U.S. patent application number 15/491619 was filed with the patent office on 2017-08-03 for carbon fiber motor rotor integrating propeller mount.
The applicant listed for this patent is X Development LLC. Invention is credited to George Edward Homsy, Damon Vander Lind.
Application Number | 20170218925 15/491619 |
Document ID | / |
Family ID | 55400377 |
Filed Date | 2017-08-03 |
United States Patent
Application |
20170218925 |
Kind Code |
A1 |
Vander Lind; Damon ; et
al. |
August 3, 2017 |
Carbon Fiber Motor Rotor Integrating Propeller Mount
Abstract
A rotor for use with an airborne wind turbine, wherein the rotor
comprises a front flange, a can, a rear flange, and a rigid insert
comprising a propeller mount, wherein the front flange, can, and
rear flange comprise one of carbon fiber and spun aluminum, wherein
a rear end of the front flange is attached to a front end of the
can, and the rear flange is mounted to a rear end of the can,
wherein the rigid insert is bonded to the front flange; and wherein
the rigid insert comprises a tube that axially extends within the
rotor to allow for the positioning of a driveshaft
therethrough.
Inventors: |
Vander Lind; Damon;
(Alameda, CA) ; Homsy; George Edward; (San Rafael,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
X Development LLC |
Mountain View |
CA |
US |
|
|
Family ID: |
55400377 |
Appl. No.: |
15/491619 |
Filed: |
April 19, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14474105 |
Aug 30, 2014 |
9664175 |
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15491619 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64F 3/02 20130101; Y02E
10/728 20130101; B64C 39/024 20130101; F05B 2280/6003 20130101;
Y02E 10/70 20130101; B64C 2201/12 20130101; F05B 2240/921 20130101;
Y02E 10/72 20130101; F03D 9/32 20160501; F03D 1/0666 20130101; F03D
1/0691 20130101; B64C 2201/021 20130101; F05B 2240/923 20130101;
F03D 9/25 20160501; F05B 2280/10 20130101; F03D 5/00 20130101; B64C
39/022 20130101 |
International
Class: |
F03D 9/32 20060101
F03D009/32; B64F 3/02 20060101 B64F003/02; B64C 39/02 20060101
B64C039/02; F03D 5/00 20060101 F03D005/00; F03D 9/25 20060101
F03D009/25 |
Claims
1. An aerial vehicle comprising: a main wing; a rotor connected to
the main wing and a propeller mounted to the rotor; wherein the
rotor comprises: a front flange; a can; a rear flange; and a rigid
insert comprising a propeller mount; wherein the front flange, can,
and rear flange comprise one of carbon fiber and spun aluminum;
wherein a rear end of the front flange is attached to a front end
of the can, and the rear flange is mounted to a rear end of the
can; wherein the rigid insert is bonded to the front flange;
wherein the rigid insert comprises a tube that axially extends
within the rotor to allow for the positioning of a driveshaft
therethrough; and wherein the rotor has a front surface that is
attached to a root of the propeller.
2. The aerial vehicle of claim 1, wherein a front surface of the
front flange is shaped to conform to a shape of a rear surface of
the root of the propeller.
3. The aerial vehicle of claim 1, wherein the rigid insert includes
a nut plate for attachment to the root of the propeller.
4. The aerial vehicle of claim 3, wherein the front surface of the
front flange includes divots around bolt holes in the nut plate to
provide an out-of-plane shape to the front surface of the front
flange.
5. The aerial vehicle of claim 4, wherein the tube is tapered
downwardly as it extends towards the rear flange.
6. The aerial vehicle of claim 1, wherein a locating flange extends
rearwardly from the rear flange for sealing engagement with a
stator positioned on the main wing.
7. The aerial vehicle of claim 1, wherein the rigid insert
comprises a metal.
8. The aerial vehicle of claim 1, wherein the rigid insert
comprises carbon fiber.
9. The aerial vehicle of claim 1, wherein the front flange is
mounted to the front end of the can by bonding to a middle flange
extending forwardly from the front end of the can.
10. The aerial vehicle of claim 1, wherein the front flange has a
conical shape as it tapers outwardly from a front surface of the
front flange to a rear surface of the front flange.
11. The aerial vehicle of claim 5, wherein the driveshaft is bonded
to or press fit to an inner surface of the can.
12. The aerial vehicle of claim 10, wherein the can has a
cylindrical outer surface.
13. A rotor for use with an aerial vehicle wherein the rotor
comprises: a front flange; a can; a rear flange; and a rigid insert
comprising a propeller mount; wherein the front flange, can, and
rear flange comprise one of carbon fiber and spun aluminum; wherein
a rear end of the front flange is attached to a front end of the
can, and the rear flange is mounted to a rear end of the can;
wherein the rigid insert is bonded to the front flange; wherein the
rigid insert comprises a tube that axially extends within the rotor
to allow for the positioning of a driveshaft therethrough; and
wherein the rotor has a front surface that is adapted for
attachment to a root of a propeller.
