Abstract:
A rotary cone rock bit, comprises a bit body including a plurality of legs extending therefrom, each of the legs having an outer surface that includes a leading surface and a trailing surface, a roller cone rotatably supported on each of the legs, a bearing system between each cone and the leg on which it is supported, and a lubricant reservoir in fluid communication with the bearing system. The reservoir can be provided with a wear resistant plug, if desired. In the present bit, the reservoir has at least one opening positioned in either the leg&#39;s leading surface, trailing surface, center surface, shoulder surface or some combination of these. Alternatively, the reservoir can be formed inside the bit body, preferably by means of a canister, which can be provided with venting means as desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims the benefit of U.S. Provisional Application Serial No. 60/025,858, filed Sep. 9, 1996, and entitled Improved Rock Drill Bit, which is incorporated herein by reference, and of U.S. Provisional Application Serial No. 60/051,373 filed Jul. 1, 1997, and entitled Protected Lubricant Reservoir For Sealed Bearing Earth Boring Drill Bit. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] Not applicable. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    The invention relates generally to sealed bearing earth boring drill bits, such as rotary cone rock bits, that utilize a fluid circulation medium. More particularly, the invention relates to such drill bits that include a protected lubricant reservoir.  
           [0004]    More specifically, drill bits are generally known, and fall into at least two categories. Drill bits used for drilling petroleum wells and drill bits used in the mining industry are both well known in the art. While these two types of bits superficially resemble each other, the parameters that affect the operation of each are completely different. Petroleum drill bits typically use a viscous, heavy drilling fluid (mud) to flush the cuttings from the vicinity of the bit and carry them out of the hole, whereas mining bits typically use compressed air to achieve the same purpose. Petroleum bits typically drill deep holes, on the order of thousands of feet, and an average bit typically drills several hundreds or thousands of feet before being removed from the hole. In many instances, a petroleum bit is not withdrawn from the hole until it has exhausted its useful life. In contrast, mining bits are each used to drill several relatively shallow holes, typically only 30-50 feet deep, and must be withdrawn from each shallow hole before being shifted to the next hole. Thus, the effect of withdrawal and backreaming wear on the body of a mining bit are much more important considerations than they are for petroleum bits. In addition, because petroleum bits drill near the surface they are more frequently subjected to cave-ins, and must ream their way backwards out of the hole through the caved-in material. For these reasons, the factors that affect the design of mining bits are very different from those that affect the design of petroleum bits.  
           [0005]    For instance, the viscosity and density of the drilling mud makes it possible to flush the cuttings from the hole even at relatively low fluid velocities. The air used to flush cuttings from mining holes, in contrast, is much less viscous and dense and therefore must maintain a rapid velocity in order to successfully remove the rock chips. This means that the cross-sectional area through which the air flows at each point along the annulus from the bit to the surface must be carefully maintained within a given range. Similarly, the rapid flow of air across and around a rock bit greatly increases the erosive effect of the cuttings, particularly on the leading portions of the bit.  
           [0006]    Furthermore, rock bits are now being developed with sealed lubrication systems that allow easier rotation of the bit parts. These sealed lubrication systems typically comprise a lubricant reservoir in fluid communication with the bearings. In many cases, the reservoir is created by drilling a cavity into the bit leg. Access to the reservoir is through the installation opening of this cavity, which can then be sealed with a conventional plug or vented plug. These sealed lubrication systems are particularly vulnerable to erosion of the bit body, as any breach of the sealed system can result in the ingress of cuttings and/or particles into the bearings, causing bit failure. Heretofore, the reservoir opening has been located on the main outer face of each leg, with the result that the reservoir plugs and the walls of the reservoir itself are vulnerable to wear on the leg.  
