U.S. patent number RE29,627 [Application Number 05/684,813] was granted by the patent office on 1978-05-09 for rotary compressor.
This patent grant is currently assigned to Calspan Corporation. Invention is credited to Roger C. Weatherston.
United States Patent |
RE29,627 |
Weatherston |
May 9, 1978 |
Rotary compressor
Abstract
A rotary compressor having mating rotary impellers defined by
lobes and well spaces therebetween, a discharge port sealed by the
peripheral surface of one of the lobes and passages for
communicating one impeller well space with a well space of the
other impeller as the discharge port is sealed by the one impeller
peripheral surface. According to one form, the passages are defined
by conduits in the compressor housing; whereas according to a
second form the passages are defined by a recess in one impeller
and the interior of the compressor housing.
Inventors: |
Weatherston; Roger C.
(Williamsville, NY) |
Assignee: |
Calspan Corporation (Buffalo,
NY)
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Family
ID: |
23754860 |
Appl.
No.: |
05/684,813 |
Filed: |
May 10, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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297576 |
Oct 13, 1972 |
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76519 |
Sep 29, 1970 |
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Reissue of: |
441929 |
Feb 12, 1974 |
03844695 |
Oct 29, 1974 |
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Current U.S.
Class: |
418/9; 418/180;
418/191; 418/206.5 |
Current CPC
Class: |
F04C
18/088 (20130101); F04C 18/126 (20130101) |
Current International
Class: |
F04C
18/08 (20060101); F04C 18/12 (20060101); F01C
001/14 (); F01C 001/18 (); F04C 017/10 (); F04C
023/00 () |
Field of
Search: |
;418/9,180,191,199,200,205,206 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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660528 |
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Feb 1929 |
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FR |
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1243816 |
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Jul 1967 |
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DT |
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Primary Examiner: Vrablik; John J.
Attorney, Agent or Firm: Jaffe; Allen J.
Parent Case Text
This is a continuation of application Ser. No. 297,576 filed Oct.
13, 1972 now abandoned and application Ser. No. 76,519 filed Sept.
29, 1970, now abandoned.
Claims
I claim: .[.9.].
1. A rotary expansible chamber apparatus, comprising:
A. a casing defining first and second working chambers,
B. a first gas passage communicating with each of said working
chambers,
C. a second gas passage communicating directly with only said
second working chamber,
D. a first impeller rotatably mounted in said first working chamber
and having two lobes with the space therebetween defining two
wells,
E. a second impeller rotatably mounted in said second working
chamber and having two lobes in mating engagement within the wells
of said first impeller, each lobe having a leading edge and a
trailing edge,
F. said second gas passage and said first and second impellers
being so constructed and arranged that the gas occupying the space
between said first impeller and said first working chamber is
blocked from any prior communication with said second gas passage
until the trailing edge of said second impeller exposes said space
to said second passage at which time said space has undergone a
reduction in volume with a resultant increase in pressure between
that existing in said first and second gas passage,
G. additional passage means for placing a closed well of said first
impeller in communication with a closed well of said second
impeller as said second passage is closed whereby the pressure of
gas in said wells .[.in.]. .Iadd.is .Iaddend.increased by continued
rotation of said impellers.
2. The .[.compressor.]. .Iadd.expansible chamber apparatus
.Iaddend.according to claim 1, wherein;
H. said additional passage means are located in a plane spaced from
that which contains said second gas passage.
3. The .[.compressor.]. .Iadd.expansible chamber apparatus
.Iaddend.according to claim 2, wherein;
I. said additional passage means are defined by peripheral surface
portions of said impellers and interior surface portions of said
working chambers.
4. The .[.compressor.]. .Iadd.expansible chamber apparatus
.Iaddend.according to claim 3, wherein;
J. said peripheral surface portion of one impeller comprises a
recess and
K. said second impeller has a peripheral surface portion which is
adapted to compliment and project into said recess.
5. The .[.compressor.]. .Iadd.expansible chamber apparatus
.Iaddend.according to claim 1, wherein;
H. said additional passage means comprise a conduit in said casing
the ends of which communicate with each of said working
chambers.
