Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02678324 2009-09-10
BEARING SUPPORT FLEXIBLE RING
TECHNICAL FIELD
[0001] The application relates generally to vibration reduction in gas turbine
engines.
BACKGROUND
[0002] In gas turbine engines, bearing-supported high speed rotating shafts
are subject to
rotor vibrations, which vibrations can be transmitted outwardly to the engine
casing. As
engine vibration is generally undesirable, various approaches have been used
in an
attempt to reduce the vibrations transmitted to the engine casing. Such
efforts include
squeeze film oil dampers, which provide a thin cushion of oil to the outer
race of the
bearing to damp out vibrations, and hence decrease transmission to the engine
case. Oil
film damping adds considerable weight, complexity and hence, cost, to the
bearing
assembly, however, due to the associated hardware required and the
modifications
required to the oil system of the engine.
[0003] Accordingly, there is a need to provide an improved solution to the
control of
engine vibration.
SUMMARY
[0004] There is provided a bearing arrangement for radially supporting a
rotatable shaft
within a gas turbine engine, the bearing arrangement comprising: a bearing
having an
inner race adapted to be mounted to the shaft and an outer race; a bearing
housing adapted
to be mounted within a casing of the gas turbine engine; and a bearing support
ring
radially disposed between the bearing housing and the outer race of the
bearing, the ring
having a plurality of circumferentially alternating and spaced apart first and
second
contact pads, the first and second contact pads respectively radially
protruding from inner
and outer circumferential surfaces of the ring, the first contact pads being
circumferentially offset from the second contact pads such as to define
flexible portions of
the ring therebetween, the flexible portions of the ring having a radial
thickness less than
that of the ring at respective locations of said first and second contact
pads, the flexible
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portions permitting elastic deflection of the ring in a radial direction
between adjacent
ones of the first and second pads, wherein a radial gap exists between the
first and second
contact pads and the outer race of the bearing and the bearing housing,
respectively, when
the flexible portions of the bearing support are un-deflected, and a plurality
of openings
extending transversely across the flexible portions of the ring, the openings
sized to
permit a substantially unrestricted flow of oil between radially inner and
outer sides of
said ring.
[00051 There is also provided a bearing support for supporting a rotating
shaft bearing
within a bearing housing of a gas turbine engine, the bearing support
comprising: an
annular body defining a radially inner circumferential and a radially outer
circumferential
surface; a plurality of circumferentially spaced apart first contact pads
disposed on the
radially inner circumferential surface of the annular body, and a plurality of
circumferentially spaced apart second contact pads disposed on the radially
outer
circumferential surface of the annular body, the second contact pads being
circumferentially offset from the first contact pads, the first and second
contact pads
having a radial thickness greater than that of portions of the annular body
circumferentially disposed between the first and second contact pads, said
portions being
elastically deflectable in a radial direction, the first contact pads being
adapted for
abutting an outer race of the bearing and the second contact pads being
adapted for
abutting the bearing housing of the gas turbine engine, and wherein a radial
gap exists
between the first contact pads and the outer race of the bearing and between
the second
contact pads and the bearing housing, when said portions of the annular body
are un-
deflected; and a plurality of oil-flow openings extending at least
transversely across the
annular body, said openings being oversized to permit substantially un-
restricted oil to
flow therethrough between radially inner and outer sides of said annular body.
[00061 There is further provided a bearing support for radially supporting a
rotating shaft
bearing within a surrounding housing in a gas turbine engine, the bearing
support
comprising: a ring having circumferentially successive first and second
portions, the first
portions being adapted for abutment with the surrounding housing and the
rotating shaft
bearing, the second portions disposed between each pair of said first portions
being more
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flexible than the first portions, such as to permit elastic deflection of said
second portions
in a radial direction; and wherein the first portions directly transmit a
radial bearing load
to the housing when forced into contact therewith by bearing misalignment or
vibration,
and the second portions elastically deflect to at least partially absorb said
bearing
misalignment or vibration.
[0007] Further details will be apparent from the detailed description and
figures included
below.