           [0007]    Hence it is desirable to provide a mining bit that provides increased protection for the reservoir and its installation opening and plug. It is further desired to provide a bit that is capable of withstanding wear on its shoulders and legs during backreaming or as the bit is being withdrawn from a hole. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings wherein:  
         [0009]    [0009]FIG. 1 is an isometric view of a rotary cone drill bit of the present invention;  
         [0010]    [0010]FIG. 2 is a side view of one leg of the drill bit of FIG. 1;  
         [0011]    [0011]FIG. 3 is a cross-sectional view of a rotary cone drill bit of the prior art in a bore hole;  
         [0012]    [0012]FIG. 4 is a front elevation view of one leg of a rotary cone drill bit having a first embodiment of a protected lubricant reservoir;  
         [0013]    [0013]FIG. 5 is a cross-sectional view at plane  5 - 5  in FIG. 4;  
         [0014]    [0014]FIG. 6 is a front elevation view of one leg of a rotary cone drill bit having a second embodiment of a protected lubricant reservoir;  
         [0015]    [0015]FIG. 7 is a front elevation view of one leg of a rotary cone drill bit having a third embodiment of a protected lubricant reservoir;  
         [0016]    [0016]FIG. 8 is a front elevation view of one leg of a rotary cone drill bit having a fourth embodiment of a protected lubricant reservoir;  
         [0017]    [0017]FIG. 9 is a cross-sectional view at plane  9 - 9  in FIG. 8;  
         [0018]    [0018]FIG. 10 is a front elevation view of one leg of a rotary cone drill bit having a fifth embodiment of a protected lubricant reservoir;  
         [0019]    [0019]FIG. 11 is a cross-sectional view at plane  11 - 11  in FIG. 10;  
         [0020]    [0020]FIG. 12 is a cross-sectional view of one leg of a rotary cone drill bit having a sixth embodiment of a protected lubricant reservoir;  
         [0021]    [0021]FIG. 13 is an exploded view of the protected lubricant reservoir of FIG. 12;  
         [0022]    [0022]FIG. 14 is a cross-sectional view of one leg of a rotary cone drill bit having a seventh embodiment of a protected lubricant reservoir;  
         [0023]    [0023]FIG. 15 is a cross-sectional view of one leg of a rotary cone drill bit having an eighth embodiment of a protected lubricant reservoir;  
         [0024]    [0024]FIG. 16 is a cross-sectional view of a rotary cone drill bit having a ninth embodiment of a protected lubricant reservoir;  
         [0025]    [0025]FIG. 16 a  is a cross-sectional view at plane  16   a  -  16   a  in FIG. 16;  
         [0026]    [0026]FIG. 17 is a cross-sectional view of a rotary cone drill bit having a tenth embodiment of a protected lubricant reservoir;  
         [0027]    [0027]FIG. 18 is a cross-sectional view of one leg of a rotary cone drill bit having an eleventh embodiment of a protected lubricant reservoir;  
         [0028]    [0028]FIG. 19 is a front elevation view of one leg of a rotary cone drill bit having a twelfth embodiment of a protected lubricant reservoir;  
         [0029]    [0029]FIG. 20 is a front elevation view of one leg of a rotary cone drill bit having three protected lubricant reservoirs in accordance with the present invention; and  
         [0030]    [0030]FIG. 21 is a cross-sectional view of one leg of a rotary cone drill bit having yet another embodiment of a protected lubricant reservoir.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    Presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. In illustrating and describing the preferred embodiments, like or identical reference numerals are used to identify common or similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form in the interest of clarity and conciseness.  
         [0032]    Referring initially to FIGS.  1 - 2 , a sealed-bearing earth boring bit  10  is shown. The bit  10  illustrated is a rotary cone rock bit used for drilling blast holes in mining operations that utilizes fluid circulation to cool and clean the bit  10  and to transport earthen cuttings and debris up the bore hole to the surface (not shown). It should be understood that the present invention is not limited to rotary cone rock bits  10  for mining operations, but may be used in other types of sealed bearing earth boring drill bits for any other desirable earthen drilling applications, such as petroleum well, pipeline, sewage and electrical conduit drilling.  
         [0033]    The bit includes a bit body  12 , a pin end  14  and a cutting end  16 . The pin end  14  includes a connector  13 , such as a threaded pin connection  15 , for connecting the bit  10  to a carrier, such as a drill string (not shown). The bit body  12  includes legs  20  extending generally between the pin end  14  and the cutting end  16  of the bit  10 . At the cutting end  16 , each leg  20  carries a cutter cone  18  having a multitude of protruding cutting elements  19  for engaging the earthen formation and boring the bore hole  17  as the bit in rotated in a clockwise direction when viewed from the pin end  14 . Typically, rotary cone drill bits  10  have three legs  20  and cones  18 , although the present invention may be used in bits  10  with any number of leg  20 /cone  18  combinations. While portions of the description of the preferred embodiments of the present invention are made herein with reference to a single leg  20 , such discussions apply equally to each leg  20  of a bit  10  in accordance with the present invention.  
