Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the field of rotating
fluid film (hydrodynamic) bearings and provides a solution
to problems inherent in prior art bearings that use com-
pound curved bearing surfaces supporting radial, thrust
and moment loads. The present invention utilizes the
- principle of operation of the SWING-PAD BEARING described
in U.S. Patent No. 3,930,691 issued to Jerome Greene
January 6, 1976, in a bearing assembly using compound curved
bearing surfaces to carry radial, thrust and moment loads.
In essence, that patent discloses a hydrodynamic
bearing pad including a movable face portion that is adja-
cent 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 rela-
tive to a base element underlying the surface portion about
a 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 movable face portion
of the pad relative to the load applying or supporting surface
under operational conditions, as described in that patent,
causes the pad face portion to swing 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 produce 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 relatively moving load apply-
ing or supporting member. Lubricant drawn into the multiple
gaps as a result of relative motion between the bearing
surfaces and hydrodynamic action maintains the face portions
of the pads and the adjacent relatively moving surface out
of contact with each other instantaneously upon onset of
, 35 relative motion, and during the operation of the bearing.
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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 substantially
at the desired center of swinging motion of the face portion.
A curved, laminated, elastomer-nonelastomeric material is
disposed between the face portion and the 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 essen-
tially rigid in a radial sense (perpendicular 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.
My 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 encountered in
the prior art in situations where it is desired to use
such a bearing for supporting high radial loads.
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,
and this eccentricity permits the generation of a wedge
of lubricant between the relatively moving bearing sur-
faces. The wedge of lubricant, through pressures generated
by hydrodynamic action, in turn keeps the bearing surfaces
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apart so that surface-to-surface contact is avoided and
frictional resistance to motion is minimized.
In situations where a sliding 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
compound curvature of the continuous bearing surfaces
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 rotational axis, tends to hold
the rotating element at the center of the bearing and there-
fore 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
necessary to keep the bearing surfaces apart.
A hydrodynamic tilting pad arrangement could be
envisioned for such an application, but the required com-
pound curvature of the bearing surface of 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 unpre-
dictable. 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
had deficiencies which limit its application in a bearing
of the type presently under consideration.
The present invention utilizes the swing pad
bearing concept as disclosed in the previous U.S. patent
referenced above, in a beari~g assembly designed to handle
radial ! thrust and moment loads.
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The invention therefore provides a fluid film bearing
assembly comprising:
(a) at least two cylindrically arranged groups of
bearing pads disposed about a longitudinal axis of rotation,
one group being longitudinally spaced along this axis with
respect to the other groups;
(b) the bearing pads including moveable face portions
having curved bearing surfaces and underlying base elements
fixed relative to each other, the face portions being connected
to their respective base elements by thin alternate layers
of laminated elastomer-inelastic material extending parallel
to and coextensive with the interface surfaces, the material
being bonded to the interface surfaces and being compliant
in a shear direction along the interface surfaces but rigid
in a radial direction with respect to the interface surfaces,
whereby each face portion is supported upon its respective base
element by the material in a manner that positively restricts
the freedom of motion of the face portion to swinging movement
relative to the base element in any direction about a swing
center corresponding to the center of curvature of the interface
surface, and no other motion relative to the base element along
the direction cf relative motion between the bearing pad and
an adjacent relatively sliding load applying or support member;
(c) the bearing surfaces having concave curvatures
that are symmetrically and uniformly disposed about the longitu-
I dinal axis, the bearing surfaces of each group of bearing pads
being inclined relative to this axis in opposite directions so
that they face away from one another along the axis.
According to the present invention, the fact that the
swing pad bearing surfaces need no specific fixed relationshipbetween their centers of pressure and their centers of swing
location results in their being especially suited for application
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in a combined radial and thrust bearing, when the bearing
surfaces have a compound curvature. Using the swing pad
bearing concept, any combination of radial and thrust loading
applied to the bearing pads by a moving surface results in the
generation of a load supporting lubricant wedge. The pad
position changes automatically to maintain pad stability,
the position depending upon the relative values of the friction
and load forces, and their relative directions of applications.
