional copper windings.
[0030] According to one aspect of the present disclosure, a
variable capacity compressor assembly is provided that is
configured to provide variable capacity modulation. The compressor
assembly includes a housing and a compressing mechanism disposed
within the housing that includes first and second mechanical
elements. The mechanical elements are shiftable relative to one
another between a loaded state and an unloaded state. The
compressor assembly further includes a driving mechanism disposed
within the housing that drivingly engages at least one of the
mechanical elements for causing the mechanical elements to move
relative to one another. The driving mechanism includes a
line-start brushless permanent magnet motor. The motor includes a
stator and a rotor rotatable about an axis and spaced away from the
stator. The rotor includes a rotor core body and a plurality of
permanent magnets mounted on the rotor core body. The permanent
magnets extend generally axially along the rotor core body.
[0031] According to another aspect of the present disclosure, in a
variable capacity compressor assembly configured to provide
variable capacity modulation, which includes a compressing
mechanism disposed within a housing with first and second
mechanical elements shiftable relative to one another between a
loaded state and an unloaded state, and a driving mechanism
disposed within the housing for drivingly engaging one of the
mechanical elements to cause the mechanical elements to move
relative to one another, the improvement includes combining the
shiftable mechanical elements with a single-speed, line-start
brushless permanent magnet motor operable to drive the one of the
mechanical elements. The motor includes a stator and a rotor
rotatable about an axis and spaced away from the stator. The rotor
includes a rotor core body and a plurality of permanent magnets
mounted on the rotor core body. The permanent magnets extend
generally axially along the rotor core body.
[0032] Another aspect of the present disclosure concerns a method
of delivering increased compressor efficiency at lower incremental
cost within a variable capacity compressor assembly configured to
provide variable capacity modulation, wherein the compressor
includes first and second scroll members generally axially
shiftable relative to one another between a loaded state and an
unloaded state. The method includes the step of driving one of the
scroll members with a single-speed, line-start brushless permanent
magnet motor, such that the driven scroll member moves in a
generally orbital relationship relative to the other scroll member
to thereby compress a working fluid when the scrolls are in the
loaded state. The method also includes the step of shifting the
scroll members into the unloaded state during continuous operation
of the single-speed motor to thereby efficiently modulate capacity
of the compressor without the expense of a complex drive unit to
vary motor speed.
[0033] Various other aspects and advantages of the present
disclosure will be apparent from the following detailed description
of the preferred embodiments and the accompanying drawing
figures.
[0034] With reference to FIGS. 1-2, a variable capacity compressor
assembly 20 constructed in accordance with the principles of an
embodiment of the present disclosure is depicted for use in various
applications. The compressor assembly 20 is configured to provide
variable capacity modulation. The compressor assembly 20 may be
used in a variety of industrial and residential applications
including, for example, an HVAC, refrigeration, heat pump, or
chiller system.
[0035] With reference to FIG. 2, the compressor assembly 20 broadly
includes a compressing mechanism 22 configured to provide variable
capacity modulation, and a driving mechanism 24 including a
line-start brushless permanent magnet motor assembly 26, described
in further detail below with reference to FIGS. 3-4.
[0036] Some conventional structural aspects of the compressor
assembly 20 are described herein only relatively briefly.
Nevertheless, it will be appreciated that various structural
details of the compressor assembly 20 will be readily understood by
one of ordinary skill in the art.
[0037] With reference to FIGS. 1 and 2, components of the
compressor assembly 20 are contained within an internal chamber 28
that is broadly defined by a case in the form of a housing 30. As
shown, the housing 30 is substantially sealed such that the
internal chamber 28 is hermetically sealed from an outside
environment. The housing 30 is generally cylindrical and presents
opposite top and bottom axial margins 32, 34. The housing 30
comprises a shell element 36, a base 38 disposed generally adjacent
the bottom margin 34, and a cap 40 disposed generally adjacent the
top margin 32.