         [0034]    Still referring to FIGS. 1 and 2, a plenum  80 , having a plenum surface  82  extends through the bit  10  to allow the supply of circulation fluid (not shown) to one or more nozzles  84  formed in legs  20 , as is known in the art. The circulation fluid, such as gas or drilling mud, is provided into the plenum  80  from a fluid supply source (not shown) and through a supply conduit, such as a drill string (not shown), attached to the pin end  14  of the bit  10 . Each nozzle  84  extends from the plenum  80  to a port  86 , which opens to the exterior  70  of the bit  10 , as is known in the art. A nozzle boss  90  is disposed on the leg  20  over the nozzle  84 . The nozzles  84  operate to direct pressurized fluid against the bottom  71  of the bore hole  17  (FIG. 3) to lift earthen cuttings and other debris up through the bore hole  17 . The nozzles  84  also direct the circulation fluid over the cones  18  and cutting elements  19  to free debris accumulating thereabout.  
         [0035]    Now referring to FIG. 5, the bit  10  includes a bearing system  50  for permitting rotation of the cone  18  about a journal  23  extending from the leg  20 . The bearing system  50  may be a roller bearing system  50   a , as is, or becomes, known in the art, such as the roller bearing system disclosed in U.S. Pat. No. 5,793,719 to Crockett et al., which is incorporated herein by reference in its entirety. The roller bearing system  50   a  includes various conventional roller bearing components, such as, for example, cone bearing surfaces  52 , journal bearing surfaces  54 , roller bearings  56  and locking balls  58 , disposed in the interior  59  of the cone  18 . A roller bearing system  50   a  compatible for use with the bit  10  of the present invention is also shown with respect to the prior art bit  10   a  of FIG. 3. Alternately, the bearing system  50  may be a friction bearing system  50   b  (FIG. 9) including conventional friction bearing system components as are or become known in the art. In either type of bearing system  50   a ,  50   b , a locking ball loading hole  57  may be formed into the leg  20  for loading the locking balls  58  into the cone interior  59 . A ball retaining plug  55  (FIG. 9) is typically disposed in the hole  57  for retaining the locking balls  58 .  
         [0036]    Referring to FIG. 9, lubricant, such as grease (not shown), is provided to the roller bearing system  50  via a lubricant reservoir system  60 . A reservoir system  60  compatible for use with the bit  10  of the present invention is also shown with respect to the prior art bit  10   a  of FIG. 3. The reservoir system  60  includes one or more reservoirs  62  disposed in the bit  10  for supplying the lubricant to the bearing system  50 , such as through a lubricant passageway  68 . Any desirable number of reservoirs  62  can be disposed in a single leg  20  or elsewhere in the bit  10 . For example, FIG. 20 shows a leg  20  having three reservoirs  62 , while FIGS.  15 - 17  show lubricant reservoirs  62  disposed in the bit plenum  80 . While the following description of the preferred embodiments of the present invention is made, in part, with respect to a single reservoir  62 , it may be applied equally to each reservoir  62  of a multiple reservoir leg  20 , or bit  10 .  
         [0037]    Still referring to FIG. 9, the reservoir  62  typically contains various reservoir system components as are known in the art, such as, for example, a flexible membrane  64  that balances the pressure between the exterior  70  of the bit  10  and the lubricated, or lubricant carrying, side  66  of the bit  10 . It should be understood, however, that the inclusion or non-use of reservoir system components in the reservoir  62  is not limiting on the present invention. To allow the  20  insertion, or loading, of the lubricant and reservoir system components into the reservoir  62  during assembly of the bit  10 , one end  76  of the reservoir is initially left accessible through a reservoir installation opening  63 . After the lubricant and: reservoir system components are inserted, or loaded, into the reservoir  62 , the installation opening  63  is typically sealed and covered, such as, for example, with a reservoir cover cap  74  held in place with a retaining, or snap, ring  75  for retaining the lubricant and reservoir system components in the reservoir  62  (see also the prior art bit  10   a  of FIG. 3). The opposite end  77  of the reservoir  62  typically forms a blind hole in the leg  20  (FIG. 11).  