6. The .[.compressor.]. .Iadd.expansible chamber apparatus
.Iaddend.according to claim 1, wherein;
H. said additional passage means comprise a conduit the ends of
which communicate with each of said working chambers .[.of.].
.Iadd.on .Iaddend.opposite sides of said .Iadd.second .Iaddend.gas
.[.discharge port.]. .Iadd.passage. .Iaddend. .[.
7. A rotary expansible chamber apparatus, comprising;
A. a casing defining first and second winding chambers
B. a first gas passage communicating with said working
chambers,
C. a second gas passage communicating with at least one of said
working chambers,
D. a first impeller rotatably mounted in said first working chamber
and having two lobes with the space therebetween defining two
wells,
E. a second impeller rotatably mounted in said second working
chamber and having two lobes in mating engagement within the wells
of said first impeller,
F. sealing means rotating in timed relation with at least one of
said impellers for cyclically sealing said secong gas passage
whereby communication between said second gas passage and said
working chambers is at least partially restricted, and
G. said sealing means comprises third and fourth coacting two-lobed
impellers located, respectively in third and fourth working
chambers with which said secong gas passage communicates..]. .[.8.
The expansible chamber apparatus according to claim 7, wherein;
H. said first and second impellers are so synchronized in movement
with respect to said third and fourth impellers that substantially
half of the gas in one of said first or second impeller wells is
captured in one well space between one pair of lobes of said third
or fourth impeller, whereas only half of said gas is returned to a
well of the other of said first or second impellers..]. .[.9. The
expansible chamber apparatus according to claim 7, wherein;
H. said first and second impellers are mounted on first and second
parallel shafts and define with said first and second working
chambers a first compressor stage,
I. said third and fourth impellers are mounted on third and fourth
parallel shafts and define with said third and fourth working
chambers a second compressor stage, and there is further
provided;
J. a third compressor stage similar to said first compressor stage,
and having impellers which are mounted respectively on said first
and second shafts, and
K. a fourth compressor stage similar to said second compressor
stage and having impellers which are mounted respectively on said
third and fourth shafts..]. .[.10. The expansible chamber apparatus
according to claim 9, wherein;
L. said first and second impellers are so synchronized in movement
with respect to said third and fourth impellers that substantially
half of the gas in one of said first or second impeller wells is
captured in the well space between one pair of lobes of said third
or fourth impeller, whereas only half of said gas is returned to a
well of the other of said first or second impellers, and
M. wherein the impellers of said third stage are similarly
synchronized
with respect to the impellers of said fourth stage..]. 11. A rotary
expansible chamber apparatus comprising;
A. a casing defining first and second working chambers,
B. a gas inlet communicating with said working chambers,
C. a gas discharge port communicating with said first working
chamber,
D. a first impeller having lobes and wells therebetween rotatably
mounted in said first working chamber,
E. a second impeller having lobes and wells therebetween rotatably
mounted in said second working chamber in mating engagement with
said first impeller,
F. said first impeller having a peripheral surface means for
cyclically sealing said gas discharge port, and
G. passage means for placing a closed well of said first impeller
in communication with a closed well of said second impeller as said
gas discharge port is closed whereby the pressure of gas in said
wells is
increased by continued rotation of said impellers. 12. The
expansible chamber apparatus according to claim 11, wherein;
H. said passage means are located in a plane spaced from that
which
contains said gas discharge port. 13. The expansible chamber
apparatus according to claim 12, wherein;
I. said passage means are defined by peripheral surface portions of
said
impellers and interior surface portions of said working chambers.
