Link and bearing for rotary coupling

Abstract: A link for use in a link-type rotary coupling (10). The link has an elastomeric bearing (35) which incorporates a pair of cavities (36 C , 36 D ) that provide discontinuities for preventing the transfer of tensile stresses in the elastomeric layers when the link (10) is tensioned axially while permitting the elastomeric layers (40 to 46) to accept compressive stresses when the link (10) is compressed axially. The resulting link (10) is durable.

Description: The present invention relates to links particularly suited for use in heavy-duty link type couplings wherein torque is transferred between drive and driven members rotatable about misaligned axes. There has been a continuous need for a constant-velocity coupling capable of transferring substantial amounts of torque between drive and driven members which rotate about misaligned axes. A particularly demanding application for such a coupling is described in EP-A-276,945 which corresponds to U.S. Patent No. 4,804,352, to Schmidt, owned by the assignee of the present application. This document shows a link according to the preamble of claim 1. The application involves the transfer of over 2984 Kilowatts (4,000 horsepower) between shafts which may rotate at up to a 10° misalignment angle in a so-called tilt rotor aircraft, i.e. an aircraft which is designed either to fly, or hover, in a helicopter-like mode or to fly in an airplane mode. While the links in the patented coupling are designed to operate in a non-lubricated manner to provide a certain service life, there is a need for links which are capable of operating for longer periods of time between inspection and replacement periods. FR-A-2214067 describes an elastomeric bearing having inner and outer metal tubes and an elastic body extending between and adhered to them. The inner tube is formed in two equal halves and the split line between them lies adjacent openings in the elastic body. These allow the inner tube to expand when a plug is inserted between its two halves to allow for problems arising if the elastic body is vulcanised in situ. The present invention provides a link including a novel elastomeric bearing; the link being of the type used in a link-type coupling to transmit torque between drive and driven members which may be rotatable about misaligned axes. Preferably the invention includes for use in heavy duty link-type coupling, a unique link which is capable of operating for a relatively long time between inspection and replacement periods. The present invention also provides a durable link which can be manufactured readily utilising state-of-the-art manufacturing techniques and materials. More specifically, the present invention provides a link particularly suited for use in link-type rotary couplings designed to transmit torque between shafts rotatable around misaligned axis. The link incorporates an elastomeric bearing assembly of a particular configuration which resists propagation of undesirable tensile stresses in the elastic layers when the link is tensioned to transfer torque from the drive member to the driven member while being capable of reacting transient reverse torque conditions that may occur. The present invention consists in a link for use in transmitting rotational torque from a drive element to a driven element, said link providing a tension and compression connection along a longitudinal axis while accommodating relative pivotal motion between the elements in a direction transverse to said axis, said link including a link body extending along said axis between said elements, first means for connecting said link body at a first location to one of said elements, and second means for connecting said link body at a second location to the other of said elements, at least one of said connecting means including an inner member and a plurality of alternating layers of elastic and inelastic material disposed between said inner member and said link body, said link being characterized by said alternating layers being arranged in separate arcuate sections extending transverse to a loading axis of said link on diametrically opposite sides of said inner member, said link comprising a pair of discontinuities between said alternating layers being arranged on opposite sides of said longitudinal axis to permit said inner member to pivot with minimal restraint relative to said link body when said link body is stressed in tension, said discontinuities creating sections extending through a major arcuate extent and sections extending through a minor arcuate extent, said discontinuities preventing the transmission of tensile stresses between the major and minor arcuate sections during normal torque transmission, whereby the link can accommodate the desired tension and compression loads and pivotal motions in a manner that minimizes undesirable stresses among the elastic layers. In the minor zone, the shims may be bonded either to the bushing or to the link body, but not to both, so that a slip joint is provided which extends between the discontinuities. A slight separation may exist along the slip joint when the link body is tensioned to transfer torque in one direction but may be engaged when the link is compressed to react reverse