Abstract:
A bearing assembly is presented having a novel lubricant sealing design that, in one embodiment, combines the sealing advantages of both a labyrinth-like seal in combination with a contact seal. The improved seal includes a non-rotating seal case working in closely spaced cooperation with a rotor to form a channel. The rotor is attached and turns with the shaft, inducing flow in the channel. Lubricant leakage is impeded by the tortuous fluid path formed by the convoluted channel of the labyrinth-like seal and the fluid shear forces developed by the turning shaft. Any lubricant leakage is further impeded by a resilient seal contacting the surface of the rotor and constricting the channel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 11/724,696, filed on Mar. 16, 2007 and entitled, “Seal For Railway Car Journal Bearing”, which is hereby incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     This invention relates to anti-friction bearings and more particularly, in one embodiment, to tapered roller bearings. 
     BACKGROUND OF THE INVENTION 
     Anti-friction bearings (also commonly known as rolling-contact bearings), such as ball bearings and tapered roller bearings, are commonly used in various industrial applications. Anti-friction bearings are typically purchased preassembled, ready for press fit onto the journal of a shaft or axle. 
     A lubricant (e.g., oil or grease) is applied to the bearing&#39;s rollers to minimize friction and wear. The quantity and quality of the lubricant has a significant effect on bearing life. To maximize the life of the bearing, bearing seals are used to retain lubricant within the bearing and exclude environmental contaminants. A good seal design strives to protect the bearing lubricant while balancing the need to minimize friction losses resulting from the bearing seal. 
     Bearings used in the railway industry to support railway car axles are a particularly demanding application, requiring energy efficiency while concurrently providing protection against environmental contaminants (such as water, dirt, sand etc.). These bearings must also effectively seal the bearing to minimize lubricant loss. 
     SUMMARY OF THE INVENTION 
     A bearing assembly is presented having a novel dual stage seal design. The seal includes a seal case working in closely spaced cooperation with a rotor to establish two types of seals: (1) a running seal similar to a labyrinth type seal and (2) a contact or rubbing type seal. 
     In one embodiment, the seal case and rotor form a channel extending in a convoluted path from the lubricated interior portion of the bearing to the exterior of the bearing. The channel allows the rotating and non-rotating bearing assembly components to move relative to each other while minimizing lubricant loss. 
     The seal case is a non-rotating component, affixed to a non-rotating portion of the bearing assembly such as the bearing cup. The rotor is a rotating component, affixed and turning with the shaft. The rotor induces fluid shear in the lubricant disposed in the channel. The closely spaced and torturous path of the channel and the fluid shear imparted by the turning (i.e., rotating) rotor creates a labyrinth-like seal. 
     Any lubricant leakage in the channel that the labyrinth-like seal does not stop is further reduced with a contact type seal. The contact seal, in one embodiment, is a resilient seal affixed to the seal case and urged against the rotor. 
     The use of two different types of seals in one bearing assembly allows this novel seal design to incorporate certain attributes from each seal type. These two different seal types are incorporated into only two components of the bearing assembly: (1) the rotor, and (2) the seal case (with the attached seal). 
     The novel seal design eliminates the need for wear rings commonly found in many bearing applications. Wear rings protect shafts from rubbing wear induced by contact sealing elements. Forming a contact seal on the running surface of the rotor eliminates the need for a wear ring found in prior art bearing assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Various embodiments of the bearing 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 is illustrated by way of example and not by limitation in the accompanying figures in which: 
         FIG. 1  is a sectional view of an exemplary embodiment of the bearing assembly; 
         FIG. 2  is a detailed sectional view of a first embodiment of the sealing portion of the exemplary bearing assembly illustrated in  FIG. 1 ; 
         FIG. 3  is a detailed sectional view of the seal in the exemplary bearing assembly illustrated in  FIG. 1 ; and 
         FIG. 4  is a detailed sectional view of a second embodiment of the sealing portion of the exemplary bearing assembly illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an exemplary bearing assembly  10  is illustrated. In this embodiment, the bearing assembly  10  is a tapered roller bearing assembly of the type commonly used in railway applications to support a low friction railcar wheel. The bearing assembly described in the following embodiments, however, may be adapted for use in many other common industrial applications. Consequently, the bearing assembly illustrated and described below in relation to a tapered roller bearing assembly for a railcar wheel is for convenience only. Furthermore, although the embodiments described and illustrated in the figures refer to tapered roller bearing assemblies, the novel bearing assembly described and claimed is generally applicable to anti-friction bearings. 
