BACKGROUND OF THE INVENTION
The present invention relates generally to the design and construction
of a magnetic thrust bearing arrangement for supporting a rotatable shaft against
axially acting forces within a high speed rotating apparatus.
An example of a gas turbine engine including a magnetic thrust bearing
to balance the thrust load of a rotating shaft, and having the features of the
pre-characterising portion of claim 1, is disclosed in UK patent number GB 2 298
It is well known that a gas turbine engine integrates a compressor
and a turbine having components that rotate at extremely high speeds in a high
temperature environment. One component being a rotor disk that carries a row of
airfoils utilized to influence the gaseous flow within the engine. The rotating
components typically cooperate with a rotatable shaft and are supported by radial
and thrust bearings that must withstand significant dynamic and static loads within
a hostile environment. During operation of the gas turbine engine the bearings
are subjected to forces including: shock loads - such as from landings; manuever
loads - associated with sudden change in direction, and centrifugal forces attendant
with the rotating components.
As engine designers continue to increase the efficiency and power
output from gas turbine engines the application of magnetic bearings for supporting
and controlling the rotor and rotatable shaft becomes desirable. The integration
of magnetic bearings into the engine would allow the rotor shaft to be supported
by magnetic forces, eliminate frictional forces, along with mechanical wear and
the lubrication system.
A magnetic thrust bearing includes a magnetic flux field and a rotatable
thrust disk that is acted upon by the magnetic flux field. The application of magnetic
bearings in flightweight gas turbine engines requires a compactness of bearing
design which ultimately equates to lighter weight. Prior designers of gas turbine
engines have utilized materials for the rotating thrust disk that experience a
loss of mechanical properties at elevated temperatures. This loss of mechanical
properties limits the maximum rotational speed that the thrust rotor disk can be
operated at, thereby effectively limiting the maximum rotating speed of the engine
Although the prior techniques utilizing magnetic thrust bearings
for gas turbine engines are steps in the right direction, the need for additional
improvements still remains. The present invention satisfies this need in a novel
and unobvious way.
According to the present invention there is provided a gas turbine
engine, comprising a magnetic thrust bearing rotor located within the engine, said
magnetic thrust bearing rotor including a rotatable magnetically attractable member
and characterised by a high strength composite ring positioned circumferentially
about said magnetically attractable member for resisting non-magnetic forces applied
to said magnetically attractable member.
Related objects and advantages of the present invention will be apparent
from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
DESCRIPTION OF THE PREFERRED EMBODIMENT
- FIG. 1 is a perspective view of an aircraft having a gas turbine engine coupled
- FIG. 2 is an enlarged side elevational view of the gas turbine engine of FIG.
- FIG. 3a is a meridional plain sectional view of the compressor comprising a
portion of the FIG. 2 gas turbine engine according to one embodiment of the present
- FIG. 3b is a meridional plain sectional view of the compressor comprising a
portion of the FIG. 2 gas turbine engine according to another form of the present
- FIG. 4 is an illustrative view of a turbine comprising a portion of the FIG.
2 gas turbine engine according to another embodiment of the present invention.
- FIG. 5 is an enlarged partial sectional view of the magnetic thrust bearing
rotor of FIG. 3a.
- FIG. 6 is an enlarged partial sectional view of an alternative embodiment of
the magnetic thrust bearing rotor of the present invention.
- FIG. 7 is an enlarged side elevational view in section of the auxiliary thrust
bearing comprising a portion of the FIG. 3a bearing system.
- FIG. 7a is a side elevational view in section of an alternate embodiment of
the auxiliary thrust bearing.
- FIG. 8 is an enlarged side elevational view in section of the auxiliary radial
bearing comprising a portion of the FIG. 3a bearing system.
- FIG. 9 is an illustrative end view showing the compliant interfaces positioning
the auxiliary bearings between the rotor shaft and the engine housing.
For the purposes of promoting an understanding of the principles
of the invention, reference will now be made to the embodiment illustrated in the
drawings and specific language will be used to describe the same. It will nevertheless
be understood that no limitation of the scope of the invention is thereby intended,
such alterations and further modifications in the illustrated device, and such
further applications of the principles of the invention as illustrated therein
being contemplated as would normally occur to one skilled in the art to which the
With reference to FIGS. 1 and 2, there is illustrated an aircraft
10 having an aircraft flight propulsion engine 11. It is understood that an aircraft
is generic and includes helicopters, tactical fighters, trainers, missiles, and
other related apparatuses. In the preferred embodiment the flight propulsion engine
11 defines a gas turbine engine integrating a compressor 12, a combustor 13, and
a power turbine 14. Gas turbine engines are one form of high speed rotating machine.
