Note: Descriptions are shown in the official language in which they were submitted.
> CA 02218044 1997-10-10
WO 96/33350 Yf'TIUS96~03079 , , ' ;
Description
HYDRODYNAMIC AIR THRUST BEARING WITH OFFSET BUI~ FOILS
Technical Field
This invention relates to hydrodynamic air thrust
bearings and particularly to the relative orientation of
the thrust bearing bump foils with respect to the backing
spring bump foils.
Background Art
As one skilled in this art appreciates, air foil
bearings are extremely sophisticated and highly technical
devices and alterations, changes and additions to the
composition and configuration of these types of bearings
are very critical and can materially affect the operation
thereof. An example of a hydrodynamic fluid film thrust
bearing is disclosed in U.S. Patent No. 4,462,700 granted
to G. L. Agrawal on July 31, 1984 entitled "Hydrodynamic
Fluid Film Thrust Bearing" and commonly assigned to United
Technologies Corporation. This invention constitutes an
improvement over the thrust bearing disclosed in this
patent.
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Typically, the thrust bearing includes a stationary
thrust plate, a rotating thrust runner axially spaced
therefrom, and one or two foils disposed therebetween. Each
of the foils include backing members having different
relative spring rates. In the thrust bearing that includes
two foil corrugated backing members, the foil member
adjacent to the rotating thrust runner typically is a
corrugated metallic member with a relatively high spring
rate which has a higher spring constant than the foil
member adjacent the stationary thrust plate. This serves to
establish and maintain an optimum fluid film geometry under
all loading, speed and other operating conditions. The
other backing member which has the lower relative spring
constant provides the bearing with compliance for adequate
load capacity and damping characteristics. It is to be
understood that for certain applications it is beneficial
to design both backing members to have equal spring rates
to achieve particular performance parameters.
As is well known in this technology the surface of the
washer shaped thrust bearing foil plate is fitted with a
plurality of wedge shaped corrugated thrust bearing bump
foils (segments) spaced about the circumference. The
leading edge of the corrugated thrust bearing bump foils
are welded to the face of the thrust bearing foil plate and
the opposite end is unattached and free to move axially.
The top foil which is similarly shaped to the corrugated
thrust plate is likewise welded at the leading edge to the
thrust bearing foil plate. The leading edge of the top
foils is spaced just upstream of the leading edge of the
corrugated thrust bearing bump foils. Depending on the
particular application, the thrust bearing will consist of
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several of such segments and the number of segments
utilized will principally depend on the optimized
performance of such application.
To obtain damping the thrust bearing includes a
second washer shaped backing spring foil plate and a
plurality of corrugated backing spring bumper foils.
Each of the corrugated backing spring bumper foils are
identical in shape and size to each of the corrugated
thrust bearing bump foils and their leading or trailing
edges are welded to the face of the backing spring foil
plate and the opposite end is unattached. The thrust
bearing pump foil is attached to the upper face of the
foil plate and the backing spring bump is attached to the
lower face of its foil plate.
As is well known in this technology, the practice is
to axially align the leading edges of the thrust bearing
bump foil with the leading edges of the backing spring
bump foil. Thus the leading edges and their respective
weld joints of all the segments are in axial alignment
with each other.
I have found that I can increase thrust bearing load
capacity while at the same time reduce running torque by
a significant amount by substantially offsetting the
leading edge of the thrust bearing bump foil relative to
the leading edge of the backing spring bump foil. This
improvement in the thrust bearing makes the difference in
certain applications of meeting the thrust bearing
requirements of certain rotating machinery.
Summary of the Invention
An object of this invention is to provide an
improved
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hydrodynamic air thrust bearing.
A feature of this invention is to provide for a
hydrodynamic air thrust bearing a pair of bump foils that
are substantially offset relative to each other.
The foregoing and other features of the present
invention will become more apparent from the following
description and accompanying drawings.
Brief Description of Drawings
Fig. 1 is an exploded view in perspective illustrating
the thrust bearing of this invention;
Fig. 2 is a partial sectional view taken through a
segment of the overlying top foil, thrust bearing bump
foil, thrust bearing foil plate and backing spring foil
plate of Fig. 1; and
Fig. 3 is a partial sectional view depicting another
embodiment of the invention which is substantially the
same as Fig. 2 except the weldment for attaching the bump
foil to the lower plate is on the trailing edge rather than
on the leading edge.
Detailed Description of the Preferred Embodiment
This invention is best understood by referring to
Figs. 1 and 2 wherein the thrust bearing generally
illustrated by reference numeral 10 includes the top plate
12 consisting of foil plate 14, bump foils I6, and top
foils 18 and the lower plate 20 consists of foil plate 22,
and bump foils 24. As noted in Fig. 1, the foil plates 14
and 22 are annular similar to a washer and
include circumferentially spaced tangs 26 and 28
respectively, that include the central recess 32 and 30,
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respectively for attachment to the bearing support (not
shown). A plurality of bump foils 16 and an equal number of
the top foils 18 of the thrust bearing top plate 12 are
circumferentially spaced and attached to the upper face 36
of foil plate 14. As noted in Figs. 2 and 3, each of the
bump foils 16 are fabricated from a metallic spring
material and are corrugated with the corrugation oriented
from the inner to outer diameter, i.e., radially, of the
foil plate 14. The leading edge 40 of each of the bump
foils are welded to support each of the truncated pie
shaped wedge segments of the bump foils 16. The top foils
18 are similarly configured and likewise are fabricated
from a high spring rate metallic material although they are
not corrugated. The leading edge 42 of each of the top
.foils is also attached to the upper face of the top plate
14. The aft ends or trailing edges 44 and 46 of each of the
bump foils 16 and top foils 18 are unattached and hence are
free to move in the axial direction . As noted in Fig . 2 ,
the leading edges 42 of the top foils 18 protrude beyond
the leading edges 40 of the bump foils 16 in the
circumferential direction.
The bump foils 24 are fabricated into a corrugated
segment and are made from a spring metallic material whose
spring rate is lower than or equal to the spring rate of
the bump foils 16 and are likewise corrugated whose
corrugations are similarly oriented. In Fig. 2 each of the
leading edges 50 are welded to the under face of the lower
plate 22. The welding is typically a spot weld process and
the weldment are represented by reference numeral 53. As is
the case of the bump foils 16 only the leading edge is
secured and the aft or trailing edge 54 is free to move
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axially. For some applications, the design may be
optimized (as noted in Fig. 3) by securing the trailing
edge 57 of the bump foil 55 by weldment 53 and the
leading edge 56 is free to move axially. As is well
known the bump foils provide the compliancy, bearing
preload, load deflection and spring rate and the use of
dual bump foils, as shown, provide the damping. For
further details of the operation of this type of bearing
reference should be made to U.S. Patent No. 4,672,700,
supra.
In accordance with this invention, the bump foils 16
and 24 are circumferentially offset such that the leading
edges 40 of bump foils 16 and the leading edges 50 of
bump foils 24 are circumferentially spaced with respect
to each other. This orientation of the leading edges of
the bump foils serves to improve the compliancy
characteristics of the thrust bearing and enhance the air
wedge to improve air flow over the top foil.
It has been found that by actual tests, this offset
bump foil arrangement provides assistance and compliance
to the top foil leading edge 42 to form an improved air
film to increase load capacity and reduce running torque.
Although this invention has been shown and described
with respect to the detailed embodiments thereof, it will
be appreciated and understood by those skilled in the art
that various changes in form and detail thereof may be
made without departing from the scope of the claims.
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