U.S. patent number 3,687,569 [Application Number 05/126,197] was granted by the patent office on 1972-08-29 for rotor with variable angle blades.
This patent grant is currently assigned to General Electric Company. Invention is credited to Nicholas Klompas.
United States Patent |
3,687,569 |
Klompas |
August 29, 1972 |
ROTOR WITH VARIABLE ANGLE BLADES
Abstract
A support, actuation, and balancing structure for rotor blades
in a variable blade angle axial flow fan, compressor or turbine as
may be used in a turbojet or turbofan engine. The supporting
structure may include a shaft attached to each rotor blade and
restrained from outward radial travel, under high centrifugal
loading, by the inwardly facing surfaces of two spaced apart discs.
Actuation may be provided by at least one fluid powered piston
which controls blade angulation through rotation of one disc member
relative to the other. Centrifugally controlled balancing means may
also be provided to insure a uniform flow condition through the
blades by maintaining the blades in a stable position of angulation
upon disengagement of the actuator. Each rotor blade preferably
includes a central axis about which the blade angle is varied, and
which is in close proximity to the intersection of the leading edge
of the blade with the blade tip.
Inventors: |
Klompas; Nicholas (Lynnfield,
MA) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
22423517 |
Appl.
No.: |
05/126,197 |
Filed: |
March 19, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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868753 |
Oct 23, 1969 |
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Current U.S.
Class: |
416/156; 416/145;
416/207; 415/140; 416/160; 416/500 |
Current CPC
Class: |
F04D
29/323 (20130101); F01D 7/00 (20130101); Y10S
416/50 (20130101); F05D 2260/74 (20130101); F05D
2220/36 (20130101); F05D 2260/76 (20130101) |
Current International
Class: |
F01D
7/00 (20060101); F01d 007/02 () |
Field of
Search: |
;416/142,147,207,208,500,152,155,156,145,205,212
;415/129,133,149 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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964,695 |
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Feb 1950 |
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FR |
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949,899 |
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Sep 1956 |
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DT |
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1,012,869 |
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Jul 1957 |
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DT |
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1,033,837 |
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Jul 1958 |
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DT |
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1,435,444 |
|
Mar 1966 |
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FR |
|
Primary Examiner: Powell, Jr.; Everette A.
Parent Case Text
CROSS REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No.
868,753 filed Oct. 23, 1969 now abandoned.
Claims
Having thus described one embodiment of the inventive combination
and sub-combinations, what is desired to be secured by letters
patent is as follows:
1. A support and actuation structure for a rotatable shaft subject
to high axial loads, said structure comprising:
a structural frame;
a first shaft rotatably supported in said frame;
a first disc secured to said first shaft and having a web portion
and an annular ring portion, said annular ring portion having an
inner surface of revolution about the axis of said first shaft;
a second disc rotatably mounted to said first shaft and having a
web portion and an annular ring portion oriented toward the annular
ring portion of said first disc, said latter mentioned annular ring
portion having an inner surface of revolution about the axis of
said first shaft;
a second shaft having an enlargement on one end thereof, said
enlargement including surfaces of revolution about the axis of said
second shaft;
means supporting the surfaces of revolution of said enlargement in
contact with the inner surfaces of said annular ring portions, said
contacting surfaces being further characterized by being
non-concentric with each other in the plane defined by intersection
of the axes of said first and second shafts;
means constraining the discs and the second shaft so that the
respective points of contact between said enlargement and said
annular ring portions are symmetrically located with respect to the
axis of said second shaft; and
means for rotating said second disc relative to said first
disc.
2. The structure recited in claim 1 wherein the inner surfaces of
said annular ring portions are spherical surfaces having equal
radii R.sub.1 and the surfaces of revolution on said enlargement
are spherical surfaces having equal radii R.sub.2, R.sub.2 being
smaller than R.sub.1 .
3. The structure recited in claim 2 wherein the means supporting
said enlargement in contact with said annular ring portions and
constraining said second shaft includes an annular surface on said
enlargement and a surface on each web in slidable contact
therewith.
