Abstract:
Addressed are couplings for transferring rotational motion from one shaft to another. The couplings may include flexible components and may be designed to accommodate angular, axial, and parallel misalignments. Included as components of the couplings may be hub portions, each having dowel pins and clearance holes, and a center member positioned intermediate the hub portions.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of U.S. patent application Ser. No. 10/761,728 filed on Jan. 21, 2004 now U.S. Pat. No. 7,235,014 entitled “Flexible Couplings,” now allowed, the contents of which are incorporated by reference herein. 

   FIELD OF THE INVENTION 
   This invention relates to assemblies for transferring motion from one shaft to another and more specifically to couplings that are flexible or may, if desired, contain flexible components. 
   BACKGROUND OF THE INVENTION 
   Couplings conventionally are used to transfer motion from one machine shaft to another. Numerous issues are presented in designing a suitable coupling, with variables such as torque, speed, misalignment, dampening, backlash, cost, size, reliability, ease of maintenance, and ease of manufacture needing to be considered. Consequently, many couplings either are designed for particular purposes or function optimally only in certain circumstances. 
   At least some couplings are rigid, providing essentially no flexibility. Often cylindrical in shape, these couplings include openings on each end of the cylinder to receive shafts. Typically set screws are used to lock the received shafts into position, although some versions of rigid couplers employ alternative fasteners (such as square keys or woodruff keys). Regardless of fastening mechanism, though, these couplings tolerate essentially no shaft misalignment and cannot provide any dampening. 
   Other existing couplings are known as “spider” couplings. Also generally cylindrically shaped, these couplings include protruding members and utilize a cushion (the “spider”) between cylindrical hubs. Although the machine shafts are locked in position relative to each hub (as they are in rigid couplings), employing a spider made of elastomeric material accommodates at least modest shaft misalignment and allows, potentially, for some dampening to occur. By contrast, possible failures of the protruding members under load or shock limit the functionality of these couplings. 
   Yet other couplings presently available are called helical beam couplings. Formed, basically, of tubes with helixes cut around the tube walls, these couplings nevertheless maintain rigid hub-shaft connections at their ends. Consequently, although they sometimes may admit some parallel misalignment, they typically permit no axial misalignment of shafts or dampening of the motion. Helical beam couplings further likely will not support high torque levels and are relatively expensive. 
   Another type of commercially-available coupling is the slotted-disc, or Oldham, coupling. In this device a hard slotted disc replaces the spider of the spider coupling, allowing the ends of the coupling to move independently of one another. Failures of the disc may occur, however, and no axial (and little angular) misalignment of shafts is permitted. Oldham couplings additionally permit only small amounts of dampening. 
   Pinhole-disc couplings (also known as Schmidt couplings) likewise are similar to spider couplings. However, rather than utilizing protruding members, pinhole-disc couplings employ dowel pins on half of the face of the coupling hub. Hubs are joined with special flexible discs that clock them at ninety degrees to each other. Again, though the (usually plastic) discs, or the dowel pins, may fail in use; additionally, no axial shaft misalignment is permitted and only limited dampening is available. 
   Bellows and gear-and-sleeve couplings provide further alternatives to the couplings heretofore described. Bellows couplings, with their accordion-style shapes, are highly flexible. They permit neither axial shaft misalignment nor dampening to occur, however, and because of their shape are relatively expensive to manufacture. Gear-and-sleeve couplings, by contrast, allow some dampening. Typically consisting of metallic hubs with external gear teeth that slide into tubular sleeves with complementary grooved teeth, these couplings are advantageous when significant axial misalignment is expected. However, they are relatively expensive to manufacture, require substantial maintenance, tend to vibrate at high speeds, and need lubrication on many metal sleeve designs. 
   Among other conventional couplings are double-loop ones, comprising two hubs with a flexible double loop of elastomeric material molded so as to provide an offset figure-eight to each hub. These couplings fail to permit dampening and are relatively expensive to manufacture; as well, because the elastomeric material is large, they require substantial space for operation. Tire couplings likewise comprise hubs (albeit large metallic ones) connected by an elastomeric “tire.” Tire walls are clamped to the large hubs while smaller quick-disconnect bushings lock the hubs to the shafts on each end. Similar to the double-loop couplings, these tire couplings require significant space in which to operate and are expensive to produce. They further are heavier than most other couplings and do not support large torques. 
   Shear couplings attempt to protect over-driven shafts from damage. These couplings include two metallic cylindrical hubs, the ends of which receive the shafts, and a molded elastomeric member between them. Rather than supporting high-torque operation, the member contains a center section designed to fail when subjected to high torque so as to reduce the risk of the shaft doing so. Shear couplings also do not permit any axial misalignment of shafts and allow only low angular and parallel misalignments. 
   Multi-flex couplings, like many others, include two metallic hubs with a central elastomeric element. Each hub has a groove on its face that contains teeth, and the elastomeric element has integrally-formed teeth on its inner and outer sides at each of its ends. The teeth of the elastomeric element fit into each hub. Possibility of failure of the elastomeric elements remains an issue for these couplings, are does their limited ability to tolerate misaligned shafts. 
