Abstract:
A bearing cage assembly ( 100 ) comprises a plurality of discrete bridge elements ( 206 ) disposed between adjacent rolling elements ( 1 12 ) and coupled between first and second axially spaced cage support wire rings ( 1 02, 1 04 ) which are appropriately tensioned. Spacers ( 1 10 ) are disposed between adjacent bridge elements and engage the bridge elements in a piloted engagement. The bridge elements maintain a separation between rolling elements, retain the rolling elements within the bearing assembly, and function as a lubrication reservoir for grease lubricated bearings. Profiled surfaces on the bridge elements position the bearing cage assembly on at least one axial end of the 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. 61/654,159 filed Jun. 1, 2012, which is herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present application is generally related to large bearing cage configurations, and in particular, but not exclusively, to a cage assembly for a large diameter bearing containing multiple heavy rolling elements and including discrete bridge elements coupled between axially-spaced cage wire rings located adjacent opposite axial ends of the rolling elements. 
         [0004]    The usual approach to designing large-bearing cages (typically 1-4 meters in diameter) has been to extend the design styles for smaller, conventional bearings to the larger bearing sizes. The first and most common attempt at meeting the needs of larger bearings uses pin style cages to facilitate placement and retention of the rolling elements. While pin style cages provide excellent retention, they are heavy, complex, and costly to assemble. Furthermore, some pin style cage designs can partially block flow of lubricants (especially grease) to critical wear surfaces. They also cannot be disassembled without damaging either the cage rings or the cage pins. 
         [0005]    Another cage design often considered is an “L” type design produced using various combinations of forging, forming, machining and precision cutting. The resulting cost of bearing cages produced using combinations of these various processes are unacceptably high, especially for the larger bearing sizes. 
         [0006]    Yet another cage design is a polymer segmented style cage. While these cages have a demonstrated ability to perform satisfactorily, there are potential limitations in scaling up this design for larger bearings containing heavy rollers. Current polymer cages for very large bearings are made from polyether ether ketone (PEEK), an organic polymer thermoplastic which is relatively expensive. For extremely large bearings containing large rollers, the size and strength of the cage must be increased. The greater amount of PEEK required to make a sufficiently strong cage can therefore often be cost prohibitive. Accordingly, polymer segmented cages appear to be most suited for bearing cages with small to medium size rollers which only require small to medium size PEEK segments. 
         [0007]    Based on the foregoing, it would be advantageous to provide a large bearing cage design having full functionality (roller retention, roller spacing, roller alignment, lubricant flow) for various sizes and types of bearings (e.g., tapered roller, cylindrical roller, spherical roller bearings, etc.) and which can be manufactured at a lower cost than is currently possible. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Briefly stated, the present disclosure provides a bearing assembly having a plurality of rolling elements (rollers) disposed about the circumference of a race member and positioned in a spaced configuration by a segmented bearing retainer assembly. The segmented bearing retainer assembly comprises a plurality of discrete bridge elements coupled between first and second wire support rings located adjacent axially opposite ends of the bearing assembly. 
         [0009]    Each discrete bridge element has a cross-sectional shape adapted to contact adjacent rolling elements on the rolling element&#39;s circumferential surface and radially displaced from the pitch diameter of the bearing. This maintains the spacing between adjacent rolling elements in the bearing assembly, and retains the rolling elements relative to the race member. A desired spacing arrangement about the circumference of the bearing assembly, between the wire support rings, is achieved using a plurality of spacers disposed on the rings. In a preferred embodiment the bridge elements and spacers have a piloted engagement. The rings extend through attachment eyelets formed in each end of each bridge element. 
         [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 bridge element includes an axially aligned bridge segment traversing between adjacent rolling elements. An end block at each axial end of the bridge element includes the attachment eyelet through which a wire support ring passes. 
         [0011]    Each discrete bridge element further has a cross-sectional profile designed to distribute a contact load between a rolling element and an adjacent bridge element above (radially outward from) a pitch diameter of the bearing assembly. At least one surface on the end block is profiled to position the cage assembly against an end surface of the rolling elements. 
