Vented, oil bath lubricated bearing structure for a motor

A venting system is disclosed in connection with a high speed electric motor having oil bath lubricated ball bearings. The bracket and cap which enclose the bearing define mating passageways which, in combination upon assembly, lead from inside the inboard bearing seal to the outside atmosphere. The venting passageway maintains a chamber next to the bearing seal at substantially outside atmospheric pressure, so that no lubricant will be sucked out of the bearing structure. However, because the passageway is formed automatically upon assembly of the cap and bracket, no extra steps or awkward assembly of parts is required.

TECHNICAL FIELD 
The present invention relates to bearings for high speed rotary devices 
such as electric motors, and more particularly relates to a vented bearing 
support structure for an oil bath lubricated ball bearing. 
BACKGROUND ART 
Large induction motors are required for many heavy duty applications, such 
as driving air conditioning compressors for large buildings. These motors 
must deliver in excess of 900 horsepower at 3600 rpm, and also must 
operate properly at low speeds under 10 rpm. In the case of D-flange 
motors, the compressor is connected directly to the motor housing, 
limiting access to the bearings after installation. Therefore, lubrication 
of the motor bearings in these applications has been an area of great 
concern. 
Grease lubrication has been used in many large motors, because of the 
difficulty in maintaining a film of oil in large sleeve bearings operating 
at low rpm. However, when bearings are lubricated with grease and operated 
at high rpm, the grease begins to churn and becomes overheated, leading to 
break down of the lubricant. Sleeve bearings on fairly large motors have 
been oil lubricated using an oil mist system or oil distribution rings 
which dip into an oil sump and then deliver oil to the bearing. However, 
sleeve bearings require very accurate alignment and therefore are not 
desirable in D-flange motors. 
The rotor of an induction motor is typically positioned on the motor shaft 
within an interior space enclosed by the stator windings and the bearing 
support structure. Motor bearings are normally captured between a bracket 
defining a cavity for receiving the bearing, and a cap which holds the 
bearing in the bracket. Bearing seals also held by the cap or bracket are 
positioned on either side of the bearing to retain lubricant and exclude 
contaminants. It is known to utilize protrusions or blades extending from 
the ends of the rotor as a fan to draw cooling air into the interior and 
to distribute the air over and between the interior parts. The action of 
these protrusions reduces the pressure within the interior space between 
the rotor end and the bracket, and may cause the bearing lubricant to be 
pulled from the bearing structure and seals into the inner portions of the 
motor. Lubricant contacting the windings of the motor tends to swell and 
deteriorate the insulation, and eventually shorts out the motor, causing 
it to fail. Other problems associated with loss of lubricant may occur in 
other rotary devices which include bearings. 
Various attempts have been made to equalize the pressure on both sides of 
bearings in order to prevent lubricant leakage. Hoses have been connected 
between the inner side of the bearing and the exterior wall of the housing 
or bearing support structure, but it is very difficult to connect the 
hoses while assembling the bearing. U.S. Pat. No. 4,039,229 discloses a 
grease-lubricated bearing with a flexible membrane enclosing the grease 
chamber. A passageway through the motor housing from the membrane to 
atmosphere allows the membrane to flex, thereby relieving any pressure 
increase within the grease chamber. U.S. Pat. No. 3,466,478 discloses 
spaces on either side of a ball bearing, connected by passages formed in 
the bracket. The pressure drop normally present is made to occur at 
restricted orifices between the spaces and the air adjacent to both sides 
of the bearing. 
Passageways through bearing support structures for the purpose of 
conducting lubricants are shown in U.S. Pat. Nos. 4,844,625 and 5,001,377. 
Such passageways do not open to the interior space within the motor, in 
order to avoid pumping lubricant to undesirable areas. U.S. Pat. No. 
2,210,705 shows a ball bearing immersed in an oil bath. 
Despite prior efforts, there has remained a need in the art for a high 
speed motor with oil lubricated ball bearings and a system for venting the 
space on the inner side of the bearings to ambient atmosphere without 
requiring any extra steps in assembling the bearing. 