[0038] While the internal chamber 28 is hermetically sealed from an
outside environment, some elements (e.g., electrical power and a
working fluid to be compressed) must pass through the housing 30
through specific sealed passageways. In this regard, the compressor
assembly 20 includes a compressor power connector 42 disposed on
the shell element 36. The compressor power connector 42 is in
electrical communication with an appropriate element of the
line-start brushless permanent magnet motor assembly 26 described
below.
[0039] Furthermore, the compressor assembly 20 includes an inlet 44
disposed on the shell element 36, and an outlet 46 disposed on the
cap 40 to transport compressible working fluid (e.g., coolant in
liquid or gas phase) into and out of the internal chamber 28 of the
compressor assembly 20. The specific dispositions of the inlet 44
and the outlet 46 could be altered without departing from the
teachings of the present disclosure.
[0040] With reference to FIG. 2, the compressor assembly 20
includes the compressing mechanism 22 and the driving mechanism 24
including the motor assembly 26, described in detail below,
disposed within the housing 30. The compressor assembly 20 further
includes an upper bearing assembly 48 and a lower bearing assembly
50 for rotatably supporting a shaft 52 of the driving mechanism 24
and components of the compressing mechanism 22.
[0041] The compressing mechanism 22 includes first and second
mechanical elements, depicted in the form of scroll members 54, 56
that cooperate to compress a working fluid. In the illustrated
embodiment, the first scroll member 54 is rotatably fixed relative
to the second scroll member 56. The first scroll member 54 is also
axially shiftably secured relative to the second scroll member 56
within the internal chamber 28 in a manner generally known in the
art. The second scroll member 56 is operably coupled with the
driving mechanism 24 to be drivingly connected to the shaft 52 of
the motor assembly 26 via a crankpin 58 and a drive bushing 60,
such that the second scroll member 56 is orbitally moveable
relative to the first scroll member 54, as described in detail
below.
[0042] The non-orbiting scroll member 54 and the orbiting scroll
member 56 are positioned in meshing engagement with one another,
and a suitable conventional coupling 57 permits generally eccentric
orbital motion (along an annular path) therebetween, but prevents
relative spinning motion therebetween.
[0043] A partition plate 62 is provided generally adjacent the top
margin 32 of the housing 30 and serves to divide the internal
chamber 28 into a discharge chamber 64 at the upper end thereof and
a suction chamber 66 at the lower end thereof.
[0044] When the first non-orbiting scroll member 54 and the second
orbiting scroll member 56 are shifted axially relative to one
another into a first position corresponding with a loaded state,
the compressing mechanism 22 is configured to compress a working
fluid and run at full (100%) capacity during rotation of the motor
assembly 26 of the driving mechanism 24. Alternatively, when the
first non-orbiting scroll member 54 and the second orbiting scroll
member 56 are shifted axially relative to one another into a second
position corresponding with an unloaded state, the compressing
mechanism 22 is configured such that it does not compress the
working fluid and runs at no (0%) capacity, even during continued
rotation of the motor assembly 26 of the driving mechanism 24. In
this way, the capacity of the variable capacity scroll compressor
assembly 20 can be changed quickly and efficiently without
necessarily altering the speed of the motor assembly 26 of the
driving mechanism 24.
[0045] The relative axial disposition between the first
non-orbiting scroll member 54 and the second orbiting scroll member
56 may be operably shifted via a control, such as a solenoid valve,
as is generally known in the art. Therefore, by appropriately
varying the loaded state time and the unloaded state time during
any given cycle time, the variable capacity scroll compressor
assembly 20 can deliver any capacity desired for a given system. In
this way, pulse width modulation can be used, with an appropriate
cycle time, to vary the capacity of the compressor assembly 20 to
any capacity between 100% capacity and 0% capacity.
