U.S. patent application number 13/344697 was filed with the patent office on 2013-07-11 for magnetically coupled contra-rotating propulsion stages.
This patent application is currently assigned to HAMILTON SUNDSTRAND CORPORATION. The applicant listed for this patent is Jacek F. Gieras, Lubomir A. Ribarov. Invention is credited to Jacek F. Gieras, Lubomir A. Ribarov.
Application Number | 20130174533 13/344697 |
Document ID | / |
Family ID | 47678560 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130174533 |
Kind Code |
A1 |
Ribarov; Lubomir A. ; et
al. |
July 11, 2013 |
MAGNETICALLY COUPLED CONTRA-ROTATING PROPULSION STAGES
Abstract
A turbomachine comprises a turbine shaft, first and second
rotors, first and second propulsion stages, and a magnetic stator.
The first rotor is rotationally coupled to the turbine shaft, and
coaxially arranged along an axis. The first propulsion stage is
rotationally coupled to the first rotor, opposite the turbine
shaft. The second rotor is coaxially arranged about the first
rotor, and the second propulsion stage is rotationally coupled to
second rotor, opposite the turbine shaft and adjacent the first
propulsion stage. The magnetic stator is coaxially arranged between
the first rotor and the second rotor, forming a magnetic coupling
between the and second rotors to drive the second propulsion stage
in contra-rotation with respect to the first propulsion stage.
Inventors: |
Ribarov; Lubomir A.; (West
Hartford, CT) ; Gieras; Jacek F.; (Glastonbury,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ribarov; Lubomir A.
Gieras; Jacek F. |
West Hartford
Glastonbury |
CT
CT |
US
US |
|
|
Assignee: |
HAMILTON SUNDSTRAND
CORPORATION
Windsor Locks
CT
|
Family ID: |
47678560 |
Appl. No.: |
13/344697 |
Filed: |
January 6, 2012 |
Current U.S.
Class: |
60/226.1 ;
415/60; 60/805 |
Current CPC
Class: |
F02C 3/067 20130101;
H02K 16/02 20130101; Y02T 50/672 20130101; B64C 11/48 20130101;
F02K 5/00 20130101; F02K 3/072 20130101; H02K 7/14 20130101; Y02T
50/66 20130101; F05D 2260/404 20130101; Y02T 50/60 20130101 |
Class at
Publication: |
60/226.1 ;
415/60; 60/805 |
International
Class: |
F02K 3/04 20060101
F02K003/04; F02C 3/04 20060101 F02C003/04; F01D 1/26 20060101
F01D001/26 |
Claims
1. A turbomachine comprising: a turbine shaft rotationally mounted
along an axis; a first rotor rotationally coupled to the turbine
shaft and coaxially arranged about the axis; a first propulsion
stage rotationally coupled to the first rotor, opposite the turbine
shaft; a second rotor coaxially arranged about the first rotor; a
second propulsion stage rotationally coupled to second rotor,
opposite the turbine shaft and adjacent the first propulsion stage;
a magnetic stator coaxially arranged between the first rotor and
the second rotor and forming a magnetic coupling between the first
rotor and the second rotor to drive the second propulsion stage in
contra-rotation with respect to the first propulsion stage.
2. The turbomachine of claim 1, wherein the first and second rotors
comprise permanent magnetic elements to form the magnetic
coupling.
3. The turbomachine of claim 1, wherein the first and second rotors
comprise cage windings to form the magnetic coupling.
4. The turbomachine of claim 1, wherein the stator coil comprises
first and second windings to form the magnetic coupling.
5. The turbomachine of claim 4, wherein the first and second
windings are switchable to drive the first and second propulsion
stages in co-rotation about the axis.
6. The turbomachine of claim 1, wherein the magnetic stator
comprises a coil having a number of poles selected to drive the
first and second propulsion stages at different rotational
speeds.
