Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED FLEXIB~E COUPLING
This invention relates generally to flexible
couplings and, more particularly, to an improved
fle~ible coupling for transmitting torque from a
driving member to a driven member.
A flexible high speed coupling shaft is often
employed in conjunction with a propulsion system to
transmit shaft torque to a load. For example, such a
shaft may be employed in conjunction with the power
turbine of a marine or industrial ~as turbine engine
to transmit torque such as to a sh:ip's propeller
reduction gearing or to the impell~3r shaft of a pump.
A flexible high speed coupling shaft is advantageous
in such instances because it compensates for axial,
parallel offset and angular propulsion system/reduction
gear positioning misalignments while transmitting the
shaft torque to the load and limiting the axial load to
be compatible with the anti-fxiction thrust bearings.
One such prior art flexible high speed coupling
shaft which is currently utilized in conjunction with a
marine gas turbine propulsion system is comprised of a
distance piece supported at its forward or driving end
by a dual disc flexible coupling which is attached to
a driving member. The aft or driven end of the distance
piece is supported by a second dual disc flexible
coupling which, in turn, is attached to a driven member.
A piston ring damper assembly is connected to the aft
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flexible coupling to dampen axial deflections and anti-
deflection rings are positioned circumferentially about
each of the couplings to limit deflections due to radial
impact loads. The axial resonance frequency of such a
flexible high speed coupling shaft spring/mass system is
a function of the coupling axial spring rates and the
coupling supported weight of the distance piece and is
generally in the 18 to 25 Hz range.
Although the above-described flexible high speed
coupling shaft performs satisfactorily with current
ocean-going vessels, it was found to be unacceptable for
use in vessels designed to operate primarily in shallow
waters. Such shallow water vessels generally have
smaller diameter propellers with higher screw-turning
speeds than those of the ocean-going vessels. The
smaller, faster propellers result in blade passing
frequencies which approach and fall within the critical
axial resonance frequency range of the prior art flexible
high speed coupling shaft spring/mass system. In
addition, it was found that the prior art piston ring
axial deflection damper assembly is subjected to wear,
which may eventually cause it to become ineffective.
It is, therefore, an object of the present
invention to provide an improved flexible coupling which
raises the axial resonance frequency of a flexible high
speed coupling shaft.
It is a further object of the present invention
to provide such a flexible coupling which maintains a
high degree of torque carrying and alignment offset
capability.
It is another object of the present invention to
provide such a flexible coupling which eliminates the
need for an axial deflection damper assembly.
It is yet another object of the present invention
to provide such a flexible coupling which includes a
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radial snubber feature to limit radial deflections of
the shaft. -
Briefly stated, these objects, as well as
additional objects and advantages which will become
apparent from the following detailed description and
the appended drawing and claims, are accomplished by
the present inventi~n which, in one form, provides an
improved 1exible coupling comprising first and second
diaphragm members with an annular flexi~le coupling
member between them. The flexible coupling member
includes a pair of radially extending discs. The first
disc is connected to the first diaphragm member and the
second disc is connected to the second diaphragm member.
The improvement is provided through a means which may
be,` for example, a tie-bolt, for increasing the axial
stiffness of the flexible coupling while maintaining
alignment offset capability.
Figure 1 is a shematic view of a flexible high
speed coupling shaft which include~s, in one form, the
present invention.
Figure 2 is an enlarged view of the forward end
of the shaft depicted in Figure 1.
Figure 3 is a series of characterizations of
various misalignments of the shaft depicted in Figure 1.
~eferring to the drawing, wherein like numerals
correspond to like elements throughout, attention is
first directed to Figure 1 wherein is depicted a drive
shaft or flexible high speed coupling shaft, shown
generally as 10, which includes in one form, the present
invention. The shaft 10 is employed in this embodiment
to transmit torque from the power turbine output shaft
through forward adapter member 60 of a marine-type gas
turbine engine (not shown) to the propeller shaft
reduction gearing of a shallow water vessel (not shown)
through member 13. It should be understood, however,
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that the above-described specific use of the shaft in
this embodiment is not intended as a limitation upon the
present invention which could be employed equally as
weIl in conjunction with any other suitable application
or with any other suitable type of propulsion system,
for example a dieseI engine, or in conjunction with any
other suitable end application, for example to provide
torque to the impeIler shaft of a pump.
