Abstract:
A bearing cage assembly consisting of a plurality of discrete bridge elements coupled between first and second cage support wire rings having selected tensions, and conforming to the surfaces of associated rolling elements. The discrete bridge elements maintain rolling element in separation, provide rolling element retention within the bearing assembly, and function as a lubrication reservoir for grease lubricated bearings. The discrete bridge elements may be disposed between adjacent rolling elements, or may be configured to pass through axial bores of hollow rolling elements

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 61/427,289 filed on Dec. 27, 2010, and which is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present application is related generally to large-bearing cage configurations, and in particular, to a large-bearing cage assembly, consisting of a plurality of discrete bridge elements coupled between axially-spaced cage wire rings which are adjacent opposite axial ends of the rolling elements. 
         [0003]    The typical approach to large-bearing cage design has been to extend the design styles for smaller conventional bearings into the large bearing sizes. The first and most common attempt at meeting the needs of larger bearings used pin style cages to facilitate placement and retention of the rolling elements. While pin style cages provide excellent retention, they are heavy, complex, costly to assemble, block the flow of lubricant to critical wear surfaces, and cannot be disassembled without damaging either the cage rings or the cage pins. 
         [0004]    Another approach is to modify a stamped-steel style cage for use in the large bearing size range. The first problem here is that for large bearing configurations, the cage designs become too large to be stamped or closed in, so alternate manufacturing processes, such as spun blanks that are water jet cut have been attempted. These alternative manufacturing processes seem to create more problems than they solve. The stamping problems for large size cages are eliminated, but at great cost. Cage costs are effectively increased, not lowered, by the use of alternative manufacturing processes. The step of closing-in is replaced by the steps of cutting the cage, adjusting the circumferential size to get appropriate clearance and welding the cage back together, a complex and costly process. Cage distortion, particularly in pocket length and location, as well as cage roundness and flatness, resulting from this manufacturing process can lead to bearing performance and roller retention issues if not controlled sufficiently. These types of cages are still relatively heavy, and are not easily serviceable. Typically, the resulting cage must be cut and re-welded when serviced. 
         [0005]    Both the pin-style and formed cages require welding in close proximity to precision bearing components. There is therefore always a risk of bearing damage due to heat and welding spatter and debris. 
         [0006]    Another alternate which has been tried is the use of segmented polymer cage structures as a more cost effective solution than the spun-blank water-jet cut steel cage, however, while polymer segmented cages have demonstrated the ability to perform satisfactorily in testing, they have potential limitations scaling up to extremely large bearings. The polymer cages currently used in ultra large bearings market have all been made from polyether ether ketone (PEEK), a colorless organic polymer thermoplastic. For extremely large bearings the size and strength of the cage will need to be increased. The greater volume of PEEK required to make a sufficiently strong cage may become cost prohibitive. 
         [0007]    An additional concern with any bearing assembly is a proper flow of lubrication to the critical wear surfaces on the bearing elements. A visual marking of rollers has been observed with water-jet cut steel cages and to a lesser extent with the polymer thermoplastic cages. Pin style cages have been known to have issues with pin wear or breakage due to lack of lubricant between the pin and roller. The large, rectangular section cage rings at each end of the rollers of the pin type may act to impede the circulation of grease in these lubrication systems. Likewise the flanges at each end of polymer segments in a polymer segmented cage, while acting to maintain grease within the roller complement, may affect the circulation of grease into and out of the complement. Alternate polymer segment flange designs can address this issue, but a significant flange is a basic requirement of the design of a polymer segmented cage 
         [0008]    Accordingly, it would be advantageous to provide a segmented bearing cage or retainer assembly which offers the ability to retain very heavy sets of rollers in large bearing assemblies, which does not impede the flow of lubricant to the wear critical surfaces of the bearing assembly, and which is relatively low cost to manufacture. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    Briefly stated, the present disclosure provides a bearing assembly having a plurality of rolling elements disposed about a circumference of a race member with a segmented bearing retainer assembly. The segmented bearing retainer assembly consists of a plurality of discrete bridge elements coupled between first and second wire support rings. Each discrete bridge element is configured to maintain a spacing between adjacent rolling elements in the bearing assembly, and to retain the rolling elements relative to said race member. 
