Rotary coupling apparatus using composite materials

To couple a driving shaft of a machine to a driven shaft, a coupling assembly is mounted to the driving and driven shafts and includes a flexible coupling element. The flexible coupling element includes a plurality of first fasteners adapted to be connected to the driving shaft and a plurality of second fasteners adapted to be connected to the driven shaft. A plurality of fibers connects different ones of the first fasteners to different ones of the second fasteners so that the first fasteners applies force to the second fasteners to transmit torque. The filaments or fibers are looped around the fasteners and the coupling element has a thickness in the range of 1 percent to 10 percent of its diameter.

BACKGROUND OF THE INVENTION 
This invention relates to methods and apparatus for coupling rotating 
shafts together and to methods of fabricating coupling elements to connect 
rotating shafts one to the other. 
In one class of coupling techniques for rotating shafts, at least one 
integrally formed coupling element is coupled by one group of 
circumferentially spaced fasteners to a first shaft and by a second group 
of circumferentially spaced fasteners to a second shaft. In this class of 
coupling elements, there are no moving parts except for flexing of the 
coupling element during rotation. 
During rotation of this class of coupling element, the fasteners of the 
driving shaft apply force to the fasteners of the driven shaft through the 
coupling element so that the driver applies force to the coupling element 
which in turn applies force to the fasteners of the driven shaft and thus 
the driven shaft. The coupling element includes an even number of holes 
and the holes may include bushings to receive fasteners for the driver and 
the load so that a fastener to the driver pulls a fastener adjacent to it 
for the load through the coupling element. 
In a prior art type of coupling technique of this class of coupling 
techniques, the coupling elements are metallic discs that are sufficiently 
thin to bend or flex and thus accommodate misalignment of the driver and 
load without intentional relative motion between the metal discs and 
without rolling or sliding parts. This prior art type of coupling in some 
embodiments uses a series or stock of thin metal discs. Because the discs 
are thin, they are capable of flexing and because a number of them are 
stacked, they may accommodate heavier loads. 
This prior art type of coupling technique has several disadvantages such 
as: (1) if a single thick metal disc is utilized, it is not sufficiently 
flexible and does not permit a high degree of misalignment without 
imparting forces to the shaft and bearings of the driven shaft that cause 
excessive wear; (2) if a number of thin discs are utilized to permit 
greater flexibility, then there is some movement between the discs and the 
motion causes wear; (3) the coupling is subject to corrosion; and (4) such 
couplings are typically limited to approximately 1/4 degree misalignment 
for normal fatigue life and 1/2 degree for almost immediate failure. 
Other types of prior art coupling techniques use elastomeric coupling 
elements, or elements formed of elastomeric material with wire or cord 
embeded in it. Such couplings have a disadvantage of not being able to 
handle large loads without excessive heating or fracturing in tension. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide a novel technique 
for coupling rotating shafts. 
It is a further object of the invention to provide a novel coupling 
element. 
It is a still further object of the invention to provide a novel technique 
for making coupling elements. 
It is a further object of the invention to provide a composite coupling 
element which utilizes the high tension strength and flexibility of 
fibrous strands to provide a coupling element that permits a wide range of 
misalignments and yet delivers high power and high torque. 
In accordance with the above and further objects of the invention, a 
composite coupling element includes an element body, a plurality of first 
fastening means for fastening the element body to a driving shaft and a 
second plurality of fastening means for fastening the element body to a 
driven shaft. The first and second plurality of fastening means are 
arranged in one or more circles and alternate in position with each other 
so that one of the first plurality of fastening means is always next to 
two of the fastening means in the second plurality of fastening means. The 
composite body includes strands of continuous fiber connecting said first 
and second fastener means so that the first fastener means applies force 
to the second fastener means through strands within a composite body. 
In the preferred embodiment, the first and second plurality of fasteners 
are in a single circle but they may be in different circles if they are 
sufficiently aligned to provide relatively smooth pulling through the 
strands. The diameter from the center of rotation of the element to the 
circle of fasteners is sufficiently large to reduce stresses caused by 
torque transmission and axial misalignment to the design tolerance and 
small enough to be light in weight and easy to install. The number of 
fastening means and segments between adjacent fastening means is 
sufficiently large to maintain the stresses caused by torque transmission 
within tolerable limits and sufficiently to reduce stresses caused by 
axial and angular misalignment. 
The number of fasteners and segments between fasteners is greater than 
twice the torque provided by the driving shaft to the driven shaft divided 
by: (1) the radius of the coupling element from its center of rotation to 
the center of a fastening means; (2) the total cross sectional area of the 
strands; (3) the tensile modulus of a strand; (4) the maximum strain 
tolerated by a strand; and (5) a safety factor of at least two. Similarly, 
the number of fasteners and segments are greater than twice the torque 
divided by: (1) the radius of the coupling element; (2) the total cross 
sectional area of the strands; (3) the maximum design stress of a strand; 
and (4) a safety factor of at least two. 
"The number of fastener means is at least twice the maximum torque provided 
by the driving shaft to the driven shaft divided by the radius of the 
coupling element from fastener means to diagonal fastener means, divided 
by the cross-sectional area of the total fibers and by the stress caused 
on a fiber by the combined effects of torque and misalignment multiplied 
by a safety factor of at least two. The cross-sectional area of a segment 
filled with strands is at least equal to twice the torque expected to be 
imposed upon the coupling element by the driving and driven shafts divided 
by the radius of the coupling element, the number of segments, the modulus 
of elasticity, and the strain due to the combined effects of torque and 
misalignment multiplied by a safety factor of at least two. The 
cross-sectional area of a segment occupied by strands is at least equal to 
twice the maximum torque imposed by the driving element against the driven 
element divided by the radius of the coupling element, the number of 
segments and the maximum stress to be imposed upon a filament by the 
combined effects of torque and misalignment multipied by a safety factor 
of at least two." 
The fastener means includes bushings for receiving fasteners such as bolts. 