14. The rotor of claim 13, wherein a front surface of the front
flange is shaped to conform to a shape of a rear surface of the
root of the propeller.
15. The rotor of claim 13, wherein the rigid insert includes a nut
plate for attachment to the root of the propeller.
16. The rotor of claim 15, wherein the front surface of the front
flange includes divots around bolt holes in the nut plate to
provide an out-of-plane shape to the front surface of the front
flange.
17. The rotor of claim 13, wherein the rotor is adapted to receive
a driveshaft that is tapered downwardly towards the rear
flange.
18. The rotor of claim 13, wherein a locating flange extends
rearwardly from the rear flange for sealing engagement with a
stator positioned on a main wing of the aerial vehicle.
19. The rotor of claim 13, wherein the rigid insert comprises
carbon fiber.
20. The rotor of claim 13, wherein the front flange is mounted to
the front end of the can by bonding to a middle flange extending
forwardly from the front end of the can.
21. The rotor of claim 13, wherein the front flange has a conical
shape as it tapers outwardly from a front surface of the front
flange to a rear surface of the front flange.
Description
BACKGROUND
[0001] Unless otherwise indicated herein, the materials described
in this section are not prior art to the claims in this application
and are not admitted to be prior art by inclusion in this
section.
[0002] Power generation systems may convert chemical and/or
mechanical energy (e.g., kinetic energy) to electrical energy for
various applications, such as utility systems. As one example, a
wind energy system may convert kinetic wind energy to electrical
energy.
[0003] The use of wind turbines as a means for harnessing energy
has been used for a number of years. Conventional wind turbines
typically include large turbine blades positioned atop a tower. The
cost of manufacturing, erecting, maintaining, and servicing such
wind turbine towers, and wind turbines is significant.
[0004] An alternative to the costly wind turbine towers that may be
used to harness wind energy is to use an aerial vehicle attached to
a ground station with an electrically conductive tether. Such an
alternative may be referred to as an Airborne Wind Turbine
(AWT).
SUMMARY
[0005] A rotor that may be used on an airborne wind turbine that is
operable in both a power generating mode and in a thrust generating
mode, wherein the rotor serves as a mount for the propeller of the
wind turbine, and is advantageously constructed of a front flange,
a can, a rear flange that are each made of carbon fiber or spun
aluminum with a rigid insert positioned with the front flange that
interfaces with the propeller, wherein the rotor design provides a
lightweight rotor having sufficient strength to serve as rotor
operable in both power generating mode and in thrust generating
mode, and also to serve as a propeller mount.
[0006] An airborne wind turbine system including an aerial vehicle
having a main wing, an electrically conductive tether having a
first end secured to the main wing of the aerial vehicle and a
second end secured to a ground station, a plurality of power
generating turbines connected to the main wing wherein at least one
of the power generating turbines are operable in a power generation
mode and in a thrust generation mode, and includes a propeller
mounted to a rotor, wherein the rotor includes a front flange, a
can, a rear flange, and a rigid insert comprising a propeller
mount, wherein the front flange, can, and rear flange comprise one
of carbon fiber and spun aluminum, wherein a rear end of the front
flange is attached to a front end of the can, and the rear flange
is mounted to a rear end of the can, wherein the rigid insert is
bonded to the front flange, and wherein the rigid insert comprises
a tube that axially extends within the rotor to allow for the
positioning of a driveshaft therethrough.
[0007] In another aspect, a rotor is provided for use with an
airborne wind turbine system wherein the rotor comprises a front
flange, a can, a rear flange, and a rigid insert comprising a
propeller mount, wherein the front flange, can, and rear flange
comprise one of carbon fiber or spun aluminum, wherein a rear end
of the front flange is attached to a front end of the can, and the
rear flange is mounted to a rear end of the can, wherein the rigid
insert is bonded to the front flange; and wherein the rigid insert
comprises a tube that axially extends within the rotor to allow for
the positioning of a driveshaft therethrough
[0008] In another aspect, a means for providing rotor with an
integrated propeller mount is provided.
[0009] These as well as other aspects, advantages, and
alternatives, will become apparent to those of ordinary skill in
the art by reading the following detailed description, with
reference where appropriate to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of an airborne wind turbine 10
including aerial vehicle 20 attached to a ground station 50 with an
electrically conductive tether 30, according to an example
embodiment.
[0011] FIG. 2 is a close-up perspective view of aerial vehicle 20
shown in FIG. 1.
[0012] FIG. 3 is a side view of aerial vehicle 120 perched on perch
panel 160 attached to ground station 150, according to an example
embodiment.
[0013] FIG. 4 is a top view of the aerial vehicle 120 and ground
station 150 shown in FIG. 3, according to an example
embodiment.