14. The expansible chamber apparatus according to claim 13,
wherein;
J. said peripheral surface portion of one impeller comprises a
recess and
K. said second impeller has a peripheral suface portion which is
adapted to
compliment and project into said recess. 15. The expansible chamber
apparatus according to claim 11, wherein;
H. said passage means comprise a conduit in said casing the ends of
which
communicate with each of said working chambers. 16. A .Iadd.rotary
.Iaddend.expansible chamber apparatus, comprising;
A. a casing defining first and second working chambers,
B. a gas inlet communicating with said working chambers,
C. a gas discharge port communicating with said first working
chamber,
D. a first impeller having lobes and wells therebetween rotatably
mounted in said first working chamber,
E. a second impeller having lobes and wells therebetween rotatably
mounted in said second working chamber in mating engagement with
said first impeller,
F. said first impeller having a peripheral surface means for
cyclically sealing said gas discharge port, and
G. relief passage means placing the space between said impellers in
communication with the adjacent well of said second impeller upon
closure of said gas discharge port by said peripheral surface of
said first
impeller. 17. The rotary expansible chamber apparatus according to
claim 16, wherein;
H. said relief passage means comprises a protruding portion of said
casing
intermediate said gas discharge port and said second working
chamber. 18. The rotary expansible chamber apparatus according to
claim 16, further comprising;
H. passage means for placing a closed well of said first impeller
in communication with a closed well of said second impeller as said
gas discharge port is closed whereby the pressure of gas in said
wells is
increased upon continued rotation of said impellers. 19. The rotary
expansible chamber apparatus according to claim 18, wherein;
I. said passage means are located in a plane spaced from that
which
contains said gas discharge port. 20. The rotary expansible chamber
apparatus according to claim 19, wherein;
J. said passage means are defined by peripheral surface portions of
said
impellers and interior surface portions of said working chambers.
21. The rotary expansible chamber apparatus according to claim 20,
wherein;
K. said peripheral surface portion of one impeller comprises a
recess and
L. said second impeller has a peripheral surface portion which is
adapted
to compliment and project into said recess. 22. A rotary expansible
chamber apparatus, comprising;
A. a casing defining first and second working chambers having
interior walls
B. a gas inlet communicating with said working chambers,
C. a gas discharge port communicating with at least said first
working chamber,
D. a first impeller having lobes and wells therebetween rotatably
mounted in said first working chamber, said first impeller having
at least two different constant cross-sectional profiles only one
of which is in the plane of said discharge port,
E. a second inpeller having lobes and wells therebetween rotatably
mounted in said second working chamber having at least two
different constant cross-sectional profiles which compliment and
are in mating engagement with respective profiles of said first
impeller
F. said wells spaced from said interior walls of said working
chambers, and
G. at least one of said impeller profiles blocking communication
between said discharge port and the space between the wells of at
least one of said, other profiles and the interior well of its
working chamber for a portion of its cycle.
Description
BACKGROUND OF THE INVENTION
The present invention relates to improved rotary compressors and,
more particularly to compressors of the Root's type which are
suitable for efficient operation at relatively high compression
ratios.
The conventional lobe or Root's-type blower or compressor has been
traditionally employed in high capacity-low pressure applications.
At high compression ratios, over two for example, the efficiency of
the compression process decreases rapidly. The reason for a low
efficiency of compression in the conventional Root's-type device is
due to the fact that the inlet charge of fresh gas that is captured
in the lobe well or pocket is not compressed until the pocket is
exposed to the high pressure discharge region. Upon such exposure
to discharge pressure, the low pressure within the pocket becomes
pressurized by a .[.block-back.]. .Iadd.blow-back .Iaddend.of gas
from the discharge region. This blow-back of gas loads or
pressurizes the impeller, causing all the input shaft work on the
fresh gas to be done against the discharge pressure level. This is
to be contrasted with an efficient isentropic compression process
wherein the work is done as the pressure of the fresh gas is
built-up gradually from the inlet pressure to the discharge
pressure. In this manner, the average pressure against which work
must be done is considerably less than that of the discharge.
SUMMARY OF THE INVENTION
The foregoing disadvantages, as well as other, of conventional
Root's-type compressors are overcome according to the present
invention which provides a Root's-type compressor suitable for
efficient compression at relatively high compression ratios.
As used herein the term "precompression" refers to an increase in
pressure that is brought about by a reduction in volume of the gas
trapped between counter rotating impellers, it is the type of
compression experienced in a reciprocating piston type of
compressor. This is to be contrasted with the compression that is
achieved by the raipd backflow of gas from the discharge region as
is characterized by the conventional Root's-type compressor. Thus,
the precompression of the present invention is brought about by
impeller rotation and not by backflow of gas at discharge pressure.
This significance of the distinction is that while the pressure of
the fresh charge of gas is being built up, the pressure loading,
against which the impellers do work, is less than the final
discharge pressure level, resulting in a work saving unloading of
the impellers during each cycle. To accomplish precompression in a
Root's-type compressor, it is necessary that there be some means of
either eliminating or partially restricting the backflow of high
pressure in large gas.
