U.S. patent number RE30,994 [Application Number 06/232,269] was granted by the patent office on 1982-07-13 for vertical axis hermetic rotary helical screw compressor with improved rotary bearings and oil management.
This patent grant is currently assigned to Dunham-Bush, Inc.. Invention is credited to David N. Shaw.
United States Patent |
RE30,994 |
Shaw |
July 13, 1982 |
Vertical axis hermetic rotary helical screw compressor with
improved rotary bearings and oil management
Abstract
In a vertical hermetic compressor, an inner cylindrical housing
coaxially mounted within a sealed outer enclosure, sealably carries
at its lower end, paired helical screw rotors defining with the
inner housing a screw compressor compression chamber and supports
coaxially with one of the screw rotors and constituting an axial
extension thereof the compressor electrical drive motor by
longitudinally spaced tapered roller bearings. Oil is bled from the
sump and fed to the suction inlet tube to the compressor upstream
of the working gas filter. Compressed working fluid is discharged
axially downwardly with the lower tapered roller bearing assembly
providing a minimal high pressure gap between the screw rotor ends
and the stationary end plates. Entrained oil from the discharge
passage which extends through the electric motor rotor seeks the
suction side of the compressor through the upper of the two tapered
roller bearing pack assemblies for controlled continuous
lubrication of the upper bearing assembly. The compressed working
fluid discharges axially through the center of the sealed outer
enclosure at its upper end free of oil which is separated by impact
with a curved plate deflector overlying the upper end of the
electric motor and by centrifugal force provided by the electric
motor rotor rotation. The upper bearing pack assembly for the screw
rotors may employ needle bearings instead of tapered roller
bearings and the lower bearing pack assemblies may incorporate
radially extending needle bearings for thrust take up in lieu of
one set of tapered roller bearings, with the needle bearings
carried by a spherical, self-aligning mounting assembly. A
capillary line passing through the compressor inlet passage carries
oil from the sump to an injection port opening to a closed thread
just after suction cut off for lubricating and sealing of the screw
rotors.
Inventors: |
Shaw; David N. (Unionville,
CT) |
Assignee: |
Dunham-Bush, Inc. (West
Hartford, CT)
|
Family
ID: |
26925826 |
Appl.
No.: |
06/232,269 |
Filed: |
February 6, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
882728 |
Mar 2, 1978 |
04181474 |
Jan 1, 1980 |
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Current U.S.
Class: |
417/366; 417/372;
417/902; 418/201.2; 418/97; 418/99 |
Current CPC
Class: |
F01C
21/02 (20130101); F04C 18/16 (20130101); F16C
19/386 (20130101); F16C 19/54 (20130101); F04C
29/0021 (20130101); F16C 2360/43 (20130101) |
Current International
Class: |
F01C
21/00 (20060101); F01C 21/02 (20060101); F04C
18/16 (20060101); F04C 29/00 (20060101); F16C
19/54 (20060101); F16C 19/38 (20060101); F16C
19/22 (20060101); F16C 19/00 (20060101); F01C
001/16 (); F01C 021/06 () |
Field of
Search: |
;417/365,366,369,372,902
;418/97,99,201 ;308/211,214 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gluck; Richard E.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak and
Seas
Claims
What is claimed is:
1. A vertical axis hermetic rotary helical screw compressor
comprising:
a closed vertical, cylindrical outer enclosure,
an inner cylindrical casing of a diameter less than that of the
outer enclosure,
means for concentrically, fixedly mounting said inner cylindrical
casing within said outer enclosure,
said inner cylindrical casing including transverse wall means
separating said cylindrical casing into upper and lower
chambers,
rotor means including intermeshed helical screw rotors,
vertical shaft means for at least one of said helical screw rotors
and coaxially fixed to said at least one helical screw rotor
intermediate of the ends of said vertical shaft means,
a casing end plate fixed to the lower end of said inner cylindrical
casing,
a vertical bore means formed within said casing for mounting said
at least one helical screw rotor and partially forming therewith a
compressor working chamber,
an upper roller bearing pack assembly carried by said casing means
at said transverse wall means for supporting the upper end of said
vertical shaft means, and
a lower roller bearing pack assembly carried by said casing end
plate for supporting the lower end of said vertical shaft means,
said lower roller bearing pack assembly including at least one
tapered roller bearing for absorbing compressor developed thrust
force,
an inlet tube opening to said casing bore means and said compressor
chamber at the upper end of said at least one helical screw rotor
for supplying working fluid to said compressor,
an electrical drive motor, said motor including a stator and a
rotor, said motor rotor being coaxially mounted to the upper end of
said vertical shaft means above said upper roller bearing pack
assembly, said stator being fixedly mounted to said inner casing,
concentrically about said motor rotor and spaced radially
therefrom,
said end plate underlying the lower end face of said at least one
helical screw rotor and including a horizontal compressor discharge
passage for receiving the compressed working fluid,
said casing further comprising a vertical compressor discharge
passage means extending from said casing end plate to said
transverse wall means and opening to the upper chamber housing said
drive motor at one end and said horizontal compressor discharge
passage at the other end,
an axial gas discharge outlet within the top of said vertical
cylindrical outer enclosure,
the upper end face of said at least one helical screw rotor being
open to the upper roller bearing pack assembly,
seal means carried by said upper roller bearing pack assembly for
sealing said upper chamber from said at least one helical screw
rotor upper end face, said seal means including a rotatable seal
element fixed to said shaft means and rotatable therewith, and
passage means carried by said electric drive motor for permitting
said compressed working fluid to pass into said cylindrical outer
enclosure at the upper end of said motor, such that during
compressor operation, compressor discharge pressure acting on the
upper end of said shaft means and on said at least one rotatable
seal element and the weight of said motor rotor and said screw
rotor partially balances the developed thrust forces acting on said
at least one helical screw rotor, while said upper and lower roller
bearing pack assemblies absorb the remaining developed thrust force
and any radial force acting on said shaft means.
2. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein said upper roller bearing pack assembly
comprises an upper tapered roller bearing pack assembly including
axially spaced tapered roller bearings, and said seal means is
mounted within said upper roller bearing pack assembly,
intermediate of said tapered roller bearings.
3. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein said seal means comprises a labyrinth
seal including a stationary labyrinth seal ring fixedly mounted
within said casing transverse wall means and a radially aligned
annular labyrinth member carried by said shaft means, said
labyrinth seal member having an outer diameter slightly less than
the inner diameter of said labyrinth seal ring, and wherein said
labyrinth seal member is provided with a serrated face facing the
opposing surface of said labyrinth seal ring and spaced slightly
therefrom.
4. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 2, wherein said seal means comprises a labyrinth
seal including a stationary labyrinth seal ring fixedly mounted
within said casing transverse wall means and a radially aligned
annular labyrinth seal spacer press fitted to said shaft means,
said labyrinth seal spacer having an outer diameter slightly less
than the inner diameter of said labyrinth seal ring, and wherein
said labyrinth seal spacer is provided with a serrated face facing
the opposing surface of said labyrinth seal ring and spaced
slightly therefrom.
5. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 2, wherein said transverse wall means comprises an
integral vertical cylindrical portion, said upper tapered roller
bearing pack assembly comprises an outer sleeve, said sleeve being
fixedly, concentrically mounted within said transverse wall
cylindrical portion and said seal means comprises a face seal
including an L-shaped seal ring having a base portion fixed to the
inner wall of said sleeve and having a radial leg portion
projecting towards said rotating shaft means, said shaft means
carries a spring retaining ring fixedly mounted thereto and
extending radially outwardly therefrom towards said sleeve and
terminating short of said base portion of said seal ring and being
spaced axially from said radial leg portion and to the side of said
base portion opposite the leg portion, a face seal element
positioned axially between said spring retaining ring and said
fixed seal ring and including a radially inwardly directed base and
a radially outwardly directed leg portion including an axial
projection, said axial projection contacting one side of said leg
portion of said face seal ring, and a wavy spring interposed
between said spring retaining ring and said face seal element, on
the side opposite said axial projection, and being compressed
therebetween for pressing the axial projection on said seal element
against the opposed face of said fixed seal ring.
6. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 5, further comprising an annular seal spacer fixed
to said shaft and rotatable therewith, said spacer being of
rectangular longitudinal .Iadd.section .Iaddend.and having a
radially outer face in contact with the base of said face seal
element, and an O-ring carried by said spacer, on said radially
outer face and bearing on the base of said face seal element for
sealing the upper end of said upper tapered bearing pack assembly
from the inlet end face of said at least one helical screw
rotor.
7. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 2, wherein said transverse wall means comprises a
vertical cylindrical portion through which one end of said shaft
means for said at least one helical screw rotor projects, and said
upper tapered roller bearing pack assembly comprises an outer
sleeve force fitted within said transverse wall cylindrical
portion, upper and lower double row tapered roller bearings, said
seal means comprises a working fluid bearing seal interposed
axially within said sleeve intermediate of said upper and lower
double row tapered roller bearings, said sleeve including three
axially spaced sets of circumferentially spaced, drilled holes, an
outer annular bearing race member for each of said double rows of
tapered roller bearings and an outer annular seal ring for said
bearing seal, pins mounted within said holes for respective sets
and being fixed respectively to said double row tapered roller
bearings outer race member and to said seal ring for axially fixing
these elements to said sleeve, .[.said outer races,.]. each of said
outer race members including oppositely directed oblique roller
contact surfaces at respective ends and facing said shaft means, a
plurality of annular bearing cones force fitted to said shaft means
facing said opposed tapered surfaces of said radially outer bearing
race members, annular spacers interposed between said cones
including an annular seal spacer interposed between respective
upper and lower double row tapered roller bearings and concentric
with said outer seal ring and defining therebetween a working fluid
seal for .[.preventing.]. .Iadd.tending to prevent .Iaddend.the
compressor discharge from returning to the upper end face of said
at least one helical screw rotor, and a rotor end face spacer
mounted to said shaft and interposed between the upper end face of
said at least one rotor and the lowermost annular cone, sets of
circumferentially spaced, tapered rollers interposed between
respective cones and the oblique surfaces of said bearing outer
race members and clamping means carried by said shaft means for
axially compressing the elements of said upper bearing pack
assembly against said .Iadd.end .Iaddend.face spacer.
8. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 7, wherein said seal ring comprises an annular
metal ring of rectangular longitudinal section and having a flat
radially inner face facing the seal spacer ring and being
interposed between the uppermost cone of said lower double row
tapered roller bearing and the lowermost cone of said upper double
row tapered roller bearing, and the radially outer surface of said
seal spacer being serrated and having a diameter slightly smaller
than the radially inner diameter of said fixed seal ring to define
a low pressure loss labyrinth seal intermediate of said upper and
lower double row tapered roller bearings.
9. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein said lower roller bearing pack assembly
comprises a lower tapered roller bearing pack assembly having two
oppositely drected tapered roller bearings, the lower end of said
shaft means projecting below said at least one helical screw rotor
comprises first and second reduced diameter portions
defining.Iadd., respectively, first and second .Iaddend.radial
shoulders .[.therebetween.]., said casing end plate including a
small diameter opening on the upper side facing said at least one
helical screw rotor for receiving the lower end of said shaft and
an enlarged diameter opening portion on its lower side as an axial
extension thereof, the upper bearing comprises a first angular cup
carried within said enlarged diameter opening of said casing end
plate with the upper end of said cup abutting a radial shoulder
formed within said casing end plate .[.intermediate.]. .Iadd.at the
juncture .Iaddend.of said small and large diameter openings, said
upper bearing further including an annular cone press fitted to
said first reduced diameter portion of said shaft means and said
second bearing comprises a second annular cone of a smaller
diameter than that of said first cone and having a radially outer
face which is oblique and faces axially downwardly, said hermetic
rotary helical screw compressor further comprises a lower bearing
pack assembly end plate including a bearing cup retainer of
cylindrical form fixed thereto and extending axially upwardly
thereof, within said large diameter opening of said end plate and
having its inner periphery stepped to define a bearing cup retainer
shoulder, and said lower bearing comprises an annular cup facing
said second cone and having its lower end abutting the shoulder of
said annular cup retainer, a first annular shim mounted to said
second reduced diameter portion of said shaft means and between the
upper end face of said second cone and said shaft means second
shoulder, said first shim having a thickness determined by the
distance between the lower end of said first cone and said second
shoulder on said shaft means when said at least one rotor lower end
face abuts the opposing surface of said casing end plate and a
predetermined minimal clearance dimension between said lower end
face of said at least one rotor and the opposing surface of said
casing end plate when said second cone is axially locked in
abutment with said first cone, means for axially locking said
second cone in axial abutment with said first cone and said first
shim, and a second shim interposed between said lower bearing pack
assembly end plate and said casing end plate and having a thickness
conforming to the desired clearance between the lower end face of
said at least one helical screw rotor and said casing end plate
when said first cup is pressed against the shoulder of said casing
end plate and means for fixedly mounting said lower bearing pack
assembly end palte against the outer wall of said casing end plate
with said second shim interposed therebetween; whereby, regardless
of whether the compressor is under compressive load or not, said
minimal clearance is maintained at the lower end face of said at
least one helical screw rotor for minimizing loss of compressed
working fluid back to the inlet side of the compressor.
10. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 7, wherein said lower roller bearing pack assembly
comprises a lower tapered roller bearing pack assembly having two
oppositely directed tapered roller bearings, the lower end of said
shaft means projecting below said at least one helical screw rotor
comprises first and second reduced diameter portions
defining.Iadd., respectively, first and second .Iaddend.radial
shoulders .[.therebetween.]., said casing end plate including a
small diameter opening on the upper side facing said at least one
helical screw rotor for receiving the lower end of said shaft and
an enlarged diameter opening portion on its lower side as an axial
extension thereof, the upper bearing comprises a first annular cup
carried within said enlarged diameter opening of said casing end
plate with the upper end of said cup abutting a radial shoulder
formed within said casing end plate .[.intermediate.]. .Iadd.at the
juncture .Iaddend.of said small and large diameter openings, said
upper bearing further including an annular cone press fitted to
said first reduced diameter portion of said shaft means and said
second bearing comprises a second annular cone of a smaller
diameter than that of said first cone and having a radially outer
face which is oblique and faces axially downwardly, said hermetic
rotary helical screw compressor further comprises a lower bearing
pack assembly end plate including a bearing cup retainer of
cylindrical form fixed thereto and extending axially upwardly
thereof, within said large diameter opening of said end plate and
having its inner periphery stepped to define a bearing cup retainer
shoulder, and said lower bearing comprises an annular cup facing
said second cone and having its lower end abutting the shoulder of
said annular cup retainer, a first annular shim mounted to said
second reduced diameter portion of said shaft means and between the
upper end face of said second cone and said shaft means second
shoulder, said first shim having a thickness determined by the
distance between the lower end of said first cone and said second
shoulder on said shaft means when said at least one rotor lower end
face abuts the opposing surface of said casing end plate and a
predetermined minimal clearance dimension between said lower end
face of said at least one rotor and the opposing surface of said
casing end plate when said second cone is axially locked in
abutment with said first cone, means for axially locking said
second cone in axial abutment with said first cone and said first
shim, and a second shim interposed between said lower bearing pack
assembly end plate and the casing end plate and having a thickness
conforming to the desired clearance between the lower end face of
said at least one helical screw rotor and said casing end plate
when said first cup is pressed against the shoulder of said casing
end plate and means for fixedly mounting said lower bearing pack
assembly end plate against the outer wall of said casing end plate
with said second shim interposed therebetween; whereby, regardless
of whether the compressor is under compressive load or not, said
minimal clearance is maintained at the lower end face of said at
least one helical screw rotor for minimizing loss of compressed
working fluid back to the inlet side of the compressor.
11. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 8, wherein said lower roller bearing pack assembly
comprises a lower tapered roller bearing pack assembly having two
oppositely directed tapered roller bearings, the lower end of said
shaft means projecting below said at least one helical screw rotor
comprises first and second reduced diameter portions define.Iadd.,
respectively, first and second .Iaddend.radial shoulders
.[.therebetween.]., said casing end plate including a small
diameter opening on the upper side facing said at least one helical
screw rotor for receiving the lower end of said shaft and an
enlarged diameter opening portion on its lower side as an axial
extension thereof, the upper bearing comprises a first annular cup
carried within said enlarged diameter opening of said end plate
with the upper end of said cup abutting a radial shoulder formed
within said casing end plate .[.intermediate.]. .Iadd.at the
juncture .Iaddend.of said small and large diameter openings, said
upper bearing further including an annular cone press fitted to
said first reduced diameter portion of said shaft means and said
second bearing comprises a second annular cone of a smaller
diameter than that of said first cone and having a radially outer
face which is oblique and faces axially downwardly, said hermetic
rotary helical screw compressor further comprises a lower bearing
pack assembly end plate including a bearing cup retainer of
cylindrical form fixed thereto and extending axially upwardly
thereof, within said large diameter opening of said end plate and
having its inner periphery stepped to define a bearing cup retainer
shoulder, and said lower bearing comprises an annular cup facing
said second cone and having its lower end abutting the shoulder of
said annular cup retainer, a first annular shim mounted to said
second reduced diameter portion of said shaft means and between the
upper end face of said second cone and said shaft means second
shoulder, said first shim having a thickness determined by the
distance between the lower end of said first cone and said second
shoulder on said shaft means when said at least one rotor lower end
face abuts the opposing surface of said casing end plate and a
predetermined minimal clearance dimension between said lower end
face of said at least one rotor and the opposing surface of said
casing end plate when said second cone ix axially locked in
abutment with said first cone, means for axially locking said
second cone in axial abutment with said first cone and said first
shim, and a second shim interposed between said lower bearing pack
assembly end plate and the casing end plate and having a thickness
conforming to the desired clearance between the lower end face of
said at least one helical screw rotor and said casing end plate
when said first cup is pressed against the shoulder of said casing
end plate and means for fixedly mounting said lower bearing pack
assembly end plate against the outer wall of said casing end plate
with said second shim interposed therebetween; whereby, regardless
of whether the compressor is under compressive load or not, said
minimal clearance is maintained at the lower end face of said at
least one helical screw rotor for minimizing loss of compressed
working fluid back to the inlet side of the compressor.
12. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein the bottom of said closed vertical
cylindrical outer enclosure constitutes an oil sump containing oil
and said compressor further comprises conduit means for fluid
communicating the interior of said lower roller bearing pack
assembly with said oil within said outer enclosure oil sump, and
wherein the oil within said sump being at discharge pressure tends
to move within the compressor towards the suction side of the
compressor, allowing oil to be entrained within the compressor
discharge gas and wherein the discharge gas passing upwardly
through said passage means within said casing and into said upper
chamber permits entrained oil to migrate, because of the pressure
differential through said upper roller bearing pack assembly
towards the upper end face of said at least one helical screw rotor
which is at compressor suction pressure, and wherein said discharge
gas in passing through said motor rotor cools said motor and by
centrifugal force due to rotation of said motor rotor separates the
entrained oil from the discharge working fluid at the upper end of
said enclosure, and said compressor further comprises a circular
plate deflector mounted to the upper end of said enclosure and
immediately overlying the motor rotor and stator and being
interposed between the motor rotor and the axial outlet such that
oil moving with the discharge gas impacts during rotation of the
motor rotor against the deflector plate to cause some oil to cling
to the lower surface of said plate and to separate from the
discharge working fluid, said gas free of oil escaping about the
deflector plate periphery and seeking the axial discharge
outlet.
13. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 12, wherein said inlet tube includes a filter
element for filtering the compressor working fluid intake and
wherein a bleed line connects said conduit means to the compressor
inlet tube upstream of said filter .[.means to the inlet tube
upstream of said filter.]. .Iadd.element .Iaddend.for bleeding a
portion of said oil to effect filtering of the oil along with the
inlet working fluid passing to the compressor screw rotor bore
means of said casing.
14. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 13, further comprising a solenoid operated valve
within said bleed line for selectively controlling the flow of oil
bled from said conduit means.
15. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein said lower roller bearing pack assembly
comprises a single tapered roller bearing, the lower end of said
shaft means projecting below said at least one helical screw rotor
comprises .[.first and second.]. .Iadd.a .Iaddend.reduced diameter
.[.portions.]. .Iadd.portion .Iaddend.defining from said rotor
.[.first and second radial shoulders therebetween.]..Iadd., a
shoulder.Iaddend., said casing end plate including a small diameter
opening at the upper side facing said at least one helical screw
rotor for receiving the lower end of said shaft and being provided
with an enlarged diameter opening portion at its lower side as an
axial extension of said small diameter opening, said single tapered
roller bearing comprising a first annular cup carried within said
enlarged diameter opening of said casing end plate with the upper
end of said cup abutting a radial shoulder formed within said
casing end plate at the juncture of said small and large diameter
openings, said lower bearing pack assembly further including an
annular cone press fitted to said .[.first.]. reduced diameter
portion of said shaft means, an annular shim having a thickness
determined by the distance between the lower end of said cone and
the .[.second.]. shoulder on said shaft means when said at least
one rotor lower end face abuts the opposing surface of said casing
end plate and a predetermined minimal clearance dimension between
said lower end face of said at least one rotor and the opposing
surface of said casing end plate with the upper end of said cup
abutting the shoulder within said casing end plate, a retainer
plate in common abutment with said shim and the lower end of said
cone and spanning said shaft means, and means for threadably,
axially locking said cup retainer plate against said cone and said
shim and fixed to the end of said shaft means; whereby, regardless
of whether said compressor is under compressive load or not, said
minimal clearance is maintained at the lower end face of said at
least one helical screw rotor for minimizing loss of compressed
working fluid back to the inlet side of the compressor.
16. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein said lower roller bearing pack assembly
comprises a tapered roller bearing and a thrust needle bearing, the
lower end of said shaft means projecting below said at least one
helical screw rotor comprises first and second reduced diameter
portions defining from said rotor outwardly, first and second
radial shoulders therebetween, said casing end plate including a
first relatively small diameter opening on the upper side facing
said at least one helical screw rotor for receiving the lower end
of said shaft means and being provided with an enlarged diameter
opening portion on its lower side as an axial extension thereof,
said tapered roller bearing comprising a first annular cup carried
within said enlarged diameter opening of said casing end plate,
with the upper end of said cup abutting a radial shoulder formed
within said casing end plate at the intersection of said small and
large diameter openings, said tapered roller bearing further
including an annular cone press fitted to said first reduced
diameter portion of said shaft means, and a circumferential array
of tapered rollers positioned between said annular cup and said
annular cone, an annular shim mounted to said second reduced
diameter portion of said shaft means and between the upper end face
of said cone and said shaft means second shoulder, said shim having
a thickness determined by the distance between the lower end of
said cone and said second shoulder on said shaft means when said at
least one rotor lower end face abuts the opposing surface of said
casing end plate plus a predetermined minimal clearance dimension
between said lower end face of said at least one rotor and the
opposing surface of said casing end plate when said cup is axially
locked in abutment with said casing end plate shoulder, said thrust
needle bearing comprising a first upper annular ring concentrically
surrounding said second reduced diameter portion of said shaft
means and abutting the lower face of said cone and said shim and
defining an upper race for said needle bearing, a second ring
underlying said first ring and forming a second race for said
needle bearing, a circumferential horizontal array of needle
bearing rollers positioned intermediate of said rings about said
second reduced diameter portion of said shaft means, an annular
collar of a diameter in excess of said second reduced diameter
portion of said shaft means and having a circular recess within its
upper face receiving the projecting lower end of said shaft means
second reduced diameter portion and having an axial end face
bearing on the second ring and positioned between said shaft means
and said lower bearing pack assembly end plate, an end plug
threadably mounted to said lower bearing pack assembly end plate
and bearing on the lower end face of said annular collar, said
lower end face of said collar bearing a spherical recess at the
center thereof and said end plug terminating in a spherical end
face conforming to that of said recess and being received therein
such that said end plug and said collar define an orthogonal
self-aligning means for said thrust needle bearing.
17. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, wherein the transverse wall means comprising a
vertical cylindrical portion through which one end of said shaft
means for said at least one helical screw rotor projects, said
shaft means comprises a portion on the suction side of said helical
screw rotor having a serrated surface over an axial extent thereof,
said wall means having an internal diameter in excess of that of
the projecting portion of said shaft means, a portion of said
projecting shaft means comprises the inner race for at least one
needle roller bearing and said upper roller bearing pack assembly
further comprises at least one outer race member carried by said
vertical cylindrical portion, snap rings carried by said vertical
cylindrical portion on the inner surface thereof and locking said
at least one race member axially, and a plurality of needle bearing
rollers constituting a vertical axis circumferential array
positioned between said portion of said shaft means and said at
least one outer race member and a fixed annular seal ring mounted
within said vertical cylindrical portion concentric to said
serrated shaft portion and spaced slightly therefrom and defining
with said serrated shaft portion a labyrinth seal for restricting
the flow of discharge gas through said upper roller bearing pack
assembly and towards the compressor inlet.
18. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 17, wherein said at least one needle roller
bearing comprises two in number and being mounted within said
vertical cylindrical portion of said transverse wall means axially
on the side of said labyrinth seal remote from said at least one
helical screw rotor.
19. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 17, wherein said at least one needle roller
bearing comprises a single needle roller bearing mounted to said
shaft immediately adjacent said at least one helical screw rotor,
and said labyrinth seal means is located to the side of said single
needle roller bearing remote from the end face of said at least one
helical screw rotor.
20. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 1, further comprising; an oil strainer, a small
diameter tube operatively coupled to the oil downstream of said oil
strainer and projecting through said compressor inlet tube and
terminating at its opposite end at an oil injection port opening to
said compressor bore at a helical screw closed thread position
adjacent the inlet side of the compressor chamber formed thereby,
such that relatively cool, highly viscous oil is injected into the
compressor to seal the threads with minimum adverse effect upon
compressor capacity.
21. The vertical axis hermetic rotary helical screw compressor as
claimed in claim 20, further comprising an oil sump and wherein
said small diameter oil tube includes an integral coil portion
within said compressor inlet tube to substantially reduce the
temperature of the oil emanating from said sump and directed by
said small diameter tube to said oil injection port. .Iadd. 22. In
a rotary helical screw compressor comprising:
a cylindrical casing,
intermeshed helical screw rotors borne by said casing,
shaft means fixed to at least one of said helical screw rotors,
a casing end plate closing off one end of said casing and facing
one end of said rotors,
said shaft means projecting through said casing end plate,
a bearing pack assembly carried by said casing end plate for
rotatably supporting said shaft means,
the improvement wherein:
said bearing pack assembly comprises a tapered roller bearing pack
assembly having first and second oppositely directed tapered roller
bearings,
said shaft means comprises first and second reduced diameter
portions defining respectively, first and second radial shoulders
therebetween,
said casing end plate including a small diameter opening on the
side facing said at least one helical screw rotor for receiving
said shaft means and an enlarged diameter opening portion on the
opposite side as an axial extension thereof,
said first bearing comprising a first angular cup carried within
said enlarged diameter opening of said casing end plate with one
end of said cup abutting a radial shoulder formed within said
casing end plate intermediate of said small and enlarged diameter
openings, and
an annular cone press fitted to said first reduced diameter portion
of said shaft means,
said second bearing comprising a second annular cone of smaller
diameter than that of said first cone and having a radially outer
face which is oblique and which faces axially away from said at
least one helical screw rotor,
a bearing pack assembly end plate including a bearing cup retainer
of cylindrical form fixed thereto and extending axially towards
said second bearing, within said enlarged diameter opening of said
casing end plate and having its inner periphery stepped to define a
bearing cup retainer shoulder,
said second bearing further comprising an annular cup facing said
second cone and having one end abutting the shoulder of said
bearing cup retainer,
a first annular shim mounted to said second reduced diameter
portion of said shaft means and between the other end of said
second cone and said shaft means second shoulder,
said first shim having a thickness determined by the distance
between the other end of said first cone and said second shoulder
on said shaft means when said at least one rotor has its end face
abutting the opposing surface of said casing end plate and a
predetermined minimal clearance dimension between the end face of
said at least one rotor and the opposing surface of said casing end
plate when said second cone is axially locked in abutment with said
first cone,
means for axially locking said second cone in axial abutment with
said first cone and said first shim,
a second shim interposed between said bearing pack assembly end
plate and said casing end plate and having a thickness conforming
to the desired clearance between the end face of said at least one
helical screw rotor and the opposing surface of said casing end
plate when said first cup is pressed against the shoulder of said
casing end plate, and
means for fixedly mounting said bearing pack assembly end plate
against the opposing wall of said casing end plate with said second
shim interposed therebetween;
whereby, regardless of whether the compressor is under compressive
load or not, said minimal clearance is maintained between the end
face of said at least one helical screw rotor and said casing end
plate for minimizing loss of compressed working fluid therebetween.
.Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to hermetic, vertical axis rotary helical
screw compressors, and more particularly, to such hermetic
compressors as disclosed in U.S. Pat. No. 3,922,114 issued Nov. 25,
1975, and assigned to the common assignee.
2. Description of the Prior Art
Hermetic, vertical axis, rotary helical screw compressors have
evolved, particularly in low horsepower size, as unitary pieces of
equipment including within the hermetic housing, means for
separating and cooling the oil which is necessary for lubrication
of the moving parts and for forming compression chambers or closed
threads between the intermeshed helical screw rotors and the
surrounding compressor housing. Further, by incorporating within
such vertical axis hermetic rotary helical screw compressor
packages, the electrical drive motor which is open to the
compressor discharge, the motor windings may be readily cooled,
that is, maintained at a relatively low operating temperature by
the discharge gas as it moves vertically upward from the compressor
which underlies the electric drive motor, prior to discharge of the
compressed gas at the upper end of the hermetic outer
enclosure.
In the hermetic, rotary helical screw compressor of U.S. Pat. No.
3,922,114, the outer, generally cylindrical and sealed enclosure
supports internally a two part inner cylindrical housing which
forms with the outer enclosure a sealed chamber, while the inner
housing itself forms a high pressure or discharge side second
chamber, housing the electric drive motor and a third low pressure
or inlet gas chamber sealed from the first and second chambers and
within which is incorporated the helical screw rotors defining the
compression chambers. In that hermetic compressor design, the
helical screw rotors and the compressor drive motor rotor are
supported for rotation about their axes by sleeve bearings or the
like. An oil pump fixed to one of the compressor helical screw
rotor shafts and being driven thereby acts to pressurize the oil
accumulating within the bottom of the outer container which acts as
a sump for the oil. Such oil under high pressure is conducted
through passages within the screw rotor shafts for lubricating the
sleeve bearings and the intermeshed helical screw rotors. Further,
in that compressor design, the suction side of the screw compressor
unit is at the lower end of the vertical assembly, the high
pressure gas discharges vertically upwards, at the upper end of the
meshed helical screw rotors and is directed through suitable
passages to the second chamber, housing the electric motor.
