U.S. patent application number 11/321354 was filed with the patent office on 2006-06-29 for miniature rotary compressor, and methods related thereto.
Invention is credited to Glenn I. Deming, William Gronemeyer, Kang P. Lee, Douglas S. Olsen, Curtis Ray Slayton.
Application Number | 20060140791 11/321354 |
Document ID | / |
Family ID | 36615503 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060140791 |
Kind Code |
A1 |
Deming; Glenn I. ; et
al. |
June 29, 2006 |
Miniature rotary compressor, and methods related thereto
Abstract
Disclosed is a rolling piston rotary compressor for use with
primary refrigerants that is miniaturized for portable and mobile
applications for which size and weight are often crucial. The
miniature rotary compressor comprises a compressor mechanism, a
brushless DC motor and a casing. The compressor mechanism
comprises, a cylinder, a shaft having an eccentric part, one or
more bearings to support the shaft, a roller, a vane, an oil sump,
openings for communicating with lubricant oil and refrigerant, and
inlet and discharge ports. The compressor mechanism and the motor
are housed in a hermetically sealed or semi-hermetically sealed
casing. The configuration and design of the present invention allow
the realization of an ultralight miniature compressor. The
miniature rotary compressor provides a higher power density and
comparable efficiency as compared to state-of-the-art
refrigerant-based rotary compressors. Also disclosed are methods of
manufacturing the miniature rotary compressor.
Inventors: |
Deming; Glenn I.;
(Lunenburg, MA) ; Olsen; Douglas S.; (Natick,
MA) ; Lee; Kang P.; (Sudbury, MA) ;
Gronemeyer; William; (Wilmington, MA) ; Slayton;
Curtis Ray; (Louisville, KY) |
Correspondence
Address: |
LUCY ELANDJIAN, COUNSELLOR AT LAW
4 LONGFELLOW PLACE
SUITE 3209
BOSTON
MA
02114
US
|
Family ID: |
36615503 |
Appl. No.: |
11/321354 |
Filed: |
December 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60640699 |
Dec 29, 2004 |
|
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|
Current U.S.
Class: |
417/410.3 |
Current CPC
Class: |
F04C 18/3564 20130101;
F04C 29/0085 20130101; F04C 23/008 20130101 |
Class at
Publication: |
417/410.3 |
International
Class: |
F04B 35/04 20060101
F04B035/04 |
Claims
1. A miniature rolling piston rotary compressor assembly,
comprising a compressor mechanism, a brushless DC motor, and a
casing, wherein the compressor assembly comprises an axial length
of up to about 3.5 in.
2. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the compressor assembly comprises a diameter of
up to about 2.5 in.
3. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the compressor assembly comprises a
displacement of up to about 3.0 cc/revolution.
4. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the compressor assembly weighs up to about 1.7
pounds.
5. A miniature rolling piston rotary compressor assembly according
to claim 1, further comprising a discharge muffler comprising
radial holes for oil separation.
6. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the casing is hermetically sealed.
7. A miniature rolling piston rotary compressor assembly according
to claim 1, further comprising three housing sections, wherein said
housing sections are joined via plasma welding.
8. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the casing is semi-hermetically sealed.
9. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the miniature rotary compressor comprises a
cooling power density in the range of from about 23.6
watts/in.sup.3 to about 36.9 watts/in.sup.3, or a cooling power
density in the range of from about 200.00 watts/lb to about 312.50
watts/lb.
10. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the miniature rotary compressor comprises COP
in the range of from about 1.85 to about 2.25 at evaporator
temperature of about 55.degree. F. and condenser temperature of
about 150.degree. F., or in the range of about 3.8 to about 4.6 at
evaporator temperature of about 55.degree. F. and condenser
temperature of about 110.degree. F.
11. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the miniature rotary compressor is controlled
by matching its speed to load demand.
12. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the motor stator and the rotor are separated by
an air gap, and wherein said air gap acts as an oil separator.
13. A miniature rolling piston rotary compressor assembly according
to claim 1, further comprising a counterweight and a lightweight
crescent shaped component, wherein said counterweight and said
lightweight crescent shaped component form a contiguous hollow
cylinder.
14. A miniature rolling piston rotary compressor assembly according
to claim 1, wherein the miniature rotary compressor is used for
portable refrigeration applications, comprising personal cooling
systems, small refrigerators and freezers, portable blood coolers,
beverage coolers, or for small stationary applications, comprising
cooling systems for microprocessors and other electronics
components that generate substantial amounts of heat.
15. A method for manufacturing a miniature rolling piston rotary
compressor assembly, comprising the steps of: a) machining parts of
a compressor mechanism at a given set of tolerances, b)
incorporating a brushless DC motor, and c) incorporating a casing,
wherein the miniature rotary compressor comprises a diameter of up
to about 2.5 in., axial length of up to about 3.5 in., and a weight
of up to about 1.7 pounds.
16. A method for manufacturing a miniature rolling piston rotary
compressor assembly according to claim 15, wherein the compressor
mechanism comprises a cylinder, a shaft, roller, a vane, a top
bearing flange and a bottom bearing flange with a drive motor, and
a casing.
17. A method for manufacturing a miniature rolling piston rotary
compressor assembly according to claim 16, further comprising
incorporating an oil sump, wherein the oil sump comprises oil at a
level greater than half the cylinder height.
18. A method for manufacturing a miniature rolling piston rotary
compressor assembly according to claim 15, further comprising
incorporating a discharge tube and a top cap, wherein the discharge
tube is placed horizontally in the side of the top cap for reducing
the axial length of the compressor assembly.
19. A method for manufacturing a miniature rolling piston rotary
compressor assembly according to claim 15, further comprising
incorporating one or more electrical feedthrough pins and a top
cap, wherein said one or more electrical feedthrough pins are
incorporated via sealing with an insulating glass directly into
said top cap.
