Elastomeric shaft coupling for concentric shafts

A dual concentric shaft coupling arrangement is provided with both inner and outer rotatable assemblies. An inner assembly comprises an inner rotatable driving member, an inner rotatable driven member and an inner rotatable intermediate member that is connected therebetween. An outer assembly comprises an outer rotatable driving member, an outer rotatable driven member and an outer rotatable intermediate member connected therebetween. Both the inner and outer rotatable intermediate members comprise first and second rigid portions which are connectable to the associated driving and driven members, respectively. Between the first and second rigid portions, a compliant portion is connected for the purpose of transmitting torque between the first and second rigid portions and, consequently, between the driving and driven members. Spline arrangements are also provided in a non-contact association with each other at low magnitudes of torque. At torque levels above a predetermined magnitude, the compliant portion permits deformation and relative rotation between the driving and driven members which moves the spline members into torque transmitting contact with each other. The radial alignment of the spline arrangements and associated compliant portions provides a degree of articulation between their associated driving and driven components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to couplings for concentric shafts 
and, more particularly, to a concentric shaft coupling which incorporates 
a compliant member in conjunction with a spline arrangement as a component 
of each of two rotatable members, wherein the rotatable members are 
disposed in generally coaxial relation with each other. 
2. Description of the Related Art 
Concentric shafts are well known to those skilled in the art. For example, 
U.S. Pat. No. 2,727,485, which issued to Combs on Dec. 20, 1955, teaches 
the use of counter rotating shafts for a device which is used to transport 
freight over bodies of water. The submarine type sea train disclosed in 
this patent incorporates shafts which are arranged in both concentric and 
coaxial relation with each other along the length of a submarine for 
purposes of providing driving torque for the propellers of the vehicle. 
U.S. Pat. No. 2,285,592, which issued to Ledwinka on June 9, 1942, 
discloses the use of counter rotating shafts that are arranged in 
concentric and coaxial relation with each other and are used to provide a 
driving force for a dual propeller system. The dual propellers are 
arranged to rotate about a common axis and are disposed proximate one 
another to neutralize the reaction torque of one propeller by the reverse 
rotation of the other propeller. Each of the propellers are driven by an 
internal gear with one q-ear being driven directly and the other gear 
being driven indirectly through an idler pinion. 
U.S. Pat. No. 4,012,923, which issued to Lundgren on Mar. 22, 1977, 
discloses a vibration damping coupling which utilizes an elastomeric 
material. The device is used to transmit torque between at least two 
rotatable members. Each of the members have complimentary peripheral 
surface portions of non-circular cross-section with coupling members that 
comprise elastomer and metal layers disposed radially between driving and 
driven components. Each of the layers is disposed around a centerline with 
a generally hexagonal cross-section being described by each of the layers 
of both the elastomer and metal members. 
U.S. Pat. No. 2,154,077, which issued to Sampson on Apr. 11, 1939, 
discloses the use of a compliant member disposed rad.:ally between an 
outer surface of one shaft and an inner surface of an associated shaft. 
The compliant member provides a drive coupling which is used as a 
universal joint to transmit torque between the coupled components. By 
yielding under stress, the compliant member accommodates misalignment and 
relative axial and angular displacement between the driving shaft and the 
driven shaft. 
U.S. Pat. No. 4,516,956, which issued to Staiert on May 14, 1985, discloses 
a device which utilizes a compliant member to transmit torque between a 
driving shaft and a driven shaft. It also discloses a weld joint structure 
for use in assembling the elastomeric flexible coupling. Although this 
patent teaches the use of a spline connection between two of its 
components, the spline connection does not provide a back-up torque 
transmitting device for use when the compliant member deforms or fails. 