Necessarily, due to the reaction forces developed during
compression of the gas, balance pistons connected to the rotors
require applied oil pressure on the side opposite the discharge gas
to balance the developed thrust forces. In order to separate the
oil entrained in the discharge gas by way of the compression
process and employed for lubricating the bearings and for sealing
the intermeshed rotary helical screw rotors, the hermetic design of
U.S. Pat. No. 3,922,114 includes an incorporated oil separation
scheme. Axial passages are provided within the electric motor rotor
to effect centrifugal oil separation and through the electric motor
stator for draining separated oil and radial, preferably canted,
discharge passages extend through the hermetic inner casing upper
chamber wall into the first chamber defined by the outer enclosure
for tangential impingement of the separated oil on the outer
enclosure wall.
While the vertical, hermetic rotary screw compressor of that design
operates satisfactorily, the structural make up is fairly
complicated, expensive to manufacture and requires overthrust
compensation for the developed axial thrust forces to insure
minimum gap dimension between the helical screw rotors on the
discharge side of the compressor and fixed end plates defining the
second and third chambers which house the electric drive motor and
the helical screw rotors respectively.
It is therefore an object of the present invention to provide an
improved, vertical axis, rotary helical screw compressor of the
hermetic type which eliminates the necessity for balance pistons
and the necessity for an oil pump without compromising the wear
life of the rotary bearings of the hermetic compressor.
It is a further objection of the present invention to provide an
improved vertical, hermetic rotary helical screw compressor in
which some oil introduced to the compressor working fluid is
distributed to the compressor and drive motor bearings during
normal passage of compressor discharge gas to the discharge outlet
of the hermetic unit.
It is a further object of the present invention to provide an
improved vertical, hermetic rotary helical screw compressor in
which oil separation is achieved in a simplified manner without the
need of internal and external sealed housings.
SUMMARY OF THE INVENTION
The vertical axis hermetic rotary helical screw compressor
constituted by a closed vertical cylindrical outer enclosure and an
inner cylindrical casing supports vertically a shaft which
coaxially mounts a helical screw rotor intermediate of its ends for
rotation about the vertical shaft axis by upper and lower roller
bearing pack assemblies, the upper roller bearing pack assembly
being mounted to the transverse wall of the inner casing and the
lower roller bearing pack assembly being mounted to an end plate.
An electrical drive motor is mounted above the screw rotor and has
its rotor coaxially mounted to the upper end of the vertical shaft
above the upper roller bearing pack assembly. The compressor inlet
tube opens through the inner casing to the helical screw rotor at
its upper end with the compressed working fluid discharging at the
lower end of the helical screw rotors. Passages within the casing
permit the discharge gas to pass upwardly about the shaft and
through the motor to act axially on the motor shaft and the rotary
seal element carried by the upper roller bearing pack assembly for
partially balancing the thrust forces generated during compression
of the working fluid. Entrained oil passes to the tapered roller
bearing pack assembly and across the seal seeking the low pressure,
suction side of the compressor. Multiple roller bearings are
applied within each pack assembly and the lower tapered roller
bearing pack assembly includes multiple shims for fixedly mounting
the shaft and its rotor spaced slightly from the casing end plate
to minimize compressed working fluid leakage in the area of the
compressor discharge passage and end plate. The bearing pack
assemblies may utilize wholly or partially, needle roller bearings
in lieu of tapered roller bearings. Also, the pack assemblies may
comprise a single roller bearing. A capillary line passing through
the compressor inlet and being looped therein to form a heat
exchanger for cooling of the oil carried thereby and projecting
from the oil sump, permits cooled oil to be injected through an
injection port open to a closed thread just after suction cut off
to lubricate and seal the screw rotors.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional, elevational view of one embodiment of the
improved vertical, hermetic rotary helical screw compressor of the
present invention.
FIG. 2 is an enlarged, sectional view of the electric drive motor
and suction tapered roller bearing assembly portion of the
compressor of FIG. 1.
FIG. 3 is an enlarged, sectional view of a portion of the bearing
assembly of FIG. 2 showing the labyrinth seal which is carried
between the double row tapered roller bearings.
FIG. 4 is a vertical, exploded sectional view of the portion of the
compressor shown in FIG. 2, exemplary showing the sequence of
operation in assembling the suction bearing assembly to the female
rotor shaft and compressor housing.
FIG. 5 is a vertical sectional view of a modified suction tapered
roller bearing assembly for use in a second embodiment of the
hermetic screw compressor of the present invention.
FIG. 6 is an enlarged, sectional view of the face seal employed
within the upper tapered roller bearing assembly of FIG. 5.
FIGS. 7A-7D are enlarged, sectional views of a portion of the
hermetic compressor of FIG. 1 showing the sequence in assembly of
the discharge tapered roller bearing pack assembly.
FIG. 8 is an enlarged vertical section of a portion of the
compressor of the present invention, as a second embodiment
utilizing the suction filter to filter compressor oil.
FIG. 9 is an enlarged vertical sectional view of a portion of the
discharge end of one of the screw rotors in a modified form of the
invention.
FIG. 10 is a vertical sectional view of a portion of another
embodiment of the improved vertical, hermetic rotary helical screw
compressor of the present invention showing a modified form of the
upper and lower bearing pack assemblies.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1-4 inclusive and FIG. 7, there is shown one
embodiment of the present invention in which FIG. 1 constitutes a
vertical sectional view thereof. The vertical axis, hermetic
helical screw compressor or unit is comprised of a generally
cylindrical outer, metal enclosure indicated generally at 10 which
consists of a central cylinder 12, a lower or bottom end wall 14,
and a cover or upper end cap wall 16. The lower end wall 14 is
welded at 18 to the lower end of cylinder 12, while in similar
fashion the upper end wall or cover 16 is welded as at 20 to the
upper end of cylinder 12, completing a sealed outer enclosure. The
hermetic unit discharges through an enclosure outlet defined by an
annular boss 22, fitting within a vertical, central opening 24
within the cover or upper end cap wall 16. The cylinder 12 carries
internally, a number of circumferentially spaced L-shaped brackets
26 which are welded or otherwise affixed to the inner surface of
cylinder 12 at a median vertical position which act as mounts for a
unitary, inner casing or housing 28 which is generally of
cylindrical form and which acts as the compressor housing for the
helical screw rotors such as female rotor 30, FIG. 1, and also for
the electric drive motor which is indicated generally at 32. Motor
32 constitutes a rotor 34 and stator 36. Casing 28 is provided with
parallel rotor bores such as bore 38 being open at its bottom end
40. The bottom end of the casing 28 is closed off by an outlet
housing or casing end plate indicated generally at 42. The casing
28 and end plate 42 act to support for each rotor, a lower outlet,
or discharge tapered roller bearing pack assembly, such as assembly
44, for helical screw female rotor 30. Assembly 44 constitutes,
along with upper or inlet or suction tapered roller bearing pack
assembly 46 for screw rotor 30, the means for rotatably supporting
this screw rotor, and in addition, similar bearing pack assemblies
(not shown) are provided for the male rotor (not shown). Casing 28
is provided with integral feet 48 at circumferentially spaced
positions corresponding to brackets 26 such that the casing 28 is
supported on the brackets, the feet being fixed to the brackets by
means (not shown). The outer enclosure cylinder 12 is further
provided with an opening 50 carrying an annular boss 52 which in
turn threadably or otherwise sealably supports a compressor inlet
or suction tube or pipe 54. Tube 54 extends from the cylinder 12 to
the wall of casing 28, tube 54 opening to the outside of the
hermetic unit to the left, FIG. 1, and opening to the interior of
bore 38 within the casing 28 at a point where the helical screw
rotors are intermeshed; at the top of the intermeshed screws and
defining the suction or inlet side of the compressor. By way of end
plate 42, there is formed at the lower end of casing 28 a
compressor discharge passage 56 which acts in conjunction with
vertical passage 58 within casing 28 to cause the compressed
working fluid of the compressor to be directed upwardly towards the
compressor drive motor 32.
In typical helical screw rotary compressor fashion, the casing 28
bears a longitudinally slidable, capacity control slide valve
member 60 which is fixed to a shaft 62 terminating in piston 64.
Piston 64 is housed within the slide valve drive motor cylinder 66
which is closed off at its lower end by cover 68, the cover 68
being mounted to the end wall 42 by way of suitable screws 70. The
piston 64 and the slide valve 60 are spring biased by means of coil
spring 72 so as to seek a fully closed position, while the
application of fluid pressure to chamber 74 defined by the piston
64, cylinder 66 and end plate 68, causes the piston to move
upwardly against the bias of the spring, permitting the slide
valve, which performs a capacity control function, to move into a
position where its upper end abuts a shoulder 76 of casing 28 for
maximum compression.
The shift in the slide valve 60 effects a variation in the amount
of gas which is returned to the suction side of the machine prior
to compression, thus varying the capacity of the compressor. The
slide valve also controls the radial discharge port of the
compressor. The operation of the slide valve is standard and does
not form a part of the present invention.
The present invention is particularly concerned with the nature of
the simplified support of the helical screw rotors such as rotor 30
and the take up of the radial and axial forces acting on the
rotors, their support shafts and the drive motor rotor 34, in the
case of the helical screw rotor 30 since it is mounted to shaft 80,
common with the helical screw rotor 30. Instead of the utilization
of sleeve bearings for take up of radial forces and thrust surfaces
and balance pistons for take up of the thrust forces, the present
invention employs the lower and upper tapered roller bearing pack
assemblies to perform this function under a simplified
manufacturing technique. Further, the helical screw rotors may be
set precisely in terms of their position relative to the end face
of the fixed compressor casing components. In FIG. 1, minimization
of the axial gap between the high pressure end face 82 of female
screw rotor 30 and the opposing face 84 of end plate 42 occurs to
limit loss of the high pressure discharge gas which tends to seek
the low pressure or suction side of the machine at and after
compressor discharge by way of slide valve 60 and discharge passage
56. Casing 28 incorporates a horizontal or transverse, integral end
wall 86 on the suction side of the compressor and intermediate of
the helical screw rotors and the electric drive motor 32. End wall
86 is provided with right angle, central, cylindrical section 88,
defining a cylindrical wall or bore 90 which receives the thin
metal sleeve 92 of suction tapered roller bearing pack assembly 46.
