USOO8753069B2

(12) United States Patent (10) Patent No.: US 8,753,069 B2

Maier (45) Date of Patent: Jun. 17, 2014

(54) EDDY CURRENT DAMPER AND METHOD (58) Field of Classification Search
USPC ....... 415/229, 104; 416/244 R, 174; 318/611,
(75) Inventor: Martin D. Maier, Allegany, NY (US) 3.18/612
See application file for complete search history.
(73) Assignee: pre-Rand Company, Olean, NY (56) References Cited
- U.S. PATENT DOCUMENTS
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35 4,517,505 A * 3.36. Angham . . . . . . . . . . . . . . . 318,611
5,104,284 A 4/1992 Hustak, Jr.
U.S.C. 154(b) by 0 days. 6.255,752 B1* 7/2001 Werner ........................ 310,905
2009,0295244 A1 12/2009 Ries
(21) Appl. No.: 13/522,431
FOREIGN PATENT DOCUMENTS
(22) PCT Filed: Jul. 30, 2011
JP 02096O16 7, 1990
(86). PCT No.: PCT/US2O11?046O45 JP 105O2722 3, 1998
JP 2007162726 6, 2007
S371 (c)(1), WO 2012O3O459 3, 2012
(2), (4) Date: Aug. 15, 2012 OTHER PUBLICATIONS
(87) PCT Pub. No.: WO2012/030459 International Application No. PCT/US2011/046045. Notification
of International Search Report and Written Opinion mailed Feb. 17.
PCT Pub. Date: Mar. 8, 2012 2012.
(65) Prior Publication Data * cited by examiner
US 2012/0321439 A1 Dec. 20, 2012 Primary Examiner — Dwayne J White
(74) Attorney, Agent, or Firm — Edmonds & Nolte, PC
Related U.S. Application Data (57) ABSTRACT
(60) Provisional application No. 61/378,169, filed on Aug. An apparatus for Supporting a shaft of a turbomachine. The
30, 2010. apparatus may include a magnetic bearing to Support the shaft
s during a normal operation of the turbomachine, and an aux
(51) Int. Cl. iliary bearing to Support the shaft during a drop event. The
FOID 3/00 (2006.01) apparatus may also include a disk coupled to the shaft and
FOID 25/6 (2006.01) comprising a substantially non-ferrous, conductive material,
FI6C32/04 (2006.01) and a magnetic assembly disposed proximal the disk, the
(52) U.S. Cl magnetic assembly configured to magnetically engage the
CPC FOID 3/00 (2013.01); F0ID 25/16 (2013.01); disk to damp vibrations during the drop event, to apply a
F16C32/0442 (2013.01); F05D 2240/515 circumferential braking force on the disk during the drop
(2013.01) event, or both.
USPC ........................................... 415/104; 41.5/229 16 Claims, 7 Drawing Sheets

-10
12

A.
U.S. Patent Jun. 17, 2014 Sheet 1 of 7 US 8,753,069 B2
U.S. Patent Jun. 17, 2014 Sheet 2 of 7 US 8,753,069 B2

26

%
2
3%
W

24

3 36
34
Z2
--> 3
26b

FIG 2
U.S. Patent Jun. 17, 2014 Sheet 3 of 7 US 8,753,069 B2
U.S. Patent Jun. 17, 2014 Sheet 4 of 7 US 8,753,069 B2

FIG 4
U.S. Patent Jun. 17, 2014 Sheet 5 of 7 US 8,753,069 B2

26a

R
60 260
22-N Z2 %
- --------- s
64
U.S. Patent Jun. 17, 2014 Sheet 6 of 7 US 8,753,069 B2

26 26a

22%% -22
2
s
24

SW WNW
32-2 26b

FIG 7
U.S. Patent Jun. 17, 2014 Sheet 7 of 7 US 8,753,069 B2

De-levitating a
magnetically-supported 102
shaft

Catching the de-levitated

shaft with auxiliary 104.
bearings

Magnetically engaging a 106

disk coupled to the shaft to
damp vibrations and/or to
apply a circumferential
braking force

