Hanging spring supported squeeze film damping system for shaft bearing

A damper film bearing assembly for supporting a rotatable shaft of a turbomachine includes a housing having a central bore sized to receive the bearing member, and an annular cavity formed within the housing around the central bore. The annular cavity includes an outer wall that is concentric with the central bore. A bearing member having an annular outer surface and an inner bearing surface is mounted within the cavity and engages the shaft to support the shaft within the housing. A fluid film damper mechanism acts between the annular outer surface and the outer wall of the cavity for damping radial movement of the bearing member within the cavity. A resiliently adjustable dead weight hanging spring support system acts between the housing and the bearing member to support the dead weight of the shaft within a vertically centered position within the central bore so that the fluid film damper means functions to maintain the shaft centered within the bore when vibrations occur during rotation of the shaft.

FIELD OF THE INVENTION 
This invention relates generally to a support structure for rotatably 
supporting a shaft. More particularly, the invention relates to a squeeze 
film damper bearing support system utilizing at least one hanging spring 
assembly to support the dead weight of the shaft in a turbomachine. 
BACKGROUND OF THE INVENTION 
The use of fluid film damping for high speed rotating shafts in 
turbomachinery is well known in the art. In general, such a damping system 
includes a radially movable non-rotating bearing support member positioned 
generally coaxially with the shaft, a bearing positioned between the 
movable bearing support member and the rotatable shaft, and a pair of 
axially spaced O-rings defining an annular fluid film chamber between the 
movable bearing support member and a fixed housing. The movable bearing 
support member can be an outer annular race of a roller bearing element or 
a cage of tilt pad bearings. The annular fluid film chamber is used to 
confine a pressurized oil film. The clearance between the movable bearing 
support member and the fixed housing is very small, so that the oil film 
can be squeezed between the two confronting surfaces. During rotation at 
high speeds, the shaft may vibrate, moving transversely radially and 
orbitally, causing the movable bearing support member to also move in the 
same direction. Such motion acts to exert a compressive force on a portion 
of the oil film so as to squeeze an annular segment of the oil film, 
thereby causing viscous flow of the oil and resistance to the motion of 
the movable bearing support member. 
To achieve acceptable damping from a squeeze film damping assembly, the 
non-rotatable bearing support member must be able to move within the 
housing. This is hard to achieve when, even though the O-rings are still 
adequate to horizontally center the movable bearing support member, the 
O-rings cannot support the weight of the shaft and bearing, thus 
permitting the movable bearing support member to rest on the bottom of the 
housing bore. 
In Streifert, U.S. Pat. No. 4,027,931, a non-rotating, movable annular 
bearing support member, which is provided with a fluid film damper, is 
positioned between a rotating shaft and a stationary bearing housing with 
the movable bearing support member carrying the bearings which act to 
support the shaft within the housing. The movable bearing support member 
is supported by a squirrel cage spring for centering the shaft, the 
squirrel cage spring being mounted coaxially with the shaft and extending 
axially relative to the movable bearing support member so that one end of 
the squirrel cage spring is secured to the stationary bearing housing and 
the other end of the squirrel cage spring is attached to the movable 
bearing support member, forming a cantilever support. The fluid film 
dampening is achieved by positioning two O-ring seals at axially spaced 
apart locations in the annular space between the inside wall of the 
stationary bearing housing and the outer wall of the movable bearing 
support member to provide a squeeze film cavity, and introducing oil under 
pressure into the squeeze film cavity to form the oil film damper. Such 
pressure can be the normal oil supply pressure, which is generally in the 
range of about 15 to about 20 psig. 
To improve the effectiveness of the oil film damping system, various 
mechanisms have been employed including springs for centering the shaft. 
One such prior art mechanism, which addresses the problem of compensating 
for the dead weight of the rotor shaft, is disclosed in Streifert, U.S. 
Pat. No. 4,027,931, wherein at least one helper spring is mounted within 
the portion of the annular squeeze film cavity below the horizontal 
centerline of the shaft so as to support the dead weight of the shaft and 
thus eliminate the harmful effects of the heavy shaft upon the squirrel 
cage spring and the squeeze film cavity. Each helper spring is a 
longitudinally extending beam having radially outwardly extending support 
pads at the axial ends of the radially outer surface of the beam and a 
radially inwardly extending pad at the center of the radially inner 
surface of the beam. 