     The bearing assembly  10  is typically preassembled before being mounted on the journal  12  of a shaft  14  (e.g., a rail car axle). At the free end of the shaft  14 , a journal  12  terminates in a slightly conical, tapered guide  18  to facilitate installation of the bearing assembly  10  onto the journal. The bearing assembly  10 , in one embodiment, is press fit on the journal  12 , which is machined to very close tolerances to accurately accommodate the press fit. The journal  12  terminates at its inner end in a contoured fillet  16  leading to a cylindrical shoulder  17  on the shaft  14 . A backing ring  22  abuts the bearing assembly  10  and the shoulder  17 , affixing the bearing assembly  10  against inward axial displacement. A bearing retaining cap  20 , having a plurality of threaded bores  19 , is mounted at the free end of the shaft  14  with threaded cap screws or bolts  21 . The bearing retaining cap  20  clamps the bearing assembly  10  into position on the shaft  14 . 
     In this embodiment, wear rings commonly used in the prior art to protect against shaft wear have been eliminated. Some prior art wear rings have been designed with polymer inserts to cushion and protect the shaft from wear ring induced fretting. For example, U.S. Pat. No. 5,549,395, “Shaft Journal Bearing Having Improved Seal Wear Ring,” dated Aug. 27, 1996 to Sink discusses such a modified wear ring, and is hereby incorporated by reference in its entirety. Because there are no wear rings in this embodiment, the bearing retaining cap  20  and the backing ring  22 , in one embodiment, have polymer inserts  27  that at least partially line their inner cylindrical surfaces. The inserts  27  may be affixed adhesively or fitted into keyways ground into the backing ring  22  or retaining cap  20 . The polymer inserts  27  in the backing ring  22  and retaining cap  20  cushion flexural loads, mitigating journal  12  fretting and the potential failure of the shaft  14 . 
     As indicated above, the bearing assembly  10  is preassembled from a number of individual components. The bearing assembly  10  includes a unitary bearing cup  31  having a pair of adjacent raceways  32 ,  34  formed on the inner surface of the bearing cup (one adjacent at each end of the bearing cup). The raceways  32 ,  34  cooperate with a pair of bearing cones  38 ,  40 , respectively, to capture and support two rows of tapered rollers  42 ,  44 . A center spacer  47  is positioned between the bearing cones  38 ,  40  to maintain the cones in accurately spaced position relative to one another and allow for proper bearing lateral clearance. In some embodiments, a cage  46 ,  48  controls the spacing of the rollers  42 ,  44  to maintain their relative position within the raceways  32 ,  34 . 
     The seal cases  50 ,  52  substantially cover each end of the bearing assembly  10 , protecting the bearing from external contaminants. The seal cases  50 ,  52 , are a component of the dual stage seal system. The seal cases  50 ,  52 , in one embodiment, are affixed to the stationary (i.e., non-rotating) side of the bearing assembly (such as the bearing cup  31 ) by interference fit or other appropriate method. 
     The rotors  80 ,  82  are another component of the dual stage seal system. In one embodiment, the rotors  80 ,  82  are affixed to the bearing cones  38 ,  40  and rotate with the shaft  14 . In another embodiment, the rotors are captured between either a bearing retaining cap  20  or backing ring  22  and the bearing assembly  10 . For example, the rotor  80  is affixed between bearing cone  38  and bearing retaining cap  20 . At the other end of the bearing assembly  10 , rotor  82  is affixed between the bearing cone  40  and backing ring  22 . 
     The rotors  80 ,  82  and seal cases  50 ,  52  together are designed to control lubricant leakage and protect the bearing assembly  10  and lubricant  25  from intrusion of external contaminants. The seal case and rotor design are the same for both sides of the bearing assembly  10 . The only difference is that one rotor is adjacent to the bearing retaining cap  20  and the other rotor to the backing ring  22 . 
     The seal cases  50 ,  52  work in closely spaced cooperation with the rotors  80 ,  82  to control lubricant leakage. The lubricant  25  used in bearing assembly  10  may be, for example, either oil or grease. The lubricant  25  is in direct contact with the rollers  42 ,  44 . Lubricant reservoirs  24 ,  26  may be provided at each end of the bearing assembly  10  to ensure adequate lubrication is supplied to the rollers  42 ,  44  and the surfaces contacting the rollers. 