[0014] FIG. 5 is a front view of airborne wind turbine assembly 240
including a propeller 247 attached to a rotor 300, according to an
example embodiment.
[0015] FIG. 6 is a top view of the wind turbine assembly 240 shown
in FIG. 5.
[0016] FIG. 7 is a close up rear perspective view of the wind
turbine assembly 240 shown in FIGS. 5 and 6.
[0017] FIG. 8 is a top view of rotor 300 of wind turbine 240 shown
in FIGS. 5-7, according to an example embodiment.
[0018] FIG. 9 is a front perspective view of rotor 300 shown in
FIGS. 5-8, according to an example embodiment.
[0019] FIG. 10 is a cross-sectional view of rotor 300 shown in
FIGS. 5-9, according to an example embodiment.
DETAILED DESCRIPTION
[0020] Example methods and systems are described herein. Any
example embodiment or feature described herein is not necessarily
to be construed as preferred or advantageous over other embodiments
or features. The example embodiments described herein are not meant
to be limiting. It will be readily understood that certain aspects
of the disclosed systems and methods can be arranged and combined
in a wide variety of different configurations, all of which are
contemplated herein.
[0021] Furthermore, the particular arrangements shown in the
Figures should not be viewed as limiting. It should be understood
that other embodiments may include more or less of each element
shown in a given Figure. Further, some of the illustrated elements
may be combined or omitted. Yet further, an example embodiment may
include elements that are not illustrated in the Figures.
1. OVERVIEW
[0022] Example embodiments relate to aerial vehicles, which may be
used in a wind energy system, such as an Airborne Wind Turbine
(AWT). In particular, illustrative embodiments may relate to or
take the form of methods and systems using an airborne vehicle that
is attached to a ground station using an electrically conductive
tether.
[0023] Wind energy systems, such as an AWT, may be used to convert
wind energy to electrical energy. An AWT is a wind based energy
generation device that may include an aerial vehicle constructed of
a rigid wing with mounted turbines. The aerial vehicle may be
operable to fly in a path across the wind, such as a substantially
circular path above the ground (or water) to convert kinetic wind
energy to electrical energy. In such cross wind flight, the aerial
vehicle flies across the wind in a circular pattern similar to the
tip of a wind turbine. The rotors attached to the rigid wing may be
used to generate power by slowing the wing down. In particular, air
moving across the turbine blades may force the blades to rotate,
driving a generator to produce electricity. The aerial vehicle may
also be connected to a ground station via an electrically
conductive tether that transmits power generated by the aerial
vehicle to the ground station, and on to the grid.
[0024] When it is desired to land the aerial vehicle, the
electrically conductive tether is wound onto a spool or drum in the
ground station and the aerial vehicle is reeled in towards a perch
on the ground station. Prior to landing on the perch, the aerial
vehicle transitions from a flying mode to a hover mode. The drum is
further rotated to further wind the tether onto the drum until the
aerial vehicle comes to rest on the perch.
[0025] As noted above, a plurality of mounted turbines may be
secured to the main wing and may be used to generate electricity in
power generation mode, or provide thrust in hover mode or in a
powered flying mode of operation. The turbines include propellers
having a plurality of turbine blades that are secured to the rotor,
or rotating portion of the turbine which is in turn secured to a
rotating shaft, that in power generation mode is used to drive the
generator to produce energy.
[0026] When the turbine blades on the propeller are rotated during
thrust generating mode or powered flying mode, the turbine is
connected to a motor/generator having a rotor and stator. The
factors that drive motor torque have primarily to do with the
fineness and diameter of the motor design. A thin and large
diameter stator and rotor will produce the most torque, but have
the drawback of requiring a significant amount of structural
rigidity and strength to hold a consistent gap width between the
electrical rotor and electrical stator, or to hold sufficient
roundness.
[0027] There are different ways to approach this problem. For
example, in-runner and out-runner motors may be built. Axial or
transverse flux machines also offer other advantages for simplicity
of structure. In each case, the common problem tends to be that the
material which is being used to hold the rotor and whatever the
motor is driving (e.g., a propeller) is often sparse or thin, and
thus either needs to be extremely thin and not very stiff (i.e.
steel), or made of a material with poor fatigue properties (i.e.
aluminum). Further the electrical rotor (magnets and back-iron) are
often supported by separate bearings from the load to be propelled,
in this case a propeller. While convenient for the sake of
compartmentalization, the use of separate bearings results in a
significantly heavier and more complex system.
[0028] An aluminum casting could be used for the rotor which
includes a propeller mount. However, the fatigue properties of
aluminum are poor, thereby requiring a larger structure to
accommodate fatigue resulting from the gyroscopic loads experienced
by the rotor during operation of the AWT. An equivalent rotor
design where the rotor is made of an aluminum casting would weigh
around 4 kilograms, a heavy component for a rotating rotor used on
an AWT where excess weight is undesirable. Furthermore, a rotor
made from a casting has other drawbacks as well including porosity,
the possibility of voids in the casting, and susceptibility to
cracking. As a result, it would be desirable to provide a rotating
motor rotor that serves as a propeller mount on the AWT that
provides improvements over an aluminum casting rotor design.
