Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~908~
The present invention relates to a fluid film bearing
assembly, and proposes to solve a problem in prior art combined
radial and thrust-type bearings using compound curved surfaces,
particularly spherically curved bearing surfaces. In addition,
to being able to handle both'radial and thrust loads, the bearing
constructed in accordance with'the'present invention can accommo-
date angular misalignment between the rotational axis of the
moving part of the bearing and the axis of the fixed part of
the bearing.
The bearing of the present invention utilizes the
principles of operation disclosed in Patent No. 3,930,691 issued
to Jerome GREENE, ~anuary 6, 1976 entitled "SWING PAD BEARING".
In essence, that patent discloses a hydrodynamic
bearing pad including a movable face portion that is adjacent
to a relatively movable load applying or supporting surface in
the presence of a lubricant, the face portion of the bearing
pad being mounted for swinging motion relative to a base element
underlying the surface portion about swinging axis or center
located toward the relatively movable load applying or supporting
surface and away from the face portion of the bearing pad to
enable generation of the lubricant wedge. Motion of the moveable
face portion of the pad,relative to the load applying or support-
ing surface under operational conditions~ as described in that
patent, causes the face portion to swlng in'minute amounts to an
inclined position relative to the load applying or supporting
surface under the combined influences of load and friction forces
to prod~ce a wedge-shaped gap that converges in the direction of
motion of the load applying or supporting surface relative to the
face portion of the pad. Multiple such bearing pads are normally
provided in a typical bearing installation for supporting a rela-
tively moving load applying or supporting member. Lubricant is
drawn into the multiple gaps as a result of relative
motion between the bearing surfaces and hydrodynamic
action maintain the face portions of the pads and the
adjacent relatively moving surface out of contact with
each other virtually instantaneously upon onset of rela-
tive motion, and during the operation of the bearing.
The shape of the lubricant wedge associated with each
bearing pad self-adjusts during operation of the bearing
under varying load and speed conditions due to its unique
design. Specifically, the face portion of each pad is
joined to an underlying base element along an arcuate
interface having a center of curvature located substan-
tially at the desired center of swinging motion of the
face portion. A curved, laminated, elastomer-nonelasto-
meric material is disposed between the face portion and the
1~ underlying base element of each pad, and is bonded on each
side to both elements. The laminate material is compliant
in the shear direction (parallel to the arcuate interface
between the face portion and the underlying base element)
but is essentially rigid in a radial sense (perpendicular
- 20 to the arcuate interface). Therefore, the face portion of
each bearing pad can readily and is actually forced to swing
to a slightly inclined position about the center or axis of
swing under the influence of friction and load forces applied
to its surface by the load supporting member while still
maintaining its basic position in the bearing assembly.
~y earlier patent referenced above discloses
radial and thrust bearing embodiments utilizing the swing
pad concept. However, the present invention is intended
to utilize the same principle in a combined radial and
thrust bearing that utilizes compound curved bearing
surfaces, the swing pad bearing overcoming problems en-
countered in the prior art in situations where it is
desired to use such a bearing for supporting highradialloads.
More specifically, it is well known that the rotary
part of plain journal radial bearings with lubricated
continuous sliding surfaces actually runs slightly eccen-
tric with respect to the longitudinal axis of the bearing~
--2--
and this eccentricity permits the generation of a wedge
of lubricant between the relatively moving bearing sur-
faces. The wedge of lubricant, through pressures gene~a-
ted by hydrodynamic action, in turn keeps the bearing
surfaces apart so that surface-to-surface contact is
avoided and frictional resistance to motion is minimized~
In situations where a sli~ing bearing having both
radial and thrust capacity is desired, it has been pro-
posed to use compound curved surfaces of various forms
(e.g., a ball in a socket~. The problem here is that the
symmetrical compound curvature of the continuous bearingsurfaces tends to prevent the moving element of the bearing
from assuming its eccentric loaded rotating position at
which the lubricant wedge is formed when the bearing is
loaded in a thrust sense. The thrust bearing surface, being
uniformly curved about the rotation axis, tends to hold the
rotating element at the center of the bearing and therefore
a radial load supporting lubricant wedge cannot be
developed by the bearing because hydrodynamic pressures
are not generated in the lubricant film to the extent neces-
sary to keep the bearing surfaces apart.
