Abstract:
A coupling between a driving and a driven shaft includes a rigid tube to which are attached by bonding, in axially spaced apart relation at least two flexible annular elements of elastomeric material, the annular elements being of various shapes; the outer periphery of each ring is bonded to an attachment ring which is attachable to a flange of a connecting hub with each hub mounted or connected to one the shafts; in one form the tube is split axially and is adjustably attachable to the periphery of the rings.

Description:
[0001]     This is continuation is part of application Ser. No. 09/696,004, filed Oct. 26, 2000, now U.S. Pat. No. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to flexible coupling devices for shafts to permit and facilitate transmission of torque between a drive and a driven shaft while accommodating misalignment between the shafts. More particularly, the present invention relates to spool type flexible couplings, where the spool will permit a relatively large variation of the distance between the shafts to be coupled and a greater degree of accommodation of distance variation between the shafts. The flexible elements of the coupling will include outer rings usually of metal to allow secure attachment to hubs provided on each of the shafts to be coupled and a central connecting tubular piece between the flexible elements. Various types of elastomeric type flexible elements are disclosed with particular emphasis on optimal construction for maximum bond strength and durability.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the field of elastomer or plastic flexible elements couplings, a number of considerations affecting the design of a flexible coupling exist. Among these are the degree of misalignment tolerated, the anticipated torque loads and design constraints relating to the installation allowed. In some arrangements, only a limited type of elastomeric material could be employed in a coupling to accommodate the torque loads desired. In other arrangements, the cost of the coupling has been increased, as a result of the complicated design of the flexible elements of the coupling. The assembly means of the flexible elements to the other coupling components has been the typical deficiency of prior art couplings. This is an essential factor in the coupling design, affecting both cost and performance capabilities.  
         [0004]     One such prior art coupling is shown in  FIG. 2  of a French Patent No. 984,089 of Jul. 2, 1951. The assembly method of the element, detailed in  FIG. 1 , shows a complicated arrangement of several typically heavy metal parts, which clamp the upper and lower extremities of the flexible element, to allow torque transmission. The main problem of clamping elastomer parts is that they do not generally retain their original shape under load and acquire a permanent set. This reduces the initial clamping force, and loss of torque capacity. The clamped areas at the upper and lower extremities of this element are also highly stressed and subject to failures in operation. The number of auxiliary parts is also increasing the fabrication cost.  
         [0005]     Another coupling construction and element assembly method is described in U.S. Pat. No. 4,411,634 to Hammelmann. The materials for the flexible elements, described as diaphragm-style in common coupling terminology, and the central spacer shaft are plastic. They are not described as having elastomer ic properties, but to a lesser extent, they exhibit similar properties in terms of stress-deformation set. The inner diaphragm connection is achieved by a press fit among several convoluted shaped parts. For this reason, the low material modulus requires a considerable thickness and weight for the center tube to allow a reasonable torque capacity and avoid compression set. Additional complications of the design are required, such as the steel sleeves pressed inside and outside the tube, as well as the convoluted steel reinforcement part mounted at the inside diameter of the diaphragm hub, fitted over the convoluted sleeve mounted over the shaft ( FIGS. 1 and 2 ). The outside flexible element connection is achieved through bolting. The thicker rim of the element is provided with holes and is clamped between two metal members. The compression stresses developed when the fasteners are tightened have a negative effect on the performance of the coupling, acting as stress concentration areas, and failures are likely to occur in this upper extremity of the plastic flexible diaphragm member.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention avoids the complications of the prior art devices yet provides a flexible coupling, which, in its basic form, accommodates a much broader range of distances between the shafts to be coupled, from relatively large to very close shafts separations, yet reliably transmits torque over a satisfactory range and through an increased degree of tolerance for misalignment.  
         [0007]     In one form of the invention for close spaced shafts, the coupling spool is split longitudinally and reinforced during assembly by a rigid ring which may be bolted in place during installation. The rigid ring serves as reinforcement for the split spool. In addition, flexible elastomeric annular diaphragms are employed as the flexing members of the coupling and are also split and attached by bonding on the respective halves of the split spool and to the outer split attachment rings prior to installation in the coupling. This allows assembly and disassembly for closely spaced shafts, without moving the hubs installed on the shafts, or the two connected machines.  
         [0008]     In another form, the present invention provides a permanently assembled coupling spool piece, consisting of two axially spaced elastomer flexible diaphragms, bonded at their inner periphery to a tubular piece, and also bonded at their outer periphery to a pair of similarly axially spaced rings, each such ring member having attachment bores for securing it to the respective flanges or hubs of the shafts to be coupled. The tube, rings and flexible elements thus form a unitary spacer assembly which is easy to install and remove.  
