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BACKGROUND 
   1. Field of Invention 
   This disclosure relates to a bearing for a roller cone bit. Specifically, the present disclosure concerns a hydrostatic bearing assembly employing a sealed lubricant reservoir located in a high stress region of the bearing. 
   2. Description of Prior Art 
   Drill bits used in drilling of subterranean well bores typically comprise drag bits and roller cone bits. Roller cone bits typically comprise a body having legs extending downward and a head bearing extending from the leg towards the axis of the bit body. Frusto-conically shaped roller cones are rotatably mounted on each of these journals and are included with cutting teeth on the outer surface of these cones. Because of the high stresses incurred during drilling operations, the bearing mating surfaces within the bit require a bearing material or a surface treatment to sustain the loads and extend the bit life. 
     FIG. 1  provides in a side cross-sectional view an example of a portion of a roller cone drill bit  10 . In this example the roller cone bit  10  includes a body  11  having a bearing pin  14  depending from its lower end. A roller cone  12  is shown rotatingly mated onto the bearing pin  14 . A set of balls  16  is provided in an annular opening formed between the cone  12  and the head  14  and serves as a cone-retention system. A secondary purpose of the balls  16  is to provide a rolling surface for facilitating rotation of the cone  12 . 
   Compacts  20  are shown extending outward from the cone  12  surface. Rotating the bit  10  on a wellbore bottomhole BH in turn rotates the cone  12  to engage the compacts  20  with the bottomhole formation  21 . Adding weight on bit force with cone  12  rotation crushes the bottomhole formation  21  under the applied force of the compacts  20 . Traditionally, a journal bearing element  18  is disposed in a recess  19  circumferentially formed within the head section  14 . The journal bearing element  18  accommodates the cone  12  rotation and the forces transferred between the cone  12  and the head section  14 . A significant amount of the transferred forces exerted on head section  14  and the roller cone  12  contact surface are concentrated in the region between the head  14  and the bottomhole BH. For the purposes of discussion herein, this region is referred to as the lower portion  22 . The concentrated force on the lower portion  22  urges lubricant between the head  14  and roller cone  12  out of the lower portion  22  thereby causing metal to metal contact, that in turn accelerates material wear along the head  14  and roller cone  12  contact surface in the lower portion  22 . 
   SUMMARY OF INVENTION 
   The disclosure herein provides an earth boring bit comprising, a bit body, a leg section depending from the body, a bearing pin extending from the leg having a journal bearing surface, a journal sleeve coaxially mounted on the journal bearing surface and enclosing the lubricant reservoir, a lubricant reservoir formed between the journal bearing surface and the journal sleeve, a reservoir seal surrounding the lubricant reservoir and in sealing contact between the journal bearing surface and the journal sleeve, a roller cone rotatingly coupled on the bearing pin over the journal sleeve, and a primary seal between the cone and the bearing pin. The cone is rotatable relative to the journal sleeve and the journal sleeve is optionally pivotable about an axis of the bearing pin. The lubricant reservoir may extend circumferentially along the journal bearing circumference up to or less than 360°. Optionally, additional reservoirs may be included on the journal bearing circumference. The earth boring bit may also include a primary seal extending circumferentially around the bearing pin for sealing lubrication between the cone and the bearing pin. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a cross-sectional view of a portion of a roller cone bit. 
       FIG. 2  is an exploded view of a portion of a roller cone bit. 
       FIG. 3  is a side view of the roller cone bit of  FIG. 2  as assembled. 
       FIG. 4  is a view of a lower side of a head section of a bit assembly in accordance with the present disclosure. 
       FIG. 5  is a sectional view of a portion of a bit in accordance with the present disclosure. 
       FIG. 6  is a sectional view of a portion of an alternative embodiment of a bit in accordance with the present disclosure. 