Longitudinally spaced pairs of double row tapered roller bearings
form the principal components of the upper bearing pack assembly
46.
The nature and make up of the assembly and the incorporated
labyrinth seal for sealing the row of tapered roller bearings of
that assembly from the lower row which are open to the suction side
of the compressor, may be seen by further reference to FIGS. 2, 3
and 4. Further, the nature, make up and assembly and mounting of
the discharge or lower tapered roller bearing pack assembly 44 may
be seen by additional reference to FIGS. 7A-7D.
Due to the weight of the screw rotors for both rotor shafts and the
drive motor rotor 30 of shaft 80, it is preferred that end plate 42
be provided with a suitable thrust bearing which bears, when the
rotors are at rest, on the end face of the rotor. As illustrated in
FIGS. 7A-7C, in this embodiment of the invention, the end plate 42
is provided with an annular recess 83 adjacent bore 91 which bears
an annular ring 85 of a low friction, long life, self-lubricating
bearing material such as DU (a registered trademark of the Glacier
Metal Company, Ltd.). In this respect, DU is a composite material
consisting of a steel backing strip having a 0.010 inch thick
sintered porous bond surface layer into which is impregnated a
homogeneous polytetrafluoroethylene-lead mixture with a thin
overlay of polytetrafluoroethylene and lead up to 0.001 inch
thickness. The internal diameter of the bearing ring 85 is slightly
larger than that of shaft 80, while the outside diameter
approximates the root diameter RD of the rotor 30 carrier by shaft
80. The thickness of the bearing ring 85 is greater than the depth
of the recess 83 receiving the same, so that at rest the end face
82 of rotor 30 is spaced slightly from the thrust surface 84 of end
plate 42. Alternatively, the ring 85 may be replaced by
anti-friction bearings such as ball bearings or the like.
End plate 42 is provided with an opening of relatively small
diameter as at 91 within face 84 which underlies the end face 82 of
the female screw rotor 30 carried by shaft 80. The end plate 42
opening 91 is enlarged at 91a to a diameter for positioning of the
components of the lower tapered roller bearing pack assembly 44
which rotatably supports shaft 80 at the lower end of the casing
28. In that respect, shaft 80 is provided, at its lower end, with a
first reduced diameter portion 80a forming a first shoulder 93, a
second reduced diameter portion 80b forming a second shoulder 94
and terminates in an end face 96. Shoulder 93 is in general radial
alignment with shoulder 98 at the enlarged diameter opening portion
91a of end plate 42. The lower tapered roller bearing pack assembly
44 comprises two single tapered roller bearings: a first tapered
roller bearing indicated generally at 100 and mounted to the shaft
80 at shaft reduced diameter portion 80a, and a second tapered
roller bearing indicated generally at 102 carried on the shaft 80
at shaft reduced diameter portion 80b. Bearing 100 comprises a
radially outer cup 104 of annular form and of trapezoidal
cross-section, and a radially inner, annular cone 106 of
trapezoidal cross-section. Interposed between the cup 104 and cone
106 are a plurality of circumferentially spaced tapered rollers
108. The bearings 100 and 102 are conventional and may constitute
for instance SKF tapered roller bearings under trade designation
TSS or TSSF, for instance. In similar fashion, the single row
tapered roller bearing 102 comprises a radially outer, annular cup
110 and a radially inner, annular cone 112, with tapered rollers
114 interposed between each of these trapezoidal cross-section
members and defining a circumferential or full annular array. The
assembly pack is completed by means of a lower bearing pack
assembly end plate 116 which spans across the opening 91 and its
enlargement 91a, with the end plate 116 having a diameter in excess
thereof and permitting by way of threaded screws 118 the fixing of
the lower bearing pack assembly end plate 116 to compressor end
plate 42. An annular cup retainer 120 which is generally L-shaped
in cross-section is integral with end plate 116 and is of a
diameter such that its radially outer periphery 122 is spaced from
wall 91a so as to define a radial gap 123 between the members. An
annular shim 124 having a thickness D which is determined on the
basis of the desired axial gap between rotor outlet end face 84 and
end plate 42, both when the compressor is at rest and when it is in
operation, and interposed between the outer face of end plate 42
and the end plate 116, acts to axially position the end plate
relative to the outlet end face 82 of the helical screw rotor 30 in
FIG. 7D, to insure under all conditions a gap of dimension "C"
therebetween.
Further, shaft 80 is provided with a tapped and threaded bore as at
126 which receives a threaded screw 128 which fixedly,
mechanically, locks cone 112 to the shaft 80 by driving that cone
axially towards shoulder 94 by pressure exerted on cone retainer
plate 129. In addition to shim 124, the present invention
particularly employs a second shim constituting an annular member
or ring 130 which has an internal diameter on the order of shaft
portion 80b and an external diameter which is slightly less than
the diameter of shaft portion 80a. The thickness of the shim 130 is
particularly important to the obtaining of the necessary clearance
or gap C between the face 84 of the end plate 42 and the outlet end
face 82 of the helical screw rotor 30.
The sequence of operation in the mounting of the shaft 80 at its
lower end, suitably supported for rotation, by the lower tapered
roller bearing pack assembly 44, for illustrated female helical
screw rotor 30 (the same technique and structure being applied to
the male rotor), is shown in FIGS. 7A-7D inclusive. Turning to FIG.
7A, it is noted that only the elements of the tapered roller
bearing 100 are shown. In this case, the cup 104 is positioned
within the larger diameter portion 91a of casing end plate 42 such
that the cup 104 abuts shoulder 98 of that member. With the rollers
108 in place, the cone 106 is pressed onto shaft portion 80a, with
the rotor end face 82 flush against the DU bearing ring 85 of the
end plate 42, achieved by gravity force acting on shaft 80,
electric motor rotor 34 and screw rotor 30. Applied force may also
be required to be exerted on the upper end of shaft 80 or on the
components fixed thereto to maintain the gap dimension between end
faces 82 and 84 as set by ring 85 during this assembly step. When
the end face of cup 104 is pressed against shoulder 98, measurement
B is taken of the distance between the lower end face 107 of cone
106 and shoulder 94. The thickness A of shim 130 is then the
desired measurement B at zero gap between the outlet end face 82 of
the female helical screw rotor 30 and bearing ring 85 of the end
plate 42, plus the desired thickness of gap C between the rotor 30
and end plate 42.
Assuming that the measurement B equals 0.015 inches and the desired
thickness of gap C is 0.003 inches, then the thickness of the shim
130 permitting this relationship becomes 0.018 inches. It should be
remembered that minimal gap dimension is required between the
outlet end face 84 of screw rotors for both female and male screws
and the end face 84 of casing 42, and the same technique applies to
that screw rotor.
Referring next to FIG. 7B, the second step in the operation is
locking of bearing 100, and particularly cone 106, to shaft
sections 90a and cone 112 of bearing 102 to shaft section 80b in
positions which will subsequently maintain the desired clearance C
between faces 82 and 84 of the rotor 30 and end plate 42
respectively. In that regard, with the shim 130 in place, cone 112
is force fitted to shaft portion 80b such that the upper end face
111 of cone 112 presses against the lower end face 107 of cone 106
and shim 130 which abuts shoulder 94. This assembly is maintained
in place by the cone retainer plate 129 which is locked to the
outer end face 132 of cone 112 by screw 128.
Finally, a measurement is made for the thickness of the shim 124.
The lower bearing pack assembly end plate 116 has provided on
annular cup retainer 120 inner periphery, a large internal diameter
portion 121, forming a shoulder 120d upon which rests the lower end
of cup 110 of bearing 102. With cup 110 so positioned, and by
placing the tapered rollers 114 in an annular array between the cup
110 and cone 112, and by pressing plate 116 and its integral cup
retainer 120 axially into the large diameter opening portion 90a of
end plate 42, shaft 80 is shifted axially upwardly until bearings
108 seat against cup 104, and cup 110 against bearings 114. At this
point, the desired clearance gap C exists between rotor end face 82
and surface 84 of the end plate 42. Further, there exists a gap D
between the outer end face 125 of end plate 42 and the inner
surface 127 of lower bearing pack assembly end plate 116. The
thickness of this gap D determines the thickness of shim 124 which
is of a diameter in excess of the outer diameter 122 of the annular
cup retainer 120 and is interposed between the end plate 42 and
surface 127 of lower bearing pack assembly end plate 116. The end
plate 42 is tapped and threaded to receive screws 118 which
permits, as shown in FIG. 7D, the fixing of the lower bearing pack
assembly end plate 116 and its integral cup retainer 120 to end
plate 42, thereby supporting shaft 80, female helical screw rotor
30 and the drive motor rotor 34 in proper position, such that,
regardless of developed forces during compression of the working
fluid, a constant, narrow clearance or gap C is maintained on the
discharge or outlet side of the compressor preventing loss of
compressed working fluid to the inlet side of the compressor from
this point.
It should be noted that by the utilization of the tapered roller
bearings, the bearings can function both to take up axial and
radial loads. In the instant case, the cup 104 of the single row
tapered roller bearing 100 performs the function of carrying the
radial load, while cup 110 of the single row tapered roller bearing
102 carries no radial load whatsoever. Cup 110 in this case is
functioning to absorb the reverse thrust load at compressor start
up, that is, an axial loading rather than radial loading. Since the
cup 110 is not functioning to carry any radial loading, there is
deliberately provided a radial gap 123 between the outside diameter
of the bearing cup retainer 120 and the the outlet end plate 42
opening 91a.
As noted previously, the thickness of shim 130 is such that gap C
is maintained as small as possible, for instance 0.003" to minimize
the escape of the high pressure compressed gas at the high pressure
or discharge side of the machine.
The thickness D of shim 124 may be readily determined by
utilization of a feeler between end plate face 84 and outlet end
face 82 of the female screw rotor and will maintain this desired
gap dimension when the bearing cup retainer 120 axially presses the
cone 112 against shim 130 and, in turn, cup 104 against shoulder
98, thus locating rotor 30 spaced with respect to the end plate
42.
Referring to FIGS. 1, 2, 3 and 4, the nature of the assembly and
make up of the inlet or suction bearing pack assembly 46 for screw
rotor 30 and shaft 80 may be seen. In this case again, only shaft
80 is illustrated. Male rotor (not shown) utilizes a similar inlet
bearing pack assembly. Shaft 80 is integral with or has fixed
thereto, the helical screw rotor 30, and is driven by the rotor 34
of the drive motor which is fixed to the upper end of that shaft.