7. The turbomachine of claim 1, further comprising an engine core
coupled to the turbine shaft opposite the first rotor, the engine
core comprising a compressor, a combustor and a turbine arranged in
flow series along the axis.
8. A turboprop engine comprising the turbomachine of claim 7,
wherein the first and second propulsion stages comprise
contra-rotating propellers.
9. The turboprop engine of claim 8, further comprising a clutch
mechanism coupled to the first rotor, wherein the clutch mechanism
is operable to rotationally decouple the contra-rotating propellers
from the turbine shaft.
10. A turbofan engine comprising the turbomachine of claim 7,
wherein the first and second propulsion stages comprise
contra-rotating fan rotors.
11. A turboshaft engine comprising the turbomachine of claim 7,
wherein the first and second propulsion stages comprise
contra-rotating lift rotors.
12. A propulsion engine comprising: an engine core comprising a
compressor, a combustor and a turbine arranged in flow series along
an axis; a primary magnetic rotor rotationally coupled to the
engine core along the axis; a primary propulsion rotor coaxially
coupled to the primary magnetic rotor, opposite the engine core
along the axis; a secondary magnetic rotor coaxially arranged about
the primary magnetic rotor; a secondary propulsion rotor coaxially
coupled to the secondary magnetic rotor, opposite the engine core
along the axis and adjacent the primary propulsion rotor; and a
magnetic stator coaxially arranged between the primary magnetic
rotor and the secondary magnetic rotor, the magnetic stator forming
a magnetic coupling between the primary and secondary magnetic
rotors to drive the primary and secondary propulsion stages in
contra-rotation about the axis.
13. The propulsion engine of claim 12, wherein the primary and
secondary magnetic rotors comprise permanent magnet elements to
form the magnetic coupling.
14. The propulsion engine of claim 12, wherein the primary and
secondary magnetic rotors comprise cage windings or solid
conductive cylinders to form the magnetic coupling.
15. The propulsion engine of claim 12, wherein the magnetic stator
comprises a two windings distributed in inner and outer slots
switchable to drive the primary and secondary propulsion rotors in
co-rotation about the axis.
16. The propulsion engine of claim 12, wherein the magnetic stator
comprises a coil having a selected number of poles to drive the
primary and secondary propulsion rotors at different rotational
speeds.
17. A turboprop engine comprising the propulsion engine of claim
12, wherein the primary and secondary propulsion rotors comprise
contra-rotating propellers.
18. The turboprop engine of claim 17, further comprising a clutch
mechanism to decouple the contra-rotating propellers from the
engine core.
19. The turboprop engine of claim 17, wherein the contra-rotating
propellers have different numbers of blades.
20. A turbofan engine comprising the propulsion engine of claim 12,
wherein the primary and secondary propulsion rotors comprise
contra-rotating fan stages.
Description
BACKGROUND
[0001] This invention relates generally to turbomachinery, and
specifically to gas turbine engines for aviation applications. In
particular, the invention concerns a propulsion turbine with
contra-rotating rotor stages.
[0002] Gas turbine engines are rotary-type combustion turbine
engines built around a power core made up of a compressor,
combustor and turbine, arranged in flow series with an upstream
inlet and downstream exhaust. The compressor compresses air from
the inlet, which is mixed with fuel in the combustor and ignited to
generate hot combustion gas. The turbine extracts energy from the
expanding combustion gas, and drives the compressor via a common
shaft. Energy is delivered in the form of rotational energy in the
shaft, reactive thrust from the exhaust, or both.
[0003] Gas turbine engines provide efficient, reliable power for a
wide range of applications, including aviation and industrial power
generation. Smaller-scale engines such as auxiliary power units
typically utilize a one-spool design, with co-rotating compressor
and turbine sections. Larger-scale jet engines and industrial gas
turbines (IGTs) are generally arranged into a number of coaxially
nested spools, which operate at different pressures and
temperatures, and rotate at different speeds.
