Oil channeling in a centrifugal compressor transmission

In the transmission of a centrifugal compressor, where a gear is located adjacent to a lubricated bearing, a barrier is provided between the bearing and the gear to restrain the flow of oil to the gear and thereby reduce the pumping and windage losses that would otherwise occur. An oil port is made to communicate with the internal area of the barrier to thereby provide drainage of the accumulated oil to a sump.

BACKGROUND OF THE INVENTION 
This invention relates generally to centrifugal compressors and, more 
particularly, to an improved lubrication method and apparatus therefor. 
Hermetic centrifugal refrigeration compressors generally use an electric 
motor to drive the impeller through a geared up transmission. In such a 
compressor, the transmission is typically vented to a source of low 
pressure refrigerant within the system to minimize the outward migration 
of oil through the shaft seals. It has been recognized that during this 
venting process, in addition to the refrigerant gas passing out of the 
transmission, some of the oil in the form of droplets or mist may become 
entrained within the refrigerant gas and also pass out from the 
transmission. This is not been a particular problem. 
With the more recent use of higher pressure and higher density 
refrigerants, such as R-22, the problem of oil carry over has become an 
issue. That is, because of the higher pressure refrigerant, it is 
necessary to operate the gears at higher speeds. This is in turn increases 
the turbulence and the oil mist generation within the transmission. 
Further, the larger pressure differentials tend to promote higher vent gas 
flow rates and therefore increased carry over. 
In addition to the refrigerant higher pressures, the higher densities also 
tend to exasperate the problem. That is, the increased densities tend to 
keep the oil droplets in suspension longer and makes separation more 
difficult. In addition, the mechanical losses from oil separation 
mechanisms are higher due to increased density. 
Considering now the result of oil carry over, when the oil entrained 
refrigerant from the transmission is vented to the compressor inlet, it 
passes through the compressor and is discharged into the condenser, where 
it may tend to coat the heat exchanger surface to thereby decrease the 
efficiency thereof. Some of the oil is then passed on to the cooler where 
the same phenomenon occurs. Thus, it will be recognized that high oil 
carry over rates tend to result in poor heat exchanger performance. More 
over, as the oil supply in the sump is diminished because of this 
phenomenon, there may no longer be sufficient amount of oil to insure that 
all of the moving parts that require lubrication are in fact receiving 
adequate supplies of oil. 
The oil carry over problem has been addressed in two different ways. First, 
the most common approach is to use a mesh type oil separator in the vent 
line to cause oil droplets to coalesce and drain back into the 
transmission. A second method uses a series of hollow rotating tubes to 
centrifuge out the unwanted oil mist component of the vent flow. Neither 
of these methods, by themselves, are found to be sufficient for containing 
oil in a centrifugal compressor using high pressure, high density 
refrigerant such as R-22. 
In addition to the loss of oil from the transmission as occasioned by the 
high speed rotation of the gear, there are also mechanical losses brought 
about by the oil from the bearings being transferred into the gear mesh 
and onto the gear face. That is, oil on the gear causes windage losses as 
well as oil pumping losses, since the gear mesh then acts as a pump. 
These, in turn, increase the load on the bearings and may reduce the life 
thereof. 
It is therefore an objection of the present invention to provide an 
improved lubrication system for a centrifugal compressor. 
Another object of the present invention is the provision in a centrifugal 
compressor for reducing mechanical losses brought about by oil being 
disposed on the gears 
Yet another object of the present invention is the provision in a 
centrifugal compressor for reducing windage losses and oil pumping losses 
in the transmission. 
Another object of the invention is to provide a mechanism by which the used 
oil is conveyed directly to the sump without being "caught up" in the 
turbulent environment within the transmission. 
Still another object of the present invention is the provision in a 
centrifugal compressor for reducing the load on the bearings. 
Yet another object of the present invention is the provision in a 
centrifugal compressor for a lubrication system which is economical and 
practical in operation. 
These objects and other features and advantages become more readily 
apparent upon reference to the following description when taken in 
conjunction with the appended drawings. 