         [0010]    In one embodiment, the discrete bridge elements of the segmented bearing retainer assembly are disposed between adjacent rolling elements in the bearing assembly. Each discrete bridge element consists of a curved retention web supported by a segment bridge between the adjacent rolling elements, and an attachment eyelet at opposite ends through which the first and second wire support rings pass. Each retention web has a curvature selected to distributed a contact load between an adjacent roller and the bridge element both above and below a centerline of the roller. The discrete bridge elements are maintained in a desired spaced arrangement about the circumference of the bearing assembly, between the first and second wire support rings, by a plurality of spacers disposed on the wire support rings between the eyelets of adjacent discrete bridge elements. 
         [0011]    In an alternate embodiment, the rolling elements are hollow rollers, and the discrete bridge elements of the segmented bearing retainer assembly are pin elements disposed coaxially through the hollow rollers in the bearing assembly. Each discrete bridge elements consists of an axial pin section, terminating in eyelets at opposite ends extending axially past the rolling elements, through which the first and second wire support rings pass. A plurality of elongated radial lobes are disposed about each axial pin section, defining piloting contact surfaces between the inner diameter of the hollow rollers and the bridge elements. Voids between adjacent elongated radial lobes provide lubricant flow passages for the unobstructed delivery of lubricant to the contact surfaces within the hollow rollers. The discrete bridge elements are maintained in a desired spaced arrangement about the circumference of the bearing assembly, between the first and second wire support rings, by a plurality of spacers disposed on the wire support rings between the eyelets of adjacent discrete bridge elements. 
         [0012]    In an alternate embodiment, the discrete bridge elements of the segmented bearing retainer assembly are formed from a powdered metal process. The discrete bridge elements may be impregnated with a lubricant, or optionally may have surface features or finishes which are configured to trap and release lubricants over time. 
         [0013]    A method of the present disclosure for assembling a segmented bearing retainer assembly about an inner race of a tapered bearing is accomplished by initially threading a plurality of discrete bridge elements and spacers onto first and second wire segments, which are then looped and secured to form the first and second wire support rings. The total number of bridge elements threaded onto the support rings is equal to N−1, where N is the total number of rollers to be utilized. The total number of spacers on each support ring is equal to N. The assembly of bridge elements, spacers, and wire support rings is positioned over the inner race, and N individual rollers are inserted into the assembly by moving the bridge elements and spacers circumferentially around the first and second wire support rings to provide sufficient space for each insertion. After the final roller is installed on the inner race, the assembled rollers, bridge elements, and spacers are parted to open a space for the final discrete bridge element. After the final bridge element is inserted into the space, it is positioned to fill the remaining gap between the rollers, and is secured in place by bolting eyelet plates over each wire support ring at opposite ends of the final bridge element. 