torque conditions. Preferably, the discontinuities are formed by cavities and the arcuate extent between the discontinuities in the minor bearing section is less than about 180° relative to the pivot axis of the inner bushing member. Among other advantages, this construction reduces the stiffness of the inner member to pivotal and cocking motion relative to the link body, and it reduces substantially tensile stresses among the elastomeric layers when the link is tensioned during transfer of torque in the normal operating direction. The reduction in tensile stresses in the elastomeric layers reduces the proclivities for cracking and, therefore, enhances the service life of the link assembly. The foregoing and other objects, features and advantages of the present invention should become apparent from the following description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a side elevational view of a link-type rotary coupling in which is mounted a series of links embodying the present invention; Fig. 2 is a side elevational view of the link coupling taken on line 2-2 of Fig. 1; Fig. 3 is an enlarged longitudinal sectional view taken on line 3-3 of Fig. 1; Fig. 4 is a partially broken away and sectioned view taken on line 4-4 of Fig. 3; and Fig. 5 is a perspective view of a link embodying the present invention. As discussed heretofore, the present invention provides an improvement on the invention disclosed in U.S. Patent 4,804,352 issued to Schmidt and owned by the assignee of the present application. The Schmidt patent includes a discussion of an aircraft power transmission application which presents a particularly severe operating environment for a link type rotary coupling. Links of the present invention are particularly suited for use in the application described in the Schmidt patent. Before discussing in detail the present invention, a brief review of the theoretical underpinnings of the subject matter of the aforementioned Schmidt patent, is believed to be in order. Referring specifically to the Schmidt patent, the disclosure of which is incorporated by reference herein, beginning at column 5, line 24 and continuing to column 7, line 22, and with particular reference to Figs. 3 and 4 thereof, the environment in which links of the present invention find utility will now be described. Referring now to FIG. 1, which is a simplified view of a link-type coupling, the coupling 10 is shown connecting a drive shaft 12 rotatable about a vertical axis R s to a driven shaft 13 rotatable about an axis R h which may be coaxial with the axis R s of the drive shaft, or may be disposed at an angle α. A drive member, or hub 15, is secured to the input drive shaft 12 by conventional means (not shown) such as bolts, weldments, splines, keys, or the like. A hub 16 is similarly connected to the driven shaft 13. In the illustrated embodiment, the hubs 15 and 16 are flat circular plates; however, it should be understood that the hubs 15 and 16 may include conventional spiders having arms extending radially outward from the shafts 12 and 13 in angularly offset relation in a plane orthogonal to the shaft rotational axes such as in a plane extending on the line A-A of FIG. 1 orthogonal to the drive shaft axis R s . To accommodate angular misalignment between the rotational axis R s of the drive shaft 12 and the rotational axis R h of the driven shaft 13, such as the misalignment angle α (FIG. 1) a plurality of connecting links are disposed between the hubs 15 and 16 and are interconnected therewith. As best seen in FIG. 1, each link, such as the link 25, has a leading end 25 a and a trailing end 25 b , the ends being defined with respect to the normal direction of rotation of the input shaft 12 as indicated by the arrow in FIG. 1 during transfer of torque. Transient reverse torque conditions may occur in the driven shaft 13 as it rotates in the same direction as the input shaft 12. In the illustrated embodiment, three links are provided between the hubs 15 and 16, the trailing end 26 b of a leading link 26 being illustrated to the right of the link 25 in FIG. 1, and the leading end 27 a of a trailing link 27 being illustrated to the left of the link 25 in FIG. 1. While a three link coupling 10 is illustrated in Fig. 1, various other numbers of links may be utilized, depending upon design requirements, including spatial and loading requirements, and the like, but at least three links spaced apart equiangularly are required to ensure a constant velocity driving relation between the shafts 12 and 13 when misaligned. Each link, such as the link 25, has its leading end portion 25 a connected to the drive hub 15, as by a clevis 15 a connected to the drive hub 15, and has its trailing end portion connected to the driven hub 16 as by a clevis 16 a connected to the driven hub 16. The drive hub clevis 15 a is located radially outward of the rotational axis R s of the input shaft 12, and hub 15 and extends axially with respect to the plane of the hub 15. In like manner, the clevis 16 a is located radially outward with respect to the rotational axis R h of the output shaft 13 and hub 16, and it extends axially with respect to the plane of the hub 16. Thus, the clevises 15 a and 16 a are disposed in spaced confronting