[0046] During operation at full (100%) capacity, as the second
orbiting scroll member 56 orbits with respect to the first
non-orbiting scroll member 54, working fluid to be compressed is
drawn into the suction chamber 66 of the internal chamber 28 of the
compressor assembly 20 via the inlet 44. From the suction chamber
66, the working fluid moves into a volume-decreasing compression
chamber 68 cooperatively defined by portions of the scroll members
54, 56. The intermeshing scroll wraps of the scroll members 54, 56
define moving pockets of working fluid within the compression
chamber 68 that progressively decrease in size as they move
radially inwardly as a result of the orbiting motion of the second
orbiting scroll member 56, thus compressing the working fluid
entering via inlet 44. The compressed working fluid is then
discharged into the discharge chamber 64 and out of the variable
capacity compressor assembly 20 via the outlet 46.
[0047] During operation at no (0%) capacity, even if the second
orbiting scroll member 56 orbits with respect to the first
non-orbiting scroll member 54, the scroll members 54, 56 are
shifted axially away from one another into the unloaded state, such
that no suction is generated by the compression chamber 68 and
there is no mass flow of the working fluid through the variable
capacity compressor assembly 20. Because the variable capacity
compressor assembly 20 can run at no (0%) capacity even as the
second orbiting scroll member 56 is moving with respect to the
first non-orbiting scroll member 54, the compressing mechanism 22
can effectively and efficiently be driven by the driving mechanism
24 including the line-start brushless permanent magnet motor
assembly 26 configured as a single-speed motor, as described in
detail below.
[0048] As also described in detail below, one embodiment of the
line-start brushless permanent magnet motor assembly 26
incorporated within the capacity compressor assembly 20
demonstrated a motor efficiency of approximately 95%. Since a motor
assembly of a driving mechanism is often one of the highest
power-consuming components of a compressor assembly (or even of an
entire system incorporating the compressor assembly, such as an air
conditioning system), the efficiency improvements provided by
incorporation of the line-start brushless permanent magnet motor
assembly 26 in the present disclosure provides significant
performance enhancements in the compressor assembly 20. In one
embodiment, the compressor assembly 20 including the line-start
brushless permanent magnet motor assembly 26, as described below,
demonstrated a higher seasonal efficiency energy rating than has
been achieved by prior compressor assemblies.
[0049] Many of the components of the compressor assembly 20 are
substantially conventional in nature, and various aspects of such
components may take alternative forms and/or otherwise vary
significantly from the illustrated embodiment without departing
from the teachings of the present disclosure. Any such
modifications to generally conventional components of the variable
capacity compressor assembly 20 are not intended to impact the
scope of the present disclosure.
[0050] With continued reference to FIGS. 1-2 and additional
reference to FIGS. 3-4, the line-start brushless permanent magnet
motor assembly 26 will be described in further detail. The motor
assembly 26 includes a rotor assembly 70, which is rotatable about
an axis 72 (FIG. 4) and a stator assembly 74. The rotor assembly 70
includes the axially disposed shaft 52 that is configured for
rotation with the rotor assembly 70 and that projects axially
outwardly from both ends of the stator assembly 74. While only one
exemplary embodiment is depicted here, of course alternative
arrangements of suitable rotor and stator assemblies are
contemplated and are clearly within the ambit of the present
disclosure.
[0051] Turning to construction details of the stator assembly 74,
the stator assembly 74 depicted in FIGS. 3-4 broadly includes a
stator core body 76 and a generally axially concentric winding 78.
The illustrated stator core body 76 is comprised of a plurality of
axially stacked stator laminations 80 (FIG. 4), as is generally
known in the art. It is noted that the winding 78 depicted in FIG.
3 is shown in a conventional schematic form, but that additional
details regarding the winding 78 are described below. The
particular configuration of the winding 78 may directly impact the
power, torque, voltage, operational speed, number of poles, etc. of
the motor assembly 26.