FIG 8
 US 8,753,069 B2
1. 2
EDDY CURRENT DAMPER AND METHOD apparatus may also include a disk coupled to the shaft and
including a Substantially non-ferrous, conductive material.
CROSS REFERENCE TO RELATED The apparatus may further include a magnetic assembly dis
APPLICATIONS posed proximal the disk, the magnetic assembly configured to
magnetically engage the disk to damp vibrations during the
This application is a United States national stage applica drop event, to apply a circumferential braking force on the
tion of PCT Patent Application No. US2011/046045, filed disk during the drop event, or both.
Jul. 30, 2011, which claims priority to U.S. Provisional appli Embodiments of the disclosure may further provide an
exemplary method for reducing vibration in a rotating shaft.
cation No. 61/378,169, filed Aug. 30, 2010. The contents of The method may include levitating the shaft with a magnetic
each priority application are incorporated herein by reference 10
bearing and de-levitating the shaft such that the shaft drops a
to the extent consistent with the disclosure. distance. The method may also include catching the de-levi
tated shaft with auxiliary bearings and magnetically engaging
BACKGROUND a non-ferrous, conductive disk when the shaft is de-levitated,
the disk being disposed around and coupled to the shaft, Such
Turbomachine shafts generally rotate at high speeds and, 15 that vibrations resulting from de-levitating the shaft are
thus, typically vibrate during operation according to a char damped.
acteristic stiffness, mass, and eccentricity. These characteris Embodiments of the disclosure may also provide an exem
tics, along with applied radial and axial loads, determine the plary turbomachine. The exemplary turbomachine may
frequency-amplitude relationship of the vibrations. It is usu include a shaft and one or more magnetic bearings disposed at
ally desirable to determine the characteristics of the shaft and least partially around the shaft and configured to Support the
then to monitor the shaft rotational speed to ensure that the shaft during normal operation. The turbomachine may also
shaft is not operating at or near a critical speed or a harmonic include one or more auxiliary bearings disposed at least par
thereof where the shaft resonates and therefore vibrates at tially around the shaft and configured to Support the shaft
maximum amplitude. This can create challenges if, for during a drop event. The turbomachine may further include a
example, a desired operating load on the turbomachine cor 25 disk including a non-ferrous conductive material, a radial
responds with the shaft rotating at or near the critical speed or inside coupled to the shaft, and a radial outside. The turbo
a harmonic thereof. Additional challenges can also be machine may also include a magnetic assembly having at
encountered in applications where the shaft is operated at least two magnets disposed about 180 degrees apart around
speeds above the critical speed or harmonics thereof, as the the disk, the magnets configured to engage the disk at least
during the drop event.
shaft must traverse the critical speed and the harmonics 30
thereof, where applicable, to reach the operating speed. To BRIEF DESCRIPTION OF THE DRAWINGS
attenuate vibration, conventional dampers, such as Squeeze
film dampers, are often provided to damp the shaft vibration The present disclosure is best understood from the follow
and thereby alter the critical speed of the shaft and/or decrease ing detailed description when read with the accompanying
the amplitude of the associated vibrations. Conventional 35 Figures. It is emphasized that, in accordance with the stan
dampers are generally Suitable for many applications; how dard practice in the industry, various features are not drawn to
ever, they often include drawbacks such as friction-related scale. In fact, the dimensions of the various features may be
efficiency losses and lubrication needs. arbitrarily increased or reduced for clarity of discussion.
Furthermore, in shafts Supported by one or more magnetic FIG. 1 illustrates a partial schematic view of an exemplary
bearings, the magnetic bearings may fail to levitate the shaft, 40 turbomachine, according to one or more aspects of the dis
thereby dropping the shaft, for example, during an emergency closure.
shutdown. Turbomachines are thus typically provided with FIG. 2 illustrates an axial end view of an exemplary eddy
auxiliary or "catcher bearings, which catch the shaft and current damper, according to one or more aspects of the
disclosure.
allow it to coast down to a stop, Substantially preventing
damage to the turbomachine. Dynamic forces, which may be 45 FIG.3a illustrates a partial, side cross-sectional view of the
both axially and radially directed, however, are often applied exemplary damper along line 3-3 of FIG. 2.
to the various components of the turbomachine during the FIG. 3b illustrates a partial, side cross-sectional view of
drop and Subsequent coast-down. Furthermore, if prior to the another embodiment of the exemplary damper along line 3-3
of FIG. 2.
drop, the shaft is operating above the critical speed and/or a FIG. 4 illustrates a side cross-sectional view of another
harmonic thereof, the rotational velocity of the shaft coasting 50
exemplary eddy current damper, according to one or more
down on the auxiliary bearings may slowly approach and aspects of the disclosure.
traverse the critical speed and/or harmonics thereof, and thus FIG. 5 illustrates an axial end view of another exemplary