         [0038]    Again referring to FIG. 9, the reservoir system  60  may be configured to relieve the expansion, or excess volume, of lubricant (not shown) contained therein. Again, any suitable technique or mechanism as is or becomes known in the art may be utilized. For example, the reservoir  62  can be configured such that there is sufficient space (not shown) in the reservoir  62  for the lubricant to expand therein, as is known in the art. For another example, excess lubricant in the reservoir system  60  may be vented from the reservoir  62 . Any suitable conventional technique may be used. For example, excess lubricant can be vented through the flexible membrane  64 , as is known in the art. Another example of venting excess lubricant from the reservoir system  60 , as shown in FIG. 9, is through a vent duct  94  extending from the reservoir  62  to the bit exterior  70 , in accordance with the present invention. According to the present invention, the opening of vent duct  94  can be located on the throat surface, the leading surface, the trailing surface, the shoulder surface, or the center panel surface, although it is preferred that the vent duct opening not be on the same surface as installation opening  63 . A control device, such as a conventional pressure relief valve  96 , may be included to enable the controlled venting of lubricant from the reservoir system  60 .  
         [0039]    It should be understood that the aforementioned operations, configurations, components and methods have been provided to assist in understanding the context of the invention and are not necessary for operation of the invention.  
         [0040]    Now referring to FIG. 1, each leg  20  of the bit body  12  of the bit  10  of the present invention includes a leading side  30 , a trailing side  36 , a shoulder  40  and a center panel  46 . The leading side  30  has an outer surface  32 , the trailing side  36  has an outer surface  38 , the shoulder  40  has an outer shoulder surface  42  and the center panel  46  has an outer backturn surface  48 . Surfaces  32 ,  38 ,  42 ,  48  form part of the outer surface  100  of the leg  20 . In the embodiment shown, for example, the leading side surface  32  extends generally from the lower end  21  of the connector  13  to the lower edge  26  of the leg  20  between the edges  45 ,  47  of the center panel  46  and shoulder  40 , respectively, and the edge  49  of the leg  20 . The trailing side surface  38  extends generally from the lower end  21  of the connector  13  to the lower edge  26  of the leg  20  between edge  91  of the nozzle boss  90  and edges  43 ,  44  of the center panel  46  and shoulder  40 , respectively. The shoulder surface  42  is shown extending from the lower end  21  of the connector  13  to the upper edge  51  of the center panel  46  between the leading and trailing sides  30 ,  36  at edges  47 ,  44 , respectively. Finally, the backturn surface  48  extends between edges  45 ,  43  and  51  and the lower edge  26  of the leg  20 .  
         [0041]    Still referring to FIG. 1, as the bit  10  rotates during operations, the leading side  30  of each leg  20  leads the clockwise rotational path of the leg  20  followed by the shoulder  40  and center panel  46 , which are followed by the trailing side  36 . During drilling, as well as extraction of the bit  10  from the bore hole  17  (FIG. 2), the bit legs  20  will contact earthen cuttings (not shown) in the bore hole  17  and may also contact the bore hole wall  72  (FIG. 2). Generally, the leading side  30 , leg shoulder  40  and center panel  46  of each leg  20  will experience such contact, while the trailing side  36  is substantially blocked from significant contact with earthen cuttings and the bore hole wall  72  by the surfaces  32 ,  42  and  48  and the leg mass  29 . Depending on various factors, such as the composition of the earthen formation being drilled, contact between the surfaces  100  of the legs  20  and earthen cuttings (and the bore hole wall) will cause varying degrees of wear and damage to the legs  20 . During backreaming in hard, or rocky, earthen formations, for example, the legs  20 , particularly the leg shoulders  40  and leading sides  30 , may be subject to significant contact with rock cuttings, causing significant erosive wear, cracking and fracturing of the bit legs  20 .  