A hydrodynamic tilting pad arrangement could beenvisioned for such an application, but the required
compound curvature of the bearing surface o~ the tilting
pad, along with the variable nature of the radial and
thrust loads, results in the position of the center of
pressure acting on the tilting pad elements to be un-
predictable. Since the center of pressure in a tilting
pad bearing arrangement must be virtually in line with
the tilt pivot point to prevent instability of the tilting
segment of the bearing, clearly a tilting pad bearing
has deficiencies which limit its application in a bearing
of the type presently under consideration.
The present invention utilizes the principle of
operation of the hydrodynamic swing pad bearing disclosed
in the patent identi~ied previously in the radial and thrust
bearing construction using compound curved bearing sur~aces
-3-
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that are arranged so that the bearing can accommodate misalign-
ment between the moving parts.
In accordance with the invention there is thus provi-
ded a fluid film bearing assembly comprising a plurality of
bearing pads disposed in a cylindrical array about a longitudi-
nal axis~support means for each pad~and a mova~le face portion
on each pad, the face portions having spherically curved bearing
surfaces having a common center of curvature lying at a point on
the longitudinal axis. Each face portion is mounted on its res-
pective support means by means positively restricting it to swing
to an inclined position relative to the support means in any di-
rection about a center of swinging motion or swing point located
outside of the bearing pad between the longitudinal axis and the
surface of the face portion of the pad, the swing point also
lying on the radius extending from the common point to the
surface of the Eace portion when the ~ace portion is in its
normal at-rest position; the face portion is also restricted'
agalnst any other motion relative to the support means.
' The face p~rtlons of the pads can swing about a point
(swing point) under friction and load forces to enable generation
of lubricant wedge films by the relative motion of the bearing
surfacesO The relative position of the center of pressure acting
' on,each bearing pad wi,th respect to the face of the pad is uncri-
, ti,cal within wide design limits, because friction and pressure
forces acting on each pad stabilize the position of the face
'- ' portion of the'pad about its respective swing point to maintain
the lubricant wedge during operation of the bearing.
Further characteristics of the present invention are
the following:
A cylindrical array or group of swing pad bearing ele-
ments ia provided adjacent the spherical outer surface portion of
a load applying or supporti,ng~ membe'r, the array of bearing pads
-- 4 --
k~.',
and the load applying or supporting member being rela-tively
rotatable with respect to each other about a longitudinal axis
of rotation. The bearing surfaces of the face portions of the
bearing pads correspond in curvature to the outer curvature of
the load carrying part of the load applying or supporting member t
and the bearing pad surfaces have centers of curvature that are
common with each other and w-ith the center of curvature of the
bearing surface of the load applying or supporting member. The
face portions of the pads are joined to supporting base ele-
ments along spherically curved interfaces that limit motion of
the face portion of the pads to swinging motion, specifically
- through a metallic-elastomer laminate material that is relati-
vely soft and compliant in the shear direction (parallel to the
arcuate interface) but rigid in the radial direction (normal
to the arcuate interface). The radius of curvature of the inter-
face is shorter than the radius of curvature of the outer
periphery of the load applying or supporting member, and like-
wise shorter than the radius of curvature of the bearing sur-
face of the bearing pad.
Thus, the face portions. of each bearing pad can swing
about a swing point or center that corresponds essentially to
the center of curvature of the interface be- -
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tween the face portion of the pad and the underlying base
element. The center of curvature of the interface of each pad
assembly lies at a point located along the radius of the
spherical bearing sur~ace of the bearing pad, somewhere ~e-
tween the center of curvature of that surface and the surface
itself, preferably approximately mid-wav along the radius that
intersects the pad surface, preferably at approximately its
center. The center of swinging motion of the face portions
of each group of bearing pads thus lie on radii extending
between the common centers of curvature referred to above
and the bearing surfaces of the pads.