DESCRIPTION OF THE DRAWINGS
[0008] Reference is now made to the accompanying figures, in which:
[0009] Fig. 1 is a schematic cross-sectional view of a gas turbine engine;
[0010] Fig. 2 is a partial, cross-sectional view of a shaft bearing of the gas
turbine engine
in the present bearing support arrangement;
100111 Fig. 3 is a perspective view of a bearing support ring of the present
bearing
support arrangement;
100121 Fig. 4a is a side view of the bearing support ring of Fig. 3;
[0013] Fig. 4b is an enlarged, partial side view of the bearing support shown
in Fig. 4a;
[0014] Fig. 5a is an enlarged, partial side view of the bearing support shown
in an un-
deflected position between a bearing outer race and a support housing; and
[0015] Fig. 5b is an enlarged, partial side view of the bearing support shown
in a
deflected position, abutted against the bearing outer race and the support
housing.
DETAILED DESCRIPTION
[0016] Fig. 1 illustrates a gas turbine engine 10 of a type preferably
provided for use in
subsonic flight, generally comprising in serial flow communication about a
longitudinal
central axis 12, fan or rotor blades 14, a low pressure compressor 16, a high
pressure
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compressor 18, an annular combustor 20, a high pressure turbine 22, and a low
pressure
turbine 24. The low pressure turbine 24 is connected to both the low pressure
compressor
16 and the fan blades 14 by a first rotor shaft 26, and the high pressure
turbine 22 is
connected to the high pressure compressor 18 by a second rotor shaft 28. The
first and
second rotor shafts 26, 28 are supported by respective bearing members, one of
which is
shown as an example and is indicated by numeral 30. This engine rotor/shaft
bearing 30
may be a roller bearing, ball bearing, or other bearing suitable for use in
the gas turbine
engine.
[0017] As seen more clearly in Fig. 2, the bearing 30 is supported by a
flexible, ring-
shaped bearing support 40, as will be described in detail below. The bearing
support 40
may be disposed in a supporting stationary structure such as bearing housing
31, which is
in turn supported by and may be fixed within an annular engine casing 34 (see
Fig. 1) of
the engine 10. The bearing support 40 is disposed radially between the bearing
housing
31 and an outer race 32 of the bearing 30 which supports a rotating shaft,
such as a main
rotor shaft 26 or 28 of the gas turbine engine 10. The bearing support 40
includes a
radially inner circumferential surface 44 which faces the outer race 32 of the
bearing 30,
and may abut thereagainst when a radial bearing load is transmitted to the
bearing support
as a result of bearing and/or shaft misalignment or vibration. This radial
load may then be
transmitted by the bearing support 40 radially outwardly to the bearing
housing 31, such
as by abutment between portions of the radially outer circumferential surface
42 of the
bearing support 40 and an inner surface of the housing 31.
[00181 Referring to Figures 3-4b, the ring-shaped bearing support 40 comprises
an
annular body 46 having thereon the radially inner circumferential surface 44
and the
radially outer circumferential surface 42 on respective inner and outer sides
of the ring.
The annular body 46 of the bearing support ring 40 includes a plurality of
circumferentially spaced part first contact pads 48 and second contact pads 50
respectively radially protruding from the inner circumferential surface 44 and
the outer
circumferential surface 42. The first and second contact pads 48 and 50 in
this example
extend an entire axial width of the bearing support 40. The first and second
contact pads
48 and 50 are clocked to circumferentially alternate, such that each first
contact pad 48 on
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the inner surface 44 of the ring is disposed between two adjacent second
contact pads 50
on the outer surface 42, for example at a midpoint therebetween. Accordingly,
the first
contact pads 48 are circumferentially offset from the second contact pads 50.
This
configuration effectively defines a flexible ring arrangement, with flexible
portions (or
spring elements) 52 of the ring between the alternating first and second
contact pads 48
and 50. The bearing support 40 provide a flexible ring, by reason of the
bearing load path
that is defined through the bearing support 40, that is, from the bearing
outer race.to first
contact pads 48, through flexible portions 52 of the ring to the second
contact pad 50, and
from there out to the bearing housing 31.