U.S. Pat. No. 4,406,640, which issued to Franklin et al, on Sept. 27, 1983, 
discloses a drive axle assembly having a limited torsional damper. This 
axle assembly incorporates rubber bushings which are compressed between a 
shell and a canister. The drive axle assembly disclosed in this patent 
comprises a drive shaft with an integral flange at one end and a second 
drive shaft with an integral hollow head at an end adjacent the flange. 
The flange and head have cooperating lugs forming a lost motion positive 
drive assembly between the shafts. The assembly also includes a limited 
torsional damper comprising a shell welded to the flange, a canister 
welded to the head and a pair of rubber bushings compressed between the 
shell and the canister. Although this patent discloses the use of teeth 
which operate in a lost motion manner as a back up device for the rubber 
bushings, the rubber bushings and the lost motion device are displaced 
axially in a manner which would prevent the device from exhibiting the 
articulation ability that is sometimes necessary to accommodate 
misalignment of the input and output shafts. Furthermore, the lost motion 
lugs described in this patent do not transmit torque unless a failure 
occurs in the rubber bushing component and therefore are not arranged to 
normally share torque when the torque between the driving and driven 
members exceeds a predetermined magnitude. 
Copending patent application Ser. No. 071,446, teaches the use of an 
elastomeric component in conjunction with a spline arrangement for the 
purpose of transmitting torque between a driving member and a driven 
member wherein the elastomeric, or compliant, component transmits the 
torque when the magnitude of the torque is less than a predefined value 
and, when the torque is greater than the predetermined magnitude, the 
torque transmission is shared between the compliant member and a spline 
arrangement. 
SUMMARY OF THE INVENTION 
The present invention provides a device which enables driving and driven 
shafts of a concentric shaft arrangement to be coupled together in a 
manner which permits relative rotation between the driving and driven 
members of each of the inner and outer components of the concentric shaft 
arrangement. The present invention comprises an inner rotatable driving 
member which has a first axis of rotation and an inner rotatable driven 
member which has a second axis of rotation. During normal operation, the 
first and second axes of rotation are aligned coaxially. Between the inner 
rotatable driving and driven members, an inner rotatable intermediate 
member is connected for the purpose of transmitting torque therebetween. 
The inner rotatable intermediate member has a first rigid portion 
connected to the inner rotatable driving member and a second rigid portion 
that is connected to the inner rotatable driven member. It is also 
provided with a compliant portion that is connected to both the first and 
second rigid portions. The second rigid portion of the inner rotatable 
intermediate member is provided with a plurality of spline teeth that are 
disposed in the interstices of a plurality of spline teeth which are 
connected to the inner rotatable driving member. 
The present invention is also provided with an outer rotatable driving 
member which has a third axis of rotation and an outer rotatable driven 
member which has a fourth axis of rotation. During normal operation, the 
third and fourth axes of rotation are aligned coaxially. An outer 
rotatable intermediate member is connected to both the outer rotatable 
driving and driven members and is provided with both first and second 
rigid portions. The first and second rigid portions of the outer rotatable 
intermediate member are connected to the outer rotatable driving and 
driven members, respectively. A compliant portion is connected between the 
first and second rigid portions and the second rigid portion of the outer 
rotatable intermediate member is provided with a plurality of spline teeth 
that are disposed in the interstices of a plurality of spline teeth 
connected to the outer rotatable driving member. Both the inner rotatable 
intermediate member and the outer rotatable intermediate member are 
removably attached to their related components for purposes o facilitating 
assembly and disassembly of the present invention. In a preferred 
embodiment of the present invention, both the inner and outer rotatable 
intermediate members are configured to be generally identical with each 
other. This similarity in structure permits interreplacability which, in 
turn, reduces the complexity of assembly and permits a reduction in the 
number of required spare parts necessary to maintain equipment utilizing 
the shaft coupling of the present invention. Furthermore, in a preferred 
embodiment of the present invention, the inner and outer rotatable 
intermediate members are configured in such a way that they can be 
individually preassembled with their first and second rigid portions being 
prefabricated in connection with their compliant members for later 
assembly in association with their respective inner and outer rotatable 
driving and driven members. 