The bearing surfaces of the pads are immersed in
a suitable lubricant so that when relatively motion occurs
between the load applying or supporting member and the
bearing pads, the face portions, under the influence of
friction and load forces acting thereon, swing to dynami-
cally stable positions in any direction to generate wedge-
shaped lubricant film gaps between the relatively moving sur-
faces. Due to t~he arrangement of the mating spherical bear~
ing surfaces, thrust loads as well as radial loads can be
supported by the swing pads, and misalignm~nt between the
rotational axis of the load applying or supporting member
and the longitudinal axis of the c~vlindrical array of bear-
` ing pads can be ac~mx~ated. The wedge-shaped lubricant
films are maintained at all times regardless of the direc-
tion of loading on the bearing surfaces.
FIGURE 1 is a diagrammatic plan view of part of a
~earing assembly embodying my invention;
FIGURE 2 iS an elevational view taken generally
along lines II-II of FIGURE 1, with the central load
supporting member removed for clarity;
FIGURE 3 is an enlarged detail View of a bearing
pad assembly; and
FIGURE 4 is a diagrammatic representation of the
bearing in operation.
With reference to the drawings, a bearing assembly
10 is shown in Figure 1 connected to a load applying or
supporting member 12 which extends along a longitudinal
axis 14. The bearing assembly 10 includes an outer casing
16 and a set of connected base elements 18 which underlie
a cylindrical array of face portions 20 of the bearing
assembly spaced about the longitudinal axis 14. The connect-
ed base elements 18 preferably are constructed as a pair of
split sleeves joined along lines 22 for enabling assembly of
the bearing about the load applying or supporting member 12.
Each face portion 20 is connected to its respective underlying
base section 18 through an elastomeric-inelastic interface
comprising, in the preferred mode, a metal-elastomer laminate,
as shown in Figure 3, where the metal layers are shown as
24 and the elastomeric layers, i.e., rubber, are shown as 26.
The combination of the face portion 20, the underlying base
element 18 and the intermediate laminate material 24, 26 is
referred to herein as a bearing pad.
The base element 18 could be made up of individual
segments (not illustrated) attached to a casing such as 16
connected to individual face portions 20 through individual
laminations 24, 26. However, the illustrated embodiment shows
a common member 18 having spaced curved interface areas for
receiving individual face portions 20 and intermediate
laminations 24, 26 bonded on either side to the face portions
and the base element. The face portions 20 each have concave
spherically curved bearing surfaces 30 that conform in
curvature to a spherical portion 32 of the load applying or
supporting member 12 ~see Figure 1). The surfaces 30 have
3Q a common center of curvature 33 lying on axis 14, and center
33 corresponds to the center of curvature of the peripheral
surface portion 32 of member 12. The casing 16 and the bear-
ing pads usually are held fixed against rotation and they
support load member 12 for rotation about an axis generally
coincidental with axis 14, in which case member 12 is a "load
applying" member. However, it will be readily understood
that this invention is not limited in any sense to such an
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arrangement, and mem~er 12 could just as well be fixed for
supporting load carrying bearing pads for rotation relative
thereto about axis 14. Thus, the term "load applying or
supporting member" with reference to mem~er 12 is not intend-
ed to-be an alternative recitation in the specification and
claims constituting this application, but rather a singular
expression relating to the structure corresponding to member
12, irrespective o~ its specific function in a particular
application.
The surfaces34 (see Figure 1) of base elements 18
underlying each face portion 20 and the underlying surface
35 of each face portion 20 are called interface surfaces
and are spherically cuxved about a center of curvature 40
located along a radius Rl extending from the point 33 to the
approximate center of bearing surface 30 of each face portion
20 of the bearing pads when the face portion is at its at rest
position. Thus, for example, the radius R2 of the surface
35 is shorter than the radius Rl of the surface 30. The
centers of curvature 40 of interfaces 34 and 35 of the bear-
ing pads are disposed preferably about a locus that is
equidistant from the axis of rotation 14, so that the radius
R2, for example, of each surface 35 is identical for all of
the bearing pads, although this is not an absolute require-
ment. As illustrated, the surfaces 34 and 35 are curves that
are concentric about point 40, which represents the swinging
axis of each face portion 20 of the bearing pads. As shown,
metal lamina 24 are likewise curved so that they are parallel
to the surfaces 34 and 35.