[0004] The individual compressor and turbine sections in each spool
are subdivided into a number of stages, which are formed of
alternating rows of rotor blade and stator vane airfoils. The
airfoils are shaped to turn, accelerate and compress the working
fluid flow, and to generate lift for conversion to rotational
energy in the turbine.
[0005] Aviation applications include turbojet, turbofan, turboprop
and turboshaft engines. In turbojet engines, thrust is generated
primarily from the exhaust. Modern fixed-wing aircraft generally
employ turbofan and turboprop designs, in which the low pressure
spool is coupled to a propulsion fan or propeller. Turboshaft
engines are typically used on rotary-wing aircraft, including
helicopters.
[0006] Turbofan engines are commonly divided into high and low
bypass configurations. High bypass turbofans generate thrust
primarily from the fan, which drives airflow through a bypass duct
oriented around the engine core. This design is common on
commercial aircraft and military transports, where noise and fuel
efficiency are primary concerns. Low bypass turbofans generate
proportionally more thrust from the exhaust flow, providing greater
specific thrust for use on high-performance aircraft including
supersonic jet fighters. Unducted (open rotor) turbofans and ducted
propeller engines are also known, in a variety of counter-rotating
and aft-mounted configurations.
[0007] In coaxial, contra-rotating propulsion engines, rotor
coupling is a critical design consideration. Where weight,
efficiency and rotor speed are concerned, moreover, they often pose
competing demands on the rotor coupling mechanism.
SUMMARY
[0008] This invention concerns magnetically coupled coaxial,
contra-rotating propulsion stages, for example in a contra-rotating
turbofan or turboprop engine. A first rotor is rotationally driven
about an axis, and coupled to a first propulsion stage. A second
rotor is coaxially mounted about the first rotor, and coupled to a
second propulsion stage. A magnetic stator is coaxially arranged
between the first and second rotors, forming a magnetic coupling to
drive the second propulsion stage in contra-rotation with respect
to the first propulsion stage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross-sectional view of a gas turbine engine
with magnetically coupled coaxial, contra-rotating propulsion
stages.
[0010] FIG. 2 is a schematic view of the magnetically coupled
contra-rotating propulsion stages.
[0011] FIG. 3A is a schematic view of a stator slotted core for a
Gramme winding.
[0012] FIG. 3B is a schematic view of a stator slotted core for a
Gramme winding or double-layer winding distributed in slots.
[0013] FIG. 4A is a cross-sectional view of a stator polyphase
winding spread flat for a Gramme winding.
[0014] FIG. 4B is a cross-sectional view of a stator polyphase
winding spread flat for a double-layer winding comprising
distributed-parameter coils.
DETAILED DESCRIPTION
[0015] FIG. 1 is a cross-sectional view of gas turbine engine 10
with magnetically coupled coaxial, contra-rotating propulsion rotor
stages 12 and 14. Gas turbine engine 10 comprises engine core 16
with compressor section 18, combustor 20 and turbine section 22.
Magnetic coupling drive system 24 is mechanically coupled to engine
core 16 via reduction gearbox 26, in order to drive propulsion
stages 12 and 14 in contra-rotation about engine axis (or
centerline) C.sub.L.
[0016] In the particular example of FIG. 1, gas turbine engine 10
is configured as a contra-rotating turboprop engine, with
three-spool engine core 16 and contra-rotating propeller rotors 12
and 14. Intake 28 is located below engine centerline C.sub.L, and
combustor 20 has a reverse-flow configuration from compressor
section 18 to turbine section 22, exhausting to downstream (jet)
nozzle 32.
[0017] Alternatively, gas turbine engine 10 is configured as an
axial-flow turbofan, with contra-rotating fan stages 12 and 14. In
other applications, engine core 16 has one-spool, two-spool and
multi-spool configurations for use in turboprop, turbofan and
turbojet engines, with compressor 18, combustor 20 and turbine 22
provided in a variety of axial, radial, and axial/radial flow
configurations. Similarly, propulsion rotors 12 and 14 have both
ducted and unducted (free) rotor blade configurations, with
different forward and aft mounting arrangements.