20. A method for manufacturing a miniature rolling piston rotary
compressor assembly according to claim 15, wherein the miniature
rotary compressor assembly comprises a vane and a cylinder, and
wherein said vane and cylinder are assembled non-selectively.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a non-provisional application claiming the benefit
of and priority to provisional patent application Ser. No.
60/640,699 filed on Dec. 29, 2004, which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates generally to rotary
compressors, and methods related thereto. Specifically, the present
invention pertains to a rolling piston type miniature rotary
compressor for use with primary refrigerants as the working fluid,
as used in vapor compression systems. This miniature rotary
compressor is especially useful in applications that require small
and ultralight cooling systems, which can be battery-powered for
portability and used in hot environments that are impractical for
conventional air conditioning.
BACKGROUND
[0003] The emergence of new small-scale technologies has created an
environment in which conventional space conditioning may be
displaced. One area where such displacement may occur is in the
thermal management of various electronic components, such as
microprocessors, telecommunications, and guidance equipment. Other
areas include man-portable systems for thermal protection of
aviators, soldiers, emergency response teams, and hazardous
materials handlers. The design of these systems place special
requirements on cooling system components not previously
encountered in stationary refrigeration systems. Due to the special
service that these applications require, the compressor and
refrigeration system must be ultra-light weight, highly compact,
very durable, shock-resistant, and perform safely in different
orientations.
[0004] Several types of compressors are currently available for use
in refrigeration systems. For home refrigerators and air
conditioners, rolling piston compressors are commonly used. Rolling
piston compressors are also referred to as fixed (or stationary)
vane rotary compressors. In such a compressor, the vane does not
rotate along with the rotor, but instead reciprocates in a slot
enclosed by the stationary part of the compressor. The cylindrical
part of the compressor that is mounted on the eccentric shaft is
named a rolling piston because it appears to roll on the
cylindrical surface of the cylinder wall. During the suction part
of the cycle, refrigerant gas is drawn through an inlet port into
the compression chamber, increasing the gas volume. During the
suction process, the compression stroke takes place in a decreasing
volume on the opposite side of the piston and vane. Therefore, gas
is compressed due to the eccentric motion of the roller. Discharge
flow is controlled via a discharge valve.
[0005] While the small size (for a given capacity) of rolling
piston compressors is advantageous, the leakage of refrigerant
along surfaces of the cylinder wall is disadvantageous. Lubricating
oil that is added to the compressor performs two functions
essential to the proper functioning of the compressor's pump parts.
The first function pertains to the lubrication of the moving parts
themselves. The second function pertains to the sealing of all
clearances between the moving parts, which minimizes direct gas
leakage that can adversely affect the capacity and efficiency of
the compressor.
[0006] There is a need for a miniature scale rotary compressor
suitable for mobile and portable applications, where grid or
vehicle power may not be available. Until now, this scale has never
before been attained or reduced to practice in a rotary compression
device for high internal pressures. In following the scaling laws
for compression devices, the miniaturization of such devices have
inevitably encountered serious technical hurdles, most notably in
the machining of parts and in specifying reasonable dimensional
tolerances. During the process of designing a miniature rotary
compressor, the dimensions and tolerances of compression elements,
including rotating shaft, bearings, roller, vane, and cylinder,
must be scaled and apportioned to the pressure and lower flow
conditions. Dimensional tolerances and surface finishes are
critical in the miniaturization process and have a direct effect on
performance variation and repeatability of each compressor.
Further, at some point in the process of reducing the size and
scale of the compressor parts, it may not be possible to
manufacture parts cost-effectively to the stringent dimensional
tolerances necessary to match the compressor's performance at the
larger scale, or to maintain the same efficiency of the larger
scale system. The packaging of these parts within a small control
volume also entails numerous technical challenges.
[0007] In dynamic turbomachinery components, the size, rotational
speed, and the pressure ratio across the machine are all related.
Moreover, the design relationships for turbo-machines present a
serious problem for a miniature system, as the compact size
requires small radii, high reliability requires slow rotation
speed, and high efficiency requires large pressure ratio. Thus,
miniaturization cannot be easily accomplished while maintaining
high efficiency. This problem can be alleviated to some extent
through the use of multiple stages, but at the cost of complexity
and size. The design of the miniature compressor is further
complicated by the requirement of a low mass flow rate,
corresponding to the low power required for the electrical motor
drive unit. The low flow rate of the refrigerant increases the
relative leakage flow rate through various gaps.
[0008] The typical design rules that are applicable to conventional
size components are not applicable to miniature sized components.
Miniaturization produces a larger surface-to-volume ratio of
compressor pump parts. In addition, refrigerant losses in a rotary
compressor are directly related to the clearances of the machined
parts, the surface area required for lubrication, and the lubricant
used. Thus, the reduced size will result in a predictable loss of
efficiency, unless the design is altered to counter those losses.
Further, a simple repackaging of a conventional design will not
provide the optimum performance in the miniature scale. The
miniature compressor must use a fresh and novel design that is
optimized for and accommodate the smaller size and fabrication
limitations associated with smaller sizes.
[0009] Until recently, existing rotary compressors have been
successfully downsized only to a limited degree. Such compressors
have relatively large overall size and weight that render them
unusable in the emerging areas defined above. The smallest
commercially available rotary compressor is about 5 inches (in.)
tall, 4 in. in diameter, and weighs more than 5 pounds. Moreover,
the efficiency/performance of such a compressor declines as its
dimensions and weight are reduced.
SUMMARY OF THE INVENTION
[0010] Various configurations for rolling piston rotary compressors
for standard refrigerants exist at present. However, even the
smallest of these known rolling piston rotary compressors are too
bulky and/or non-mobile and/or do not provide sufficient cooling
effect for applications that require small and ultralight portable
compressors.