Upon relative movement between member 12 and the
face portions 20, the latter, because of friction forces,
will immediately tend to swing about their respective swing
axes 40 to an inclined position relative to the base 18 and
the outer surface of the spherical portion 32, as shown in
Figure 4. The laminates 24, 26 being com~liant in shear but
substantially rigid in a radial sense readily accommodate
the swinging motion of the face portions 20 of each pad. In
actuality, the swinging motion is quite miniscule so that the
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space bet-ween the load applying or supporting member 12 and
the bearing pads is maintained de~spite the ver~r sligh-t swing-
ing movement of each face portion 20. In addition, eccentric
loads (non-radial to interface 347 35) applied to the face
portion 20 cause them to swing in a direction tending to
cause the load vector to be radially aligned with the inter-
face surface curvature. The total swinging motion is small
and is always towards the adjacen-t bearing surface in the
direction of swinging motion. Swinging motion stabilizes
the face portion so that the net forces acting thereon are
in balance continuously7 as explained in Patent No. 379307691.
In Figure 4, a fluid lubricant is provided between
the load appl~ing or supporting member portion 32 and the
bearing pads so that a hyd~odynamic lubricant wedge is main-
tained between the face portions 20 and the member 32 in the
manner of a hydrodynamic fluid film bearing. Since the face
portions 20 are supported upon spherical underlying surfaces,
each face portion 20 can swing to a stable~ balanced position
under the combined radial and thrust components of friction
and load forces. The ball joint-like relationship between
spherical portion 32 of load applying or supporting member
12 and each bearing pad allows the bearing to handle thrust
loads and to accommodate angular misalignment between the
axis 14 of the cylindrical array of bearing pads and the
longitudinal axis of load applying or supporting member 12.
The latter axis, of course7 will pass through point 33.
It should be understood that the relative sizes of
the thicknass o~ the laminations 24, 26, as ~rell as the
- wedge-shaped gaps 42 in Eiigure 4 all have been exaggerated
for the sake o~ clarity.
It is thus evident that the swing pad elements oE
the present invention will automatically swing to stable
positions to generate wedge films of lubricant regardless
of radial and thrust load forces. Radial loads cause the
bearing surfaces to swing about their swing points in dlrec-
tions parallel to the direction Oe motion of the a~jacent
bearing surface of the load applying or supporting member7
while thrust loads cause the movable bearing face elements
to swing back towards the source of the thrust load so that
the fluid film pressures between the moving surfaces are in
balance. Most importantly, thrust loads do not disturb the
ability of the bearing to generate the desired lubricant
wedge.
Various modifications of the illustrated embodi-
ment of the invention are possible, and only an exemplary,
presently preferred construction has been disclosedO For
example, as described in my previous patent relating to the
swing pad bearing, the interface between the face portions
20 and the underlying base elements 18 could comprise con-
tiguous mating surfaces separated by a low friction film, as
aslong as the face portion was limited strictly to swinging
motion about the swing point. The principle of operation of
the bearing pads would still be the same for purposes of
the present invention. Likewise, the construction of the
load applying or supporting member 12 could be varied in
numerous manners while still providing a spherical portion
32 adjacent the cylindrical array of bearing pads. It is
furthermore envisioned that multiple circular arrays of bear-
ing pads could be provided about a single spherical load
supporting member portion 32 or a single set of pads could
be located in an area other than about a diameter of the
spherical portion of the member 32. More laminations 24, 26
could be provided in the interface area. However, all of
these modifications are envisioned as being fully within
the scope of my invention disclosed in the present applica-
tion, which invention is to be limited only by the scope of
the claims appended hereto.