         [0009]     In another form, the present invention provides a coupling spool on which are initially movably mounted two coupling sleeves at opposite ends thereof. Each coupling sleeve is provided with a flexible diaphragm in the form of an elastomeric element bonded to an outer ring preferably of metal, which can be coupled directly to a flange of a coupling hub, which in turn is mounted on a drive or a driven shaft. The flexible elements are spaced apart a distance that is typically more substantial than in the prior art arrangements. Minor manufacturing changes will enable the coupling of this form of the present invention to accommodate a broad range of distances between the shafts to be coupled. The coupling tube combinations will be such that these members can be readily assembled together by adhesive bonding, riveting or the like. As noted above, the flexible elements incorporated in the coupling are preferably made from a flexible elastomeric material that is shaped to accommodate the degree of flexibility needed for a particular application without experiencing stresses leading to failures in normal use. In one form, the flexible elements are formed with a curve so that the outer end of the elements will be axially spaced from the center of the base of the element. With the flexible element preferably manufactured in an annular shape, a taper is provided where the element narrows as one moves radially outwardly from the inner periphery of the element to adjacent the outer rim which is narrower in axial extent. The actual cross-sectional shape and taper are designed for the application requirements. The element may be manufactured using various common elastomer processing methods, such as compression, gravity casting or injection molding.  
         [0010]     In terms of the flexible element/adjacent parts attachment method used in the present invention, bonding has been chosen for it&#39;s simplicity and absence of auxiliary parts. The reliability of elastomer adhesives has evolved over the years, the modern ones exhibiting a much higher strength than in the past. Lord Chemical Corporation is one of the manufacturers of such adhesives.  
         [0011]     With the flexible couplings of the present invention, a user a will be able to transmit high torque loads while accommodating high degrees of misalignment. Further, the coupling is characterized by ease of installation in either narrow or extended spaces between the shafts and by a low number of individual parts for assembly. With even widely spaced apart shafts, the flexible coupling of this invention will provide high-speed capability due to the high radial rigidity of the flexible elements.  
         [0012]     The foregoing and other advantages will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a side view in elevation of one embodiment showing an arrangement of the elements of the present invention using a split spool;  
         [0014]      FIG. 2  is a view along lines  2 - 2  of  FIG. 1 ;  
         [0015]      FIG. 3  is a side view in elevation of an alternate arrangement of the elements of the present invention;  
         [0016]      FIG. 4  is a side view in elevation of a further arrangement of the elements of the present invention;  
         [0017]      FIG. 5  is a perspective view in section of a further embodiment of the present invention;  
         [0018]      FIG. 6A  is a side view in elevation of the coupling of the present invention; and  
         [0019]      FIG. 6B  is a view similar to  FIG. 6A  but with the telescoping feature shown in a different condition.  
         [0020]      FIGS. 7-9  are respective side views in elevation, partly in section, of several further forms of the invention;  
         [0021]     FIGS.  10  is a detailed view in elevation of the curved flexible ring of  FIG. 9 ; and  
         [0022]      FIG. 11  is a side view in elevation of an alternate arrangement of the elements of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring to the drawings, in  FIGS. 1 and 2 , there is shown an embodiment of the present invention which is adapted for close-coupled shafts, that is, shafts the ends of which are in close proximity to one another and which cannot be moved away from each other than at an unacceptable cost. In this arrangement, the spool is in the form of a split tube  32  which is reinforced by an inner ring  34  and which is held in place typically by four bolts such as at  36 , which are evenly spaced about the periphery of the split tube  32 . The ring  34  is preferably located at the midpoint of the tube  32  as shown in  FIG. 1 . The ring  34  may be integral or provided in two halves, with two bolts provided to retain each half of the ring  34  in place against the inner surface but bridging over the edges as at  41 ,  43  of the tube halves which it is reinforcing. As shown in the sectional view of  FIG. 2 , the tube  32  is split longitudinally along its entire length to provide two semi cylindrical bodies  32 ′ and  32 ″. Similarly, the flexible elastomeric rings  16  may each be split into two parts  16 ′ and  16 ″. The radially inner peripheral edges of the ring parts  16 ′ and  16 ″ will each be easily secured by a suitable, commercially available adhesive to the radially outer peripheral surface of the split tubes  32 ′ and  32 ″. According to this embodiment, the diameter of the split tube  32  is made large enough to accommodate the hubs  26  as shown in  FIG. 1 . This will allow a substantially more compact configuration for the elements when achieving coupling between two closely located shaft ends  28  and  30  and yet will provide a coupling with adequate flexibility and tolerance for axial misalignment. The radially extending flanges  22  of hubs  26  are continuous to provide adequate torque transfer through the split rings  16 ′ and  16 ″. The axial extent of the hubs  26  allows it to be easily secured as by welding to the outer surfaces of their respective shafts  28  and  30 . Since the spool is provided in two parts  32 ′ and  32 ”, the coupling will be easily reassembled whenever it is necessary to repair or replace elements such as the flexible rings  16 ′ and  16 ″.  