     The closely spaced, cooperative relationship between the seal cases  50 ,  52  and the rotors  80 ,  82  form two types of seals: (1) a seal similar to a labyrinth type seal, and (2) a contact type seal. Each of these seal types has advantages and characteristics not offered by the other. 
     Referring now to  FIG. 2 , a detailed view of one embodiment of the cooperative, closely spaced relationship between the seal case and rotor of the bearing assembly  10  of  FIG. 1  is illustrated. The rotor  82  is a generally cylindrical piece having a rotor outer section  84  with the largest diameter. The rotor outer section  84  terminates in the rotor distal end section  86 . The rotor intermediate circular section  90  extends from the rotor outer section  84  inward radially to the rotor inner section  88 . The rotor root section  93  extends radially inward from the rotor intermediate circular section  90  past the rotor inner section  88 . 
     In this embodiment, the rotor  82  is affixed to the backing ring  22 . In turn, rotor  82  is affixed to the bearing cone  40 . In the embodiment illustrated in  FIG. 2 , the backing ring  22  is locked in place by the rotor retaining lip  94  which is adapted to snap into the undercut retaining groove  23  in the backing ring  22 . In turn, the rotor  82  is affixed to the bearing cone  40  with a second rotor retaining lip  96  similarly engaging an undercut retaining groove  41  in the bearing cone  40 . The rotor root section  93  is captured between the bearing cone  40  and the backing ring  22 , further acting to limit axial movement of the rotor  82 . As the bearing cone  40  is affixed onto journal  12  (e.g., press fit), the backing ring  22 , rotor  82 , and bearing cone  40  are all locked together on and turn with the shaft  14 . 
     The seal case  52  is closely spaced and works cooperatively with the rotor  82  to substantially seal the end of the bearing assembly  10 . In one embodiment, the seal case  52  has a large diameter open end section  54  press fit into the counterbore  35  in the bearing cup  31 . Alternatively, in another embodiment, the seal case  52  may have a retaining lip  56  adapted to snap into an undercut retaining groove  37  in the bearing cup  31 . This design allows the seal case  52  to be releaseably retained on the bearing assembly  10 . 
     A seal case intermediate section  58  has a smaller diameter cylindrical section running parallel to the open end section  54 . A stator  66  of smaller diameter than the intermediate section  58  is a cylindrical section running parallel to the intermediate section  58 . An inner circular section  62  extends between the intermediate section  58  and the stator  66 . The seal case  52  terminates in a seal case distal end  64 . A mounting ring  69  extends from the seal case  52  generally at the intersection of the inner circular section  62  and the stator  66 . 
     The seal case and rotor combination function together to provide a dual stage lubrication seal. The seal case  52  works in closely spaced cooperation with rotor  82  to form a channel  97 . The motion of the rotor  82  rotating with the shaft  14  relative to the non-rotating seal case  52  creates a rotating side of the channel  97  (i.e., the rotor side) and a stationary side of the channel (i.e., the seal case side). This relative motion induces shear stresses in the lubricant in the channel, impeding lubricant loss from the reservoir. 
     In one embodiment, the rotor and the seal case form a closely spaced, straight channel. In one embodiment, the channel may include chaplets (i.e., small surface projections acting similar to pump impellers) to help force lubricant from the channel toward the reservoir. 
     In another embodiment, the channel  97  is convoluted and forms a tortuous fluid flow path. The outer section  84 , rotor distal end  86 , and rotor inner section  88  of the rotor  82  form the rotor side of the channel  97 . Closely spaced and cooperating with the rotor  82  is the seal case  52  which forms the seal case side of the channel  97  with seal case intermediate section  58 , the seal case inner circular section  62 , and the stator  66 . 
     Consequently, in one embodiment, the channel  97  begins with the closely spaced outer surface  83  of the rotor outer section  84  and the inner surface  59  of the seal case intermediate section  58 . The channel  97  continues around the rotor distal end  86  closely spaced to the circular surface  63  of the seal case inner circular section  62 , reversing the direction of the channel. The channel  97  continues between the inner surface  85  of the rotor outer section  84  and the outer surface  65  of the seal case stator  66 . The channel  97  continues around the seal case distal end  64  closely spaced to the rotor intermediate circular section  90 , reversing the direction of the channel again. The channel  97  continues between the inner surface  67  of stator  66  and the outer surface  87  of the rotor inner section  88 , exiting to the exterior of the bearing assembly  10  past the seal member (or seal)  72 . 
     In one embodiment, the seal  72  is molded on and permanently bonded to mounting ring  69  projecting from the seal case  52 . The seal  72  makes contact with rotor  82  to create a sealing surface to limit lubricant leakage. 