4. The structure recited in claim 3 wherein a bevel gear is
attached to each web portion, said gears facing each other, and a
beveled pinion is secured to said second shaft and meshes with said
bevel gears, the pitch cone of said pinion being defined by
revolution of the lines joining the points of contact between the
spherical surfaces to the intersection of said shafts, about the
axis of said second shaft, whereby said gears and pinion will
provide positive synchronization of the relative motion between
said discs with the corresponding rolling motion between the
spherical surface of said enlargement and the inner surfaces of
said annular ring portions.
5. In an axial flow apparatus having a stator and a rotor, a
variable angle rotor blade system comprising at least one row of
variable rotor blades peripherally disposed on said rotor with each
blade having a central axis about which the blade angle may be
varied, and support structure for said blades, said structure
comprising:
a first disc attached to said rotor and having a web portion and an
annular ring portion, said annular ring portion having an inner
surface of revolution about the axis of said rotor;
a second disc rotatably mounted to the rotor and having a web
portion and an annular ring portion oriented toward the annular
ring portion of said first disc, said latter mentioned annular ring
portion having an inner surface of revolution about the axis of the
rotor;
a blade shaft attached to the inner end of each blade, said blade
shaft having an enlargement on its inner end, said enlargement
including surfaces of revolution about the axis of said blade shaft
which face outwardly with respect to the rotor axis;
means supporting the surfaces of revolution of said enlargements in
contact with the inner surfaces of said annular ring portions, said
contacting surfaces being further characterized by being
non-concentric with each other in the planes defined by
inter-section of the central axes of said blade and said rotor;
means constraining the central axis of each blade in a plane
substantially normal to the rotor axis;
means constraining the spacing of said discs so that the respective
points of contact between each enlargement and said annular ring
portions are symmetrically located with respect to the central
blade axis, so that said blades will be radially supported against
centrifugal loads by essentially point contact between each
enlargement and each annular ring portion and relative rotation
between said discs will cause said blades to rotate about their
central axes with minimum friction.
6. The system recited in claim 5 wherein the means supporting each
enlargement in contact with said annular ring portion and
constraining said central blade axis includes an annular surface on
each said enlargement normal to the blade axis and facing the rotor
axis, and a surface on each said web in slidable contact with said
annular surface.
7. The system recited in claim 6 wherein a bevel gear is attached
to each web portion, said gears facing each other, and a beveled
pinion is secured to each blade shaft and meshes with said bevel
gears, the pitch cone of said pinion being defined by revolution of
the lines joining the points of contact between said contacting
surfaces and the intersection of the central blade axes and rotor
axis, about the central axis of said blade whereby said gears and
pinion will provide positive synchronization of the relative motion
between said discs with the corresponding rolling motion between
the surface of revolution of said enlargement and the inner surface
of said annular ring portions.
8. The system recited in claim 7 wherein said surfaces of
revolution are spherical.
9. The system recited in claim 7 wherein the means securing said
pinion to said blade shaft comprises:
a surface formed on the end of said blade shaft;
a seat formed on a first face of said pinion and mated with said
surface;
a recess formed in the second face of said pinion opposite said
first face, said recess including at least two female splines;
a center hole defined through said pinion;
an adapter extending through said center hole and secured to said
blade shaft, said adapter comprising two webs having male splines
at their ends engaged with said female splines, said adapter
additionally holding said surface and said seat in contact with
each other, said webs being nominally located in a direction
parallel with the axis of said rotor and being further
characterized by flexibility adequate to isolate said meshed pinion
and gears from loading caused by lateral vibration or misalignment
of said blade shaft;
a pair of lugs on the inner end of said blade shaft and radially
spaced from the axis thereof in planes nominally normal to the axis
of said rotor; and
a pair of slots in said pinion mated with said lugs.
10. The system recited in claim 5 including actuating means for
rotating said second disc relative to said first disc wherein said
actuating means include at least one fluid powered actuator having
a range of positions from one end stop to another end stop.
11. The system recited in claim 10 wherein said actuation structure
further includes centrifugal balance means responsive to the
rotation of said rotor for urging the blades to and maintaining the
blades at the nearest end stop upon disengagement of the actuation
force.