In one aspect of the invention the precompression is accomplished
by the provision of structure when cyclically seals off the
discharge port which coacts with passage means which provides
communication between the pocket or well volume of one impeller
with the pocket volume of the other impeller before either of the
volumes become exposed to the discharge or outlet passage. The
structure which provides the sealing off of the discharge port may
be the peripheral surface of one of the impellers.
In one form of the invention the passage means may comprise
conduits in the compressor housing or externally thereof, whereas
in a second form the passage means may be defined by at least a
portion of the peripheral surface of each impeller and the working
chamber interior walls and located substantially out of the plane
of the discharge port.
In a second aspect of the present invention wherein the gear well
volumes of each impeller are separately discharged the backflow of
gas from the discharge is restricted by a very close and
coordinated action of a second compressor stage. According to this
embodiment about half of the fresh gas charge from each well volume
of the first stage is captured by one impeller well volume in the
second stage at a pressure level equal to about twice the fresh gas
intake pressure of the first stage. The remaining half of each
fresh gas charge from the well volume is permitted to backflow into
one low pressure well of the first stage for the next cycle. This
action raises the pressure in the first stage to a level about
midway between the intake and final discharge pressure. Thus, the
first stage impellers are about one-half unloaded with respect to
the final discharge pressure level. According to this aspect of the
present invention a third and fourth stage may be provided wherein
the impellers of which are mounted on the first and second stage
shafts, respectively; providing a compact, efficient and economical
arrangement.
Other objects and advantages of the present invention not
specifically mentioned hereinabove will become apparent as the
detailed discussion of the same proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the present invention, references
should now be had to the following detailed description taken in
conjunction with the accompanying drawings, wherein;
FIG. 1 is a schematic cross-sectional view of .Iadd.an
.Iaddend.embodiment of a rotary compressor according to the present
invention;
FIG. 2 is a sectional view similar to FIG. 1 illustrating the
impellers in a second rotational position.
FIG. 3 is similar to FIG. 1 illustrating the impellers in a third
rotational position;
FIG. 4 is similar to FIG. 1 illustrating the impellers in a fourth
rotational position;
FIG. 5 is a schematic cross-sectional view illustrating a slight
modification of the FIG. 1 compressor;
FIG. 6 is a pictorial representation of the coacting impellers of a
modification;
FIG. 7 is a sectional view taken along line 7--7 of FIG. 6 with the
impeller casing added;
FIG. 8 is a sectional view taken along line 8--8 of FIG. 6;
FIG. 9 is a view similar to FIG. 7 illustrating the impellers in a
different rotational position;
FIG. 10 is an elevational view with parts broken away of a
modification illustrating a four stage compressor arrangement
according to the invention;
FIG. 11 is a sectional view taken along line 11--11 of FIG. 10;
FIG. 12 is a fragmentary sectional view taken along line 12--12 of
FIG. 11;
FIG. 13 is a view taken along line 13--13 of FIG. 12; and
FIG. 14 is a view taken along line 14--14 of FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings and, more particularly, to the
embodiment illustrated in FIGS. 1-4, the compressor casing or
housing is schematically depicted at 10 and has rotatably supported
therein a pair of working members in the form of coacting impellers
12 and 14, which are driven by suitable conventional driving and
timing gears (not illustrated). Impeller 12 is supported in
cylindrical working chamber 13 for clockwise rotation in the
direction of arrow A and impeller 14 is supported in cylindrical
working chamber 15 for opposed counterclockwise rotation in the
direction of arrow B. As illustrated impeller 12 has two lobes 16
and 18 and impeller 14 has two lobes 20 and 22. Since rotary
devices are basically leak type mechanisms it is important to
achieve maximum displacement per unit depth of impeller. To this
end, each impeller profile may contain about the same radial depth
both inside of and outside of the path circle, as is conventional
on a Root's-type machanism. In FIG. 1, the pitch diameter is
depicted by the dashed line c.