         [0012]    In another disclosed embodiment, each discrete bridge element has a cross-sectional shape adapted to contact adjacent rolling elements on the rolling body&#39;s circumferential surface at a position which is radially inward from the pitch diameter of the bearing. 
         [0013]    Additional surface profiling on a bridge element&#39;s end faces may be optimized to position the segmented bearing retainer assembly on the large end of the rolling elements so to establish and maintain a beneficial lubricant film between them. 
         [0014]    In a preferred embodiment, the discrete bridge elements are of a powdered metal or sintered steel. The discrete bridge elements may be impregnated with a lubricant, or dipped in a lubricant for a period of time for the lubricant to be absorbed into the bridge element, or the bridge element may be vacuum impregnated with a lubricant. Optionally, the bridge elements may have surface features or finishes configured to, over time, trap and release lubricants. 
         [0015]    The rings are initially open ended to allow for assembly of the bridge segments and spacers onto the rings. The free ends of the rings have a feature which facilitates subsequently joining the ends together as part of the final assembly. In one embodiment the rings have a groove near each end which allows the rings to be connected by a joining spacer, using a crimp joint. In another embodiment the free ends of the rings are threaded with opposite handed threads and a joining spacer in the form of a turnbuckle is used to join the ends of the rings together. This embodiment allows the spacers and bridge segments to be drawn together to a desired degree of force. By drawing the spacers and bridge elements tightly together a more rigid cage structure is obtained. In another embodiment one end of the ring has a groove formed in it to receive a crimp connection and the other end of the ring is threaded. In this embodiment, the common right handed threads only may be used and the need to use the less common left handed threads is eliminated. The joining spacer in this case has threads on only one side and is crimped on the other end. 
         [0016]    For the embodiments using a threaded joining spacer to connect the respective ends of each ring together, a means to prevent the threaded engagement from backing off is desired. This may be accomplished by a thread adhesive, by a set screw engaging the spacer and ring or by welding the adjusting spacer to the ring. 
         [0017]    The joining spacer may have features to make rotation easier when drawing the cage together. Common features employed are one or more flats, or octagonal or hexagon external geometries that will accept an open end wrench, or radial holes for rotation by a simple pin or by a spanner wrench. 
         [0018]    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 ends of the first and second wire support rings. Each wire ring is then formed into an open loop and the ends of the rings are threaded with opposite handed threads. Discrete bridge elements and the spacers between them are first inserted onto the wire support rings. Individual rollers (rolling elements) are then inserted into the assembly by moving the bridge elements and spacers circumferentially around the wire support rings so to provide sufficient space for insertion of the rollers. After the final roller is installed on the inner race, the rings are parted in opposite directions to open up a space for insertion of a turnbuckle. The turnbuckle is then used to draw all of the bridge elements and spacers tightly together. 
         [0019]    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 
         [0020]    In the accompanying drawings which form part of the specification: 
           [0021]      FIG. 1  is a view, partly in section, of a portion of a segmented bearing retainer assembly of the present disclosure; 
           [0022]      FIG. 2  is a perspective view of a discrete bridge element of the segmented bearing retainer assembly of  FIG. 1 ; 
           [0023]      FIG. 3  is a sectional view of the discrete bridge element taken along line  3 - 3  in  FIG. 2 ; 
           [0024]      FIG. 4  is a perspective view of an alternate embodiment of a discrete bridge element in which each eyelet has a counter-bore formed at each of its ends; 
           [0025]      FIG. 5  is a sectional view, taken along line  5 - 5  in  FIG. 4 , of an end block and illustrating the counter-bores formed at the ends of an eyelet; 
           [0026]      FIG. 6  is a perspective view of another alternate embodiment of a discrete bridge element in which bosses are formed at the ends of the eyelets; 
           [0027]      FIGS. 7A-7C  illustrate different assembly methods by which a piloted spacer is secured to a wire support ring; 
           [0028]      FIGS. 8 and 9  represent portions of the segmented bearing retainer assembly using differently shaped turnbuckles; and. 