12. The system recited in claim 11 wherein said balance means
comprises:
a first annular support member secured to said second disc;
a second annular support member secured to said rotor shaft;
a plurality of links pinned to said first annular support member
for rotation with respect thereto and secured to said second
annular support member for limited radial sliding motion and
rotation with respect thereto;
said links further including a mass of material for generating
centrifugal force located at their inner ends.
13. The system recited in claim 5 wherein the central axis about
which the blade angle may be varied is in close proximity to the
intersection of the leading edge of the blade with the blade tip
and the locus of incremental centers of gravity for the incremental
blade sections which lie in planes orthogonal to the central blade
axis is arranged so that the centrifugal forces acting on all
points on the locus balance about the central blade axis to cause
no bending moment at the point of blade attachment to the
rotor.
14. In an axial flow apparatus having a stator and a rotor, a
variable angle rotor blade system comprising at least one row of
variable rotor blades peripherally disposed on said rotor and
support and actuation structure for said blades, said structure
comprising:
a support member movably disposed on said rotor;
actuating means for moving said supporting member relative to said
rotor;
connecting means for transmitting movement of said support member
relative to said rotor into blade angle orientation;
and balance means having a second support member secured to said
rotor shaft and spaced radially inward of said first support member
together with a plurality of links each of which is rotatably
attached to said first and second support members wherein one of
the rotatable attachments of each link is adapted for limited
radial sliding motion with respect to the support members and each
link includes a mass of material for generating a centrifugal force
for urging the blades to a stable position thereby insuring a
stable flow through the blades upon disengagement of actuator
force.
15. The axial flow apparatus of claim 14 wherein the second support
member is an annulus having a plurality of radially oriented
elongated slider tracks around its periphery and the inner radial
end of each link is rotatably pinned to a slide which slidably
engages a slider track to provide said limited radial sliding
motion.
Description
BACKGROUND OF THE INVENTION
This invention relates to support, actuation, and balancing
structures for shafts which are subjected in operation to high
axial loads, and more specifically to support, actuation, and
balancing structures for variable angle rotor blades in the
compressor, fan or turbine of a gas turbine engine, including
particular blade configurations suited for variable angle
application.
Greater flexibility in operation of gas turbine and turbofan
engines over a wide range of operating conditions could be achieved
if it were practical to provide rotors with variable angle blading.
The shafts upon which variable angle blades are supported become
subjected to high axial loads under the influence of centrifugal
force. Therefore, one requirement of a variable angle blading
system is a relatively low friction bearing structure for
supporting rotor blade shafts in a high centrifugal force field. It
has been common in the art relating to variable angle aircraft
propellers to provide this support with separate relatively large
anti-friction bearings at each propeller blade shaft; however, such
a technique is not practical in a gas turbine rotor because of the
combination of high centrifugal loading on a large plurality of
rotor blades and the lack of adequate space in a compressor, fan or
turbine rotor for providing individual bearings for each blade.
Simple sliding face bearings could be provided to retain blades
under high centrifugal load and meet physical space limitations.
However, they would involve excessive friction and make variation
of blade angle difficult if not impractical during operation of the
rotor. What is needed, therefore, is a bearing support arrangement
which features the essential rolling contact of an anti-friction
bearing combined with the structurally efficient configuration of a
sliding face bearing.
Blade actuation structure must also be simple and rugged to
withstand the high centrifugal loading upon rotation of the rotor.
In addition, should a failure occur in the actuating structure, a
means for balancing the blades must be provided for operation
independently of the actuating means to insure a stable flow
condition eliminating the risk of stalling or other malfunction of
the engine.
It has also been found that rotor blade configurations well known
to the art are not efficient for variable angle applications.
Clearance between the blade tip and stator surface becomes
excessive in order to avoid interference between the blade and
stator during variations of blade angle. The excessive clearance
adversely affects engine performance by increasing flow losses and
reducing efficiency.
Therefore it is an object of this invention to provide a variable
angle blade support which provides a structurally efficient
configuration for restraining outward radial travel under high
centrifugal loading while still retaining the rolling contact of a
typical anti-friction bearing.
It is another object of this invention to provide a variable angle
blade actuation and balancing structure which insures a stable flow
condition through the blades upon actuator disengagement.
It is a further object of this invention to provide a novel blade
configuration that maximizes the blade efficiency by reducing the
effective clearance between the blade tip and the interior surface
of the stator casing.