Similarly, Marmol et al, U.S. Pat. No. 4,981,415 discloses the use of one 
or two segmented arcuate springs mounted between a fixed support member 
and a non-rotatable movable bearing support member, with the damper film 
being formed between the movable bearing support member and the fixed 
support member, and with a roller bearing positioned between the movable 
bearing support member and the shaft. Each segmented arcuate spring 
consists of five segments positioned to form an annular ring generally 
coaxial with the shaft, with each segment having a radially outwardly 
directed land at each end of its radially outer surface and an inwardly 
directed land at the center of its radially inner surface, whereby when 
the inwardly directed land contacts the shaft the center portion of the 
segment is caused to flex radially outwardly. The segmented arcuate 
springs function to absorb the energy attendant the vibration of the shaft 
during operation. In the static condition, the springs also serve to 
center the shaft. 
Important to the proper functioning of any of the foregoing described fluid 
film damper systems is proper attention to the stiffness and damping of 
the system. Effective damping of vibrational movement of the shaft in a 
turbomachine is enhanced if uniformity of the damper film is preserved 
between the movable bearing support member and the fixed housing. The 
uniformity of the damper film is difficult to achieve in a squeeze film 
bearing support system for a horizontally extending shaft, since the 
weight of the shaft places a high unidirectional loading upon the movable 
bearing support member. As a result of this loading, the movable bearing 
support member is hindered in its ability to move vertically within the 
housing, and consequently is unable to respond freely to vertical shaft 
vibrations. By supporting the movable bearing support member in a manner 
that reduces the stiffness associated with its radial movement, the 
movable bearing support member is permitted to respond freely to vertical 
shaft vibrations as well as to horizontal shaft vibrations, and the 
uniformity of the damper film can be more effectively maintained. 
SUMMARY OF THE INVENTION 
An objective of one aspect of the present invention is to provide a new and 
improved damper film bearing assembly which is particularly adapted for 
use in supporting a heavy dead weight rotor load. An object of another 
aspect of the invention is to provide a damper film bearing assembly that 
is adjustable over a range of different heavy dead weight loads so as to 
obtain optimum levels of stiffness and damping for the particular dead 
weight load involved. More specifically, the present invention aims to 
achieve the foregoing through the use of a hanging spring support 
assembly, in conjunction with the fluid damping mechanism, to minimize or 
eliminate the effect of the dead weight load of the rotor assembly on the 
damper bearing mechanism. 
In accordance with the present invention, a damper film bearing assembly 
for supporting a rotatable shaft of a turbomachine comprises a fixed 
housing having a bore therethrough sized to receive the shaft with a 
longitudinal axis of the shaft extending at least generally horizontally 
through the bore. The fixed housing has an annular cavity which is open to 
the bore around the circumference of the bore. The annular cavity has an 
annular wall surface which extends generally parallel to the longitudinal 
axis of the housing bore. A bearing member is mounted within the cavity 
and includes an annular radially outer surface, confronting the annular 
wall surface of the cavity, and a radially inner surface, confronting the 
shaft so as to provide bearing support for the shaft within the fixed 
housing. A fluid film damper is formed between the annular radially outer 
surface of the bearing member and the annular wall surface of the cavity 
for damping movement of the bearing member within the cavity. At least one 
hanging support spring assembly is provided, with each hanging support 
spring assembly being mounted so as to be secured to and extend generally 
upwardly from an upper portion of the bearing member to the fixed housing 
for resiliently supporting the bearing member within a vertically centered 
position within the bore in opposition to a dead weight of the shaft, so 
that the at least one hanging spring assembly can function to center the 
bearing member within the bore of the housing and permit the fluid film 
damper to function to suppress both horizontal and vertical vibration of 
the shaft. 
In a presently preferred embodiment, two support spring assemblies are 
positioned on opposite sides of and symmetrical to a vertical plane 
containing the longitudinal axis of the shaft. For each support spring 
assembly, the fixed housing has at least one outwardly facing shoulder 
associated with a hole in the fixed housing. Each support spring assembly 
comprises an elongated connector, with a first end of the connector being 
secured to an upper portion of the bearing member. The elongated connector 
extends upwardly through the hole so that the second end of the connector 
is positioned above the outwardly facing shoulder in the fixed housing. A 
support spring is positioned between the outwardly facing shoulder and the 
second end of the connector so as to resiliently urge the connector and 
the bearing member upwardly and thereby assist in maintaining the shaft in 
a vertically centered position within the bore. In one version, each 
elongated connector extends generally radially with respect to the 
longitudinal axis of the housing bore, while in another version each 
elongated connector extends at least substantially vertically. In either 
version, the angle between the vertical plane, containing the longitudinal 
axis of the shaft, and a line extending upwardly through the longitudinal 
axis of the shaft to the point of attachment of a support spring assembly 
to the bearing member is preferably less than about 25.degree., and more 
preferably is less than about 20.degree.. 
