U.S. patent application number 09/767965 was filed with the patent office on 2002-07-25 for harmonic drive system for the retraction/extension of variable diameter rotor systems.
This patent application is currently assigned to Sikorsky Aircraft Corporation. Invention is credited to Gmirya, Yuriy.
Application Number | 20020098087 09/767965 |
Document ID | / |
Family ID | 25081108 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020098087 |
Kind Code |
A1 |
Gmirya, Yuriy |
July 25, 2002 |
HARMONIC DRIVE SYSTEM FOR THE RETRACTION/EXTENSION OF VARIABLE
DIAMETER ROTOR SYSTEMS
Abstract
A drive system for a variable diameter rotor system includes a
plurality of rotor blade assemblies with inner and outer blade
segments. The outer blade segment being telescopically mounted to
the inner blade segment. The VDR retraction/extension system
includes a reeling system driven by a harmonic gear system. The
reeling system includes a strap drum for winding and unwinding a
strap attached to the outer blade segments. In operation, a control
shaft drives the wave generator at a higher or lower rotational
speed relative to a main rotor drive shaft assembly thereby causing
the wave generator to rotate relative to the rotor hub assembly. In
turn, the wave generator causes the external flex gear teeth to
sequentially engage the ring gear internal gear teeth as the wave
generator rotates within the flex gear. As the flex gear is mounted
to the strap drum, the differential rotation between the flex gear
and ring gear causes the strap drum to rotate relative the rotor
hub assembly. Rotation of the strap drum thereby causes the strap
to be wound about or off of the drum and, consequently, effecting
retraction/extension of each VDR blade assembly.
Inventors: |
Gmirya, Yuriy; (Rego Park,
NY) |
Correspondence
Address: |
David L. Wisz
Carlson, Gaskey & Olds, P.C.
Suite 350
400 W. Maple
Birmingham
MI
48009
US
|
Assignee: |
Sikorsky Aircraft
Corporation
|
Family ID: |
25081108 |
Appl. No.: |
09/767965 |
Filed: |
January 23, 2001 |
Current U.S.
Class: |
416/87 |
Current CPC
Class: |
B64C 29/0033 20130101;
Y10T 74/19 20150115; B64C 27/473 20130101; B64C 11/28 20130101 |
Class at
Publication: |
416/87 |
International
Class: |
B64C 011/28 |
Goverment Interests
[0001] This invention was made with government support under
Contract No.: DABT63-99-3-0002 awarded by the Department of the
Army. The government therefore has certain rights in this
invention.
Claims
What is claimed is:
1. A retraction/extension system for a variable diameter rotor
blade system having a rotor hub and a multiple of rotor blade
assemblies, each of said rotor blade assemblies having an outboard
blade section telescopically mounted to an inboard blade section,
said system comprising: a reeling assembly including attached to
each of said outboard blade sections; and a harmonic gear system
for driving said reeling assembly to effect telescopic transition
of each of the outboard blade section relative to each inboard
blade section.
2. The system as recited in claim 1, further comprising a main
rotor shaft attached to the rotor hub and a control shaft attached
to said harmonic gear system, said control shaft coaxially mounted
within said main rotor shaft along a first axis, said control shaft
rotatable relative to said main rotor shaft to selectively drive
said harmonic gear system.
3. The system as recited in claim 1, wherein said harmonic gear
system includes a ring gear attached to the rotor hub.
4. The system as recited in claim 1, wherein said reeling assembly
includes a strap drum to windingly extend and retract a drive strap
attached to the outboard blade section.
5. The system as recited in claim 4, wherein said harmonic gear
system includes a flexible gear attached to said strap drum.
6. The system as recited in claim 4, further comprising a constant
velocity joint mounted to a control shaft, said strap drum mounted
through a bearing to said constant velocity joint.
7. The system as recited in claim 4, wherein said harmonic gear
system includes a wave generator mounted to said strap drum.