   

   While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF INVENTION 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
   An embodiment of a roller cone bit  28  in accordance with the present disclosure is shown in a side exploded view in  FIG. 2 . A bit leg  30  lower portion is shown having a bearing pin  32  laterally extending from the leg  30 . The bearing pin  32  is a cylindrical member having a journal bearing surface  33  adjacent its attachment to the leg  30 . A ball race  39  is provided coaxially adjacent the journal bearing surface  33  on the side opposite the leg  30 . The ball race  39  provides a surface for a series of balls  38  that affix a roller cone to the bearing pin  32 . An optional shoulder  44  is shown included between the leg  30  and journal bearing surface  33 . The shoulder  44  circumscribes the bearing pin  32  and has an outer diameter exceeding the journal bearing surface  33  outer diameter. 
   Formed on the journal bearing surface  33  is a lubricant reservoir  34  having a lubricant  35  therein. In the embodiment of  FIG. 2 , the reservoir  34  is largely rectangular having sides substantially parallel with the respective ends of the journal bearing surface  33 . The reservoir  34  extends along the lower portion of the journal bearing surface  33  having ends shown perpendicular to the reservoir  34  sides. A seal  36  extends around the reservoir  34  outer periphery. The seal  36  may be comprised of any suitable seal material, such as an elastomeric, a metal, or, as described in more detail below, corresponding grooves and indentations. Still referring to  FIG. 2 , an annular journal sleeve  40  is illustrated aligned for insertion onto the bearing pin  32 . When inserted on the bearing pin  32 , the journal sleeve  40  circumscribes the bearing pin  32  around the journal bearing surface  33 . The seal  36  should be sized such that when the journal sleeve  40  is positioned around the journal bearing surface  33 , the seal  36  extends into sealing contact with both the journal bearing surface  33  and the journal sleeve  40  inner annular surface. The seal  36  thus forms a sealing barrier between the journal bearing surface  33  and the journal sleeve  40  and around the lubricant reservoir  34 . The seal  36 , by encircling the reservoir  34 , prevents any substance from within the reservoir  34  from migrating past the seal  36  thereby forming a hydrostatic region within the space bounded by the seal  36 . 
   A force applied to the sealed hydrostatic region pressurizes the entrapped lubricant. When the lubricant comprises a fluid like substance, the lubricant pressure will be substantially equal throughout. Accordingly, an applied force to a fluid like lubricant distributes the applied force substantially equally throughout the lubricant. Distributing the pressure throughout the lubricant in turn equally distributes force from the entrapped lubricant to the journal bearing surface  33  portion adjacent the reservoir  34 . Distributing the force through the reservoir  34  prevents load concentrations on the journal bearing surface  33 . Thus when the bit  28  is in use loads transferred between the roller cone  42  and the bearing pin  32  can be evenly distributed to the journal bearing surface  33  along an area substantially equal to the reservoir  34  area. Examples of substances provided within the reservoir  34  include lubricants and other friction reducing materials. The lubricants can comprise any known lubricant including Newtonian and non-Newtonian fluids, grease, silicon, thixotropic substances, and combinations thereof. 
   As noted above, increased loading occurs on the lower region  37  of the bearing pin  32 . As such, the reservoir  34  is illustrated in the embodiment of  FIG. 2  as being located primarily in the lower region  37 . However, other embodiments exist wherein the reservoir  34  extends into other regions of the bearing pin  32  along the journal bearing surface  33 , the reservoir  34  can also extend around the entire circumference of the journal bearing surface  33 . Other embodiments exist where multiple reservoirs  34  are provided on the bearing pin  32 . 