     Referring to  FIG. 3 , one embodiment of a seal  72  typically used in tapered bearing assemblies is illustrated. In this embodiment, the seal  72  is an integrally molded annular ring of elastomeric or rubber like material of suitable density and hardness selected for the particular application as is known in the art. For example, common materials of construction for the seal  72  include Nitrile Butadiene Rubber (NBR), Viton, silicone, etc. The seal  72 , however, may be constructed of non-elastomeric materials (e.g., felt, thermoplastic and thermosetting polymers) or combinations of materials (e.g., a fabric reinforced elastomeric material). 
     Seals constructed from elastomeric materials are useful for providing a resilient seal. The resiliency of the seal urges the seal  72  against the surface of the rotor  82 , exerting a substantially constant pressure to resist lubricant leakage. 
     To further increase the sealing force of the seal  72 , a mechanical spring (not shown), such as an endless coil or garter spring may back the seal. These springs are designed to maintain a continuous, controlled sealing pressure between the seal and the rotor. This spring is optional, and may be omitted to enable a lighter contact or non-contacting seal to be formed. An example of such a spring assembly is described in U.S. Pat. No. 5,186,548, entitled “Bearing Shaft Seal,” granted Feb. 16, 1993, to Sink which is hereby incorporated by reference in its entirety. 
     The seal  72  may be designed in any number of different embodiments. For example, the seal may be a simple felt type seal. Alternatively, the seal  72  may be technically sophisticated. For example, in one embodiment, the seal may have a separate lubricant seal lip  71  and primary dust seal lip  73 . The lubricant seal lip  71  provides the primary lubricant sealing area against the rotor  82 . 
     Various design variations may be incorporated into the lubricant seal lip  71 . These include projections from the lubricant seal lip  71  that act as a pump to counter lubricant leakage. These seal designs are discussed in detail in U.S. Pat. No. 5,511,886, entitled “Bearing Seal With Oil Deflectors,” granted Apr. 30, 1996, to Sink which is hereby incorporated by reference in its entirety. 
     At its outer end, the seal  72  is provided with a primary dust seal lip  73  to exclude contaminants. In one embodiment, the seal  72  may have a pair of dust seal lips. In this embodiment, the seal  72  includes an outwardly directed primary dust seal lip  73  and an auxiliary, inwardly spaced; outwardly directed secondary dust seal lip  74 . The primary dust seal lip  73  and the secondary dust seal lip  74  are generally located axially outward from the bearing assembly. 
     The seal  72  has a concave inner surface  75  between lubrication seal lip  71  and secondary dust lip  74  which, together with the outer surface  87  of the rotor  82  defines a first annular chamber  76  when the seal  72  is installed. This first annular chamber  76  may be packed with a suitable lubricant prior to installing the seal case  52 . 
     Similarly, a second annular chamber  77  is provided between the adjacent surfaces of the primary dust seal lip  73  and the secondary dust seal lip  74  and the outer surface  87  of rotor  82 . This second annular chamber  77  may also be packed with lubricant prior to installation on the shaft  14 . 
     Referring now to  FIG. 4 , a detailed view of bearing assembly  110  having an alternative embodiment of the seal case and rotor sealing arrangement is illustrated. The only difference between the bearing assemblies depicted in  FIG. 2  and  FIG. 4  is the attachment of the modified rotor  182  to the backing ring  122  and the bearing cone  140 . 
     The rotor  182  has a return section  195  extending normally from the rotor root section  193 . This return section  195  is accommodated between an annular space formed between the bearing cone  140  and the backing ring  122 . The rotor return section  195  has a first retaining lip  194  that fits into the retaining groove  123  in backing ring  122 . 
     Similar to the rotor  82  depicted in  FIG. 2 , the rotor  182  also has a second retaining lip  196  on the rotor root section  193  that fits into an undercut retaining groove  141  in the bearing cone  140 . Consequently, the two retaining lips  194 ,  196  on the rotor  182  respectively connect with the bearing ring  122  and the backing cone  140  to connect these components together as one rotating assembly on the shaft  14 . 
     Although the discussion above relating to  FIG. 2  and  FIG. 4  details the design and operation of the rotor and seal case adjacent to the backing ring, the design and operation of the rotor and seal case adjacent to the bearing retaining cap is identical. Instead of the rotor connecting to the backing ring, the rotor connects to the bearing retaining cap. 
     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.