Each support spring can comprise at least one resilient member, e.g., a 
coil spring, a Belleville washer, etc., but is preferably a plurality of 
Belleville washers positioned in a stacked arrangement with respect to 
each other, with the stacked arrangement being positioned coaxially with 
the associated elongated connector. 
Each support spring assembly is adjustable. In one embodiment, a spacer is 
positioned coaxially with and about the elongated connector between the 
outwardly facing shoulder and the support spring to provide the desired 
length along the longitudinal axis of the elongated connector for the 
support spring. The lengthwise portion of the elongated connector 
extending from the outer surface of the bearing member to the second end 
of the connector can be adjusted by varying the portion of the first end 
of the connector which is secured within the bearing member. 
The bearing member can be an annular ring having a plurality of bearing 
shoes positioned circumferentially about the shaft and between the shaft 
and the inner surface of the annular ring, with each of the bearing shoes 
being loosely connected to the annular ring and having a radially inner 
surface confronting the shaft to provide bearing support for the shaft 
within the fixed housing. 
The fluid film damper can comprise first and second O-rings positioned 
between the bearing member and the fixed housing, the O-rings being spaced 
apart from each other along the longitudinal axis of the housing bore to 
define a squeeze film chamber, and a passageway in the housing for 
supplying pressurized oil to the squeeze film chamber. 
The foregoing and other objects and advantages of the present invention 
will become more apparent from the following description of the best mode 
for carrying out the invention when taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
A presently preferred embodiment of the present invention is illustrated in 
FIGS. 1 and 2 as a damper squeeze film bearing assembly 10 for supporting 
a rotatable shaft 11 of a turbomachine. 
The damper squeeze film bearing assembly 10 is shown disposed 
circumferentially about and concentric with the rotatable shaft 11, with 
the longitudinal central axis 12 constituting the longitudinal axis of the 
damper film bearing assembly 10 and the longitudinal central axis of the 
rotatable shaft 11. Unless otherwise stated, radial directions are 
directions which are radial to the central longitudinal axis 12, and 
longitudinal directions are parallel to the central longitudinal axis 12. 
The damper squeeze film bearing assembly 10 is positioned in an annular 
chamber 13 formed by a first casing component 14 and an axially adjacent 
second casing component 15, each of the first and second casing components 
14 and 15 having a bore therethrough for coaxially receiving the shaft 11. 
The diameter of the inner annular surface 16 of the bore through the first 
casing component 14 is slightly larger than the diameter of the adjacent 
portion of the rotatable shaft 11 to form an annular gap 17 therebetween. 
The diameter of the inner annular surface 18 of the bore through the 
second casing component 15 is only slightly larger than the diameter of 
the outer cylindrical surface 19 of the damper squeeze film bearing 
assembly 10 to form a tight fit of the damper squeeze film bearing 
assembly 10 within the casing component 15. 
