Note: Descriptions are shown in the official language in which they were submitted.
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SPRING ASSEMBLY FOR A HIGH PRESSVRE THRUST BEARING
Background of the Invention
The invention relates to high pressure thrust
bearing assemblies and, more particularly, to the -~
arrangement of a plurality of stiff spring subassemblies
in such a thrust bearing to provide flexible mounting for
a plurality of bearing thrust plates that are positioned
to support a bearing ring for rotation.
Long before the present invention it was generally ~-
well-known that frusto-conical spring discs are useful
in providing a relatively stiff, resilient force capable
of supporting heavy loading with a uniform resilient
pressure. Such spring discs have come to be called
Belleville spring discs since the issuance of U.S. Patent
No. 75,970 to Mr. Belleville in which he disclosed the
so-called Belleville spring. Over the years a plurality
of different spring assemblies have been developed to
more efficiently utilize Belleville spring d~scs.
For example, such spring discs have been stacked in
concentric, parallel relation as explained in U.S.
Patent No. 3,029,071 issued to J. Wells. And Belleville
spring discs have been stacked in coaxial relationship
with centering rings and retainer flanges disposed
around their respective inner and outer abutting
peripheral surfaces to maintain concentricity of the
discs and to counteract the hysteresis problems that
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cause some Belleville spring systems to be faulty or
non-uniform in operation. One example of such retainer
rings and supporting flanges used with a Belleville spring
assembly is shown in U.S. Patent 3,873,079 to S. Kuus.
In addition to the various prior art improvements
in Belleville spring assemblies, per se, the use of
Belleville springs in a wide spectrum of different
applications has occurred. In general, so far as the
present applicant knows, such prior applications have
been limited to relatively light loading on the springs
where considerable movement or vibration is induced in
the spring by the load. An example of such a vibration
dampaning shock mount utilizing a Belleville-type spring
is shown in U.S. Patent 3,113,755 issued to Stevens et al.
At the other end of the loading spectrum stiff Belleville
spring assemblies have been used to support heavy,
relatively static loads as explained in U.S. Patent
No. 2,191,901 and U.S. Patent No. 2,708,110 which describe
the use of such springs for supporting heavy loads where
little movement on the spring is anticipated in normal
use of the system.
Despite the general familiarity of those skilled
in the high pressure thrust bearing art with Belleville
spring arrangements and their advantages, it continues to
be common practice to rely on conventional coil spring
subassemblies to support flexibly movable thrust bearing
plates in high pressure thrust bearing applications,
despite the fact that the pressure has steadily increased -
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from the early 1920's to the present time. This
increasing pressure on thrust bearings has been observed,
for example, in the evolution of the type waterwheel-
driven electric generators that are commonly supported in
rotating relationship by such bearings. In order to
accommodate these increases in pressure, tighter packing
of coil spring subassemblies has been resorted to in
order to adequately support the thrust bearing plates in
such bearing assemblies without exceeding predetermined
overall dimensions for the bearing assembly. However,
at the present time the existing space limitations and
requirements of low friction losses for thrust bearings in
larger waterwheel generator installations requires that
stiffer spring subassemblies than any heretofore employed
be developed for these applications. Moreover, in order
to provide desired load distribution on the bottom surfaces
of flexible thrust plates for such high pressure thrust
bearings it is desirable to utilize stiff spring sub-
assemblies that can have their stiffness readily modified
without changing their exterior dimensions. The present
invention provides the necessary spring stiffness and easy
adjustment of individual spring subassembly stiffness to
accommodate substantial anticipated increases in thrust
bearing pressures. As explained in detail below such
increased pressures are typically applied from a rotatable
bearing runner ring that transmits thrust load from a
generator shaft to flexible thrust plates supported by a
plurality of such spring subassemblies in a thrust bearing
made according to the invention.
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Objects of the Invention
A primary object of the present invention is to
provide a spring subassembly for a high pressure thrust
bearing that incorporates a plurality of such subassemblies
to form a bearing having a plurality of resiliently
supported thrust plates loaded to accommodate thrust
bearing pressures beyond the capacity of conventional
coil spring subassemblies.
Another object of the invention is to provide a
means of optimizing the stiffness of individual spring
subassemblies in a thrust bearing in order to compensate
for the flexural stiffness of the bearing plates by means
of providing a readily adjustable number and arrangement
of spring discs within the respective spring subassemblies.
Yet another object of the invention is to provide a
thrust bearing assembly having a plurality of stiff spring
subassemblies that can be economically and reliably
manufactured to provide resilient support and uniform
stiffness over the range of movement desired for the
flexible thrust plates of such a high pressure thrust
bearing.
Additional objects and advantages of the invention
will be apparent to those skilled in the art from the
description of it presented herein, taken in conjunction
with the accompanying drawings.
Summary of the Invention
In one preferred embodiment of the invention a high
pressure thrust bearing having a runner ring supported on
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a plurality of flexible thrust plates is provided with
a plurality of Belleville spring disc subassemblies
arranged, respectively, between the thrust plates and
a base member to provide a uniform stiffness to the
thrust plate supports over their range of vertical
movement, which is determined by selectively establishing
the stiffness and positioning of each spring subassembly.