Casing 10 has a gas inlet 24 which may be a slot, as illustrated,
or a series of ports extending substantially the depth of the
impellers. Inlet 24 is about equally spaced from the axis of each
impeller. Communicating with the chamber 15 interiorly of casing 10
is a gas discharge port 26, the axis of which is offset with
respect to the axis of inlet 24; being closer to the axis of
impeller 14. The arrangement is such that the peripheral surfaces
of lobes 20 and 22 function to substantially seal the outlet 26
during part of their rotational cycle, as will be discussed in
greater detail hereinbelow.
In the position illustrated in FIG. 1 the high pressure gas between
the impellers 12 and 14 has just been discharged through conduit 26
and fresh charges of gas are captured in the closed well volumes
between lobes 16 and 18 and 20 and 22, depicted as volumes D and E,
respectively. Casing 10 contains an arcuate conduit 28 which is
adapted to place volume D in communication with volume E as soon as
discharge port 26 is sealed by the lobes of impeller 24. To
facilitate the delivery of gas in volume D after the discharge port
26 is reopened a branch passage 30 is provided extending from
conduit 28 to chamber 15. Conduit 28, which is depicted internally
of casing 10, could obviously be located externally thereof and out
of the plane of discharge port 26.
The operation of the FIG. 1 embodiment will be discussed with
reference to FIGS. 1-4. In the position of the impellers shown in
FIG. 1, the constant pressure delivery process is nearing an end
and the peripheral surface of lobe 20 is closing off the discharge
port 26. There remains between the two impellers and in conduit 28
some residual gas at high pressure after the discharge is closed.
When the impellers move to the position shown in FIG. 2, this
residual gas expands into well volume D and into well volume E via
conduit 28. Well volumes D and E, which were at the intake pressure
level before exposure to the residual gas, now have their pressure
levels raised somewhat due to the exposure. In addition, the high
pressure acting against the forward face of lobe 20 is now
substantially unloaded. As the impellers rotate further from the
position illustrated in FIG. 2 toward the position illustrated in
FIG. 3 gas is transferred from well volume D to well volume E via
passage 28. Since volume D is diminishing while volume E remains
constant and discharge port 26 is not yet open, the gas undergoes a
substantial precompression before it is discharged to the outlet
pressure level. In FIG. 3 the discharge passage 26 has just been
exposed and the gas in volume E is discharged. It is to be noted
that branch passage 30 is now open to accommodate the continued
transfer of gas from volume D to volume E, thence to discharge port
26, until the volume D is open to volume E as shown in FIG. 4. From
which position the discharge continues until the impellers assume
the position of FIG. 1 to repeat the cycle.
Since the peripheral surface of lobe 20 or 22 functions as a
valving member to seal discharge 26, it should be apparent that the
amount of precompression in volume E is governed by the extent of
these surfaces. Although as illustrated in FIGS. 1-4 the extent of
the peripheral surface at constnat radius of each lobe is about
65.degree. (angle .alpha. in FIG. 2) it has been found that for a
compression ratio of at least 2, a mimimum of 45.degree. is
desirable.
If higher compression ratios are desired, it is advantageous to
increase the extent of the precompression build-up prior to
discharge. This means that the discharge port must be closed a
greater percentage of the cycle time. The embodiment of FIG. 5
illustrates modified structure to produce such a higher compression
ratio. In this embodiment like numerals with the addition of primes
refer to parts which are similar to the like numbered parts in the
FIGS. 1-4 embodiment.
In FIG. 5, the extent of the peripheral surfaces of lobes 20' and
22' of impeller 14' has been increased such that discharge port 26'
is sealed thereby a greater proportion of the cycle time than was
the case in the FIG. 1 embodiment. To accommodate this increase in
lobe profile at the outer radius and the reduced inner radius
profile of impeller 14', impeller 12' is changed accordingly such
that lobes 16' and 18' thereof mate smoothly with the volumes
between lobes 20' and 22'. As shown in FIG. 5 the arc length (angle
.alpha.') of the peripheral lobe surface 20' is about 95.degree..
It therefore should be clear that the volume E' between lobes 20'
and 22' has much more time to increase its pressure. For
compression ratios of over 3 the angle .alpha.' for each lobe
should be a minimum of .[..alpha..degree..]. .Iadd.60.degree..
.Iaddend.
FIGS. 6 through 9 illustrate a still further modification for
achieving gas precompression in the basic Root's type apparatus.