[0052] Each individual stator lamination 80 includes a
substantially annular steel body, such that the plurality of
axially stacked stator laminations 80 forming the stator core body
76 cooperatively presents a generally central axial bore 82 for
receiving the rotor assembly 70. An air gap 84 extends radially
between the stator core body 76 of the stator assembly 74 and the
rotor assembly 70, such that the rotor assembly 70 is able to
rotate freely within the stator assembly 74.
[0053] The plurality of axially stacked stator laminations 80
forming the stator core body 76 also cooperatively presents a
plurality of generally arcuate slots 86 extending axially
therethrough, with each depicted slot 86 being in communication
with the air gap 84. Electrically conductive wires make up the
winding 78, which passes through the slots 86 for receipt therein.
It is noted that in the illustrated embodiment, the stator core
body 76 of the stator assembly 74 includes twenty-four slots 86,
although various numbers of slots may be alternatively provided
without departing from the teachings of the present disclosure.
[0054] The motor assembly 26 of the depicted embodiment is
configured as a three-phase motor. Shifting briefly now to
operation considerations of three-phase motors, and to details of
the windings used therein, a three-phase motor is often more
compact and can be less costly than a single-phase motor of the
same voltage class and duty rating. In addition, many three-phase
motors often exhibit less vibration and may therefore last longer
than corresponding single-phase motors of the same power used under
the same conditions. The principles of the present disclosure,
however, are not limited to a three-phase motor, but also apply
with equal force to a single-phase motor. Further, the motor
assembly 26 of the depicted embodiment is configured as a
single-speed motor.
[0055] The winding 78 comprises a phase winding for each of the
three power phases. Winding configurations for three-phase motors
are generally known and are not described in detail herein. With
reference to FIG. 3, in the depicted embodiment of the present
disclosure, the stator assembly 74 includes a power connector 88
that includes three leads to be connected to a power source, with
one of each of the leads corresponding to each of the three power
phases. As will be readily understood, and with brief reference to
FIG. 2, the stator power connector 88 is in electrical
communication with the compressor power connector 42 described
above.
[0056] It is contemplated that the winding 78 of the line-start
brushless permanent magnet motor assembly 26 may comprise copper,
or may comprise aluminum as described further below. While it is
noted that the winding 78 comprising aluminum may also include
other materials (e.g., aluminum alloys or copper-cladded aluminum),
the winding 78 of the illustrated embodiment consists essentially
of aluminum wire. Additional details and unforeseen advantages of
this atypical winding material within the line-start brushless
permanent magnet motor assembly 26 will be described in further
detail below.
[0057] Turning next to construction details of the rotor assembly
70, and with specific reference to FIG. 4, the rotor assembly 70
broadly includes a rotor core body 90 comprising a plurality of
axially stacked rotor laminations 92 integrally formed (such as by
die casting) with a plurality of aluminum bars 94. The bars 94
extend axially along the plurality of rotor laminations 92 and may
include aluminum rings disposed along respective axial margins
thereof. The particular configuration of the bars 94 may directly
impact startup operation of the motor assembly 26. Other
configurations of bars may be used and are within the ambit of the
present disclosure, including, but not limited to, bars that skew
helically around the rotor core body 90 or bars that have no skew
at all.
[0058] With continued reference to FIG. 4, each individual rotor
lamination 92 includes a substantially annular steel body, such
that the plurality of axially stacked rotor laminations 92 forming
the rotor core body 90 cooperatively presents a radially outer
periphery 96 and an axially aligned shaft hole 98 extending axially
therethrough to receive the shaft 52. Additionally, the plurality
of axially stacked rotor laminations 92 forming the rotor core body
90 further cooperatively presents a plurality of a generally
arcuate slots 100 extending axially therethrough, with each slot
100 being disposed at least adjacent (if not in communication with)
the radially outer periphery 96. The aluminum bars 94 are formed to
pass through the slots 100 to be disposed at least adjacent the
radially outer periphery 96 of the rotor core body 90 to
cooperatively define at least a portion thereof (if not
cooperatively forming an exposed bar a rotor body). It is noted
that in the illustrated embodiment, each rotor lamination 92
includes thirty-four slots 100, although various numbers of slots
may be similarly provided without departing from the teachings of
the present disclosure.