Specifically, two groups of swing pad bearings are
cylindrically positioned about the longitudinal axis of a load
applying or supporting member, the pads of each set having
compound curved surfaces that are adjacent to similarly curved
surfaces on the load applying or supporting member. The
bearing pad surfaces of each group of bearings have curvatures
that are symmetrical about the longitudinal axis (between
spherical and conical) and are inclined relative to the
longitudinal axis in opposite directions, so that radial,
thrust and moment loads can be carried by the bearing assembly.
The movable bearing pad face elements will always move about
their respective swing points because of the construction of
the bearing pads so that dynamically stable and balance fluid
lubricant wedges are formed between the relatively moving
bearing surfaces, irrespective of thrust and radial loads
acting on the bearing. Friction forces caused by moving
radial loads cause the bearing pad surfaces to swing about
!their swing points in directions parallel to the direction of
motion of the adjacent bearing surface of the load applying
or supporting member, 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
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the moving surfaces are in balance. Most importantly,
thrust loads do not disturb the ability of the bearing to
generate the desired lubricant wedges.
FIGURE 1 is a diagrammatic elevational view of a
combined radial, thrust and moment load carrying bearing
embodying my invention;
- FIGURE 2 is a partial end view of the bearing of
FIGURE l;
FIGURE 3 is a detail view of an alternate
laminate construction;
FIGURE 4 shows an alternate embodiment of the
invention illustrated in FIGURE l; and
FIGURE 5 shows the principle of operation of the
swing pad elements.
With reference to Figures 1 and 2, the bearing
embodying a presently preferred mode of construction
comprises two cylindrically arranged groups of bearing
pads 10 and 12 disposed about a longitudinal axis 14
between a load applying or supporting member 16 and an
outer member 18, the latter comprising a series of con-
nected base elements for the bearing pads shown. All the
base elements are fixed relative to each other and the
fixed bearing housing structure (not illustrated).
The pads 10 and 12 each comprise a movable face
portion 20 connected to its respective section of base
18 through spherically arcuate interface surfaces 22, 24.
A metal-elastomer laminate material 26, 28 is preferably
bonded on opposite sides to both interface surfaces 22,
24, the layers 26, 28 being soft in shear (parallel to
surfaces 22, 24) but rigid in a radial compressive direc-
tion (normal to surfaces 22, 24). Layers 28 preferably
are made of rubber and layers 26 of metal.
The bearing surfaces 19 of the movable face
portions 20 of each bearing group 20 are spherical, and
their centers of curvature are located at a common point 30
on longitudinal axis 14. The center of curvature of inter-
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face surfaces 22, 24 are located at swing centers or points
32 on radii Rl, extending from axis 14 to the surface 19
of each pad, preferably the at-rest center point of each
surface 19. The swing point 32 is always located between
the axis 14 and the surfaces 19, preferably approximately
mid-way along radii Rl, so that, for example, the interface
surface 22 underlying each face portion 20 is always curved
about a radius R2 that is shorter than radius Rl. The lam-
inate layers 26, 28 are likewise curved parallel to inter-
face surfaces 22 and 24. The points 32 of the pads are
preferably equidistant from axis 14. The spherically
arced interface underlying the face portions 20 enables
the latter to move in a swinging motion about the respective
centers of swing of each pad (points 32) when they are
; 15 subjected to displacing forces acting along sectors that
: do not pass through the swing point 32. Such displacing
forces result from friction and load influences acting
on the movable face portions of the bearing pads.
The second group of bearing pads 12, here shown
in back-to-back relationship with bearing pad set 10, is
constructed similarly to pad set 10, only the pad face por-
tions are oriented about axis 14 so that their surfaces
have a common center of curvature 34 axially spaced along
axis 14 from point 30, with the radii Rl of each bearing
~ 25 pad set converging towards each other; that is, radii
Rl of bearing pad set 10 converge towards the radii Rl of
bearing sét 12. Otherwise, the relationships between
points 34, 32, Rl and R2 are identical for both bearing
pad sets 10 and 12. Thus, the bearing surfaces 10 of
each group are inclined relative to axis 14 so that they
face away from each other, and the supports 18 of each
group are fixed relative to the other group.