Whereas in the embodiments previously described the means for
achieving precompression took the form of passage means in the
blower casing, in the FIGS. 6 through 9 embodiment the passage
means is defined by a recess in one impeller and the interior wall
of the casing out of the plane of the discharge port. Thus, as
shown in FIG. 6 the impellers 50 and 56 are generally similar to
the impellers 12 and 14 of the FIG. 1 embodiment except for
.[.and.]. an outer recessed portion 52 on impeller 50 and a
coacting projecting surface 58 on impeller 56. As illustrated
recessed portion 52 is located at one end of the impeller and
extending from the outermost peripheral curved surfaces 53 thereof
inwardly to an arcuate surface 54. Surface 58 is an outer curved
surface which projects between lobes 57 and which compliments the
recesses 52 of impeller 50.
As shown in FIGS. 7-9 the impellers 50 and 56 are mounted for
rotation in the direction of arrows A and B in the housing 59 which
defines generally cylindrical working chambers 60 and 62. An inlet
64 communicates with chambers 60 and 62 and an offset output 66
directly communicates only with chamber 60. The outlet 66 lies out
of the plane containing the coacting recesses and projections 52
and 58, respectively, such that the outlet is sealed by the
outermost surface 53 of impeller 50 as illustrated in FIG. 8.
In the position shown in FIGS. 7 and 8, the discharge to outlet 66
has just been completed and the outlet is substantially sealed by
surface 53 of impeller 50. Further rotation of the impellers
establishes communication between well volume F defined by impeller
56 and working chamber 62 and well volume G defined by impeller 50
and working chamber 60. As shown in FIG. 9 this communication is
established by the recess 52 while the outlet 66 is sealed. As in
the previous embodiments, the gas in well volumes G and F is
precompressed as the impellers rotate towards each other before
port 66 is exposed. When port 66 is exposed, the discharge process
will begin until port 66 is again closed by the outermost surface
53 of impeller 50. To rapidly relieve the residual pressure that is
built up between the impellers at volume H (FIG. 8), immediately
after discharge port 66 is closed the housing 59 may have a
protruding portion 68 intermediate the discharge port and the
chamber 62 which provides a passage for the residual gas to expand
into well volume F and into well volume G via recess 52. As a
result, the pressure against which the impellers must work is
relieved as soon as the discharge process is complete which thereby
maximizes the efficiency of the compressor.
FIGS. 10 through 14 illustrate a multi-staged embodiment
incorporating means for attaining precompression. A four stage
compact housing 100 is interiorly divided by means of partitions
102, 104, 106 and 108 into four sets of chambers, depicted
generally as 110, 112, 114 and 116 which function respectively as
first, second, third and fourth stages of the compressor. An inlet
118 communicates with the first stage chambers 110. A second stage
outlet 120 is adapted for communication with a third stage inlet
122 as indicated schematically at 124. A fourth stage outlet is
provided at 126 for supplying fluid to a point of use.
FIG. 11 illustrates a cross-sectional view of the first and second
stages; it is to be understood that since the cross-sectional view
of the third and fourth stages is similar, these stages are not
separately illustrated. The first stage 110 comprises a pair of
generally cylindrical working chambers 128 and 130, in which are
respectively mounted mating two-lobed impellers 132 and 134.
Impellers 132 and 134 are mounted for rotation with respective
drive shafts 136 and 138, which shafts, as partially shown in FIG.
10, are common to the mating impellers of the third stage 114.
Thus, one of the impellers of the third stage is keyed to shaft 136
whereas the other impeller of the third stage is keyed to shaft
138.
A short internal passage 140 in partition 106 provides
communication between the outlet of the first stage with the inlet
of the second stage. A similar passage (not illustrated) in
partition 108 provides communication between the third and fourth
stages. A by-pass or capacity turndown passage 142 branches from
passage 140 and communicates with the inlet pressure region of
working chamber 130 as illustrated. As illustrated the termination
of line 142 is directed against the back side of impeller 134 to
augment its motion. This makes use of the turndown gas rather than
completely wasting it by allowing it to dump back to the first
stage inlet 118. A suitable valve 144 is provided in passage 140
for controlling the flow therethrough.