         [0014]    The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments will become more apparent from the reading of the following description in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0015]    In the accompanying drawings which form part of the specification: 
           [0016]      FIG. 1  is a perspective view of a pre-assembled segmented bearing retainer assembly or cage of the present disclosure; 
           [0017]      FIG. 2  is an partial axial end view of the retainer assembly of  FIG. 1 , illustrating discrete bridge elements or segments arranged with tubular spacers on a wire support ring between adjacent rollers; 
           [0018]      FIG. 3  is a perspective illustration of one embodiment of a discrete bridge element of the present disclosure for threading onto the first and second wire support rings between adjacent rollers; 
           [0019]      FIG. 4  is a perspective illustration of a final discrete bridge element of the present disclosure for clamping onto the first and second wire support rings between adjacent rollers, after all other discrete bridge elements are in place; 
           [0020]      FIG. 5  is a radial sectional view of a retainer assembly installed between an inner race and an outer race, illustrating a lubricant flow past a discrete bridge element and towards critical wear surfaces within the bearing assembly; 
           [0021]      FIG. 6  is an alternative final discrete bridge element, which further functions to secure opposite ends of the first and second wire support rings together at a desired tension; 
           [0022]      FIGS. 7A ,  7 B, and  7 C illustrate an alternate method for securing opposite male ends of the first and second wire support rings together to form closed loops, using a female-female crimping tube segment; 
           [0023]      FIG. 8  illustrates an alternate variation of the method shown in  FIGS. 7A-7C , employing a male-male segment for crimping engagement with opposite female ends of the first and second wire support rings; 
           [0024]      FIG. 9  illustrates a tensioning collar for securing opposite threaded ends of the first and second wire support rings together to form closed loops with adjustable tension; 
           [0025]      FIG. 10  illustrates a radial view of a portion of a segmented bearing retainer assembly which has been assembled using tensioning collars of  FIG. 9 ; 
           [0026]      FIG. 11  is a side view of the discrete bridge element of  FIG. 3 , illustrating surface features for the entrapment and release of lubricant; 
           [0027]      FIG. 12  is a radial sectional view of an alternate embodiment segmented bearing retainer assembly or cage of the present invention, employing discrete pin-elements passing axially through hollow tapered rollers for threaded coupling on first and second wire support rings; 
           [0028]      FIG. 13  is an axial end view of a hollow tapered roller of  FIG. 12 , illustrating elongated radial lobes disposed about each axial pin section of the pin-element, defining piloting contact surfaces between the inner diameter of the hollow tapered rollers, as well as voids adjacent each elongated radial lobe to provide lubricant flow passages within the hollow rollers; 
           [0029]      FIG. 14  is a perspective view of the pin-element of  FIG. 12 ; and 
           [0030]      FIG. 15  is a partial axial view of the segmented bearing retainer assembly or cage of  FIG. 12  illustrating discrete bridge elements or segments arranged with tubular spacers on a wire support ring between adjacent rollers. 
       
    
    
       [0031]    Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts set forth in the present disclosure and are not to scale. 
         [0032]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. 
       DETAILED DESCRIPTION 
       [0033]    The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the present disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the present disclosure, including what is presently believed to be the best mode of carrying out the present disclosure. 
         [0034]    Refer to figures, and to  FIGS. 1 and 2  in particular, a preassembled bearing retainer or cage of the present disclosure is shown generally at  100 . The bearing retainer or cage  100  is comprised of a first circular hoop or ring  102 , a second circular hoop or ring  104 , multiple discrete bridge elements or segments  106 , a single final bridge element or segment  108 , and tubular spacers  110  (shown in  FIG. 2 ) positioned on the first and second rings  102 ,  104  between each set of bridge elements or segments  106 ,  108 .  FIG. 2  shows how the tubular spacers  110  are positioned between each bridge element or segment  106 ,  108  on the rings  102 ,  104 . These spacers  110  are designed to be long enough so that the radius R′ of a circle described by the inside surface of adjacent bridge elements or segments  106 ,  108  is greater than a radius R of the rollers  112  within the bearing retainer or cage  100 . Designed in this manner, each roller  112  is free to move within its respective pocket in the bearing retainer  100 , such that the load on any bridge element or segment  106 ,  108  is a function of just the mass of the roller  112  either ahead of it or behind it, or a combination of both, depending on the dynamic condition. 