The damper squeeze film bearing assembly 10 comprises a circumferentially 
continuous annular housing 22 and an annular end cover 23. Each of the 
annular housing 22 and the end cover 23 has a bore therethrough for 
substantially coaxially receiving the shaft 11. The housing 22 has a 
radially inner generally cylindrical surface 24, formed by the bore 
through the housing 22, and a radially outer generally cylindrical surface 
which serves as the outer surface 19 of the damper squeeze film bearing 
assembly 10. The annular housing 22 also has a first axial end portion 25 
and a second axial end portion 26 which are spaced apart along the central 
axis 12. The radius of the radially inner generally cylindrical surface 24 
is only slightly greater than the radius of the adjacent portion of the 
rotatable shaft 11, so that the annular housing 22 serves as a bushing 
seal to provide a fluid film sealing clearance 27 between the shaft 11 and 
the annular housing 22. In general, the radial clearance 27 between the 
radially inner generally cylindrical surface 24 and the shaft 11 is 
substantially less than the radial clearance 17 between the shaft 11 and 
the first casing component 14. The end cover 23 fits within a recess 28 in 
the end portion 26 of the housing 22, with the radius of the radially 
inner generally cylindrical bore surface 29 of the end cover 23 being only 
slightly greater than the radius of the adjacent portion of the rotatable 
shaft 11, so that the end cover 23 also serves as a bushing seal to 
provide a fluid film sealing clearance 31 between the shaft 11 and the end 
cover 23. As shown in FIG. 1, the annular housing 22 is preferably formed 
as two halves 22a and 22b of a cylinder having a concentrically located 
bore, so that the two halves 22a and 22b can be positioned about the shaft 
11 and then secured together by one or more bolts 32 on each side of the 
shaft 11. If desired, the end cover 23 can also be formed as two halves of 
a cylinder having a concentrically located bore, with the orientation of 
the dividing line between the two halves of the end cover 23 being 
generally perpendicular to the dividing line of the two halves of the 
annular housing 22. The annular housing 22 and the annular end cover 23 
can be secured to each other and fixed to the first casing component 14 by 
a plurality of bolts 33 which extend generally parallel to the 
longitudinal axis 12, thereby preventing any movement of the annular 
housing 22 and the end cover 23. This arrangement permits the annular 
housing 22 to be inserted axially into the cavity 13 of the second casing 
component 15 in situations where the second casing component 15 is in one 
piece, i.e., not split. 
The fixed annular housing 22 is provided with an annular chamber 34, which 
is open to the cylindrical bore surface 27 and to the axial end 26 and is 
sized to receive the annular bearing support member 35 which in turn 
supports the shaft 11. The annular chamber 34 has a longitudinally 
extending cylindrical wall surface 36, which is concentric with the 
cylindrical bore surfaces 27, 29 and is substantially coaxial with the 
shaft 11, and an axial end wall surface 37. The cover 23 forms the 
opposite axial end wall surface of the chamber 34. 
In the illustrated embodiment of the invention, the annular bearing support 
member 35 is a bearing support cage for a plurality of tilt pad bearing 
shoes 38. The bearing support cage 35 is in the form of an annular ring 
having a radially outer cylindrical wall surface 39 and a radially inner 
cylindrical wall surface 41. The annular ring can be either 
circumferentially continuous or split into two 180.degree.halves. Each of 
the tilt pad bearing shoes 38 is positioned between the radially inner 
cylindrical wall surface 41 of the bearing support cage 35 and the 
exterior surface of the shaft 11, with the bearing shoes 38 being spaced 
apart from each other circumferentially about the shaft 11 so that there 
is a gap 42 between each adjacent pair of the bearing shoes 38. Each 
bearing shoe 38 has a radially outer wall surface that is sized and 
arranged to confront the radially inner cylindrical wall surface 41 of the 
bearing support cage 35 so that the bearing shoe 38 can pivot slightly 
about an axis which is parallel to the longitudinal axis of the bearing 
support cage 35. Each bearing shoe 38 has a radially inner wall surface 43 
that is sized and arranged to slidingly mate with the exterior surface of 
the radially adjacent portion of the shaft 11 so as to provide support for 
the shaft 11. 
Each of the bearing shoes 38 is supported by a respective threaded 
fastener, e.g., bolt 44, that extends loosely through a respective 
radially extending hole 45 in the bearing support cage 35, with the 
radially inner end of each bolt 44 being in threaded engagement with a 
respective internally threaded radially extending hole 46 in the bearing 
shoe 38, and the radially outer end of each bolt 44 being a head which is 
positioned within a counterbore 47 which is coaxial with the respective 
hole 45, with the head of the bolt 44 having a diameter which is larger 
than the diameter of the hole 45 and smaller than the diameter of the 
counterbore 47, so that each bearing shoe 38 is loosely secured to the 
bearing support cage 35 during assembly, and is permitted to freely move 
radially, within obvious mechanical limits, relative to the bearing 
support cage 35 so as to contact the exterior surface of the shaft 11 when 
the bearing support cage 35 and bearing shoes 38 have been assembled about 
the shaft 11. Each bearing shoe 38 can also rock or tilt about an axis 
which is generally parallel with the longitudinal axis 12 of the shaft 11 
and which extends through the longitudinal axis of the associated bolt 44. 
