Abstract:
A bearing assembly is presented having a novel lubricant sealing design that, in one embodiment, combines the advantages of contacting and non-contacting dust seals to balance energy efficiency while still providing an effective method for contaminant exclusion. The contacting and non-contacting dust seals further arranged to maximize the service life of the dust seals and prolong the maintenance intervals required on the bearing assembly.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to anti-friction bearings and more particularly, in one embodiment, to tapered roller bearings. 
       BACKGROUND OF THE INVENTION 
       [0002]    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 a shaft. 
         [0003]    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 have a significant effect on bearing life. A bearing operating with inadequate lubrication may quickly overheat and fail. 
         [0004]    To maximize the life of the 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. 
         [0005]    Bearings used in the railway industry to support railcar axles are a particularly demanding application, requiring energy efficiency while providing protection against environmental contaminants (such as water, dirt, sand etc.). Even within the railway industry, certain types of railcars (and their bearings) are exposed to particularly severe environmental operating conditions. 
         [0006]    For example, the bearings of hopper cars must withstand contaminants introduced by the cargo itself. Coal dust, gypsum, cement, and any variety of industrial chemicals and minerals may be hauled in bulk and potentially contaminate the bearing. Particulate contaminants entering the bearing can potentially cause abrasive damage and bearing failure. 
         [0007]    The abrasive action of even small amounts of contaminants can increase bearing friction, causing overheating of the lubricant or directly damaging bearing components. Consequently, it is critically important that a bearing effectively exclude environmental contaminants from the bearing while simultaneously sealing the lubricant within the bearing while providing reliable, low maintenance, and energy efficient service. 
       SUMMARY OF THE INVENTION 
       [0008]    A bearing assembly is presented having a novel bearing seal for excluding environmental contaminants and retaining bearing lubricant. In one embodiment, the seal body has two portions: a lubricant seal portion and a dust seal portion. The dust seal portion of the seal body has a novel design that incorporates features to preclude contaminants from entering and migrating to the interior of the bearing assembly. One feature is the use of a primary dust seal and a secondary seal (known together as a double dust seal) in conjunction with an auxiliary dust seal. 
         [0009]    The dust seals are designed in various embodiments as either contacting seals or non-contacting seals to achieve a balance between contaminant exclusion, energy efficiency, and service life. The primary dust seal is a contacting seal providing the first defense against contaminant intrusion. The secondary seal is a non-contacting seal selected for energy efficiency and yet still provides effective contaminant exclusion. The auxiliary seal, depending upon the embodiment, may be either contacting or non-contacting. The non-contacting embodiment is an energy-efficient design for trapping particulate contaminants escaping the primary and secondary seals. In the alternative embodiment, the auxiliary seal is a contacting seal. Although less energy-efficient, the contacting auxiliary seal embodiment provides a tighter seal against contaminant intrusion. 
         [0010]    In addition to the sealing capability of the dust seals, contaminant intrusion into the bearing is further inhibited by the annular chambers created by the dust seals. The annular chambers form a particulate trap for contaminants such as dirt, dust, sand. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]    Various embodiments of the bearing assembly and seal body 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 and seal body are illustrated by way of example and not by limitation in the accompanying figures in which: 
           [0012]      FIG. 1  is a sectional view of one embodiment of the bearing assembly; 
           [0013]      FIG. 2  is a detailed sectional view of one embodiment of the seal case depicted in the bearing assembly embodiment illustrated in  FIG. 1 ; 
           [0014]      FIG. 3  is a perspective view of the seal body embodiment illustrated in  FIG. 2 ; and 
           [0015]      FIG. 4  is a detailed sectional view of the seal body embodiment illustrated in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1 , an exemplary bearing assembly  10  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 low friction 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. Furthermore, although the embodiments described and illustrated in the figures refer to tapered roller bearing assemblies, the novel bearing assembly and sealing system described and claimed is generally applicable to anti-friction bearings. 
         [0017]    The bearing assembly  10  is typically preassembled before being mounted on a shaft  11  (e.g., a railcar axle). At the free end of the shaft  11 , a journal  12  terminates in a slightly conical, tapered guide  13  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  of the shaft  11 . The journal  12  is machined to very close tolerances to accurately accommodate the press fit. 