SUMMARY OF THE INVENTION 
The present invention addresses the problem of lubricant loss from bearings 
caused by low pressure generated within an interior space of a rotary 
device by providing venting passageways designed into the bearing support 
structure. Passageway segments in the parts of the support structure are 
positioned to matingly communicate with each other as the bearing is 
assembled within such parts. The result is a venting passageway to outside 
atmospheric pressure formed automatically as a result of routine bearing 
assembly steps. The venting passageway protects the bearing and associated 
bearing seals from the effects of low pressure in the interior space 
within the device. 
Generally described, the present invention provides a bearing support 
structure positioned between an enclosed interior space and an outside 
atmosphere, comprising an inner bearing support member defining therein a 
first passageway segment extending from an inner opening communicating 
with the interior space to a first mating opening; a shaft seal carried by 
the inner support member at a location on the outward side of the inner 
opening; and an outer bearing support member defining therein a second 
passageway segment extending from a second mating opening to an outer 
opening communicating with the outside atmosphere; the inner and outer 
support members defining a receptacle therebetween for receiving a bearing 
positioned outwardly of the shaft seal, and being attached to one another 
with the mating openings aligned so as to create a vent passageway 
extending from the interior space to the outside atmosphere. 
The first passageway segment preferably comprises an inner radial bore 
extending from the inner chamber into the inner support member, and an 
inner axial bore extending from the first mating opening to intersect the 
inner radial bore. The second passageway segment preferably comprises an 
outer radial bore extending from the outer opening to a point within the 
outer bearing support member, and an outer axial bore extending from the 
second mating opening to intersect the outer radial bore. 
In order to maximize the top speed of the shaft while providing sufficient 
lubrication at slow speeds, the bearing is preferably a ball bearing 
immersed in an oil bath contained in the sump defined by the bearing 
support structure. 
The present invention also provides a method of venting a bearing and 
associated shaft seal contained in a bearing support structure positioned 
between an enclosed interior space and an outside atmosphere, comprising 
the steps of providing in an inner bearing support member a first 
passageway segment extending from an inner opening communicating with the 
interior space to a first mating opening; providing in an outer bearing 
support member a second passageway segment extending from a second mating 
opening to an outer opening communication with the outside atmosphere; and 
assembling the inner and outer support members to receive the bearing 
therebetween and to meet one another with the mating openings aligned so 
as to create a vent passageway extending from the interior space to the 
outside atmosphere. 
Thus, it is an object of the present invention to provide an improved 
bearing construction for rotary devices. 
It is a further object of the present invention to provide an improved oil 
lubricated bearing structure for a high speed rotary device. 
It is a further object of the present invention to provide an improved high 
speed electric motor not subject to problems caused by low pressure 
created within the motor. 
It is a further object of the present invention to provide an improved 
venting system for a bearing. 
It is a further object of the present invention to provide an easily 
assembled venting system for bearings of an electric motor. 
Other objects, features and advantages of the present invention will be 
appreciated upon reviewing the following description of a preferred 
embodiment of the invention in conjunction with the attached drawing.

DETAILED DESCRIPTION 
Referring now in more detail to the drawings, in which like numerals refer 
to like parts throughout the several views, FIG. 1 shows a cross sectional 
view of a bearing support structure assembly 10 embodying the present 
invention. The support structure assembly 10 supports a ball bearing 12 
which is shrink fit onto a shaft 13. The bearing 12 fits into a bracket 15 
and is held in the bracket 15 by a cap 16 in a manner described in detail 
below. The bracket is attached at its periphery to a motor housing 18, 
within which are positioned conventional stator windings 20 and a rotor 21 
on the shaft 13. A plurality of fan blades 22 extend from the rotor 21 
toward the support structure 10. 