8. The system as recited in claim 1, wherein said harmonic gear
system includes, a ring gear attached to the rotor hub; a flex gear
mounted to said reeling assembly; and a wave generator rotatable
within said flex gear, rotation of said wave generator causing
rotation of said flex gear relative to said ring gear to drive said
reeling assembly.
9. The system as recited in claim 8, further comprising a main
rotor shaft attached to the rotor hub and a control shaft attached
to said wave genitor, said control shaft coaxially mounted within
said main rotor shaft along a first axis, said control shaft
rotatable relative to said main rotor shaft to selectively drive
said wave generator.
10. A retraction/extension system for a variable diameter rotor
blade system having a rotor hub and a multiple of rotor blade
assemblies, each of said rotor blade assemblies having an outboard
blade section telescopically mounted to an inboard blade section,
said system comprising: a reeling assembly including a strap drum
for driving a strap attached to each of said outboard blade
sections; a ring gear attached to the rotor hub; a flex gear
mounted to said strap drum; and a wave generator rotatable within
said flex gear, rotation of said wave generator causing rotation of
said flex gear relative to said ring gear to drive said strap drum
and effect telescopic transition of each of said outboard blade
section relative to each inboard blade section.
11. The system as recited in claim 10, further comprising a main
rotor shaft attached to the rotor hub and a control shaft attached
to said harmonic gear system, said control shaft coaxially mounted
within said main rotor shaft along a first axis, said control shaft
rotatable relative to said main rotor shaft to selectively drive
said wave generator.
12. The system as recited in claim 10, further comprising a
constant velocity joint mounted to said control shaft, said strap
drum mounted through a bearing to said constant velocity joint.
13. The system as recited in claim 10, further comprising a bearing
assembly between said wave generator and said flex gear.
14. The system as recited in claim 10, wherein said wave generator
includes an elliptical plate-like member.
14. The system as recited in claim 10, wherein said wave generator
includes a rotatable arm having a circular bearing rotatably
mounted at each end of said rotatable arm.
15. The system as recited in claim 10, wherein said ring gear
includes a plurality of ring gear teeth along an inner diameter of
said ring gear and said flex gear includes a plurality of flex gear
teeth along an outer diameter of said flex gear, said plurality or
ring gear teeth being greater than said plurality of flex gear
teeth.
16. The system as recited in claim 15, wherein said plurality of
ring gear teeth engage said plurality of flex gear teeth at equally
spaced locations apart on their respective circumferences.
17. A variable diameter rotor blade system, comprising: a rotor hub
having a multiple of rotor blade assemblies, each of said rotor
blade assemblies having an outboard blade section telescopically
mounted to an inboard blade section; a main rotor shaft for driving
said rotor hub, said min rotor shaft defining a first axis; a
control shaft mounted along said first axis coaxially with said
main rotor shaft; a reeling assembly including a strap drum for
winding and unwinding a strap attached to each of said outboard
blade sections; a ring gear attached to said rotor hub; a flex gear
mounted to said strap drum; and a wave generator attached to said
control shaft, said control shaft rotatable relative to said main
rotor shaft such that said wave generator is rotatable within said
flex gear, rotation of said wave generator causing rotation of said
flex gear relative to said ring gear to drive said strap drum and
effect telescopic transition of each of said outboard blade section
relative to each inboard blade section.
18. The system as recited in claim 17, wherein said ring gear
includes a plurality of ring gear teeth along an inner diameter of
said ring gear and said flex gear includes a plurality of flex gear
teeth along an outer diameter of said flex gear, said plurality or
ring gear teeth being greater than said plurality of flex gear
teeth.
19. The system as recited in claim 18, wherein said plurality of
ring gear teeth engage said plurality of flex gear teeth at equally
spaced locations apart on their respective circumferences.
20. The system as recited in claim 17, further comprising a
constant velocity joint mounted to said control shaft, said strap
drum mounted through a bearing to said constant velocity joint.
Description
BACKGROUND OF THE INVENTION
[0002] The present invention provides a drive system for a variable
diameter rotor blade system, and more particularly to a harmonic
gear system to selectively extend and retract the variable diameter
rotor blade system.