Shaft 80 is provided above rotor 30 with a reduced diameter portion
80c forming a shoulder 132 upon which the lowermost laminae of
rotor 30 abuts, the rotor laminae being hollow as at 133 to permit
the rotor to receive portion 80c of shaft 80. Prior thereto, the
inlet bearing pack assembly 46 is mounted on the shaft 80
intermediate of the reduced diameter portion 80c and rotor 30. The
low pressure suction or inlet end face 134 of the female helical
screw rotor 30 faces upwardly. In immediate contact with the inlet
end face 134 of rotor 30 on shaft 80 is an annular spacer 136
having an inside diameter slightly larger than shaft 80 and an
outside diameter which is slightly less than the metal sleeve 92 of
the outlet bearing pack assembly 46.
Sleeve 92 of the inlet bearing pack assembly 46 may be formed of
seamless steel and is provided with three axially spaced sets of
circumferentially spaced drilled holes, the holes being at 138, 140
and 142 for respective sets. Holes 138, 140 and 142 support
retaining pins which may be hollow metal tubes as at 144, 146 and
148. The upper bearing pack assembly 46 consists essentially of two
double row, tapered roller bearings, generally at 150 and 152,
respectively, separated by a labyrinth seal indicated generally at
154. The double row tapered roller bearing 150 is maintained
axially within and properly positioned relative sleeve 92 by pins
144, the labyrinth seal outer ring 156 by pins 146 and double row
tapered roller bearing 152 by pins 148. While only one pin is
illustrated as maintaining the outer races or cups of the tapered
roller bearings and the outer element of the labyrinth seal mounted
to the sleeve 92, in fact a plurality of such pins are employed
circumferentially spaced, for instance at 120.degree., with respect
to each other and about the periphery of sleeve 92.
With annular spacer 136 in place, in the sequence, FIG. 4, the
lower cone 160 being of annular form and trapezoidal in
cross-section and having an internal diameter slightly less than
the diameter of a main shaft portion 80 is pressed or heat shrunk
axially onto that shaft and in contact with the female rotor end
face spacer 136. Next, a metal ring or intermediate spacer 162 is
concentrically applied to the shaft and forced axially into
position so as to abut the upper end of cone 160. A series of
bearing rollers 164 are provided to cone 160 and constitute an
annular array in contact with cone 160.
It is at this point that the major components of the upper and
lower double row tapered roller bearings 150 and 152 are forcibly
mounted to the main portion of shaft 80, while the sleeve 92 is
press fitted into cylinder 88. The subassembly which is pressed
into that position constitutes, as seen in FIG. 4, not only sleeve
92, but outer race 166 for the upper double tapered row roller
bearing 150, labyrinth ring 156, outer race 168 of the lower double
row tapered roller bearings 152; these elements being suitably
coupled to sleeve 92 and remaining axially fixed by way of the
series of pins 144, 146 and 148 for respective members. Due to the
oppositely tapered surfaces at the ends of the outer races 166,
168, not only are the rollers 170 for the upper double row tapered
roller bearing 150 and 172 for the lower double row tapered roller
bearing 152, maintained in position, but since these rollers bear
on their respective annular cones 173 and 174 separated by a
labyrinth seal spacer 176, all of these elements are maintained in
proper radial and axial positions. At the same time, the sleeve 92
is press fitted to the inner surface of cylinder 88 and cones 173
and 174 and the inner space 176 of the labyrinth seal are press
fitted to the central portion of shaft 80. Members 173, 174 and 176
have an inner diameter somewhat less than the diameter of the
central portion of shaft 80.
Subsequently, the assembly is completed by axially press fitting
spacer 178 of rectangular cross-section onto the main portion of
shaft 80, and in abutting contact with the upper end of cone 173
and force fitting annular cone 180 of double row tapered roller
bearing 150 onto the main portion of shaft 80 such that the rollers
182 contact the axially tapered face of the outer race 166 of that
bearing. The rollers 182 constitute a circumferential or annular
array interposed between outer race 166 and cone 180. In effecting
the assembly of these elements for both the inlet tapered roller
bearing pack assembly 46 and the outlet tapered roller bearing pack
assembly 44, the elements may be appropriately shrunk fit to the
portions of the shaft receiving the same or to sleeve 92 of casing
end plate 42 or forcibly press fitted by axially applied pressure
in accordance with conventional assembly techniques.
Reference to FIG. 3 illustrates in greater detail the make up of
the labyrinth seal 154 for the upper, inlet tapered roller bearing
pack assembly 46. In that respect, the labyrinth ring 156 and the
labyrinth spacer 176 are both annular elements of generally
rectangular cross-sectional configuration. The radial inner face
184 of the ring 156 is smooth, while the opposite radially outward
face 186 of the spacer is serrated with circumferential grooves
forming a longitudinal array and defining a very small and finite
air gap between members 156 and 176. As may be seen in FIG. 1, the
discharge gas from the compressor as controlled by the slide valve
60 in passing upwardly through passage 58 to the opposite side of
transverse inlet end wall 86 and in entering a chamber or casing
portion 188 within casing 28 causes the upper double row tapered
roller bearing 150 to be subjected to discharge pressure. This
discharge pressure tends to seek the suction side of tapered roller
bearing pack assembly 46, but is prevented from directly reaching
the inlet end face 134 of the female rotor 30 by the labyrinth seal
154. A major pressure drop exists across the gap defined by the
serrated face 186 and the smooth face 184 of the seal members 176
and 156 respectively. The lower double row tapered roller bearing
152, is close to the suction pressure of the compressor, while the
upper tapered roller bearing 150 is essentially at compressor
discharge pressure. This pressure differential results in migration
of oil through the inlet bearing pack assembly 46 towards the
suction side of the compressor.
FIGS. 5 and 6 show an alternate embodiment of the invention
incorporating a slightly different seal intermediate of the upper
and lower double row tapered roller bearings 150 and 152. In the
case of the embodiment of FIGS. 5 and 6, like elements are given
like numerical designations to that of the embodiment shown in
FIGS. 1-4 inclusive. In this embodiment, the series of pins 146
within sleeve 92 project within openings 190 of an L-shaped fixed,
annular face element or member 192. It being L-shaped in
longitudinal section, includes a base portion 192a abutting sleeve
92 and a projecting leg portion 192b which extends radially towards
the shaft 80. The fixed seal element 192 has an outer diameter on
the order of the inner diameter of the sleeve 92, so as to be
sealably in contact with that member. Leg portion 192b has an inner
diameter defining annular end wall 194, which is spaced radially
from a rotating annulus or seal ring 196 which is press fitted to
or heat shrunk onto shaft 80 with one end 198 in contact with cone
174 of the lower of the two double rows tapered roller bearings.
The annulus 196 is of rectangular cross-section including a
radially outer face 200 which faces the fixed seal element 192. A
thin, spring retainer ring 202 having an inner diameter slightly
less than shaft 80 and having an outer diameter in excess of the
annulus 196 is sandwiched between the upper end of the rotating
annulus or ring 196 and cone 173 of bearing 150. The spring
retainer ring 202 has an outer diameter which is somewhat less than
the inner diameter of base 192a of the fixed seal element 192.
Mounted within a cavity or chamber 204 defined by the rotating
annulus 196, the fixed seal element 192 and the spring retainer
ring 202, is a carbon seal element 206 in the form of a complete
annulus or ring but being of irregular configuration. The
configuration of carbon face seal element 206 is of modified
L-shape, in longitudinal section, including a base portion 206a in
contact with the radially outer periphery 200 of the rotating
annulus or seal ring 196. The L-shaped carbon face seal element 206
further includes a radially outwardly directed portion 206b which
extends towards but terminates short of the base portion 192a of
the fixed seal element 192. Further, an axial projection 206c
extends from one axial wall 208 towards and abuts with the facing
surface 210 of the fixed seal element 192. These members are
maintained in contact during rotation of the shaft by means of an
annular, wavy spring 212 which is interposed within cavity 204 and
which abuts axially the spring retaining ring 202 and a radial face
or surface 214 of the portion 206b of the carbon face seal element.
Preferably, ring 196 on face 200 is provided with an annular groove
216 within which is carried an O-ring 218 to assist in sealing the
upper bearing 150 which is at discharge pressure from bearing 152
at near suction pressure.
In the face seal arrangement, the wavy spring 212 is compressed
between the carbon seal element 206 and the spring retaining ring
202, to cause projection 206a to be frictionally pressed against
the radial leg 190b of the fixed seal element. The fixed seal
element, of course, remains fixed while the spring retainer ring
202, the wavy spring 212, the rotating ring 196 and the carbon face
seal element 206 rotate with the shaft 80. Since the carbon face
seal element 206 is not fixed to either the rotating annulus or
ring 196 or the fixed seal element 192, and since the spring force
is axial or longitudinal, the O-ring tends to maintain a seal at
this point so as to prevent axial passage of the high pressure
discharge gas between the upper tapered roller bearing 150 and
lower tapered roller bearing 152 of tapered roller bearing pack
assembly 46.
With either the tapered roller bearing pack assembly 46 of the
embodiment of FIG. 2 or 46' of the embodiment of FIGS. 5 and 6,
mounted as shown in FIGS. 2 and 5, the assembly may be completed by
placing the motor rotor 34 consisting of a series of laminated
metal sheets 210 as a stacked array on the upper, reduced diameter
portion 80c of shaft 80. In that respect, a tapered ring 213 is
mounted to the bearing pack assembly 46, abutting the upper cup 180
on its lower end face 215 and having its upper end face 217
abutting the lowermost laminate sheet 219 of rotor 34. The upper
end of the shaft portion 80c bears a tapped and threaded axial hole
221 which receives the threaded end of a screw 220 which passes
through and has its head abutting a circular shaft end plate 222.
The end plate 222 presses against the rotor which in turn presses
the elements axially bearing pack assemblies 46 or 46' against the
unitary female helical screw rotor 30.