An interior space 25 is defined generally between the bearing support 
structure 10, the rotor 21, and a cone-shaped baffle 23 which is attached 
to the bracket 15 and extends slightly between the stator windings 20 and 
the rotor fan blades 22. The blades 22 act as a fan as the rotor 21 and 
shaft 13 rotate, pulling cooling air through openings (not shown) in the 
bracket. The cooling air is directed by the baffle 23 into the rotor fan 
22, and discharged into the space between the rotor and stator, and other 
interior parts of the motor. At high motor speeds, the suction creating 
this air flow reduces the pressure within the interior space 25 to a level 
at which there is a danger of lubricant being pulled out of the bearing 
support structure and spread into the motor's interior. As explained 
above, lubricant in the windings of the motor can result in motor failure. 
The construction of the bearing support structure assembly 10 can be 
understood in more detail with reference to FIGS. 2-7. FIG. 2 is an 
exploded vertical cross sectional view of the bracket 15, cap 16, and 
parts positioned therein. The bracket 15 includes a peripheral collar 31 
which attaches to the motor housing 18. A central portion 30 of the 
bracket includes a throat 32 which defines a shaft seal opening 33. An 
outboard seal 34 fits into the opening 33 and includes a fluoroelastomer 
o-ring seal 35 between the stationary portion of the seal 34 and the 
throat 32. The rotor portion of the seal 34 engages the shaft 13 with an 
o-ring 36 between the two parts. The outboard seal preferably is a 
commercially available, labyrinth type seal, such as INPRO/SEAL Bearing 
Isolator Part No. M5904928A. 
In its concave surface facing the motor interior, the bracket 15 defines an 
annular recess 37 for receiving the bearing 12, which preferably is a 
brass-caged ball bearing. At the lower portion of the bracket, a sump 
opening 38 is cast for holding oil. The lubricant is preferably a light 
turbine oil with an anti-foaming agent, or Mobil DTE Light, ISO VG32. A 
drain opening 39 extends from the bottom of the sump 38 to an accessible 
plug, as shown in FIG. 1. Spaced slightly below the bearing recess 37, a 
plurality of sump passageways 40 connect the sump 38 to the interior of 
the cap 16. 
Referring now to FIGS. 5-7, a radial vent bore 42 is drilled from an outer 
opening 43 radially into the bracket 15. The opening 43 communicates with 
the ambient air within a protective recess 47 along the outer periphery of 
the bracket. An axial vent bore 45 is drilled into the bracket from an 
opening 46 until it intersects the bore 42. The opening 46 is formed in a 
radial surface 48 of the bracket which faces the cap 16. Radially inwardly 
from the surface 48, an annular protrusion 49 extends toward the cap, 
separating the surface 48 from the bearing 12. 
The cap 16, shown in detail in FIGS. 2-4, defines an annular peripheral lip 
50 which fits over the protrusion 49 of the bracket 15. Three bolt holes 
51 are provided for attachment of the cap to the bracket. At the 
horizontal midpoint of the cap, as shown in FIG. 4, the lip extends 
outwardly to form a radial surface 52 which fits flush against the radial 
surface 48 of the bracket. O-ring seals 53 positioned between the lip 50 
and the bracket seal the joint between the cap and the bracket. Radially 
inwardly from the lip 50, an annular surface 54 of the cap is positioned 
to clamp the bearing 12 into the recess 37 in the bracket. A body portion 
55 of the cap extends from the lip 50 away from the bearing and toward the 
shaft 13. 
On the concave side of the cap a shoulder 56 is formed, and an inboard seal 
58 is received axially against the shoulder 56. The seal 58 includes a 
fluoroelastomer o-ring seal 59 between the stationary portion of the seal 
58 and the cap 16. The rotor portion of the seal 58 engages the shaft 13 
with an o-ring 60 between the two parts. A snap ring 63 fits into a groove 
in the cap to retain the seal 58 against the shoulder 56. Extending still 
farther from the bearing, the cap defines a throat 65 which extends 
radially inwardly to a shaft opening 66 closely adjacent to the shaft 13. 
A chamber 67 is formed between the throat 65 and the inboard seal 58, and 
is open to the shaft 13. The throat 65 restricts free flow of air from the 
chamber 67 through the shaft opening 66 into the interior space 25. The 
inboard seal preferably is a commercially available, labyrinth type seal 
which allows passage of air through the seal, such as INPRO/SEAL Bearing 
Isolator Part No. BI05012A. 