In both the outer rotatable intermediate member and the inner rotatable 
intermediate member, the compliant portion is selected to permit the 
associated driving and driven assemblies to rotate relative to each other 
when the torque between the driving members and driven members exceeds a 
predetermined magnitude. In both of these rotatable intermediate members 
and their associated driving members, the spline teeth are arranged in 
non-contact relation with each other until a predetermined degree of 
deformation occurs in the compliant member. As this deformation occurs, 
relative rotation between the driving and driven components causes the 
spline teeth to move into contact relation with each other and, as a 
result, provides an alternate and complimentary torque transmission path 
between the driving and driven members. 
The inner assembly and outer assembly of the present invention are 
configured to operate independently from each other. The inner assembly of 
the present invention comprises the inner rotatable driving member and the 
inner rotatable driven member along with the inner rotatable intermediate 
member and the outer assembly of the present invention comprises the outer 
rotatable driving member, the outer rotatable driven member and the outer 
rotatable intermediate member. The present invention is especially 
suitable for use in applications wherein counter rotating shafts are 
arranged in concentric and coaxial relation with each other. These types 
of applications arise in situations in which propellers are counter 
rotated for purposes of balancing the torque effect on a carrier assembly. 
However, it should be understood that the present invention can be used in 
cases where the concentric shafts are configured to rotate in either the 
same direction or, as described above, in opposite directions. The 
elastomeric device which provides the compliant member of the present 
invention serves several useful purposes. First, it permits a quiet 
coupling between the driving and driven shafts used in conjunction with 
the present invention. Also, when the compliant member deforms in response 
to magnitudes of torque which exceed a predetermined value, relative 
rotation between the driving and driven members causes a spline 
arrangement to share the torque transmitting function of the present 
invention between the spline arrangement and the compliant member. This 
occurs because of the fact that the teeth of one spline member move into 
contact with the teeth of the associated spline member when the driving 
component and driven component of the present invention experience 
relative rotation. Another function of the present invention is to permit 
a degree of articulation between the driving and driven shafts because of 
the fact that the compliant member and the spline arrangement are arranged 
in radial alignment with each other for both the inner coupling assembly 
and outer coupling assembly of the present invention. Additionally, the 
spline arrangement of the present invention provides a back up torque 
transmitting device for use if the compliant component fails.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates an inner rotatable assembly of the present invention. 
The inner rotatable assembly comprises an inner rotatable driving member 
10 which has a first axis of rotation 12. An inner rotatable driven member 
14 is also provided. The inner rotatable driven member 14 has a second 
axis of rotation which, as shown in FIG. 1, is generally coaxial with the 
first axis of rotation 12 of the inner rotatable driving member during 
normal operation. However, it should be understood that the inner 
rotatable driving member 10 and the inner rotatable driven member 14 are 
arranged in such a way that they can rotate about individual axes of 
rotation which are not coaxial with each other. 
An inner rotatable intermediate member 15 is connected between the inner 
rotatable driving member 10 and the inner rotatable driven member 14. It 
is provided with a first rigid portion 16 and a second rigid portion 18 
with a compliant portion 20 connected between the first 16 and second 18 
rigid portions of the inner rotatable intermediate member 15. As can be 
seen in FIG. 1, the first portion 16 of the inner rotatable intermediate 
member 15 is connected to the inner rotatable driving member 10 and the 
second rigid portion 18 of the inner rotatable intermediate member is 
connected to the inner rotatable driven member 14. 
As illustrated in FIG. 1, the inner rotatable intermediate member 15 is 
removably attached to both the inner rotatable driving and driven members. 
For example, bolts 22 provide a connection between the inner rotatable 
driving member 10 and the first rigid portion 16 of the inner rotatable 
intermediate member 15 and bolts 24 provide a connection between the inner 
rotatable driven member 14 and the second portion 18 of the inner 
rotatable intermediate member 15. 