         [0024]     The assembly of the elements of the coupling of  FIG. 1  and  2  is important to obtain the full benefit of the invention. To avoid distortions of the split elements under torque, the presence of the reinforcing ring is mandatory. In the case of a split ring it is preferable to offset the split edges  41 , 43  of the spool halves  32 ′ and  32 ″ by ninety degrees to the edges  47 ,  48  of the split ring  34  as shown in  FIG. 2 , so that the rigidity of the assembly is not affected.  
         [0025]     In  FIGS. 6A, 6B , and  11 , illustrate invention forms designed for extra-long or adjustable length spools for wide shaft spacing. The telescoping form of the inventions  10 ,  10   a  are shown, where a spool  12  and  12   a  is interposed between two relatively larger diameter sleeves  14 . Each of the sleeves  14  and  14   a  is identically configured so that a description of only the right hand sleeve will be provided.  
         [0026]     The sleeves  14  and  14   a  and spool  12  and  12   a  are preferably made of a material such as steel or fiberglass that is easily bonded together with a conventional adhesive such as an epoxy or connected mechanically such as by rivets. Additionally, annular ring members  16  and  16   a  are readily bonded about their respective inner openings to the outer peripheral surface of each sleeve  14  and  14   a  as shown with conventionally available adhesives such as epoxies. The flexible element member  16 ,  16   a  is bonded at its outer periphery to the inner surface of a ring member  19 ,  19   a  which has equally spaced about its body bores  18 ,  18   a  in which locking bolts  20  are located. A connection hub  26 ,  26   a  is provided with an annular flange  22 ,  22   a,  which is provided with openings for receiving the bolts  20 ,  20   a.  Locking nuts  25  are employed to effect the attachment of the coupling flange  26 ,  26   a  to the flexible element member&#39;s  16 ,  16   a  as shown in these Figures.  
         [0027]     The flexible coupling  10  as described above is particularly adapted to accommodate spaced apart annular flexible rings  16 ,  16   a  for a range of distances “I” to “L” between the coupling flanges  22 . In  FIG. 11 , the corresponding elements are denoted with the suffix “a” with the general designation  10   a  corresponding to the tube or spool  10  in  FIGS. 6   a  and  6   b.  In this construction, the intermediate sleeves are inserted into the open ends of each sleeve  14   a  and preferably bonded to intermediate connecting bushings  13   a  by an adhesive although riveting or bolting may suffice in some applications. Thus, by simply selecting spools  12  and  12   a  of a desired length, a user can accommodate a broad range of coupling distances between shafts.  
         [0028]     As will be apparent from  FIG. 3 , where a telescoping facility is not used, the spool  12  may be employed alone as shown in  FIG. 3  to provide a flexible coupling employing spaced apart flexible, elastomeric rings  16  which are securely bonded to the outer periphery of the spool  12  adjacent the ends of the spool  12 . This form of the invention is used for fixed lengths, such as  3 ,  5  and  7  inches, typical for industry-established standards. The use of a suitable elastomeric material such as polyurethane elastomer for the diaphragm elements  16  makes it particularly easy to install. In this and the other forms using a hub flange  22 , an outer lip  23  may be provided to stabilize the parts during assembly as well as use.  
         [0029]     A modification of the coupling of  FIG. 1  is shown in  FIG. 4  where a spool member  40  surrounds the coupling elements including two hubs or sleeves  42  and  44 . The flexible, elastomeric ring members  16  are bonded at their interior periphery directly to the outer periphery of each of the hub members  42  and  44 . The outer periphery of each of the members  16  are similarly bonded to the inner periphery of the reinforcing rings  46  and  48 . The spool  40  may be either bonded or riveted as through holes  50  to the outer periphery surface of the rings  46  and  48 . The shafts to be coupled will be inserted into the interior of a hub  42  to an extent to allow the second shaft to be inserted as through end  51  into hub  44 . The shafts will then be fixed to their respective hubs  42 ,  44  by welding, bolting, riveting, or the like. The spool  40  may be split parallel to its longitudinal axis to facilitate installation where the shafts are too closely placed together at the site to allow easy installation.  