SUMMARY OF THE INVENTION 
Briefly, in accordance with one aspect of the invention, an oil containment 
barrier is provided around a bearing so as to impede the outward flow of 
oil onto the gear(s) of the transmission into and into the transmission 
chamber in general. In this way, the bearings may be lubricated without 
allowing the oil to subsequently flow to the gear(s) where it would cause 
mechanical losses and/or add to the oil mist within the transmission. 
By yet another aspect of the invention, provision is made to drain oil away 
from the barrier and into the sump such that there will be no substantial 
accumulation of oil within the barrier. This is accomplished by the way of 
a series of ports which allow the oil to drain to the sump by way of 
gravity. Passages are well protected from effects of swirling gas, and oil 
is isolated from the turbulence. 
In the drawings as hereinafter described, a preferred embodiment is 
depicted; however, various other modifications and alternate constructions 
can be made thereto without departing from the true spirit and scope of 
the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, the invention is shown generally at 10 as embodied 
in a centrifugal compressor system 11 having an electric motor 12 at its 
one end and a centrifugal compressor 13 at its other end, with the two 
being interconnected by a transmission 14. The motor 12 includes an outer 
casing 16 with a stator coil 17 disposed around its inner circumference. 
The rotor 18 is then rotatably disposed within the stator winding 17 by 
way of a rotor shaft 19 which is overhung from, and supported by, the 
transmission 14. 
The transmission 14 includes a transmission assembly 21 having a radially 
extending annular flange 22 which is secured between the motor casing 16 
and the compressor casing 23 by plurality of bolts 24. Rotatably mounted 
within the transmission assembly 21, by way of a pair of axially spaced 
bearings 26 and 27 is a transmission shaft 28 which is preferably 
integrally formed as an extension of the motor shaft 19. The collar 29, 
which is attached or installed by shrink fit, is provided to transmit the 
thrust forces from the shaft 28 to the thrust bearing portion of the 
bearing 26. The end of shaft 28 extends beyond the transmission assembly 
21 where a drive gear 31 is attached by way of a retaining plate 32 and a 
bolt 33. 
The drive gear 31 engages a driven gear 34 which in turn drives a high 
speed shaft 36 for directly driving the compressor impeller 37. Typical 
speeds for the respective shafts are 3550 rpm for the transmission shaft 
28 and 16,000 rpm for the high speed driven shaft 36. The high speed shaft 
36 is supported by bearings, one of which is shown at 38 and the other at 
39. A thrust bearing 40, which is engaged by a collar 41 on the shaft 36, 
is provided to counteract the axial thrust that is developed by the 
impeller 37. 
Lubrication of the bearings occurs as follows. Oil is provided to the 
bearing 26 and 27 by way of the transmission assembly 21. Oil from the 
bearing 26 flows through the passage 42 and then through the opening 43 to 
the sump 44. From an oil feed annulus surrounding bearing 27 supply oil 
flows into passage 46 to lubricate the bearing 38. The oil then runs from 
the left side of the bearing 38 through the opening 43 to enter the sump 
44. Similarly, it flows from the right side of the bearing 38 through the 
opening 47 into the sump 44. 
Referring now to the bearing 39 at the other end of the high speed shaft 
36, an oil feed passage 48 is provided as a conduit for oil flowing 
radially inwardly to the bearing surfaces. Oil discharge from the bearing 
39, on the right side, flows toward slinger 49 and is slung outwardly into 
cavity 51. Oil discharge from the bearing 39, on the left side, flows 
toward thrust bearing 40, where it mixes with thrust bearing oil and is 
discharged into cavity 101. As the oil accumulates in the sump 44, it is 
drawn into the inlet 52 of the oil pump 53, which functions to pump it 
through a filter 54 and then to the system components for lubrication 
thereof. 
In order to limit the migration of oil from the transmission 14 by way of 
the shaft seals, the transmission 14 is vented to a source of low pressure 
refrigerant (i.e. to the compressor inlet 46) by way of a transmission 
vent opening 47. An oil separator or demister 48 is provided to recover a 
certain amount of entrained oil before the refrigerant passes into the 
opening 47. Such an oil separator, however, will not, by itself, suffice 
if the amount of oil that is so entrained is excessive, such as tends to 
be the case with high speed, high pressure machines such as those used 
with R-22 refrigerant. 
