Rotary coupling technique

Abstract: To couple a driving shaft (32, 18) of a machine to a driven shaft (34, 22), a coupling assembly is mounted to said driving and driven shafts and includes a flexible coupling element (30). The flexible coupling element (30) includes a plurality of first fastener means (50A,50C) adapted to be connected to the driving shaft (32,18) and a plurality of second fastener means (50B,50D) adapted to be connected to the driven shaft (34,22). A plurality of fibers (56) connects different ones of said first fastener means to different ones of said second fastening means so that said first fastener means applies force to said second fastener means to transmit torque. The filaments or fibers are looped around said fastening means and the coupling element has a thickness in the range of 1 percent to 10 percent of its diameter.

Description: 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 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 composite coupling techniques use elastomeric composite coupling elements. Such couplings are known, for example, from United Kingdom patent specification 321,999. They have a disadvantage of not being able to handle large loads without excessive heating or fracturing in tension. Accordingly, it is a task of the invention to provide a novel composite coupling for coupling rotating shafts that permits a wide range of misalignments and yet delivers high power and high torque. To accomplish this task, a composite coupling element comprises: a first plurality of bushings, a plurality of first fasteners for fastening the plurality of first bushings to a driving shaft, a plurality of second bushings and second fasteners for fastening the plurality of second bushings to a driven shaft. The first bushings are spaced substantially in a circle on the composite coupling element and the second bushings are spaced substantially in a circle in said composite coupling element. The bushings are connected by segments of a composite material having strands wherein said first fastener means applies force to the second fastener means through the strands within said composite coupling element. The composite coupling element is characterized in that the strands are embedded in a resin and form flattened bands have diameters of less than 5.1 mm (millimeters) but occupy between 10 percent and 75 percent of the segment volume extending between the first and second fastener means. The bands have a thickness of between one percent and ten percent of the diameter of the composite coupling element and no more than 20 percent of the cross-sectional area of a segment. Preferably, the strands are wound in a loop between adjacent fastener means having a pattern which crosses near the center of a location between adjacent fastener means and are looped in opposite directions around adjacent fastener means. From the above description, it can be understood 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 a fraction of a watt to hundreds of thousands of kilowatts, 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 resistant to chemical corrosion and has a long fatigue life. The above noted and other features of the invention will be better understood from the following detailed description when considered with reference to the accompanying drawings in which: FIG. 1 is a fragmentary, broken-away, partly sectioned elevational view of an embodiment of driver, shafts, coupling elements and driven elements in accordance with an embodiment of the invention; FIG. 2 is a plan view of a coupling element usable in the embodiment of FIG. 2; FIG. 3 is an enlarged fragmentary view of a portion of the coupling element of FIG. 2; FIG. 4 is a side view, partly sectioned of the coupling element of FIG. 2; FIG. 5 is a block diagram illustrating the manufacture and use of the coupling element in accordance with an embodiment of the invention; FIG. 6 is a block diagram illustrating a portion of the process of the block diagram of FIG. 5; FIG. 7 is a block diagram illustrating another portion of the process of the block diagram of FIG. 5; FIG. 8 is a block diagram illustrating still another portion of the process of the block diagram of FIG. 5; and FIG. 9 is a block diagram illustrating still another portion of the process of the block diagram of FIG. 5. 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 1.2 m or 6 m (meters) 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. 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. 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 5.1 mm and includes elongated members formed by twisting, weaving or grouping together smaller fibers or strands to form a single compact elongated member which can be treated individually in the winding process. 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. 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 watts to hundreds of thousandths of kilowatts with only the scale of the items being changed for the different kilowatts 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 and 50B 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 7.62 cm to 152.4 cm (centimeters) and in a preferred embodiment is 17.78 cm. 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. In the preferred embodiment, an epoxy resin with a maximum elongation of approximately 5 percent, an elastic modulus of 3.45 G N/m² (giganewtons per square meter), a glass transition temperature above 121 degrees Centigrade 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 connected together by strands 56. The resin is not shown in this view to provide greater clarity. As best shown in this view, each of the means for receiving fasteners or bushings 50C and 50D (50A-50F in FIG. 2). 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 .32 cm but it should generally be between .13 cm and 7.62 cm and the bushing length in one embodiment is 2.22 cm but should generally be between .51 cm and 7.62 cm. 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 annual 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 1 percent and 10 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 .51 cm 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 2.07 G N/m² or greater and a tensile modulus of 345 G N/m² or less. Certainly, the tensile strength should be greater than 1.38 G N/m² and the tensile modulus should be less than 515 T N/m² (teranewtons per square meter). 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 is 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. 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 2.07 G N/m² 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 4.48 G N/m² 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 2.07 G N/m² 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 3.45 M N/m² (meganewtons per square meter). 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 kilowatt 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 1.57 cm, the bolt diameter is 1.27 cm, the strand is known as S2 glass, the strand tensile modulus is 86.2 G N/m², the strand tensile strength is 4.48 G N/m², the strand yield point is 5 percent, the strand cross section area is 1.05 cm², the segment width is 2.54 cm, 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 904 neuton meters, the axial misalignment is .25 cm, the angular misalignment is 3.25 degrees, and the approximate kilowatt is 150 kilowatts at 1800 rpm. Although a specific design as described in connection with FIG. 4 is suitable for use in applications where approximately 150 kw 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 .25 cm to .51 cm for long periods of time and short periods of time respectively. The same invention may be scaled to accommodate a range from a fraction of a watt to hundreds of thousands of kilowatts 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 FIG. 5, there is shown a block diagram of a manufacturing process 80 generally involved in the making of the composite coupling element 30 (FIGS. 1-4) 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. 5, the coupling under some circumstances is mounted directly after molding without encapsulating. In FIG. 6, 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. 7, 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 1 percent and 10 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. 8, 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. 7) 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. 5) to provide a coating that assists in prevention of damage to the element 30 due to mechanical effects such as foreign objects. In FIG. 9 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. 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 a fraction of a watt to hundreds of thousandths of kilowatts 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.