[0003] A tilt rotor or tilt wing aircraft typically employs a pair
of rotor systems which are pivotable such that the rotors may
assume a vertical or horizontal orientation. In a horizontal
orientation (i.e., horizontal rotor plane), the aircraft is capable
of hovering flight, while in a vertical orientation (i.e., vertical
rotor plane), the aircraft is propelled in the same manner as
conventional propeller-driven fixed-wing aircraft.
[0004] Variable Diameter Rotor (VDR) systems are known to provide
distinct advantages. That is, when the plane of the rotor is
oriented horizontally, the rotor diameter is enlarged for improved
hovering efficiency and, when oriented vertically, the rotor
diameter is reduced for improved propulsive efficiency.
[0005] One known example of a VDR blade assembly provides an outer
blade segment configured to telescope over a torque tube member. A
retraction/extension mechanism includes a planetary gear
arrangement which is selectively drivable in either direction by a
control shaft coaxially mounted within the rotor system drive
shaft. The control shaft is selectively driven to extend and
retract a reeling assembly attached to the outer blade segment.
Controlling the extension and/or retraction of the outer blade
segment relative to the torque tube thereby varies the rotor
diameter.
[0006] The extension or retraction of the VDR system typically
takes place in approximately 15-30 seconds. The remainder of the
operational time there is no relative rotation between the
planetary gear arrangement. An undesirable combination of high
loads placed upon the non-rotating planetary gear arrangement may
thereby cause fretting and pitting between the many intermeshed
gears and bearings. Undesirable life reduction of the planetary
gear arrangement may thereby result.
[0007] Accordingly, it is desirable to provide a VDR
retraction/extension system which is light and compact while
minimizing negative impact upon the VDR retraction/extension system
when it is not being utilized.
SUMMARY OF THE INVENTION
[0008] The VDR retraction/extension system according to the present
invention includes a reeling system driven by a harmonic gear
system. The reeling system includes a strap drum rotatable about an
axis of rotation. The harmonic gear system includes a ring gear, a
flexible gear, and a wave generator. The harmonic gear system is
mounted about the axis of rotation to selectively extend and
retract each VDR blade assembly.
[0009] The ring gear is rigidly attached to the rotor hub assembly
through a spline or the like, and includes a plurality of internal
gear teeth within the ring gear inner diameter. The rotor hub
assembly thus drives the attached ring gear.
[0010] The flex gear is attached to the strap drum and includes a
plurality of external gear teeth about the flex gear outer
diameter. The number of external flex gear teeth about the flex
gear are less numerous than the number of internal gear teeth
within the ring gear. The strap drum is thereby rotatably drivable
by the attached flex gear.
[0011] The wave generator includes an elliptical disk enclosed
within a bearing assembly. The wave generator is mounted within the
bore of the flex gear to impart the shape of the elliptical disk to
the flex gear.
[0012] In operation, a control shaft drives the wave generator at a
higher or lower rotational speed relative to a main rotor drive
shaft assembly thereby causing the wave generator to rotate
relative to the rotor hub assembly. The wave generator may be
driven in either direction depending upon the speed differential
between the control shaft and the main rotor shaft. In turn, the
wave generator causes the external flex gear teeth to sequentially
engage the ring gear internal gear teeth as the wave generator
rotates within the flex gear.
[0013] As the flex gear has fewer teeth than the ring gear, one
revolution of wave generator causes relative motion between the
flex gear and ring gear which equals the difference in teeth. As
the flex gear is mounted to the strap drum, the differential
rotation between the flex gear and ring gear causes the strap drum
to rotate relative the rotor hub assembly. Rotation of the strap
drum thereby causes the strap to be wound about or off of the drum
and, consequently, effecting retraction/extension of each VDR blade
assembly.