the shaft will vibrate at or near the resonance frequency, or a eddy current damper, according to one or more aspects of the
harmonic thereof, for an extended period of time as the shaft disclosure.
slowly decelerates to, through, and away from the critical 55 FIG. 6 illustrates a side cross-sectional view of the exem
speed and/or the harmonics thereof. plary eddy current damper of FIG. 5 along line 6-6.
What is needed, therefore, is an apparatus and method that FIG. 7 illustrates an axial end view of another exemplary
provides frictionless damping and/or increased braking eddy current damper, according to one or more aspects of the
speed. disclosure.
60 FIG. 8 illustrates a flow chart of an exemplary method for
SUMMARY reducing vibration in a magnetically-supported shaft, accord
ing to one or more aspects of the disclosure.
Embodiments of the disclosure may provide an exemplary
apparatus for Supporting a shaft of a turbomachine. The appa DETAILED DESCRIPTION
ratus may include a magnetic bearing to Support the shaft 65
during a normal operation of the turbomachine, and an aux It is to be understood that the following disclosure
iliary bearing to Support the shaft during a drop event. The describes several exemplary embodiments for implementing
 US 8,753,069 B2
3 4
different features, structures, or functions of the invention. chine 10. Since the magnetic bearing 18 supports the shaft 16
Exemplary embodiments of components, arrangements, and during normal operation, a gap 19 may exist between the
configurations are described below to simplify the present auxiliary bearing 20 and the shaft 16, as shown, which the
disclosure; however, these exemplary embodiments are pro shaft 16 traverses during a drop event. Since the shaft 16 is
vided merely as examples and are not intended to limit the loosely fit in the auxiliary bearing 20 to provide the gap 19.
Scope of the invention. Additionally, the present disclosure the rotation of the shaft 16 during coast down may apply
may repeat reference numerals and/or letters in the various cyclic loading on the auxiliary bearing 20 as the shaft 16 shifts
exemplary embodiments and across the Figures provided therein.
herein. This repetition is for the purpose of simplicity and The turbomachine 10 may also include an eddy current
clarity and does not in itself dictate a relationship between the 10 damper 22. The eddy current damper 22 generally includes a
various exemplary embodiments and/or configurations dis disk 24 and a magnetic assembly 26. The disk 24 may be
cussed in the various Figures. Moreover, the formation of a coupled to the shaft 16 using any coupling devices and/or
first feature over or on a second feature in the description that bearings. Accordingly, in various exemplary embodiments,
follows may include embodiments in which the first and the disk 24 may or may not rotate with the rotating shaft 16.
second features are formed in direct contact, and may also 15 The disk 24 may be made of a substantially non-ferrous,
include embodiments in which additional features may be conductive material Such as aluminum, copper, non-magnetic
formed interposing the first and second features, such that the stainless steel, titanium, combinations thereof, alloys thereof,
first and second features may not be in direct contact. Finally, or like materials.
the exemplary embodiments presented below may be com The magnetic assembly 26 may be or include one or more
bined in any combination of ways, i.e., any element from one magnets and may be configured to magnetically engage the
exemplary embodiment may be used in any other exemplary disk 24. For example, the magnet(s) of the magnetic assembly
embodiment, without departing from the scope of the disclo 26 may be permanent magnets. When it is desired to mag
SUC. netically engage the disk 24, the magnet(s) may be brought
Additionally, certain terms are used throughout the follow into close proximity with the disk 24 such that eddy currents
ing description and claims to refer to particular components. 25 are produced in the disk 24 to resist motion of the shaft 16, as
As one skilled in the art will appreciate, various entities may will be described in greater detail below. Similarly, the mag
refer to the same component by different names, and as such, net(s) of the magnetic assembly 26 may be electromagnets;
the naming convention for the elements described herein is thus, when it is desired to magnetically engage the disk 24.
not intended to limit the scope of the invention, unless other electric current may be provided to the electromagnets Such
wise specifically defined herein. Further, the naming conven 30 that the electromagnets magnetically engage the disk 24.
tion used herein is not intended to distinguish between com FIG. 2 illustrates an axial view of an exemplary embodi
ponents that differ in name but not function. Additionally, in ment of the eddy current damper 22, showing the disk 24 of
the following discussion and in the claims, the terms “includ the eddy current damper 22 coupled to the shaft 16. The
ing” and "comprising are used in an open-ended fashion, and magnetic assembly 26 includes one or more magnets (two are
thus should be interpreted to mean “including, but not limited 35 shown: 26a, 26b), which may extend entirely or partially
to. All numerical values in this disclosure may be exact or around the disk 24. In at least one exemplary embodiment, the
approximate values unless otherwise specifically stated. magnets 26a, b are positioned Substantially opposite each