[0018] In operation of gas turbine engine 10, air from inlet 28 is
compressed in compressor section 18 and mixed with fuel in
combustor 20. The fuel/air mixture is ignited to produce hot
combustion gas, which drives turbine section 22, and is exhausted
downstream through nozzle 32.
[0019] Turbine section 22 is rotationally coupled to compressor
section 18 via a series of coaxial shafts. Compressor section 18 is
rotationally coupled to magnetic drive 24 via reduction gearbox 26,
for example a planetary gear or spur gear transmission. Magnetic
drive 24 couples upstream propulsion rotor 12 to downstream
propulsion rotor 14, driving stages 12 and 14 in contra-rotation
about centerline C.sub.L to generate thrust for gas turbine engine
10.
[0020] In typical turboprop engines, a single-stage propeller is
coupled to the power core (or turbine) through an offset reduction
gear. The offset gearing converts high RPM, low torque engine shaft
output to lower RPM, higher torque propeller shaft output, keeping
the tips of the propeller blades below sonic speeds. In constant
speed systems, thrust control is provided by a variable pitch
mechanism.
[0021] Gas turbine engine 10, in contrast, utilizes coaxial,
contra-rotating propulsion stages 12 and 14, arranged coaxially and
spaced one behind the other along engine centerline C.sub.L. This
is distinguished from, and should not be confused with,
counter-rotating propeller designs, in which the propellers on two
or more different engines turn in opposite directions to reduce
torque effects.
[0022] As shown in FIG. 1, power is transferred from engine core 16
to magnetic drive 24 via coaxial gearbox 26 on turbine engine shaft
34. In other designs, a direct coupling is used, and reduction
gearbox 26 is not present. Alternatively, gearbox 26 has an offset
configuration, with magnetic drive 24 and propulsion stages 12 and
14 rotating about a common axis parallel to engine centerline
C.sub.L.
[0023] Turboprop engines are known for their low specific fuel
consumption (SFC), high reliability, simple design, and high
power-to-weight ratios, and are commonly used by regional and
commuter airlines. Turboprop aircraft allow for quick roll-out and
climb from short take-off locations, combined with effective
reverse thrust braking. These capabilities make turboprop aircraft
ideal for smaller regional and municipal airports, where larger and
heavier aircraft are unable to operate efficiently.
[0024] Traditional turboprop-powered aircraft do have limitations,
however, including lower service altitude (<20,000 ft, or about
6,000 m), lower cruise speed (<450 mph, or about 725 km/hr), and
limited cabin pressurization. In addition, turboprop aircraft often
rely on ground support for cabin power, pre-heat and pre-cool
capabilities.
[0025] From a thrust perspective, the air mass flowing through a
propeller disk (or disc) also generates tangential (or
circumferential) airflow. The effect can be substantial at low
airspeed, and the energy of this rotational airflow is lost in
single-stage propeller designs. P-factor effects are also
experienced at high wing angles of attack, when the propeller rotor
is not perpendicular to the airflow. This results in asymmetric
propeller loading on the upper and lower blade rotation, producing
an off-center or asymmetric center of thrust.
[0026] To address these problems, gas turbine engine 10 utilizes a
second contra-rotating propulsion stage 14, positioned coaxially
with and directly behind (downstream of) first propulsion stage 12.
Second (downstream) propulsion stage 14 takes advantage of the
rotational airflow generated by first (upstream) propulsion stage
12, increasing performance and efficiency by utilizing the
rotational flow energy to generate additional thrust.
[0027] Contra-rotating propulsion stages 12 and 14 also reduce
P-factor effects, eliminating directional biasing due to asymmetric
propeller torque for greater maximum power and efficiency during
takeoff and landing operations. Contra-rotating propulsion stages
12 and 14 thus drive air more uniformly, with less thrust asymmetry
and rotation in the downstream airflow, providing higher
performance and lower induced energy losses.
[0028] As a result, contra-rotating propulsion stages 12 and 14
typically 5-15% more efficient than a traditional (single-stage)
turboprop engine. These efficiency gains can be offset, however, by
increased weight and mechanical complexity. Traditional
contra-rotating propellers can also be noisy, particularly at
higher engine frequencies due to the increased blade passing
frequency (BPF).
[0029] Noise and vibration effects can be reduced by using a
different number of blades on contra-rotating propulsion stages 12
and 14, for example three, four or five blades on upstream
(forward) stage 12, and four, five or six blades on downstream
(aft) stage 14. In addition, magnetic drive 24 reduces weight and
heat losses, as compared to a planetary gear drive or other
contra-rotating mechanical drive. Magnetic drive 24 can also be
configured to drive propulsion stages 12 and 14 at different
speeds, or to decouple one or both of propulsion stages 12 and 14,
in order to reduce noise, improve efficiency, and provide greater
power and climate control capability for ground operations.
[0030] FIG. 2 is a schematic view of magnetic drive 24 for gas
turbine (propulsion engine) 10, with coaxial, contra-rotating
propulsion stages 12 and 14. In this configuration, magnetic drive
24 is directly coupled to turbine engine shaft 34, without a
reduction gearbox. Turbine shaft 34 is rotationally coupled to the
power core of propulsion engine 10, for example using a coaxial or
offset reduction gearing, or via direct mechanical coupling to a
low spool or other turbine shaft.
[0031] Magnetic drive 24 drives first (primary) propulsion stage 12
in rotation about centerline C.sub.L via a mechanical coupling
between turbine shaft 34 and primary magnetic rotor 36. Magnetic
drive 24 drives second (secondary) propulsion stage 14 in
contra-rotation about centerline C.sub.L via a magnetic coupling
formed by magnetic stator 38 between primary magnetic rotor 36 and
secondary magnetic rotor 40.
[0032] Primary propulsion rotor stage 12 is mechanically and
rotationally coupled to primary (inner) magnetic rotor 36 via
primary drive shaft 42. Primary drive shaft 42 is mechanically and
rotationally coupled to turbine shaft 34 at the aft (downstream)
end, opposite primary propulsion stage 12 on the forward (upstream)
end.
[0033] Secondary propulsion rotor stage 14 is mechanically and
rotationally coupled to secondary (outer) magnetic rotor 40 via
secondary drive shaft 44. Secondary drive shaft 44 is magnetically
coupled to primary drive shaft 42 and turbine shaft 34 via magnetic
stator 38, which forms the magnetic coupling between primary rotor
36 and secondary rotor 40.
[0034] Primary (inner) drive shaft 42 and secondary (outer) drive
shaft 44 are rotationally supported in a coaxial arrangement on
bearings 46. Magnetic stator 38 is coaxially arranged about primary
magnetic rotor 36 and secondary magnetic rotor 40 is coaxially
arranged about magnetic stator 38, such that magnetic stator 38
located between primary rotor 36 and secondary rotor 40.
Alternatively, primary and secondary drive shafts 42 and 44 may be
reversed, with the primary (drive) spool components arranged
outside the secondary (driven) spool components.
[0035] The various rotational and thrust bearings 46 provide radial
and axial support to the components of magnetic drive 24, while
mechanically and rotationally decoupling propulsion stage 12 on
primary drive shaft 42 from contra-rotating propulsion stage 14 on
secondary drive shaft 44. As a result, the rotational coupling
between contra-rotating propulsion stages 12 and 14 is magnetic,
rather than mechanical, as provided by magnetic stator 38 between
primary rotor 36 and secondary rotor 40.
[0036] Magnetic coupling drive system 24 thus replaces traditional
planetary gear trains and other heavy mechanical components with a
magnetic coupling between contra-rotating stages 12 and 14,
reducing weight and gearing losses as compared to traditional
designs. Contra-rotating propulsion stages 12 and 14 may also be
configured as fixed-pitch rotor stages, eliminating additional
mechanical elements.