[0011] In view of the above, there is a need for a compact,
ultralight, miniature rolling piston rotary compressor for use with
standard refrigerants. There is also a need for methods of
manufacturing an ultralight, miniature rotary compressor.
[0012] It is, therefore, an aspect of the present invention to
provide a compact, ultralight, miniature rolling piston rotary
compressor having a diameter of up to about 2.5 in., axial length
of up to about 3.5 in., weight of up to about 1.7 pounds, and
displacement of up to about 3.0 cc/revolution.
[0013] It is another aspect of the present invention to provide an
ultralight, miniature rolling piston rotary compressor that
provides a higher power density and comparable efficiency as
compared to state-of-the-art refrigerant-based rotary
compressors.
[0014] It is another aspect of the present invention to provide an
ultralight, miniature rolling piston rotary compressor that is
reliable, that can be used with a range of refrigerants and can be
produced cost-effectively
[0015] It is another aspect of the present invention to provide a
miniature rolling piston rotary compressor suitable for portable
refrigeration applications, such as personal cooling systems, small
refrigerators and freezers, portable blood coolers, beverage
coolers, etc. where size, weight, and other factors, such as
efficiency, do not inhibit functionality, and for small stationary
applications, such as cooling for microprocessors and other
electronics components that generate substantial amounts of
heat.
[0016] It is also an aspect of the present invention to provide
methods for manufacturing an ultralight, miniature rolling piston
rotary compressor.
[0017] The present invention pertains to an ultralight, miniature
rolling piston rotary compressor comprising a compressor mechanism,
a casing and a brushless DC motor. The miniature rotary
compressor's mechanism is housed in a hermetically or
semi-hermetically sealed casing. The compressor mechanism comprises
a compression cylinder, a shaft having an eccentric part, top and
bottom bearings to support the shaft, openings for communicating
with lubricant oil, a roller, a vane, and inlet (also referred to
as suction) and discharge ports. The compressor mechanism may
further comprise an oil pump and an oil separator. The bottom
portion of the casing acts as a lubricant oil reservoir.
[0018] In one embodiment, a hermetically-sealed miniature rolling
piston rotary compressor comprises three housing sections, the top
cap, the casing, and the bottom cap, that are preferably joined by
welding. In another embodiment, the compressor comprises three or
more electrical feedthrough pins, wherein the three or more
electrical feedthrough pins are incorporated via sealing with an
insulating glass directly into the top cap.
[0019] The miniature rotary compressor of the present invention is
significantly smaller and lighter than state-of-the art rotary
compressors, while providing comparable efficiency/performance. In
one embodiment of the present invention, the miniature rolling
piston rotary compressor has a diameter of about 2.2 in., axial
length of about 2.7 in., and weight of about 1.4 pounds. In another
embodiment, the displacement of the miniature rolling piston rotary
compressor is 20 percent of the smallest state-of-the-art
compressor's displacement. In another embodiment, the physical size
volume of the miniature rolling piston rotary compressor is 7.5
percent of the smallest state-of-the-art compressor's size volume.
In another embodiment, the oil pump of the miniature rolling piston
rotary compressor pumps oil volume that is about 61 percent the oil
volume of the state-of-the-art compressor, at comparable motor
speeds. In another embodiment, the miniature rolling piston rotary
compressor comprises an inlet hole having a diameter that is 76
percent that of the state-of-the-art compressor. In yet another
embodiment, the miniature rolling piston rotary compressor
comprises an upper flange bearing having a length that is 40
percent that of the state-of-the-art compressor, while the lower
flange bearing length is 84 percent that of the state-of-the-art
compressor.
[0020] In one embodiment, a three-pin feed through for powering the
motor drive is assembled and placed within the casing. In another
embodiment, a thin-walled compressor casing is utilized while
meeting the structural requirements of the ASME Pressure Vessel
Code, and the hydrostatic test requirements of UL for hermetic
compressors. In another embodiment, a support structure is utilized
for the side-mounted outlet connection, which is used to keep the
overall axial length to a minimum. In another embodiment, a muffler
is incorporated in a way that oil loss is minimized while allowing
for the smallest casing axial length and diameter to provide the
desired cooling capacity and coefficient of performance. In another
embodiment, the motor is fastened to the shaft without the use of
heat shrinking.
[0021] The present invention also pertains to methods for
manufacturing a miniature rolling piston rotary compressor. In one
embodiment, a method for manufacturing a miniature rolling piston
rotary compressor comprises the machining of component parts at a
given set of tight tolerances, and incorporating a brushless DC
motor that operates preferably at speeds of up to 7000 rpm. In
another embodiment, a manufacturing method comprises assembling a
cylinder, a shaft, roller, a vane, top and bottom bearing flanges
with a drive motor and a casing. In another embodiment, the
cylinder, roller, vane, shaft, top and bottom bearing flanges are
each assembled prior to assembly with the drive motor, and casing.
In another embodiment, the rotor is attached to the shaft in such a
way as to avoid heating, which may damage the motor magnet. In
another embodiment, a method of plasma-welding the casing is
utilized in such a way as to avoid heat damage to the motor.
[0022] The above summary of the present invention is not intended
to describe each illustrated embodiment or every implementation of
the present invention. The figures and the detailed description
that follow particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0024] FIG. 1a illustrates a cross-sectional side view of a
hermetically sealed miniature rolling piston rotary compressor
having an inlet tube and a discharge tube, according to an
embodiment of the present invention;
[0025] FIG. 1b illustrates an enlarged cross-sectional side view of
the rotor mounting, according to an embodiment of the present
invention;
[0026] FIG. 1c illustrates an enlarged cross-sectional top view of
the rotor mounting, according to an embodiment of the present
invention;
[0027] FIG. 1d illustrates an enlarged cross-sectional side view of
an alternative rotor mounting, according to an embodiment of the
present invention;
[0028] FIG. 2 illustrates a cross-sectional top view of a
hermetically sealed miniature rolling piston rotary compressor of
FIG. 1a (defined as view A-A), according to an embodiment of the
present invention;
[0029] FIG. 3 schematically illustrates an exploded view of the
compressor assembly components of FIG. 1a, according to an
embodiment of the present invention;
[0030] FIG. 4a illustrates a cross-sectional side view of a
semi-hermetically sealed miniature rolling piston rotary
compressor, according to an embodiment of the present
invention;
[0031] FIG. 4b illustrates a cross-sectional top view of a
semi-hermetically sealed miniature rolling piston rotary
compressor, according to an embodiment of the present invention;
and
[0032] FIG. 5 illustrates slanted slots inside of the stack of
stator laminations, according to an embodiment of the present
invention.