Description of the Drawing
FIGURE l is a side elevation of a portion of a
high-pressure thrust bearing including a plurality of
Belleville spring subassemblies constructed pursuant to
the present invention and shown in their normal operating
positions with respect to the other components of the
overall bearing assembly.
FIGURE 2 is an enlarged side elevation, partly in
cross-section through the center of one of the Belleville
spring subassemblies illustrated in Figure 1, showing
the preferred orientation of Belleville spring discs and
spring-confining washers of the illustrated preferred
embodiment of the invention.
Description of the Preferred Embodiment
Referring first to Figure 1, there is shown a
portion of an annular high-pressure thrust bearing 1
having a machined steel base member 2 with an annular,
generally flat upper surface, a plurality of substantially
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identical flexible steel thrust plates, some of which are
designated as the plates 3, and an annular rotatable
steel runner ring 4 the bottom bearing surface of which
is substantially flat to provide smooth sliding engagement
with the cooperating upper surfaces of the respective
thrust bearing plates 3. It will be understood that
although only three thrust plates 3 are shown in the
fragmentary view of the bearing 1 illustrated in Figure 1,
additional thrust plates will be disposed around the
circumference of the bearing to support the rot~table
runner 4 at equally spaced points around its circumference,
in a manner well-known in the high-pressure thrust bearing
field. A plurality of spring subassemblies 5 are positioned
respectively on the upper surface of the base member 2 -~
between it and the respective thrust plates 3, in order to
provide precisely controllable resilient support for the
thrust plates according to the invention.
As shown in Figure 1, the spring assemblies 5 are
clustered on the upper surface of the base member 2 between
raised radial keys 2a, 2b, etc., that are bolted or other-
wise suitably secured to the member 2 at spaced intervals
around its circumference, as shown, to position the spring
subassemblies under the thrust plates and at the same time
hold the thrust plates 3 against annular movement while
allowing them to move vertically on the spring subassemblies.
As described generally thus far, the high pressure
thrust bearing assembly 1, shown in Figure 1, is relatively
conventional, except that each of the spring subassemblies 5
utilized in the bearing assembly is constructed with a
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Belleville spring disc arrangement. It will be understood
that according to the invention each of the spring
subassemblies 5 can be substantially identical in structure '!
and function; accordingly, a detailed description of only ~ --
one such spring subassembly 5 will now be given, with
reference to Figure 2 or the drawing, in order to provide
a complete understanding of the invention. However, it
will be apparent from the description of the invention that
for some bearing applications a variety of arrangements of
spring discs within respective subassemblies 5 may be used
in a single thrust bearing in order to optimize control of ~ -
thrust plate flexure, in a manner that will be described
in more detail below.
As shown in Figure 2, the preferred embodiment of
a spring assembly 5 of the invention comprises a first
annular washer 6, a second annular washer 7, a threaded
screw 8, and a plurality of Belleville spring discs 9
that are supported in coaxial relation on the screw 8
between the first and second washers. To provide a
desired range of vertical movement for the first washer 6,
a recess 6a is formed in the outermost surface thereof to
slidably receive the head 8a of screw 8. The second
washer 7 is provided with threads on its inner surface 7a
to rotatably receive therein the threads 8a of screw 8.
In its assembled form, the spring subassembly 5 has
the screw 8 slidably inserted through the aperture in the
first washer 6 and threaded into the second washer 7 so
that the head 8a of the screw is slidably seated on the
bottom, sloped wall of a recess 6a in the head 6, as is
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clearly shown in Figure 2. A predetermined pre-compression
of the Belleville spring discs 9 is set forth the spring
subassembly 5 by rotating the screw 8. This can be done
simply by loading the first washer 6 until the desired
pre-compression of the discs 9 is attained, then rotating
the screw 8 threading it into the second washer 7 until
the screw head 8a is snugly seated on the surface 6a.
After a predetermined compressive force is thus applied
to all of the spring subassemblies 5 to be used in a given
high pressure thrust bearing, such as the bearing assembly 1
shown in Figure 1, the individual screws 8 are preferably
welded to the respective second washers 7 to assure
continuous maintenance of the selected pre-compression
in all of the spring subassemblies. Obviously, other
suitable means can be used to lock the screws to the
second washers, if desired. When thus assembled, the
spring discs 9 are each compressed between associated
washers 6 and 7 to continuously apply a biasing force
to the washers that tends to move them away from one
another. A desirable feature of this Belleville spring
arrangement is that the stiffness of the spring
subassemblies 5 remains relatively uniform over the
range of movement of the respective first washers 6
relative to the second washers 7.
This desired uniform stiffness of each spring
subassembly 5 is assured by the arrangement of the
preferred embodiment of the invention wherein the spring
discs are arranged in pairs, as shown in Figure 2, such
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that the two endmost discs have their respective concave
side abutting the closest of the washers 6 and 7 thereto,
and the convex sides of each pair of spring discs 9 is in
abutting engagement. This arrangement holds the first
washer 6 in a relatively flat position with respect to
the base member 2 and respective thrust plates 3 of the
bearing assembly 1, as shown in Figure 1.