In the present invention it is preferred that the turbine has a rotational speed
greater than twelve thousand revolutions per minute, and the compressor has a
rotational speed greater than twelve thousand revolutions per minute. However,
other rotational speeds are contemplated herein. It is important to realize that
there are a multitude of ways in which the components can be linked together.
Additional compressors and turbines could be added with intercoolers connecting
between the compressors and reheat combustion chambers could be added between
the turbines. Further, gas turbine engines are equally suited to be used for industrial
application. Historically, there has been widespread application of industrial
gas turbine engines, such as pumping sets for gas and oil transmission lines, electricity
generation, and naval propulsion.
With reference to FIG. 3a, there is illustrated the axial flow compressor
12 having a mechanical housing 15 and a plurality of airfoil (blades) rows that
are fixedly mounted to a rotatable central shaft 16 for pressurizing a fluid.
The rows of airfoils 19 include a tip 19a that is maintained radially spaced from
the housing 15 in order to provide clearance therebetween. Airfoils 19 being fixedly
coupled to a rotor 22 that rotates relative to the housing 15 when the shaft 16
is rotated by power from the turbine 14. A plurality of corresponding stationary
airfoil rows 20 (stators) are coupled to the compressor housing 15. The flow of
compressible fluid through a passageway 21 within the compressor housing 15 is
influenced by the rows of airfoils. In the preferred embodiment the compressible
fluid is air. The blade rows being generally designed to behave as diffusers,
with a corresponding increase in static pressure from the upstream region to the
The central shaft 16 being normally supported by an active electromagnetic
bearing system. With reference to FIG. 4, there is an illustrated a schematic of
a turbine having a rotatable shaft supported by a magnetic bearing system and
auxiliary bearing system that is substantially identical to the system set forth
for the compressor in FIG. 3a. It is understood that the bearing systems set forth
herein are equally applicable to both turbines and compressors within the gas
turbine engine. In the preferred embodiment the magnetic bearing system is a five
axis system. The use of magnetic bearings instead of conventional oil lubrication
bearings will allow the engine lubrication system to be removed, resulting in significant
system weight reduction, reduced parasitic losses, simplification of the engine
design and improved engine reliability through the elimination of bearing wear.
Further, the use of magnetic bearings instead of conventional oil lubrication
bearings will benefit the environment by eliminating the handling, storing, and
disposing of synthetic oils.
A magnetic bearing system can serve as an integrated actuator for
a high speed piece of turbomachinery. One of such applications being for a compressor
wherein the actuator is utilized to provide compressor active stability control,
compressor active tip clearance control, and for the active control of rotor dynamic
instabilities by providing damping. Magnetic bearing systems are well suited for
the application of these performance and operability enhancement active control
techniques for gas turbine engines such as described in GB-A-2 298 901.
In one form of the present invention the magnetic bearing system
includes a first active magnetic radial bearing 25 positioned at one end of shaft
16 and a second magnetic radial bearing 27 positioned at the other end of the
shaft 16. The magnetic bearings of the present invention are active electromagnetic
bearings. An active electromagnetic thrust bearing 26 is positioned so as to act
on shaft 16 and counteract axial thrust loading. Active electromagnetic thrust
bearing 26 includes a high speed high temperature hybrid thrust disk rotor 26a
coupled to shaft 16, and a stator 26b coupled to the mechanical housing 15. Hybrid
thrust disk rotor 26a being axially spaced from rotor 22. The stator includes a
metal core and a wire coil connected to a power supply. When the electromagnetic
is turned on, the power supply induces a current in the coil which produces the
magnetic flux field, which in turn intercepts the thrust disk rotor 26a. The active
electromagnetic bearings 25, 26, and 27 have the capability to adapt to the change
in requirements for the rotor system, diagnose engine conditions, minimize blade
tip clearance and further provide stability control. Electromagnetic bearings
25, 26, and 27 are connected to a controller 200 that provides the functionality
necessary to control the magnetic bearings.