           [0029]      FIG. 10  is a perspective view of a slotted or open sided spacer used in the assembly. 
       
    
    
       [0030]    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. 
       DETAILED DESCRIPTION 
       [0031]    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. 
         [0032]    Referring to  FIGS. 1 ,  8 , and  9 , a preassembled segmented bearing retainer or cage  100  comprises first circular hoop or ring  102  and a second and correspondingly sized and shaped circular hoop or ring  104 . As particularly shown in  FIG. 1 , ring  104  is axially displaced from ring  102 . Cage  100  also includes multiple discrete bridge elements  206  each of which spans the axial distance between rings  102 ,  104 . The bridge elements are preferably made of a powdered metal material including sintered steel. Cage  100  further includes tubular spacers  110  each of which has a longitudinal bore  111  (see  FIGS. 7A-7C ) by which the spacers are inserted onto one of the rings  102 ,  104  and positioned between adjacent bridge elements  206  as shown in  FIGS. 1 ,  8 , and  9 . As shown in  FIGS. 1 ,  7 A, and  7 B, the spacers (which may comprise a turnbuckle  140 ) have a reduced diameter section at each of their ends. Also, while the outer surface of the spacers is generally round, as shown in  FIG. 9 , a spacer (turnbuckle)  150  has a polygonal shaped outer contour; for example, it may have a hexagonal or octagonal outer contour. Such a construction results in at least one flat surface on the outer contour of the spacer. 
         [0033]    Referring to  FIG. 7C , a spacer (turnbuckle)  160  has a threaded longitudinal bore  161  in which threaded ends of rings  102 ,  104  are received. In this embodiment, the spacer has a uniform outer diameter throughout its length. 
         [0034]    As designed and constructed, each roller  112  moves freely within its respective pocket in bearing retainer  100  such that the load on any bridge element  206  is only a function of the mass of the roller  112  either ahead of or behind it, or a combination of the masses of both rollers, depending on the dynamic conditions. 
         [0035]    Different embodiments of bridge element  206  are shown in  FIGS. 2-6 . Regardless of the particular bridge element design, at each end of the bridge element an end block  208  is formed. The end blocks are axially spaced from each other and an eyelet  214  is formed in each end block. Each eyelet comprises a bore extending longitudinally through the end block, and the eyelets are sized to allow one of the rings  102 ,  104  to be inserted through a respective one of the end blocks as shown in  FIGS. 1 ,  8 , and  9 . 
         [0036]    Referring to  FIGS. 2 ,  4 , and  6 , the end blocks  208  of each bridge element  206  are separated by a retention web  216  which is attached to the inner surface of a bridge  215  that extends between the end blocks. Retention web  216  helps keep bridge element  206  in alignment with the external curvature of the rollers  112 . This, in turn, helps restrict radial deflection of cage  100  during operation, as well as maintain adequate lubrication. As shown in  FIG. 1 , for example, as a roller  112  travels through a load zone of the bearing, it moves through a pocket space S formed between adjacent bridge elements  206  until the roller contacts the bridge element rotationally ahead of it. 
         [0037]    In a preferred embodiment, retention web  216  of a bridge element  206  has straight and flat surfaces  217  (see  FIG. 3 ) which distribute the contact load between a roller  112  and the bridge element. A contact region is disposed radially outward from the pitch diameter of the bearing in substantially the same location as the contact region provided by a conventional above centerline “L” type bearing cage. If retention web  216  does not extend radially inwardly past the bearing pitch diameter, additional space is provided between adjacent rollers  112  as to permit the storage and resupply of grease (or other lubricant) to the various contact regions located about the roller. Those of ordinary skill in the art will recognize that bridge element  206  may be configured with a retention web  216  and bridge  215  in a position which is radially inward from the pitch circle or diameter of the bearing. Thus, the contact load between a roller  112  and a bridge element  206  is within a contact region which is correspondingly disposed radially inward from the pitch diameter of the bearing. Those of ordinary skill in the art will further understand that the particular construction of a bridge  215  and retention web  216  depends upon the particular usage of the segmented bearing retainer  100 . 