The shaft 10 is comprised of an annular distance
piece 12 which is supported at its forward and aft ends
by flexible couplings 14 and 16, respectiveIy. (As used
herein forward shall mean toward the left and aft shall
mean toward the right as viewed in the figures,)
The aft flexible coupling 16, which is typical of
the prior art dual disc flexible couplings described
above, is comprised o a flexible coupling member 18
which includes a pair of annular discs 20 and 22
extending radially outwardly therei-rom. An annular
flange 24 at the radially outer encl of the first disc 20
is connected by means of a pluralit.y of bolts and
locknuts 26 and 28, respectively tonly one pair o~ which
is shown for purposes of clarity) to a radially oriented
annular flange 30 at the at end of the distance piece
12. In a similar manner, an annular flange 32 at the
radially outer end o the second disc 22 is likewise
connected by means of a plurality of bolts and locknuts
34 and 36, respectively (again only one pair of which is
shown) to a radially oriented annular flange 38 at the
forward end of an annular aft adapter member 40. The
aft adapter member 40 in turn is connected through member
13 to the vessel's propeIler reduction gearing (not
shown).
An annular anti-deflection ring 42 is also
connected to the aft adapter member 40 by bolts 34 and
locknuts 36. The anti-deflection ring 42 includes an
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annular lip portion 44 which ex-tends axially forward
from the aft adapter member 40 along the radially outer
ends of the distance piece flange 30 and the aft
coupling disc flanges 24 and 32. A small annular gap 46
of a predetermined size is maintained between the inner
diameter of the anti-deflection ring lip portion 44 and
the outer diameter of the distance piece flange 30/first
coupling disc flanye 24 combination. The purpose of
anti-deflection ring 42 is to limit radial (or lateral)
deflection of the aft end of the distance piece 12
(which may, for example, be caused by high impact radial
shock loading) to the small predetermined distance of the
annular gap 46. The flexible coupling 16 thus described
is essentially the same as the dual disc flexible
coupling of the above-described prior art high speed
coupling shaft.
Referring now to Figures 1 and 2 there is
depicted the forward flexible coupling 14 which comprises
one form of the present invention. The forward flexible
~0 coupling 14 is comprised of a pair of deflection limiter
diaphragm members 48 and 50. The axial thickness of the
diaphragm members 48 and S0 is substantially unif~rm at
their radial center sections and gradually decreases with
increasing radial distance so that a generally uniform
torsional shear stress due to shaft torque is maintained
and substantially uniform axial bending stress occurs.
The first or forward diaphragm member 48 includes at its
radially outer end a radially oriented flange portion 52
which is connected by a plurality of bolts and locknuts
(54 and 56, respectively) to a radially oriented annular
flange 58 at the aft end of forward adapter member or
driving member 60. The forward adapter member, in turn,
is connected to the power turbine output shaft of the gas
turbine engine (not shown). In a similar manner, the
second or aft diaphragm member 50 includes at its radial
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outer end a radially oriented annular flange`portion 62
which is likewise connected by a plurality of bolts and
locknuts (64 and 66, respectively) to a radially oriented
annular flange 68 at the forward end of the distance
piece 12.
A flexible annular coupling member 70 is disposed
axially between the diaphragm members 48 and 50. The
coupling member 70, which is substantially the same as
the aft flexible coupling member 18, includes a pair of
annular discs 72 and 74 which extend radially outwardly
therefrom. An annular flange 76 at the radially outer
end o disc 72 is connected (by bolts and locknuts-54
and 56, respectiveIy) to the`'forward diaphragm member
~lange portion 52 and the ~orward adapter member flange
58. In a similar manner, an annular flange 78 at the .
radially outer end of disc 74 is connected (by bolts and
locknuts 64 and 66, res.pectively) to the aft diaphragm
flan~e portion 62 and the forward distance piece flange
6~. .
In order to raise the axial resonance frequency
of the flexible high speed coupling shaft 10 it is
necessary to increase the axial stif~ness of the flexible
coupling 14. This objective is accomplished by means 80,
comprising in this embodiment a tie-bolt, for maintaining
an essentially constant axial distance between the radial
center's of the diaphragm members 48 and 50. The tie-bolt:
80.includes a pair of annular'bosses 82 and 84 which abut
the'radial centers of the diaphragm members 48 and 50 to
prevent them from axially conYerging. The tie-bolt 80
also includes a reduced diameter threaded shank on each
end'86 and 88. The threaded tie-bolt shanks 86 and 88
extend respectiveIy through appropriately sized axially
oriented openings 90 and 92.at the radial centers of the
. diaphragm members 48 and 50. Means, for example locknuts
94:and 96,.are installed and tightened on the tie-bolt
shanks 86 and 88 in order.to prevent the radial centers
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of the diaphragm members 48 and 50 from axially
diverging. Thus, the tie-bolt 80 acts to restrain the
forward flexible coupling 14 from any axial deflection
in order to increase the axial stiffness of the flexible
coupling 14 while maintaining a high degree of alignment
offset capability (as is hereinafter described).