With reference to FIG. 5, there is an illustrated a sectional view
of the preferred embodiment of electromagnetic thrust disk rotor 26a coupled to
the rotatable shaft 16. Electromagnetic thrust disk rotor 26a being a substantially
annular ring member that is press fit onto the shaft 16. In the preferred embodiment
the electromagnetic thrust disk rotor being symmetrical about an axial centerline
X. The electromagnetic thrust disk rotor 26a having two portions formed of different
materials; a magnetically responsive/attractive portion 500, and a high strength
support portion 501. The magnetically responsive portion 500 upon being subjected
to the magnetic field is attracted towards the stator 26b. High strength support
portion 501 providing mechanical strength to the rotor disk 26a for resisting
the non-magnetic forces applied to disk 26a. Further, the high strength support
portion 501 being formed of a material having magnetic permeability less than
the magnetically responsive/attractable portion 500.
The high strength support portion 501 is made of a composite material,
and more specifically a high specific strength material system. In a more preferred
embodiment the high strength support portion 501 is a high specific strength metal
matrix composite (MMC), which comprises a plurality of fibers 502 extending circumferentially
around the high strength support portion. It is understood that the quantity, size
and spacing of the fibers 502 shown herein, is merely illustrative and is not
intended to be a limitation as to the spacing, quantity or fiber size. The plurality
of circumferentially extending fibers 502 are spaced from one another in both an
axial and radial direction. In a most preferred embodiment the plurality of fibers
502 are of a silicon carbide composition, and the plurality of fibers 40 are held
together by a titanium alloy 503. Further the titanium alloy 503 forms an exterior
covering for the plurality of silicon carbide fibers 502 and titanium alloy which
comprises the high strength support portion 501.
The high strength support portion 501 is manufactured by laying up
a plurality of circumferentially extending silicone carbide fibers 502, which are
separated by a titanium alloy foil. The network of silicon carbide fibers 502
and titanium alloy foil is then hot isostatically pressed to produce the high strength
support portion 501. The metal matrix composite high strength support portion 501
being extremely resistant to compressive loads and their attendant compressive
stress. It is understood that the process of making a metal matrix composite part
is generally well known to those skilled in the art. Further, in alternate forms
of the present invention the high strength support portion 501 is constructed of
other high specific strength material systems including organic matrix composites
(OMC) and ceramic matrix composites (CMC).
The high strength support portion 501 being connected to the circumferential
surface 506 of the magnetically responsive/attractable portion 500. In the preferred
embodiment the high strength support portion 501 is press fit with the magnetically
responsive/attractable portion 500. The coefficient of thermal expansion for the
metal matrix composite is in the range of about 2,22 - 3,33 x 10-6
cm/cm per degree Celsius. (4-6 x 10-6 in/in per degree fahrenheit).
The magnetically responsive/ attractable portion 500 being formed
of a highly magnetically responsive/attractable material. More particularly, the
material utilized for the magnetically responsive portion is a high permeability
magnetic material. In the most preferred embodiment the material is a Cobalt-Iron
sold under the tradename HIPERCO 27. The material having a coefficient of thermal
expansion of about 3,33 x 10-6 cm/cm per degree Celsius (6.0 x 10-6
in/in per degrees fahrenheit). It is understood that other materials are contemplated
herein provided they have similar properties to the above material, such as good
magnetic properties at elevated temperatures.
In one form of the present invention the magnetically responsive
portion 500 forming a unitary solid disk having a axial width corresponding to
the axial width of the high strength support portion 501. The non-magnetic forces
acting upon the responsive portion 500 are transferred to the high strength support
portion 501, such that it is loaded in compression. Further, the disk 26a being
operable at steady state temperatures of up to about 650 degrees Celsius (twelve
hundred degrees fahrenheit). In an alternate form of the present invention the
magnetically responsive portion being a laminated structure.
With reference to FIG. 6, there is illustrated an alternative embodiment
of the magnetic bearing thrust disk 600. Disk 600 being substantially similar to
rotor disk 26a, with the major distinctions being related to geometric differences.
The magnetic bearing thrust disk 600 having a magnetically responsive/attractable
portion 601 and a high strength portion 602. Further, the high strength portion
602 being an annular ring that is mounted around the circumference of the magnetically
responsive/attractable portion 601. It is understood that other geometric configurations
are contemplated herein provided that any load transferred between the abutting
portions is a substantially compressive force.