[0019] The contact pads 48, 50 are depicted in this example as being
integrally formed as
part of the annular ring body 46, e.g. such as would be provided when support
40 is
machined from solid. In such a monolithic configuration, relatively thin
radial thickness
of the flexible portions 52 provides relatively flexibility versus the thicker
(and therefore
stiffer) contact pads 48, 50. Flexible steel may be used as a material. It is
also to be
understood, however, that the bearing support 40 may be manufactured in any
suitable
manner providing the functionality described herein, such as by suitably
affixing contact
pads 48, 50 to a separate ring body, or by the press-fitting or shrink-fitting
of multiple
concentric rings together, and so on. As such, the contact pads 48, 50 may be
formed of a
different material than the remainder of the ring, and therefore than the
flexible portions
52 of the bearing support. For example the ring body 46 may be formed of a
relative thin,
flexible steel, to which the thicker (and therefore stiffer) contact pads 48,
50 may be
affixed, such as by welding, brazing or another suitable attachment method.
The contact
pads 48, 50 may also be formed of the same material as the ring but having a
greater
radial thickness, or may be, for example, made of an abradable material.
[0020[ The annular body 46 of the bearing support 40 may be integrally formed
of a
single piece of material and may thus be a single continuous, uninterrupted,
ring.
However, it is also possible that the annular body 46 of the bearing support
is composed
of two or more arcuate portions which are circumferentially arranged end-to-
end such as
to form a discontinuous ring which is received within the annular gap between
the bearing
30 and the outer housing 31.
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[00211 The flexible portions 52 are such that these portions 52 elastically
deflect, for
example in a substantially radial direction, when forced to do so by bearing
loads and/or
radial unbalances in the bearing 30 and/or the rotating shaft supported by the
bearing with
respect to the stationary outer bearing housing 31. The portions 52 of the
annular body 46
are relatively less stiff than the contact pad portions 48, 50 thereof. This
may be by virtue
of the material of the ring and/or the relative difference in thickness,
radial thickness for
example, between the flexible portions 52 and the contact pads 48, 50. At one
possible
embodiment, the entire ring body 46 is made of high temperature steel, however
other
materials are possible providing they are suitable for gas turbine engine
environment
envelopes (high temperature, etc.) and can provide the desired spring effect.
The spring
constant of the material selected for at least the spring elements 52 of the
annular body 46
is such that elastic deflection of these portions is possible as a result of
vibrations and/or
other bearing induced radial loads imposed on the bearing support 40 during
operation of
the gas turbine engine.
[00221 In at least one embodiment the flexible portions 52 of the ring have a
radial
thickness which is less than that of the ring at the circumferential locations
of the contact
pads 48, 50. In other words, given that the first and second contact pads 48,
50 radially
protrude from the respective inner and outer surfaces 44, 42 of the annular
body 46, these
circumferential regions of the bearing support ring 40 are necessarily
radially thicker than
the portions 52 therebetween, the portions 52 thereby permitting greater
elastic deflection
in a radial direction and thus being relatively more flexible.
[00231 The bearing support 40, and particularly contact pads 48, 50, are sized
to create a
loose fit between the bearing outer race 32 and the inner diameter 44 of the
ring (or
sleeve) 46 of the bearing support 40, as well as a loose fit between the outer
diameter 42
of the bearing support ring/sleeve 40 and the surrounding housing 31. In one
embodiment, this loose fit is substantially equal on either radial side of the
ring 46 (i.e.
the clearance between bearing outer race and the ring 46 is about the same as
the
clearance between the bearing housing and the ring 46). The loose fit of the
bearing
support is intended so that the ring 46, and particularly the flexible
portions 52 thereof,
are not pre-loaded (pre-stressed).
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[00241 As seen in Fig. 5a, this loose fit between the bearing support 40 and
the bearing 30
on an inner side and the housing 31 on an outer side is such that a small
radial gap 38
exists between each of the first and second contact pads 48, 50 and their
respective facing
surfaces of the bearing outer race 32 and the inner diameter of the housing
31.
Accordingly, although the contact pads 48, 50 may be abutted, when deflection
of the
flexible portions 52 of the ring occurs as shown in Fig. 5b, against the
respective adjacent
surfaces of the bearing 30 and the housing 31 disposed on each radial side
thereof, the
central and un-deflected position of the bearing support 40 is such that the
small radial
gaps 38 exists about the full circumference of the ring between the first
contact pads 48
and the bearing 30 and between the second contact pads 50 and the housing 31.