[0033] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0034] The present invention pertains to a miniature rolling piston
rotary compressor for primary refrigerants designed primarily for
portable refrigeration applications, such as in personal cooling
systems, small refrigerators and freezers, portable blood coolers,
beverage coolers, etc. where size, weight, and factors, such as
efficiency, do not inhibit functionality. This miniature rolling
piston rotary compressor is also suitable for small stationary
applications, such as cooling for microprocessors, lasers, x-rays,
and other electronic components that generate substantial amounts
of heat.
1. Definitions
[0035] The term "ultralight" or "ultralight weight", as used
herein, refers to a mass that is low enough that when included
within a complete refrigeration system with portable power supply,
it can be mounted upon a person comfortably without encumbrance.
Within this context, a compressor weight of less than 2.0 pounds
and a cooling capacity of about 100 to about 500 Watts, can meet
the requirements for portability for personal cooling. However, the
final resultant mass of the portable cooling system is not only
dependent on the mass of the compressor, but also on the
compressor's efficiency which governs the size and mass of the
power source, e.g. battery, fuel cell, or solar cell.
[0036] The term "displacement", as used herein, refers to the
volume of gas that is pumped by a single revolution of the piston
in a compressor.
[0037] The term "COP" or "coefficient of performance", as used
herein, refers to the dimensionless ratio of cooling output (in
Watts) to power input (in Watts).
[0038] The term "tolerance", as used herein, refers to the
allowable amount of variation of specified quantity in the
dimensions of a given part.
[0039] It is to be understood that the singular forms of "a", "an",
and "the", as used herein and in the appended claims, include
plural reference unless the context clearly dictates otherwise.
2. The Miniature Rolling Piston Rotary Compressor
[0040] The present invention is configured and designed for the
realization of an ultralight, miniature rolling piston rotary
compressor. The present miniature rolling piston rotary compressor
provides a high power density and efficiency as compared to
state-of-the-art refrigerant-based and non-refrigerant based rotary
compressors. The combination of its unique features, such as its
size, weight, durability (particularly with a hermetic casing), and
lubrication system, make the present compressor well-suited for
portable applications, however, it may also be used in small
stationary applications.
[0041] The miniature rolling piston rotary compressor of the
present invention is an assembly that comprises a compressor
mechanism, a casing, and a brushless DC motor for driving the
compressor mechanism. Preferably, the brushless DC motor operates
at a variable speed ranging up to a maximum of about 7000 rpm. The
DC compressor motor can be powered by batteries, fuel cells, or
solar cells. When generated power is available, the compressor can
be powered through a DC power supply.
[0042] In one embodiment of the present invention, a compressor
assembly 100 comprises a compression cylinder 117, a shaft (also
referred to as a crankshaft) 102 having an eccentric part, an upper
bearing (also referred to as top flange) 103a and a lower bearing
(also referred to as bottom flange) 103b to support the shaft 102,
a roller 104, a vane 106, and a suction tube assembly 105
comprising a case suction sleeve 105a, a suction tube 105b, and a
suction collar 105c, and a discharge tube 116 for communicating a
refrigerant with the compressor assembly 100, as illustrated in
FIG. 1a. As illustrated in FIG. 1a and FIG. 3, the rotor 118 of
brushless DC motor is in mechanical communication with the
compressor mechanism via the shaft 102. The miniature rolling
piston rotary compressor also comprises a lubricant oil sump 123
and an oil pump 115 for pumping lubricating oil. The lubricating
oil may be any oil compatible with the primary refrigerant selected
for use in the miniature rolling piston rotary compressor. Examples
of suitable lubricants for use with HFC refrigerants include
Polyolester (POE) and Polyvinylchloride (PVC) lubricants. For
cooling applications, the refrigerant HFC-134a may be used, whereas
for low temperature (freezing) applications, HFC-404A may be
selected. The refrigerant may be any suitable primary refrigerant
that is effective in a given temperature range of interest,
preferably any standard halocarbon refrigerant, or a blend
thereof.
[0043] The miniature rolling piston rotary compressor may be
controlled by an external controller, which is not part of the
compressor assembly 100. In one embodiment of the present
invention, the compressor is controlled by varying the speed of the
motor to meet the load demand. The motor can start at very low
speeds and increased to any speed within a wide range to closely
follow the cooling capacity of the compressor assembly to meet the
instantaneous load requirement.
[0044] In one embodiment of the present invention shown in FIG. 1a,
the miniature rotary compressor of the present invention is housed
in a hermetically sealed casing. In such a casing, the miniature
rotary compressor assembly comprises three housing sections; the
top cap 101a, bottom cap 10b, and case sleeve 114 that are
preferably joined by welding. In another embodiment, the compressor
assembly 100 is housed in a semi-hermetically sealed casing. In
such a casing, the miniature rolling piston rotary compressor
assembly may further comprise one or more o-ring seals.