         [0018]    Wear rings  14 ,  16  fit over the journal  12  and abut the bearing assembly  10 . The wear rings  14 ,  16  typically have an inner diameter dimension to provide an interference fit with the journal  12  over least a portion of its length so that the entire assembly, in one embodiment, is pressed as a unit onto the end of the journal  12 . The wear rings  14 ,  16  become, in effect, an integral part of the shaft  11 , rotating with the shaft as it turns. 
         [0019]    The journal  12  terminates at its inner end in a contoured fillet  18  leading to a cylindrical shoulder  19  on the shaft  11 . A backing ring  22  is affixed by the shoulder  19 . A wear ring  16  is captured between the backing ring  22  and the bearing assembly  10 . 
         [0020]    A bearing retaining cap  20  having a plurality of bores is mounted at the free end of the shaft  11  with threaded cap screws or bolts  21 . The bearing retaining cap  20  captures the wear ring  14  against the bearing assembly  10 . The bearing retaining  20  and the backing ring  22  effectively clamping the bearing assembly  10 , including the wear rings  14 ,  16 , into position on the journal  12  of the shaft  11 . 
         [0021]    As indicated above, the bearing assembly  10  is preassembled from a number of individual components. The bearing assembly  10  includes a bearing cup  31  having raceways  32 ,  34  formed on the inner surface of the bearing cup. The raceways  32 ,  34  cooperate with bearing cones  38 ,  39  to capture and support two rows of tapered rollers  42 ,  44  respectively. In some embodiments, cages  46 ,  48  maintain the spatial position of the rollers  42 ,  44  within the raceways  32 ,  34 . A center spacer  41  is positioned between the bearing cones  38 ,  39  to maintain the cones in accurately spaced position relative to one another and allow for proper bearing lateral clearance. 
         [0022]    Seal cases  50 ,  52  cover the ends of the bearing assembly  10 , helping to protect the bearing from external contaminants and substantially sealing the lubricant within the bearing assembly. In one embodiment, the seal cases  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. The seal case design and sealing function are described in greater detail below. 
         [0023]    Referring to  FIG. 2 , the seal case  50  of the bearing assembly  10  of  FIG. 1  is illustrated in a detailed sectional view (with only one end portion depicted). The seal case  50  in one embodiment, as discussed above, may be affixed to the bearing cup  31  with an interference fit. For example, the seal case  50  has a large diameter open end section  54  which may be press fit into the counterbore  33  in the bearing cup  31 . Alternatively, in another embodiment, the seal case  50  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  50  to be releaseably retained on the bearing assembly  10 . 
         [0024]    The seal case  50  has a generally cylindrical form. A seal case intermediate section  58  has a smaller diameter cylindrical section running parallel to the open end section  54 . A seal case outer radial section  57  extends between the seal case intermediate section  58  and the open end section  54 . An inner radial section  62  extends radially inward from the intermediate section  58 . The seal case  50  terminates in a mounting ring  65  extending from the inner radial section  62 . 
         [0025]    A seal body  70  is attached to the mounting ring  65  and extends to contact a wear surface  15 . The wear surface  15  may be provided by either the journal  12  or a wear ring  14  fitted over the journal  12 . For example, in one embodiment, a wear surface is established between the stationary seal body  70  and the rotating wear ring  14 , allowing the rotating and non-rotating bearing assembly  10  components to move relative to each other. The seal case  50  (and the seal body  70 ) operating in conjunction with the wear ring  14  (or shaft in some embodiments) is designed to control lubricant leakage and protect both the bearing assembly  10  and lubricant  25  from contaminants. 
         [0026]    In one embodiment, the seal body  70  is molded on and permanently bonded to mounting ring  65 . In this embodiment, the seal body  70  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 body  70  include Nitrile Butadiene Rubber (NBR), Viton™, silicone, etc. The seal body  70 , however, may be constructed of other materials (e.g., felt, thermoplastic and thermosetting polymers) or combinations of materials (e.g., a fabric reinforced elastomeric material). 
         [0027]    Seals constructed from elastomeric materials are useful for providing a resilient seal. The resiliency of the seal urges the seal body  70  against the wear surface  15 , exerting a substantially constant pressure to resist lubricant leakage and contaminant intrusion. 
         [0028]    To further increase the sealing force exerted by the seal body  70  on the wear surface  15 , a mechanical spring  90  (such as an endless coil or garter spring) may back the seal body  70 . These springs are designed to maintain a continuous, controlled sealing pressure between the seal body  70  and wear surface  15 . In one embodiment, a spring retaining groove  91 , located circumferentially around the exterior surface of the seal body  70 , captures the spring  90 . The spring  90  is optional, and may be omitted to enable a lighter contact or non-contacting seal to be formed. An example of such a spring backed seal 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. 
         [0029]    The seal body  70 , in one embodiment, is urged against the wear ring  14  to seal the bearing assembly  10 . The wear ring  14  protects the journal  12  against rubbing wear from the seal body  70 . Direct contact between the seal body  70  and the journal  12  could potentially create sufficient rubbing wear to degrade and potentially cause shaft failure. This wear is accelerated by the presence of abrasive particulate contaminants such as sand in the lubricant. 
         [0030]    The wear ring  14  is designed and manufactured to produce a surface hardness capable of resisting rubbing wear damage from the seal body  70 . In the event that the wear ring  14  does become damaged it can be replaced relatively easily, particularly in comparison to the cost of replacing a shaft. 
         [0031]    It is possible, in one embodiment, to eliminate the wear ring  14  and urge the seal body  70  directly against the shaft. For reasons noted above, this is generally not the best practice. Consequently, for these reasons and for ease of description, the subsequent descriptions of the bearing assembly  10  will assume the use of a wear ring  14  in conjunction with the bearing assembly. 
         [0032]    The bearing assembly  10  is typically pre-lubricated prior to shipment by the manufacturer. The lubricant  25  most commonly used in the bearing assembly  10  is grease. During assembly, grease is typically applied to both the rollers  42  and to the seal body  70 . This pre-packed grease helps ensure that the bearing assembly  10 , when first installed, receives sufficient lubrication to minimize startup wear on the new assembly. 
         [0033]    In this embodiment, the seal body  70  has a lubricant seal  74  at one end and dust seals  71 ,  72 , and  73  at the other end. The lubricant seal  74 , in one embodiment, is directed axially inward (i.e., toward the bearing cup  31 ) and is resiliently urged against the wear surface  15  of wear ring  14  to impede lubricant loss from the bearing assembly. 
         [0034]    Referring now to  FIG. 3 , a detailed perspective view of one embodiment of the seal body  70  of  FIG. 2  is illustrated. Various designs may be incorporated into the lubricant seal  74  to enhance the seal&#39;s ability to minimize lubricant loss. This includes the use of hydrodynamic surfaces  75  located axially outward (i.e., away from the bearing cup) from the lubricant seal  74  and lubricant deflectors  76  located axially inward (i.e., toward the bearing cup) of the lubricant seal  74 . These lubricant 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. 
         [0035]    The lubricant deflectors  76  are designed to minimize lubricant in the area axially inward and adjacent to the lubricant seal  74 . Lubricant deflectors  76  are aligned circumferentially around the seal body  70  and extend radially inward. Like stationary impellers, the lubricant deflectors  76  force lubricant near the lubricant seal  74  back into the bearing cavity. Lubricant entrained by the rotating wear ring, impinges on the projecting deflectors  76  and is redirected toward the bearing cavity away from the lubricant seal  74 , reducing lubricant leakage under the lubricant seal. 
         [0036]    Similar to the lubricant deflectors  76 , the hydrodynamic surfaces  75  are stationary and deflect lubricant entrained by the rotating wear ring axially inward toward the lubricant seal  74 . The hydrodynamic surfaces  75  are aligned circumferentially around the seal body  70 , axially outward of the lubricant seal  74 . Projecting radially inward, the hydrodynamic surfaces  75  present a curved surface facing axially inward. Lubricant entrained by the viscous shear forces imparted by the rotating wear ring impinges these hydrodynamic surfaces  75 . The hydrodynamic surfaces  75  redirect the lubricant axially inward toward the lubricant seal  74  and into the bearing cavity. 
         [0037]    In some embodiments, neither the hydrodynamic surfaces  75  nor the lubricant deflectors  76  are necessary. In still other embodiments, only the hydrodynamic surfaces  75  or only the lubricant deflectors  76  are used in conjunction with the lubricant seal  74 . 
         [0038]    Referring to  FIG. 4 , the seal body  70  embodiment illustrated in  FIG. 3  is shown in detailed cross-section to illustrate the contact points between the seal body  70  and the wear surface  15 . As noted above, the seal body  70  has a plurality of dust seals at one end of the seal body. The first line of defense against external contaminants is the primary dust seal  71 . The primary dust seal  71  is outwardly directed at the axially outward, distal end of the seal body  70 . The primary dust seal  71  is a contacting seal, extending and rubbing against the wear surface  15 . 