   Roller-chain couplings provide yet other alternative devices. Consisting of hubs with external gear teeth on an end, these couplings are joined y a roller chain set into the gear teeth so as to lock the hubs together. A cover wraps each set of hubs and chain to complete an assembly. Lubrication is required for the couplings, however, and misalignment tolerances are small. Failure of the chain, further, will result in the coupling being unable to transfer rotational motion. 
   Frontline Industries, Inc. of Irvington, N.J. advertises yet another coupling under the name “Big Boy.” This coupling consists of a hub with a center hole to mount shafts and multiple bores positioned around the hub face. A center ring, containing twice as many holes as the number of hub bores, accepts threaded, bullet-shaped pins. Each assembly includes a hub, pins installed on each side of the hub, and a cylindrical rubber bushing placed over the pins, which are then inserted into the bores. Among disadvantages of the “Big Boy” coupling are that it appears to require close tolerances for operation and is expensive to manufacture. The coupling also could disengage if axial misalignment exists above a modest level. 
   Finally, also advertised as commercially available is the “Superflex Super Elastic Coupling.” This coupling incorporates a flexible center section connected to two metallic hubs with through bolts positioned in an alternating pattern. It is large in size, however, and both expensive and designed for heavy industrial use. 
   SUMMARY OF THE INVENTION 
   The present invention provides alternatives to these and other existing couplings. Designed to accommodate substantial angular misalignment, medium speeds, and high torques, the couplings of the invention also permit simultaneous axial and parallel shaft misalignments. The couplings additionally are reliable, relatively inexpensive to manufacture, and do not require maintenance of close tolerances. They further may be small in size yet scalable if necessary to meet demand for larger sizes. Other beneficial characteristics of the couplings include maintenance of rotational motion transfer notwithstanding failures of portions of the couplings, relatively few parts, minimal backlash, good dampening qualities, no need for lubrication, and ability to withstand high shock force loads without failure. 
   Certain preferred embodiments of the invention include pairs of metallic hubs with multiple dowel-like pins and large, offset clearance holes. A center member, advantageously made of elastomeric material with multiple openings, may be fitted between the hubs. Dowel pins also may be pressed, threaded, or otherwise positioned into each hub. The pins preferably (although not necessarily) are tapered toward their free ends to provide additional angular clearance. 
   To assemble these couplings, a center member may be slid onto the pins of a hub. Thereafter, a second hub may be rotated sixty degrees so that the pins slip into the holes of the center member. Pins from one hub slip through the clearance holes of the opposing hub but do not touch the opposing hub during normal operation. Openings in each hub receive shafts, with fasteners such as (but not necessarily) key slots and set screws locking them in place. 
   This structure transmits rotational force through one shaft to a hub and dowel pins, then to the center member (in shear), to the opposing dowel pins in the opposing hub, and finally to the other shaft. In some embodiments, angular misalignment tolerance may be as great as ten degrees. Parallel misalignment may be tolerated as a function of clearance hole sizes, while axial misalignment is tolerated as a function of dowel pin length. If parallel misalignment is significant, the dowel pins will move diametrically around the clearance holes of the opposing hub as the coupling rotates. Should a pin fail, the remaining pins would enable the coupling to transmit rotational motion (assuming the loads are not so great as to cause the coupling itself to fail). 
   Various embodiments of the invention allow the center member to be made of either elastomeric or rigid material. Using elastomeric material to form the center member likely would improve torsional dampening characteristics of the couplings while increasing backlash. Employing rigid plastic or other material for the center member should result in decreased backlash but decreased dampening as well. 
   Embodiments of the invention also may permit removal and replacement of the center member. Similarly, they allow for use of dowel pins other than as described above. As an example, rather than tapering, the dowel pins may be headed to limit axial misalignment in certain circumstances. 
   It thus is an optional, non-exclusive object of the present invention to provide couplings for transferring rotational motion. 
   It also is an optional, non-exclusive object of the present invention to provide couplings adapted to accommodate angular, axial, and parallel shaft misalignments. 
   It is another optional, non-exclusive object of the present invention to provide couplings utilizing hub components having both pins and clearance holes. 
   It is an additional optional, non-exclusive object of the present invention to provide couplings utilizing a center member received by the pins. 
   It is a further optional, non-exclusive object of the present invention to provide couplings in which pins from one hub assembly slip through clearance holes of an opposing assembly. 
   Other objects, features, and advantages of the present invention will be apparent to those skilled in the relevant field with reference to the remaining text and the drawings of this application. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric, partially exploded view of a hub of the present invention. 
       FIG. 2  is a side view of the hub of  FIG. 1 . 
       FIG. 3  is an isometric, partially exploded view of a coupling of the present invention utilizing hubs of  FIG. 1 . 
       FIG. 4  is an end view of the coupling of  FIG. 3 . 
       FIG. 5  is a side view of the coupling of  FIG. 3 . 
       FIG. 6  is another side view of the coupling of  FIG. 3  illustrating tolerance of substantial angular shaft misalignment. 