         [0042]    Referring to the prior art bit  10   a  of FIG. 3, it is a concern that damage to the bit legs  20  as described above can lead to damage to the lubricant reservoir  62 , which can lead to premature bit failure. For example, the introduction of foreign material, such as earthen cuttings, into the reservoir or bearing systems  60 ,  50 , will lead to contamination and deterioration of the lubricant and the reservoir and bearing system components, causing premature bit failure. It is thus an object of the present invention to provide improved protection of the reservoir  62  and reservoir opening  63  from damage caused by contact between the bit  10  and earthen cuttings (and the bore hole wall) during drilling and bit extraction.  
         [0043]    In prior art bits  10   a , as shown in FIG. 3, the reservoir installation opening  63  was typically located on the leg shoulder  40 , or across the intersection of the shoulder and center panel (not shown), facing angularly upwardly relative to the bore hole wall  72 , or from the central axis  11  of the bit  10   a . For example, a typical prior art bit reservoir opening  63  located on the shoulder  40  was oriented with its axis at an angle  31  of about 75 degrees or less relative to the central axis  11  of the bit  10   a . The prior art reservoir opening  63  orientation has been known to subject the reservoir opening  63  and reservoir  62  to damage as described above, particularly during backreaming.  
         [0044]    It should be understood that each of the following aspects of the invention may be utilized alone or in combination with one or more other such aspects. In one aspect of the invention, the installation opening  63  is accessible from the outer leg surface  100 , but located so as to decrease the susceptibility of the reservoir  62  and opening  63  to damage from contact between the leg  20  and bore hole debris, or the bore hole wall  72  (FIGS. 4, 7,  8 ). The installation opening  63  can be disposed anywhere on the leading side  30  (FIG. 7), trailing side  36  (FIG. 4) or center panel  46  (FIG. 8). In accordance with this aspect, as the bit  10  rotates in the bore hole  17 , particularly during extraction and backreaming, the reservoir installation opening  63  is generally more substantially blocked, or protected, from contact with the bore hole wall  72  and earthen cuttings in the bore hole  17  by the leg mass  29 , as compared to the prior art location of the installation opening  63  on the leg shoulder  40  (FIG. 3). In the preferred embodiments shown, the reservoir installation opening  63  is disposed above the bit throat level  22 . The “bit throat level”  22  refers to the cross-section of each leg  20  and the bit  10  taken generally along line  27  (FIG. 2), which extends proximate to the level of the nozzle ports  86 . The “bit throat”  33 , also shown in FIG. 2, refers to the interior, or facing, portions of each leg  20  between its lower edge  26  and the lower end  81  of the bit plenum  80 . However, the opening  63  may, in accordance with this aspect of the invention, also be disposed at, or below, the bit throat level  22 .  
         [0045]    In another aspect of the invention, the reservoir  62  may be oriented so that the installation opening  63  is on the outer surface  100  of leg  20 , but is oriented on the shoulder  40  (FIG. 21) so that it axis is at an angle  31  of between about 76 degrees and about 180 degrees relative to the central axis  11  of the bit  10 , or disposed at any angular orientation anywhere on the leading side  30  (FIG. 7), trailing side  36  (FIG. 4), or center panel  46  (FIG. 8) of leg  20 . For example, the opening  63  in FIGS. 4 and 7 are on the trailing and leading sides  36 ,  30 , respectively, oriented generally perpendicularly relative to the central axis  11  of the bit  10 , respectively. In FIG. 21, the opening  63  is oriented at an angle  31  of about  81  degrees relative to the central axis  11  of the bit  10 .  
         [0046]    In a further aspect of the invention, as shown, for example, in FIGS. 4, 7 and  8 , the reservoir  62  and installation opening  63  may be isolated from contact with bore hole debris and the bore hole wall by recessing the installation opening  63  into the leg  20 . The reservoir opening  63  of the leg  20  of FIG. 4, for example, is shown recessed into the trailing side  36  of the leg  20 , while the opening  63  of FIG. 7 is recessed in the leading side  30 . In FIG. 8, the reservoir installation opening  63  is shown recessed into the center panel  46 . The installation opening  63  thus lies recessed relative to the shoulder and backturn surfaces  42 ,  48 , respectively, and is shielded thereby and by the leg mass  29 . Further, the leg  20  may be configured so that the shoulder  40  serves as a protective ledge above the installation opening  63 , as shown, for example, in FIG. 9. In FIG. 9, the shoulder  40  extends radially outwardly from the leg  20  toward the bore hole wall  72  relative to the reservoir opening  63  by a distance  79  equal to between about 50% and about 100% of the exposed radial dimension  78  of the reservoir opening  63 , substantially blocking the reservoir opening  63  from contact with bore hole debris during backreaming.  