relation with respect to one another but are angularly offset in a horizontal plane passing through their paths of movement orthogonal to the rotational axis R s in FIG. 1. As best seen in FIG. 2, each clevis, such as the clevis 15 b mounting the link 27, includes a pair of upstanding trunions 30 and 31 mounted to the drive hub in spaced relation for receiving the end portion of the link 27 therebetween. A connecting bolt, and/or other attachment structure, 32 extends through the trunions 30 and 31 and transversely through the link 27. The link 25 is connected by bolts 33 and 34 to its associated clevises 15 a and 16 a , respectively. With the rotational axes of the shafts 12 and 13 aligned, i.e. arranged coaxially, the links, such as the link 25, of the coupling 10 advance endwise in a plane P₁ orthogonal to the rotational axis R s of the aligned shafts 12 and 13. However, when the shaft 13 is misaligned with respect to the shaft 12, such as when it is displaced through the angle α as illustrated in FIG. 1, and the shafts 12 and 13 rotate, the links move in a complex manner when transmitting torque at a constant velocity between the input drive hub 15 and the output drive hub 16. For instance, when the shafts 12 and 13 are aligned, the link 25 advances endwise tangentially of the axis R s substantially coplanar with the plane P₁ orthogonal to the shaft rotational axis R s . However, when the output hub 16 and its shaft 13 are offset angularly, such as illustrated in FIG. 1, the leading end portion 25 a of the link 25 remains substantially in the plane P₁, but the trailing end portion 25 b thereof is cyclically displaced axially above and below the plane P₁ when rotated such as illustrated in FIGS. 1 and 2. Such trailing end displacement causes a change in the distance between the bolts 33 and 34 which must be accommodated dynamically by the links in order to ensure a constant velocity connection between the hubs 15 and 16, and such change in distance occurs twice during each revolution. In order to transmit torque while accommodating the aforementioned link motion, each link, such as the link 25, is provided with a first or leading elastomeric bearing means 35 mounted in its leading end portion 25 a and a second trailing end elastomeric bearing means 36 mounted in its trailing end portion 25 b . See FIG. 4. Between the elastomeric bearings 35 and 36, the link 25 has a body 25 c which is axially, flexurally and torsionally stiff, but which in the illustrated embodiment, has an aperture 25′ in its central portion to minimize weight. In other words, the link body 25 c resists flexural and torsional deflection and axial deflections caused by tensile and compressive loads. To this end, the link body 25 c is preferably fabricated of strong lightweight metal, such as titanium, aluminum, or the like, but it may be of other strong lightweight materials, including composites in those applications admitting of such materials. In the preferred embodiment, as best seen in Fig. 5, the trailing end elastomeric bearing means 36 comprises a laminated spherical component surrounding an inner bushing 53b. The laminated elastomeric bearing 35 at the opposite end of the link 25 is preferably of like construction surrounding an inner bushing 53 a . As best seen in FIGS. 3 and 4, each elastomeric bearing includes a series of layers of elastomeric material of predetermined thickness, such as the layers 40, 41, 42, 43, 44, 45 and 46 separated by a series of concave relatively inelastic, or non-extensible, members, such as metal shims, 47, 48, 49, 50, 51 and 52 between the layers, respectively. The outermost elastomeric layer 40 is disposed adjacent to a spherical concave surface 25″ formed integral within the end portion of the body 25 c of the link 25. The innermost elastomeric layer 46 is disposed adjacent to a convex spherical surface 53′ provided on a first attachment means, or the inner bushing member 53 b , which extends transversely across the link body 25 c . The leading end 25 a of the link 25 has a concave surface 25‴ which surrounds an inner mounting bushing 53 a that is slightly different in configuration from the bushing member 53 b in details not affecting the present invention. The elastomeric layers and shims 40-46 and 47-52 respectively in both the leading and trailing elastomeric bearings 35 and 36, respectively, are shaped so that their focal points F p are coincident with the longitudinal axis of the attachment bushing. In the links illustrated and described in the aforementioned Schmidt patent, the various elastomeric layers extend continuously about the inner mounting bushings, or sleeves. The shims are split to facilitate manufacture. When the links are in their normal torque transmitting operating mode, i.e. wherein the leading end 25 a preceeds the trailing end 25 b during rotation of the coupling 10, the elastomeric layers at the furthermost leading and trailing ends of the link are subjected substantially entirely to compressive loads on surfaces 25″ and 25‴ while the diametrically-opposite elastomeric layers of each elastomeric bearing are tensioned. In conditions of transient reverse torque, which is typically of a lower magnitude than the normal operating torque, the layers adjacent the