   In  FIG. 3 , a side partial sectional view of the drilling bit  28  as assembled. Here the journal sleeve  40  circumscribes the journal bearing surface  33  and the roller cone  42  is affixed on the bearing pin  32 . In one embodiment, the journal sleeve  40  is non rotatable about the bearing pin  32 . This may be accomplished by a key arrangement (not shown) that extends between the journal bearing surface  33  and the journal sleeve  40 . However, other methods of preventing rotation about the journal sleeve  40  over the journal bearing surface  33  are available and included within the scope of this disclosure. Although the journal sleeve  40  may be prevented from rotating around the bearing pin  32 ; clearance between the journal sleeve  40  and the bearing pin  32  allows the journal sleeve  40  to pivot with respect to the axis A H  of the bearing pin  32 . For the purposes of illustration, the journal sleeve  40  axis A S  is included to illustrate an example of pivoting motion having a range defined by the angle θ. Thus although the roller cone  42  rotates about the journal sleeve  40 , the journal sleeve  40  pivots in response to cone  42  pivoting movement induced by torque applied to the cone  42  during excavating operations. The efficacy of the seal  36  however is not compromised by journal sleeve  40  pivoting and will continue to provide its sealing barrier function. Also illustrated in  FIG. 3  is a primary seal  41  in sealing contact between the roller cone  42  and the journal sleeve  40 . An inlay material  43  inserted between the roller cone  42  and the journal sleeve  40 . 
     FIG. 4  depicts an upward looking view of an embodiment of the head section  32  with a lubricant reservoir  34  provided on a lower portion of the head section  32  along the journal bearing surface  33 . The seal  36  extends along the outer periphery of the reservoir  34 . An optional second reservoir  34   a  with second seal  36   a  is also provided on the bearing pin  32 . In one embodiment, the reservoir  34  extends approximately 70° to about 100° along the journal bearing surface  33  outer perimeter. Optionally, the lubricant reservoir may extend about 90° along the journal bearing surface  33  circumference. A line L is shown substantially parallel with the bearing pin  32  axis A H . The line L represents the bearing pin  32  region (lower most region of the bearing pin  32 ) closest to the borehole surface B H  ( FIG. 3 ) during earth boring operations. In one optional embodiment, the reservoir  34  is bisected into two substantially equal sections by line L. Other embodiments exist where the reservoir  34  is asymmetric about line L. 
   A cross sectional view of a portion of the bit  28  in accordance with the present disclosure as provided in  FIG. 5 . As shown, the seal  36  is in sealing engagement between the journal bearing surface  33  outer circumference and the inner circumference of the journal sleeve  40 . Fluid  35 , such as lubricant from the reservoir  34  extends from within the reservoir  34  and into the space between the journal bearing surface  33  and the journal sleeve  40 . Seal  36  retains the lubricant  35  within the predefined region within a circumferential portion of the journal bearing surface  33  and the journal sleeve  40 . Moreover, the seal  36  retains the lubricant  35  within this region during pivoting movement of the bearing sleeve  40  about its axis A S . The forces transferred from the rotating roller cone  42  to the bearing pin  32  are first transferred to the journal sleeve  40  and to the lubricant  35  within the lubricant reservoir  34 . As previously discussed, the lubricant  35  has a substantially equal pressure throughout the reservoir  34  thereby imparting substantially distributed forces into the journal bearing surface  33  and avoiding a force concentration. Accordingly, discreet portions of the bearing pin  32  should not experience excessive wear, instead an even amount of wear should be distributed along that surface, thereby prolonging the useful life of the bearing pin  32  and the drill bit  28 . 
   A portion of an alternative bit  28   a  embodiment is illustrated in side sectional view in  FIG. 6 . In this embodiment a recess  45  is provided on the surface of the journal sleeve  40   a  facing the journal bearing surface  33   a . Lubricant  35  is retained in the space between the journal sleeve  40   a  and the journal bearing surface  33   a  by a seal  36  circumscribing the reservoir  45 . Bit embodiments of the present disclosure include reservoirs between other moving surfaces, such as the thrust face, pilot pin to name but a few. Also optionally, a fluid circuit may be included for directing and/or replenishing lubricant to the reservoir. To prevent backflow to the lubricant supply, a check valve may be included within the fluid circuit. 
   It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.

Summary:
A roller cone bit having a sealed lubricant reservoir between a roller cone and a head section. A journal sleeve is included on the head section that circumscribes the journal bearing surface of the head section. The sleeve can axially pivot on the head section, but does not rotate thereon. The reservoir is formed into a journal bearing surface of the head section body and may be sealed by placing a seal around its periphery that extends between the journal bearing surface and journal sleeve. Sealing the reservoir results in a hydrostatic condition therein and substantially equalized pressures.