Accordingly, various embodiments of the disclosure may other around the disk 24. For example, the magnets 26a,b may
deviate from the numbers, values, and ranges disclosed herein be offset by approximately 180 degrees from each other
without departing from the intended scope. Furthermore, as it 40 around the periphery of the disk 24. Additionally, poles 30, 32
is used in the claims or specification, the term “or' is intended of magnet 26a may be reversed compared to poles 34.36 of
to encompass both exclusive and inclusive cases, i.e., “A or the magnet 26b, as shown. As such, the magnetic fields pro
B' is intended to be synonymous with “at least one of A and duced by the magnets 26a,b may be directionally opposed
B. unless otherwise expressly specified herein. with respect to each other. It will be appreciated, however,
FIG. 1 illustrates a partial schematic view of an exemplary 45 that the illustration of the two magnets 26a,b is merely exem
turbomachine 10. In various exemplary embodiments, the plary and additional or fewer magnets may be incorporated
turbomachine 10 may be a turbine, pump, separator, any type without departing from the scope of this disclosure.
of compressor, a combination thereof, or any other type of The magnets 26a,b may be disposed proximal the disk 24.
rotating machinery. For descriptive purposes only, the turbo i.e., close enough to magnetically engage the disk 24 along a
machine 10 is illustrated as a centrifugal compressor and 50 radial outside 52 thereof. In an exemplary embodiment, the
includes one or more impellers (two are shown: 12, 14) dis magnets 26a,b may be electromagnets, which may be pow
posed on a shaft 16, which rotates about an axis 28. The shaft ered using any suitable electric circuit (not shown). Alterna
16 is Supported by one or more bearings, which, in an exem tively, the magnets 26a, b may be permanent magnets, which
plary embodiment, may be or include an active magnetic may be moved radially and/or axially toward and/or away
bearing 18. It will be appreciated that additional bearings, for 55 from the disk 24, for example, using a servomotor, a Solenoid,
example, a second magnetic bearing (not shown) disposed on a manual mechanical linkage, or the like to control the mag
the right side of the impeller 14, between impellers 12 and 14, netic engagement of the disk 24. In various exemplary
or elsewhere, may be included without departing from the embodiments, the position and/or current provided to the
scope of this disclosure. The shaft 16 may be supported by the magnets 26a,b may be controlled by a feedback control loop
magnetic bearing 18 during normal operation; however, dur 60 and any electric circuits and/or mechanical linkages (none
ing an emergency Such as a turbine trip, a power outage, or if shown).
the magnetic bearing 18 fails for any reason, the magnetic FIGS. 3a and 3b illustrate two exemplary embodiments of
bearing 18 may fail to levitate the shaft 16, causing a drop the disk 24 in cross-section along line 3-3 of FIG. 2, omitting
event. One or more auxiliary bearings, e.g., auxiliary bearing the magnetic assembly 26 for simplicity of illustration. FIG.
20, may be provided to support the shaft 16 during such a drop 65 3a illustrates a substantially uniformly-constructed disk 24
event so that the shaft 16 can decelerate or “coast down' to a made of non-ferrous, conductive material Substantially
stop, thereby reducing or avoiding damage to the turboma throughout, except for a central bore 38 formed axially there
 US 8,753,069 B2
5 6
through for receiving the shaft 16 (FIGS. 1 and 2). FIG. 3b versely oriented with respect to the radially-extending con
illustrates another exemplary embodiment of the disk 24, in necting section 58, such that the outer ring 60 provides a
which the disk 24 is constructed of alternating layers of insu relatively large radial Surface area. As also described above,
lation 37, such as rubber, plastic, or another non-conductive the magnets 26a-d (only 26d is shown in FIG. 6) may be
material, and laminated non-ferrous metallic layers 39, which aligned with and magnetically engage at least one axial end
are disposed around the central bore 38. In an exemplary 64 of the outer ring 60.
embodiment, each layer of insulation 37 may be disposed In an exemplary embodiment, the hub 56, connecting sec
between two laminated metallic layers 39. Although not tion 58, and outer ring 60 may together provide a generally
shown, in various exemplary embodiments, one, Some, or all annular disk-shaped structure, which may, for example, also
of the layers of insulation 37 may include multiple layers of 10 be used as a balance piston. One with skill in the art will
insulation. Furthermore, the sequence of layers of insulation appreciate that a balance piston may be used to counteract any
37 and laminated metallic layers 39 may not be alternating, axial thrust forces on the turbomachine 10. Accordingly, the
and several laminated layers 39 may be disposed between balance piston may be in communication with a source of
layers of insulation 37, or vice versa. pressurized gas (not shown) to balance thrust forces applied
FIG. 4 illustrates a side cross-sectional view of another 15 by pressure differentials along the axis 28 (FIG. 1) of the
exemplary embodiment of the eddy current damper 22. As turbomachine 10. Furthermore, the generally annular disk
shown, the eddy current damper 22 includes the disk 24, with shaped structure may provide a relatively large mass, Such