furthermost leading and trailing ends of the links are subjected to tensile stresses and the diametrically-opposite elastomeric layers undergo compression. In the design of elastomeric bearing subjected to cyclic loading, it is desirable to avoid the creation of tensile stresses among the various elastomeric layers in order to avoid molecular tearing, or cavitation, due to a state of hydrostatic stress within the layers. Cavitation modes of failure are generally initiated within an elastomeric layer in which damage sites develop and accelerate propagation of fatigue cracking and elastomer degradation. It is desirable therefore, to prohibit the initiation and propagation of elastomer fatigue cracking in order to enhance the overall fatigue life of the elastomeric bearing. According to the present invention, undesirable tension stresses due to normal transfer of torque are avoided in the elastomeric bearings provided in the coupling links. To this end, each elastomeric bearing, such as the leading end elastomeric bearing 35 is divided into separate arcuate sections which are discontinuous about the periphery of the inner mounting bushing 53 a . The trailing end elastomeric bearing 36 is similarly divided. By providing such separations in each of the bearings, tensile type stresses in the elastomeric layers can be avoided, thereby enhancing the fatigue life of the bearing assembly and, of course, the link itself. Referring now to Fig. 4, it may be seen that the trailing end elastomeric bearing 36 is divided into two sections: 36 A and 36 B . The section 36 A extends through a major arcuate extent greater than 180° with respect to a line perpendicular to the longitudinal axis B-B of the link 25, or greater than pi radians. The remaining portion of the bearing 36 B extends through a smaller, or minor, arcuate extent which, in the illustrated embodiment, is defined within an arc subtended by an angle β of about 90°, or Pi/2 radians, relative to the central axis of the inner mounting bushing 53 b (See Fig. 4). The arcuate bearing sections 36 A and 36 B are separated from one another by means of discontinuities which, in the present instance, are provided by cavities 36 C and 36 D . Preferably, the cavities 36 C and 36 D extend transversely of the link body 25 c between the inner mounting bushing 53 b and the inner surface of the link 25. Additionally, the cavities 36 C and 36 D preferably extend completely across the entire width of the link body 25 c and are open at opposite ends. Thus, the cavities 36 C and 36 D provide discontinuities between the various elastomeric layers and the inelastic shims on opposite axial sides of the inner mounting bushings. In order to avoid completely the transfer of loads or stresses between the arcuate sections 36 A and 36 B under tensile and compressive loading of the link, the present invention also contemplates the provision of a means providing a slip joint between the minor arcuate bearing section 36 B and either the inner bushing member 53 b or the link body 25 c . Preferably, this is accomplished by providing an unbonded connection either between one of the surfaces of one of the inelastic shims adjacent to an elastomeric layer, or between the inner concave surface of the link body 25 c and the outermost elastomeric layer adjacent thereto, or between the outer surface of the mounting bushing 53 b and the innermost elastomeric layer 46. A bond should exist between the balance of the elastomeric layers and inelastic shims in order to provide a centering restorative force for the minor bearing section 36 B . Preferably, the unbonded connection should permit the inner bushing 53 b to separate slightly when the link is tensioned under conditions of normal torque loads on the coupling and to move relative to its adjacent elastomeric surface during the various motions of the link as the coupling rotates. By way of example, the best mode presently contemplated for practicing the invention includes providing the unbonded connection between the concave inner surface of the inelastic shim 57 a (Fig. 4) and its adjacent elastomeric layer 46 a . The present invention provides a number of advantages. During the application of loads on the link 25 between its leading end 25 a and its trailing end 25 b during transfer of normal torque, the cavities 36 C and 36 D in conjunction with the unbonded connection prevent the transfer of tensile stresses from the various elastomeric layers in the minor arcuate section 36 B of the elastomeric bearing 36 to the various elastomeric layers in the major arcuate section 36 A of the bearing 36. At the same time, when so loaded, the inside surface of the shim 57 a separates from its adjacent surface of elastomeric layer 46 a to prevent the transmission of tensile stresses between the inner bushings 53 a and 53 b and the central portion of the link body 25 c . Due to the separation at this location, abrasion is avoided as the link body 25 c undergoes various motions relative to the mounting bushings 53 a and 53 b as the coupling 10 rotates about misaligned axes. As a result, the various elastomeric layers in the major arcuate sections 36 A and 35 A are subjected substantially entirely to compressive and shear loading. Since the various elastomeric