[0045] The miniature rolling piston rotary compressor of the
present invention is significantly smaller and lighter than the
state-of-the art rotary compressors, while providing comparable
efficiency/performance. The miniature rolling piston rotary
compressor of the present invention comprises a diameter of up to
about 2.5 in., preferably in the range from about 1.5 in. to about
2.5 in., axial length of up to about 3.5 in., preferably in the
range of from about 1.5 in. to about 3.0 in., more preferably from
about 2.0 in to about 2.8 in., displacement of up to about 3.0
cc/revolution, preferably in the range of from about 0.90 cc/rev to
about 3.0 cc/rev, more preferably from about 1.2 cc/rev. to about
3.0 cc/rev., and weight of up to about 1.7 pounds, preferably in
the range of from about 0.8 lbs to about 1.5 lbs, more preferably
from about 1.0 lbs to about 1.4 lbs. In one embodiment of the
present invention, the miniature rolling piston rotary compressor
comprises a diameter of about 2.2 in., axial length of about 3.0
in., and weight of about 1.2 pound.
[0046] In one embodiment of the present invention, the miniature
rolling piston rotary compressor comprises a displacement that is
20 percent of the smallest state-of-the-art compressor's
displacement. In another embodiment, the physical size volume of
the miniature rolling piston rotary compressor is 7.5 percent of
the smallest state-of-the-art compressor's size volume. In another
embodiment, the oil pump of the miniature rolling piston rotary
compressor is designed to pump oil volume that is about 61 percent
the oil volume of the state-of-the-art compressor at comparable
motor speeds. In another embodiment, the miniature rolling piston
rotary compressor comprises an inlet port having a diameter that is
76 percent that of the state-of-the-art compressor. This removes
any flow restrictions, particularly at high compressor speeds, and
enhances compressor thermodynamic performance. In yet another
embodiment, the miniature rolling piston rotary compressor
comprises a top flange bearing having a length that is 40 percent
that of the state-of-the-art compressor, while the bottom flange
bearing length is 84 percent that of the state-of-the-art
compressor. In relative terms, the design of the present miniature
rolling piston rotary compressor provides for a stiffer support
system given the longer bottom flange.
[0047] In one embodiment of the present invention, a hermetically
sealed miniature rolling piston rotary compressor comprises a
hermetic casing 114, which may comprise a top cap 101a and a bottom
cap 101b. A brushless DC motor stator 110 is interference fitted
into the casing 114 in coaxial relation with the shaft 102 which is
driven by the motor. As illustrated in FIG. 1a, FIG. 2 and FIG. 3,
the compressor mechanism 100 comprises a cylinder 117, upper 103a
and lower 103b bearing members mounted to close the upper and lower
end surfaces of the cylinder 117, a shaft 102 with the motor rotor
118 mounted on one end and supported on the top side by the upper
bearing member 103a and the bottom side by the lower bearing member
103b, a rotary compression mechanism, for example, a roller 104
eccentrically rotated within in the cylinder 117 by the shaft
eccentric 102a, a suction port 121 is placed in the cylinder wall,
a discharge valve port 113 is placed in the top flange 103a and in
communication with the cylinder 117, and a vane 106 that is
slidably mounted for engagement with the roller 104 to divide the
cylinder 117 into a high pressure 128 and low pressure 129 sides or
chambers.
[0048] In state of the art compressors, compressor assembly
contains a fixed motor stator. The stator comprises multiple layers
of sheet metal referred to as laminations. The stack of laminations
forms slots which are located on the inside diameter of the stator
for the purpose of providing a space for the motor windings. In a
typical motor of the state-of-the-art compressors, these slots are
oriented in a vertical fashion. In one embodiment of the present
invention, as shown in FIG. 5, the stator 110, comprising a stack
of laminations 110a, comprises slanted slots 137 that are sloped
from top to bottom in the direction of the rotating shaft 102. The
sloped slots act as an oil groove allowing oil entrained in the
refrigerant gas to be gathered and returned to the oil sump 123. In
this embodiment, the oil return is enhanced due to the rotational
flow created by the spinning rotor resulting in oil flow toward the
sump. The motor air gap is the primary path for lubricant to leave
the compressor assembly 100, and this reverse oil flow in the slots
in the lamination stack will tend to reduce the amount of oil
leaving the compressor assembly 100 entrained in the refrigerant.
The slots 137 in the laminations stack 110a of stator 110 are
preferably slanted to divert oil toward the sump 123, and thus
function to reduce the oil circulation rate and to retain a higher
oil level in the oil sump.
[0049] In one embodiment of the present invention, the top cap 101a
is positioned such that the weld to the casing 114 is located in
the center of the motor stator laminations 110a. This configuration
allows the use of the stator laminations as a heat sink, and
thereby minimizes or even prevents the possibility of damaging the
stator windings from heat from the welding operation.
[0050] The compressor assembly parts and the casing 114 are
fabricated from mostly metallic materials that may comprise
different grades of ferritic alloys as used in current
state-of-the-art art rolling piston compressors.
[0051] In one embodiment of the present invention, the
cross-sectional area of the gas leakage in the miniature rolling
piston rotary compressor is smaller than that of state-of-the-art
rotary compressors, allowing reduced size of the vane width, vane
length, and roller wall thickness while maintaining high
efficiency.
[0052] In one embodiment of the present invention, the shaft 102
and rotor 118 are joined with a mechanical fastener without the use
of heat to prevent heat damage to the rotor magnet. Rather than
heat shrinking, a flat 131 is ground onto the shaft 102, matching a
flat on the rotor 118. Alternatively, a key way 133 can be machined
in the rotor 118 for a woodruff key 134.
[0053] The miniature rolling piston rotary compressor of the
present invention is an ultralight and small rotary compressor that
provides efficiency/performance comparable to the larger
state-of-the-art rotary compressors. The COP for the present
miniature rotary compressor is in the range of from about 1.5 to
about 4.5 at the operating conditions of interest of evaporator
temperature in the range of from about 40.degree. F. to about
60.degree. F. and condenser temperature in the range from about
85.degree. F. to about 160.degree. F., for personal cooling
applications. In one embodiment, the miniature rotary compressor
comprises a maximum COP in the range of from about 1.85 to about
2.25, at evaporator temperature of 55.degree. F. and condenser
temperature of 150.degree. F. In another embodiment, the miniature
rotary compressor comprises a maximum COP in the range of from
about 3.8 to about 4.6, at evaporator temperature of 55.degree. F.
and condenser temperature of 110.degree. F.