SUMMARY OF THE INVENTION
An axial flow apparatus includes a stator, a rotor, and a variable
angle rotor blade system. The rotor blade system includes at least
one row of variable angle rotor blades peripherally disposed on the
rotor together with support and actuation structure for the blades.
The support and actuation structure comprise a support member
movably disposed on the rotor together with actuating means for
moving the supporting member relative to the rotor. Connecting
means transmit movement of the support member relative to the rotor
into various angles of blade orientation. Balance means which are
responsive to rotation of the rotor, transmit centrifugal force to
the support member to maintain the support member in a stable
position upon disengagement of the actuator.
The support structure may include a shaft at the bottom of each
blade with an enlargement at one end of the shaft. The enlargement
may include a spherical bearing surface of radius R.sub.1
symmetrical with respect to the axis of the shaft and restrained
from outward radial travel under centrifugal loading by a first
disc secured to a rotor and a second disc rotatably mounted to the
rotor. Each disc may have an annular ring portion oriented toward
the corresponding annular ring on the opposite disc. The annular
ring portions each may have a spherical inner surface of radius
R.sub.2 (R.sub.2 being larger than R.sub.1) symmetrical with
respect to the axis of the rotor shaft. Outward radial restraint is
provided by supporting the spherical surface of the enlargement in
contact with the inner surface of the annular ring portions.
Actuation means may be provided for rotating the second disc
relative to the first disc. Relative rotation between the discs
will cause a corresponding rotation of the shaft and a rolling
contact between the spherical surface of the enlargement and the
spherical surfaces of the annular ring portions.
Each rotor blade includes a central axis about which the blade
angle is varied. The central axis is generally normal to the rotor
axis and intersects the point of blade attachment to the rotor. The
central axis is also preferably in close proximity to the
intersection of the leading edge of the blade with the blade tip.
The incremental centers of gravity for the incremental blade
sections should be arranged so that together they present a
balanced force condition at the point of blade attachment to the
rotor.
DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims distinctly claiming
and particularly pointing out the invention described herein, it is
believed that the invention will be more readily understood by
reference to the discussion below and the accompanying drawings in
which:
FIG. 1 is a partially fragmented section view of the forward end of
a turbofan engine embodying the invention;
FIG. 2 is a section view taken along the line 2--2 of FIG. 1;
FIG. 3 is a section view taken along the line 3--3 of FIG. 2;
FIG. 4 is a section view illustrating on an enlarged scale the fan
blade bearing structure also shown in FIG. 1;
FIG. 5 is a section view taken along the line 5--5 of FIG. 4;
FIG. 6 is a section view taken along the line 6--6 of FIG. 1
showing the actuation means of this invention;
FIG. 7 is a section view taken along the line 7--7 of FIG. 1
showing the balancing means of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows in cross section the forward end of a typical dual
rotor turbofan engine in which the invention has been incorporated
to provide variable angle rotor blades. While the invention is
shown in the environment of a turbofan engine, it is to be
understood that it is equally applicable to a gas generator
compressor and to turbine rotors for a gas generator turbine, fan
turbine, or the power turbine of a turboshaft engine. Additionally,
the invention could be similarly applied in any environment in
which a thrust bearing and actuation means is required for a shaft
(such as the blade shaft) which is subject to high axial loads.
The engine structure comprises an engine frame 10, an inner casing
12 beginning in the region of the fan inlet guide vane and
extending to the first stage of compressor rotor blades, a fan
outer casing 14 surrounding the fan rotor 16, and a gas generator
casing 18 shown as surrounding the compressor rotor 20 blading and
which would extend beyond the breakoff point of FIG. 1 to the aft
end of the engine. The gas generator compressor rotor 20 is
suitably supported on the engine frame 10 by bearing means 22, and
the rotor assembly 16 is similarly supported at the rotor shaft 24
by bearing means 26.