         [0047]    In yet another aspect of the present invention, a protective plug  110  may be emplaced over the reservoir opening  63 , as shown, for example, in FIGS.  7 ,  10 - 13 . The plug  110  protects the installation opening  63  and reservoir  62  by serving as an outer contact and wear surface and by absorbing impact energy from contact with bore hole debris and the bore hole wall  72  (FIG. 11). The plug  110  may be any suitable size and configuration, and may be constructed of any suitable material having strength, or wear, characteristics similar to, or better than, steel. For example, referring to FIG. 13, the plug  110  may have a thickness  152  of about 10% or greater of its diameter or smallest width  154 . Any suitable technique may be used to connect the plug  110  to the bit  10 , such as by welding, matable members or mechanical connectors (not shown). Still referring to FIG. 13, the bit  10  may be configured so that the plug  110  rests upon a plug base  112  formed into the leg  20 , whereby the base  112  absorbs energy from impact force to the plug  110  during drilling and bit extraction. Further, a gap  113  may be formed between the plug  110 , or plug base  112 , and reservoir opening  63  to allow space for the accumulation of excess lubricant from the reservoir  62 , or to isolate the reservoir  62  from the plug  110 . A bleed hole (not shown) may be formed in the plug  110 , or the leg  20 , and extends to the exterior  70  of the bit  10  to allow the venting of excess lubricant from the gap  113 .  
         [0048]    Alternately, the installation opening  63  may be entirely isolated from the outer surface  100  of the legs  20 , as shown, for example, in FIGS.  14 - 18 , to reduce the susceptibility of damage to the reservoir  62  and opening  63  from contact between the bit  10  and bore hole debris or the bore hole wall  72 . FIGS.  14 - 17 , for example, show the reservoir  62  configured so that the reservoir opening  63  opens to the bit plenum  80 . In FIG. 14, the reservoir  62  and installation opening  63  are accessible via the plenum  80  and communicate with bearing system  50  of leg  20 , such as through lubricant passageway  68 . The reservoir  62  is shown as a reservoir housing  65  disposed in a cavity, or receiving pocket,  69  formed in the leg  20 . The housing  65  may be any suitable container, such as a canister, having any form and construction suitable for use as a reserved  62  is described above or as known in the art. When a housing  65  is used, it is inserted into the cavity  69  or otherwise formed into bit leg  20  during assembly of the bit  10  and may be connected to the bit  10  with any suitable conventional technique, such as a threaded matable connector  101 , retaining rings, pins, or by weld (not shown). The reservoir  62 , however, need not be a housing  65 , but can take other suitable forms. For example, the cavity, or receiving pocket,  69  can itself be used as the reservoir  62 .  
         [0049]    In FIGS.  15 - 17 , the reservoir  62 , such as housing  65  as described above, is located within the bit plenum  80 . The reservoir housing  65  is mounted to the plenum surface  82  with pins  98  (FIG. 15), brackets  99  (FIG. 16, 16 a ) or any other suitable conventional technique, such as by weld or retaining rings (not shown). The reservoir  62  may be capable of supplying the bearing system  50  of a single leg  20 , as shown, for example, in FIG. 15, or multiple legs (FIGS. 16, 17). Further, the reservoir system  60 , such as shown in FIGS. 15 and 16, may include tubes  104  that connect the reservoir  62  with the leg bearing systems  50 , such as through passageways  68 . As illustrated in FIG. 16 a , the reservoir system  60  may have numerous tubes  104  for supplying lubricant to numerous bit legs (not shown).  