         [0039]    Immediately adjacent and axially inward of the primary dust seal  71  is the outwardly directed, secondary dust seal  72 . The secondary dust seal  72  is closely spaced (i.e., does not contact the wear surface  15 ). The primary dust seal  71  and the secondary dust seal  72  (also known as a double dust seal) operate in conjunction to exclude contaminants from the bearing assembly. 
         [0040]    The primary and secondary dust seals are dimensioned such that the primary dust seal  71  is relatively flexible while the secondary dust seal  72  provides greater rigidity and consequently, stability to maintain close tolerance spacing with the wear surface  15 . In practice, the difference between the diameter of the secondary dust seal  72  and the diameter of the wear surface  15  is maintained as low as practical to produce an effective seal without resulting in actual rubbing contact. In most applications, this difference should be within the range of about 0.001 to 0.008 inches. 
         [0041]    Axially inward of the secondary dust seal  72  is the auxiliary seal  73 . In one embodiment, the auxiliary seal  73  is a non-contacting seal, closely spaced but not contacting the wear surface  15 . In another embodiment, however, the auxiliary seal  73 , may contact the wear surface  15 . The auxiliary seal  73  is available to impede particulate contaminants escaping the secondary seal  72 . 
         [0042]    In both of the above embodiments, the auxiliary seal  73  operates as a barrier to contaminant migration further into the bearing assembly. In the embodiment of the non-contacting auxiliary seal  73 , significantly less degradation is expected from particle abrasion and running wear to the seal because of its non-contacting design. The non-contacting auxiliary dust seal  73  has approximately the same dimensional tolerances as the secondary dust seal  72 . As a result, the non-contacting seal embodiment is expected to have a longer service life than the contacting auxiliary seal embodiment while still providing a defense against contaminate intrusion. 
         [0043]    The contacting auxiliary seal embodiment, however, provides a tighter seal against contaminate intrusion. Although it is a contacting seal, it will still experience less wear by virtue of the effectiveness of the secondary seal  72  in reducing contaminate migration, thereby protecting the contacting auxiliary seal from excessive contaminant abrasion. The non-contacting secondary seal  72  prolongs the service life of the contacting auxiliary seal. In light of the non-contacting design of the secondary seal  72 , the secondary seal  72  should experience relatively little wear, and provide protection to the contacting auxiliary seal  73  for its service life. 
         [0044]    The effectiveness of the dust seal arrangement is further augmented by the first and second annular chambers  81 ,  82  formed by the dust seals around the wear ring  14 . In addition to the barrier created by the dust seals, the lubricant in the annular chambers  81 ,  82  pins contaminants and impedes contaminant migration. 
         [0045]    The first annular chamber  81  is created between the primary dust seal  71  and the secondary dust seal  72 . Primary dust seal  71  has a circumferential surface  84  intersecting with the circumferential surface  85  of secondary dust seal  72  creating a first annular chamber  81  against the wear surface  15 . Similarly, a second annular chamber  82  is formed between the circumferential surface  86  of the secondary dust seal  72  and the circumferential surface  87  of the auxiliary dust seal  73  against the wear surface  15 . Finally, a third annular chamber  83  having a concave inner surface  88  is formed between the auxiliary seal  73 , the lubricant seal  74 , and the wear surface  15 . 
         [0046]    Each of the annular chambers provides a defense against contaminant intrusion into the bearing cavity. The annular chambers are typically pre-packed with a suitable lubricant (e.g., a grease). Contaminants entering the bearing assembly are blocked by the physical presence of the lubricant. In addition, the grease acts as a pinning agent to entrap and impede the further migration of contaminants. 
         [0047]    The rotating wear surface  15  (e.g., the wear ring) enhances the ability of the annular chambers to capture contaminates. Particulate contaminants must travel along the rotating wear ring in order to pass under the dust seals into the bearing assembly and bearing cavity. As a result, contaminants are initially closely spaced or on the wear surface  15 . The wear ring, because of its rotation, entrains lubricant and acts like a flinger, forcing particulate contaminates radially outward into the annular chamber. The grease pins the particulates in the chamber, preventing further migration of the particulates into the bearing assembly. 
         [0048]    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.