FIELD OF THE INVENTION
The invention relates to bearings that damp motion between a shaft and a
housing, and particularly to bearings that damp oscillations of an object supported on
legs or columns.
BACKGROUND OF THE INVENTION
An expression of the ability of a structure to dissipate kinetic energy when
subjected to harmonic motion is termed "damping". Most structures have an inherent
ability to damp. It is an engineering practice to associate a level of damping with a
particular form, material, construction method, or level of stress of a structure. If a
structure can be shown to dissipate more kinetic energy than would normally be
attributed to that type of structure, then there may be a reduction in loading for certain
types of forces. This, in turn, allows a reduction in the strength requirement of the
structure, and thus a cost saving.
An electric power line reactor is an electrical component including one or more
inductor elements wired between a power source and an electrical load. The reactor
opposes rapid changes in current, thus, it attenuates spikes of current and limits peak
currents. Reactors generate lateral accelerations that must be accommodated by their
support structure. They need separation from the ground by electrical insulators and
distance, resulting in elongated support legs with some lateral flexibility. They are
therefore subject to oscillations. Current damping devices for such support structures
are expensive and large, requiring extra real estate below the reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in the following description in view of the drawings that
show:
FIG. 1 is a side sectional view of a damping bearing assembly according to
aspects of an embodiment of the invention.
FIG 2 is an exploded view of the assembly of FIG 1.
FIG 3 illustrates a plurality of damping bearing assemblies supporting a structure
such as an air core reactor coil.
DETAILED DESCRIPTION OF THE INVENTION
FIG 1 is a side sectional view of a damping bearing assembly 20 according to
aspects of an embodiment of the invention. A bearing housing 22 may have a threaded
bore 24 leading to a damping fluid chamber 28 defined by clearance between an end of
a support shaft 32 and the housing 22. A fluid sealing set screw 26 in the bore may
provide access to the chamber 28, and may further provide a fluid pressure adjustment
to a damping fluid therein. Herein "damping fluid" includes viscous fluids, semi-fluids,
gels, and especially greases. The fluid used in tests of the invention described herein is
an aluminum complex automotive/machine grease called Permalube™ Red, which has
a National Lubricating Grease Institute (NLGI) consistency number of 2 . The
consistency of the damping fluid may be selected in combination with designing the
shape and size of the damping fluid chamber 28 to cause a desired damping effect.
The damping fluid chamber 28 is a void defined between inner surfaces of the housing
and elements on the end of the shaft.
A spherical bearing on the end of the shaft 32 has an inner ball portion 34
surrounded by a mating outer collar portion 30, the two portions having a common
center of rotation 35 relative to each other. The inner surface of the outer collar portion
30 may closely fit around and against an annular portion of the inner ball portion 34.
The inner and outer portions of the bearing may be formed as respective rings with
respective outer and inner mating spherical surfaces with a common geometric center
35. The inner ball portion 34 of the damping bearing may be mounted on a
diametrically reduced portion of the shaft 32, and retained thereon by a shaft cap 36.
The ball 34 and collar 30 portions of the bearing may be made of a hard material such
as chrome steel for example to support the weight and tolerate the oscillations of a
supported structure. The pressure of the damping fluid can contribute to supporting the
weight of the supported structure, thereby reducing the load on the bearing surfaces
somewhat. The set-screw 26 may be torqued to adjust fluid pressure for this purpose
and/or to modify its damping properties. A second locking set-screw (not shown) may
be provided. The bearing outer collar portion 30 may be retained in the housing 22 by a
bearing retainer plate 38. A flexible dust seal 40 may be retained on the shaft by a dust
seal retention plate 42. A lower mounting plate 44 may be attached to the shaft 32, and
an upper mounting plate 46 may be attached to the housing 22 for mounting the
damping bearing assembly 20 in a supporting structure.
The damping fluid chamber 28 changes shape upon relative rotation between the
housing and shaft, causing the damping fluid to shift in the chamber. This characteristic
is provided by at least first and second opposed bounding surfaces 29, 37 of the
chamber that are not spherical surfaces centered on the bearing center of rotation 35.