[0037] This contrasts with traditional turboprop engine designs,
where complex oil and cooling systems are required to service the
heavy (contra-rotating) reduction gear transmission and
controllable pitch mechanisms, as well as the power core. This
results in more frequent maintenance, with lower mean time between
scheduled repair/removal (MTBSR) and mean time between failures
(MTBF). Magnetic drive system 24 allows propulsion engine 10 to
eliminate this additional mechanical complexity in the oil and
cooling systems, reducing engine weight and improving MTBSR and
MTBF for better overall reliability and operational dispatch
readiness.
[0038] In one design of magnetic drive 24, the magnetic coupling is
provided by strong permanent magnet (PM) field components 50 on
primary rotor 36 and (contra-rotating) secondary rotor 40, with
copper windings or other magnetic coils 52 distributed in slots
along magnetic stator (or armature) 38. Suitable materials for PM
field components 50 include rare earth magnets, such as neodymium
magnets. Occasionally, samarium-cobalt magnet field components 50
are used for high-temperature applications.
[0039] In PM configurations, field components 50 provide constant
(contra-rotating), substantially radial magnetic fields on primary
and secondary rotors 36 and 40. The contra-rotating fields cross
air gaps 54A and 54B to interact with the field generated by stator
coil 52, transferring torque from primary rotor 36 to secondary
rotor 40 to drive secondary propulsion stage 14 in contra-rotation
with respect to primary propulsion stage 12. Alternatively, an
axial field configuration is utilized.
[0040] As shown in FIG. 2, each stator coil 52 has two active
elements, inner surface (or inner coil) 52A facing rotating
magnetic element 50 on primary (inner) rotor 36 across inner air
gap 54A, and outer surface (or outer coil) 52B facing
contra-rotating magnetic element 50 on secondary (outer) rotor 40
across outer air gap 54B. Electric current is provided to coils 52,
52A and 52B from the aircraft's on-board (e.g., 28 VDC) power
supply, or other current source, generating a magnetic field to
couple primary and secondary rotors 36 and 40.
[0041] Rotating magnetic elements 50 on primary and secondary
rotors 36 and 40 thus create strong coupling forces between coaxial
propulsion stages 12 and 14. The field is switched to provide the
proper phase relationship for torque transfer between primary and
secondary rotors 36 and 40, based on the total field contribution
of the coil current (or driving voltage) in combination with the
induced EMF (electromagnetic force) generated by rotation of
magnetic elements 50 about stator windings 52A and 52B.
[0042] The electric currents in magnetic stator 38 and windings 52,
52A and 52B are controlled by brushless contacts, so that
counter-rotating magnetic fields are produced in annular air gaps
54A and 54B between stator 38 and primary and secondary magnetic
rotors 36 and 40, driving secondary drive shaft 44 into
contra-rotation about primary drive shaft 42.
[0043] In synchronous operation of magnetic drive 24, an AC supply
current is provided or the DC supply current is switched to provide
an alternating (AC) or rotating magnetic field in stator coils 52A
and 52B, and the field is synchronized to the rotational speeds of
contra-rotating rotors 36 and 40. The field switching frequency and
phase depend on the number of poles in magnetic elements 50, the
number of separate coil (flux generating) elements in stator coils
52A and 52B, and the desired phase relationship to produce
contra-rotation of secondary rotor 40 with respect to primary rotor
36.
[0044] In asynchronous operation of magnetic drive 24, torque is
transferred from primary rotor 36 to secondary rotor 40 via
electromagnetic induction. In this configuration, magnetic drive 24
may operate as an induction motor or induction drive, with magnetic
stator 38 and magnetic rotors 36 and 40 operating as phased
rotating transformers.