Each of the active electromagnetic radial bearings 25 and 27 include;
stators 25a, 27a, and rotors 25b and 27b. The nominal clearance (air gap) between
the magnetic radial bearing stators and rotors is in the range of about 0,254
- 0,305 m (0.010-0.012 inches). However, it is understood that this clearance
between the magnetic radial bearing rotors and stators will change as the magnetic
bearings fail or there is peaked loading. Further, the air gap changes will also
occur during the active closed loop control of the magnetic bearing system.
In one embodiment the maximum static load that each of the magnetic
radial bearings 25 and 27 can support is about 500 pounds. Additionally, the maximum
dynamic load that each of the magnetic radial bearings 25 and 27 can support is
about 500 pounds. It is understood that other bearing support loads are contemplated
herein; these loads being dependent upon the space available for the bearings,
bearing size, bearing material and other characteristics of the bearing.
Aircraft gas turbine engines are subject to a wide range of dynamic
and static loading. Some of these loads, especially maneuvering and landing loads,
can be quite severe and in the magnitude of up to about twenty times the earth's
gravitational pull. In one embodiment a lightweight high temperature combination
bearing is utilized for sharing the applied load acting on shaft 16. Auxiliary
bearing units 30 and 31 run at the shaft speed of the respective component of
the gas turbine engine and load share as needed with the magnetic bearing system.
Referring to FIG. 7, there is illustrated an enlarged side elevational
view in section of the auxiliary bearing unit 30 that is a dry solid lubricated
rolling element type bearing. However, other lubrication schemes are contemplated
herein. Bearing 33 comprising a portion of bearing unit 30 and has an outer bearing
race 32 coupled to the housing 15, and in one embodiment is a ball bearing. The
inner bearing race 34 of bearing 33 being coupled to the rotatable shaft 16. A
compliant interface 35 couples the outer bearing race 32 to the housing 15 and
a second compliant interface 36 couples the inner bearing race 34 to shaft 16.
Compliant interfaces 35 and 36 function to soft mount the bearing 33 of auxiliary
bearing unit 30 between the rotatable shaft 16 and the housing 15. The light loading
of the outer race of bearing 33 allows the inner bearing race 34 and the plurality
of rolling balls to continuously rotate with the rotor shaft 16.
The compliant interfaces 35 and 36 are elastic enough to permit the
shaft 16 to seek its own dynamic center yet stiff enough to limit the radial and
axial movement of the shaft. Compliant interfaces 35a each provide a light preload
on the shaft, and in one embodiment the preload is about 50 pounds. Compliant
interfaces 35a are springs having a spring rate of about 8750 Ncm
lbs/in). It is understood that the bearing preload on the shaft can be adjusted
as necessary for tuning the systems rotordynamics.
With reference to FIG. 9, there is illustrated an end view of one
embodiment of the bearing 33 being soft mounted between the rotatable shaft 16
and the mechanical housing 15. Compliant interfaces 35 and 36 are springs and more
particularly compliant interface 35 is a leaf spring, and compliant interface
36 is a continuous wave spring. In one form the spring rate for compliant interface
35 is about 17500 N/cm. (one hundred thousand lbs/in), and for compliant interface
36 is about 87500N/cm (fifty thousand lbs/in). It is understood that the compliant
interfaces are not intended herein to be limited to springs, and that the appropriate
spring rates are dependent upon the particular system parameters.
The soft mounting of the bearing 33 between the housing 15 and the
shaft 16 enables a substantially stable transition from the all magnetic bearing
support of rotor shaft 16 to a physically contacting mechanically assisted support
of the shaft. The auxiliary bearing unit 30 sharing the load with the magnetic
forces from the magnetic bearing to support the shaft 30. While the shaft 16 is
normally supported by the magnetic force from the magnetic bearing and rotates
about its centerline the auxiliary bearing units 30 and 31 provide a light load
on the shaft and rotate at the shaft speed. Upon the failure of a magnetic bearing
and/or the onset of a maneuver or other activity that generates a peak load the
auxiliary bearing units 30 and 31 share the load on the shaft 16. Further, the
auxiliary bearing units provide static support for the shaft 16 when the shaft
Upon the radial displacement of shaft 16 about five to seven thousandths
of an inch the compliant interface 35 bottoms out and the outer bearing race 32
becomes hard coupled to housing 15. The compression of the compliant interface
35 allows the continued transfer of the bearing support from the magnetic bearing
system to the auxiliary bearing units 30 and 31, and if necessary the auxiliary
bearing units carry the complete shaft load to enable the flight mission to be
completed. Soft coupling of the auxiliary units 30 and 31 to shaft 16 allows for
the accommodation of the considerable differences in the thermal expansion coefficients
between the shaft 16 and the inner bearing races.