At least one of the cylindrical chamber wall surface 36 of the fixed 
housing 22 and the radially outer cylindrical surface 39 of the bearing 
support cage 35 is provided with a pair of annular grooves for receiving 
O-rings 48, 49. As the annular grooves are for the purpose of maintaining 
the longitudinal positions of the O-rings 48, 49, they can be provided in 
only the cylindrical surface 36 or in only the cylindrical surface 39 or 
in both of the cylindrical surfaces 36, 39. In the illustrated embodiment, 
the cylindrical chamber wall surface 36 has annular grooves 51, 52 formed 
therein, while the cylindrical surface 39 has annular grooves 53, 54 
formed therein, with groove 51 facing and cooperating with groove 53 to 
collectively receive the O-ring 48 therein, and with groove 52 facing and 
cooperating with groove 54 to collectively receive the O-ring 49 therein. 
The grooves 51, 53 are spaced apart from grooves 52, 54 along the 
longitudinal axis of the shaft 11, and the diameter of each of the O-rings 
48, 49 is greater than the total depths of the associated pair of grooves 
such that there is radial gap between the cylindrical wall surfaces 36, 
39, so that an annular damper film chamber 55 is defined by the O-rings 
48, 49, the annular portion of the cylindrical wall surface 36 between the 
grooves 51, 52, and the annular portion of the cylindrical wall surface 39 
between the grooves 53, 54. 
An annular passageway 56 is formed in the housing 22 so as to open in the 
cylindrical wall surface 36 throughout the circumference of the 
cylindrical wall surface 36 at a location between the O-rings 48, 49. An 
oil supply passageway 57 is provided in the housing 22 to provide fluid 
communication from an oil supply (not shown) to the damper film chamber 55 
via the annular passageway 56, thereby supplying pressurized oil to the 
damper film chamber 55. The O-rings 48, 49 seal the damper film chamber 55 
such that the oil does not leak past the axial ends of the bearing support 
cage 35, as well as support the bearing support cage 35. The fluid film 
damper acts between the annular outer cylindrical wall surface 39 and the 
cylindrical wall surface 36 of the annular cavity 34 so as to dampen any 
radial movement of the bearing support cage 35 within the annular cavity 
34. Orifice passageways (not shown) can be drilled radially through the 
bearing support cage 35 to provide restricted flow between the annular 
damper film chamber 55 and the gaps 42 between adjacent pair of bearing 
shoes 38, in order to lubricate the pads 38 and facilitate the sliding of 
the shaft 11. It is presently preferred that the pressurized oil be 
continuously supplied through oil supply passageway 57 to the damper film 
chamber 55, thereby replacing oil which passes from the damper film 
chamber 55 to the gaps 42 via the flow restricted orifice passageways. 
In accordance with the present invention, the improved damper film bearing 
assembly 10 is particularly adapted for use in adjustably supporting a 
heavy dead weight rotor load over a range of different heavy dead weight 
loads to obtain optimum stiffness and damping during operation of the 
turbomachine for the particular dead weight load involved. This is 
achieved through the use of at least one adjustable hanging spring support 
assembly resiliently connecting the annular housing 22 and the upper 
portion of the bearing support cage 35 so as to support the dead weight of 
the shaft 11 in a vertically centered position within the central bore 16. 
This enables the fluid film damper mechanism to maintain the shaft 11 
centered both vertically and horizontally within the bore 16 by damping 
both vertical and horizontal vibrations of the shaft. It is presently 
preferred that the at least one adjustable hanging spring support assembly 
be the only mechanical spring support for the bearing support cage 35. 
A single adjustable spring support assembly can be employed, extending from 
the upper portion of the bearing support cage 35 generally radially 
upwardly in the vertical plane containing the longitudinal axis 12. An 
even number of adjustable spring support assemblies can be provided at 
locations which are on opposite sides of and symmetrical to the vertical 
plane through the longitudinal axis 12. An odd number of adjustable spring 
support assemblies can be provided, with one being located in the vertical 
plane containing the longitudinal axis 12 and the remaining ones being at 
locations which are on opposite sides of and symmetrical to that vertical 
plane. Each such adjustable spring support assembly can extend either 
radially with respect to the longitudinal axis 12, or vertically, or at a 
non-radial angle to the vertical, so long as the adjustable spring support 
assembly is connected to an upper portion of the bearing support cage 35 
and provides a vertical lifting force to the shaft 11 via the bearing 
support cage 35 in opposition to the gravitational force on the shaft 11. 