[0045] In asynchronous or induction motor configurations of
magnetic drive 24, magnetic elements 50 may be provided as solid
conductive cylindrical or "squirrel cage" windings on one or both
of primary magnetic rotor 36 and secondary magnetic rotor 40,
rather than PM elements. Alternatively, a wound-rotor design or
Gramme winding is used for magnetic elements 50.
[0046] FIG. 3A is a schematic view of magnetic stator 38 with
slotted core 56 for a Gramme winding distributed in radial slots
58. The construction of stator core (yoke) 56 is shown in an end
view (left) and in a top view (right), with magnetic stator 38
coaxially oriented about centerline C.sub.L of magnetic drive 24,
as shown in FIG. 2.
[0047] Stator core 56 is formed of a magnetic material such as
laminated magnetic steel or a soft magnetic composite (SMC)
material. Stator core (yoke) 56 has inner radius r.sub.A and outer
radius r.sub.B, measured from centerline C.sub.L, and axial length
L, measured along centerline C.sub.L.
[0048] Slots 58 for a Gramme-type single winding (see FIG. 4A) are
formed between teeth 60 on stator core 56. Slots 58 and teeth 60
extend the effective radial dimensions of magnetic stator 38 to
r.sub.A' (inner radius) and r.sub.B' (outer radius). Slots 58 and
teeth 60 also extend axially at either end (i.e., from the front
and back) of stator core 56, increasing the effective axial length
of magnetic stator 38 from L to L'.
[0049] FIG. 3B is a schematic view of magnetic stator 38 with
slotted core 56 for a Gramme winding or double-layer winding
distributed in slots 58. Slots 58 are defined between teeth 60, as
described above.
[0050] In this configuration, slots 58 and teeth 60 do not extend
axially from the front and back of stator core 56, along centerline
C.sub.L. This design allows for magnetic stator 38 to accommodate
either a single Gramme winding (FIG. 4A) or a double-layer winding
(FIG. 4B).
[0051] FIG. 4A is a cross-sectional (end) schematic view of
magnetic stator 38 with polyphase winding 52 spread flat, in a
Gramme winding configuration. In this configuration, a single or
common (Gramme) coil or winding 52 is distributed in slots 58,
extending axially between teeth 60.
[0052] Coil 52 and stator core 56 are spread flat in the end view
of FIG. 4A (with arbitrarily high radius of curvature), in order to
illustrate the structure of magnetic stator 38. For this top
section of stator core 56, radially inward surface 52A of coil
winding 52 is defined along the bottom of stator core 56, and
radially outward surface 52B of coil winding 52 is defined along
the top of stator core 56. For a bottom section, radially inward
and outward surfaces 52A and 52B are reversed (see, e.g., FIG.
2).
[0053] FIG. 4B is a cross-sectional (end) schematic view of
magnetic stator 38, with polyphase winding 52 spread flat, in a
double-layer winding configuration comprising distributed-parameter
coils 52A and 52B. In this configuration, radially inward and
outward coils (or coil surfaces) 52A and 52B are formed as
independent polyphase windings.
[0054] The winding shown in FIG. 4A is referred to a Gramme winding
or Gramme-type coil. In this configuration, the rotational speeds
of the two contra-rotating propellers (or propulsion stages) are
typically the same. Brushes, commutators and other switching
mechanisms are used to determine the direction of field rotation,
or to switch between co-rotating and contra-rotating modes.
[0055] The double-layer winding shown in FIG. 4B is more typical
for the stator of an AC (alternating-current) electrical machine
with distributed parameters. In this configuration, the rational
speeds and directions of each propeller or propulsion stage can be
independently controlled.
[0056] Concentrated-parameter, nonoverlapping coils 52, 52A and 52B
can also be used for magnetic stator 38. Asynchronous operation can
also be utilized to transfer torque between the primary and
secondary rotors, provided that rotors are equipped with
squirrel-cage windings or solid conductive cylinders.
[0057] The slip rate is determined by the difference in stator
field frequency, as compared to the rotating magnetic fields.