As illustrated in FIG. 1, the compliant member 20 is connected between the 
inner rotatable driving and driven members for the purpose of transmitting 
torque therebetween. If an inner driving shaft 26, which is attached to 
the inner rotatable driving member 10, is rotated in the direction shown 
by the arrow in FIG. 1, torque is transmitted by the compliant member 20 
through the inner rotatable driven member 14 and to an inner driven shaft 
28 which is shown connected to the inner rotatable driven member 14. 
The inner rotatable intermediate member 15 is provided with a plurality of 
spline teeth on its second rigid portion 18. In FIG. 1, these spline teeth 
of the second rigid portion 18 are directed radially inward toward the 
axis of rotation 12 and are disposed within the interstices o a plurality 
of spline teeth connected to a portion 30 of the inner rotatable driving 
member 10. It should be understood that the spline teeth connected to the 
portion 30 of the inner rotatable driving member 10 are not always in 
contact with the spline teeth connected to the second rigid portion 18 of 
the inner rotatable intermediate member 15. The two spline members are 
arranged in noncontact relation with each other with the teeth of each 
spline member being disposed in the interstices of the teeth of the other 
spline member. During operation of the present invention at low magnitudes 
of torque, all of the torque transmitted between the inner driving shaft 
26 and the inner driven shaft 28 is transmitted by the compliant portion 
20 of the inner rotatable intermediate member 15. As the magnitude of the 
torque being transmitted increases, the compliant member will deform to 
permit a slight degree of relative rotation to occur between the first 16 
and second 18 rigid portions of the inner rotatable intermediate member 15 
and, as a result of this relative rotation, the inner rotatable driving 
member 10 will experience a rotation relative to the inner rotatable 
driven member 14 because of the attachment of the first 16 and second 18 
rigid portions of the inner rotatable intermediate member 15 to the inner 
rotatable driving member 10 and inner rotatable driven member 14, 
respectively. 
When this relative rotation occurs as the compliant member 20 deforms, the 
spline members described above will move into contact relation with each 
other and into torque transmitting relation between the second rigid 
portion 18 of the inner rotatable intermediate member 15 and the portion 
30 of the inner rotatable driving member 10. This contact relation between 
the spline members occurs when the magnitude of torque between the inner 
rotatable driving and driven members exceeds a predetermined value. When 
the torque exceeds this predetermined value, the deformation of the 
compliant member 20 permits the spline teeth to move into torque 
transmitting relation with each other and, as a result of this movement, 
torque is also transmitted through the spline arrangement. It should be 
understood that, after the spline arrangement begins to transmit torque as 
described above, torque will be shared between the spline arrangement and 
the compliant member 20. It should also be understood that, as described 
above, the spline arrangement will transmit torque in the event that the 
compliant member 20 fails during operation and no longer is capable of 
transmitting torque between the inner rotatable driving member 10 and the 
inner rotatable driven member 14. Although the inner rotatable assembly of 
the present invention has been described in terms of driving and driven 
members, it should be understood that an alternative embodiment of the 
present invention could reverse the functions of these rotatable members. 
In other words, motive power could be provided to drive the inner 
rotatable driven member and torque could be provided through the inner 
rotatable intermediate member for the purpose of causing the rotation of 
the inner rotatable driving member. Therefore, the present invention 
should not be considered to be limited to any particular location of a 
prime mover and it should be understood that either the inner rotatable 
driving member 10 or the inner rotatable driven member 14 can be rotated 
by a prime mover with the resulting torque being transmitted through the 
inner rotatable intermediate member 15 to the other component of the 
present invention. 