In one embodiment the auxiliary bearing unit 30 includes two angular
contact ball bearings 33 and 37. The second ball bearing 37 being mounted substantially
identical to the first ball bearing 33. It is understood that the two ball bearings
33 and 37 are substantially identical and like figure numbers will be utilized
herein to represent like elements. The second ball bearing 37 being mounted at
it's inner bearing race 34 through a compliant interface 36 to shaft 16 and having
its outer bearing race 32 coupled to the housing 15 by a compliant interface 35.
One of the ball bearings having a high contact angle to react the greater thrust
load, and the other bearing having a low contact angle to react reverse thrust
loads and corresponding radial loads. The auxiliary bearing unit 30 accommodates
preloading and limits the axial and radial movement of the shaft 16 to prevent
contact with the magnetic bearing system.
With reference to FIG. 7a, there is illustrated an alternative embodiment
130 of the auxiliary bearing unit. The auxiliary bearing unit 130 is designed and
constructed for providing auxiliary thrust and radial bearing support for shaft
16. The auxiliary bearing unit 130 is substantially similar to auxiliary bearing
unit 30, but only includes one ball type rolling bearing element. The bearing
element 133 being a ball type element wherein the plurality of balls roll between
an inner bearing race 135 and an outer bearing race 134. The auxiliary bearing
unit 130 being soft mounted to shaft 16 and housing 15 in substantially the same
manner as bearing unit 30.
The bearing utilized in the auxiliary bearings units are rolling
element ball type bearings. In one form of the present invention the bearings are
ceramic bearings (silicone nitride) having a ceramic inner bearing race, a ceramic
outer bearing race, and ceramic rolling ball elements. In another embodiment the
bearing units are hybrid bearings having a steel alloy inner and outer bearing
race and a ceramic rolling element. The bearing units 30 and 130 and their related
components are dry solid lubricated.
Positioned at the other end of the shaft 16 for load sharing with
radial magnetic bearing 27 is auxiliary bearing unit 31. In the one embodiment
the auxiliary bearing unit 31 is a radial rolling element bearing. With reference
to FIG. 8,there is illustrated an enlarged partial sectional view of the radial
roller bearing unit 31. The rolling element 40 comprising a cylindrical bearing
element for supporting the radial load transmitted from shaft 16 that is not carried
by the magnetic bearing system. The cylindrical roller bearing 40 rolls between
an inner bearing race 41 coupled to shaft 16 and an outer bearing race 42 coupled
to housing 15. The auxiliary bearing unit 31 being mounted between shaft 16 and
housing 15 by compliant interfaces 43 and 44. The compliant interfaces 43 and 44
are designed to soft mount the bearings between the shaft 16 and the housing 15
in a manner substantially identical to that for bearing units 30 and 130.
The bearing utilized in the auxiliary bearings units 31 are rolling
element roller type bearings. In one form of the present invention the bearings
are ceramic bearings (silicone nitride) having a ceramic inner bearing race, a
ceramic outer bearing race, and ceramic rolling roller elements. In another embodiment
of the present invention the bearing units include hybrid bearings having a steel
alloy inner and outer bearing race and a ceramic rolling element. The bearing
unit 31 and their related components are dry solid lubricated.
with reference to FIG. 3b, there is illustrated another embodiment
of the combination bearing system. The combination bearing system is substantially
identical to the FIG. 3a system, with one significant change relating to the relocation
of the auxiliary bearing unit 30 from being tucked in the magnetic bearing 25 to
being spaced therefrom. The auxiliary bearing unit 30 has been axially offset
to optimize the gas turbine engine's rotordynamics. It is understood that the position
of the combination bearing components will allow the tuning of the engine rotor
While the invention has been illustrated and described in detail
in the drawings and foregoing description, the same is to be considered as illustrative
and not restrictive in character, it being understood that only the preferred
embodiment has been shown and described and that all changes and modifications
that come within the scope of the claims are desired to be protected.