[0029] In an example embodiment, an aerial vehicle is provided
having a plurality turbines mounted to vertically extending pylons
on the main wing. Each turbine includes a rotor that may also serve
as a mount for the propeller, which has a plurality of turbine
blades. In alternate embodiments, the propeller may attach by clips
or bolts at the diameter of the rotor. The present embodiments
advantageously include a rotor constructed of a number of carbon
fiber components that may be used in place of the aluminum casting
of the prior design, and that may be used as a mount for the
propeller. Alternately, the components could be formed of spun
aluminum.
[0030] In an exemplary embodiment, the rotor is comprised of three
primary elements that are constructed from carbon fiber. The three
primary elements include a front flange, a central cylindrical can
or shell, and a rear flange which are each made of carbon fiber.
The design advantageously creates an open space by joining together
the two flanges at the bearing so that there is a hollow space.
Gussets are not required providing for an improvement in fatigue
properties.
[0031] In operation, the rotor is a hollow member that may have
permanent magnets mounted to inside of the periphery of the central
can or shell. A stationary stator may be positioned within the
central shell having coils and power electronics that cooperate
with the permanent magnets to rotate the rotor.
[0032] The propeller of the turbine may be mounted to the front
flange of the rotor. It should be noted that the front surface of
the front flange may be shaped to closely match the shape of the
propeller root, removing the need for any substantive metal fixture
to mount the propeller. Such a mounting also conveys the torque
directly from the propeller to the electromagnetic rotor, and thus
may avoid putting any torque through the central driveshaft which
is secured to the rotor. An alternate design could be used to
attach the propeller at the diameter of the rotor which could allow
for the use of smaller bolts.
[0033] The front flange may be advantageously bonded to the central
can or shell at the time of assembly, while the rear flange may be
bolted onto the can or shell, such that the rotor may still be
removed from the stator. The rear flange attachment has the added
advantage of both stiffening the central can or shell, and allowing
an interface which further stiffens the shell through attachment to
the rear flange. A number of bolts or clamping elements may be used
around the rim of the can or shell to attach the rear flange. The
mold surface of the front flange points forward so as to have a
clean interface for attachment to the propeller. All three carbon
fiber parts may be easily made through autoclave, bladder molding,
vacuum bagging, infusion, or other single side production
methods.
[0034] A metal insert may be placed in the front flange, which may
be a cast insert that is used to stiffen the joint between the
front flange at the area where it mates to the propeller. In
alternate designs, the metal insert might be replaced with a foam
or low density wood insert, or might be replaced with another
carbon fiber element that resolves the out of plane stresses
occurring between the mounting face of the propeller, and the
remainder of the front flange. The front flange is bonded to the
central can or shell which blends to a cylindrical cross section.
The front flange may be bonded to the central shell in the area of
this blend.
[0035] A main steel driveshaft may be bonded to, or press fit into,
the can or shell, which provides the most accurate reference of the
shell to the shaft and thus minimizes error in the gap on the
electromagnetic device, i.e., the gap between the permanent magnets
on the rotor and the coils on the stator. The steel shaft may be
tapered downwardly as it extends towards the rear flange so that
the rear bearing and rear part of the shaft are no heavier than
needed, while the front bearing and shaft may be sufficiently large
to resolve both the bending and side force generated by the
combination of propeller and motor. The bearings may be tapered
roller bearings but may also be cup-and-cone style bearings, or
deep groove cartridge ball bearings, or spherical roller
bearings.
[0036] A main driveshaft may be constructed of steel primarily to
avoid high bearing mass. Because long life bearings do not have
large diameters, a steel material is desirable which handles high
mohr stress, has good fatigue resistance, which is compact, and
which can be shaped with high fidelity to meet the tolerances of a
set of bearings. Because long life bearings tend to have large
rolling elements they are either quite heavy or have relatively
small inner diameters. Steel allows all of these constraints to be
met, while keeping the bearing diameter small and thus allowing
long life bearings. However, a carbon fiber shaft could also be
used, or titanium or other materials could be used for the shaft.
In the exemplary embodiment, steel is used as it is quite practical
to work with.
[0037] The carbon fiber rotor design described above advantageously
provides a rotor with superior fatigue properties compared to an
aluminum casting rotor design. In addition, the carbon fiber rotor
design only weighs 800 grams, providing significant weight
reduction advantages, particularly when considering AWT designs,
where 8 or more such rotors may be used. As a result, a weight
reduction of over 25 kilograms may be achieved using the carbon
fiber rotor design described above.