the central bore 38 receiving the shaft 16 substantially as that the generally annular disk-shaped structure is effective as
described above. The eddy current damper 22 also includes a heat sink for heat generated by the magnetic engagement
the magnetic assembly 26, which may include the magnets between the magnetic assembly 26 and the outer ring 60, as
26a,b. The magnets 26a,b may include radial extensions 40. described in greater detail below.
42, which may extend radially-inward toward the shaft 16. Referring now to FIGS. 2-6, exemplary operation of the
The magnets 26a, b may also include disk engaging sections eddy current damper 22 may be appreciated. Since the disk 24
44,46 that are coupled to the radial extensions 40, 42, respec is made at least partially of non-ferrous conductive material,
tively, and extend axially therefrom toward the disk 24. The 25 the motion of the disk 24 in the magnetic field produced by the
disk 24 includes first and secondaxial ends 48.50, which may magnetic assembly 26 creates eddy currents E in the disk 24.
be substantially flat in profile, as shown, or may include When the shaft 16 rotates, there are generally three directions
grooves adapted to receive the disk engaging sections 44, 46 in which the disk 24 may move: the disk 24 may vibrate
or the like. The shaft 16 may be supported by the magnetic radially, for example, along arrow R of FIGS. 2 and 6, and/or
bearing 18 and/or the auxiliary bearing 20 such that a clear 30 any other radial direction; the disk 24 may vibrate axially,
ance 51 exists between a radial outside 52 of the disk 24 a along arrow A of FIGS. 4 and 6; and/or the disk 24 may rotate
radial inside 54 of the magnetic assembly 26, as shown. along arrow C of FIG. 2. When the magnetic assembly 26
FIG. 5 illustrates an axial view of another exemplary engages the disk 24, any of these movements create eddy
embodiment of the eddy current damper 22. As described currents E in a plane normal to the movement. The eddy
above with reference to FIG. 4, the eddy current damper 22 35 currents E create a second magnetic field, which opposes the
may include the disk 24 with the central bore 38 sized to movement of the disk 24 in any direction. The magnitude of
receive the shaft 16. The disk 24, however, may also include Such opposing force is proportional to the velocity of the
a hub 56, a connecting section 58, and an outer ring 60. The movement of the disk 24. Accordingly, when the eddy cur
hub 56 may define the central bore 38 and may be coupled to rents E are produced in reaction to radial or axial vibration,
the shaft 16 by any suitable coupling device and/or method. 40 the resistive forces created by the eddy currents E reduces
The connecting section 58 may extend radially from the hub shaft 16 motion through the dissipation of kinetic energy.
56 and may be coupled thereto or formed integrally therewith. Furthermore, such damping can be selective or continuous.
The outer ring 60 may be disposed around the outside of the For example, if the damping is desired to be selective, the
connecting section 58 and may be coupled thereto or formed eddy current damper 22 may be turned on or off as necessary.
integrally therewith. 45 When the eddy current damper 22 is turned on, the magnetic
The eddy current damper 22 may further include the mag assembly 26 engages the disk 24, i.e., any permanent magnets
netic assembly 26, which, in an exemplary embodiment, is of the magnetic assembly 26 are brought into close proximity
shown as four magnets 26a-d; however, in other embodi with the disk 24, and any electromagnets of the magnetic
ments the illustrated four magnets 26a-d may be four poles of assembly 26 are provided electric current. When the eddy
two magnets. The magnets 26a-d may be radially-aligned 50 current damper 22 is turned off, the disk 24 is generally free
with the outer ring 60, as may better be appreciated from FIG. from magnetic engagement with the magnetic assembly 26,
6, described below, and may be positioned at predetermined i.e., any permanent magnets of the magnetic assembly 26 are
intervals around the shaft 16. For example, the magnets 26a-d moved away from the disk 24, and current is cut off from any
may be positioned at approximately 90 degree intervals electromagnets of the magnetic assembly 26. In an exemplary
around the disk 24, although other equal or unequal intervals 55 embodiment, the eddy current damper 22 may be turned on
may instead be chosen. Furthermore, the polarity of the mag when the shaft 16 is proximal to and/or traverses a critical
nets 26a-d may alternate proceeding around the shaft 16, Such speed, reducing the amplitude of the vibrations during accel
that, for example, the magnet 26a has a reversepolarity as the eration or deceleration of the shaft 16. Since circumferential
magnet 26b, which in turn has a reverse polarity as magnet motion along arrow C of the disk 24, and thus the shaft 16, is
26C, and so on. 60 opposed by the eddy current damper 22, the eddy current
FIG. 6 illustrates a side cross-sectional view of the exem damper 22 may incur an efficiency loss during the rotation of
plary eddy current damper 22 of FIG. 5 taken along section the shaft 16; therefore, it may be desirable to turn the eddy
line 6-6. As described above with reference to FIG. 5, the current damper 22 off when shaft 16 vibration is within tol
eddy current damper 22 may include the hub 56 coupled to the erable ranges, thereby avoiding efficiency losses.
shaft 16, the connecting section 58 extending radially from 65 Another example where selective damping using the eddy
the hub 56, and the outer ring 60 coupled to the connecting current damper 22 may be employed is during a drop event, as
section 58. The outer ring 60 may be orthogonally or trans described above with reference to FIG. 1. During a drop
 US 8,753,069 B2
7 8
event, the auxiliary bearing 20 (FIG. 1) may rapidly acceler Additionally, the eddy currents E produce heat. This too
ate from generally stationary to the speed of the shaft 16. The represents inefficiency and may also damage components of
force required to accelerate the auxiliary bearing 20 may the turbomachine 10. To minimize such heat production, the
provide a dynamic load on the shaft 16. Additionally, the laminated disk 24 of FIG. 3b may be employed to minimize
thrust-compensating forces Supplied by the magnetic bearing the eddy current E. Alternatively or additionally, the eddy
18 during normal operation may be removed, leaving a net current damper 22 including the balance piston, as shown in
axial thrust on the auxiliary bearing 20. Furthermore, the FIG. 6, may be employed. Since the balance piston provides
shaft 16 rotating in the loose-fitting auxiliary bearing 20, as a relatively large mass, it may act as a heat sink to dissipate the
described above with reference to FIG. 1, may apply a cyclic heat produced by the eddy currents E.
or otherwise varying load on the shaft 16 while the shaft 16
10 FIG. 7 illustrates another exemplary eddy current damper
rotates on the auxiliary bearing 20. Any or all of these forces 22, which includes a bearing 66 interposed between the disk
may result in a period of intense shaft 16 radial and/or axial 24 and the shaft 16. The bearing 66 may include inner and
outer races 68, 70, with the inner race 68 attached to the shaft
vibration after a drop event. To attenuate the vibrations, the 16 and rotatable therewith, and the outer race 70 attached to
eddy current damper 22 may be turned on just Subsequent to 15 the disk 24. In an exemplary embodiment, between the inner
the drop, to increase the damping on the shaft 16 during the and outer races 68, 70, there may be disposed a plurality of
coast-down. Furthermore, the eddy current damper 22 may be rolling elements 72, for example, ball bearings. It will be
turned on just prior to the drop, thereby transferring at least appreciated, however, that other types of rolling elements 72,
some of the force of the dropping shaft 16 to the support and indeed other types of bearings 66, may be employed
structure (not shown) of the eddy current damper 22, allowing without departing from the scope of this disclosure.
the eddy current damper 22 to act as a shock-absorber for the In exemplary operation of the eddy current damper 22
auxiliary bearing 20. including the bearing 66, the shaft 16 rotates, but the rotation
During a drop event, the drag force applied by the eddy of the shaft 16 is generally de-coupled from the disk 24 by the
current damper 22 on the disk 24 that resists circumferential bearing 66. When the rotation is de-coupled, the shaft 16
motion may be harnessed to provide a magnetic braking 25 rotating generally does not directly cause the disk 24 to rotate,
device. As noted above, the circumferential motion of the disk except to the extent the bearing 66 applies a friction force on
24 along arrow C in the magnetic field creates eddy currents the disk 24. Accordingly, the disk 24 may be substantially free
E that induce a second magnetic field, thereby resisting the to rotate from other forces or devices or may remain at sub
circumferential motion. In Such exemplary operation, this stantially Zero rotational Velocity. As such, the magnets 26a,b
drag force is employed to more rapidly decrease the rotational 30 of the magnetic assembly 26 generally may not create eddy
velocity of the coasting shaft 16, thereby abbreviating the currents in the disk 24 based solely on the rotational move
coast-down time. This may reduce the number of cycles of ment of the shaft 16 along arrow C. However, as explained
dynamic loading applied on the shaft 16, thereby reducing above, the characteristics of the shaft 16 and/or the turboma
wear on the auxiliary bearing 20 and/or the shaft 16. chine 10 (FIG. 1), or dynamic forces from a drop event, may
Moreover, with specific reference to FIG. 2, the eddy cur 35 cause the rotating shaft 16, and thus the disk 24, to vibrate in
rent damper 22 illustrated therein may be well-suited for the radial direction, for example, as illustrated by arrow R.
controlling radial vibrations, for example, along arrow R, as Although not shown, it will be appreciated that vibration in
the magnetic assembly 26 is configured to engage the radial the axial direction may also be caused by cyclic and/or
outside of the disk 24. In comparison, the eddy current dynamic axial thrust forces on the shaft 16, as described
damper 22 illustrated in FIG.4 may be well-suited to control 40 above. Accordingly, the axial and radial movement caused by
axial vibrations along arrow A, since the magnetic assembly the vibration moves the disk 24 within the magnetic field
26 thereof is configured to engage the axial ends 48,50 of the produced by the magnetic assembly 26, thereby generating
disk 24. Further, the eddy current damper 22 illustrated in the eddy currents E. As described above, the eddy currents E
FIG. 6 may be well-suited to control vibrations in the radial provide a force on the disk 24 opposing the direction of
direction, for example, along arrow R, and/or the axial direc 45 motion proportional to the velocity of the disk 24 movement,
tion along arrow A. As explanation, the orientation of the thereby damping the vibration of the disk 24 and the shaft 16.
magnetic assembly 26 may be determined by the degree of FIG. 8 illustrates a flowchart of an exemplary method 100
freedom in the shaft 16 that requires the greatest amount of for reducing vibration in a magnetically-supported shaft. The
damping (i.e., energy dissipation). For example, a greater method 100 may proceed by operation of the eddy current
amount of energy dissipation may occur when the motion is 50 damper 22 and the turbomachine 10 described above and may
normal to the Surface of a magnet. Thus, the eddy current thus be best understood with reference thereto. The method
damper 22 illustrated in FIG. 2 efficiently reduces radial 100 may include de-levitating the shaft such that the shaft
vibration, while the eddy current damper 22 illustrated in drops a distance, as at 102. This may occur in a shaft that is
FIG. 4 efficiently reduces axial vibration, and the eddy cur Supported by one or more magnetic bearings, as described
rent damper 22 illustrated in FIG. 6 may be configured to 55 above with reference to FIG.1. The de-levitation may be the
efficiently reduce both. result of a failure of the magnetic bearings, which may occur
In various exemplary embodiments, any of the eddy cur for a variety of different reasons. Once the de-levitation
rent dampers 22 of FIGS. 1, 2, and 4-6 may remain on during occurs, the method 100 may include catching the de-levitated
normal operation. The induced eddy currents E, however, shaft with one or more auxiliary bearings, as at 104. The
resist the circumferential movement of the disk 24, and thus 60 auxiliary bearings may constrain the motion of the shaft after
may incur drag-type efficiency losses in the shaft 16 rotation. the de-levitation. However, while rotating in the auxiliary
To minimize this inefficiency, the eddy currents E may be bearings, the shaft may be subject to cyclic and/or dynamic
minimized by employing the laminated disk 24 shown in and loading as it coasts-down on the auxiliary bearings. Accord
described above with reference to FIG.3b. In contrast, where ingly, the method 100 may include magnetically engaging a
large movement-opposing forces are desired. Such as in the 65 non-ferrous, conductive disk disposed around and coupled to
described selective damping or in magnetic braking, the Sub the shaft to induce eddy currents, as at 106, for example, with
stantially-uniform disk 24 of FIG. 3a may be more suitable. a magnetic assembly. As also indicated at 106, inducing the
 US 8,753,069 B2
10
eddy currents may damp vibrations resulting from the de metallic layers being disposed between at least two of
levitation of the shaft by inducing a magnetic field that the plurality of insulation layers; and
opposes the magnetic field of the magnets, thereby opposing a magnetic assembly disposed proximal the disk, the mag
motion in the disk, and thus the shaft. netic assembly configured to magnetically engage the
The vibrations in the shaft may be axially and/or radially disk to damp vibrations during the drop event, to apply a
directed. Accordingly, in an exemplary embodiment, mag circumferential braking force on the disk during the drop
netically engaging the disk may include damping at least one event, or both.
of axial and radial vibrations in the de-levitated shaft. As 2. The apparatus of claim 1, wherein the magnetic assem
Such, magnetically engaging the disk may generally include bly magnetically engages the disk when a shaft rotation speed
magnetically engaging at least one of a radial outside of the 10
is proximate a critical speed of the shaft and is magnetically
disk and an axial end of the disk, to provide the magnetic field disengaged from the disk at other times.
suitable for inducing the desired eddy currents. 3. The apparatus of claim 1, wherein the magnetic assem
In some exemplary embodiments, it may be desirable to bly comprises first and second magnets disposed about 180
avoid inducing eddy currents by the rotation of the disk in the
magnetic field. Accordingly, the method 100 may include 15 degrees apart around the shaft.
decoupling the rotation of the shaft from the disk, for 4. The apparatus of claim 3, wherein the first and second
example, using a bearing interposed between the shaft and the magnets engage a radial outside of the disk.
disk, as described above with reference to FIG. 7. Accord 5. The apparatus of claim 3, wherein the first and second
ingly, eddy currents may be produced in the disk in response magnets engage at least one axial end of the disk.
to shaft vibration, but substantially avoided in response to 6. The apparatus of claim 1, wherein the disk comprises a
circumferential movement of the shaft, since Such motion balance piston including:
may generally not be translated to the disk. In other exem a hub coupled to the shaft;
plary embodiments, the disk may be directly coupled to the a connecting section extending radially from the hub; and
shaft, such that the disk rotates along with the shaft. In such a an outer ring extending axially with respect to the shaft,
situation, eddy currents are produced which resist the rotation 25 coupled to the connecting section, and having an axial
of the disk, and thus the shaft, when the magnets magnetically end, wherein the magnetic assembly engages the axial
engage the disk. Such embodiments may provide a magnetic end of the balance piston.