         [0030]     Referring to  FIG. 5 , there is shown a perspective, sectional view of a further modification of the invention where a split spool  50  is employed in a configuration similar to that of  FIG. 4  but with the hubs projecting externally of the ends of the spool  50 . Again, the elastomeric elements  16  are bonded to the inner periphery of reinforcing rings  56 ,  58  and to the outer periphery of the shaft mounting hubs  52  and  54 . Again, the use of a split spool facilitates installation without sacrificing the integrity of the coupling or its torque transmission ability. In addition, the rings  56 ,  58  may be positioned at positions located axially inwardly of the outer edges  60  of the spool  50  sections by the provision of alternate fastener bores  62  located, as shown, inwardly of the edges and the outermost holes in which the screws, two of which are indicated at  64 , are positioned. A plurality of sets of bores  62  may be provided to expand the range of adjustability.  
         [0031]     The use of spaced apart flexible rings as described in the foregoing embodiments increases the misalignment tolerated by the couplings while allowing significant latitude in installation. Moreover, the couplings described above will provide high torque transmission while retaining the advantages of lightweight installations.  
         [0032]     With respect to the embodiments shown in  FIGS. 7-10 , these forms use a modified flexible ring element, which is characterized by the provision of an extended base or pedestal and/or a curvature along the radial extent of the ring element.  
         [0033]     In  FIG. 7 , there is shown a coupling similar to that shown in  FIG. 3  but one where the flexible elements  70  are shaped to include a larger surface area for the base  72  to improve the bonding strength and durability for the elements  70  to the surface of the spool  12   c.    
         [0034]     This form of the invention is based on the construction of the spacer coupling component in  FIG. 7  and presented in its most general form: a single piece assembly comprising five permanently assembled parts: two outer rings  19   c,  which may be metal, two axially spaced, annular elastomer flexible elements  70  and one central tubular piece  12   c.  The assembly is affected by bonding the peripheral areas at the inside and outside interfaces of the flexible elements  70  with the tube  12   c  and rings  19   c,  respectively. The rings and the tube are significantly more rigid than the elastomer flex elements material, which is preferably a polyurethane formulation and which features better properties for torque transmission than other elastomer classes. The tube  12   c  can be made of metal and composite materials such as fiberglass can also be used. The interface bond is formed by using one of many commercially available adhesives, formulated specifically for the attachment of urethane to metal or fiberglass parts. Their strength, resistance to temperature and chemical agents is constantly improving.  
         [0035]     Referring again to  FIG. 7 , it will be appreciated that each of the elastomer elements  70 , which are substantially annular shaped extend a radial distance H from the outer radius of the tube  12   c  to the inner radius of the ring  19   c.  Each element  70  comprises two main portions: a thicker and more rigid radially inner base  74 , which provides bond reinforcement, of radial height “a” and a flexible portion profiled and tapered according to the application requirements, the profile having a neutral axis  72  (defined as the curve or line equally spaced from the two sides of the profile), its radial extent being “H-a”. A large degree of flexibility for a given profile is associated with a high “(H-a)/H” ratio.  
         [0036]     The base portion  74  is typically the thickest at the inner periphery, and the thinnest area of the profile “t” is generally situated towards the outer periphery. The height and thickness H and a may be theoretically and empirically determined relative to the torque load and rotational speed of the coupling. It has been found that, for the widest range of loads and rotational speeds, the flexible elements  70  should be curved at least on one side as shown in  FIGS. 1 and 7  and preferably two sides as well as shown in  FIG. 8 . The thickness of the base  74  portion may also be increased to control the flexibility of the elements  70  as shown in  FIG. 8  and the axial width may also be increased as shown in  FIG. 9 . These modifications result in a stronger and therefore longer lasting bond between the base  74  of the flexible elements  70  and the supporting spool  12   c.    
         [0037]     As shown in detail in  FIG. 10 , the flexible coupling elements of this invention are preferably curved outwardly, that is, away from each other, as shown in  FIG. 9 . As noted above, each flexible element will have a neutral axis  72  and the range of curvature may vary depending on the specific application including torque load and rotational speed.  