[0059] The rotor assembly 70 further includes a plurality of
permanent magnets 102 mounted on the rotor core body 90, with the
permanent magnets 102 extending generally axially along the rotor
core body 90. In the illustrated embodiment, the permanent magnets
102 are received within generally elongated openings 104
cooperatively defined within the plurality of rotor laminations 92
of the rotor core body 90. At least one of the rotor laminations 92
is disposed in contact with each of the plurality of permanent
magnets 102 to retain the permanent magnets 102 in place within the
rotor core body 90.
[0060] In more detail, and with continued reference to FIG. 4, each
of the plurality of permanent magnets 102 is disposed generally
parallel to the axis 72. Furthermore, each of the plurality of
permanent magnets 102 is disposed substantially adjacent the
radially outer periphery 96 of the rotor core body 90. While the
permanent magnets 102 mounted on the rotor core body 90 may be
present in various numbers and configurations, one advantageous
configuration is depicted in the drawings.
[0061] In the illustrated configuration, the rotor assembly 70
includes four permanent magnets 102, with each of the permanent
magnets 102 being of substantially equal size. As can be seen in
the sectional view of FIG. 4, the four permanent magnets 102 are
arranged across a section of the rotor core body 90 in two pairs,
with each of the pairs of permanent magnets 102 being generally
symmetrical to the other of the pairs of permanent magnets 102 with
respect to the axis 72. In the depicted embodiment, each of the
permanent magnets 102 of the line-start brushless permanent magnet
motor assembly 26 comprises neodymium.
[0062] Turning briefly now to electric motor efficiency, an energy
cost associated with the operation of an electric motor over the
lifetime of the motor can amount to a significant financial burden
for an end user. Thus, an improvement in overall motor efficiency,
even if such an improvement is only a relatively small percentage,
can result in significant savings in energy costs over the lifetime
of the motor. An improvement to motor design or construction
resulting in an efficiency gain, therefore, may provide significant
competitive advantage, not only for the motor itself, but also for
a device (such as the compressor assembly 20) into which the
improved motor is incorporated.
[0063] Against the efficiency backdrop above, it is noted that in
some embodiments of the present disclosure, the combination within
the line-start brushless permanent magnet motor assembly 26 of the
rotor assembly 70 including the plurality of permanent magnets 102,
and the stator assembly 74 including the winding 78 formed of
aluminum, yields significant motor performance enhancements at
considerably lower incremental cost than has been realized by prior
line-start brushless permanent magnet motors. These performance
enhancements were unexpected.
[0064] More specifically, a winding formed of aluminum (which is a
less expensive material than copper from which to construct a
winding) has historically corresponded with a relatively
significant loss in overall motor efficiency compared with a
winding formed of copper. For example, from previous testing it was
observed that in a prior embodiment of an induction motor, a
transition from a winding formed of copper to a winding formed of
aluminum resulted in a relatively significant loss in overall motor
efficiency of approximately 2% (efficiency dropped from
approximately 91% to approximately 89%).
[0065] The correspondence between high efficiency and high cost has
made traditional line-start brushless permanent magnet motors a
premium category of motors, designed with maximum performance in
mind. Further, permanent magnets add significant material cost to
an otherwise typical induction motor. Conventional design,
therefore, of prior line-start brushless permanent magnet motors
has consistently taught that the high-cost, high-grade permanent
magnets of the rotor be paired with correspondingly high-cost,
high-grade copper windings of the stator.