Depending on the slip rate and phase, asynchronous operation also
allows for switching between co-rotating and contra-rotating
modes.
[0058] With respect to FIG. 2, the use of PM magnetic elements 50
on rotors 36 and 40 eliminates the need for brushed rotor
couplings, so that magnetic drive 24 has a brushless configuration.
In general, however, magnetic elements 50 have permanent magnet,
cage-type and wound-rotor configurations, and magnetic drive 24
utilizes a variety of brushless, commutator, slip-ring and external
(electronic) switching elements, in both synchronous and
asynchronous modes. This allows magnetic drive 24 to selectively
drive secondary rotor 40 in contra-rotation or co-rotation about
primary rotor 36, or to switch between contra-rotating and
co-rotating modes.
[0059] In additional configurations of magnetic drive 24, a second
copper winding or coil 52 is provided on magnetic stator 38. The
secondary coil is switched to reverse the rotating field direction,
in order to drive secondary drive shaft 44 in either
contra-rotation or co-rotation about primary drive shaft 42.
Primary and secondary rotor stages 12 and 14 thus turn in either
the same or opposite directions, according to the mode selected for
magnetic drive 24.
[0060] Typically, the rotor blades in secondary stage 14 are
oppositely pitched with respect to the rotor blades in primary
stage 12, in order to produce thrust in contra-rotation. When
stages 12 and 14 co-rotate, therefore, secondary stage 14 produces
reverse thrust for braking and ground maneuvers. In some designs,
co-rotating or contra-rotating propulsion stages 12 and 14 are also
provided with variable pitch mechanisms for additional thrust
control and braking capability.
[0061] The number of poles on coil 52 can also selected to drive
propulsion stages 12 and 14 at different speed ratios of, for
example, 1:1, 2:1 or 3:2, and in either contra-rotation or
co-rotation about centerline C.sub.L. Alternatively, windings 52A
and 52B may be de-energized, in order to decouple or disable
secondary propulsion stage 14, for example during cruise
operations. Clutch mechanism 58 may also be provided to decouple
primary propulsion stage 12 from turbine shaft 34, for operation of
propulsion engine 10 to provide cabin power and environmental
control (pre-heat and pre-cool capabilities) during ground
operations.
[0062] Contra- and co-rotation switching and rotor speed control
are fully integrated with the aircraft EEC (electronic engine
control) and FADEC (full authority digital engine control) system
architecture. This provides seamless automated thrust reversal and
rotor speed settings in short landing operations, with enhanced
breaking capability in adverse weather conditions and on slippery
runways. Electrical resistive heating systems 62 may also be used,
in order to prevent unwanted ice and snow accumulation on the blade
leading edges and other surfaces of propulsion rotor stages 12 and
14.
[0063] Magnetic drive system 24 also reduces noise and vibration
levels during operation of propulsion engine 10, as compared to a
planetary or spur gear transmission. In particular, the rotational
coupling mechanism between primary rotor 36 and secondary rotor 40
is magnetic, without torque transfer through highly loaded moving
parts. Propulsion engine 10 also consumes less lubricating oil,
with smaller reservoir requirements for further weight and cost
reductions.
[0064] To achieve these advantages, propulsion engine 10 may be
configured either as a contra-rotating turboprop or contra-rotating
turbofan engine, as described above with respect to FIG. 1.
Alternatively, propulsion engine 10 may be configured as a
contra-rotating turboshaft engine for a rotary-wing aircraft, for
example a heavy-lift helicopter with contra-rotating main rotors,
or for use on a small unmanned aircraft. Propulsion engine 10 can
also be configured as an integrated turbo-ramjet, for use as a high
speed missile propulsion system.
[0065] While this invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the spirit
and scope of the invention. In addition, modifications may be made
to adapt a particular situation or material to the teachings of the
invention, without departing from the essential scope thereof.
Therefore, the invention is not limited to the particular
embodiments disclosed herein, but includes all embodiments falling
within the scope of the appended claims.
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