FIG. 2 illustrates an outer rotatable assembly portion of the present 
invention. An outer rotatable driving member 40 is disposed around a third 
axis of rotation 42 and an outer rotatable driven member 44 is disposed 
around a fourth axis of rotation. In FIG. 2, the third and fourth axes of 
rotation are shown being coaxial with each other and coincident along the 
axis of rotation 42. An outer rotatable intermediate member, designated 
generally by reference numeral 45 in FIG. 2, comprises a first rigid 
portion 46 and a second rigid portion 48. Connected between the first and 
second rigid portions is a compliant portion 50. 
An extension 52 is connected to the outer rotatable driven member 44 for 
the purposes of providing a means for connecting the outer rotatable 
driven member 44 to the outer rotatable intermediate member 45. As will be 
described in greater detail below, the inner rotatable assembly described 
above will be disposed radially inward from portions of the outer 
rotatable assembly described herein and the extension 52 provides a 
removable portion of the outer rotatable driven assembly to permit 
clearance for assembly of the inner and outer rotatable components of the 
present invention together. For the purposes of this discussion, the 
connection portion 52 will be considered as a part of the outer rotatable 
driven member 44. 
As can be seen in FIG. 2, the outer rotatable intermediate member 45 is 
connected to both the outer rotatable driving member 40 and the outer 
rotatable driven member 44 in a manner similar to that described above in 
conjunction with the inner rotatable intermediate member 15. When an outer 
driving shaft 56 is rotated, as indicated by the arrow in FIG. 2, torque 
is transmitted through the outer assembly of the present invention to an 
outer driven shaft 58 which is caused to rotate in the direction indicated 
by the arrow in FIG. 2. This torque is transmitted by the compliant 
portion 50 of the outer rotatable intermediate member 45. As described 
above in conjunction with the inner rotatable intermediate member 15, the 
second rigid portion 48 of the outer rotatable intermediate member 45 is 
provided with a plurality of spline teeth which are disposed in the 
interstices of another plurality of spline teeth connected to a portion 60 
of the outer rotatable driving member 40. At low magnitudes of torque, the 
compliant portion 50 transmits all of the torque between the outer 
rotatable driving member 40 and the outer rotatable driven member 44. 
However as the magnitude of torque transmission between the outer driving 
shaft 56 and the outer driven shaft 58 increases, the compliant portion 50 
deforms to permit relative rotation to occur between the outer rotatable 
driving member 40 and the outer rotatable driven member 44. As this 
deformation occurs, the spline teeth begin to move into contact relation 
with each other and, after a predetermined magnitude of torque exists 
between the outer rotatable driving member 40 and the outer rotatable 
driven member 44, the spline members move into torque transmitting contact 
with each other and begin to share the total torque load between the 
driving components and driven components. At magnitudes of torque above 
this predetermined value, torque is transmitted between the outer 
rotatable driving member 40 and the outer rotatable driven member 44 
through both the compliant portion 50 of the outer rotatable intermediate 
member 45 and the spline arrangement disposed between the second rigid 
portion 48 of the outer rotatable intermediate member 45 and the portion 
60 of the outer rotatable driving member 40. 
As can be seen in FIG. 2, bolts 62 provide a means for removably connecting 
the outer rotatable intermediate member 45 to the outer rotatable driving 
member 40. These bolts 62 connect the outer rotatable driving member 40 to 
the first rigid portion 46 of the outer rotatable intermediate member 45. 
Also, bolts 64 connect the second rigid portion 48 of the outer rotatable 
intermediate member 45 to the outer rotatable driven member 44. As 
described above, the extension portion 52 is considered to be a part of 
the outer rotatable driven member 44. In FIG. 2, the extension portion 52 
is shown to be removably connected to the outer rotatable driven member 44 
by bolts 66. 
FIG. 3 shows the assembly of the inner and outer components, shown in FIGS. 
1 and 2, associated together for rotation about a common axis of rotation. 