[0054] The size and weight of the miniature rolling piston rotary
compressor enable it to be better adapted for portable applications
than the state-of-the-art rotary compressors. The present
compressor may be used in portable refrigeration applications, such
as personal cooling systems, small refrigerators and freezers,
portable blood coolers, beverage coolers, etc. where size, weight,
and other factors do not inhibit functional mobility. The miniature
rolling piston rotary compressor may also be used in small
stationary applications, such as electronics cooling for
microprocessors and other components that generate substantial
amounts of heat.
3. Methods of Manufacturing a Miniature Rolling Piston Rotary
Compressor
[0055] The present invention also pertains to methods for
manufacturing a miniature rolling piston rotary compressor. In one
embodiment, a manufacturing method comprises the steps of machining
parts of the compressor assembly at a given set of tolerances, and
incorporating a brushless DC motor that operates preferably at high
revolutions per minute (rpm), e.g., up to about 7000 rpm. In
another embodiment, a manufacturing method comprises assembling a
cylinder, a shaft, roller, a vane, top and bottom bearing flanges
with a drive motor, and a casing. In another embodiment, the
cylinder, roller, vane, shaft, top and bottom bearing flanges are
assembled into the compressor pump assembly prior to final assembly
with the drive motor and casing.
[0056] The design and manufacture of the miniature rolling piston
rotary compressor of the present invention are such that parts
geometries are scaled down as necessary but performance clearances,
e.g., between vane width and vane slot, vane height and cylinder
height, roller height and cylinder height, roller and the cylinder
inner diameter and journal bearing clearance were kept the same as
that of a state-of-the-art rotary compressor providing
thermodynamic performance and reliability comparable to the state
of the art. Even though the compressor assembly is significantly
smaller in the present invention, it did not incur deterioration in
performance. In one embodiment of the present invention, the
various compressor clearances are: vane width clearance
0.0009/0.0004; vane end clearance -0.0007/0.0003; roller end
clearance -0.0008/0.0004; cylinder set clearance -0.0005/0.0003;
and journal bearing clearance (with manganese phosphate dry
lubricant, also referred to as Lubrite) -0.0008/0.0002.
[0057] The primary parameters for the miniature rolling piston
rotary compressor of the present invention are presented in Table
1. TABLE-US-00001 TABLE 1 Miniature Rolling Piston Rotary
Compressor Parameters PARAMETER RANGE PREFERRED RANGE Lubricated
Surface Area about 5.45 in.sup.2 to about 9.10 in.sup.2 about 6.15
in.sup.2 to about 8.20 in.sup.2 Oil Volume about 10 cc to about
46.25 cc about 20 cc to about 40 cc Oil Pump Rate about 0.75 cc/min
to about 6.2 about 0.90 cc/min to about cc/min 5.50 cc/min Cooling
Power Density about 13.6 watts/in.sup.3 to about 26.85
watts/in.sup.3 to 41 watts/in.sup.3 32.50 watts/in.sup.3 Cooling
Power Density about 200.00 watts/lb to 227.50 watts/lb to (at
145.degree. F. Condensing) about 312.50 watts/lb 275.00 watts/lb
Compressor Weight about 0.8 lbs to about 1.7 lbs about 0.8 lbs to
about 1.5 lbs; about 1.0 lbs to about 1.4 lbs Compressor Volume
about 7.50 in.sup.3 to about 8.50 in.sup.3 to about 20.00 in.sup.3
about 12.10 in.sup.3; Compressor Diameter up to about 2.5 in. about
1.5 in. to about 2.5 in. Compressor Axial up to about 35 in. about
1.5 in. to about 3.0 in.; Length about 2.0 in. to about 2.8 in.
Displacement (measured up to about 3.00 cc about 0.90 cc to about
3.0 cc; per revolution) about 1.8 cc to about 3.0 cc COP (for the
operating about 1.5 to about 4.5 conditions of interest) Upper
flange bearing about 0.40 in. to about 0.50 in. about 0.44 in. to
about 0.45 in. length Lower flange bearing about 0.35 in. to about
0.40 in. about 0.36 in. to about 0.37 in. length Discharge port
diameter about 0.08 in. to about 0.20 in. about 0.12 in. to about
0.14 in. Inlet port diameter about 0.125 in. to about 0.19 in. to
about 0.21 in. about 0.375 in. Oil pump shaft hole about 0.16 in.
to about 0.24 in. about 0.19 in. to about 0.21 in. diameter Vane
width about 0.09 in. to about 0.15 in. about 0.12 in. to about 0.13
in. Vane slot length about 0.28 in. to about 0.33 in. about 0.31
in. to about 0.32 in. Roller wall thickness about 0.10 in. to about
0.13 in. about 0.11 in. to about 0.12 in Case/end cap thickness
about 0.03 in. to about 0.07 in. about 0.04 in. to about 0.06 in.
Bore/height ratio about 2.0 to about 2.4 about 2.0 to about 2.1
[0058] The design and manufacture of the miniature rolling piston
rotary compressor of the present invention are such that parts
geometries were scaled down as necessary but dimensional tolerances
for individual parts were kept the same as the state of the art
rotary compressor. The only exception is the vane slot 135 in
cylinder 117 in which the vane reciprocates. The vane slot
tolerance is +/-0.0002'', which is tighter than that for the
state-of-the-art compressors. This is achieved by the novel use of
wire EDM (Electrical Discharge Machining) instead of a "broaching"
process that is currently used for the state of the art. The
tighter tolerance of the vane slot 135 eliminates the need for
selective vane 106/cylinder 117 matching done for state-of-the-art
compressors to achieve the desired clearance. This vastly
simplifies the assembly process. The interchangeability aspect
consequently makes the present invention more cost-effective.
[0059] The design and manufacture of the miniature compressor
differs significantly from the state-of-the-art rotary compressor
design and manufacture. In state-of-the-art rotary compressor
design and manufacture, hermetically sealed electrical contacts are
achieved with a separate feedthrough that is mass-produced from a
stamped steel cup of about 1.5 in. in diameter and three
nickel-coated steel pins that are sealed into the steel cup with
insulating glass, with the steel cup welded to the top cap, and a
nylon terminal block is used for attaching the motor wires on the
inside of the compressor casing, and the electrical conductors from
the power source are attached to the outside of the feedthrough
using standard electrical terminals. Whereas, the design and
manufacture of the present miniature compressor involves the
installation of the feedthrough pins 108 directly into a custom
stamped top cap 101a, with one standard nylon terminal block 111a
being used for making the connection to the motor on the inside and
another standard nylon terminal block 111b being used for making
the connection to the power source on the outside of the compressor
assembly 100. For the miniature rolling piston rotary compressor,
the holes for the glass insulation 109 and steel pins 108 are
extruded in the stamping process. Generally, the size of the
feedthrough cup, pins and the connectors limit the minimization of
compressor axial length. The design of the miniature rolling piston
rotary compressor of the present invention enables the reduction in
compressor axial length, reduction in raw materials used, and
reduction in manufacturing costs. Further, this design also
eliminates the need for welding the feedthrough into the top cap
101a.
[0060] In state-of-the-art rotary compressor design and
manufacture, the discharge tube is placed vertically in the center
of the top cap, preventing the minimization of the compressor axial
length, and the tube connecting the compressor to the condenser
being brazed to the discharge tube, thereby adding an additional
height requirement. Whereas, the miniature compressor of the
present invention is designed and manufactured such that the
discharge tube 116 is placed horizontally in the side of the top
cap 101a, which then reduces the axial length of the compressor and
tubes that would be attached to the compressor.
[0061] In state-of-the-art rotary compressor design and
manufacture, a top cap is inserted into the inside diameter of the
main casing and welded to provide the hermetic seal, which requires
sufficient room inside the compressor to overlap the top cap and
casing, and provide a location for welding the two pieces that is
sufficiently far from the motor windings to prevent heat damage
from the conventional MIG welding process. Whereas, the design and
manufacture of the present miniature compressor involve the
placement of a top cap 101a over the outside diameter of the casing
114 where a weld seam is located directly adjacent the motor stator
110. In one embodiment, heat damage to the motor is prevented by
using a plasma weld technique that focuses a smaller amount of
energy directly on the weld seam. The compressor assembly weld is
achieved quickly without the need of the filler wire so that very
little heat is conducted away from the welded material to other
parts of the miniature compressor, such as the motor.
[0062] In state-of-the-art rotary compressor design and
manufacture, an AC induction motor is typically used. This motor
type is relatively inexpensive to manufacture, however, it has a
low power density that results in a fairly large diameter and large
axial length to meet the torque requirement of the compressor.
Further, the AC motor is a single speed motor, typically operating
at about 3500 rpm, and requires a large start capacitor to handle
the start-up current surge. Whereas, the design and manufacture of
the miniature compressor involves the use of a high speed brushless
DC motor (comprising a stator 110 and rotor 118). This motor has a
very high power density that results in reductions in diameter,
axial length, and weight of the compressor. In addition, the
brushless motor can operate at speeds of up to 10,000 rpm, thereby
enabling the compressor size reduction while providing an
equivalent capacity.
[0063] In state-of-the-art rotary compressor design and
manufacture, the AC induction motor used in the typical rotary
compressor, as described above, operates at a single speed. This
results in the requirement of the cooling system, which utilizes
the state-of-the-art compressor to cycle on and off, to match
cooling capacity to the changing load. This leads to inefficiencies
as the compressor has large start-up current surges and the cooling
system will have off-cycle thermal losses, both leading to higher
operating costs. Whereas, the design and manufacture of the
miniature compressor involve the use of a variable speed brushless
DC motor. This motor can start at very low speeds to eliminate the
start-up current surge. It also can operate at any speed within a
wide range to closely match the cooling capacity of the compressor
to the changing load. The cooling system will ultimately use less
energy to operate, which thus leads to reduced operating costs as
well as reduced system weight for battery-operated systems. This is
especially advantageous in portable personal cooling systems where
the entire cooling system and power source are carried by the
user.
[0064] In state-of-the-art rotary compressor design and
manufacture, a large oil sump is provided at the base of the
compressor case. All rotary compressors lose some of the oil in the
sump to the refrigeration system during operation. Oil mist or
droplets mix with discharge gas and are carried out of the
discharge tube and into the condenser. Oil will flow through the
system and eventually return to the compressor via the suction
tube. Eventually, system equilibrium is reached and oil flow into
the compressor is equivalent to the oil flow out of the compressor.
However, a certain amount of oil always remains in the system,
resulting in a decrease of oil in the compressor sump. If this oil
level decreases below a certain level, oil will not be provided to
the oil pump at the end of the shaft and lubrication to the
compressor will be lost. This results in increased leakage and
friction. Both factors result in high power consumption and
premature compressor failure. For this reason, the amount of oil in
the compressor sump must be maximized. However, the oil level in
the sump cannot exceed about the middle of the cylinder. If the oil
level is higher than this, it will flow into the compressor and
fill the compression chamber during the off-cycle. When the
compressor is started, an extremely high current surge would result
due to the incompressibility of the oil. This current surge would
exceed a safe limit and normally blow a fuse or trip a circuit
breaker. Also, the oil forced out of the discharge valve 113b would
damage the valve backer 113a and render the compressor useless. To
prevent this from happening, state-of-the-art rotary compressor
casings are large enough to provide adequate oil sump capacity
without overfilling the sump. Whereas, the design and manufacture
of the miniature compressor involves the use of the variable speed
brushless motor (comprising stator 110 and rotor 118) and a novel
control scheme to achieve a compact design while having a
sufficient oil quantity in the sump 123. The oil level in the
miniature rolling piston rotary compressor of the present invention
is typically above the mid-point of the cylinder 117. The miniature
rolling piston rotary compressor uses a start-up process that
slowly purges oil out of the cylinder compression chamber 128
without a surge in current and without damage to any compressor
parts. The electronic control for the compressor speed may be set
to start-up at a relatively low speed, such as 5 rpm. This start-up
speed very slowly moves the oil from the cylinder compression
chamber 128 and out of the discharge valve port 113 at very low
torque and thus low current draw. Once the oil has been purged from
the chamber 128, the compressor speed may be safely ramped up to
operating speed (several thousand rpm). This novel start-up control
scheme results in the ability to fill the sump 123 with oil to
higher levels, and thus enables the reduction in the size of the
compressor assembly 100, thereby resulting in reduced compressor
size, weight and manufacturing costs.
[0065] In state-of-the-art rotary compressor manufacture, casings
are typically welded together using a MIG welding process. MIG
welding automatically feeds a filler wire into the two materials
that are being welded. Whereas, in one embodiment of the present
invention, manufacturing the miniature compressor involves plasma
welding as a safeguard against motor damage. Plasma welding process
is preferable because it inputs less heat to the parts being joined
and does not require the addition of a filler wire.
[0066] During the manufacturing process, the compressor pump parts
are typically positioned inside the compressor casing 114 for
welding. This involves the addition of three holes in the
compressor casing 114 to facilitate tack welding of the compressor
pump to the casing 114. The state-of-the-art rotary compressors do
not typically have holes in the casing for tack welding. Because of
the larger size of the state-of-the-art compressors, a hole can be
burned through the casing 114 during the tack welding process
without having adverse effects on the tack weld. Due to the small
size of the present miniature compressor and the preferable thin
casing material, it would be impractical to burn through the casing
as it would be difficult to control the size of the hole being
burned. Instead, the present miniature rotary compressor comprises
a pilot hole in the casing at the location of the tack welds to
facilitate the tack welding process.
[0067] In state-of-the-art rotary compressor design and
manufacture, a counterweight is used on the motor rotor to balance
the rotating assembly. The counterweight is located on the bottom
side of the rotor above the discharge muffler and discharge port.
The counterweight is typically a crescent shaped mass with a
significantly large cross sectional frontal area that is
perpendicular to the direction of rotation. This counterweight
frontal area plows through the refrigerant vapor and oil mist
adding significant turbulence resulting in a thorough mixing of the
refrigerant and oil. The well mixed oil and refrigerant mixture
leads to more oil being pumped out of the compressor through the
discharge tube and reduces the level of oil left in the sump. As
explained above, this reduced oil level can lead to premature
compressor failure. Whereas, the design and manufacture of the
miniature compressor of the present invention involves masking the
frontal area of the counterweight 122 with a lightweight crescent
shaped component 125 mounted on the top and the bottom of the rotor
118 opposite the counterweight 122 in order to reduce the oil
leaving the compressor assembly 100, as illustrated in FIG. 1a.
This novel component 125 forms a contiguous hollow cylinder,
similar to a washer, so that there is no frontal area that would
create turbulence and mixing of the refrigerant vapor with the oil
as well as consume power due to churning of the mixture and high
drag coefficient. The addition of this component does not hinder
the balancing of the rotating assembly as it is fabricated from a
very lightweight material and may also be hollow. Because less oil
is pumped out of the compressor assembly 100, the oil sump 123 can
be small, which leads to a further miniaturization of the
compressor.
[0068] In state-of-the-art rotary compressor manufacture, a muffler
(also referred to as discharge muffler), manufactured from stamped
sheet metal, covers the top flange where the compression chamber
discharge port and discharge valve are located. The compression gas
exiting the compression cylinder enters the muffler and travels a
short distance where it exits the muffler via several holes located
on the top surface. In this manner, the gas flow is directed at the
bottom of the motor rotor where it impinges on the rotor and the
rotating counterweight. In the present miniature compressor, where
the rotor 118 and counterweight 122 are located very close to the
top of the muffler 112, gas and oil exiting the muffler 112 are in
immediate contact with the spinning rotor 118. This adds turbulence
and increases the likelihood of oil remaining mixed with the gas
and ultimately leaving the compressor. The present miniature
compressor design incorporates a muffler 112 comprising radial
holes to facilitate oil separation. This design allows for the
reduction in oil that leaves the compressor assembly 100 by placing
the radial holes of the muffler 112 on the vertical sides of the
muffler 112. Thus, the gas and oil flow do not strike the rotating
motor directly, but instead are directed horizontally outward. The
refrigerant gas and oil mixture impinges on the inside diameter of
the casing 114, where the oil tends to separate and return to the
oil sump 123. In one embodiment, oil loss from the compressor is
reduced, allowing the rotor 118 to be placed very close to the top
of the discharge muffler 112, which thus results in the reduction
in the size of the compressor assembly.
[0069] As noted above, the present invention pertains to a
miniature rolling piston rotary compressor for use with primary
refrigerants, and methods related thereto. The present invention
should not be considered limited to the particular embodiments
described above, but rather should be understood to cover all
aspects of the invention as fairly set out in the appended claims.
Various modifications, equivalent processes, as well as numerous
structures to which the present invention may be applicable will be
readily apparent to those skilled in the art to which the present
invention is directed upon review of the present specification. The
claims are intended to cover such modifications.
* * * * *