[0066] In the case of some embodiments of the present disclosure,
however, it has been unexpectedly determined that the line-start
brushless permanent magnet motor assembly 26 with the winding 78
formed of aluminum exhibited only a slight performance difference
compared to a prior line-start brushless permanent magnet motor
with copper windings. For example, it was observed that, as opposed
to an efficiency drop relatively consistent with that exhibited in
the induction motor testing above, the counterintuitive combination
of the present disclosure results in a relatively small loss in
overall motor efficiency of approximately only one-half of the loss
observed in the induction motor testing described above. More
specifically, the line-start brushless permanent magnet motor
assembly 26 with the winding 78 formed of aluminum exhibited a loss
in overall motor efficiency of only approximately 1% (efficiency
dropped from approximately 95% to approximately 94%).
[0067] Moreover, the aluminum material used for the winding 78 of
some embodiments of the line-start brushless permanent magnet motor
assembly 26 can offset a considerable portion of the material cost
of the permanent magnets 102. In one embodiment, as referenced
above, the line-start brushless permanent magnet motor assembly 26
with the winding 78 formed of aluminum was constructed for a lower
incremental cost than would have been the case had the winding been
formed of copper, and the lower-cost motor assembly 26 demonstrated
a motor efficiency of approximately 94%.
[0068] It is again emphasized, however, that not all embodiments of
the line-start brushless permanent magnet motor assembly 26 include
the winding 78 being formed of aluminum. Rather, it is specifically
noted that some embodiments of the line-start brushless permanent
magnet motor assembly 26 include the winding 78 being formed of
copper. Such embodiments of the line-start brushless permanent
magnet motor assembly 26 including a copper winding may result in
an efficiency of approximately 95%, which may result in even higher
overall system performance of the variable capacity compressor
assembly 20.
[0069] As discussed above, the line-start brushless permanent
magnet motor assembly 26 described above may be used in conjunction
with other mechanical compressor capacity modulation technologies
that vary the capacity of the compressor. For example, the
line-start brushless permanent magnet motor assembly 26 described
above may be used as the electric motor in compressors that include
delayed suction devices, blocked suction devices, pulse width
modulation of delayed suction devices, and pulse width modulation
of blocked suction devices. Further, the line-start brushless
permanent magnet motor assembly 26 described above may be used in
scroll compressors, reciprocating compressors, rotary vane
compressors, and the like.
[0070] For example, with reference to FIG. 5, a scroll compressor
is shown with a delayed suction device and the line-start brushless
permanent magnet motor assembly described above. A similar
compressor is described in detail in U.S. Pat. No. 7,988,433,
issued Aug. 2, 2011, titled "Compressor Having Capacity Modulation
Assembly," which is incorporated herein by reference in its
entirety. In FIG. 5, a compressor 510 may include a hermetic shell
assembly 512, a compression mechanism 518, a seal assembly 520, a
refrigerant discharge fitting 522, a suction gas inlet fitting 526,
and a capacity modulation assembly 528. The compressor 510 includes
a line-start brushless permanent magnet motor assembly 516 in
accordance with the above described line-start brushless permanent
magnet motor assembly 26, described with reference to FIGS. 2-4.
Shell assembly 512 houses the line-start brushless permanent magnet
motor assembly 516, compression mechanism 518, and capacity
modulation assembly 528.
[0071] Shell assembly 512 may include a transversely extending
partition 534 that defines a discharge chamber 538. Partition 534
may include a discharge passage 544 therethrough providing
communication between compression mechanism 518 and discharge
chamber 538.
[0072] As described above, the motor assembly 516 includes a rotor
assembly 560, which is rotatable about an axis 72 (FIG. 4) and a
stator assembly 558. The rotor assembly 560 includes an axially
disposed shaft 562 that is configured for rotation with the rotor
assembly 560 and that projects axially outwardly from both ends of
the stator assembly 558.
[0073] Compression mechanism 518 may generally include an orbiting
scroll 568 and a non-orbiting scroll 570. The orbiting scroll 568
and non-orbiting scroll 570 may be meshingly engaged with one
another defining compression pockets 594, 596, 598, 500, 502, and
504. It is understood that the pockets 594, 596, 598, 500, 502, and
504 change throughout compressor operation.