Shaft torque is transmitted through the forward
flexible coupling 14 along the load path from the
forward outer diameter bolts 54 with a torque split
between the flexible coupling member 70 and the
diaphragm members (48 and 50)/tie bolt (80) assembly
and back to the aft outer diameter bolts 64. The ratio
of the split in torque between the flexible coupling
membar 70 and the diaphragm membersftie-bolt assembly
is a function of the flexi.ble coupling member to tie-bolt
torsional flexibility. (Torsional flexibility is a
function of the axial length of a member over its cross-
sectional diameter and is measured in units of
rad/ft-lb.) Since the axial length o~ the tie-bolt 80
is large relative to that of the f:Lexible coupling member
70 (approximately 3:1) and the tie-bolt 80 diameter is
small relative to that of the flex:ible coupling member
70 (approximately 1:4) the tie-bolt 80 has a much greater
torsional flexibility than the flexible coupling member
70. Therefore, practically all of the sha~t torque is
transmitted through the flexible coupling member 70.
The flexible high speed coupling shaft 10 also
has the ability to compensate for axial, parallel offset
and angular misalignments while transmitting the shaft
torque loads. Referring now to Figure 3, there is
depicted a characterization of how the shaft 10 accepts
the various types of misalignments. Figure 3A shows the
shaft 10 when there is per:fect alignment between the gas
turbine engine (propulsion system) and the reduction
gear. Figure 3B depicts a pure axial misalignment
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situation in which the forward flexible coupling 14 is
restrained from any axial deflection, thereby the entire
axial misalignment is transmitted to the flexure of the
aft flexible coupling 16. Figure 3C shows the result of
a parallel offset misalignment. The results of
propulsion system angular misalignment and reduction
- gear misalignment are shown in Figures 3D and 3E,
respectiveIy. Combinations of the various types of ~
misalignments, for example a propulsion system angular `
misalignment in combination with a reduction gear
paralleI offset misalignment, are compensated for ln a
similar manner.
Referring again to Figures 1 and 2, the forward
diaphragm member 48 includes a cylinder-like annular
flange 98 which extends axially aft to surround a portion
of the tie-bolt 80. For purposes which will hereinafter
become apparent, a portion of the aft end of flange 98
has a reduced inner diameter 100
In a similar manner, the aft diaphragm member 50
includes a cylinder-like annular flange 102 having
substantially the same diameter as that of flange 98 but
which extends axially ~orward. A portion of the forward
end of flange 102 has a reduced outer diameter 104 such
that the two flanges 98 and 102 overlap. A small annular
lip 106 extends radially outwardly from the axially
forward end of flange 102 and engages the inner diameter
of the forward diaphragm member flange 98. The contact
point between the two flanges 98 and 102 is substantially
midway between the two diaphragm members 48 and 50.
The purpose of the above-described diaphragm
member flanges 98 and 102 is to provide a snubber feature
to limit radial (lateral) deflection of the forward end
of the distance piece 12. This snubber feature thus
serves the same purpose as does the anti-deflection ring
42 which is associated with the aft flexible coupling 16.
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The radially outer surface of the annular lip 106 is
rounded in order to allow for angular deflections o
the flexible coupling 14 without resulting in undesired
snubber contact.
From the foregoing description it can be seen
that the present invention comprises a 1exible coupling
for a high speed flexible coupling shaft which effective-
ly raises the axial resonance frequency of the shaft
while maintaining the torque carrying and alignment
offset capabilities of the shaft. It will be
recognized by those skilled in the art that changes may
be made to the above-described invention without
departing from the broad inventive concepts thereof.
For example, the forward flexible coupling 14 and the
aft flexible coupling 16 may be reversed. It is to be
understood, therefore, that this invention is not
limited to the particular embodiment disclosed, but it
is intended to cover all modifications which are within
the spirit and scope of the appended claims.
