Abstract:
A low friction tapered roller bearing is provided that implements either needle rollers, nested needle rollers, nested balls, or a thrust washer between the tapered rollers and the large rib of the inner ring. The nested needle rollers and balls options can either be cage guided or full complement.

Description:
TECHNICAL FIELD 
       [0001]    Example aspects described herein relate to bearing assemblies, particularly of tapered roller bearing assemblies that contain additional rolling elements to reduce friction in the axial or thrust direction. 
       BACKGROUND 
       [0002]    Bearing assemblies are typically circular in shape, and generally comprise of rolling elements, normally contained by a cage, disposed between inner and outer raceways. Rolling elements take many forms, including spherical balls, cylindrical rollers, needle rollers, or various other configurations, such as cone-shaped tapered rollers or barrel-shaped spherical rollers. Cages are often used to contain the rolling elements and guide them throughout the rotating motion of the bearing, but are not a necessity in some configurations. The material of a cage can vary from steel to plastic, depending on the application, duty cycle, along with noise and weight requirements. 
         [0003]    The type of bearing used for a particular application depends on multiple factors including the magnitude of the load and the load direction. Angular contact ball bearings are able to withstand combined radial and axial loads. Tapered roller bearings are also able to withstand combined radial and axial loads, but, for a given bearing envelope size, have a higher load capacity than angular contact ball bearings. The design of tapered roller bearings is such that the inner and outer raceways are angled with respect to the central axis of the bearing. For a given width of envelope space, the angled raceway increases the amount of line contact between the roller and raceway which increases the load capacity of the bearing. The angled raceway also allows the tapered roller bearing to carry combinations of radial and thrust loads. Resultant loads on a tapered roller bearing generate a force that pushes the roller against the large rib of the inner raceway as shown in  FIG. 7 , which is a source of friction that this invention addresses. 
       SUMMARY OF THE INVENTION 
       [0004]    A new design for a tapered roller bearing is disclosed that reduces the inherent friction that occurs between the roller and the large rib of the inner raceway. In one example embodiment of the invention, needle rollers are placed between the large diameter end of the tapered roller and the corresponding large rib interface of the inner raceway in order to reduce the friction. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    The above mentioned and other features and advantages of the embodiments described herein, and the manner of attaining them, will become apparent and be better understood by reference to the following descriptions of multiple example embodiments in conjunction with the accompanying drawings. A brief description of the drawings now follows. 
           [0006]      FIG. 1  is a perspective view of a first example embodiment of a tapered roller bearing assembly with a needle roller placed between the large diameter end of the tapered roller and the large rib of the inner ring. 
           [0007]      FIG. 2  is a perspective view of the inner ring of the tapered roller bearing assembly of  FIG. 1 . 
           [0008]      FIG. 3  is a perspective view of the outer ring of the tapered roller bearing assembly of  FIG. 1 . 
           [0009]      FIG. 4  is a sectioned view of the tapered roller bearing assembly of  FIG. 1 . 
           [0010]      FIG. 5  is a sectioned view of a second example embodiment of a tapered roller bearing assembly with nested balls placed between the large diameter end of the tapered roller and the large rib of the inner ring. 
           [0011]      FIG. 6  is a sectioned view of a third example embodiment of a tapered roller bearing assembly with a thrust washer placed between the large diameter end of the tapered roller and the large rib of the inner ring. 
           [0012]      FIG. 7  is a sectioned view of a prior art tapered roller bearing assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Identically labeled elements appearing in different figures refer to the same elements but may not be referenced in the description for all figures. The exemplification set out herein illustrates embodiments which should not be construed as limiting the scope of the claims in any manner. A radially inward direction is from an outer radial surface of the outer raceway, toward the central axis or radial center of the outer raceway. Conversely, a radial outward direction indicates the direction from the central axis or radial center of the outer raceway toward the outer surface. Axially refers to directions along a diametric central axis. 
         [0014]      FIG. 7  is a sectioned view of a prior art tapered roller bearing assembly  100 . The bearing assembly comprises of the outer ring  101 , tapered rollers  102 , cage  103 , and inner ring  104 . The inner ring  104  contains a large rib  105  for contact with the tapered rollers. Contact at this interface and the subsequent resultant sliding friction occurs in most tapered roller bearings. 