         [0050]    Referring to the embodiment shown in FIG. 17, the reservoir  62  may be located generally proximate to the lower end  81  of the plenum  80  and in direct communication with the passageways  68  of legs  20  for supplying lubricant to the bearing systems  50 . The reservoir  62 , such as housing  65 , may be easily installed into an assembled bit  10  by inserting the reservoir  62  into the plenum  80  at the pin end  14  of the bit  10  and securing it with any suitable conventional technique, such as with a centralizing ring  120 , or by weld. Alternately, the reservoir  62  may be easily installed through a bore  162  in the lower end  81  of the plenum  80 . Using this method, once the reservoir  62  is positioned as desired, the bore  162  and reservoir  62  may be welded together at the lower end  81  of the plenum  80  to secure the reservoir  62  in the bit  10  and, if desired, to substantially seal the plenum  80 .  
         [0051]    When the installation opening  63  opens to the bit plenum  80 , such as shown in FIGS.  14 - 17 , the reservoir system  60  may be configured to allow the flow of circulating fluid through the entire length of the plenum  80 . For example, a gap  88  (FIGS. 15, 16) can be formed between the reservoir  62  and the plenum surface  82 . For another example, the reservoir  62  can include a fluid bypass annulus (not shown), such as when the reservoir  62  is formed with a donut-shape (not shown).  
         [0052]    Excess lubricant may be vented from the reservoir system  60  with any suitable technique, such as those described above, if venting is desired. For example, excess lubricant may be vented through a vent passage  94  extending from the passageway  68  (FIGS.  14 - 16 ) to the bit exterior  70 . Excess lubricant may additionally, or alternately, be vented from the reservoir  62  into the plenum  80  (FIGS. 15, 16) or to the bit exterior  70  (FIG. 17), such as through a vent hole  87  in the reservoir housing  65 . Further, the vent passageway  94  or vent hole  87  may be equipped with a control device, such as a pressure relief valve  96 , to enable the controlled venting of lubricant from the reservoir system  60 . The reservoir system  60  may also, or alternately, be equipped with a piston vent  138  (FIGS. 15, 16) disposed within the reservoir  62 , or housing  65 . The piston vent  138  includes a piston member  144  and biasing member, such as a spring  140 , connected between the cover, or end,  142  of the reservoir  62  and the piston member  144 . The piston member  144  substantially sealingly engages the interior wall  160  of the reservoir  62 . Pressure changes in the reservoir  62  will cause the piston member  144  to move upwardly and downwardly therein. When the pressure within the reservoir or housing  65  forces the piston member  144  above predetermined height, or level, of  3  bleed hole  150  in the reservoir  62  excess lubricant and pressure in the reservoir system  60  is released into the plenum  80  through the bleed hole  150 . It should be understood, however, that the venting of excess lubricant from the reservoir system  60  with these or any other methods and structure is not required for, or limiting upon, the present invention.  
         [0053]    In another configuration of the present invention, such as shown in FIG. 18, the reservoir opening  63  is located in the proximity of the bit throat  33 . The reservoir  62  communicates with the leg bearing system  50 , such as through passageway  68 . By opening to the bit exterior  70  in the proximity of the bit throat  33 , the reservoir  62  and reservoir opening  63  are isolated and protected from contact between the bit  10  and bore hole debris and the bore hole wall. The reservoir  62  is shown in FIG. 18 having a housing  65  (as described above) disposed in a cavity, or receiving pocket,  69  formed in the leg  20 . The reservoir  62 , such as the housing  65 , may be connected to the bit  10  with any suitable conventional technique, such as a threaded mateable connector, retaining rings, pins, or by weld (not shown). The reservoir  62 , however, need not include a housing  65 , but can take any suitable form or configuration. For example, the cavity  69  can serve as the reservoir  62 .  
         [0054]    In a further aspect of the invention, a hard, wear resistant material  122  may be incorporated into, or upon, the bit  10  to strengthen the bit  10  and inhibit erosive wear and contact damage to the bit  10 , reservoir  62  and reservoir opening  63 , as shown, for example in FIGS. 6 and 19. The hard wear resistant material  122  may have any suitable shape and size and may be set flush with (FIG. 14), protrude from (FIG. 9), or be recessed (not shown) in the outer surface  100  of one or more legs  20  of the bit  10 , as is desired. Further, the hard wear resistant material  122  may be attached to the bit  10  with any suitable technique that is or becomes known in the art.  