         [0035]    A typical bridge element or retainer  106  is illustrated in  FIG. 3 . Each bridge element or segment contains an eyelet  114  at each end through which the first and second rings  102 ,  104  are passed. The bridge element  106  also contains a segment retention web  116  attached to the underside of a segment bridge  115 , extending between the eyelets. The retention web  116  is a feature of this design that helps to keep the bridge element in alignment with the external curvature of the rollers  112 , and which helps restrict radial deflection of the retainer assembly or cage  100  during operation. For example, in  FIG. 2 , as roller  112   a  travels through a load zone of the bearing, the roller can advance in its pocket space between adjacent bridge elements or segments  106   a  and  106   b  until it contacts the segment  106   a  ahead of it. The curvature of retention web  116  distributes the contact load between roller  112   a  and the bridge element  106   a  above and below the roller axial centerline, thereby reducing the tendency to lift and radially deflect the segment bridge  106   a  away from an inner race  118  and towards an outer race  120 . 
         [0036]    Since the first and second rings  102 ,  104  are passed through the eyelets  114  at each end of the discrete bridge elements or segments  106 , assembly of the bearing assembly requires that a final bridge element or segment  108  be provided which can be secured onto the first and second rings  102 ,  104  by a different manner. The final bridge element  108  is distinctly different from all the other segments  106  in that it has no curved retention web  116  on the underside of its bridge portion. Rather, the bridge portion  115  terminates at a flat surface  116 A permitting it to be inserted into a space between the last two rollers  112  placed in the bearing assembly  100 . The final bearing element  108  also contains eyelet plates  122 A and  122 B located at each end, to be affixed to the bridge  115  with cap screws  124  applied one at each end, thereby securing the first and second rings  102 ,  104  within channels  114 A covered by the eyelet plates  122 A,  122 B. 
         [0037]    Those of ordinary skill in the art will recognize that other suitable attachment mechanisms such as rivets, adhesives, crimps and all other means of attachment may be considered in place of the cap screws. For example, as seen in  FIG. 6 , the ends of the first and second rings  102 ,  104  may be secured inside crimped passages  114 B in the final bridge element  108 , after a suitable tension has been achieved in the rings. 
         [0038]    Construction of the bearing retainer or cage  100  as shown in  FIG. 1  for use with a tapered bearing is as follows. Based on the size of the inner race  118 , the required diameters of the first ring  102  and the second ring  104  are determined. Using a cutting procedure that has a thin kerf, each ring is cut through at one point, allowing all of segments  106 , and spacers  110  to be threaded onto and positioned around the rings  102 ,  104 , leaving out the final segment  108 . The total number of discrete bridge elements or segments  106 , not including the final bridge element  108 , is equal to one less than the total number of rollers  112  to be employed in the bearing. The total number of spacers  110 , on each ring  102 ,  104 , is equal to the number of rollers  112 . The first and second rings  102 ,  104  are then are welded or joined back together to form solid continuous rings. 
         [0039]    Assembly of the bearing is next accomplished by supporting the inner race  118  on a work table or other surface with its back face or large end faced downward. The assembled cage  100  without the final segment  108  is brought into position over and around the bearing inner race  118 . One by one, each of the rollers, typified by roller  112 , are inserted onto the assembly by moving the bridge elements or segments  106  and spacers  110  (if required) circumferentially around the rings  102  and  104  to make space for insertion of the rollers  112 . For installation of the final roller into its space on the inner race  118 , it is necessary to separate the already assembled rollers  112 , segments  106  and spacers  110  in opposite directions about the circumference of the rings  102 ,  104  to open sufficient space for the final roller. After the final roller is inserted into the opened space, the final bridge element or segment  108  is positioned to fill the remaining gap between the rollers  112 , and the eyelet plates  122 A and  122 B are then bolted into position with cap screws  124  over the first and second rings  102 ,  104 . 