A load applying or supporting member 16 extends
generally along axis 14 and is rotatable relative to the
bearing pads. A pair of spherically curved segments 40,
41 are fixedly joined to member 16, the segments 40, 41
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having sliding bearing surfaces in sliding relationship
with respect to curved be~ring pad surfaces 29. The
surfaces of the segments 40, 41 correspond in curvature to
the bearing pad surfaces 29 (having curvatures about
axis 14 that are between conical and spherical).
In Figure 3, there is illustrated the use of a
- slightly modified lamination 26, 28 to show that multiple
curved metal layers 26 may be provided, and to show the
bearing pads in closer detail.
In Figure 4, the member 16 is provided with a
pair of conical curved elements 42, 44 that cooperate in
sliding relationship with conical curved surfaces of
movable pad faces 46 that are swingable about swing
points 32. Radius R2 in Figure 4 corresponds with radius
R2 in Figure 1. The dimension R3 is one radius that
extends perpendicular to the conical surfaces of the face
portions 46 from substantially the centers thereof and
they intersect a common point 30 on axis 14. Preferably,
point 32 would be located on such a radius.
In Figure 5, the principle of operation of the
invention is illustrated in a radial and rotational
sense, the various dimensions of laminated thickness and
lubricant gap thickness being exaggerated for clarity.
Rotation of member 16 in the direction of the arrow
creates friction forces on the surfaces 29 of face portions
` 20 of the bearing pads 10 and 12, causing them to each
swing towards the direction of motion of the surface of
member 41 relative to surface 19 of the bearing pads. The
swinging action creates a wedge-shaped gap between each
face portion and member 16 that tapers in the direction of
swinging motion into which lubricant, in which the
bearing pads are immersed, is drawn by the viscous forces
between the lubricant and the moving surface. A lubricant
wedge is thus generated between the moving bearing surfaces
that keeps them apart and permits relative motion between ;
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the parts with extremely low coefficients of friction.
The radial and thrust loads of the bearing acting at the
centers of pressure of each pad surface balance the
friction-induced swinging moments acting on the surfaces,
so that the inclination of each pad surfaces stabilizes
at some point of equilibrium for each combination of
pressure and friction forces.
Radial and thrust loadings of the bearing assem-
bly will cause the bearing pad surfaces to find an inclined
position of equilibrium that in all cases will enable
generation of a load carrying lubricant wedge between the
relatively moving surfaces of the assembly. Moment loads
applied to or by member 16 about radially transverse axes
will be resisted in a similar manner by the bearing assem-
bly as the radial and thrust loads, since such moment
loads can be broken down into their radial and thrust
components, and reacted by the swing pad elements as such
forces. Thrust loads will simply cause the movable pad
' faces to swing in a manner tending to equalize fluid film
pressure along the bearing surfaces parallel to the axis
of rotation.
Various other modifications to the specific
embodiment disclosed are possible.' Also it should be
understood that the term "load applying or supporting mem-
ber" is not an alternative expression, but a unitary term
referring to member 16 or its equivalent. This term is used
to signify that, in any application of the invention,
member 16 could be rotated while member 18 is held against
fixed rotation; member 16 could be fixed while member 18
and the bearing pads rotate about member 16 under load
; carrying conditions; or both members 16 and 18 could be
rotating at different angular velocities or directions.
In all cases, the load could come from the direction of
the bearing pads or from the direction of member 16.
While member 18 is shown as a singular element
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supporting two sets of bearing pads 10 and 12, it could
- be divided along a radial plane and each half spaced along
the longitudinal axis 14 in fixed relationship. Various
other changes and modifications could be made without
departing from the spirit and scope of the invention, which
is intended to be limited solely by the claims appended
hereto.
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