It is recognized that a certain amount of oil is going to be thrown 
radially outwardly by the drive gear 31. In order to prevent that oil from 
creating a mist and being entrained within the refrigerant surrounding the 
transmission 14, a gear shroud 59 is provided in close surrounding 
relationship to the gear 31. The shroud 59 functions to direct the oil 
that is collected by the gear shroud 59 in a downward direction toward the 
oil pump 53. 
In addition to the desirability of limiting the amount of oil that is 
centrifuged radially outwardly by the drive gear 31, it is also desirable 
to limit the amount of oil that flows over the face of the drive gear 31 
and eventually to the mesh between the drive gear 31 and the driven gear 
34. In this regard, it is recognized that a significant amount of heat is 
generated by the interaction of the two gears during operation, and that 
the introduction of oil at the mesh is desirable to transfer that heat 
away from the mesh. This is accomplished in the present case by 
introducing a flow of oil on the leaving side of the mesh between the two 
gears. A stripper is then provided in the near vicinity to strip the oil 
free from the drive gear 31 and prevent it from being carried around as 
the gear continues to rotate away from the mesh point. The only oil that 
remains then is a thin film which performs the necessary lubrication 
function at the entering side of the mesh point between the gears. The 
remaining oil is stripped free to drop down into the oil sump 44. 
Another source of oil that is available to the drive gear 31, however, is 
that which is used to lubricate the journal bearing 27. That is, at the 
interface of the journal bearing 27 and the drive gear 31, there is 
tendency for the oil to flow over on to the face of the drive gear 31 and 
then be propelled across its face and finally enter the mesh between the 
drive gear 31 and the driven gear 34. Similarly, oil from the journal 
bearing 38 tends to flow onto the high speed gear 34 and enter the gear 
mesh. In each case, this excessive oil at the gear mesh tends to introduce 
oil pumping and windage losses to the system. The oil pumping that occurs 
at the mesh also tends to add additional loading on the bearings 27 and 
38. 
In addition to the oil that is introduced to the gears by way of the 
journal bearings 27 and 38, the applicants have found that the oil 
discharged from thrust bearing 40 impinges on the face of gears 31 and 34 
and enters the mesh. Additional pumping and windage losses are therefore 
experienced in this manner. In order to reduce these losses, the 
applicants have provided structural barriers to limit the amount of oil 
that migrates from the bearings toward the gears. Structural barriers are 
shown generally at 61, 62 and 63 in FIG. 2 and are shown in greater detail 
in FIGS. 3-13. 
The oil barrier 61 as shown in FIGS. 2-5 comprises a ring 64 having a 
cylindrical section 65 and a flange section 66. A cover plate 67 having 
holes 68 is attached to one end of the cylindrical section 65 by 
appropriate fasteners that register with the holes 69 in the cylindrical 
section 65. These fasteners also function to secure the ring 64 to the 
transmission assembly 21 as will be seen in FIG. 2. The barrier structure 
61, which is U-shaped in axial cross section, provides a barrier to 
prevent the migration of oil from the bearing 27 to the drive gear 31, 
with the cylindrical section 65 tending to provide a barrier against 
radial movement of the oil and the cover 67 tending to provide a barrier 
against the axial movement of oil to the drive gear 31. 
As the barrier 61 restricts the flow of oil to the drive gear 31, the oil 
will tend to accumulate within the barrier 61 and flow to the bottom 
section thereof. Provision is therefore made to drain this oil from the 
barrier 61 by way of a pair of passages in a transmission assembly 21, one 
of which is shown at 70 in FIG. 2. To accommodate this flow, there are a 
pair of openings 71 and 72 in the bottom portion of the plate section 66 
as shown in FIG. 4. That is, the openings 71 and 72 register with the 
passages 70 of the transmission assembly 21. Thus, the oil from the 
general bearing 27 is caught by the barrier 61 and caused to flow through 
the passages 70 and the opening 43 to the sump 44 below. 