         [0038]    Construction of the bearing retainer or cage  100 , as shown in  FIG. 1 , is for use with a tapered bearing. Based on the size of an inner race  118  (see  FIGS. 1 and 8 ), the required diameters of rings  102 ,  104  are determined. 
         [0039]    During assembly, each ring  102 ,  104  is initially open, thus allowing all of the bridge elements  206 , spacers  110 , and a turnbuckle  140  (see  FIG. 1 ) if one is used, to be slipped onto and positioned around the respective rings. In a preferred embodiment, the number of spacers  110  is one less (N−1) than the number N of rollers  112  employed in the bearing. In alternate embodiments, the number of bridge elements  206  equals the number N of rollers  112 . After all the bridge elements and spacers are installed on the rings, the ends of the rings are brought together and joined together. For example, as shown in  FIG. 1 , the opposite ends of rings  102 ,  104  are threaded, as indicated at T, and the respective ends of each ring are threaded into a turnbuckle  140  to form a continuous ring. 
         [0040]    Alternate ways of closing rings  102 ,  104  are shown in  FIGS. 7A-7C . In  FIG. 7A , a turnbuckle/spacer  141  has a radial bore  142  extending both through it and the ring  102 ,  104  whose ends are captured in the turnbuckle/spacer. An anti-rotation pin  143  is inserted through this bore. In  FIG. 7B , bore  142  extends only through one side of the turnbuckle/spacer and a set screw  144  is used to secure the turnbuckle/spacer to the ring. In  FIG. 7C , a weld W is formed at the inner end of a radial bore  162  in spacer  160  to attach the turnbuckle/spacer and the ring together. 
         [0041]    Also, although not shown in the drawings, the ends of the spacer  141  can be crimped about the ends of the support ring inserted in the spacer. It will be appreciated that the ends of the ring can be secured to a turnbuckle/spacer using a combination of the above techniques. For example, one end of the ring may be threadably received in a turnbuckle with the other end of the ring crimped in place in the other end of it. Attachment of the ends of ring  102 ,  104  to the spacer can further be done using an adhesive material. Regardless of the method (or methods) of attachment used, in addition to securely attaching the ends of ring  102 ,  104  together to form a completed ring, the turnbuckle/spacer to which the ring ends are secured is now prevented from rotational movement which could otherwise, over time, loosen the connection. 
         [0042]    Those of ordinary skill in the art will recognize that the spacers  110  may float on the rings  102 ,  104  between the discrete bridge elements  206 . Referring to  FIGS. 2 and 3 , the outer ends of the bores  214  formed in each end block  208  of a bridge element  206  are flush with the sides of the end block. Accordingly, spacers  110  installed between the adjacent bridge elements float between the bridge elements. 
         [0043]    Referring to the bridge element  206  shown in  FIGS. 4 and 5 , spacers installed between adjacent bridge elements as shown in these figures may be in a piloted engagement with the discrete bridge elements so to maintain a desired relative positioning of the components. In this embodiment of bridge element  206 , each end block  208  includes a counter-bore  214   cb  formed at the outer end of each bore (eyelet)  214  that extends through the respective end block. As shown in  FIG. 1 , the counter-bores are sized to receive the spacers  110 . 
         [0044]    Alternatively, as shown in  FIG. 6 , each end block  208  on a bridge segment  206  is formed to have a raised boss  214   b  surrounding the outer ends of each bore  214 . The bosses  214   b  are sized to seat inside the inner end of an adjacent spacer  160  as shown in  FIG. 7C . 
