Abstract:
A novel two-piece backing ring assembly for a railcar axle is presented. The backing ring assembly has an annular body affixed to the fillet of the journal and a locking ring for further affixing the annular body into position on the journal. The locking ring has an inboard end affixed to the dust guard of the shaft and an outboard end for engaging a slot in the annular body. The locking ring assembly may be retrofitted to older generation railcar axles to increase the structural rigidity of the bearing assembly and minimize fretting wear caused by railcar axle deflection.

Description:
FIELD OF THE INVENTION 
     This invention relates to anti-friction bearings, and more particularly, in one embodiment, to the backing rings used with tapered roller bearings on railcar axles. 
     BACKGROUND OF THE INVENTION 
     Tapered roller bearings on railcar axles support operating loads capable of producing significant flexural deflections in the axle, and in particular, the journal portion of the shaft on which the tapered roller bearing is affixed. The stresses imposed by the operating loads are particularly high in the journal portion of the shaft at or near the backing ring. 
     As result of shaft deflections, the backing ring and the journal often experience fretting wear as the backing ring moves relative to the journal. Fretting wear may be sufficient to loosen the backing ring, increasing the axial play of the bearing on the journal. The loose backing ring accelerates wear on the bearing assembly and journal, potentially leading to shaft or bearing failure. 
     In an effort to reduce fretting wear failures, new backing ring and axle standards were developed and standardized for application to the railway industry. This new design is now embodied in the current generation backing ring which is in service today on many railcar axles. 
     The current generation backing ring design is a single piece component having an annular lip extending concentrically over the dust guard portion of the shaft. The lip of the backing ring produces an interference fit with the dust guard. The current generation backing ring is termed a “fitted” backing ring because of this interference fit. This is also the basis for distinguishing between the current generation fitted backing ring and the prior generation non-fitted backing ring. The prior generation non-fitted backing ring does not have a projecting lip and cannot connect to the dust guard. This substantially reduces the rigidity of the non-fitted backing ring in comparison to the fitted backing ring. As a result, prior generation railcar axle assemblies have higher wear rates than the current generation. 
     The specifications under the new standards apply not only to the fitted backing ring, but also to the dust guard on the railcar axle. The new standards require a closely toleranced dust guard diameter in order to produce an interference fit with the lip of the fitted backing ring. 
     New axles using the current generation fitted backing ring have slightly larger dust guard outer diameters than the prior generation railcar axles. The current generation fitted backing rings, however, can still be used interchangeably with the prior generation railcar axles. Although fitted backing rings will fit prior generation railcar axles, they will not produce an interference fit over the dust guard outer diameter. Consequently, certain advantages of fitted backing rings are not realized when used to recondition bearings on prior generation railcar axles. 
     SUMMARY OF THE INVENTION 
     To reduce the potential for fretting wear on journals and backing rings, a novel backing ring assembly is presented having increased stability to reduce fretting wear. The novel backing ring assembly is composed of two components: (1) an annular body affixed to the fillet of the journal and (2) a locking ring to connect with and further affix the annular body on the journal. The locking ring has an outboard end engaging the annular body and an inboard end affixed to the outer diameter of the dust guard. The locking ring reduces axial movement in the annular body resulting from shaft and journal deflection. 
     Because bearings are a high-value component, manufactured to stringent quality standards, it is generally the practice of the railway industry to recondition worn bearing assemblies. This backing ring assembly may be retrofitted to prior generation railcar axles with the modification of the prior generation backing ring. Likewise, fitted backing rings may be modified to accept a locking ring to produce the novel backing ring assembly. Alternatively, in either the prior generation or the current generation railcar axles, a new backing ring assembly may be installed during bearing reconditioning. This novel backing ring assembly may also be manufactured and used in conjunction with newly manufactured current generation railcar axles to produce an alternative to the fitted backing ring. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Various embodiments of the novel backing ring assembly are described and illustrated in the accompanying figures. The figures are provided as examples only and are not intended to be considered as limitations to the invention. Consequently, the bearing assembly including the backing ring assembly are illustrated by way of example and not by limitation in the accompanying figures in which: 
         FIG. 1  is a sectional view of one embodiment of the novel backing ring assembly; 
         FIG. 2  is an exploded isometric view of one embodiment of the backing ring assembly; 
         FIG. 3  is an enlarged sectional view of the backing ring assembly for the bearing assembly illustrated in  FIG. 1 ; 
         FIG. 4  is an enlarged sectional view of the backing ring assembly for the bearing illustrated in  FIG. 3  with a backing ring seal; and 
         FIG. 5  is an enlarged sectional view of one embodiment of the backing ring assembly retrofitted to a current generation backing ring and railcar axle assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , one embodiment of the backing ring assembly is illustrated. In this embodiment, the bearing assembly  10  is a tapered roller bearing of the type commonly used in railway applications to support a railcar wheel. The bearing assembly  10  described in the following embodiments, however, may be adapted for use in many other common industrial applications. Consequently, the bearing assembly  10  illustrated and described below in relation to a tapered roller bearing assembly for a railcar wheel is for convenience only. 