It should be appreciated that the relative stiffness
of each spring subassembly 5 can be easily varied by
rearranging the spring discs 9 therein. This feature is
a major improvement over prior art thrust bearings that
include thrust-plate-supporting spring subassemblies
that incorporate coil springs. In addition to enabling
the construction of spring subassemblies having greater
stiffness than is possible with coil springs of equivalent
outside diameter, the discs 9 in the subassemblies of the
invention can be stacked in various groupings of parallel
and/or series coaxial arrangements that differ from one
spring subassembly to another in a given thrust bearing.
Consequently, it is possible to more precisely control
the overall flexure of the thrust plates 3 with the
Belleville spring subassemblies 5 than with prior art
coil spring subassemblies. To help understand the
advantages of this feature of the invention, consider,
for example, that in a given thrust bearing it is
determined that the thrust loading on a bearing runner 4
will apply greater pressure to the center area of each
plate 3, than to the surfaces near their respective edges.
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To optimize this flexure, for example, by maintaining the
runner-supporting surfaces of the plates as nearly planar
as possible (if desired) under given pressure and thermal
conditions, certain of the spring subassemblies S can be
assembled with a selected number of their respective
spring discs 9 arranged in parallel, or in a combination
of parallel and series arrangements, while other selected
subassemblies 5 will have their spring discs 9 arranged in
other parallel and/or series arrangements, such as that
shown in Figure 2. The individual spring subassembly height
can be adjusted by varying the lower washer 7 thicknesses,
as needed to accommodate the shortening of the stiffer,
parallel disc arrangements relative to the series disc
arrangements. Finally, the spring subassemblies are
mounted between the plates 3 and the base member 2 so that
the stiffer subassemblies are positioned under the
respective center areas of the plates 3, while the other
subassemblies are disposed closer to the edges of the-
plates. Accordingly, the plates 3 will have the stiffest
springs directly under the areas of greatest pressure
transmitted by the ring so that vertical deflection of the ;
plates is lessened in these areas relative to the plate
edges, thus the plates are resiliently supported in a nearly
flat orientation, if desired. It should be understood
that other combinations of spring disc arrangements can be
readily constructed with the invention, in order to
accurately control the flexure of thrust plates that are
subjected to a variety of combined pressure and thermal
loadings.
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Another feature of the invention is that the
respective diameters of each of the spring discs 9 is
made no greater than the minimum outer diameters of
the washers 6 and 7, while the outer diameter of each of
these washers is made substantially equal. With these
relative dimensions, when the spring subassemblies 5 are
mounted in operating position on the upper surface of the
base member 2, as shown in Figure 1, the spring sub-
assemblies can be positioned with the washers 6 and 7 of
the respective subassemblies in contact, with adjacent
upper and lower washers of the other spring subassemblies,
without causing the outer edges of the spring discs 9 in
the respective subassemblies to contact one another.
Consequently, no additional spring subassembly spacing
lS means is needed in the bearing assembly 1, aside from
the keys 2a, 2b, etc. on the base member 2.
A modification of the basic preferred embodiment
of the spring subassembly 5 described above is illustrated
in Figure 2. This modification entails the positioning
of a washer lO on the upper surface of second washer 7 to
protect the top surface of washer 7 from the possibility
of fretting due to contact with the possibly harder material
of the lowest disc 9. Where such a problem is not antici-
pated, the washer 10 need not be used.
Those skilled in the bearing art will generally
understand the operation of the invention from the
structural arrangement of it described above, however,
to assure a complete description of the invention herein
it should be understood that after a suitable plurality of
spring subassemblies ~ are constructed in the manner
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described above with reference to Figure 2, (or in
alternative, stiffer configurations for some of the
subassemblies if a certain flexure pattern of plates 3 is
to be controlled, as pointed out by the example described
above), they are mounted in groups between the respective
keys 2a, 2b, etc. on the upper surface of the base member 2
of a high pressure thrust bearing assembly such as the
assembly 1 shown in Figure 1. A plurality of thrust
bearing plates 3 are then positioned on the upper washers 6
of the respective subassemblies, so that the thrust plates
can move vertically between the respective keys. The above-
mentioned arrangement of the spring discs 9 in the
respective spring subassemblies 5 serves to provide uniform
pre-selected stiffness to predetermined areas of the
bearing plates over their vertical range of movement,
pursuant to the present invention. Finally, the rotatable
bearing runner ring 4 is slidably mounted on the upper ~`
surface of the respective thrust plates 3 and normally
the runner ring will be coupled by a suitable collar to
the shaft of a generator or equivalent piece of machinery
supported on such a shaft in a well-known manner.
Those skilled in the art will recognize that various
alternative embodiments and modifications of the invention
may be utilized without departing from the scope of the
invention. Accordingly, it is my intention to encompass
within the following claims the true limits of the
invention.