The cap 16 also defines a sump portion 68 directly opposite the sump 38 of 
the bracket 15. The sump 68 communicates with the sump pass through 
openings 40 so that oil can pass freely between the sumps 38 and 68. On 
the convex side of the cap opposite the sump 68, a plurality of cooling 
fins 73 extend into the interior space 25. The flow of cooling air created 
by the blades 22 cools the fins 73 and, by conduction and convection, the 
oil in the sump 68. As best shown in FIG. 1, a drain opening 70 is 
provided in the bottom of the cap between the inboard seal 58 and the 
throat 65. Any oil or condensate escaping through the seal 58 will have an 
opportunity to drain through the opening 70 and an attached hose 71 to the 
exterior of the motor. The presence of any oil exiting through this hose 
may provide an early warning that oil is escaping from the bearing seal 
before the oil contaminates the interior of the motor. 
Again at the horizontal midpoint of the cap 16, a protrusion 74 is cast on 
the convex side of the cap between the surface 52 and the throat 65, as 
best shown in FIG. 3. Referring to FIG. 7, a radial vent bore 75 is 
drilled through the protrusion 74 from the chamber 67 starting at an inner 
opening 76. An approximately axial vent bore 78 is drilled from a cap 
mating opening 79 in the surface 52 into the protrusion 74 until it 
intersects the radial vent bore 75. A plug 80 is used to close off the 
open outer end of the radial vent bore 75, although the bore may be ended 
inside the cap as an alternative. 
It will be understood from the foregoing that the vent bores 42, 45, 75 and 
78 form a venting passageway from the outside ambient atmosphere to the 
chamber 67. The mating openings 46 and 79 align when the radial surfaces 
48 and 52 abut one another during assembly of the cap and bracket about 
the bearing 12. Thus, in the assembly stage of motor manufacture, the 
bearing may be vented without any extra steps or installation of awkward 
parts, as was the case with hose vents. The chamber 67 isolates and 
protects the inboard seal 58 and the bearing 12 from low pressure created 
by the rotor fan blades 22. The negative pressure in the space 25 draws 
air from the chamber through the shaft opening 66, but the restriction at 
the throat 65 causes the pressure drop to occur at the restriction, rather 
than at the seal 58. The pressure within the chamber 67 remains near 
outside atmospheric pressure because of the unrestricted venting passage 
to the outside. 
The oil in the sumps 58, 68 is maintained at a level 90, shown in FIG. 1, 
which immerses a portion of the balls of the ball bearing 12. As shown in 
FIG. 5, a fill passage 92 extends through the bracket 15 from a fill 
opening 93 in the recess 47 to the sump 58. Alternately, the oil level may 
be automatically maintained through passageways 94 by a conventional 
constant level oiler 95. 
The bearing support structure 10 is assembled by first placing the inboard 
seal into cap 16, inserting the snap ring 63, and sliding the cap over the 
shaft 13. Then the bearing is heated for expansion and placed onto the 
shaft against a locating shoulder in a conventional manner. As the bearing 
cools it becomes shrink fit onto the shaft. After the rotor is inserted 
into the motor, the bracket with baffle 23 installed is placed over the 
shaft and bolted to the cap and to the housing 18. Finally, the outboard 
seal is slid onto the shaft into the seal opening 33 in engagement with 
the throat 32 of the bracket. If desired, the constant level oiler 95 may 
then be attached. 
In operation, the rotation of the blades 22 of the rotor 21 may cause a 
pressure differential in the space 25, as explained above. However, such a 
differential will not affect the bearing or inboard seal because of free 
air flow through the venting passageway formed in the cap and bracket to 
the chamber 67, which will remain near outside ambient pressure. 
Furthermore, air can flow through the seals 35 and 58 to equalize the 
pressure on both sides of the bearing 12. As a result, no lubricant will 
be sucked out of the bearing structure and problems associated with 
lubricant spreading into the interior of the motor will be avoided. 
While this invention has been described with particular reference to a 
preferred embodiment, it should be understood that variations and 
modifications may be made without departing from the spirit and scope of 
the invention as defined in the appended claims.