   

   DETAILED DESCRIPTION 
   Illustrated in  FIGS. 1-2  is hub assembly  10 . Assembly  10  comprises hub  14  and one or more pins  18 . Also included as part of assembly  10  may be fastener  22 , which is shown in  FIGS. 1-2  as comprising a set screw. However, those skilled in the appropriate art understand that devices other than or in addition to a set screw may be utilized as fastener  22 . 
   Depicted in hub  14  is bore  26 , defined by collar  28  and designed to receive, in use, a rotating shaft. After such a shaft is received in bore  26 , fastener  22  may be tightened to fix the position of the shaft relative to hub  14 . One or more openings  30  in hub  14  receive pins  18 . Pins  18  typically are pressed into openings  30  and maintained therein with a friction fit. They need not, however, be so pressed, but instead may be connected to hub  14  in any suitable way or integrally formed therewith. 
   Also illustrated in hub  14  are one or more clearance holes  34 . Shown as interspersed radially with openings  30 , clearance holes  34  are adapted to receive pins  30  from another hub  14 . In the embodiment of hub  14  detailed in  FIG. 1 , three each of openings  30  and clearance holes  34  are present in the hub  14 , with each hole  34  being offset radially from an adjacent opening  30  by sixty degrees. Fewer or greater numbers of openings  30  and clearance holes  34  may exist, however, if necessary or desirable. 
   Pins  18  are shown in  FIGS. 1-2  as being generally in the form of dowels. Preferred versions of pins  18  are tapered adjacent their free ends  38 . Fixed ends  42 , by contrast, are configured for fitting into openings  30 , preferably (although not necessarily) flush with outer face  46 . As fitted, pins  18  protrude from inner face  50  of hub  14 . 
     FIG. 3  illustrates, in exploded form, coupling  54 . Coupling  54  typically comprises a pair of hub assemblies  10  (denominated  10 A and  10 B) together with center member  58 . As constructed, center member  58  is positioned intermediate the hub assemblies  10  and received by both such assemblies  10 A and  10 B. 
   In particular, center member  58  includes a plurality of openings  62 , at least one opening  62  for each pin  18  of each hub assembly  10 . Thus, in the exemplary version of coupling  54  depicted in  FIG. 3 , center member  58  includes six openings  62 , equaling the total number of pins  18  present in exemplary hub assemblies  10 A and  10 B. These six openings  62  are spaced radially about center member  58 , with one present every sixty degrees. Again, however, fewer or greater numbers of openings  62 , and different spacings, may be utilized instead. 
   In use, center member  58  is positioned between respective inner faces  50 A and  50 B of hub assemblies  10 A and  10 B. By appropriately rotating one hub assembly ( 10 A or  10 B), each pin  18  will align with and pass through an opening  62  of center member  58 . Such rotation would equal sixty degrees in the exemplary coupling  54  of  FIG. 3 . Each opening  62  advantageously is only slightly larger than the diameter of its associated pin  18 , although other size relationships could exist instead (particularly if pin  18  is not generally cylindrically shaped or opening  62  is non-circular). 
   After passing through a corresponding opening  62  of center member  58 , each pin  18  is then received by a corresponding hole  34  of the associated hub assembly  10 A or  10 B. Stated differently, for a particular pin  18 ′ of hub assembly  10 B, the pin  18 ′ passes first through opening  62 ′ of center member  58  and then through hole  34 ′ of hub assembly  10 A. The result is depicted in  FIGS. 5-6 , which show pins having a length sufficient to be received by and extend substantially into a corresponding hole of the opposite hub. Generally, the diameter of hole  34  is substantially larger than the diameter of pin  18  so as to provide clearance therefore. If either pin  18  or hole  34  lacks circular cross-section, hole  34  preferably still will provide significant clearance for pin  18 . 
     FIG. 6  illustrates the ability of coupling  54  to tolerate substantial angular misalignment of respective shafts. Because holes  34  are larger than ends  38  of pins  18 , pins  18  are able to move some before abutting the boundaries defining holes  34 . Shown in  FIG. 6  is hub assembly  10 B misaligned approximately five degrees from axis AX, although greater angular misalignments may also be tolerated. In instances in which substantial parallel misalignment exists, pins  18  will move diametrically within their corresponding clearance holes  34  as coupling  54  rotates. 
   Coupling  54  is designed to function satisfactorily at medium speeds and high torques and without lubrication. Hubs  14  preferably (but not necessarily) are made of metal; if so, the metal may be cast, forged, sintered, machined, or otherwise processed as appropriate. Center member  58  preferably is made of flexible material such as (but not limited to) plastics or natural or synthetic rubbers. Alternatively, center member  58  may be made of more rigid plastics or other materials. Center member  58  additionally may be removable if desired for repair, replacement, or otherwise. 
   The foregoing is provided for purposes of illustrating, explaining, and describing exemplary embodiments and certain benefits of the present invention. Modifications and adaptations to the illustrated and described embodiments will be apparent to those skilled in the relevant art and may be made without departing from the scope or spirit of the invention. Additionally, although coupling  54  is designed principally for use in aircraft seats with moveable components, it may be used in other seats (vehicular or otherwise) or for other purposes as appropriate or desired.