[0074] A first pocket, pocket 594, may define a suction pocket in
communication with a suction pressure region 506 operating at a
suction pressure and a second pocket, pocket 504, may define a
discharge pocket in communication with a discharge pressure region
508 operating at a discharge pressure via discharge passage 92.
Pockets intermediate the first and second pockets, pockets 596,
598, 500, and 502, may form intermediate compression pockets
operating at intermediate pressures between the suction pressure
and the discharge pressure.
[0075] The non-orbiting scroll 570 may include first and second
modulation ports 513 and 514, each in fluid communication with one
of the intermediate compression pockets.
[0076] Capacity modulation assembly 528 may include a modulation
valve ring 526, a modulation lift ring 529. During operation,
capacity modulation assembly 528 may operate modulation valve ring
526 and modulation lift ring 529 to open and close the first and
second modulation ports 513 and 514. When open (as shown in FIG.
5), the first and second modulation ports 513 vent the
corresponding intermediate compression pockets back to suction
pressure region 506. With the vented intermediate compression
pockets being at suction pressure, compression within the
compression mechanism 518 commences with the intermediate
compression pockets inward of the first and second modulation ports
513 and 514.
[0077] In this way, by delaying the start of compression within the
compression mechanism 518, the capacity modulation assembly 528 is
able to modulate capacity of the compressor 510 between two
capacities, including full capacity (loaded state) and an
intermediate capacity (partially unloaded state). Additional
modulation ports may also be used such that additional intermediate
capacities may be provided.
[0078] Additionally, the capacity modulation assembly 528 may use
pulse width modulation. Therefore, by appropriately varying the
loaded state time and the partially unloaded state time during any
given cycle time, the capacity modulation assembly 528 can deliver
any capacity desired for a given system between full capacity and
the intermediate capacity. In this way, pulse width modulation can
be used, with an appropriate cycle time, to vary the capacity of
the compressor 510 to any capacity between full capacity and the
intermediate capacity.
[0079] In this way, pulse width modulation can be used, with an
appropriate cycle time, to vary the capacity of the compressor 510
to any capacity between full capacity and the intermediate
capacity.
[0080] With reference to FIG. 6, a reciprocating compressor 600 is
shown with a blocked suction device. A similar compressor is
described in detail in U.S. Pub. No. 2009/0028723, published Jan.
29, 2009, titled "Capacity Modulation System for Compressor and
Method," which is incorporated herein by reference in its entirety.
The reciprocating compressor 600 includes a line-start brushless
permanent magnet motor assembly in accordance with the above
described line-start brushless permanent magnet motor assembly 26,
described with reference to FIGS. 2-4. In FIG. 6, the reciprocating
compressor 600 includes a manifold 612, a compression mechanism
614, and a discharge assembly. The manifold 612 may be disposed in
close proximity to a valve plate 607 and may include at least one
suction chamber 618. The compression mechanism 614 may similarly be
disposed within the manifold 612 and may include at least one
piston 622 received generally within a cylinder 624 formed in the
manifold 612. The discharge assembly may be disposed at an outlet
of the cylinder 624 and may include a discharge-valve that controls
a flow of discharge-pressure gas from the cylinder 624.
[0081] The reciprocating compressor 600 includes a plurality of
pistons 610 (shown raised and lowered for illustration purposes
only), each having a reed or valve ring 640 slidably disposed
within the lower end of the piston 610. Operation of the valve ring
640 is such that discharge-pressure gas on top of the valve ring
640 holds the valve ring 640 against the valve seat 608 when the
piston 610 is moved to the "down" position. Discharge-pressure gas
above seal 690 is confined by the outside and inside diameter of
the seal 690. The valve ring 640 is loaded against the valve seat
608 by the pressure in the piston 610 acting against seal 690,
which has a high pressure above the seal 690 and a lower pressure
(system suction and/or a vacuum) under the seal 690. When the
piston 610 is in the unloaded (downward) position and the valve
ring 640 is against the valve seat 608, suction gas may have the
potential to leak between the upper surface of the valve ring 640
and the bottom surface of seal 690.