With the rotor 34 mounted to the shaft 80, stator 36 may be
positioned fixedly on casing 28 at its upper end above the
horizontal end wall 86, or alternatively the stator 36 may be
predisposed prior to disposition of shaft 80 on the same casing by
way of the lower and upper bearing pack assemblies 44 and 46,
respectively. Casing 28 is enlarged at its upper end and is
internally relieved as at 224 to form a small shoulder 226 for
locating the laminate sheets 219 of stator 36. Stator 36 carries
windings 232. The windings 232 surround windings 233 carried by
rotor 34, the stator and rotor being separated by an annular gap
228 which may act as an annular passage for the discharge gas which
is caused to move upwardly particularly by the rotation of rotor 34
since the rotor is provided with a plurality of axially extending,
circumferentially spaced, passages 234 within the rotor
laminations. The rotor acts as a centrifugal pump with the
discharge gas moving in the direction of arrows, FIG. 1, into
chamber 188 housing the rotor and stator, flowing about the lower
end of the stator windings 232 and between those windings and the
cylinder 88. It then enters an annular cavity 236 between annular
spacer 213 and the rotor windings 233. Since the gas must take
several turns and since the lower end of the bearing pack assembly
46 is subjected to suction or inlet pressure, there is a tendency
for some of the oil entrained in the discharge gas to migrate into
the tapered roller bearing 150 and to lubricate this bearing.
Further, with the pressure on the lower side of the labyrinth seal
154 being less than that on the upper side, oil passes along with
the small volume flow of discharge gas between labyrinth seal
members 156 and 176 to further lubricate tapered roller bearing
152.
The oil indicated by the letter O, FIG. 1, fills the hermetic
casing or housing to approximately the level of the inlet or
suction tube 54, FIG. 1. In this embodiment, oil is cleaned by
passing through strainer 240. The oil being at the discharge
pressure of the compressor, thus tends to move by pressure
differential through passages (not shown) internally of casing 28,
seeking compressor suction pressure. Those passages connect to tube
or pipe 242 leading from the strainer 30 to end plate 42, FIG. 1.
In the present invention, in the multiple embodiments, the shafts
for both the female and male rotors may be hollowed or otherwise
provided with passages leading to the various bearings and
components of the hermetic unit which require oil lubrication.
Alternatively, the fixed housing or casing 28 may incorporate oil
passages to insure suitable lubrication to the moving elements
within the hermetic unit. Since oil is conventionally provided to
the helical screw rotor such as rotor 30, the working fluid, such
as a freon refrigerant or the like, in entering as a vapor through
inlet or suction tube 54 to the compression chamber as partially
defined by bore 38, will entrain the oil which is used for
lubrication and sealing purposes and will carry this oil in the gas
discharge stream as evidenced by the arrows, FIG. 1.
As mentioned previously, a portion of this oil will be lost to the
bearing pack assemblies, since the upper bearing pack assembly 46
for instance has its lower end open to the suction side of the
compressor, below the horizontal end plate 86, and in an area in
close proximity to compressor inlet as defined by the juncture of
tube 54 and casing 28. The majority of the oil as entrained within
the discharge gas is carried through the axially extending passages
234 within rotor 34, parallel to the axis of shaft 80. This
discharge gas is swirled as a result of high speed rotation of the
motor rotor 34, oil tends to be separated from the discharge gas by
centrifugal force action at the upper end of the motor 36, while at
the same time, due to the axial movement of the gas flow, a portion
of the entrained oil strikes the lower surface 244 of metal sheet
deflector 246 which is mounted to fitting or boss 22 by means of
rods 248. The deflector 246 is of disc shape and is concave
downwardly, such that the accumulated oil tends to flow to the
peripheral edge 250 of deflector 246 and falls down and over the
stator and accumulates within the bottom of the outer casing 10
such that the outer casing 10 acts as a sump for the oil. The
deflector 246 is spaced only slightly in an axial direction with
respect to the windings 232 to maximize the separation of oil by
impact and attachment to the lower surface 244 of that member,
while at the same time, this properly correlates the flow of the
oil free gas which passes about the peripheral edges 250 of the
deflector and between the deflector 246 and cover 16 for exiting in
the direction of the arrow shown.
Further, and most importantly, in addition to the discharge gas
tending to effect oil separation by centrifugal force due to
passage through the bores 243 within rotor 34, the discharge gas
tends to act axially on the upper end of shaft 80 towards gap C
between the outlet end face 82 of the female rotor 30 and surface
84 of the fixed end plate 42. The same effect occurs with respect
to the male rotor and its shaft (not shown).
Thus, in this type of arrangement, rather than requiring the
utilization of a separate balance piston to which hydraulic
pressure such as oil under pressure from a separate oil pump as in
the referred to patent, the present invention utilizes to a
maximum, the cross-sectional area of the shaft 80 at its upper end,
and the maximum effective diameter of that shaft by way of the
labyrinth seal annular spacer 176, the upper axial end face of that
member also being subjected to discharge pressure to partially
balance out developed thrust forces during compression. The major
portion of the developed thrust which acts during compression to
force the screws upwardly, is balanced out by the discharge gas
acting on the upper end of shaft 80 and on the upper face of
annular spacer 176 of the labyrinth seal 154, in the embodiment of
FIG. 1 and the spring retainer ring 202 of the FIG. 6 embodiment.
Further, in the present arrangement, the rotor 34 which has some
mass has its weight acting in opposition to the developed thrust
adding to the counterbalance forces by the discharge gas acting on
shaft 80 and on its rotating elements. This permits in the instant
case the utilization of the tapered roller bearings to take up both
radial and axial forces, it being sufficient that dual tapered
roller bearings are provided for the inlet tapered roller bearing
pack assembly 46 and outlet tapered roller bearing pack assembly
44.
Further, as shown in FIG. 1, preferably a small capillary tube 243
is coupled to the oil supply pipe 242 downstream of strainer 240,
whereby a small portion of the filtered oil may be directed through
the capillary tube 243 to a looped portion or coil 245 within the
compressor suction or inlet 54, where the oil is cooled by the
refrigerant vapor returning to the compressor which is
approximately 40.degree. F. The capillary tube 243 terminates at
compressor casing 28 and opens to an oil injection port 247, which,
in turn, opens to a closed thread just after rotor suction cut off
from inlet 54. Thus, the high viscosity of the oil increases the
sealing action of the oil, and the low temperature reduces the
evolution of refrigerant from the oil flow itself, thus
contributing substantially to an increase in volumetric efficiency
of the compressor without a subsequent increase in the power
required for the motor driving that compressor. Effectively, the
oil may be cooled down from approximately 160.degree. which is the
temperature in the sump to 100.degree. F. by means of the
40.degree. F. suction gas to the compressor.
Turning to FIG. 8, an alternate form of the invention incorporates
in a simple and expedient manner an arrangement for effectively
filtering the oil to remove micron size contaminants by utilization
of the filter assembly associated with the compressor suction or
inlet tube 54. As in the prior embodiments, like elements are given
like numerical designations. Thus, the compressor outer casing
cylinder 12 is provided with an opening 50 mounting an annular boss
52 through which protrudes the inlet or suction pipe or tube 54,
the inner end of which is coupled to casing 28 and open to the
helical screw rotors. Further, the hermetic compressor unit is
provided with an oil strainer 240 which connects by way of pipe or
tube 242 to casing 28 and specifically by way of the end plate 42
to deliver oil to flow passages (not shown) through the rotor
and/or stator casing portions of the screw compressor for
lubricating the bearings within this alternative embodiment and for
sealing of the hermetic screw rotors (not shown).
This embodiment employs a fine mesh filter sleeve as at 260 which
is mounted by way of an annular ring 262 to the leading end of the
inlet tube 54, being sandwiched between a flanged portion 54a of
that element and a cylindrical valve casing 264 which is fixed to
and constitutes an axial extension of the inlet tube 54 external of
casing cylinder 12. A conduit 266 which feeds working fluid such as
freon refrigerant in vapor form to the compressor, is mounted to
valve casing 264 and the valve casing carries internally a
pivotable check valve 268 which closes off an opening 270 within
the vertical wall 272 of valve casing 264 which is aligned with
conduit 266. The filter element 260 is therefore downstream of the
check valve to selectively permit vapor to enter the compressor but
prevents reverse flow. Valve casing 264 is provided with a radial
passage 274 within the sidewall of that member, within which is
mounted one end of an oil bleed tube 276, the opposite end
projecting through the cylinder wall 12 of the compressor hermetic
casing or housing and terminates at fitting 278, opening to the
interior of tube 242 feeding oil to the compressor casing 28.
Within line 276, is the solenoid operated valve 280 which is
selectively energized by appropriate controls to permit upon start
up of the compressor, the bleeding by way of pressure differential
of a portion of the oil being circulated through the system as
picked up by oil strainer 240, this oil entering into the intake or
suction gas stream upstream of filter 260 and thus being filtered
by this element. Particles of a size 4 mm will be filtered out from
the oil, thus permitting the oil circulating through the system to
be continuously cleaned by the same means which effectively cleans
the gas as it returns to the suction side of the compressor.
In an alternate embodiment of the invention, the lower bearing pack
assembly is modified to some extent as may be seen in FIG. 9,
wherein in this embodiment elements common to the embodiment of
FIGS. 7A-7D inclusive bear like numerals. The end plate 42 is
provided with a recess 83 within its thrust surface 84 identical to
that of the earlier embodiment, but instead of receiving a bearing
ring formed of DU, it receives a ball bearing assembly 87 being
appropriately sized to that of the DU bearing ring and maintaining
a predetermined minimal clearance between the thrust surface or end
face 84 of the end plate 42 and outlet end face 82 of rotor 30 and
occupying a surface area from shaft 80 to the root diameter RD of
rotor 30. Instead of two rows of tapered roller bearings, a single
tapered roller bearing 100 is provided consisting of cup 104, cone
106 and rollers 108. The cup 104 abuts shoulder 98 of the end plate
42 and the cone 106 bears on the surface of shaft portion 80a. An
annular shim or ring 130 determines the axial position of cone 106
and provides for the desired clearance C between the opposed end
face 84 of end plate 42 and end face 82 of rotor 30. In a
simplified manner, the shaft terminates with a reduced diameter
section 80a, this shaft portion bearing a tapped and threaded bore
131 which receives the threaded end of a screw 133 which projects
through a hole 135 within a bearing assembly thrust plate 137. A
washer as at 139 may be interposed between the head of the screw
133 and the plate 137. The lower bearing pack assembly end plate
116' is simply mounted to end plate 42 by suitable screws 118.
However, in this case, it does not bear directly or indirectly on
either the cone 106 or cup 104 of the tapered roller bearing 100.