The barrier 62, as shown in FIGS. 2, 6 and 7, performs a similar function 
to prevent the flow of oil between the journal bearing 38 and the high 
speed gear 34. The annulus 73 comprises a cylindrical section 74 and a 
plate section 75. The cylindrical section 73 includes a plurality of holes 
76 for mounting the annulus 73 to the bearing 38 by appropriate fasteners. 
At the bottom portion of the annulus 73 there is a portion of the 
cylindrical section 74 removed to present a channel 77 through which oil 
may be drained from the annulus 73 to a passage 78 where it finally enters 
the sump 44. Thus, the oil that would otherwise flow from the bearing 38 
to the high speed gear 34 is collected by the annulus 73 and caused to 
flow through the channel 77 and the passage 78 to enter the sump 44. 
The barrier 63, is shown in FIG. 2 and in FIGS. 8-14. It comprises a 
retaining ring 79, a seal ring 80 and a spacer ring 81. As will be seen, 
the seal ring 80 is retained in surrounding relationship with the collar 
82 of shaft 36 by way of the retaining ring 79 and spacer ring 81 disposed 
on either side thereof. The combination forms a cavity 83 surrounding the 
thrust bearing collar 41 with oil from cavity 83 being discharged into 
cavity 101. Oil from the cavity 101 is drained out through the passage 84 
to the oil sump 44 as shown in FIG. 2. 
Referring now to FIG. 9 and 10, the retaining ring is T-shaped in axial 
cross section and includes outer flange 87 and inner flange 86 to 
cooperatively define the open end surface 88. On the other side of the 
inner flange 86 is a radially extending, seal retaining surface 89 and an 
axially extending seal retaining surface 90. A plurality of holes 91 are 
provided around the circumference of the retaining ring for the insertion 
of bolts to secure the retaining ring 79 to the bearing 39. A pair of 
holes 92 are also provided near the bottom of the retaining ring 79 to 
vent the cavity 51, by way of the openings 102 in the bearing 39, to that 
area surrounding the transmission 14 such that oil can be drained from the 
cavity 51 without the occurrence of vapor locks. 
The seal ring 80, shown in FIGS. 11 and 12, is a simple bronze ring with an 
outer circumference 93 having a smaller diameter than the inner diameter 
of the axially extending seal retaining surface 90 of the retaining ring 
79. Its inner circumference 94 is just slightly greater than that of the 
collar 82 such that when the seal ring 80 is installed over the collar 82, 
there is a sealing relationship therebetween to prevent the flow of oil 
out of the cavity 83. 
The spacer ring 81, which is held in place against the bearing 39 with the 
same bolts as the retaining rings 79, is shown in FIGS. 13 and 14 and 
comprises a ring having a cylindrical portion 96 and an inwardly extending 
flange 97. When installed, the outer surface 98 of the flange 97 engages 
the seal ring 80 and retains it in its axial position. A plurality of 
holes 99 are provided for receiving the bolts (not shown) for retaining 
the spacer ring 81 against the bearing 39. A semi-circular opening 100 is 
formed in the outer circumference of the spacer ring 81 as shown to 
provide a channel for fluidly communicating between the cavity 83 and 
anular cavity 101 which is drained by passage 84 (FIG. 2). That is, oil 
passes from the vicinity of the journal bearing 39 and the thrust bearing 
40 into the cavity 83 and is retained therein by the combination of the 
spacer ring 81, the seal ring 80 and the retaining ring 79. Because of the 
rotation of the collar 49 within the cavity 83 the oil within the cavity 
is circumferentially circulated to the opening 100, which is in the 2 
o'clock position. The oil passes out of the opening 100 into the annular 
cavity 101, between the spacer ring 81 and the passage 84, and then passes 
through the passage 84 and into the oil sump 44. 
While the present invention has been disclosed with particular reference to 
three particular embodiments, concepts of this invention are readily 
adapted to other embodiments, and those skilled in the art may vary the 
structure thereof with departing from the essential spirit of the present 
invention.