braking device, for example, to hasten the coast-down of the 7. The apparatus of claim 1, further comprising a bearing
shaft after a drop. disposed radially between the disk and the shaft, the bearing
Furthermore, the method 100 may include magnetically 30 configured to substantially de-couple rotation of the shaft
engaging the disk prior to de-levitating the shaft. For from rotation of the disk.
example, magnetically engaging the disk may include mag 8. The apparatus of claim 7, wherein the bearing com
netically engaging the disk during normal operation of the prises:
shaft, during start up, during shut down, or any combination an inner race coupled to the shaft and rotatable therewith:
thereof. In such cases, it may be desirable to induce smaller 35 an outer race coupled to the disk; and
eddy currents, to avoid substantial drag losses and/or to avoid a plurality of roller elements disposed between the inner
creating large amounts of heat. Accordingly, the disk may and outer races.
include layers of insulation interposed between layers of 9. A method for reducing vibration in a rotating shaft,
laminated non-ferrous disks, as shown in and described above comprising:
with reference to FIG. 3b. Additionally, or alternatively, it 40 levitating the shaft with a magnetic bearing;
may be desirable to minimize rotation of the disk on the shaft; de-levitating the shaft such that the shaft drops a distance;
accordingly, a bearing may be provided between the shaft and catching the de-levitated shaft with at least one auxiliary
the disk to substantially cut off rotational translation of the bearing; and
disk on the shaft. magnetically engaging a non-ferrous, conductive disk
The foregoing has outlined features of several embodi 45 prior to de-levitating the shaft and when the shaft is
ments so that those skilled in the art may better understand the de-levitated, the disk being disposed around and coupled
present disclosure. Those skilled in the art should appreciate to the shaft, such that vibrations resulting from de-levi
that they may readily use the present disclosure as a basis for tating the shaft are damped, wherein the disk comprises
designing or modifying other processes and structures for layers of insulation and metallic layers.
carrying out the same purposes and/or achieving the same 50 10. The method of claim 9, wherein magnetically engaging
advantages of the embodiments introduced herein. Those the disk comprises magnetically engaging a radial outside of
skilled in the art should also realize that such equivalent the disk to damp at least one of axial and radial vibrations
constructions do not depart from the spirit and scope of the resulting from de-levitating the shaft.
present disclosure, and that they may make various changes, 11. The method of claim 9, wherein magnetically engaging
Substitutions and alterations herein without departing from 55 the disk comprises magnetically engaging at least one axial
the spirit and scope of the present disclosure. end of the disk to damp at least one of axial and radial
I claim: vibrations resulting from de-levitating the shaft.
1. An apparatus for Supporting a shaft of a turbomachine, 12. The method of claim 9, further comprising de-coupling
comprising: a rotation of the shaft from the disk, wherein magnetically
a magnetic bearing to Support the shaft during a normal 60 engaging the disk further comprises magnetically engaging
operation of the turbomachine; the disk during normal operation of the shaft.
an auxiliary bearing to Support the shaft during a drop 13. The method of claim 9, further comprising:
event; magnetically engaging the disk during normal operation of
a disk coupled to the shaft and comprising a substantially the shaft; and
non-ferrous, conductive material, wherein the disk fur 65 conducting heat with the disk, wherein the disk provides at
ther comprises a plurality of metallic layers and a plu least part of a balance piston configured to balance axial
rality of insulation layers, at least one of the plurality of thrust on the shaft.
 US 8,753,069 B2
11
14. A turbomachine, comprising:
a shaft;
one or more magnetic bearings disposed at least partially
around the shaft and configured to Support the shaft
during normal operation; 5
one or more auxiliary bearings disposed at least partially
around the shaft and configured to Support the shaft at
least during a drop event;
a disk comprising a non-ferrous conductive material, a
radial inside coupled to the shaft, and a radial outside, 10
wherein the disk is rotatable with the shaft and further
comprises a plurality of laminated metallic layers and a
plurality of insulation layers, each of the plurality of
insulation layers being disposed between at least two of
the plurality of laminated metallic layers; and 15
a magnetic assembly comprising at least two magnets dis
posed about 180 degrees apart around the disk, the mag
nets configured to engage the disk at least during the
drop event.
15. The turbomachine of claim 14, wherein the disk com- 20
prises a balance piston including a hub coupled to the shaft, a
connecting section coupled to the hub and extending radially
outward therefrom, and an outer ring coupled to the connect
ing section, disposed transversely in relation thereto, and
providing an axial end of the disk, wherein the magnetic 25
assembly engages the axial end of the disk.
16. The turbomachine of claim 14, wherein the magnetic
assembly is configured to engage at least one of the radial
outside of the disk and an axial end of the disk.
k k k k k 30