The second stage 112 comprises a pair of generally cylindrical
working chambers 146 and 148, in which are respectively mounting
mating two lobed impellers 150 and 152. Impellers 150 and 152 are
mounted for rotation with respective drive shafts 154 and 156,
which shafts as partially shown in FIG. 10 are common to the mating
impellers of the fourth stage 116. Thus, as shown in FIG. 12
impeller 150 is keyed to shaft 154 which also carries impeller 150'
of the fourth stage. In a like manner, not illustrated the other
impeller of the fourth stage is mounted on shaft 156 which also
carries the other impeller 152 of the second stage.
An outlet region 158 is provided between the second stage working
chambers 112 and the second stage outlet 120; an opening 160 at the
joinder of the chambers 146 and 148 provides communication between
the working chambers and the outlet region 158. A plurality of
feedback passages 162 provide additional communication between
outlet region 158 and the working chamber interiors. Similar
structure (not illustrated) is to be found in the fourth stage.
Shafts 136, 138, 154 and 156 are driven by suitable timing and
synchronizing, gears to maintain constant the angular relationship
between the impellers of the first and second stage in the relative
position as shown in FIG. 11. The same angular relationship is
maintained between the third and fourth stages. Thus, as
illustrated in FIG. 11 when upper stage impeller 152 first seals
the volume 0 from the connecting passage 140 lower stage impeller
132 is just about to expose volume P to the passage 140 and to the
volumes N and M. A similar relationship exists between impellers
150 and 134 when the impellers have turned 180.degree. from the
positions shown in FIG. 11. Although not illustrated, the
relationships just described are alike between the impellers of the
third and fourth stages.
In the position of the impellers illustrated in FIG. 11 the
transfer of gas from the first stage volume M to the second stage
has just been completed. About half of the pressurized gas is
captured in volume O for delivery to the second stage outlet; the
remaining portion of this gas remains in volume N, passage 140 and
volume M. If it is not relieved this pressurized gas pressure would
represent a high residual load against which the first stage
impellers would have to do work, thereby decreasing the efficiency
of the compressors. This disadvantageous result is avoided in the
present invention because the angular relationship between impeller
132 and 152 is such that the low pressure volume P is exposed to
the residual volumes N, 140 and M just as the gas is captured in
volume O. The residual gas therefore expands into volume P and the
loading pressure between the impellers of the first stage is
reduced significantly.
Continued rotation of the impellers cause gas in volume P to be
delivered to the upper stage which is captured between the impeller
150 and the chamber 106 corresponding to volume O of impeller 152
of the previous half cycle. The residual portion of the gas is
relieved by expansion into the well volume between impeller 134 and
chamber 130 which has just become exposed to volumes between the
impellers and the connecting passage 140, corresponding to the
exposure of volume P of impeller 132 180.degree. before.
It is to be noted that the working depth and hence the displacement
rate of the first stage impeller is greater than that of the second
stage impellers. As such the gas in the first stage increases in
pressure during the first to second stage transfer process, being a
maximum when volumes N and M are minimal as shown in FIG. 11.
Feedback passages 162 function in the manner described in
application Ser. No. 742,890 filed July 5, 1968 for Gear
Compressors and Expanders, .Iadd.now Pat. No. 3,531,227
.Iaddend.assigned to the assignee of the present invention to
smooth out pulsations, reduce noise and augment the shaft work.
As illustrated in FIGS. 12 through 14 the second stage impeller 150
is substantially 90.degree. or one half cycle out of phase with the
fourth stage impeller 150' on common shaft 154. This relationship
is the same for the other impellers on a common shaft. Thus, the
vector relation of loads from the first and third stage impellers
and the second and fourth stage impellers are at a 90.degree. angle
with respect to each other and, as a consequence, the maximum load
on the impeller shafts is less than for the case where each
impeller is in phase. Additionally, the variation in torsional
loading on each shaft is reduced and the torque requirement in the
driving and timing gears is made more uniform.
Although preferred embodiments of the present invention have been
disclosed and described changes will occur to those skilled in the
art. .Iadd.For example, a reversal in the direction of flow will
permit the present apparatus to function as an expander with the
mating gears rotating opposite to that for compressor operation.
.Iaddend.It is therefore intended that the present invention is to
be limited only by the scope of the appended claims.
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