The first bounding surface 29 may be a planar inner surface in the housing and the
second bounding surface 37 may be an outer surface on the end of the shaft parallel to
the first bounding surface. These surfaces 29, 37 may be normal to the shaft centerline
33, and may define a flat cylindrical portion of the damping fluid chamber, where "flat"
means having a height of less than 1/4 the diameter of the cylindrical void. The
chamber may for example have a volumetric shape of rotation about the shaft centerline
33. In such geometry, damping is maximal for bearing rotations about axes
perpendicular to the shaft centerline 33, and is minimal for rotations about the shaft
centerline. The chamber may have a cup shape over and around the end of the shaft,
which end may be defined by the shaft cap 36.
Clearance between the opposed bounding surfaces 29, 37 may be at least
sufficient to accommodate a predetermined bearing rotation range with a safety margin.
For example, a rotation range of ± 4 degrees may be accommodated by clearance
between the opposed surface 29, 37, and between other parts, that allows rotation of at
least ± 4 degrees without interference, or it may allow ± 5 or 6 degrees or more for
safety. Minimizing the clearance between the opposed surfaces 29, 37 can increase
damping, depending on type of damping fluid, so clearance provided by the damping
chamber 28 may be limited, for example, to less than ± 10 degrees of relative rotation.
The clearance between opposed surfaces 29, 37 bounding the damping fluid
chamber may be designed based on the diameter of the chamber, the viscosity of the
damping fluid, the number of damping bearings, the weight of the supported structure,
and the resonant frequencies of the structure being damped in order to maximize
damping effectiveness in general and/or to maximize damping at a particular frequency.
FIG 2 is an exploded view of the assembly of FIG 1. The bearing ball 34 and
collar 30 may be purchased as a pre-assembled unit as shown.
FIG 3 illustrates an application of the present invention to support a structure 50
on multiple legs or columns 52. The supported structure may be anything that benefits
from damping, especially anything with self-induced lateral accelerations, such as
combustion engines and electrical coils, capacitors, and motors. Any structure that
experiences harmonic oscillations under self-induced or external accelerations may
benefit, such as water towers and wind turbines. Tests were performed in which the
supported structure 50 was an air-core reactor coil for electric power, and the columns
52 were provided with porcelain insulators per installation requirements. The tests
showed a doubling of the damping ratio using the present damping bearings compared
to control tests without damping bearings. The tests were performed as follows:
1. Install a reactor coil 50 on a support structure 20, 52 as in FIG 3 .
2 . Use a hydraulic piston attached to an adjacent building structure to pull the
coil laterally with a force of 4500 lbs.
3 . Release the system, and capture the structural oscillations with a laser
sensor.
4 . Plot the captured oscillations with MathCAD/Excel to obtain the magnitudes
of successive peaks of the oscillation.
5 . The damping calculation method is Logarithmic Decrement.
6 . Repeat the test five times.
Linearity and Precision: The linearity is 0.1 % of Full Scale (Full Scale = 250
mm). The precision of the sensor is 3 decimal places. Ambient temperature during test
is 24 degrees Celsius.
RESULTS WITHOUT DAMPING BEARINGS
Test # Damping Ratio Frequency
A 1 2.97 % 0.855 Hz
A2 2.70 % 0.854 Hz
A3 2.79 % 0.854 Hz
A4 3.15 % 0.854 Hz
A5 3.21 % 0.854 Hz
RESULTS WITH DAMPING BEARINGS
The present damping bearing does not require an orifice for fluid friction as in
automotive hydraulic shock absorbers. Thus, only one fluid chamber is needed. No
chamber partitions, valves, springs, or pistons are needed. The lack of a fluid friction
orifice reduces the possibility of cavitation in the damping fluid. The damping fluid can
be more viscous than the liquid hydraulic oils used in automotive shock absorbers. This
reduces leakage. The inventors have found that the Permalube™ Red used in the
present invention does not leak through or around the bearing ball and collar, even
when fluid pressure is increased by the set-screw 26. The bearing ball 34 and collar 30
do not need to be custom made for the invention if a pre-assembled ball/collar bearing
is available off-the-shelf in a desired size and shape. The present damping bearing
damps rotary motions, which piston type shock absorbers do not. The relatively small
size of the chamber 28 allows a high range of pressure adjustment by a simple setscrew
26, which can thus easily adjust for different weights of supported structures,
reducing wear on the ball/collar bearing. The present damping bearing is small and
compact compared to prior art damping devices such as hydraulic piston dampers.