Comparing FIGS. 1, 2 and 3, it can be seen that the first, second, third 
and fourth axes of rotation described above are all arranged coaxially 
along a single axis of rotation in FIG. 3. For purposes of this 
discussion, the axis of rotation shown in FIG. 3 is labeled both with 
reference numerals 12 and 42 to designate this relationship. It should be 
understood that a bearing assembly, is provided between the inner 
rotatable driven member 14 and the outer rotatable driven member 44. This 
bearing assembly 70 provides a degree of coaxial alignment of the inner 14 
and outer rotatable driven members. Also shown in FIG. 3, a bearing 
assembly 72 is disposed between the outer 44 surface of the outer 
rotatable driven member 44 and a grounded member 74. The first bearing 
member 70 is held axially in place with a spacer 76 which is disposed 
around the inner rotatable driven shaft 28 to fix the axial location of 
the first bearing 70 between the spacer 76 and a portion 78 of the inner 
rotatable driven member 14. Similarly, a spacer 80 is provided in 
association around the outer rotatable driven shaft 58 for the purpose of 
holding the second bearing 72 axially in place. The bearings, 70 and 72, 
provide for relative rotation between the inner rotatable driven member 14 
and the outer rotatable driven member 44 while maintaining a space between 
these coaxially disposed members. This space is shown by reference numeral 
82 to indicate the clearance between the inner rotatable driven shaft 28 
and the outer rotatable driven shaft 58 and reference numeral 84 to 
indicate the clearance between the inner rotatable driving shaft 26 and 
the outer rotatable driving shaft 56. It should be understood that 
additional supporting means (not shown in FIG. 3) would normally be 
provided to support the prime mover which rotates the inner and outer 
driving shafts. 
The structure of both the inner 15 and outer 45 rotatable intermediate 
members permits both the inner and outer assemblies shown in FIG. 3 to 
possess a degree of articulation which permits the driving members and 
driven members to move into non-coaxial alignment with each other. This 
articulation is provided by the compliant members, 20 and 50, and the 
relative spacing of the spline members. It should be understood that the 
inner and outer rotatable intermediate members are constructed to dispose 
the spline members and the compliant members along a line of radial 
alignment for the purpose of providing this articulation. As an example, 
if the inner rotatable driving and driven members of the present invention 
move into non-coaxial alignment with each other, the intersection of their 
respective axes of rotation will be generally coincident with a plane 
drawn through the center of both the compliant member and the spline 
arrangement of the inner rotatable intermediate member. If the compliant 
portion and the spline arrangement were not arranged in generally radial 
alignment with each other, this articulation would not be possible because 
of the interference that would be provided by either one or both of these 
components. Both the inner and outer assemblies illustrated in FIG. 3 are 
provided with a specific criterion of radial alignment of the components 
of their rotatable intermediate members. 
FIG. 4 is a section view taken through the outer rotatable intermediate 
member 45 in FIG. 3. However, it should be clearly understood that the 
inner 15 and outer 45 rotatable intermediate members are generally 
identical to each other in the present invention and the section view 
shown in FIG. 4 could also represent the inner rotatable intermediate 
member 15 shown in FIGS. 1 and 3. For this reason, these components in 
FIG. 4 will be designated by both reference numerals which could 
alternatively represent their reference numerals in either the inner 
rotatable intermediate member 15 or the outer rotatable intermediate 
member 45. As can be seen in FIG. 4, the first rigid portion 16 is 
connected to the second rigid portion 18 by a compliant portion 20 
connected therebetween. As the first rigid portion 16 rotates, as 
indicated by its arrow, torque is transmitted through the compliant 
portion 20 to the second rigid portion 18 which is attached to the 
rotatable driven member of the present invention. The portion 30 of the 
rotatable driving member rotates in rigid connection with the first rigid 
portion 16. Therefore, as torque between the driving and driven members 
increases, a deformation can occur within the compliant portion 20. The 
spline teeth 90, shown schematically in FIG. 4, which are connected to the 
portion 30 of the rotatable driving member, move rotationally relative to 
the second rigid portion 18 and its spline teeth 92. The space 94 between 
these spline teeth will continue to decrease until the spline teeth 90 
move into contact with the spline teeth 92 and provide a torque 
transmitting means between the rotatable driving and driven members. When 
this occurs, torque will be transmitted through two complimentary torque 
transmission paths. One torque transmission path will comprise the 
compliant portion 20 of the rotatable intermediate member and the other 
torque transmission path will comprise the spline arrangement disposed 
between the second rigid portion 18 of the rotatable intermediate member 
15. 