These bushings are sufficiently large to spread out the stress on thee 
fasteners but sufficiently short to increase segment length and thus 
reduce strain per unit length of the strand. Generally, the diameter of 
the bushing measured from the bottom of a groove on the bushings that 
receives the strands and the center of the central opening that holds the 
fastener is in the range of from 1/64 to 1/4 of the diameter of the 
coupling element itself. 
To provide adequate strength, the strands fill between 10 percent and 75 
percent of the segment of the coupling between fastener means. The strands 
themselves may be circularly wound around the fasteners or crossed under 
each other and may be at differing angles with the axis of rotation of the 
coupling element. Preferably, the strands are circularly wound and do not 
cross in the center. Generally, the thickness of the coupling element in a 
direction perpendicular to its direction of rotation is in a range of 
between 0.1 percent and 2 percent of its diagonal diameter between 
fastening means or segments. 
The strands: (1) have diameters of less then 0.2 inch; (2) contain a 
multiplicity of individual fibers with diameters in the range of 5 to 15 
microns (3) are elongated; (4) may be of any conventional material such as 
glass fiber, aramid fiber, carbon fiber or linear chain polyethylene 
fiber; (5) have a tensile strength greater than 200,000 psi (pounds per 
square inch) and a tensile modulus of less than 75 million psi; and (6) 
the fibers and strands are substantially aligned with the longitudinal 
axis of the segments between bushings and have the same radius of 
curvature where the segments touch and curve around the outer periphery. 
The tensile modulus of the strands should be twice the required torque 
divided by the radius of the coupling element, the cross sectional area of 
the segment of strands and the maximum strain due to torque tolerated by 
the strand multiplied by a safety factor such as two. Similarly, the 
strain capability of the material should be at least equal to twice the 
expected maximum torque divided by the radius of the coupling element, the 
cross sectional area of the strands in a single segment, the number of 
segments, and the strand modulus of elasticity, plus the strain induced by 
misalignment. The stress capability should be at least equal to twice the 
expected torque divided by the radius of the coupling element, the cross 
sectional strand area of a segment, and the number of segments, plus the 
stress induced by misalignment. 
In making the composite coupling element, strands are selected to provide 
the proper strand modulus and strand ultimate strength to accommodate 
torque transmission and misalignment. They are wound in a looping pattern 
over adjacent bushings in a mold. The loops may be elliptical or may cross 
between bushings but are preferably elliptical without crossing each other 
between bushings. 
The bands are flattened in the mold to provide a flat cross section in the 
range of 0.1 percent to 2 percent of the diameter between opposite 
fastening means within the mold and fill the mold along a segment between 
bushings within the range of 10 percent to 75 percent. Resin is applied to 
the mold either before or after the winding and the mold closed. The 
resulting assembly is then cured in accordance with normal methods for the 
resin system being used, such as by the application of heat. 
After removal from the mold, the coupling element may be installed by 
placing it on a driven or driving shaft adjacent to a coupling flange and 
passing bolts through alternate ones of the means for receiving fasteners 
and the flange. Then the other of the driven or the driving shaft is 
placed adjacent to it and bolts are passed through aligned holes in it. In 
one embodiment, loops are formed and molded with risers and then placed 
over adjacent bushings and further resin added. Moreover, in embodiments 
that are to be rotated in only one direction, more strands are included 
around alternate coupling pairs that are to pull in tension than the 
coupling pairs which will be in compression for ease of bending. 
In use, as the driving shaft rotates, the bolts connecting the flange of 
the driving shaft pull in tension against the bolts of the driven shaft, 
thus straining the strands and the resin. Some misalignment caused by out 
of center portions or the like, is accommodated by flexing of the 
composite material formed by the strands and the resin without breaking or 
cracking the composite. 
From the above description, it can be seen that the composite flexible 
coupling of this invention has several advantages such as: (1) it operates 
for long periods of time while being subject to angular misalignments 
between the driver and the load of any where of between 0 degrees and 6 
degrees and with axial misalignments causing size dependent excursions 
from the normal location of parts equivalent to that caused by angular 
misalignments of between 0 degrees and 6 degrees; (2) it transmits a wide 
range of torque in practical sizes ranging from fractional horsepower to 
hundreds of thousands of horsepower, being scalable from one end of the 
range to the other; (3) it contains no sliding, rolling or slipping parts 
subject to wear; (4) it requires no lubrication; (5) it induces low 
unwanted loads to the shafts and bearings of the driver and loads; (6) it 
exhibits a high inherent resistance to corrosion; (7) it provides a high 
resistance to fatigue failure; (8) it is inexpensive and contained in 
sizes practical for a wide range of applications; and (9) is low in weight 
.

DETAILED DESCRIPTION 
In FIG. 1, there is shown a machine 10 having a motor 12, a transmission 
assembly 14, and a driven apparatus 16. The machine 10 may be of any type 
and the motor 12 may be any driving apparatus which rotates the 
transmission assembly 14 to transmit rotational forces or torque to a 
driven apparatus 16. The driven apparatus 16 may also be of any type and 
except insofar as they cooperate with the transmission assembly 14, are 
not part of the invention. 
Generally, the function of the transmission assembly 14 is to transmit 
rotary power from a motor 12 to a driven unit. The transmission assembly 
14 may include elements which change motion from rotary to reciprocal or 
elliptical motion or the like but is intended to provide a superior rotary 
coupling for coupling a rotary driving unit to a rotary driven unit. 
For example, one typical use of such a coupling unit is to couple a motor 
to a fan through an elongated shaft of a cooling tower. In this use the 
motor is typically mounted at the outer diameter of a tower and rotates 
the shaft through a coupling assembly located along a radius of the tower. 
Near the center of the tower, the shaft is coupled by another coupling 
assembly and a right angle gear box to a fan for forcing cool air across 
water as provided in the cooling tower. In such equipment, an electric 
motor may rotate a shaft having a length 4 or 20 feet long at rotational 
rates such as 1800 rpm (revolutions per minute). This rotational force 
stresses the shafts, the coupling assemblies and the bearings of the 
motor, particularly if the coupling members are not perfectly aligned or 
are slightly out of center. 