While various embodiments of the present invention have been shown and
described herein, it will be obvious that such embodiments are provided by way of
example only. Numerous variations, changes and substitutions may be made without
departing from the invention herein. Accordingly, it is intended that the invention be
limited only by the spirit and scope of the appended claims.

WE CLAIMS:-
The invention claimed is:
1. A damping bearing comprising:
a ball portion on an end of a shaft;
a collar portion encircling the ball portion and retained thereon for rotation
relative to the ball portion about a bearing center point;
a housing fixed to the collar portion;
a damping fluid chamber defined by a void between the end of the shaft and the
housing, wherein the fluid chamber changes shape upon a rotation of the housing
relative to the shaft.
2 . The damping bearing of claim 1, wherein the damping fluid chamber
comprises a first bounding surface on the housing and an opposed second bounding
surface on the end of the shaft, wherein the first and second bounding surfaces
comprise planar surfaces that are parallel in one position of rotation of the housing
relative to the shaft.
3 . The damping bearing of claim 1, wherein the end of the shaft comprises a
shaft cap that retains the ball bearing on a diametrically reduced portion of the shaft.
4 . The damping bearing of claim 3 , wherein damping fluid chamber
comprises a cup shaped void over and around the shaft cap.
5 . The damping bearing of claim 1, further comprising:
a threaded access bore between the damping fluid chamber and an outer
surface of the housing; and
a set-screw threaded in the access bore that seals the damping fluid in the
chamber.
6 . The damping bearing of claim 5 , wherein the damping fluid chamber
provides only enough clearance for less than ± 10 degrees of relative rotation between
the shaft and the housing about the bearing center point.
7 . A damping bearing comprising:
an inner ball portion attached to an end of a support shaft;
an outer collar portion fitted around the ball portion;
a housing attached to the collar portion for rotation of the housing relative to the
support shaft about a bearing center point;
a damping fluid chamber defined by a clearance between an end of the support
shaft and the housing;
wherein the damping fluid chamber comprises first and second opposed
bounding surfaces that are not spherical surfaces of rotation about the bearing center
point;
wherein a rotation of housing about the bearing center point changes a shape of
the damping fluid chamber.
8 . The damping bearing of claim 7 , wherein the first bounding surface
comprises a planar inner surface in the housing normal to a centerline of the support
shaft and the second bounding surface comprises an outer planar surface on the end of
the shaft.
9 . The damping bearing of claim 7 , wherein the end of the support shaft
comprises a shaft cap that retains the ball bearing on a diametrically reduced portion of
the shaft.
10. The damping bearing of claim 9 , wherein the damping fluid chamber
comprises a cup-shaped void over and around the shaft cap.
11. The damping bearing of claim 7 , further comprising:
a threaded access bore between the damping fluid chamber and an outer
surface of the housing; and
a set-screw threaded in the access bore that seals the damping fluid in the
chamber.
12. The damping bearing of claim 11, wherein the set-screw is rotatably
positionable to pressurize the damping fluid in the chamber.
13. A damping bearing comprising:
a first structure comprising a first bearing surface rotatable about a second
structure comprising a second bearing surface;
a damping fluid chamber defined by portions of the first and second structures
such that a shape of the chamber changes in response to rotation of the first structure
about the second structure;
a damping fluid in the damping fluid chamber caused to shift in response to
changes in the shape of the chamber and effective to damp the rotation of the first
structure about the second structure.
14. The damping bearing of claim 13, wherein the first structure comprises a
housing and the second structure comprises a shaft.
15. The damping bearing of claim 13, wherein the damping fluid chamber is at
least partially defined by a planar surface in the housing and a planar surface on an end
of the shaft.
16 . The damping bearing of claim 13 , further comprising:
a threaded access bore opening into the damping fluid chamber; and
a set-screw threaded in the access bore that seals the damping fluid in the
chamber, such that adjustment of a position of the set-screw in the access bore is
effective to change a pressure of the damping fluid and to affect the damping of the
rotation.
17 . The damping bearing of claim 13 , wherein the first and second bearing
surfaces partially define a spherical shape such that the rotation of the first structure
about the second structure is about a point of rotation.
18. The damping bearing of claim 13, wherein the damping fluid chamber is
without partitions.