2. ILLUSTRATIVE AIRBORNE WIND TURBINES
[0038] As disclosed in FIGS. 1-2, an airborne wind turbine (AWT) 10
is disclosed, according to an example embodiment. AWT 10 is a wind
based energy generation device that includes an aerial vehicle 20
constructed of a rigid wing 22 with mounted turbines 40 that flies
in a path, such as a substantially circular path, across the wind.
In an example embodiment, the aerial vehicle may fly between 250
and 600 meters above the ground (or water) to convert kinetic wind
energy to electrical energy. However, an aerial vehicle may fly at
other heights without departing from the scope of the invention. In
the cross wind flight, the aerial vehicle 20 flies across the wind
in a circular pattern similar to the tip of a wind turbine. The
rotors 40 attached to the rigid wing 22 are used to generate power
by slowing the wing 22 down. Air moving across the turbine blades
forces them to rotate, driving a generator to produce electricity.
The aerial vehicle 20 is connected to a ground station 50 via an
electrically conductive tether 30 that transmits power generated by
the aerial vehicle to the ground station 50, and on to the
grid.
[0039] As shown in FIG. 1, the aerial vehicle 20 may be connected
to the tether 30, and the tether 30 may be connected to the ground
station 50. In this example, the tether 30 may be attached to the
ground station 50 at one location on the ground station 50, and
attached to the aerial vehicle 20 at three locations on the aerial
vehicle 2 using bridle 32a, 32b, and 32c. However, in other
examples, the tether 30 may be attached at multiple locations to
any part of the ground station 50 and/or the aerial vehicle 20.
[0040] The ground station 50 may be used to hold and/or support the
aerial vehicle 20 until it is in an operational mode. The ground
station may include a tower 52 that may be on the order of 15
meters tall. The ground station may also include a drum 52
rotatable about drum axis 53 that is used to reel in aerial vehicle
20 by winding the tether 30 onto the rotatable drum 52. In this
example, the drum 52 is oriented vertically, although the drum may
also be oriented horizontally (or at an angle). Further, the ground
station 50 may be further configured to receive the aerial vehicle
20 during a landing. For example, support members 56 are attached
to perch panels 58 that extend from the ground station 50. When the
tether 30 is wound onto drum 52 and the aerial vehicle 20 is reeled
in towards the ground station 50, the aerial vehicle may come to
rest upon perch panels 58. The ground station 50 may be formed of
any material that can suitably keep the aerial vehicle 20 attached
and/or anchored to the ground while in hover flight, forward
flight, or crosswind flight. In some implementations, ground
station 50 may be configured for use on land. However, ground
station 50 may also be implemented on a body of water, such as a
lake, river, sea, or ocean. For example, a ground station could
include or be arranged on a floating off-shore platform or a boat,
among other possibilities. Further, ground station 50 may be
configured to remain stationary or to move relative to the ground
or the surface of a body of water.
[0041] The tether 30 may transmit electrical energy generated by
the aerial vehicle 20 to the ground station 50. In addition, the
tether 30 may transmit electricity to the aerial vehicle 20 in
order to power the aerial vehicle 20 during takeoff, landing, hover
flight, and/or forward flight. The tether 30 may be constructed in
any form and using any material which may allow for the
transmission, delivery, and/or harnessing of electrical energy
generated by the aerial vehicle 20 and/or transmission of
electricity to the aerial vehicle 20. The tether 30 may also be
configured to withstand one or more forces of the aerial vehicle 20
when the aerial vehicle 20 is in an operational mode. For example,
the tether 30 may include a core configured to withstand one or
more forces of the aerial vehicle 20 when the aerial vehicle 20 is
in hover flight, forward flight, and/or crosswind flight. The core
may be constructed of any high strength fibers or a carbon fiber
rod. In some examples, the tether 30 may have a fixed length and/or
a variable length. For example, in one example, the tether has a
fixed length of 500 meters.
[0042] The aerial vehicle 20 may include or take the form of
various types of devices, such as a kite, a helicopter, a wing
and/or an airplane, among other possibilities. The aerial vehicle
20 may be formed of solid structures of metal, plastic and/or other
polymers. The aerial vehicle 20 may be formed of any material which
allows for a high thrust-to-weight ratio and generation of
electrical energy which may be used in utility applications.
Additionally, the materials may be chosen to allow for a lightning
hardened, redundant and/or fault tolerant design which may be
capable of handling large and/or sudden shifts in wind speed and
wind direction. Other materials may be possible as well.
[0043] As shown in FIG. 1, and in greater detail in FIG. 2, the
aerial vehicle 20 may include a main wing 22, rotors 40a and 40b,
tail boom or fuselage 24, and tail wing 26. Any of these components
may be shaped in any form which allows for the use of components of
lift to resist gravity and/or move the aerial vehicle 20
forward.