[0082] The use of a porting plate 680 provides a means for routing
suction or discharge-pressure gas from a solenoid valve 630 to the
chambers 620 on top of single or multiple pistons 610. The port on
the solenoid valve 630 that controls the flow of gas to load or
unload the pistons is a "common" port 670, which communicate via
control pressure passage 624 to chambers 620. The solenoid valve
630 in this application may be a three-port valve in communication
with suction and discharge-pressure gas and a common port 670 that
is charged with suction or discharge-pressure gas depending on the
desired state of the piston 610.
[0083] Capacity may be regulated by opening and closing one or more
of the plurality of pistons 610 to control flow capacity. A
predetermined number of pistons 610 may be used, for example, to
block the flow of suction gas to the cylinder 624. The percentage
of capacity reduction is approximately equal to the ratio of the
number of "blocked" cylinders to the total number of cylinders.
Capacity reduction may be achieved by the various disclosed valve
mechanism features and methods of controlling the valve mechanism.
The valve's control of discharge-pressure gas and suction-pressure
gas may also be used in either a blocked suction application or in
a manner where capacity is modulated by activating and
de-activating the blocking pistons 610 using pulse width modulation
and an appropriate duty cycle and cycle time. In this way, pulse
width modulation can be used, with an appropriate cycle time, to
vary the capacity of the compressor 600 to any capacity between
full capacity and either no capacity or one or more intermediate
capacities, depending on the number of blocking pistons
available.
[0084] With reference to FIGS. 7 and 8, a rotary compressor 754 is
shown with a capacity modulation device. A similar compressor is
described in detail in U.S. Pat. No. RE40,830, issued Jul. 7, 2009,
titled "Compressor Capacity Modulation," which is incorporated
herein by reference in its entirety. The rotary compressor 754
includes a line-start brushless permanent magnet motor assembly 758
in accordance with the above described line-start brushless
permanent magnet motor assembly 26, described with reference to
FIGS. 2-4.
[0085] The rotary compressor 754 includes an outer shell 756 within
which is disposed a compressor assembly and the motor assembly 758
with the stator 760 and rotor 762 that turns a shaft 766. A
compression rotor 772 is eccentrically mounted on and adapted to be
driven by the shaft 766. Compression rotor 772 is disposed within
cylinder 774 provided in housing 776 and cooperates with a vane 778
(shown in FIG. 8) to compress fluid drawn into cylinder 774 through
inlet passage 780. Inlet passage 780 is connected to suction
fitting 782 provided in shell 756 to provide a supply of suction
gas to compressor 754.
[0086] A three-way valve 790 operates to alternately connect
between suction gas and discharge gas to control the vane 778. When
the three-way valve applies discharge gas to the vane 778, the vane
is biased against the compression rotor 772 to load the rotary
compressor 754. When the three-way valve applies suction gas to the
vane 778, the vane is biased away from the compression rotor 772
(as shown in FIG. 8) to unload the rotary compressor 754.
[0087] Additionally, the three-way valve 790 may be controlled with
pulse width modulation to appropriately vary the loaded state time
and the unloaded state time during any given cycle time. In this
way, pulse width modulation can be used, with an appropriate cycle
time, to vary the capacity of the rotary compressor 754 to any
capacity between full capacity and the intermediate capacity.
[0088] The preferred forms of the disclosure described above are to
be used as illustration only, and should not be utilized in a
limiting sense in interpreting the scope of the present disclosure.
Obvious modifications to the exemplary embodiments, as hereinabove
set forth, could be readily made by those skilled in the art
without departing from the spirit of the present disclosure.
* * * * *