     The bearing assembly  10  is typically preassembled before being mounted on a shaft  14  (e.g., a railcar axle). At each free end of the shaft  14 , a journal  12  terminates in a slightly conical tapered section  15  to facilitate installation of the bearing assembly  10  onto the journal. The bearing assembly  10  is pressed onto the journal  12  of the shaft  14  to establish an interference fit. 
     A dust guard  18  with a larger diameter than the journal  12  is located axially inward from the journal  12 . Axially inward from the dust guard  18 , the shaft  14  extends to its largest diameter. The weight of the railcar is transferred through the bearing assembly  10  to the shaft and further transferred to ground through the railcar wheels (not shown) fitted inboard of the dust guard on the shaft. 
     Some bearing assemblies  10  have wear rings  22 ,  24  fitted over the journal  12  and which abut each end of the bearing assembly  10 . The wear rings  22 ,  24  typically have an inner diameter dimension to provide an interference fit with the journal  12  over at least a portion of their length. The wear rings  22 ,  24  rotate with the shaft as it turns. 
     Although the bearing assembly  10  is pressed onto the journal  12 , further restraint is generally required against axial loads. To provide this axial restraint, the bearing assembly  10  is captured between a backing ring assembly  60  at the inboard side and a bearing retaining cap  20  at the outboard side of the bearing assembly  10 . 
     At the inboard side of the journal  12 , the bearing assembly  10  is captured by the annular body  61  through the interposed and abutting wear ring  24 . The annular body  61  has an inner contoured surface  66  allowing a tight or is affixed to a complementary surface fit with a complementary surface on the fillet  16  on the inboard end of the journal  12 . The fillet  16  leads to a shoulder  17 , the shoulder extending to form a dust guard  18  having a cylindrical surface  19 . The annular body  61  has an inboard distal edge  63  at the contoured surface  66 , generally abutting the shoulder  17 . 
     A locking ring  71 , affixed to the dust guard  18 , engages the annular body  61  and restrains the annular body against deflection and axial displacement. The annular body  61  and the locking ring  71  together form the backing ring assembly  60 . The annular body  61 , the furthest inboard component affixed to the journal  12 , affixes the bearing assembly  10  against axially inward displacement. 
     At the outboard end of the journal, the bearing assembly  10  is captured by the bearing retaining cap  20  through the interposed and abutting outboard wear ring  22 . The bearing retaining cap  20  is affixed to the free end of the journal  12  with cap screws or bolts  21  threaded into a plurality of threaded bores. The bearing retaining cap  20  completes the mounting of the bearing assembly  10  onto the journal  12 , providing a clamping force to restrain the bearing assembly against axially outward displacement. 
     The bearing assembly  10  is preassembled from a number of individual components, including two bearing cones  38 ,  40  and a bearing cup  31 . The bearing cup  31  has an inner surface having radially inward directed outer raceways  32 ,  34 . The bearing cones  38 ,  40  have radially outward directed inner raceways  39 ,  41 . A center spacer  47  is positioned between the bearing cones  38 ,  40  to maintain the cones in accurately spaced position relative to each other and allow for proper bearing lateral clearance. The outer raceways  32 ,  34  in the bearing cup  31  cooperate with the inner raceways  39 ,  41  in the bearing cones  38 ,  40  to capture and support two rows of the tapered rollers  42 ,  44 . In some embodiments, cages  46 ,  48  maintain the circumferential spatial positioning of the rollers  42 ,  44 . 
     Bearing seals  50 ,  52  cover the ends of the bearing assembly  10  to minimize both lubricant leakage from the bearing and intrusion of contaminants into the bearing. In one embodiment, the bearing seals  50 ,  52  are affixed to the stationary (i.e., non-rotating) side of the bearing assembly  10  (such as the bearing cup  31 ) by interference fit or other appropriate method. 
     A seal body  54 ,  56  (typically of elastomeric construction) is attached to the bearing seal  50 ,  52  to form a dynamic seal between stationary and moving bearing assembly components. In one embodiment, the seal body  54 ,  56  is urged against the wear ring  22 ,  24  to seal the bearing assembly  10 . 
     The wear rings  22 ,  24  protect the journal  12  against rubbing wear from the seal body  54 ,  56  by providing a wear surface  23 . Direct contact between the seal body  54 ,  56  and the journal  12  could potentially create sufficient rubbing wear to degrade and potentially cause shaft failure. 