         [0015]      FIG. 1  is a perspective view of a tapered roller bearing assembly according to a first example embodiment.  FIGS. 2 and 3  are perspective views of the respective inner and outer rings of the bearing of  FIG. 1 .  FIG. 4  is a sectioned view of the bearing of  FIG. 1 . The following description should be viewed in light of  FIGS. 1-4 . The bearing assembly  1  consists of an outer ring  12 , tapered rollers  14 , tapered roller cage  16 , inner ring  18 , needle rollers  30  and needle roller cage  26 . Outer ring  12  contains an angled outer raceway  13  which is a direct interface for the tapered rollers. Inner ring  18  contains an angled raceway  17  that is recessed within the inner ring such that a small rib  15  and large rib  11  are formed at the ends of the raceway. The thrust surfaces of the small rib and large rib are approximately perpendicular to the angled raceway  17 . Angled raceway  17  is a direct interface for the tapered rollers. Needle rollers  30  and needle roller cage  26  are located between the end of the tapered rollers and the large rib of the inner ring. Under application loads as the tapered rollers orbit around central axis  10 , the tapered rollers are pushed against the needle rollers to facilitate a rolling interface as opposed to a sliding interface between the tapered roller end and the large rib that occurs in the prior art bearing. Therefore, a lower friction condition exists with the presence of a needle roller placed between the tapered roller and the large rib of the inner ring. 
         [0016]      FIG. 5  is a sectioned view of a tapered roller bearing assembly according to a second example embodiment. This embodiment utilizes balls  31  placed between the tapered rollers  14  and large rib  11 , however, the inner ring  22  contains a flange  23  on the large rib that extends axially such that the balls are captured, and, as shown, a cage can be optionally omitted resulting in a full complement configuration. Rolling elements other than balls can also be used in this embodiment. 
         [0017]      FIG. 6  is a sectioned view of a tapered roller bearing assembly according to a third example embodiment, in which a thrust washer  33  is utilized between the ends of the tapered rollers  14  and the large rib  25  of the inner ring  24 . The use of a thrust washer eliminates the need for expensive finish machining operations, such as grinding and honing, that are typically applied to the large rib of the inner ring to ensure a robust thrust interface for the tapered roller. Therefore, the application of a thrust washer, with the appropriate hardness and surface characteristics, provides a means of reducing the cost of the tapered roller bearing. 
         [0018]    In the foregoing description, example embodiments are described. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense. It will, however, be evident that various modifications and changes may be made thereto, without departing from the broader spirit and scope of the present invention. 
         [0019]    In addition, it should be understood that the figures illustrated in the attachments, which highlight the functionality and advantages of the example embodiments, are presented for example purposes only. The architecture or construction of example embodiments described herein is sufficiently flexible and configurable, such that it may be utilized (and navigated) in ways other than that shown in the accompanying figures. 
         [0020]    Although example embodiments have been described herein, many additional modifications and variations would be apparent to those skilled in the art. It is therefore to be understood that this invention may be practiced otherwise than as specifically described. Thus, the present example embodiments should be considered in all respects as illustrative and not restrictive. 
       LIST OF REFERENCE SYMBOLS 
       [0021]      1  Tapered Roller Bearing Assembly, Needle Roller Design 
         [0022]      3  Tapered Roller Bearing Assembly, Nested Ball Design 
         [0023]      4  Tapered Roller Bearing Assembly, Thrust Washer Design 
         [0024]      10  Central Axis, Needle Roller Design 
         [0025]      11  Large Rib, Needle Roller Design 
         [0026]      12  Outer Ring, Needle Roller Design 
         [0027]      13  Outer Raceway, Needle Roller Design 
         [0028]      14  Tapered Rollers 
         [0029]      15  Small Rib, Needle Roller Design 
         [0030]      16  Cage, Tapered Roller 
         [0031]      17  Inner Raceway, Needle Roller Design 
         [0032]      18  Inner Ring, Needle Roller Design 
         [0033]      22  Inner Ring, Nested Ball Design 
         [0034]      23  Flange on Large Rib, Nested Ball Design 
         [0035]      24  Inner Ring, Thrust Washer Design 
         [0036]      26  Cage, Needle Roller Design 
         [0037]      30  Needle Rollers 
         [0038]      31  Balls 
         [0039]      33  Thrust Washer 
         [0040]      100  Prior Art Tapered Roller Bearing Assembly 
         [0041]      101  Outer Ring 
         [0042]      102  Tapered Roller 
         [0043]      103  Cage 
         [0044]      104  Inner Ring 
         [0045]      105  Thrust Contact Surface