The fan rotor assembly 16 comprises the rotor shaft 24, a fixed
disc 28 which is either integrally formed with or secured to the
rotor shaft 24, a disc 30 rotatably mounted to the rotor shaft 24
so as to permit rotation relative to fixed disc 28, a plurality of
rotor blades 34 supported by the blade bearing and actuation
structure 36 which forms one aspect of this invention together with
disc actuation means 38 and balance means 40 both of which will be
explained in the discussion below. Each blade includes a central
axis 88 which is generally normal to the rotor axis 74 and about
which the blade angle is varied. Axial location of rotatable disc
30 is maintained by thrust bearing 44 and a radial bearing 46 to
provide radial support for disc 30.
Referring to both FIGS. 1 and 2, the blade mounting in relation to
the inner casing includes blade shafts 48 supported by bearing and
actuation structure 36, platforms 50 located radially outward from
the bearing and actuation structure 36 in a position to form a
smooth flow path with rotatable annular ring 52 adapted to be
movable with respect to the inner casing 12, and the blade air foil
34 which terminates at platform 50. The movable ring 52 is provided
because, as will become apparent, relative rotation between disc 30
and disc 28 will cause the blade 34 centers to move with respect to
fixed disc 28.
Referring to FIGS. 2 and 3, ring 52 comprises a pair of scalloped
members 54 held in axially spaced relation by structure which
includes spacer bars 56. Platforms 50 are circular segments whose
arcuate front and rear edges 58 mate with the scallops on members
54, and whose straight side edges 60 abut when the blades 34 are in
either of the two end positions shown in FIG. 3, there being
freedom for limited rotation between the end positions.
FIGS. 1 and 2 show a single stage of blades 34; however, in some
applications it may be desirable to provide a plurality of stages
thereof, it being within the capabilities of a person skilled in
the art to design a particular configuration which differs from the
embodiment shown in this respect.
Details of the blade support and actuation structure 36 are shown
in FIGS. 4 and 5. Referring first to FIG. 4, the fixed disc 28 and
the rotatable disc 30 include annular ring portions 62, 64
respectively, which extend toward each other from the disc webs 66,
68. The inner surfaces 70, 72 of annular ring portions 62, 64 are
spherical segments, each having a spherical radius R.sub.1 which
originates on the rotor axis 74. Contacting with spherical surfaces
70, 72 are spherical surfaces 76, 78 on the bearing plates 80, 82,
which are secured to enlargement 85 on the end of each blade shaft
48 by pins 84, 86, and have a spherical radius R.sub.2 originating
on the central blade axis 88, R.sub.2 being smaller than radius
R.sub.1. 6 Constraint on the axial relationship of the discs 28, 30
is such that, in the plane of intersection of rotor axis 74 and
central blade axis 88, spherical radii through points P on bearing
plates 80, 82 are colinear with the corresponding spherical radii
of disc surfaces 70, 72. Since radius R.sub.2 is smaller than
radius R.sub.1, points P represent geometric points of contact. It
is readily seen that for no sliding at points P rotation of front
disc 30 relative to rear disc 28 produces a corresponding rotation
of blade 34 about its central axis 88. The relative motion between
bearing plates 80, 82 and disc surfaces 70, 72 at any instant may
be described by two components-- rotation about the common radii
through points P and rolling about points P in a direction
tangential to rotor 16. Since the contacting surfaces are
completely axi-symmetric, each blade axis remains radial and points
P remain in the plane of intersection of the rotor axis 74 and the
central blade axis 88. The contact points P, however, move relative
to bearing plates 80, 82 and the disc surfaces 70, 72. In practice,
because of the high load and the elasticity of the materials,
contact pressure spreads over small circular areas with centers at
points P, and the frictional torque developed on the loaded
surfaces is only that due to rotation about the points P.
While the drawings illustrate and the discussion above speaks of
the surfaces on bearing plates 80, 82 and the disc surfaces 70, 72
being spherical, it is not necessary that such be the case, and in
some applications other surfaces may be preferable. However, it is
necessary that the surfaces mentioned be surfaces of revolution
about the pertinent axis and that the surfaces on plates 80, 82 be
non-concentric with surfaces 70, 72 in the area surrounding points
P to preserve the point contact between mating load bearing
surfaces. For example, surfaces 70, 72 could be conical and the
outer surfaces on plates 80, 82 can be segments of an appropriate
surface of revolution about the blade axis.