[0044] The main wing 22 may provide a primary lift for the aerial
vehicle 20. The main wing 22 may be one or more rigid or flexible
airfoils, and may include various control surfaces, such as
winglets, flaps, rudders, elevators, etc. The control surfaces may
be used to stabilize the aerial vehicle 20 and/or reduce drag on
the aerial vehicle 20 during hover flight, forward flight, and/or
crosswind flight. The main wing 22 may be any suitable material for
the aerial vehicle 20 to engage in hover flight, forward flight,
and/or crosswind flight. For example, the main wing 20 may include
carbon fiber and/or e-glass.
[0045] Rotor connectors 43 may be used to connect the upper rotors
40a to the main wing 22, and rotor connectors 41 may be used to
connect the lower rotors 40b to the main wing 22. In some examples,
the rotor connectors 43 and 41 may take the form of or be similar
in form to one or more pylons. In this example, the rotor
connectors 43 and 41 are arranged such that the upper rotors 40a
are positioned above the wing 22 and the lower rotors 40b are
positioned below the wing 22.
[0046] The rotors 40a and 40b may be configured to drive one or
more generators for the purpose of generating electrical energy. In
this example, the rotors 40a and 40b may each include one or more
blades 45, such as three blades. The one or more rotor blades 45
may rotate via interactions with the wind and which could be used
to drive the one or more generators. In addition, the rotors 40a
and 40b may also be configured to provide a thrust to the aerial
vehicle 20 during flight. With this arrangement, the rotors 40a and
40b may function as one or more propulsion units, such as a
propeller. Although the rotors 40a and 40b are depicted as four
rotors in this example, in other examples the aerial vehicle 20 may
include any number of rotors, such as less than four rotors or more
than four rotors, e.g. six or eight rotors.
[0047] Referring back to FIG. 1, when it is desired to land the
aerial vehicle 20, the drum 52 is rotated to reel in the aerial
vehicle 20 towards the perch panels 58 on the ground station 50,
and the electrically conductive tether 30 is wound onto drum 52.
Prior to landing on the perch panels 58, the aerial vehicle 20
transitions from a flying mode to a hover mode. The drum 52 is
further rotated to further wind the tether 30 onto the drum 52
until the aerial vehicle 20 comes to rest on the perch panels
58.
[0048] FIG. 3 is a side view of an airborne wind turbine including
aerial vehicle 120 perched on perch panel 176 attached to ground
station 150, and FIG. 4 is a top view of the aerial vehicle 120 and
ground station 150 shown in FIG. 3, according to an example
embodiment. In FIGS. 3 and 4, ground station 150 includes a tower
152 upon which rotatable drum 180 is positioned, with perch panel
extensions 170 and 172 extending outwardly and attached to perch
panel 176. In an embodiment, the tower 152 may be 15 meters in
height. An electrically conductive tether 130 extends from the
levelwind 160 and is attached to wing 122 of aerial vehicle 120
using bridle lines 132a, 132b, and 132c. In one embodiment the
bridle lines 132a, 132b, and 132c may be attached at asymmetric
locations along the span of the wing 122, such that the inboard
side of wing 122 has the bridle attached further from the wingtip,
and the outboard side of the wing 122 has the bridle attached
closer to the outboard wingtip. Such an asymmetric configuration
allows the bridle lines 132a and 132c to better clear a larger
sized perch panel.
[0049] Aerial vehicle 120 includes lower rotors 140a, 140c, 140e,
and 140g mounted on lower pylons 143 attached to wing 122 and upper
rotors 140b, 140d, 140f, and 140g mounted on upper pylons 143
attached to wing having propellers 145. In an embodiment, wing 122
is 4 meters long and includes fuselage 124 and rear elevator mount
126.
3. EXAMPLE EMBODIMENT OF CARBON FIBER ROTOR WITH INTEGRATED
PROPELLER MOUNT
[0050] FIGS. 5-10 illustrated an example embodiment of a carbon
fiber rotor having an integrated propeller mount. In particular,
FIG. 5 is a front view of airborne wind turbine assembly 240 having
propeller 247 having turbine blades 245 mounted to rotor 300. FIG.
6 is a top view of airborne wind turbine assembly 240 showing the
propeller 247 mounted to front flange 310 of rotor 300. Rotor 300
is positioned on the rear side of the propeller 247, and the rotor
300 includes front flange 310, central can or shell 320, and rear
flange 330 having rearwardly extending circular locating flange
332.
[0051] FIG. 7 is a close up rear perspective view of airborne wind
turbine assembly 240 showing propeller 247 mounted to rotor 300,
where rear flange 330 is shown attached to can or shell 320. A
circular locating flange 332 is shown extending rearwardly from the
rear flange 330 where it may sealingly engage a stator (not shown).