The transmission assembly 14 includes a motor output shaft 18, a first 
coupling assembly 20, a shaft 22, a second coupling assembly 20A, and an 
input shaft 24 for the driven apparatus 16. The three shafts 18, 22 and 24 
are shown broken away and may be of any conventional type. In some 
applications, the shaft 22 may be a spacer shaft and may be an elongated 
light weight composite shaft. 
The transmission assembly 14 thus includes driven shafts and driving shafts 
coupled together by coupling assemblies such as 20 and 20A with the motor 
output shaft 18 driving the shaft 22 through the first coupling assembly 
20 and the shaft 22 driving the input shaft 24 of the driven apparatus 16 
through the second coupling assembly 20A. In other applications, shaft 22 
and coupling 20A may be omitted and shaft 18 coupled to shaft 24 by means 
of coupling 20 directly. 
Because the coupling assemblies 20 and 20A are identical in structure, only 
one description will be given and it will refer to both coupling 
assemblies. Identical parts in the two coupling assemblies bear identical 
reference numerals except the second coupling assembly 20A contains 
references numbers with a suffix "A". Otherwise, the descriptions will be 
freely mingled together to describe the parts of the coupling assemblies 
20 and 20A. 
As best shown with reference to the first coupling assembly 20, the 
coupling assemblies 20 and 20A include a composite coupling element 30, a 
first or driving flange 32, and a second or driven flange 34. The 
composite coupling element 30 is located physically between the first and 
second flanges and coupled to them but coupled to each of the different 
flanges at different locations. More specifically, the first flange 32 is 
fastened by several circumferentially spaced fastening means to the 
composite coupling element 30 at several locations and the second flange 
34 is fastened by a plurality of fastening means circumferentially spaced 
around the composite coupling element 30 with the fastening means for each 
of the two different flanges being located physically between each other 
along the circumferential perimeter of the composite coupling element 30. 
The composite coupling element 30 must be sufficiently flexible to bend 
without breaking between its fasteners to the driving element and the 
driven element. In the embodiment of FIG. 1, the bolts connecting the 
flange 32 and the flange 34 to the composite coupling element 30 may, 
because of misalignment or rotary force problems, slightly change the 
distance between the two and the composite coupling element 30 must bend 
slightly to permit that change in dimensions without undue fatigue wear. 
In one embodiment, it must also provide sufficient strength in both 
directions to permit rotation in both directions with substantial torque 
between the driving and the driven element. In another embodiment, the 
shafts are intended to turn in only one direction and the tensile-stressed 
strands connecting the leading bushings of the driving flange to the 
following bushing of the driven flange are greater in number than the 
strands that do not pull a following bushing and are thus in compression. 
Because of these functions, the composite coupling element 30 includes 
strands connecting the fasteners and subject to tensile forces in response 
to the torque but able to bend in response to forces which tend to move 
the fasteners together while maintaining their strength against the forces 
which tend to pull the fasteners away from each other. 
In this specification, the word "strand" means an elongated flexible member 
having substantial strength in tension with a diameter no greater than 
2/10ths of an inch and includes elongated members formed by twisting, 
weaving or grouping together smaller fibers or strands having a diameter 
of between 5 to 15 microns each to form a single compact elongated member 
which can be treated individually in the winding process. In the preferred 
embodiment, the strands are zero twist graphite fiber having a modulus of 
elasticity greater than 30,000,000 pounds per square inch, and generally 
in the range of 40,000,000 psi to 48,000,000 psi. 
The composite coupling element 30 is generally flat and shaped as a disc. 
It includes means for transmitting torque between the alternate pairs of 
fasteners to the driving and driven element. This means for transmitting 
torque includes: (1) means for spreading induced loads over a wider area 
of the bolt; and (2) a continuous strand connection between the means for 
spreading load for adjacent bolts. 
With this arrangement, a substantial portion of the strands carries much of 
the load in tension with a smaller portion of the load exerting 
compressive forces against different strands. The coupling element is able 
to flex to some degree without harm. Although it is flexible, it is not 
elastomeric nor subject to the fatiguing and heating properties of 
elastomeric materials inasmuch as it is generally not capable of 
stretching by more than 5 percent from a lightly loaded condition to a 
heavily loaded condition. The space between strands is filled with 
non-elastomeric resin having a modulus of elasticity of between 350,000 
and 650,000. The density of the composite is less than 0.1 pounds per 
cubic inch. 
In the preferred embodiment, the fasteners are bolts, with bolts in the 
first coupling assembly 20 such as 36 passing through the lower flange 32 
and bolts such as 38 through the upper flange 34, such bolts being spaced 
circumferentially about the periphery of the composite coupling element 30 
and being in alternate locations. Similarly, the bolts such as 38A are 
shown passing through a portion of the flexible coupling element 30A in 
the sectional view of the coupling assembly 20A and the bolt 36A passes 
through a different location. 
Guard rings such as 40 and 40A for the flexible element may be provided for 
the nuts and bolt heads connecting the shaft 22 to the motor 12 and the 
driven apparatus 16. Flange elements with the guard rings 40 and 40A are 
riveted or otherwise fastened by any convenient means to the hollow shaft 
22 to provide a strong connection. 
With the structure described in connection with FIG. 1, a coupling assembly 
is provided which: (1) can remain in position and operate for long periods 
of time even though there are angular misalignments between the driver and 
the load of between 0 degrees and 6 degrees or axial misalignments between 
the driver and the driven shaft which cause size dependent excursions from 
the normal location of parts that are the equivalent of angular 
misalignments between the range of 0 degrees and 6 degrees; (2) can 
transmit torque ranging from fractional horsepower to hundreds of 
thousands of horsepower with only the scale of the items being changed for 
the different horsepowers without the torque causing failure; (3) does not 
include any rolling, sliding or slipping parts that cause frictional wear; 
(4) does not require lubrication; (5) does not transmit excessive loads to 
the shafts or the bearings of the driver and the load; (6) has high 
resistance to corrosion; and (7) is resistant to fatigue failure. 
In FIG. 2, there is shown a composite coupling element 30 formed as a ring 
having a plurality of means for receiving fasteners 50A-50F, first and 
second aligning notches 54A and 54B, continuous strands 56 connecting the 
means for receiving fasteners and a filler material 58 formed as a flat 
disc-like ring to coat the strands 56. With this arrangement, the ring of 
filler material 58 provides a damage resistant cover over the strands 56 
and provides a relatively stiff flat ring. Circumferentially spaced in the 
ring are the fastener means 50A-50F which receive fasteners in their 
centers, with alternate rings being fastened to different ones of the 
driven and the driving members. Connecting the fastener means are the 
continuous strands 56 so that the fastener receiving means which are 
pulled by the driven element pull the fastener receiving means that 
connect the driven element in tension through the strands 56. Thus, 
one-half of the ring will be pulling in tension and the other half being 
in compression but the main torque force will be absorbed by the fastener 
receiving means and the strands. The ring itself is flexible and permits a 
certain amount of flexing to accommodate misalignment without excessive 
fatigue. 
To permit easy alignment, the aligning notches 54A and 54B are provided. 
These are not essential but make it easier to assemble the first coupling 
assembly 20 (FIG. 1). Although fastener receiving means which are solid 
and tend to spread the force between strands 56 are used in the preferred 
embodiment, they may be omitted and only fasteners used in which case the 
strands 56 will connect fastener to fastener. Moreover, while a flat 
disc-shaped ring is shown, other configurations may be utilized including 
a solid disc-type or an annulus or donut or rectangular but having 
regularly spaced rings positioned to connect strands between one fastener 
receiving means and another fastener receiving means. 
The size of the composite coupling element 30 is related to the load to be 
carried. To increase the load capacity, more strands are used. Similarly, 
to provide effective coupling, the ring should be sized to accommodate the 
driven and driving shafts, thus avoiding excessively sized flanges. The 
ring may be smaller than the shafts if a specially shaped flange is used 
to conveniently connect fastener means passing through the flanges to the 
fastener receiving means 50A-50F. 
To receive fasteners such as bolts, the means for receiving fasteners 
50A-50F are spool-like bushings each having a corresponding axial aperture 
60A-60F passing through it perpendicular to the plane of composite 
coupling element and having centers which are arranged to transmit forces 
rotationally to other means for holding fasteners to which they are 
coupled by the tension strands 56. 
In the preferred embodiment, the centers form a single circle but may be 
staggered to form more than one circle as long as the rotational forces 
may be passed for transmission between the driven and driving shafts. The 
generally circular configurations of the centers of the means for 
receiving fasteners form a circle about a center of rotation of the 
composite coupling element. The diameter of this circle affects the 
efficiency of the coupling element with a large diameter tending to reduce 
stresses caused by torque transmission and axial misalignment and a small 
diameter tending to be more practical, lighter and easier to balance and 
easier to install. Thus the diameter of these circles are compromises 
which are established to be sufficiently large as to reduce stresses 
caused by torque transmission and axial misalignment but sufficiently 
small to reduce weight and foster balancing. 
In the preferred embodiment, a single circle of fasteners are each 
connected one to the other so that the coupling element may change 
directions with the driving shaft and still function. However, if the 
rotation is only in one direction, then it is only necessary for the 
fasteners 50A-50F which are connected to the driving flange to be 
connected in tension to the fasteners which are connected to the driven 
shaft when rotation is in that one direction by strong tensile strand 
members. However, connecting each of the means for receiving fasteners 
50A-50F to adjacent members in a single circle forms a compact versatile 
coupling element. 
Generally, the diameter from segment to segment is in the range of 3 inches 
to 60 inches and in a preferred embodiment is 7 inches. There are between 
six and eight means for receiving fasteners although any even number may 
be used. Similarly, there are generally between six and eight segments 
containing bundles of strands between the fastening means although any 
number may be used. The larger the number of segments and fastening means, 
the lower the stress caused by torque transmission. The smaller the number 
of segments, the longer each segment may be for a given diameter and this 
reduces stress caused by axial and angular misalignment. 
Generally, the number and strand area of segments and the number and size 
of fastener means should be sufficient to maintain the stress on the 
strands caused by torque within the design tolerance and safety factor of 
the stress that the strands can withstand and small enough to reduce the 
stresses caused by axial and angular misalignment. 
To provide adequate stiffness for handling, a resin is embedded in the 
strands. This resin may be selected from any organic resin or elastomer 
that exhibits a maximum elongation value at least equal to the strand 
yield point and providing modest mechanical properties in the required 
environment. Maximum elongation is sometimes referred to as 
strain-to-failure. The resin or elastomer must be able to stretch as much 
as the strands but does not have to bear significant load. Because of the 
small area of the fibers, there is a large surface area of contact between 
the resin and fibers, resulting in a large ratio of surface area to fiber 
volume and greater adhesion between fiber and resin. This results in less 
slippage and frictional heat. 
In the preferred embodiment, an epoxy resin with a maximum elongation of 
approximately 5 percent, an elastic modulus of 500,000 psi, a glass 
transition temperature above 250 degrees Fahrenheit good adhesion to the 
fibers and good chemical resistance is utilized. Other organic matrices, 
including but not limited to, other thermosetting resins such as 
vinylesters, polyesters or phenolics, thermoplastic resins or elastomeric 
material may also be utilized. 
For better chemical resistance and better weathering, a barrier coating is, 
in some embodiments, separately applied external to the resin to form the 
ring 58. This provides protection against damage to the strand in handling 
or from foreign objects. Alternatively, in some embodiments, the same 
material as the embedding resin may be used and concurrently applied with 
the embedding resin. In the preferred embodiment, the barrier coating is a 
separately applied elastomeric resin. Generally, the critical 
characteristics are sufficient bending with a thin member and a maximum 
elongation exceeding 5 percent. It must have a maximum elongation which is 
at least equal to the strain for the same torque and misalignment as 
provided by the strands. 
In FIG. 3, there is shown an enlarged fragmentary view of two of the means 
for receiving fasteners 50C and 50D (50A-50F are shown in FIG. 2) 
connected together by strands 56. The resin is not shown in this view to 
provide greater clarity. 
Since in the preferred embodiment the bushings are all identical, only the 
bushing 50C will be described. It is generally spool-shaped, having: (1) a 
cylindrical opening 60C to receive a fastener such as a bolt; (2) 
generally circular side members 62C; and (3) an interior groove 64C 
between the circular side members adapted to receive the strands 56. An 
epoxy outer ring 66C may result from the application of epoxy intended to 
bind strands 56 together and to hold the strands within the groove 64C. 
The bushings serve the function of spreading induced loads over a wider 
area of a fastener means such as a bolt. They provide solid areas for the 
bolts to bear against and solid holding surfaces for the strands 56. The 
diameter of the bushing from its center 60C to the bottom of the groove 
64C and the width of the groove 64C (perpendicular to its radial diameter) 
and aligned with its axis through the center 60C together determine the 
area over which forces are spread for the strands 56. 
A small diameter bushing and strand groove is desirable to increase segment 
length and reduce the stress caused by axial and angular misalignment. 
Thus, the diameter is selected to be sufficiently small to maintain the 
stresses caused by axial and angular misalignment within design tolerances 
but large enough to spread the stress forces in a manner that accommodates 
the strength of the fasteners. 
Generally, the bushings from the center 60C to the groove 64C should have a 
dimension from 1/64 to 1/4 of the fastener circular diameter or the 
diameter between the centers of opposite fastener means (e.g., 60A and 
60D, FIG. 2). In one embodiment, the depth of the groove for the strands 
is 0.125 inches but it should generally be between 0.05 and 3 inches and 
the bushing length in one embodiment is 0.875 inches but should generally 
be between 0.2 inches and 3 inches. The bushing may be made of any solid 
material such as metal, wood or composite construction and in some 
embodiments, may be entirely eliminated. 
The arrangement of the strand structure is such that, for a given direction 
or rotation, one-half of the coupling segments carry substantially all of 
the torque load in tension, the preferred loading direction for 
filamentary materials. The coupling segments not in the primary load path 
may be slightly buckled by compressive forces and carry only a small part 
of the torque load. When directional rotation is reversed, the roles of 
the segments are also reversed, with the segments in tension being those 
previously in compression. Alternatively, the segment geometry may be 
selected such that the load is shared between the members in tension and 
the members in compression such that buckling of the compression member 
does not occur. 
Generally, the filamentary material includes a plurality of bands such as 
the bands 70 and 72 which are wound around the means for receiving a 
fastener or a fastener itself in an elliptical or annular construction of 
bands so that the band 70 is on the outermost location of the composite 
coupling element 30 (FIG. 2) and the band 72 on the inner side near the 
center of rotation. Each band will include multiple strands. 
Another pattern which may be used consists of cross bands such as those 
shown at 74 and 76 in FIG. 3 which are wound around a fastener or a means 
for receiving a fastener crossed between two fasteners and wound around 
the alternate fastener. This crossed pattern provides strength in tension 
at an angle to the fasteners and in some configurations is more desirable 
than the pattern formed by bands 70 and 72 or may be used in combination 
with the bands. Moreover, such a cross pattern formed by bands 74 and 76 
may be at a sharp angle to the plane of the bands 70 and 72 or the plane 
shown for the bands 74 and 76 to increase bearing area on the fastener or 
means for receiving the fasteners 60C and 60D. 
The wind pattern itself is designed to produce bands of continuous strand 
nearly aligned with the chords tangent to adjacent bushing or fasteners 
and of a thickness of approximately 10 percent of the maximum width across 
the entire segment. The preferred pattern consists of a group of two 
straight bands of strands and one crossed band of strands but other 
patterns may be used. This pattern may be repeated several times, if 
required, to produce the required strand cross sectional area. 
The crossed bands may also be crossed in the axial direction of the bolt or 
of means for receiving a fastener in an over and under manner to fully 
occupy a space within a strand groove of the bushing such as that shown at 
64C and 64D. 
The bands are flattened to maintain the thickness of no more than 20 
percent and preferably 10 percent of the cross sectional width of the 
segment to provide an adequate thinness to length and width ratio for 
flexibility. Preferably, the peripheral ring between the fasteners should 
be approximately 50 percent solidly filled with strand and at least within 
the range of 10 percent to 75 percent. Resin may make up the rest of the 
ring. 
In the finished product, the segments between the means for receiving 
fasteners or the fasteners should have a thickness of between 0.05 percent 
and 4 percent of the diameter of the composite coupling element 30 (FIG. 
3) diagonally across from fastener to fastener or means for receiving a 
fastener to means for receiving a fastener. The cross section between 
fasteners such as the cross section including the bands 70, 72, 74 and 76 
provide two measures of cross sectional area, one of which is only the 
cross sectional area of the strand itself and the other of which is the 
total cross sectional area including both the area occupied by strands and 
that occupied by resin. The amount occupied by strands should be at least 
10 percent of the total area and generally not more than 75 percent and 
should have a relatively thin dimension. Generally, this will be referred 
to as the cross sectional area of a segment and the length of the segment 
will generally be considered in this specification as the distance between 
adjacent means for receiving fasteners such as for example the distance 
between the centers 60C and 60D of the two adjacent fasteners 50C and 50D 
in FIG. 3. 
The strands themselves may be of many types and are generally elongated and 
flexible, having a diameter of less than 0.2 inch and contain a 
multiplicity of individual fibers. They may be selected from materials 
such as glass fiber, aramid fiber, carbon fiber, linear chain polyethylene 
fiber or such other fibrous materials as may exhibit high tensile strength 
on the order of 300,000 psi or greater and a tensile modulus of 50 million 
(50,000,000) or less. Certainly, the tensile strength should be greater 
than 200,000 psi and the tensile modulus should be less than 75 million. 
The segment cross sectional area should be sufficiently large to reduce 
stress caused by torque transmission but sufficiently small to reduce 
stress due to element bending and to reduce loading on supporting 
bearings. The significant portion of the cross sectional area is that 
filled by the strand elements. The strand modulus should be sufficiently 
high to reduce rotational deflections caused by torque transmission but 
sufficiently low to reduce stresses caused by axial and angular 
misalignment. The strand ultimate strength should be as high as possible 
and consistent with the other strand characteristics. 
More specifically, the cross sectional area of the strand in a segment is 
sized to provide a combined stress from torque and misalignment components 
of 25 percent to 35 percent of the ultimate stress allowable in the strand 
materials. This stress level permits the predicted life of the coupling to 
approach 10 billion (10,000,000,000) cycles of operation or 100,000 hours 
at normal rotational speeds of 1800 rpm. 
The width of the segment in terms of coupling material is as a practical 
matter from 1/64 to 1/4 of the diameter of composite coupling element 30 
itself such as between centers of means for receiving fasteners 60D and 
60C. The area of strand s generally equal to twice the maximum torque 
expected between the driven and the driving shaft divided by: (1) the 
radius of the coupling element 30; (2) the maximum strain permissible on a 
strand; (3) a safety factor of at least two; (4) the number of segments; 
and (5) the modulus of elasticity of a strand. Similarly, it should be at 
least equal to twice the maximum torque divided by: (1) the radius of the 
composite coupling element 30; (2) the number of segments; and (3) the 
maximum allowable stress due to the torque. 
The strands must have a maximum elongation rating at least equal to a safty 
factor of at least two multiplied by the sum of: (1) the amount of 
stretching necessary to compensate for axial misalignment divided by the 
length of the segment: (2) the amount of stretching caused by angular 
misalignment divided by the original length; and (3) the strain induced by 
torque transmission. The maximum elongation must compensate for stretching 
caused by bending as well as torque transmission. 
Generally, the individual strands should be continuous, essentially 
unbroken over a strand length of at least twice the separation between the 
centers such as 60C and 60D of the means for receiving fasteners 50C and 
50D or the corresponding fasteners themselves and should be aligned within 
30 degrees of a line between the centers 60C and 60D or adjacent 
fasteners. They should have an ultimate tensile strength of at least 
300,000 psi and maximum elongation of at least 1 percent. They may be 
embedded in any thermosetting, thermoplastic or elastomeric resin with a 
yield point at least as large as that exhibited by the strand. 
In the preferred embodiment, the strands are a high strength glass 
formulation and exhibit tensile strength nominally of 650,000 psi and 5 
percent maximum elongation. Fibers with high impact resistance may be 
required for some applications and such strands would be aramid or 
polyethylene strand. 
The strands may also be carbon strand, aramid strand, polyethylene strand 
or other strand exhibiting a tensile ultimate strength of at least 300,000 
psi and tensile maximum elongation of at least 1 percent. Although the 
preferred embodiment uses an expoxy resin as a binder between strands, 
other thermosetting resins, thermoplastic resins or elastomeric resins may 
be utilized, so long as their tensile maximum elongation exceeds the 
maximum elongation of the strand and tensile strength of the resin exceeds 
500 psi. 
In FIG. 4, there is shown a sectional view of the composite coupling 
element 30, having strands within the segment 56 wound within grooves 64E 
to form the segments which permit the composite coupling element 30 to 
stress strands in tension and provide sufficient strength. 
The spools 50B-50E (50A-50F are shown in FIG. 2) are generally spools in 
the preferred embodiment having a diameter of approximately 1/8 of the 
composite coupling element 30 diameter. The grooves 64B-64E are 
sufficiently deep to accommodate the strand wrap over a height of 
approximately 3/4 of the bushing length. The bushing length is selected to 
be sufficient to assure clearance between the mounting flanges when 
misaligned and is also approximately 1/8 of the bolt circle diameter. The 
inner diameter of the bushing is a close fit to the bolt diameter which is 
selected to carry the loads to the bushings to the flanges at a stress 
level allowable by good design practice for the bolt material. This stress 
level permits the predicted life of the preferred embodiment coupling to 
approach 10 billion cycles of operation or 100,000 hours at normal 
rotational speeds of 1800 rpm. 
The thickness of the segments is between 1 percent and 10 percent of its 
width. This is done to permit adequate flexing. If the thickness is not 
consistent with the torque and horsepower to be accommodated, several 
coupling elements may be utilized and stacked with the fasteners to share 
loads and yet be sufficiently thin to permit flexing. 
The segments of the coupling element 30 that are in compression during a 
portion of a cycle of rotation may generally be permitted to buckle 
without harm. Thus for low torque applications, the coupling may be thin 
and the links that are in compression may be permitted to buckle. However, 
if the deformation of the compression links is such that the stresses in 
the outer fibers of the beam exceed twenty five percent of the ultimate 
strength of the fibers by a substantial amount, the coupling element may 
eventually prematurely fail. 
To avoid such failure in high torque applications, the thickness of the 
links may be increased to cause them to share an adequate amount of the 
load without buckling, or if greater flexibility is desired, the links may 
be left relatively thin, of a geometry that would ordinarily result in 
bucking but the coupling element may be pre-tensioned by mounting it on a 
bolt circle slightly larger than the bolt circle used in the winding mold. 
This pre-tensioning is superimposed on the compressive stresses induced 
during operation, such that the link normally subject to compression 
simply is subject to a reduced tension load and hence does not buckle. 
In the preferred embodiment, the strand groove length is 0.62 inches, the 
bolt diameter is 0.5 inches, the strand is known as S2 glass, the strand 
tensile modulus is 12,500,000 psi, the strand tensile strength is 650,000 
psi, the strand yield point is 5 percent, the strand cross section area is 
(1.162 square inches, the segment width is 1 inch, the number of straight 
bands is 12 between fasteners, the number of cross bands between fasteners 
is 6, the combined performance for 30 percent stress (of maximum is equal 
to 8,000 inch-pounds, the axial misalignment is 0.1 inches, the angular 
misalignment is 3.25 degrees, and the approximate horsepower is 200 
horsepower at 1800 rpm. 
Although a specific design as described in connection with FIG. 4 is 
suitable for use in applications where approximately 200 horsepower at 
1800 rpm are transmitted between the driver and driven devices, when the 
devices are angularly misaligned up to 2.5 degrees for long periods of 
time or 5 degrees for short periods of time and axially misaligned from 
0.100 inches to 0.200 inches for long periods of time and short periods of 
time respectively, the same invention may be scaled to accommodate a range 
of fractional horsepower to hundreds of thousands of horsepower and from 
very low speeds under 1 rpm to very high speeds up to 50,000 rpm. They can 
also be applied to devices requiring the transmission of high static 
torque. 
In FIGS. 5 and 6, there is shown an elevational side view and plan view 
respectively of another embodiment of coupling element similar to the 
embodiment of FIGS. 2 and 4 but specially designed for heavier loading. In 
the embodiment of FIGS. 5 and 6, the same reference numerals are used as 
in the embodiment of FIGS. 2 and 4 except that letters used as suffixes 
for the reference numerals have been changed. 
The embodiment of FIGS. 5 and 6 utilizes the same spacial and tensile 
strength ranges as the other embodiments and is connected in the same way 
to a transmission but, as best shown in FIG. 5, the embodiment of FIGS. 5 
and 6 includes 26 composite segments formed in sets of three parallel sets 
of composite connecting segments consisting of fillers 58A-58X and 
corresponding filaments, fibers or strands 56A-56X to connect each pair of 
adjacent bushings. 
In this embodiment, there are eight bushings 60G-60N, with each bushing 
receiving six composite segments engaging it in six adjacent rings. Each 
of the three composite segments of combined fillers and strands connect 
two adjoining bushings. The strands and fillers of one bushing extending 
to one of its two adjacent bushings are spaced from each other on the 
bushing by three parallel segments of fillers and strands connecting the 
bushing to the other adjacent bushing. Thus, eight different chords of 
each of three parallel circles are formed by the composite segments, with 
each of the three circles having a center on a line passing through the 
centers of each of the bushings. 
As in the other embodiments, the bushings are equidistant from each other 
and connected by the endless belts, fillers and strands or filaments. 
Unlike the previous embodiments, the fillers and strands or filaments form 
loops around the bushings so that there is a space where there are no 
fillers and no strands between parallel sides of each of the strands lying 
along the circle that passes through the center of all of the bushings. 
In this embodiment, because there are three sets of composite endless loops 
linking each pair of bushings: (1) a greater load can be handled; (2) 
there is better cooling of each segment because of the air space between 
them; (3) less heat is generated from flexing because of segments that are 
more flexible; and (4) there is better vibration damping. Moreover, 
because the strands do not cross for each endless loop, there is less 
friction and wear of the strands and the spacing between loops aids in 
cooling the composite material against heating caused by the flexing. 
In FIG. 7, there is shown a block diagram of a manufacturing process 80 
generally involved in the making of the composite coupling element 30 
(FIGS. 1-6) and using it in a machine 10 (FIG. 1) including the step 79 of 
preparing to mold, the step 81 of molding, the step 90 of encapsulating, 
and the step 97 of using the coupling. Each of these steps includes a 
series of substeps that select sizes and material and prepare the proper 
configuration of composit coupling from the materials for the application. 
Normally the coupling is encapsulated after it is molded and before it is 
mounted for use but as indicated in FIG. 7, the coupling under some 
circumstances is mounted directly after molding without encapsulating. 
In FIG. 8, there is shown a block diagram of the step 79 of preparing to 
mold including the substep 82 of selecting bushings and mounting them in a 
fixture, the substep 83 of selecting strands and mounting them on a payout 
device, and the substep 84 of selecting and mixing a resin material that 
is appropriate for the application. This may be done when weather and 
impact damage are not factors. Although bushings are not necessary in all 
embodiments, they should be used in others. They are spool-like composite 
bushings in the preferred embodiment. They are formed with a strand groove 
in them of sufficient area to reduce the stress on the bolts. If there are 
to be no bushings, then the bolts themselves or pins of a diameter equal 
to the bolts are mounted in a fixture to be wound by strands. The process 
may include resin application before the strands are wound on the bushings 
or the resin may be applied after winding. 
Strands are selected in accordance with the application of the machine 10 
(FIG. 1). The amount of torque, the size of the shafts, the amount of 
misalignment and the expected rotational speeds all play a role in 
selecting the strands. Generally, the strands will have high tensile 
strength, be flexible and elongated. They are wound on the bushings or 
connectors to form continuous unbroken loops. 
If the resin is already in the resin bath, resin is applied at the same 
time as the strands are wound but if not, a suitable resin may be applied 
to the strands before winding or may be applied in the mold. The resin is 
selected so that it may stretch at least as much as the strands will under 
loading to prevent cracking and must be sufficiently elastomeric or have 
an appropriate modulus so it will not crack under modest bending. 
In FIG. 9, there is shown a block diagram of the step 81 of molding 
including the substep 85 of adjusting the resin bath for the desired fiber 
(resin ratio and impregnating the fibers), the substep 86 of winding the 
impregnated strands on the bushings, the substep 87 of flattening the 
segments in the mold, the substep 88 of curing the composite coupling 
element 30 and the substep 89 of removing the coupling element 30 from the 
winding mold. 
The step 87 of flattening the segments is performed by the mold prior to 
curing. The depth of the mold is selected so that the thickness of the 
segment will be between 0.1 percent and 2 percent of its width. The exact 
value is selected to permit adequate flexing. 
Once the winding is performed and the resin is in place, the composite 
coupling element 30 is cured such as by temperature. The exact curing 
technique is selected to be appropriate to the resin to be cured but the 
parameters are controlled to not damage the strands within the resin. A 
final protective coating may be applied on the outside to increase impact 
resistance or the like for some applications as in step 90. 
In FIG. 10, there is shown a block diagram of the step 90 of encapsulating 
including the substep 91 of positioning the molded element obtained from 
step 89 (FIG. 9) in an encapsulation mold, substep 92 of selecting and 
mixing the encapsulation resin, the substep 93 of casting the 
encapsulation resin about the molded element, the step 94 of curing the 
encapsulation resin, and the substep 95 of removing the encapsulated 
element 30 from the encapsulation mold. In the preferred embodiment, the 
step 90 of encapulating the composite element 30 is done between steps 89 
and 96 (FIG. 7) to provide a coat that assists in prevention of damage to 
the element 30 due to mechanical effects such as foreign objects. 
In FIG. 11 there is shown a block diagram of the step 97 of using the 
coupling including the substep 96 of manufacturing/assembly of the 
flanges/shaft as needed, the substep 98 of mounting the coupling element 
to the flanges of the driving and driven shafts and the substep 99 of 
rotating the driving and driven shafts. Once the composite coupling 
element 30 has been formed, it is mounted to a driven and driving shaft. 
For this purpose, a metallic sleeve or hub in a manner known in the art is 
attached to the driving shaft and contains an outwardly extending annular 
flange with fastener holes circumferentially spaced around it and located 
to accommodate alternate openings in the coupling element. Similarly, the 
driven shaft has mounted to it a coupling unit having a flange with 
circumferentially spaced apertures in it aligned with other alternate 
openings in the composite coupling element 30. The shafts are then aligned 
with the openings in the flanges and the composite coupling element 30 
aligned. Bolts or other fasteners are used to fasten alternate holes in 
the composite coupling element 30 to the holes in the flange of the driven 
element. Other bolts or fasteners are used to fasten the apertures in the 
flange of the driven element to the alternate flanges in the composite 
coupling element 30. 
When the driven and driving elements are coupled together, they may be 
rotated. When rotated in one direction, the fasteners of the driving shaft 
pull the strands 56 within the composite coupling element 30 and these 
strands 56 in turn pull the fasteners of the driven shaft so that they are 
in tension. The axial misalignment and the angular misalignment of the 
openings will cause minor flexing of the composite coupling element 30 but 
this flexing is accommodated easily by the resin and the strands 56 which 
are especially adapted for such flexing. 
In FIG. 12, there is shown a diagramatic view of a cooling tower 100 having 
a water tower 102, a drive assembly 104, and a coupling shaft assembly 
106. The drive assembly 104 is coupled to the water tower 102 through the 
coupling shaft assembly 106. With this arrangement, the drive assembly 104 
rotates the coupling shaft assembly 106 which in turn rotates a fan in the 
water tower 102 to cool liquid being recirculated through the water tower 
102. 
The water tower 102 includes a fan assembly 108, a conduit for heated 
liquid 110, a collecting conduit 112 and a vented tower 114. The conduit 
for heated liquid 110 is positioned upwardly up near the top of the vented 
tower 114 and the collecting conduit 112 is positioned near the bottom 
where liquid collects. The conduit for heated liquid 110 includes a 
sprayer which sprays liquid downwardly through the vented tower 114 where 
the liquid is collected for recirculation by the collecting conduit 112. 
Air is counterflowed upwardly to cool the dropping liquid. The fan 
assembly 108 is mounted above the conduit for heated liquid 110 and draws 
air upwardly through the vents of the vented tower 114 to provide the 
counterflow of cooling air. 
To provide a driving force, the drive assembly 104 includes a motor tower 
116 and a drive motor 118 with the motor tower 116 being mounted adjacent 
to the water tower 102 to hold the motor 116 substantially vertically with 
a gear box for the fan assembly 108. 
To drive the fan assembly 108, the coupling shaft assembly 106 includes the 
driving output shaft of the motor 118, a first composite coupling 120, a 
centrally located driving shaft 122 and a second composite coupling 124 
mounted to the input shaft of the gear box for the fan assembly 108. The 
coupling 120 mounts the driving shaft 122 to the output shaft of the motor 
118 and the coupling 124 mounts the driving shaft 122 to the fan assembly 
108. Each of these couplings includes a corresponding set of driving 
bushings and driven bushings having a plurality of thin composite members 
so as to rotate the driven shaft and transmit rotational force from the 
motor 118 to the gear box of the fan assembly 108. 
During this rotation, the weight of the shaft assembly 106 creates a 
tendency for misalignment. Under these conditions, the composite couplings 
120 and 124 compensate for such misalignment. 
From the above description, it can be understood that the coupling 
technique of this invention has several advantages such as: (1) it can 
operate for a long period of time while being subjected to angular 
misalignments and axial misalignments between the driver and the load of 
anywhere between 0 degrees and 6 degrees for the angular misalignments and 
equivalent size of linear dimension excursions due to axial misalignments; 
(2) it can transmit a wide range or torque in practical sizes ranging from 
fractional horsepower to hundreds of thousandths of horsepower and is 
scalable across the ranges with ease; (3) it contains no sliding, rolling 
or slipping parts which are subject to wear and maintenance problems; (4) 
it requires no lubrication; (5) it induces low unwanted loads to the 
shafts and bearing of the driver and to the bearing and shaft of the load; 
(6) it exhibits high inherent resistance to corrosion; (7) it provides 
high resistance to fatigue failure; and (8) it is relatively inexpensive, 
simple to make and in a practical size for a wide range of applications. 
Although a preferred embodiment of the invention has been described with 
some particularity, many modifications and variations in the invention are 
possible within the light of the above teachings. Therefore, it is to be 
understood that, within the scope of the appended claims, the invention 
may be practiced other than as specifically described.