The screw 133 may be torqued to preload the roller bearing 100 by a
given value, say approximately 50 pounds. This may be particularly
appropriate where the casing portions as for instance end plate 42
are formed of a light weight metal such as aluminum while the
rotors are formed of stainless steel, thus exhibiting differing
thermal expansion and contraction characteristics.
Turning next to FIG. 10, a portion of an alternate embodiment of
the invention is shown with the vertical sectional view
illustrating both the female and male rotors and the shafts and
bearing assemblies for the vertical, hermetic screw compressor
unit. In the fragmentary view of the compressor and motor, portions
of the hermetic unit which are internal of the outer enclosure (not
shown) include an inner casing or housing indicated generally at
328 including an upper casing section 328a and a lower casing
section 328b. These sections are of modified cylindrical shape, and
the lower section 328b is closed off by means of a casing end plate
342 which is screwed thereto by means of screws 343. The motor
indicated generally at 332 comprises a rotor 334 and a stator 336,
with the rotor 334 being concentrically mounted internally of the
stator 336 for rotation about its axis on a shaft indicated
generally at 380 and bearing in addition to the motor rotor 334,
the female rotor indicated generally at 330. In addition, a second
shaft 300 acts to support the male rotor 302 in side-by-side
fashion for rotation about an axis parallel to that of shaft 380
with the male and female rotors being of the helical screw variety
and having their helical surfaces is mesh. This embodiment of the
invention is characterized by the specific upper and lower bearing
pack assemblies for the shafts 380 and 300 bearing respectively the
female and male rotors. In that respect, shaft 380 is provided with
an upper bearing pack assembly indicated generally at 346 and a
lower bearing pack assembly indicated generally at 344. For shaft
300, there is provided an upper bearing pack assembly indicated
generally at 304, and a lower bearing pack assembly indicated
generally at 306. The lower bearing pack assembly 306 is identical
to bearing pack assembly 344, while the upper bearing pack
assemblies 304 and 346, having some common characteristics, but are
not identical. With respect to shaft 380, this shaft includes on
the discharge or outlet side of the female rotor 330, a reduced
diameter portion 380a and terminates in a further reduced diameter
portion 380b. Also, there is an enlarged diameter portion as at
380c which extends upwardly and away from the suction side of the
female rotor 330. The lower casing section 328b is provided with
the end plate 342 which is mounted thereto and bears a bore 391 for
receiving shaft 380, shaft 300 being borne within bore 308 of that
casing end plate 342.
With respect to the female rotor, the end plate 342 is counterbored
at 391a forming a shoulder 398 against which the radially outer cup
404 of tapered roller bearing assembly 400 bears, the tapered
roller bearing assembly 400 being completed by a radially inner
annular cone 406 and a plurality of tapered rollers 408. Contrary
to the embodiment particularly illustrated in FIGS. 7A-7D, instead
of a second tapered roller bearing, a needle thrust bearing 348 is
provided. In this regard, the casing section 328b which is closed
off by lower roller bearing pack assembly end plate 316 supporting
a cylinder or collar 312 which is centrally recessed as at 314 on
its upper end face 315 and terminates and has its lower end face
318 provided with a spherical recess 320. The end plate 316 is
tapped and threaded as at 322 and receives a hex headed, threaded
plug 324 whose end face 326 is spherical conforming to the
spherical recess 320 within the end face of cylinder 312. The
recess 314 is somewhat larger than the diameter of shaft section
380b and receives the end of that shaft section. Further, the
portion 380b carries needle bearing 348 for taking up a portion of
the thrust load provided by the weight of the assembly of the
shaft, female rotor and the motor rotor 334. In that respect, the
shaft portion 380b is tapped and threaded at its center as at 329
and receives the threaded end of a screw 331 which bears against a
circular retainer plate 333. The circular plate 333 is apertured as
at the center to permit the screw 331 to pass therethrough and has
an external diameter which is larger than the diameter of the shaft
portion 380b but less than that of the circular recess 314 of
collar 312. The bearing assembly is further made up of an annular
ring 335 having an internal diameter slightly larger than the
diameter of shaft portion 380b and an external diameter on the
order of that of cone 406 with its upper surface abutting that
cone. Further, shim 430 is provided, which in like manner to the
embodiment of FIGS. 7A-7D, and acts the same as shim 130 in that
embodiment, to provide a predetermined clearance C between the end
face of the female rotor 330 and the end face or thrust surface of
end plate 342. The assembly further comprises a sleeve or cylinder
337 which abuts plate 333 at one end and ring 335 at the opposite
end, thereby permitting the tapered roller bearing 400 to be
pressed axially on shaft section 380a and to effect the desired
clearance C between the rotor 330 and the end plate 342. This
portion of the assembly is in many respects similar to that of the
embodiment of FIG. 9. However, a distinction may be made in that
the annular ring 335 performs an additional function as it acts as
one race for the second bearing constituting needle bearing 348,
the other components comprising an annular ring 350 defining the
lower race for the needle bearing and a plurality of non-tapered
needle bearing rollers 352. The ring or lower race 350 has an
internal diameter equal to the external diameter of sleeve 337 and
an external diameter less than that of the collar 312. With end
face 315 bearing the lower race or ring 350, it may be readily
appreciated that by rotation of the threaded plug 324, the thrust
needle bearing assembly may be preloaded to a degree determined by
the torque applied to the hex headed threaded plug 324. The
cylinder or annular collar 312 is provided with one or more holes
354 which open to a cavity 355 within casing 328 common to both
roller bearing pack assemblies 400 and 400', the cavity 355 being
open either to compressor suction or to a closed thread after
suction cut-off. Due to the interfitting spherical fit between the
end face 327 of plug 324 and the spherical recess 320 within the
collar or cylinder 312, the collar 312 will tilt slightly to adapt
itself to the proper position necessary to insure alignment of the
needle bearing assembly to the shaft 380, thus defining a
self-aligning bearing assembly. This is particularly important in
two respects. The end plug 324 and collar 312 permits preloading
and the absence of end play between the tapered roller bearing and
the needle bearing. Otherwise, the gap C would have to be larger by
a magnitude in order to prevent the rotors 330 and 302 from
contacting the outlet end plate 342. Further, with respect to the
straight needle thrust bearing 348, improper loading is possible
due to misalignment of the bearing assembly. However, the tapered
roller bearing indicated generally at 400 can take up to 2.degree.
of angular misalignment without problem.
With respect to the male rotor 302 and shaft 300, the lower bearing
pack assembly is identically structured, in this case there being a
tapered roller bearing 400' and a needle thrust bearing 348' with
the needle bearing 348' being mounted by way of a second collar or
cylinder 312' by way of a threaded end plug 324'. However, at the
opposite end of the shafts, the upper bearing pack assemblies are
somewhat different. With respect to the upper bearing pack assembly
346 for shaft 380, as mentioned previously, the shaft 380 employs
an enlarged diameter shaft portion 380c which is machined
throughout its axial length to provide surface portion functioning
as bearing inner races. The upper casing section 328a is provided
with a transverse wall 368 including a right angle cylindrical
section 388 which projects axially to each side of the remaining
portion of the transverse or end wall 386. This cylindrical section
388 is provided with a bore of given diameter and along its axial
extent, it is provided with circular grooves 392 and 394 which
carry snap rings 396 and 398 respectively. A portion of the shaft
section 380c adjacent the suction or inlet end face 360 of the
rotor 330 is serrated as at 362 and faces an annular sealing ring
364 which is fixedly pressed into and preferably is force fitted to
the inner wall or bore 390 of cylindrical section 388 of the end
wall. Further, the sealing ring 364 has an internal diameter which
is slightly larger than the diameter of the shaft section 380c at
the serrations 362 so as to form with those serrations a labyrinth
seal. The upper bearing pack assembly 346 is characterized by an
upper needle 366 and a lower needle bearing 368. In this respect,
the shaft portion 380 forms the radially inner races for the needle
bearings, while separate outer races are employed as at 370 and 372
respectively for bearings 366 and 368. An annular spacer or ring
374 of a given axial length is interposed between the outer race
members 370 and 372 and the snap rings 396 and 398 lock the races
and the spacer in axial position with the races supporting
therebetween, the uniform diameter needle bearing rollers 378 for
each of the bearings 366 and 368. The roller bearings 366 and 368
may comprise HJM- 445628 matched heavy duty roller bearings and the
needle thrust bearings 348, 348' may comprise FA-49937 TRD-2840
bearings for the lower bearing assemblies 344 and 306. Since the
housing or casing 328 may be formed of aluminum, the aluminum
cylinder section 388 may be easily machined to provide for bore 390
and ring grooves 392. The bearing pack assembly components may be
axially pressed into the bore 390 of cylindrical section 388 and
maintained axially by way of the snap rings 396 and 398.
Turning to the upper bearing pack assembly 304 for shaft 300, a
single needle bearing 406 is employed. The end transverse wall 386
is bored at 387 and receives the serrated end 300a of shaft 300
which is of slightly less diameter than that of bore 387 to define
with bore 387 a highly effective labyrinth seal at this point.
Inwardly of shaft portion 300a in the direction of the male rotor
302, there is located a radially inner race member as at 389, this
cylindrical race member 389 abutting at one end a spacer 391, which
abuts the end face 303 of male rotor 302, the cylindrical inner
race member 389 being maintained in position by way of a snap ring
393 fixed to the shaft 300 via a slot and bearing against the
opposite end of that member. An outer race member 395 is mounted
within a counterbore 397 within the end wall 386 and is maintained
in position by a second snap ring 399.
A plurality of non-tapered needle bearing rollers 401 are
interposed between the radially inner and outer races 389 and 395
forming the radially loaded needle bearing 406 for the upper end of
shaft 300. It should be remembered that in this embodiment the
upper bearing pack assemblies do not bear any thrust loads, but
simply take up radial loading of the shafts at that end of the
machine.
With respect to the invention as disclosed in all embodiments, the
operation of the compressor is believed to be readily understood by
the previous description. It should be remembered that since the
discharge or outlet end of the compressor is vertically downward
and the generated thrust is in the opposite direction, the weight
of the componentry tends to balance out this generated thrust along
with the application of discharge gas pressure on the upper end of
the shaft commonly supporting the motor rotor and the female screw
rotor, for the rotor and on the upper end of the shaft supporting
male rotor (not shown).
* * * * *