[0014] The present invention thereby provides a VDR drive system
which is light and compact while minimizing any negative impact
upon the VDR retraction/extension system when it is not being
utilized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The various features and advantages of this invention will
become apparent to those skilled in the art from the following
detailed description of the currently preferred embodiment. The
drawings that accompany the detailed description can be briefly
described as follows:
[0016] FIG. 1A is a plan view of a tilt-rotor aircraft illustrating
the variable diameter rotor system according to the present
invention in its horizontal position;
[0017] FIG. 1B is a front view of a tilt-rotor aircraft
illustrating the variable diameter rotor system according to the
present invention in its vertical position;
[0018] FIG. 2 is an expanded view of a Variable Diameter rotor
blade assembly;
[0019] FIG. 3A is a sectional view of a VDR drive system designed
according to the present invention;
[0020] FIG. 3B is a top view of the VDR drive system illustrating a
reeling assembly;
[0021] FIG. 3C is a top view of the VDR drive system illustrated a
harmonic gear system according to the present invention; and
[0022] FIG. 4 is another embodiment of a harmonic gear system
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] FIG. 1 schematically illustrates a tilt rotor aircraft that
includes a pair of variable diameter rotor blade (VDR) systems 10.
The VDR systems 10 are shown pivotally mounted on laterally
extending wing sections 12 of an aircraft. The VDR systems 10 are
pivotable between a horizontal or hover flight position, shown in
FIG. 1A, and a vertical or forward flight position, shown in FIG.
1B.
[0024] Each VDR system 10 includes a plurality of variable diameter
rotor blade assemblies 14 which are capable of being extended and
retracted to vary the size of the rotor diameter (RD) as required.
In order to effectuate the change in diameter, the VDR blade
assemblies 14 include an inboard rotor blade section 16 and an
outboard rotor blade section 18 which telescopes relative to the
inboard rotor blade section 16. The VDR blade assembly 14 is
mounted to and driven by a rotor hub assembly 20 about an axis of
rotation 21.
[0025] Referring to FIG. 2, each VDR blade assembly 14 includes the
movable outboard rotor blade section 18 which telescopes over the
inboard rotor blade section 16 (hereinafter referred to as a torque
tube) along a longitudinal axis 22. The outboard rotor blade
section 18 includes a hollow spar member 24 which is enveloped by a
leading edge 26 and a trailing edge 27 to define the requisite
aerodynamic contour of the outboard rotor blade section 18. The
spar member 24 and thus the outboard rotor blade section 18 are
thereby telescopically retractable and extendable relative to the
torque tube 16 by a drive strap 28 or the like attached to the
outboard rotor blade section 18. Preferably, the drive strap
includes multi-fiber materials and/or multi-cable construction to
provide redundant load paths for ballistic survivability.
[0026] Referring to FIG. 3A, a cross-sectional view of the variable
diameter rotor system 10 is illustrated. The rotor hub assembly 20
is mounted to a main rotor shaft 30 which rotatably drives the
rotor hub assembly 20 about the rotational axis 21. The main rotor
shaft 30 is attached to a transmission (not shown) which rotates
the main rotor shaft in a prescribed direction and speed.
[0027] The main rotor shaft 30 is preferably attached to the rotor
blade assemblies 14 through a gimbaled bearing assembly 32. The
gimbaled bearing 32 transmits rotor thrust loads to the main rotor
shaft and permits the hub assembly 20 to have limited angular
(pivotal) movement with respect to the main rotor shaft 30. The
gimbaled bearing 32 provides tilting of the rotor plane relative to
the rotational axis 21 resulting in a thrust vector to maneuver the
aircraft in the helicopter mode. The gimbaled bearing 32 also
provides reduced blade root stresses resulting from out of plane
blade flapping motion that occurs from rotor cyclic and vertical
gust inputs.
[0028] In order to control extension and retraction of the outer
blade segment 18 (FIG. 2), the present invention includes a second
drive shaft or actuation input control shaft 34 which is preferably
located within the main rotor shaft 30 concentrically within and
rotatable with respect to the main rotor shaft 30. The blade
actuation shaft 34 is engaged with a suitable actuation system (not
shown) so as to be rotatable relative to the main rotor shaft
30.
[0029] The control shaft 34 drives a VDR retraction/extension
system 36 which collectively controls each VDR blade assembly 14 of
the variable diameter rotor system 10. Insofar as each VDR blade
assembly 14 is essentially identical, it should be understood that
the following description of the exemplary VDR blade assembly 14
and the interacting components of the retraction/extension system
36 are applicable to all blade assemblies 14 of the VDR system.
[0030] An inboard portion of the torque tube member 16 is mounted
to a cuff assembly 38 which is mounted to a radial arm 39 of the
rotor hub assembly 20. The cuff assembly 38 includes a pitch
control arm 40 (FIG. 3B) through which pitch control inputs are
made about the longitudinal axis 22 of the VDR blade assembly
14.
[0031] The retraction/extension system 36 according to the present
invention includes a reeling system 42 (also shown in FIG. 3b)
driven by a harmonic gear system 44. The reeling system 42 includes
a strap drum 46 rotatable about the rotational axis 21.
[0032] The reeling system 42 extends and retracts the drive strap
28 which is wound about or wound off of the strap drum 46. The
strap 28 is disposed in winding combination with the strap drum 46
and extends between a multiple of guide pulleys 48, or other
suitable guides, for centering the strap 28 in substantial
alignment with the longitudinal axis 22 of the rotor blade assembly
14. The strap 28 extends through the torque tube 16 and is affixed
at its outboard end to the spar member 24 (FIG. 2).
[0033] The harmonic gear system 44 includes a ring gear 50, a
flexible gear 52, and a wave generator 54 (also illustrated in FIG.
3C). The harmonic gear system 44 is preferably mounted about the
axis of rotation 21 to selectively extend and retract each VDR
blade assembly 14.
[0034] The ring gear 50 is rigidly attached to the rotor hub
assembly 20 through a spline or the like, and includes a plurality
of internal gear teeth 56 within the ring gear 50 inner diameter.
The ring gear 50 is mounted concentrically about the axis of
rotation 21. The rotor hub assembly 20 thus drives the attached
ring gear 50.
[0035] The flex gear 52 is attached to the strap drum 46 and
includes a plurality of external gear teeth 58 about the flex gear
52 outer diameter. The number of external flex gear teeth 58 about
the flex gear 52 are less numerous than the number of internal gear
teeth 56 within the ring gear 50. Preferably, a gear reduction of
350:1 is provided. The flex gear 52 is a substantially non-rigid
cylinder preferably manufactured of a spring steel or the like. The
strap drum 46 is thereby rotatably drivable by the flex gear
52.
[0036] The wave generator 54 includes an elliptical disk 60
enclosed within a bearing assembly 62. The wave generator 54 is
mounted within the bore of the flex gear 52 (also illustrated in
FIG. 3B) to impart the shape of the elliptical disk 60 to the flex
gear 52.
[0037] By mounting the wave generator 54 within the bore of the
flex gear 52, the external flex gear teeth 58 engage the internal
gear teeth 56 within the ring gear 50 preferably at two equally
spaced locations (A, B: FIG. 3C) 180 degrees apart on their
respective circumferences. A positive gear mesh is thus formed at
these points of engagement.
[0038] The strap drum 46 is disposed internally of the rotor hub
assembly 20. The outer diameter of the strap drum 46 rotatably
engages the rotor hub assembly 20 through an outer bearing assembly
64. The inner diameter of the strap drum 46 rotatably engages a
constant velocity joint assembly 66 affixed to the control shaft
34. An inner bearing assembly 68 further mounts the inner diameter
of the strap drum 46 to the constant velocity joint assembly 66.
The strap drum 46 may thereby rotate independently of the constant
velocity joint assembly 66 and the rotor hub assembly 20. It should
be realized that although a constant velocity joint is illustrated
in the disclosed embodiment, other strap drum 46 mounting
arrangements will benefit from the present invention.
[0039] The constant velocity joint assembly 66 includes a spider 70
mounted to the control shaft 34 through splines 75 or the like.