         [0040]    In an alternate method of assembly, the first and second rings  102 ,  104  remain cut during the assembly process. The cut rings are brought into position over and around the naked inner race  118 , and are expanded, creating a circumferential gap at the region of the cuts which is of sufficient width to allow the bridge elements  106  and spacers  110  (if the design requires them) to be threaded onto the first and second rings  102 ,  104 . These bridge elements  106  and spacers  110  are spread equally around the inner race  118  with rollers  112  positioned in between. When all of the rollers, bridge elements and spacers are installed, the cut ends of each ring are drawn together with the proper tension so that the appropriate clearance will be established between the rollers and the cage assembly. This clearance is referred to as “cage shake”. Once the proper cage shake is established through proper tensioning of the rings, they must be joined through some means such as crimping (shown in  FIG. 6 ), welding, or mechanical fastening as shown in  FIGS. 7A-7C  and  8 . 
         [0041]    An exemplary means for mechanical fastening is shown in  FIGS. 7A-7C , in which each of the rings  102 ,  104  is initially formed from a length of wire having couplings  103  formed at each end. The length of wire is wrapped to form the ring configuration, with the couplings  103  at opposite ends facing towards each other. The couplings  103  are inserted into a fastening sleeve  126 , (as seen in  FIG. 7B ) which is then crimped as shown in  FIG. 7C  to secure the couplings  103  in place, forming the continuous rings  102 ,  104 . Alternatively, as shown in  FIG. 8 , the rings  102 ,  104  may be formed from a length of wire having female connectors  132  at each end, which each receive the couplings  130  from a connecting member  128  when looped to form the ring configuration. Each connecting member  128  is retained within the female connectors  132  by crimps  134  applied to the rings  102 ,  104  after they are positioned in the circular configuration. 
         [0042]    It is important that the method used for rejoining the wire rings  102 ,  104  employs a suitable means to close the gap in the daisy chain of components so that the correct amount of circumferential clearance exists in the stack up of spacers  110  and bridge elements  106 . When spacers  110  are used, this can be conveniently accomplished by modifying the spacer width(s) if necessary. If spacers  110  are not to be used, then the same circumferential clearance between rollers  112  and bridge elements  106  must also be controlled, for example by altering the width of the tab or coupling where the rings  102 ,  104  are rejoined with welding, fastening, crimping or other means. 
         [0043]    Alternatively, as seen in  FIGS. 9 and 10 , an adjustable tensioning collar or turnbuckle  140  may be utilized to secure the opposite ends of threaded wire rings  102 T and  104 T together. In order to utilize an adjustable tensioning collar or turnbuckle  140 , opposite ends of each wire ring  102 T,  104 T must be threaded with threads of opposite directions,  102 T-RHT,  102 T-LHT,  104 T-RHT, and  104 T-LHT. To complete the close/rejoining of the wire rings  102 T,  104 T, the opposite ends of each wire ring are placed into the opposite ends of an axial bore through the adjustable tensioning collar or turnbuckle  140 . A portion of the axial bore in the turnbuckle adjacent to each axial end face is threaded with an appropriate thread pitch diameter to receive the threaded ends of the wire rings  102 T,  104 T without binding, such that rotation of the adjustable tensioning collar or turnbuckle  140  in a first direction about a longitudinal axis will act to draw the ends of the rings  102 T,  104 T together within the axial bore, while rotation in the opposite direction will act to spread the ends apart. By rotationally adjusting the tensioning collar or turnbuckle a desired tension can be achieved for each wire ring  102 T,  104 T within the bearing assembly. Once the desired tension is reached, the tensioning collar or turnbuckle may be secured against further rotational adjustment by the placement of set screws or welds through radial passages  142 . Preferably, as best seen in  FIG. 10 , the axial length of each tensioning collar  140  is selected to correspond to the required spacing between the ends of the bridge elements  106 , such that the adjustable tensioning collar or turnbuckle  140  acts substantially the same as a spacer  110 . 