Surfaces 70, 72 and the outer surfaces 76, 78 of bearing plates 80,
82 may be asymmetric with respect to the colinear radii passing
through points P to provide a non-circular contact between the
contacting bearing surfaces, or may be machined with a small degree
of asymmetry in the unloaded condition to provide allowance for
blade or disc deflection. One possible reason for providing
non-circular loaded contact between the bearing surfaces would be
to change the blade root stiffness, as, for example, by providing
for a tangentially oriented elliptical contact in the loaded
condition.
To synchronize the motion and to absorb torque and tangential
loading on each blade 34, a beveled pinion 90 at the inner end of
each blade shaft 48 engages mating gears 92, 94 fixed to each disc
28, 30. The greatest portion of the load on the gear teeth is due
to blade centrifugal torque. To transmit this torque, two lugs 96
are provided on the inner end of the blade shaft 48 and engage with
corresponding slots 98 on the pinion 90. Lugs 96 are located
nominally in a plane normal to the rotor axis 74, thus leaving the
bearing plate 80, 82 spherical surfaces 76, 78 free to rock on the
inner surfaces 70, 72 of the disc annular ring portions 62, 64 in a
mode in which the central blade axis would be free to deviate from
a rotor radius passing through the blade center at its root, i.e.,
the blades would be free to move in response to forces having
components in a plane which is normal to both the rotor axis 74 and
the central blade axis 88, hereinafter referred to as tangential
forces. These tangential forces, which are relatively low, are
transmitted to the beveled pinion 90 through an adapter 100 which
extends through a center hole 101 in pinion 90 and is securely
fastened to the end of the blade shaft 48. Adapter 100 includes
radially extending webs 102 having male splines 104 on their outer
ends which mate with corresponding female splines 106 formed in a
recess on the pinion 90 face. Webs 102 are nominally oriented in a
direction normal to the direction of the tangential forces (i.e.,
parallel to rotor axis 74) and have a degree of flexibility
adequate to effectively isolate the gear teeth from possible
loading due to blade 34 vibration or misalignment, yet have
sufficient rigidity to maintain the central blade axis 88 colinear
with a rotor radius passing through the blade root under steady
state load conditions.
To assure synchronization of the pinion 90-gear 92, 94 interaction
with the rolling contact interaction between the bearing plate 80,
82 surfaces 76, 78 and the disc annular ring portion surfaces 70,
72, the pitch cone of the beveled pinion 90 is constructed to
coincide with the surface of revolution which would be generated by
rotating the lines connecting points P with the intersection of
central blade axis 88 and rotor axis 74 about the central blade
axis 88.
During rotation of the fan rotor 16, centrifugal loading on the
blades 34 will urge them radially outwardly from the center of the
rotor and assure the contacts at points P between bearing plates
80, 82 spherical surfaces 76, 78 and the disc annular ring portion
spherical surfaces 70, 72. However, mechanical support means should
be provided to aid in maintaining the radial position of the blades
34 when the rotor 16 is at rest. To this end, the enlargement 85 on
each blade shaft 48 has been provided with an annular surface 108
facing the rotor axis 74, and a circular ridge 110 is provided on
each of webs 66, 68, which ridges 110 are in slidable contact with
the flat annular surface 108 when rotor 16 is stationary.
Referring now to FIG. 4 only, response of central blade axis 88 to
relative rotation between rotatable disc 30 and fixed disc 28 can
be visualized. As the discs 28, 30 are moved relative to each
other, pinion 90 and gears 92, 94 will interact in a rack and
pinion type interaction, and the central blade axis 88 will move
about the rotor axis 74 with respect to a point on fixed disc 28.
Thus, the need for the movable rings 52 described in connection
with FIGS. 1 and 2 is established.
Referring again to FIG. 1, it is desirable that the clearance
between the tip of blade 34 and the outer casing 14 be minimized
throughout the blade's range of angulation to maximize performance.
In order to reduce the aforementioned clearance, each blade of this
invention is formed so that the central axis 88 about which the
blade angle is varied, is in close proximity to the intersection of
the leading edge of the blade with the blade tip at 61. For known
blades, the intersection of the leading edge with the blade tip
must be substantially forward of the central axis in order to avoid
unbalanced force conditions which act to cause high bending
stresses at the point of blade attachment to the rotor. The result
is an excessive clearance over that portion of the blade tip that
is forward of the central axis.