layers and inelastic shims in the minor arcuate bearing section 36 B are bonded together and to the link body 25 c (except for the slip joint) restoring forces are provided to maintain the arcuate bearing section 36 B ready to accept transient compressive loads such as are applied when reverse torque conditions exist and the inner bushings 53 a and 53 b are displaced axially away from their respective link ends 25 a and 25 b . In such event, the various elastomeric layers in the minor arcuate bearing section 36 B and 35 B are subjected to compressive and shear loading, but the transmission of tensile stresses from the major bearing section 36 A is avoided as a result of the discontinuity cavities 36 C , 36 D . As should be understood by those skilled in the art, the various layers in the leading end elastomeric bearing 35 undergo similar motions under similar loading conditions. The aforedescribed structure provides a number of benefits. Chief among these benefits is the avoidance of undesirable tensile stresses and strains among the various elastomeric layers which might enable undesirable fatigue conditions to develop. As a result, the link of the present invention has enhanced durability and can be operated for relatively long periods between inspection and replacement. In addition, the load carrying capability of the elastomeric bearings is maximized while simultaneously maintaining the link stiffness at or under a desired maximum value. This is accomplished in the present invention by eliminating the "negative" effects of the stresses on the "tension side" of the elastomeric bearing, i.e. the minor portion 36 B adjacent the central part 25 c of the link body. In addition, the overall stiffness of the link to cocking and torsional motions is reduced, and this is desirable. The torsional and cocking spring rates provides the further advantage of reducing the hysteresis heat generated within the elastomeric layers during operation of the link, and lower steady state operating temperatures enhance the endurance of the link. Some variations in the aforedescribed construction may provide additional advantages. For instance, the relative sliding connection between the inelastic shim and its adjacent elastomeric layer may be provided by means of a low friction connection, such as a layer of Teflon® (polytetraflouroethylene)polymer. In addition, the elastomeric and inelastic shims in the minor arcuate bearing section 36 B may be of a construction different from those in its companion major section 36 A to maximize the compression moduli while still providing desirable shear moduli which will accommodate the required torsional and cocking motions present when the link is loaded in a compressive direction. In other words, the minor bearing section 36 B may be designed to provide a "snubber action". In the illustrated embodiment, the shims and elastomeric layers in the major arcuate extent of each bearing are bonded both together and to both the inner bushing and the link body. The various layers are thereby retained in operative relation. It is noted, however, that the spherical shapes of the shims and cavities in the link body also provide a captive, or retention, function of the bearing to the link so that, for certain applications where less than all of the advantages of the preferred embodiment may be adequate, there may be no need for the elastic layers to be bonded to either the inner bushing or the link body. Preferably, the various inelastic layers are provided by metal shims formed to provide the desired parallel, hemispheric curvatures and nesting relationships illustrated. All of the shims are preferably continuous throughout the major arcuate extent of each bearing. Such continuity further aids in reducing fatigue-inducing stresses among the elastomeric layers and in the body of the link itself adjacent its ends. The various elastomeric layers may be of uniform thickness, or they may be of different thicknesses in a radial direction. A preferred elastomer includes type SPE® X type elastomer manufactured by Lord Corporation of Erie, Pennsylvania. For a more complete description of the manner in which the various elastomeric layers and inelastic shims may be configured to interact in an elastomeric bearing, reference is made to U.S. Patents 4,804,352 and RE 30,262 both issued to Schmidt and owned by the assignee of the present application. In view of the foregoing, it should be apparent that the present invention now provides an improved link and elastomeric bearing assembly which is durable and which can be manufactured readily utilizing state-of-the-art manufacturing techniques. Because of its durability, the link and its associated elastomeric bearings can be operated for relatively long periods of time between inspection and replacement. As a result, the link of the present invention is particularly suited for use in severe heavy duty applications involving the transmission of substantial horsepower in link-type rotary couplings connecting misaligned shafts. While a preferred embodiment of the present invention has been described in detail, various modifications, alterations and changes may be made without departing from the scope of the present invention as defined in the appended claims.