A main driveshaft 340 is shown extending through the rear flange
330 and locating flange 332. As noted above, the propeller 247 is
mounted to a front end of the carbon fiber rotor 300 where it is
mounted to front flange 310 of the rotor 300, which is in turn
bonded to the main driveshaft 340. As shown in FIGS. 9 and 10, the
front flange 310 is also bonded to a metal insert 350 which
distributes load.
[0052] FIGS. 8-10 show details of the rotor 300 shown in FIGS. 5-7.
FIG. 8 is a top view of rotor 300 shown in FIGS. 5-7, with front
flange 310 shown as semi-transparent. Rotor 300 includes a metal
insert 350 that may be a cast insert that is used to stiffen the
joint between the front surface of front flange 310 and the
interface with the root of propeller 247. Metal insert 350 may be
bonded to the front flange 310 and may include a nut plate 354 that
is used for mounting to the propeller 247, and a hollow cylindrical
portion 352 that extends rearwardly from the front surface 314 of
front flange and positioned about the main driveshaft 340 (shown in
FIGS. 7 and 8) to provide increased strength and distribute
load.
[0053] In alternate designs, the metal insert 350 might be replaced
with a foam or low density wood insert, or might be replaced with
another carbon fiber element that resolves the out of plane
stresses occurring between the mounting face of the propeller, and
the remaining conical section of the front flange 310 that extends
from the front surface 314 of the front flange to the middle flange
322 of the central can or shell 320. The front flange 310 may be
bonded to the can or shell 320 which blends to a cylindrical cross
section, inside of which the motor rotor is bonded or press fit.
The front flange 310 is bonded to the can or shell 320 in the area
of this blend at middle flange 322 (discussed further below).
[0054] FIG. 9 is a perspective rear view of rotor 300, again with
front flange 310 shown as semi-transparent. FIG. 10 is a
cross-sectional view of rotor 300. Metal insert 350 is shown with
nut plate 354 positioned in front face 314 of front flange 310, and
with hollow cylindrical section 352 extending within rotor 300
towards rear flange 330. Rear flange 330 is mounted to the central
can or shell 320, where a periphery 334 of rear flange 330 may
extend beyond the diameter of central can or shell 320.
[0055] The main steel driveshaft 340 may be bonded to, or press fit
into, the rotor along inner surfaces 364, 362, and 360 within the
rotor, which provides the most accurate reference of the shell 320
to the shaft and thus minimizes error in the gap on the
electromagnetic device, i.e., the gap between the permanent magnets
on the rotor 300 and the coils on the stator. As shown here, the
steel driveshaft 340 may be tapered downwardly to conform to
surface 360 as it extends towards the rear flange 330 so that the
rear bearing and rear part of the shaft are no heavier than needed,
while the front bearing and shaft may be sufficiently large to
resolve both the bending and side force generated by the
combination of propeller and motor. The bearings (not shown) may be
tapered roller bearings but may also be cup-and-cone style
bearings, or deep groove cartridge ball bearings, or spherical
roller bearings.
[0056] In an exemplary embodiment, the rotor 300 is comprised of
three primary elements that are constructed from carbon fiber. The
three primary elements include the front flange 310, a cylindrical
central can or shell 320, and a rear flange 330 which are each made
of carbon fiber. The front flange 310 may be bonded to the can 320
at the time of assembly, and the can 320 may include a middle
flange 322 to provide a surface for bonding with the front flange
310.
[0057] The rear flange 330 may be bolted onto the can or shell 320,
allowing the rotor to be removed from the stator (not shown). The
attachment of the rear flange 330 to the can 320 provides the added
advantage of both stiffening the can or shell 320, and allowing an
interface which further stiffens the can or shell 320 through
attachment to the rear flange 330. A number of bolts or clamping
elements may be used around the rim of the can or shell 320 to
attach the rear flange 330. The mold surface of the front flange
310 may point forward to provide a clean attachment to the root of
the propeller 247. All three carbon fiber elements discussed above
may be easily made through autoclave, bladder molding, vacuum
bagging, infusion, or other single side production methods.
[0058] The main driveshaft may be constructed of steel primarily to
avoid high bearing mass. Because long life bearings do not have
large diameters, a material is required which handles high mohr
stress, has good fatigue resistance, which is compact, and which
can be shaped with high fidelity to meet the tolerances of a set of
bearings. Because long life bearings tend to have large rolling
elements they are either quite heavy or have relatively small inner
diameters. The use of steel for the main driveshaft allows all of
these constraints to be met, while keeping the bearing diameter
small and thus allowing long life bearings.
[0059] Furthermore, the main driveshaft can be press fit in the
normal way relative to the inner surfaces 364, 362, and 360, if
desired. An appropriate driveshaft material may be 17-4 stainless
steel, although there are other appropriate materials. In some
embodiments, a titanium shaft might be used. When using titanium,
it is more likely the shaft would not be tapered. As shown in the
cross-sectional view shown in FIG. 10, when using a main shaft, the
shaft 340 may be tapered to optimize stiffness relative to mass. In
a titanium design, a constant cross section shaft might be more
likely given availability of materials.