     In another embodiment, wear rings  22 ,  24  are not required. Instead, the bearing seal itself  50 ,  52  (instead of the wear rings  22 ,  24 ) provides the wear surface (i.e., a rotating surface) against which the seal body  54 ,  56  forms a seal. In this embodiment, the bearing seals  50 ,  52  comprise two components: an outer seal case and an inner seal case (inner and outer seal case not shown). 
     The outer seal case, similar to the embodiment described above, is affixed to the bearing cup and has a seal body. The inner seal case is a generally cylindrical housing affixed to the bearing cone which rotates with the shaft  14 . The inner seal case has a wear surface to which the seal body extends to contact and create a dynamic seal. This type of bearing seal may be referred to as a cone riding bearing seal because the inner seal case is affixed to the bearing cone. 
     With the cone riding bearing seal, the bearing assembly  10  does not have wear rings. In this embodiment, the bearing assembly is clamped directly between the backing ring assembly and the bearing retaining cap. In contrast, in the other bearing assembly embodiment, wear rings directly abut each end of the bearing assembly at the inboard and outboard ends of the bearing cones. Regardless of the type of bearing seal employed, the novel backing ring assembly  60  can be applied to either type of bearing seal embodiment. 
     In addition to its application to a wide variety of bearing assembly designs, this novel backing ring assembly can also be applied to a variety of current and prior generation railcar axles and bearing assemblies. For example, this novel backing ring assembly can be incorporated into the production of new axle and bearing assemblies as an alternative to railcar axles with fitted backing rings; or retrofitted into previous generation railcar axles and bearing assemblies with non-fitted backing rings. The novel backing ring assembly can also be retrofitted into current generation railcar axles with tightly toleranced, fitted backing rings. 
     Referring to  FIG. 2 , an exploded isometric illustration of the backing ring assembly  60  is provided. The backing ring assembly  60  comprises two interlocking components: 1) an annular body  61  and 2) a locking ring  71 . The locking ring  71  has an outboard end  72  to engage with a slot  65  in the axially inward directed surface  62  of the annular body  61 . 
     In this embodiment, the inboard end  74  and the outboard end  72  have distinct and separate annular shapes: the inboard end  74  and the outboard end  72  having different inner and outer diameters. In other embodiments, the inboard end and the outboard end may have the same sized outer or inner diameters. 
     Referring to  FIG. 3 , the backing ring assembly  60  of  FIGS. 1 and 2  is illustrated in an enlarged sectional view. The annular body  61  has an inner contoured surface  66  affixed to the journal  12  at the complementary surface of the fillet  16 . In this embodiment, the inner contoured surface  66  departs from the complementary surface of the fillet  16 , creating a gap  13  between the annular body  61  and the fillet near the axially outward directed surface  64  of the annular body. 
     A slot  65  in the axially inward directed surface  62  of the annular body  61  receives the outboard end  72  of the locking ring  71  in an interference fit. In one embodiment, the slot  65  depth is sufficient to allow the outboard end  72  of the locking ring  71  to engage the annular body without contacting the cylindrical surface  19  of the dust guard  18  (i.e., generally disposing the outboard end  72  in the slot  65  radially outward from the fillet  16 ). 
     The locking ring  71  further has an inboard end  74  for receiving the cylindrical surface of the dust guard  18 . In this embodiment, the annular inboard end  74  encircles the dust guard  18  in an interference fit. 
     The inboard end  74  and the outboard end  72  are connected, in one embodiment, by a connecting member  78 . In one embodiment, the connecting member  78  has an annular shape with an inner surface  73  and outer surface  75 . The connecting member  78 , in one embodiment, depending upon the inner and outer diameters of the inboard and outboard ends of the locking ring  71 , may obliquely connect each end of the locking ring. This establishes a type of cantilever in the connecting member  78  between the two ends of the locking ring  71 . 
     In one embodiment, the locking ring  71  may have a circumferential, inner groove  76  in its inner cylindrical surface  73 . The inner groove  76  in the locking ring  71  increases the flexibility of the locking ring between the inboard end  74  and the outboard end  72 . 
     In another embodiment, a circumferential outer groove  77  may be in the outer cylindrical surface  75  of the locking ring  71 . This further reduces the axial cross-section of the locking ring  71 , increasing its flexibility. Any combination of inner and outer grooves, or no grooves, may be present in the locking ring  71 . 
     The locking ring  71 , with its connection between the annular body  61  and the cylindrical surface  19  of the dust guard  18 , reinforces and anchors the annular body  61  against axial displacement and deflection. It is believed that the flexibility of the locking ring  71  allows the annular body  61  to more readily move with the deflection of the journal  12 , yet, still allow the locking ring to restrain the axial displacement of the annular body, reducing its movement relative to the journal. 