         [0055]    The term “hard wear resistant material” as used herein generally includes any material, or composition of materials, that is known or becomes known to have strength, or wear, characteristics equal to or better than steel, and which can be affixed onto, or formed into, the drill bit  10 . The hard wear resistant material  122  may, for example, be inserts  124  (FIG. 4), as are known in the art for strengthening and inhibiting wear to the bit  10 . Inserts  124  may also be used for engaging and grinding loose rock in the bore hole during operations, such as disclosed in U.S. Pat. No. 5,415,243 to Lyon et al., which is incorporated herein by reference in its entirety. The inserts  124  may be tungsten carbide inserts, inserts constructed of a tungsten carbide substrate and having a natural or synthetic diamond wear surface, or inserts constructed of other suitable material. Any type of insert that is, or becomes, know for use with drill bits may be used with the present invention, such as “flat-top,” dome shaped, chisel shaped and conical shaped inserts. The inserts  124  may be embedded into the bit  10  as is known in the art or otherwise attached to the bit  10  with any suitable technique. For another example, the hard wear resistant material  122  may be hard facing, or deposits  134 , such as the guard member  136  of FIG. 18. As shown in FIG. 18, the hard facing or deposits  134 , such as the guard member  136 , may itself carry inserts  124 . The hard facing or deposits  134  are applied to the bit  10  with any suitable technique, such as by being brazed or welded thereto.  
         [0056]    The hard wear resistant material  122  can be placed at any location on the bit  10  as is desirable for assisting in protecting the reservoir  62  and reservoir opening  63 . As shown, for example, in FIGS. 14 and 18, the material  122  can be located on the bit  10  outward of the entire reservoir system  60  relative to the bore hole wall  72 . FIG. 14 shown inserts  124 , while FIG. 18 shows guard member  136 , each located on the shoulder  40  to assist in protecting the reservoir  62  and reservoir system  60  located within the leg  20 . For another example, hard wear resistant material  122 , such as inserts  124 , can be embedded into, or attached to, the plug  110  of the present invention, such as shown in FIGS.  7 ,  10 - 13 .  
         [0057]    When the reservoir installation opening  63  opens to the leg surface  100 , hard wear resistant material  122  may be used to protect the reservoir  62  and installation opening  63 . For example, a protective ledge, or protrusion,  126  of hard wear resistant material  122 , such as shown in FIG. 6, may be strategically formed into or attached to the leg  20 , such as above or around the installation opening  63 . The protrusion  126  may be connected to the bit  10  with any suitable conventional method, such as by welding or mechanical attachment means (not shown). For another example, hard wear resistant material  122 , such as inserts  124 , may be placed anywhere on the outside surface  100  of the leg  20  to assist in protecting the reservoir  62  and installation opening  63  (FIGS. 6, 12). FIGS. 4 and 7 shows the use of hard wear resistant material  122 , such as inserts  124 , on the shoulder  40  and center panel  46  when the installation opening  63  is on the trailing and leading sides  36 ,  30 , respectively. FIG. 20 illustrates an example of the use of inserts  124  in conjunction with a leg  20  having two reservoir openings  63  on the shoulder  40  and a third installation opening  63  on the trailing side  36 . Other examples of legs  20  having inserts  124  on the surface  100  when the installation opening  63  is on the shoulder  40  are shown in FIGS. 12, 13 and  19 . In FIG. 6, the installation opening  63  is shown located at the intersection of the shoulder  40 , center panel  46  and trailing side  36  of the leg  20  within a protrusion  126 . Hard wear resistant materials  122 , such as inserts  124 , are strategically disposed on the leg  20 , such as on the shoulder  40  and center panel  46 , to protect the reservoir  62  and installation opening  63 . FIGS. 8 and 11 show examples of the use of hard wear resistant material  122 , such as inserts  124 , to assist in protecting the reservoir  62  and installation opening  63  when the installation opening  63  is on the center panel  46 . It should be understood, however, that the particular arrangements, locations and quantities of hard wear resistant material  122 , such as inserts  124 , shown in the appended drawings are not limiting on the present invention.  
         [0058]    Each of the foregoing aspects of the invention may be used alone or in combination with other such aspects. While preferred embodiments of the present invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teachings of this invention. The embodiments described herein are exemplary only and are not limiting of the invention. Many variations and modifications of the embodiments described herein are thus possible and within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein.