A COMPRESSOR AND A COOLING SYSTEM
Field of the Invention
The invention relates to compressors, and more particularly to screw-type
compressors.
Background of the invention
Screw-type compressors are commonly used in air conditioning and
refrigeration applications. In such a compressor, intermeshed male and
female lobed rotors or screws are rotated about their axes to pump the
working fluid (refrigerant) from a low pressure inlet end to a high pressure
outlet end. During rotation, sequential lobes of the male rotor serve as
pistons driving refrigerant downstream and compressing it within the
space (compression pocket) between an adjacent pair of female rotor
lobes and the housing. Likewise sequential lobes of the female rotor
produce compression of refrigerant within a male rotor compression
pocket between an adjacent pair of male rotor lobes and the housing. In
one implementation, the male rotor is coaxial with an electric driving motor
and is supported by bearings on inlet and outlet sides of its lobed working
portion. There may be multiple female rotors engaged to a given male
rotor or vice versa. With such a compressor, male and female
compression pockets may also have multiple inlet and outlet ports.
When a compression pocket is exposed to an inlet port, the refrigerant
enters the pocket essentially at suction pressure. As the pocket continues
to rotate, at some point during its rotation, the pocket is no longer in
communication with the inlet port and the flow of refrigerant to the pocket
is cut off. Typically the inlet port geometry is arranged in such a way that
the flow of refrigerant is cut off at the time in the cycle when the pocket
volume reaches its maximum value. Typically the inlet port geometry is

such that both male and female compression pockets are cut off at the
same time. The inlet port is typically a combination of an axial port and a
radial port. After the inlet port is closed, the refrigerant is compressed as
the pockets continue to rotate and their volume is reduced. At some point
during the rotation, each compression pocket intersects the associated
outlet port and the closed compression process terminates. Typically
outlet port geometry is such that both male and female pockets are
exposed to the outlet port at the same time. As with the inlet port, the
outlet port is normally a combination of an axial port and a radial port. By
combining axial and radial ports into one design configuration, the overall
combined port area is increased, minimizing throttling losses associated
with pressure drop through a finite port opening area. In an exemplary
three-rotor configuration, the inlet and outlet ports are respectively formed
at common inlet and outlet plenums.
The compressor may be designed and sized for its intended use (e.g., to
provide a given compression or volume index and operate at a given flow
at a given speed or combination thereof). Different compressors or at
least different components (rotors, motors, and the like) may be required
for different uses.
SUMMARY OF THE INVENTION
One aspect of the invention involves an apparatus comprising: a first rotor
enmeshed with second rotors. The rotors are held within a housing for
rotation about respective first, second, and third axes. The housing has: a
first surface cooperating with the first and second rotors to define a first
inlet port; a second surface cooperating with the first and second rotors to
define a first outlet port; a third surface cooperating with the first and third
rotors to define a second inlet port; and a third surface cooperating with
the first and third rotors to define a second outlet port. Either the first and

second inlet ports are at a different pressure or the first and second outlet
ports are at a different pressure.
In various implementations, the apparatus may further include: a first
condenser; a first evaporator; and one or more first conduits coupling the
first condenser and the first evaporator to the housing to define a first
flowpath from the first outlet port through the first evaporator and first
condenser and to the first inlet port. The apparatus may further include: a
second condenser; a second evaporator; and one or more second
conduits coupling the second condenser and the second evaporator to the
housing to define a second flowpath from the second outlet port through
the second evaporator and second condenser and to the second inlet
port.
The first outlet port may be at the same pressure as the second inlet port.
The apparatus of may further include a first condenser, a first expansion
device, and a first evaporator. One or more first conduits may couple the
first condenser, the first expansion device and the first evaporator to the
housing to define a first flowpath from the second outlet port to the first
inlet port. There may be no economizer branches off the first flowpath.
There may be an economizer heat exchanger having a first leg along the
first flowpath and a second leg, in heat exchange relation with the first leg.
The second leg may be along a diversion flowpath from a location along
the first flowpath between the first condenser and the first leg to join a
second flowpath from the first outlet port to the second inlet port.
Either the first and second inlet ports may form a common inlet port or the
first and second outlet ports may form a common outlet port. Either the
first and second inlet ports may be at like pressure or the first and second
outlet ports may be at like pressure. The first rotor may be a male rotor
and the second and third rotors may be female rotors

Another aspect of the invention involves an apparatus comprising a first
rotor enmeshed with second and third rotors. The rotors are held within a
housing for rotation about respective first, second, and third axes. Means
cooperate with the first, second, and third rotors for providing: a first
volume index associated with interaction of the first and second rotors
when the first rotor is driven in the first direction; and a second volume
index associated with interaction of the first and third rotors when the first
rotor is driven in the first direction. The second volume index is different
from the first volume index.
In various implementations, the apparatus may be combined with first and
second refrigerant flows along non intersecting first and second flowpaths
through the apparatus. T he apparatus may be combined with first and
second refrigerant flows along first and second flowpaths through the
apparatus intersecting at a suction side of the apparatus. The apparatus
may be combined with first and second refrigerant flows along first and
second flowpaths through the apparatus intersecting at a discharge side
of the apparatus.
The details of one or more embodiments of the invention are set forth in
the accompanying drawings and the description below. Other features,
objects, and advantages of the invention will be apparent from the
description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a partial semi-schematic longitudinal cutaway sectional view of a
compressor.
FIG. 2 is a schematic view of a first system including a compressor
according to principles of the invention.

FIG. 3 is a schematic view of a second system including a compressor
according to principles of the invention.
FIG. 4 is a schematic view of a third system including a compressor
according to principles of the invention.
FIG. 5 is a schematic view of a fourth system including a compressor
according to principles of the invention.
FIG. 6 is a schematic view of a fifth system including a compressor
according to principles of the invention.
Like reference numbers and designations in the various drawings indicate
like elements.
DETAILED DESCRIPTION
FIG. 1 shows a compressor 20 having a housing assembly 22 containing
a motor 24 driving rotors 26, 27 and 28 having respective central
longitudinal axes 500, 501 and 502. In the exemplary embodiment, the
male rotor 26 is centrally positioned within the compressor and has a
male lobed body or working portion 30 enmeshed with female lobed body
or working portion 34; 35 of each female rotor 27; 28. Each rotor includes
shaft portions (e.g., stubs 39, 40, 41, and 42, 43,44 unitarily formed with
the associated working portion) extending from first and second ends of
the associated working portion. Each of these shaft stubs is mounted to
the housing by one or more bearing assemblies 50 for rotation about the
associated rotor axis.
In the exemplary embodiment, the motor 24 is an electric motor having a
rotor and a stator. A portion of the first shaft stub 39 of the male rotor 26
extends within the stator and is secured thereto so as to permit the motor
24 to drive the male rotor 26 about the axis 500. When so driven in an

operative first direction about the axis 500, the male rotor drives the
female rotors in opposite directions about their axes 501 and 502.
Surfaces of the housing combine with the enmeshed rotor bodies to
define inlet and outlet ports to a two pairs of compression pockets: a first
pair of male and female compression pockets formed by the housing,
male rotor, and the first female rotor; and a second pair of male and
female compression pockets formed by the housing, male rotor and the
second female rotor. In each pair, one such pocket is located between a
pair of adjacent lobes of each rotor associated rotor. Depending on the
implementation, the ports may be radial, axial, or a hybrid of the two. FIG.
1 shows first and second radial inlet ports 46 and 47 and first and second
radial outlet ports 48 and 49. The resulting enmeshed rotation of the rotor
working portions tends to drive fluid from a first (inlet/suction) end to a
second (outlet/discharge) end while compressing such fluid. This defines
a downstream direction.
According to the invention, the compression paths associated with two
compression pockets do not meet at one or both of the inlet and outlet
ends. In the exemplary embodiment, separate first and second inlet
plenums 61 and 62 are respectively associated with the first and second
pairs of compression pockets as are first and second outlet plenums 63
and 64. This may be achieved by a simple modification of the housing
(e.g. a modification of an actual housing or a modification of the functional
design thereof) of a conventional compressor to bifurcate one or both of
an initially common suction port and an initially common discharge port.
This modification may leave other components (e.g., rotors, motors, and
the like) unchanged. More drastic modifications and clean sheet designs
are also possible. Reuse of existing designs for varied applications can
produce a variety of efficiencies (e.g., economies of scale).

FIG. 2 shows a system 100 wherein the compressor 20 drives first and
second independent refrigerant flows along first and second
circuits/flowpaths 102 and 104. The first and second flowpaths each
proceed downstream from the associated discharge plenum through a
discharge conduit 106; 108 to a condenser 110; 112. From the condenser,
the flowpaths proceed through an intermediate conduit 114,116 in which a
thermostatic expansion valve (TXV) 118; 120 is located to an evaporator
122,124. From the evaporator, the flowpaths proceed through a
suction/return conduit 126; 128 to the associated inlet plenum. In normal
operation, the first and second flowpaths are separate (except for
incidental leakage). Such a configuration may allow one compressor and
associated hardware to replace two. This causes certain direct
efficiencies and indirect efficiencies (e.g., associating a larger number of
uses with a given basic compressor configuration).
Alternative implementations may involve flowpaths that intersect at one or
more individual points or overlap. FIG. 3 shows a system 150 wherein the
compressor 20 drives first and second refrigerant flows along first and
second circuits/flowpaths 152 and 154 that have a common upstream
length and separate downstream lengths. The outlet plenums may be
merged in the housing (e.g., as a single common outlet plenum) or by a
T/Y-fitting in the discharge conduit 156. The combined first and second
flowpaths proceed downstream through the discharge conduit to a single
common condenser 158. From the condenser, the combined flowpaths
proceed through the trunk of an intermediate conduit 160 which has a
T/Y-fitting to separate into a first and second branches to separate the
flowpaths. A TXV 162;164 is located in each branch and the associated
flowpath proceeds downstream therefrom to an evaporator 166; 168. From
the evaporator, the flowpaths proceed through a suction/return conduit
170; 172 to the associated inlet plenum.

FIG. 4 shows a system 200 that may be constructed similarly to the
system 150 but has first and second circuits/flowpaths 202 and 204 that
have a common downstream length with a common evaporator 206 and
separate upstream lengths with separate condensers 208 and 210 and
TXVs 212 and 214.
FIG. 5 shows a system 250 that has a single flowpath 252 in which the
two compression paths are in series. The flowpath proceeds downstream
from the first outlet plenum through a conduit 254 to the second inlet
plenum. From the second outlet plenum, the flowpath proceeds through a
discharge conduit 256 to a condenser 258. From the condenser, the
flowpath proceeds through an intermediate conduit 260 in which a TXV
262 is located to an evaporator 264. From the evaporator, the flowpath
proceed through a suction/return conduit 266 to the first inlet plenum.
In a variation on the basic two-stage system of FIG. 5, FIG 6 shows a
system 300 that has a flowpath 302 providing a selective diversion along
a diversion path 304 passing within an ecomomizer heat exchanger (HE)
306. A discharge conduit 308, condenser 310, TXV 312, evaporator 314,
and suction/return conduit 316 may be similar to corresponding elements
of the system 250. The intermediate conduit 318 includes a portion 320
within the HE. A diversion conduit 322 branches from the intermediate
conduit between the condenser and HE to define the diversion path 304.
The diversion conduit includes a portion 324 within the HE in heat
exchange relation (e.g., parallel flow, counterflow, or crossflow) with the
portion 320. A diversion TXV 326 is located in the diversion conduit to
control the diversion flow. The diversion conduit joins the conduit 334 that
feedsback from the first outlet plenum to the second inlet plenum.
One or more embodiments of the present invention have been described.
Nevertheless, it will be understood that various modifications may be

made without departing from the spirit and scope of the invention. For
example, additional features may be included as are known in the art or
are subsequently developed. Accordingly, other embodiments are within
the scope of the following claims.

We claim:
1. A system (250; 300) comprising:
a compressor (20) comprising:
a housing (22);
a first rotor (26) held by the housing for rotation about a first
axis (500);
a second rotor (27) held by the housing for rotation about a
second axis (501);
a third rotor (28) held by the housing for rotation about a
third axis (502);
a first compression path associated with the first rotor and
the second rotor and having suction and discharge ends; and
a second compression path associated with the first rotor
and the third rotor, independent of the first compression path and
having suction and discharge ends,
wherein at least one of:
the discharge end of the first compression path is at a
different pressure than the discharge end of the second
compression path; and
the suction end of the first compression path is at a
different pressure than the suction end of the second
compression path;
a first condenser (258; 310);
a first expansion device (262; 312);
a first evaporator (264; 314); and
one or more first conduits coupling the first condenser, the first
expansion device and the first evaporator to the housing to define a
first flowpath from the discharge end of the second compression
path to the suction end of the first compression path, the discharge
end of the first compression path is at the same pressure as the
suction end of the second compression path.

2. An apparatus comprising:
a housing (22);
a first rotor (26) held within the housing for rotation about a first
axis (500);
a second rotor (27) enmeshed with the first rotor and held within
the housing for rotation about a second axis (501); and
a third rotor (28) enmeshed with the first rotor and held within the
housing for rotation about a third axis (502),
wherein:
the housing comprises:
a first surface cooperating with the first and second
rotors to define a first inlet port;
a second surface cooperating with the first and
second rotors to define a first outlet port;
a third surface cooperating with the first and third
rotors to define a second inlet port; and
a fourth surface cooperating with the first and third
rotors to define a second outlet port; and
at least one of: the first and second inlet ports are at a
different pressure than each other; and the first and second outlet
ports are at a different pressure than each other; and
the first outlet port is at the same pressure as the second inlet port;
a first condenser (258; 310);
a first expansion device(262; 312);
a first evaporator (264; 314); and
one or more first conduits coupling the first condenser, the
first expansion device and the first evaporator to the housing to
define a first flowpath from the second outlet port to the first inlet
port.
3. The apparatus (250) as claimed in claim 2 wherein:
there are no economizer branches off the first flowpath.

4. The apparatus (300) as claimed in claim 2 further comprising:
an economizer heat exchanger (306) having:
a first leg along the first flowpath; and
a second leg, in heat exchange relation with the first leg, the
second leg being along a diversion flowpath from a location along
the first flowpath between the first condenser and the first leg to
join a second flowpath from the first outlet port to the second inlet
port.
5. The apparatus as claimed in claim 2 wherein:
the first rotor is a male rotor; and
the second and third rotors are female rotors.

ABSTRACT

A COMPRESSOR AND A COOLING SYSTEM
A compressor has at least three-rotors. A first compression path between
first inlet and outlet ports is associated with interaction of the first and
second rotors. A second compression path between second inlet and
outlet ports is associated with interaction of the first and third rotors. At
least partial independence of the ports permits the first and second inlet
ports to be at a different pressure or the first and second outlet ports to be
at a different pressure. Fully or partially separate circuits in a refrigeration
or air conditioning system may be associated with the first and second
compression paths.