The novel blade configuration of this invention, however, achieves
a central axis of angulation in close proximity to the intersection
of the leading edge of the blade with the blade tip at 61, in
combination with a balanced force condition at the point of blade
attachment to the rotor. The balanced force condition is achieved
by adjusting the incremental centers of gravity for each
incremental blade section in the following manner. Broken line A
illustrates the locus of incremental centers of gravity for the
incremental blade sections wherein each incremental blade section
lies in a plane orthogonal to the central axis 88. The locus is
arranged so that the sum of the centrifugal forces acting on each
point on the locus are balanced and in the aggregate cause no
bending moment at the point of blade attachment to the rotor. The
locus is also displaced relative to the plane of intersection of
rotor axis 74 and central blade axis 88 so as not to produce any
bending moments that would act to distort the curvilinear surface
of each blade face. The outer radial limits for the blade tip are
defined by a spherical surface generated by a radius originating at
the intersection of the central blade axis 88 with the rotor axis
74 and terminating at a point which passes through the intersection
of the leading edge with the blade tip at 61. This limit is imposed
in order to avoid interference between the blade tip and stator
casing for all blade positions. Thus, the blade may be balanced at
the point of blade attachment to the rotor and the steady bending
stresses due to curvature of the airfoil, fail to distort the
curvilinear surfaces of each blade face.
Referring now to FIG. 6, the configuration of disc actuation means
38 is illustrated in more detail. Brackets 112 are secured to rotor
shaft 24, and fluid operated actuators 113 are pinned with a clevis
arrangement to brackets 112. The actuation rods 114 of actuators
113 are connected to inwardly directed extensions 115 of annular
member 116 which is connected to rotatable disc 30 (see FIG. 1) so
that motion thereof will be transmitted to disc 30. Actuators 113
can be controlled from a remote location and include end stops
designed to give positive positioning of the actuation system at
two end points. Actuator fluid is supplied through the generally
radial conduits 140, 141 such that an imbalance in fluid pressure
acts to cause translation of slidable balance piston 143. Conduits
140, 141 are in flow connection with a central discharge hub
assembly 142 which extends along the rotor axis 74 and supplies
actuator fluid from a source which is not shown.
FIG. 7 illustrates the balance means 40 provided to utilize the
rotational energy of rotor shaft 24 to maintain the actuation
structure in selected positions without requiring pressurization of
the actuator 113 fluid except for transition from one position to
another. The balance means operates to insure a stable flow through
the blades upon disengagement of the actuator whether by design or
by accident. An annular support member 117 is secured or integrally
formed with rotatable disc 30 (see FIG. 1) and includes a plurality
of peripherally spaced holes 118 to which a like plurality of links
120 are rotatably pinned. A second annular support member 122 is
secured to rotor shaft 24 and includes a plurality of radially
oriented elongated slider tracks 124 around its periphery. The
inner ends of links 120 are each pinned to a slider 126 which is
slidably engaged in a track 124, and each link 120 further includes
a relatively large mass of material 128 symmetric with respect to
the pinned joint. When the balance system is in the position shown
by the solid lines of FIG. 7, each link is oriented angularly in a
counter-clockwise direction with respect to a rotor radius 130
passing through a track 124. The centrifugal forces generated by
the rotating masses 128 are transmitted through links 120 and
establish a counter-clockwise tangential force component acting on
the first annular support member 117. Thus, the transmitted
tangential force component urges and maintains the actuation
structure in its counter-clockwise end position even upon
disengagement of the actuator.
When the actuator 113 (see FIG. 6) is pressurized to transition the
actuation structure from the solid line position shown in FIG. 7 to
the over center, clockwise position shown by broken lines, each
slider 126 moves radially inward in its track 124 until the
actuation structure is in its approximate center position, and then
moves radially outward in its track 124. It is readily seen that
the same centrifugal forces which urged the actuation structure to
its counter-clockwise end position will also urge the structure
towards its clockwise end position. Thus balance means 40 will
assure stability of the actuation system should the actuators 113
for some reason lose fluid pressure in that there will be stable
maintenance of the structure in one end position or another.
* * * * *