The
bearing support may therefore be concentric with both the bearing and the
bearing
housing when un-deflected and/or not displaced by loads imposed thereon by
vibration
and/or misalignment of the bearing and shaft. It is to be understood, however,
that the
outer and inner radial gaps 38 may be different sizes.
[00251 The aforementioned loose fit between the ring 46 of the bearing support
40 and
the radially inner bearing 30 and the radially outer housing 31, thereby
defines an inner oil
chamber between each adjacent pairs of the first contact pads 48 on the inner
surface 44
of the ring 46 and the outer race of the bearing, and an outer oil chamber
between each
adjacent pairs of the second contact pads 50 on the outer surface 42 of the
ring 46 and the
bearing housing 31. These inner and outer oil chambers are in fluid flow
communication
with each other via one or more openings 54 which transversely extend through
the ring
body 46, as will be described in further detail below. The openings 54 are
sufficiently
large such as not to significantly restrict the flow of oil between the inner
and outer oil
chambers, so that the oil is free to flow therebetween within the annular gap
defined
between the bearing 30 and the housing 31, as schematically shown at 60 in
Fig. 4a. The
openings 54 will be described further below.
[00261 The annular body 46 of the bearing supporting 40 also includes a
plurality of fluid
flow openings 54 extending transversely through the flexible portions 52 of
the ring body
46. The openings 54 are sized, or rather over-sized, such as to permit
substantially
unrestricted oil flow communication between the radially inner and outer sides
of the
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annular body 46. The fluid typically used to lubricate bearings includes oil,
and therefore
the openings 54 are sized such as to allow oil to pass relatively unrestricted
from one
radial side of the ring 46 to the other, without causing significant pressure
build-ups and
thereby substantially reducing and/or eliminating the effect of hydraulic
stiffening (i.e.
hydraulic damping) of the bearing retained within the bearing support 40.
Accordingly,
the bearing support 40 locates and retains a rotating shaft bearing 30
therewithin, without
acting as a damped bearing arrangement. Rather, the oil is allowed to flow
relatively
freely within the annular space defined between the bearing outer race 32 and
the
surrounding housing 31, and therefore is able to flow from one radial side of
the bearing
support ring 40 to the other within this same annular space. In other
embodiments, holes
54 may be replaced with slots, reduced axial-length portions of the ring, or
any other
configuration which permits oil communication radially across the support 40.
[00271 Unlike prior art oil-damping arrangements, it is believed (without
intending to
limit the generality of the appended claims) that the present bearing support
decouples
(rather than dampens) the bearing from the bearing housing, and hence (in this
example)
decouples the shaft rotor from the engine case. The solution therefore
provides a lower
cost, simpler alternative to a squeeze film damper, in part because of its
simple
construction and because of its minimal impact on adjacent hardware and on the
engine
oils system.
100281 The bearing support 40 therefore acts as a flexible ring (or "flex-
ring") which
provides a centralization feature by supporting and centralizing the bearing
30 during
rotation of the shaft 26,28 supported by the bearing 30, and therefore during
typical gas
turbine engine operating conditions (temperatures, rotational speeds, etc.).
The bearing
support 40 has been found particularly useful at maintaining the bearing
centralized
during middle rotational speed ranges of the gas turbine engine shafts 26, 28,
during
which vibration sometimes tends to pose an issue.
[00291 The bearing support 40 may also include one or more anti-rotation
elements 58
thereon, which prevent unwanted circumferential rotation of the annular body
46 of the
bearing support 40 within the gap formed between the bearing 30 and the outer
housing
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31. The anti-rotation elements 58 may include, as depicted in Fig. 3, axially
protruding
tangs which engage a corresponding slot or opening provided in the bearing
housing 31.
[0030] The above description is meant to be exemplary only, and one skilled in
the art
will recognize that changes may be made to the embodiments described without
departing
from the scope of the claims. A turbofan gas turbine engine is illustrated as
an example
for application of this bearing support. However, the described bearing
support may be
applicable to various types of bearings in various types of gas turbine
engines, as well as
various types of bearings. Still other modifications which fall within the
scope of the
present application will be apparent to those skilled in the art, in light of
a review of this
disclosure, and such modifications are intended to fall within the appended
claims.
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