Claims: A link (25,26,27) for use in transmitting rotational torque from a drive element (12) to a driven element (13), said link providing a tension and compression connection along a longitudinal axis (B-B) while accommodating relative pivotal motion between the elements in a direction transverse to said axis, said link including a link body (25 c ) extending along said axis between said elements, first means (25 a ) for connecting said link body at a first location to one of said elements, and second means (25 b ) for connecting said link body at a second location to the other of said elements, at least one of said connecting means including an inner member (53 a ,53 b ) and a plurality of alternating layers of elastic (40,41,42,43,44,45,46) and inelastic material (47,48,49,50,51,52) disposed between said inner member and said link body, said link being characterized by said alternating layers being arranged in separate arcuate sections (36A,36B) extending transverse to a loading axis of said link on diametrically opposite sides of said inner member, said link comprising a pair of discontinuities (36C,36D) between said alternating layers being arranged on opposite sides of said longitudinal axis to permit said inner member to pivot with minimal restraint relative to said link body when said link body is stressed in tension, said discontinuities creating sections (35A,36A) extending through a major arcuate extent and sections (35B,36B) extending through a minor arcuate extent, said discontinuities preventing the transmission of tensile stresses between the major and minor arcuate sections during normal torque transmission, whereby the link can accommodate the desired tension and compression loads and pivotal motions in a manner that minimizes undesirable stresses among the elastic layers. A link according to Claim 1 further characterized by means (46 a ,57 a ) providing a slip joint extending through a predetermined arcuate extent between said discontinuities and between one of said layers of elastic material and an adjacent layer. A link according to Claim 2 further characterized by said one layer of elastic material (46 a ) being located adjacent to said inner member and is bonded thereto, and said adjacent layer includes a shim (57 a ). A link according to Claim 3 further characterized by said shim having a first surface confronting said one layer of elastic material and a second surface opposite said first surface bonded to said link body by means of intervening bonded layers of said elastic and inelastic material bonded together between said discontinuities (36 C ,36 D ). A link according to any one of Claims 1 to 4 being further characterized by said pair of discontinuities being defined by a pair of cavities (36 C ,36 D ) extending along the pivot axis of said inner member between said inner member and said link body. A link according to Claim 5 being further characterized by said pair of cavities being located on opposite sides of said longitudinal axis equidistant therefrom within an arc subtended by an included angle of less than about 180° from the pivot axis of said inner member. A link according to any of Claims 1 to 4 further characterized by said alternating layers being bonded between said inner member and said outer member in an arcuate zone (36 A ). A link according to Claim 7 further characterized by said relatively inelastic layers in one of said zones (36 A ) extending through an arcuate extent greater than pi radians for normally accepting compressive loads.

Inventors: POTTER JAMES L, RUSSELL DONALD D, STAPLES FRANK E, POTTER, JAMES L., RUSSELL, DONALD D., STAPLES, FRANK E.
Applicants: LORD CORP, LORD CORPORATION
Application year: 1991
Main classification: F16F1
IPC codes: B64C27, F16D3, F16F1, F16C33, F16C11, F16C27