Referring again to FIG. 4, it should be understood that the space 94 
between the teeth 90 and the teeth 92 will be at its maximum dimension 
when the present invention is operating at no torque or low torque 
magnitudes. As the torque between the driving and driven components 
increases, the deformation of the compliant portion 20 will increase and 
the magnitude of relative rotation between the driving and driven 
components will increase. This relative rotation will cause the space 94 
to decrease as the teeth 90 move toward the teeth 92. In FIG. 4, this 
relative movement of the teeth 90 to the teeth 92 can be illustrated by 
imagining that the second rigid portion 18 is stationary and the portion 
30 moves in a clockwise direction. As this relative motion occurs, the 
teeth 90 will move clockwise into eventual contact with the teeth 92 and 
will dispose the spline member of the portion 30 into contact and torque 
transmitting relation with the teeth 92 of the spline member of the second 
rigid portion 18. 
It should be understood that, in a preferred embodiment of the present 
invention, the inner and outer rotatable intermediate members (i.e. 
reference numeral 15 and 45) are identical in structure to each other. 
Their first rigid portions (i.e. reference numerals 16 and 46) are 
identical to each other and their second rigid portions (i.e. reference 
numerals 18 and 48) are identical to each other along with their compliant 
portions (i.e. reference numerals 20 and 50). Therefore, the inner and 
outer rotatable intermediate members can be interchanged because of this 
similarity of these components. This similarity, which is permitted by the 
overall structure of the present invention, reduces the cost of the 
concentric coupling. 
Referring again to FIG. 3, it can be seen that the structure of the present 
invention permits ease of assembly and disassembly. For example, it should 
be apparent that the inner rotatable driving member 10 and the outer 
rotatable driving member 40 can be disconnected from their respective 
rotatable intermediate members and removed, in an axial direction toward 
the left, for the purpose of performing maintenance on the inner and outer 
rotatable driven members or, for any other reason. The identical structure 
of the inner and outer rotatable intermediate members permits a reduction 
in spare parts requirements and its modular structure permits the first 
and second rigid portions to be prefabricated and attached to the 
compliant portion as a separate subassembly prior to the connection of the 
rotatable intermediate member to the other components. 
Although the present invention has been described with particular 
specificity and illustrated with significant detail, it should be 
understood that many other alternative embodiments are to be considered 
within the scope of the present invention. As discussed above, it should 
also be understood that the inner and outer rotatable driven members can 
be alternatively connected to a prime mover and used to drive the inner 
and outer rotatable driving members. In other words, although the present 
invention has been described in terms of torque being provided to rotate 
the driving members which then cause the driven members to rotate, the 
opposite configuration of the present invention is equally operable. In 
the description of the preferred embodiment, it has been assumed that a 
prime mover is connected to the driving shafts which are, in turn, 
connected to the inner and outer rotatable driving members with the inner 
and outer rotatable driven members being connected to a device which is to 
be driven. However, the opposite configuration is equally possible within 
the scope of the present invention. A prime mover could be connected to 
the inner and outer driven shafts which are connected to the inner and 
outer rotatable driven members. In this configuration, torque will be 
transmitted through the inner and outer rotatable intermediate members to 
the inner and outer rotatable driving members for the purpose of driving 
the inner and outer driving shafts which could be connected to devices 
which are to be rotated. Therefore, either of these two configurations 
should be considered to be within the scope of the present invention along 
with alternative embodiments of the individual components described above.