         [0038]     A general range of the curvature amount can be defined by the included angles between lines:  76 ,  84  and  88  shown in  FIG. 10 . As shown in  FIG. 10 , the curvature on the right side of the vertical radial line  84  may be represented as the included angle φ, defined by a line  76  which extends from the inner end  80  of the neutral axis to the outer end  82  of this axis and a radial line  84  extending from the inner end  80  of the neutral axis of the flexible element  70 . The angle may range from 0° to about 20°. Additionally, the total curvature amplitude may be represented as the included angle “A” formed by line  76  and line  88  which extends from the inner end  80  of the neutral axis to the point on the neutral axis marked “t/2”, corresponding to the location of the minimum thickness “t”. Angle “A” may vary typically between 15° to about 25°. As shown in  FIG. 10 , the curvature is formed by smoothly arcuate portions, forming the curved shaped neutral axis, resembling an elongated letter “c”. Additionally, the neutral axis  72 , and the vertical axis  84 , starting from the same inner base point  80 , further intersect each other only once, towards the outer periphery of the element. It will be understood that a specific application may require greater or lesser amounts of curvature for the flexible elements  70 .  
         [0039]     A flexible portion profiled and tapered according to the application requirements will have a profile having its neutral axis  72  (defined as the curve or line equally spaced from the two faces or sides of the profile), its radial extent being “H-a” where the neutral axis curve is shaped as shown. This curvature results in a reduction in the bond stresses, typically highest at the joint between the bond reinforcement area  74  and tube  12   c.    
         [0040]     The outer end of the element is preferably provided with an axially extending, annular extension  78  and radially extending face  80  defining a ledge in which the metal reinforcing ring  82  is adhesively bonded. This structure facilitates assembly and imparts additional stability to the coupling. The ring  82  is provided with the conventional bores  84  for receiving bolts to attach the ring  82  to hubs  26 . Preferably, the bores  84  are threaded and blind so as not to interfere with the adhesive bond or the material of the outer end of the flexible element  70  with the metal ring  82 . Lip  86  will act like a protective shroud, providing a coverage area against impact, mishandling, or ingress of chemicals in the bonded zone, which may affect its integrity. Each respective reinforcing ring has surfaces complimentary to the radially extending and the axially extending surfaces of the outer periphery, as shown in  FIG. 10 , with said axially extending surface being positioned radially inwardly of said radially extending surface.  
         [0041]     The bond stresses need to be minimized under torque loading, which are typically the highest at the center of the inner bond of the base portion  74  of the tube or spool  12   c.  For any given profile shape, the stresses on the bond can be reduced by being redistributed away from the critical center, and averaged over a wider portion. The addition of the bond reinforcement area achieves this purpose. Its width “w” of the base portion also contributes to the bond strength, but past a certain magnitude, it does not become proportionately effective. Thus, the bond strength and the degree of flexibility are related at least empirically. Where the torque load to be imposed on a coupling is low, the flexible elements  70  may have an enhanced degree of flexibility but where the torque load is relatively higher, only moderate flexibility can be had.  
         [0042]     The preferred ratios for the conditions noted above are “H/a” ratio in the range of  4  to  16  and with the “w/t” ratio in the range of 2 to 4 for a high degree to flexibility where “t” is the thickness of the flexible element at its narrowest part as shown in  FIGS. 10   a  and  10   b    FIG. 10 . For more moderate flexibility “H/a” should be in the range of 4 to 8 with the ratio w/t in the range of 4 to 8 also.  
         [0043]     The shape of the flexible element, and the general orientation of the neutral axis are additional means of reducing the bond stresses. For example, the two forms of the invention shown in  FIGS. 7 and 8 , designed for lower torque and higher flexibility, exhibit higher bond stresses than the invention in  FIGS. 9 and 10 , described above. For example, the flexible element shown in  FIG. 7  has one flat side and a curved side, for ease of manufacturing through gravity molding. The neutral axis is slightly curved but slanted at the top towards the center of the spool. Additionally, as opposed to the invention in  FIG. 10 , the neutral axis and the vertical centerline starting from a common point close to the inner periphery, do not have another point of intersection towards the outer periphery.  
         [0044]     The element in  FIG. 8  has both sides symmetrically profiled, hence the neutral axis and the vertical centerline coincide. The bond stresses are better averaged than in the case of  FIG. 7 , but the direct vertical path of torque leads to higher bond stresses than in the case of the “c” shaped neutral axis element.  
         [0045]     Having described the inventions, it will be understood that various modifications are possible without departing from the spirit and scope of the invention as defined in the appended claims.