         [0044]    The bearing retainer  100  of the present disclosure is configured to provide an improved flow of lubricant to critical wear surfaces within a bearing assembly, such as between the bridge elements  115  and the rollers  112 . As seen in  FIG. 5 , the use of round cross-section rings  102 ,  104  and eyelet couplings  114  for the bridge elements  106  does not impede a flow of lubricant  200  axially entering the spaces between adjacent rollers  112 . To further enhance lubrication, as shown in  FIG. 9 , the exposed surfaces  115 A of the bridge elements or segments  106  may receive special finishes or textures intended to trap and release lubricant  200  in the contacts between the bridge elements  106  and rollers  112 . These features can be applied to these surfaces  115 A by pressing, forming, machining, molding or by other suitable means. While those of ordinary skill in the art will recognize that the bridge elements  106 ,  108  may be formed from a variety of materials, including polymers, metals, and powdered metals, it will be recognized that it is preferable to employ a compacted and sintered powered metal construction which produces very strong bridge elements suitable for use in very large bearing applications, and which can be optionally impregnated with lubricating materials, providing improved resistance to wear at the critical surfaces within the bearing assembly. 
         [0045]    Turning next to  FIGS. 12-15 , it is shown that the concepts of the bearing retainer assembly  100  of the present disclosure may be adapted for use with axially hollow rollers  300 , such as shown in  FIG. 12 . In this configuration, each bridge element or segment  106  previously positioned between the rollers  112  is replaced with a pin-bridge element  302  that is located axially inside of the hollow roller  300 . The pin-bridge elements  302  are still held in position with the first and second rings or hoops  102 ,  104  that pass through eyelet holes  114  at opposite ends of the bridge element  302 . 
         [0046]    An exemplary configuration for a pin-bridge element  302  is seen in  FIG. 13 , taken at A-A of  FIG. 12  and in the perspective illustration of  FIG. 14 . This configuration is shown to illustrate two important functions. First, four elongated radial lobes  304  center the pin-bridge  302  axially inside the hollow roller  300 . Second, there are four axial voids  306  around the pin-bridge section within the hollow roller  300  which act as lubricant reservoirs to store lubricant and help maintain a continuous supply of lubricant in the close clearance contact regions at the outer surfaces of the elongated radial lobes  304  which engage the inner diameter surface  308  of the hollow roller  300 . 
         [0047]    Assembly of a bearing retainer assembly with the pin-bridge elements  302  is substantially similar to that previously described, but for the necessary placement of the hollow rollers  300  onto the pin-bridge elements  302  at the time of assembly.  FIG. 15  represents a view from either axial end of an assembled bearing employing hollow rollers  300  and the pin-bridge elements  302  of the present disclosure. The assembly consists of a string of pin-bridge elements  302  inside the bores of the rollers  300  and spacers  110 . This design is similar to the embodiment shown in  FIG. 2 , except the pin-bridge segments  302  pass through the rollers  300  instead of between them. 
         [0048]    The use of pin-bridge elements  302  to couple the first and second rings  102 ,  104  when using hollow rollers  300  facilitates at least two things. First, unlike conventional pin cage configurations where rectangular sectioned cage rings cover access to the bores at each end of the hollow rollers  300 , restricting flow of lubricant (especially higher consistency greases) into this critical interface, the present design uses the rings  102 ,  104  and spacers  110  in combination which allows for an improved flow of lubricant to the axial openings of the hollow rollers  300 , so that the lubricant can fill the space inside the hollow rollers. Allowing lubricant to gain easy access into this area is important so that the interface between the surfaces of the pin-bridge element  302  and roller inner diameter surfaces  308  can be constantly replenished with lubricant, thereby reducing the potential for wear. 
         [0049]    The second benefit is that this bearing retainer or cage design  100  is particularly well suited for a bearing design in which the hollow rollers  300  are designed and manufactured with oversized axial bores to reduce the roller mass and cost. The bridge sections  304  of the pin-bridge element  302  can be increased to add strength and piloting without resorting to a round section pin which adds back the weight saved from the hollow roller  300 . Other pin-bridge element configurations which differ from the one shown in  FIGS. 12-15  can be designed which will accomplish the same function, such as by varying the number or shape of the elongated radial lobes  304 . 
         [0050]    As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.