[0060] Referring back to FIG. 7, rotor 300 is shown mated together
with propeller 247 in a flight configuration. Only the rotor 330
part of the motor is shown, showing the cylindrical central can or
shell 320, the front flange 310 (facing away in this image), and
the rear flange 330 (shown in the foreground in this image). The
rotor comprise a front flange 310, can or shell 320, and rear
flange 330 in order to have a sufficiently stiff structure between
the steel driveshaft 340 to the electromagnetic rotor. In this
embodiment, the rear flange 330 includes a rearwardly extending
circular flange 332 positioned about the driveshaft 340 that is
used to reduce the diameter of the rear seal, which seals the rear
flange 330 against the stator (not shown), and thus reduce both the
size and speed of the seal so as to increase its life while also
reducing the required size of the stator, which might be of a cast
material. Because the rotor 300 sees much higher fatigue stresses
than the stator, the three parts of the rotor may be made of
carbon-fiber-reinforced polymer ("CFRP"), which is both very stiff
and very resistant to fatigue.
[0061] The present embodiments advantageously include a rotor 300
constructed of a number of carbon fiber components that may be used
in place of the aluminum casting of the prior design, and that may
be used as a mount for the propeller. In particular, the propeller
247 mounts to a carbon fiber front flange 310, which in turn is
bonded to a main driveshaft 340 and a metal insert 350 which
distributes load. It should be noted that the front surface 314 of
the front flange 310 is shaped to closely match the propeller root,
removing the need for any substantive metal fixture to mount the
propeller 247. This also conveys the torque directly from the
propeller 247 to the electromagnetic rotor 300, and thus helps to
avoid putting any torque through the central driveshaft 340.
[0062] Referring back to the cross-sectional view shown in FIG. 10,
the cylindrical can 320 and middle flange 322 attached thereto are
made as a single part on an aluminum male mandrel. This allows the
part to be demolded after construction. The front flange 310 may be
bonded to the metal insert 350, and the front flange 310 also has a
front surface 314 that conforms to the contours of the propeller
shape. The features or divots around the bolt holes in the nut
plate 354 may be used to transfer shear because carbon on carbon
surfaces are relatively poor in both compression (in particular
through-thickness) and shear load transfer (again, in particular
through-thickness). The molded surface on the front flange 310 is
the front surface 314, so that it can mate to the propeller 247
appropriately. Therefore, the non-mold surface of the front flange
310 may be bonded to the non-mold surface of the middle flange 322
of the cylindrical can 320, wherein a bonding jig may be
required.
[0063] In addition, the mold surface of the middle flange 322 and
can 320 may be the inside surface so that the fit of the can 320 to
the permanent magnets within the motor rotor is clean, and may not
require an epoxy or glue, as it could be press fit.
[0064] The rear flange 330 to can 320 mating surface may be a
simple rolled out surface that is molded both as part of the
can/middle flange 320/322 and, as a matching surface on the rear
flange 330, allowing the rear flange 330 to be accurately mounted.
The rearwardly extending circular flange 332 of rear flange 330 may
be used to locate a seal for sealing engagement with a stator (not
shown). Therefore, all structure and wiring and cooling must route
inside the diameter of the circular flange 332 on the motor. The
carbon fiber rotor design described above advantageously provides a
rotor with superior fatigue properties compared to the prior
aluminum casting rotor design. In addition, the carbon fiber rotor
design only weighs 800 grams, providing significant weight
reduction advantages, particularly when considering AWT designs,
where 8 or more such rotors may be used. As a result, a weight
reduction of over 25 kilograms may be achieved using the carbon
fiber rotor design described above.
[0065] While the above embodiments have been described in
connection with the front flange, can or shell, and rear flange
comprised of carbon fiber, in an alternate embodiment, those
components may be made of spun aluminum. The spun aluminum
components may be bonded or stir welded together, and a CNC bracket
used for mounting to the driveshaft. When using either carbon fiber
of aluminum components, the present design advantageously utilizes
a hollow space to create a very strong structure out of sheet
elements. Carbon fiber is one very appropriate material for such
elements, and spun aluminum is also an appropriate material. While
the fatigue strength of aluminum is not superior, the configuration
allows enough efficiency in the layout of the structure to keep the
loads very low. Both a carbon fiber design and a spun aluminum
design provide lower weight advantages over an equivalent design
using a cast aluminum rotor design.
4. CONCLUSION
[0066] The above detailed description describes various features
and functions of the disclosed systems, devices, and methods with
reference to the accompanying figures. While various aspects and
embodiments have been disclosed herein, other aspects and
embodiments will be apparent to those skilled in the art. The
various aspects and embodiments disclosed herein are for purposes
of illustration and are not intended to be limiting, with the true
scope and spirit being indicated by the following claims.
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