The use of two or more hanging spring assemblies is advantageous where the 
forces, to which the threads on the cap screw 64 are subjected as a result 
of a violent vibration, could result in a stripping of the threads of a 
single cap screw 64. 
In the illustrated embodiment, the first and second adjustable spring 
support assemblies 61, 62 extend generally vertically upwardly from first 
and second locations on the upper portion of the bearing support cage 35, 
the first and second locations being on opposite sides of and equally 
spaced from the vertical plane 63 containing the longitudinal axis 12. The 
angle between the vertical plane 63, containing the longitudinal axis 12 
of the shaft 11, and a line extending upwardly through the longitudinal 
axis 12 of the shaft 11 to the point of attachment of a support spring 
assembly 61 or 62 to the bearing support cage 35 is preferably less than 
about 25.degree., and more preferably is less than about 20.degree.. As 
the two assemblies 61, 62 are constructed and mounted in a substantially 
identical manner, only assembly 61 will be described in detail, it being 
understood that such description applies also to the assembly 62. 
As shown in FIG. 2, the spring support assembly 61 comprises an elongated 
connector in the form of a bolt or cap screw 64 which extends through a 
vertical hole 65 in the fixed housing 22, through the annular passageway 
56, and into a threaded hole 66 in the bearing support cage 35, the hole 
66 being coaxial with the hole 65 and being formed at a position which is 
located between the O-rings 48, 49. The lower end 67 of the bolt 64 is 
provided with external threads which engage the internal threads of the 
tapped hole 66 in the bearing support cage 35, while the lengthwise 
portion of the bolt 64 positioned within the hole 65 has a diameter which 
is smaller than the diameter of the hole 65 so that the bolt 64 and the 
bearing support cage 35 can move vertically with respect to the fixed 
housing 22. The head 68 of the bolt 64 is positioned in a counterbore 69, 
formed in the housing 22 so as to be coaxial with the hole 65, such that 
the radially outermost surface of the head 68 is even with, or recessed 
radially inwardly with respect to, the outer cylindrical surface 19 of the 
housing 22. As the diameter of the counterbore 69 is greater than the 
diameter of the hole 65, the bottom wall surface of the counterbore 69 is 
in the form of an upwardly and outwardly facing annular shoulder 71. If 
during installation it is determined that the bearing support cage 35 is 
too high or too low in the housing bore, the cap screws 64 can be rotated 
in the appropriate direction to better center the bearing support cage 35. 
An annular spacer 72, having an external diameter which is smaller than the 
diameter of the counterbore 69, can be positioned coaxially with the bolt 
64 so that the bottom surface of the annular spacer 72 rests on the 
upwardly facing annular shoulder 71 of the counterbore 69. A sleeve 73, 
having an internal diameter only slightly larger than the diameter of the 
bolt 64, is positioned coaxially about the bolt 64 and within the 
counterbore 69. The spacer 72 has an internal diameter which is greater 
than the diameter of the radially adjacent portion of the sleeve 73 such 
that the sleeve 73 can move vertically with respect to the spacer 72. The 
sleeve 73 prevents the Belleville washers from rubbing on the relatively 
soft metal of the bolt 64. An annular flange 74, which extends outwardly 
from the upper end of the sleeve 73 in a plane perpendicular to the 
longitudinal axis of the bolt 64, has an upper annular surface 75 and a 
lower annular surface 76. The diameter of the head 68 of the bolt 64 is 
greater than the inner diameter of the annular flange 74 and smaller than 
the external diameter of the annular flange 74, such that the head 68 
contacts and is supported by the upper annular surface 75 of the annular 
flange 74. 
A support spring 77 is positioned between and in contact with the upper 
surface of the annular spacer 72 and the lower annular surface 76 of the 
annular flange 74 in order to provide an upwardly directed force to 
counterbalance the weight of the shaft 11 and the bearing and thereby 
resiliently urge the bearing support cage 35 and the shaft 11 upwardly 
into a centered position within the central bore 17. In the illustrated 
embodiment, the support spring 77 comprises a plurality of Belleville 
washers, each having a frustoconical shape, which are in a stacked 
relationship with one another and which are coaxially positioned about the 
bolt 64. The stacked relationship can be any suitable configuration, e.g., 
all of the frustoconical washers facing in the same direction, downwardly 
facing frustoconical washers alternating with upwardly facing 
frustoconical washers, etc. The Belleville washers, which are made of hard 
steel, tend to flatten when subjected to compression parallel to the 
longitudinal axis of the bolt 64. 