         [0045]    In one method of assembly, bearing retainer  100  is formed by supporting inner race  118  on a work table (or other surface) with its back face or large end facing downward. The assembled cage is then brought into position over and around the inner race. One by one, each roller  112  is inserted onto the assembly by moving the bridge elements  206  and spacers  110  (if required) circumferentially around the rings  102 ,  104  so to make space available for insertion of the next roller. For installation of the final roller into its space on inner race  118 , the already assembled rollers  112 , bridge segments  206 , and spacers  110  are moved in opposite directions about the circumference of the rings thereby to create sufficient space into which to fit this roller. If required, after the last roller is inserted into place, a final bridge element  206  is installed to fill any remaining gap between the rollers  112 . 
         [0046]    In an alternate method of assembly, the ends of rings  102 ,  104  remain separated during the assembly process. The rings are brought into position over and around inner race  118  and are moved apart to create a circumferential gap of sufficient width to allow bridge elements  206  and spacers  110  (if the design so requires them) to be slipped onto the rings. The bridge elements and spacers are spread equally around inner race  118  with rollers  112  positioned between them. When all of the rollers, bridge elements and spacers are installed, the ends of each ring are drawn together until a proper tension is created and an appropriate clearance is established between the rollers and the cage assembly. This clearance is referred to as “cage shake”. Once the requisite cage shake is established through proper tensioning of the rings, the ends of the rings are joined together as previously described. 
         [0047]    The method used for joining the separated ends of rings  102 ,  104  must close the gap between the installed components so a correct amount of circumferential clearance exists in the “stack up” of spacers  110  and bridge elements  206 . This is conveniently accomplished by modifying the width(s) of one or more spacers, if necessary. 
         [0048]    The assembly methods described with respect to  FIGS. 7A-7C  limit circumferential movement of the spacers and bridge segments  206  on the ring should tension on the ring be lost over time due, for example, to creep or wear. By limiting the stack of potential gaps between the spacers and bridge elements, the ability of cage  100  to retain rollers  112  will be preserved for longer periods should the cage begin to lose tension. 
         [0049]    To further limit the stack up of potential gaps, one or more spacers  110  are fixed to a ring  102 ,  104  by welding. This will limit the stack up of accumulated gap between each of the fixed spacers, including the turnbuckle spacer. To facilitate spacing, the spacers  141 ,  150 , and  160  have a radial bore  142 ,  162  respectively, in which a welding material is deposited. Or, as shown in  FIG. 10 , a spacer  170  is a split spacer having a longitudinal slot  171  extending the length of the spacer as shown in  FIG. 10 . When spacer  170  is used, the welding material is deposited in slot  171  to attach the spacer to a ring  102 ,  104 . 
         [0050]    Compared with some previous segmented bearing cage designs, bearing retainer  100  of the present disclosure is configured to provide an improved flow of lubricant to critical wear surfaces within the bearing assembly; for example, between bridge elements  206  and rollers  112 . Use of circular cross-section rings  102 ,  104  and eyelet couplings  214  for the bridge elements provides openings for the axial movement of lubricant into the spaces between adjacent rollers. Again to further enhance lubrication, exposed surfaces of the bridge elements or segments may receive special finishes or textures to entrap and release lubricants in the contact regions between the bridge elements and rollers. These features can be applied to the appropriate surfaces as previously described. Those of ordinary skill in the art will recognize that the bridge elements  206  may have more complex geometries than those shown in the drawings without departing from the scope of the invention. 
         [0051]    While, as previously noted, the bridge segments are preferably made of a powdered metal, they may also be formed from a variety of materials including polymers and metals. Examples of suitable constructions include a compacted and sintered powered metal or steel construction which produces very strong bridge elements suitable for use with very large and heavy bearing designs, and which can optionally be impregnated (for example, by vacuum impregnation) with lubricating materials so to provide improved resistance to wear at critical surfaces within the bearing assembly. These type bridge elements may also have surface features or finishes which promote the trapping and releasing of lubricants. 
         [0052]    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.