Claims: A composite coupling element (30) comprising: a plurality of first bushings (e.g. 50A, 50C, etc.); a plurality of first fasteners (36, 38) for fastening the plurality of first bushings to a driving shaft (32, 18); a plurality of second bushings (e.g. 50B, 50D, etc.) and fasteners (36, 38) for fastening the second plurality of bushings (e.g. 50B, 50D, etc.) to a driven shaft (34, 22); said first bushings (50A-50F) being spaced substantially in a circle in the composite coupling element (30); the second bushings (50B, 50D, etc.) being spaced substantially in a circle in said composite coupling element (30); the first and second bushings (50A-50F) are connected by segments of a composite material (58) having strands (e.g. 56), wherein said first plurality of bushings applies force to the second plurality of bushings through the strands (56) within said composite coupling element (30), characterized in that the strands (56) are embedded in a resin and form flattened bands (70-76), the diameters of the strands (e.g. 56) are less than 5.1 millimeters but occupy between 10 percent and 75 percent of the segment volume extending between the first and second bushings, said bands (70-76) having a thickness of between one percent and ten percent of the diameter of the composite coupling element (30) and no more than 20 percent of the cross-sectional area of a segment. A composite coupling element (30) in accordance with claim 1 characterized in that the strands (56) are wound in a loop between adjacent bushings (50A-50D) having a pattern which crosses near the center of a location between adjacent bushings and are looped in opposite directions around adjacent bushings.

Inventors: KEESTER LOUIS JACKSON, KEESTER, LOUIS JACKSON
Applicants: ADDAX INC, ADDAX, INC.
Application year: 1989
Main classification: F16D3
IPC codes: F16D3, B29C53, B29C70, B29K105