The spring rate of the Belleville spring 77 is determined by the number and 
orientation of the Belleville washers, and can be further adjusted by 
altering the length of the engagement between the bolt 64 and the bearing 
support cage 35, thereby adjusting the length of the portion of the bolt 
64 between the outer surface 39 of the bearing support cage 35 and the 
lower surface of the flange 74, and thus adjusting the axial space 
available for the support spring 77. The axial space available for the 
support spring 77 can also be varied by selecting a sleeve 73 having a 
flange 74 with the desired thickness, and/or by replacing one or more of 
the Belleville washers with a flat washer, thereby permitting a maximum 
engagement between the external threads on the bolt 64 and the internal 
threads in the hole 66 in the bearing support cage 35 to be maintained. 
The spacer 72 can be a single annular member or a plurality of flat steel 
washers, whereby the number of the steel washers can be selected to 
provide the desired height of the spacer 72 which corresponds to the 
number of Belleville washers used in the support spring 77. Thus, the 
number of Belleville washers can be selected to provide the desired degree 
of resilient support for the bearing support cage 35 and the shaft 11, and 
then the number of flat steel washers needed for the spacer 72 can be 
determined. While the spacer 72 has been illustrated as being between the 
support spring 77 and the upwardly facing shoulder 71, if desired, the 
spacer 72 can be positioned between the upper surface of the support 
spring 77 and the lower surface 76 of the annular flange 74, or two 
spacers can be employed, with one spacer being between the support spring 
77 and the shoulder 71 and the other one being between the support spring 
77 and the flange 74. At least the washers in the spacers which are in 
contact with the support spring 77 should be formed of hardened steel so 
as to resist the rubbing of the Belleville washers on the spacers as the 
Belleville washers deflect in response to vertical movement of the bearing 
support cage 35. 
An O-ring 78 can be positioned in an annular groove 79, which is formed in 
the wall surface of the hole 65 and in the annular shoulder 71. The O-ring 
78 is securely retained in the groove 79 by the spacer 72, and serves to 
prevent oil in the damper film chamber 55 from escaping through the hole 
65. 
The hanging spring assemblies of the present invention can support the 
gravity load of the shaft and bearing and lift the bearing support to a 
vertical center of the housing bore. The hanging spring assemblies can 
support a much larger gravity load than the O-rings, and thus are 
particularly advantageous with rotor assemblies having heavy loads. 
The invention provides a particularly simple hanger spring arrangement 
which is easily adjustable within a range of selected spring rates to 
accurately position the shaft in a centered position within the housing 
and at the same time obtain the optimum damping and stiffness required for 
the rotor dead weight involved. Furthermore, the hanging spring support 
assembly provides a compact construction, which permits relatively easy 
adjustment of the spring force when mounting the shaft in the damper 
squeeze film bearing assembly. 
The invention reduces the stiffness of the bearing support by removing the 
force otherwise required of the O-rings 48, 49 to vertically support the 
bearing cage 35 and the shaft 11 within the housing 22. With the hanging 
spring arrangements supporting the weight of the bearing as well as the 
shaft 11, the bearing support member 35 is centered in the housing bore, 
and the crush of each of the O-rings 48, 49 is essentially the same 
through the circumference of the squeeze film chamber 55, enabling the 
damping film to dampen out vertical vibrational movement of the rotating 
shaft as well as horizontal vibrational movement of the rotating shaft. 
Thus, the present invention provides a new and improved damper film 
bearing assembly which is particularly adapted for supporting a heavy dead 
weight rotor load. Moreover, the damper film bearing assembly is readily 
adjustable for a range of heavy dead weight loads, thereby providing the 
optimum levels of stiffness and damping for the particular dead weight 
load involved. 
Reasonable variation and modifications are possible within the scope of the 
foregoing description, the drawings and the appended claims to the 
invention. For example, instead of utilizing the connectors 44, each of 
the bearing shoes 38 can be pivotally supported by one or two pivot pins 
extending into a radially extending slot, whereby the bearing shoe can 
pivot about the pins and movable radially with respect to the shaft 11.