Roller bearings 74 are rotatably mounted to the spider 66 and fit
within an outer housing 72. The inner bearing assembly 68 rides
upon the outer housing 72 of the constant velocity joint assembly
66 such that the strap drum 46 freely rotates about the constant
velocity joint assembly 66. The strap drum 46 thus rotates upon the
constant velocity joint assembly 66 independently of the control
shaft 34, i.e., in either direction relative thereto. The constant
velocity joint assembly 64 provides axial and pivotal movement of
the strap drum 46 and synchronized tilting with the rotor hub
assembly 20. The CV joint is included in the design because of the
gimbaled hub. If the hub is rigid the drive system would not
require the CV joint.
[0040] An extension 78 mounted between the constant velocity joint
assembly 66 and the wave generator 54 allows input from the control
shaft 34 to drive the wave generator 54. Although the extensions
are illustrated as spoke like members, other attachments such as
complete or partial disks may alternatively or additionally attach
the constant velocity joint assembly 66 and the wave generator 54.
Other harmonic gear systems with other wave generators will also
benefit from the present invention. In another embodiment (FIG. 4),
the wave generator includes a rotatable arm member 60' mounted to a
control shaft 34' to rotate circular bearing assembly 61' on each
end of the arm member 60'.
[0041] In operation, the control shaft 34 drives the wave generator
54 at a higher or lower rotational speed relative to the main drive
shaft 22 thereby causing the wave generator to rotate relative to
the rotor hub assembly 20. The wave generator 54 may be driven in
either direction depending upon the speed differential between the
control shaft 34 and the main rotor shaft 22. In turn, the wave
generator 54 causes the external flex gear teeth 58 to sequentially
engage the ring gear internal gear teeth 56 as the wave generator
54 rotates within the flex gear 52.
[0042] As the flex gear 52 has fewer teeth than the ring gear, one
revolution of wave generator 54 causes relative motion between the
flex gear 52 and ring gear 50 which equals the difference in teeth.
Preferably, the number of teeth and the difference therebetween
equates to a gear reduction of 350:1. The reduction ratio maybe
calculated, by the following relationship:
[0043] Reduction ratio=Z.sub.1/Z.sub.2-Z.sub.1,
[0044] Where:
[0045] Z.sub.1=number of teeth on the flexible gear; and
[0046] Z.sub.2=number of teeth on the fixed gear.
[0047] Thus, if Z.sub.1=700, and Z.sub.2=702 .fwdarw.
[0048] The reduction ratio=700/702-700=350.
[0049] As the flex gear 52 is mounted to the strap drum 46, the
differential rotation between the flex gear 52 and ring gear 50
causes the strap drum 46 to rotate relative the rotor hub assembly
20. Rotation of the strap drum 46 thereby causes the strap 28 to be
wound about or off of the drum 46 and, consequently, effecting
retraction/extension of each VDR blade assembly 14. Preferably, the
strap drum 46 is driven at a rotational speed which effects full
retraction/extension in about a 10 to 20 second interval.
[0050] It should be realized that when the VDR blade assemblies 14
are not being extended or retracted, the control shaft 34 rotates
at the same relative velocity as the main rotor shaft 30 and
attached rotor hub assembly 20. Likewise, the ring gear 50,
flexible gear 52, and wave generator 54 rotate at the same velocity
as the main rotor shaft 30 and attached rotor hub assembly 20. The
external flex gear teeth 58 thus only movably engage the internal
gear teeth 56 when there is differential rotation between the
control shaft 34 and the main rotor shaft 30.
[0051] The foregoing description is exemplary rather than defined
by the limitations within. Many modifications and variations of the
present invention are possible in light of the above teachings. The
preferred embodiments of this invention have been disclosed,
however, one of ordinary skill in the art would recognize that
certain modifications would come within the scope of this
invention. It is, therefore, to be understood that within the scope
of the appended claims, the invention may be practiced otherwise
than as specifically described. For that reason the following
claims should be studied to determine the true scope and content of
this invention.
* * * * *