     In addition to providing resistance to deflection from dynamic loads applied to the shaft  14 , the inner groove  76  provides an opportunity to seal the circumferential joint along the abutment of the distal edge  63  of the annular body  61  with the shaft  14 . The joint produced by this abutment provides a potential pathway for moisture intrusion into the bearing assembly. In this embodiment, after the backing ring assembly  60  is affixed to the shaft, the circumferential, inner groove  76  is generally located radially outward of the circumferential joint. The inner groove in this configuration forms an annular volume  79 . 
     Referring to  FIG. 4 , the annular volume formed by the inner groove  76  may be, in one embodiment, connected by a passage  81  to the exterior of the bearing and may terminate at a fitting  82 . The annular volume may be filled with a sealant  83  (e.g., such as silicone RTV) through the passage  81 . When set (e.g., cross-linked), the sealant  83  produces a moisture resistant, backing ring seal  80  around the circumference of the joint. In another embodiment, a backing ring seal may be formed in both the inner groove  76  and the outer groove  77  of the backing ring assembly  60 . 
     In still another embodiment, the inner groove  76  may be dimensioned to accept an o-ring, quad ring, or other similar type of elastomeric seal ring. The o-ring may be pre-fitted into the locking ring  71  prior to press fitting the locking ring onto the cylindrical surface  19  of the dust guard  18 . 
     The novel backing ring assembly discussed above, may be incorporated as a retrofit into both current and prior generation bearing assemblies requiring reconditioning. These retrofit procedures generally require machining the fitted or non-fitted backing ring into a configuration that can accept a locking ring. 
     For the prior generation, non-fitted backing ring, a retrofit procedure can be implemented to machine the appropriate sized slot into the axially inward directed surface of the non-fitted backing ring (in effect creating the annular body  61  of the backing ring assembly  60 ) to accommodate a locking ring  71 . 
     Although prior generation railcar axles have smaller and loosely toleranced dust guards to which the inboard end  74  of the locking ring  71  is affixed, press type interference fits are achieved even with a standardized size backing ring assembly  60  for installation on either prior or current generation rail car axles. It is believed that the flexibility of the connecting member  78 , bridging the outboard end  72  and inboard end  74  of the locking ring  71 , provides a mechanism for achieving this press type interference fit. 
     In addition to reconditioning prior generation railcar axle assemblies, the backing ring assembly can also be retrofitted to the current generation of railcar axles with fitted backing rings. Although much improved, the current generation of fitted backing rings and railcar axles are still susceptible to wear related degradation and periodically require reconditioning. 
     Referring to  FIG. 5 , an illustration of a fitted backing ring, modified to accept the novel backing ring assembly  60  is depicted. The modified backing ring was machined from a fitted backing ring to form an annular body  61  capable of engaging with a locking ring  71 . In this embodiment, two different machining processes were required for this retrofit. 
     The first machining process requires a counterbore in the fitted backing ring to accommodate the locking ring  71 . The fitted backing ring has an annular lip  67  extending concentrically over the cylindrical surface  19  of the dust guard  18 . The lip  67 , however, interferes with the engagement of the locking ring  71 . To accommodate the locking ring  71 , a counterbore  69  is machined into the inner cylindrical surface of the annular lip  67 . 
     The second machining process allows the annular body  61  to engage the locking ring  71 . A slot  65  is machined into the axially inward directed surface  62  to accommodate the outboard end  72  of the locking ring  71 . Machining these surfaces converts the fitted backing ring into the annular body  61 , capable of accommodating the locking ring  71 . 
     In this embodiment, the inboard end  74  of the locking ring  71  receives the cylindrical surface  19  of the dust guard  18  in an interference fit. The interference fit is readily controlled and reproducible because the current generation railcar axle has a closely toleranced dust guard. The final result is the incorporation of the backing ring assembly  60  into a fitted backing ring and railcar axle. 
     In another embodiment, the inboard end  74  of the locking ring  71  may have an interference fit not only with the cylindrical surface  19  of the dust guard  18 , but also with the inner cylindrical surface of the annular lip  67 . 
     Although the above discussion relates to the reconditioning of both current and prior generation railcar axle assemblies, is also possible to simply retrofit the railcar axle, either current or prior generation, with a new backing ring assembly. As noted above, the backing ring assembly can readily establish a press fit with the closely toleranced, current generation dust guard. Further, the locking ring, because of its connecting member, can also readily produce an interference fit with the prior generation railcar axle despite its loose tolerances. 
     While the invention has been illustrated with respect to several specific embodiments, these embodiments are illustrative rather than limiting. Various modifications and additions could be made to each of these embodiments as will be apparent to those skilled in the art. Accordingly, the invention should not be limited by the above description or of the specific embodiments provided as examples. Rather, the invention should be defined only by the following claims.