Protected lubricant reservoir with pressure control for sealed bearing earth boring drill bit

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of application Ser. No. 08/925,869, filed Sep. 9, 1997, and entitled “Protected Lubricant Reservoir for Sealed Bearing Earth Boring Drill Bit,” now abandoned, which in turn 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.”

BACKGROUND OF THE INVENTION

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.

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 In many instances, a petroleum bit is not withdrawn from the hole until it has exhausted its useful life.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mining bits are each used to drill several relatively shallow holes, typically only 30-50 feet deep, and must be withdrawn from each shallow hole before being shifted to the next hole.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.

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.

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.

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.

In addition, it has been found that the pressure in the lubricant reservoir, and more particularly the pressure drop across the dynamic seals, can affect the performance of the dynamic seals and of the lubricant system in general. Hence, it has become desirable to control the fluid pressure in the lubricant reservoir. It is further desirable to do so without compromising the integrity of the sealed bearing system or rendering it vulnerable to excessive wear.

SUMMARY OF THE INVENTION

The present invention relates to a rock bit having a sealed lubricant system with a lubricant reservoir in at least one, and preferably at least each of the legs of the bit. The lubricant reservoir preferably has an installation opening that is protected from damage during back reaming operations. According to various embodiments, an installation opening for each reservoir can be located on the leading surface, center panel surface, trailing surface, and/or on the shoulder of the leg in which the reservoir is formed. The lubricant reservoir further includes, a pressure equilibrating device, such as a membrane or diaphragm, in fluid communication with either the bit plenum or the annulus surrounding the bit, so that the pressure inside the reservoir can be controlled to desired levels. The pressure equilibrating device is preferably located in the passage formed by the installation opening.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings wherein:

FIG. 1

is an isometric view of a rotary cone drill bit of the present invention;

FIG. 2

is a side view of one leg of the drill bit of

FIG. 1

;

FIG. 3

is a cross-sectional view of a rotary cone drill bit of the prior art in a bore hole;

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;

FIG. 5

is a cross-sectional view at plane

5

—

5

in

FIG. 4

;

FIG. 5A

is an alternative embodiment of the leg shown in

FIGS. 4 and 5

;

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;

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;

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;

FIG. 9

is a cross-sectional view at plane

9

—

9

in

FIG. 8

;

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;

FIG. 11

is a cross-sectional view at plane

11

—

11

in

FIG. 10

;

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;

FIG. 13

is an exploded view of the protected lubricant reservoir of

FIG. 12

;

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;

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;

FIG. 16

is a cross-sectional view of a rotary cone drill bit having a ninth embodiment of a protected lubricant reservoir;

FIG. 16

a

is a cross-sectional view at plane

16

a

—

16

a

in

FIG. 16

;

FIG. 17

is a cross-sectional view of a rotary cone drill bit having a tenth embodiment of a protected lubricant reservoir;

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;

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;

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

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

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.

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.

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

10

is 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.

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.

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

.

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

.

To allow the 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

).

Still referring to

FIG. 9

, the reservoir

62

may contain various reservoir system components, 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.

As discussed herein, reservoir

62

can be pressurized or non-pressurized. According to one preferred embodiment, a pressurized reservoir is pressurized by pressure communication with the circulation fluid, either inside or outside the bit, through a conduit

92

. Any suitable pressure-transmitting device, such as a plate, piston, diaphragm, or the like can be positioned in conduit

92

so as to transmit pressure from the desired circulation area to the lubricant in the reservoir

62

, while maintaining the fluid in the reservoir in fluid isolation from the circulation fluid. In

FIG. 5

, while installation opening

63

is on the trailing side of the bit, conduit

92

communicates with the plenum. In

FIG. 5A

, conduit

92

again communicates with the plenum, but installation opening

63

is on the shoulder of the bit. In

FIG. 5A

, cover

95

in installation opening

63

prevents any outward flow of fluid from chamber

93

and prevents transmission of fluid pressure. Hence, fluid pressure from plenum

82

is transmitted through conduit

92

, across flexible membrane

64

to reservoir

62

.

In instances where the seal(s) protecting the bearing are susceptible to damage by excessive pressure, it is desirable to limit the pressure differential across the seal(s). One method of limiting the amount of pressure on the lubricant is to limit the pressure drop across the nozzle, which in turn limits the back pressure in the plenum. If flexible membrane

64

is in fluid communication with the plenum (such as through a reservoir installation opening in the plenum), pressure in the reservoir will equal the pressure in the plenum. As long as the difference between the pressure in the plenum and the pressure in the annulus outside the bit is less than the desired amount, the seal(s) will not be subjected to excessive pressure. Control of pressure in the plenum is preferably accomplished by adjusting the nozzle exit orifice (nozzle diameter). It has been found through field experimentation that a pressure difference of 100 psig or less is preferable and a pressure difference of 40 psig or less is optimum. Alternatively, the lubricant reservoir without requiring fluid communication with the plenum, such as by the use a pressure-applying means, such as a spring-biased piston or the like.

Alternatively, excessive pressure across the seal(s) can be avoided by balancing the pressure on both sides of the seal so that the lubricant pressure is neutral to the annulus pressure. Placement of flexible membrane

64

in fluid communication with the annulus (such as through a reservoir installation opening in the annulus, e.g. on the leading face, central panel, trailing face or shoulder, as described below), pressure in the reservoir will equal the pressure in the annulus. Similarly, pressure in the lubricant reservoir can be balanced with the pressure in the annulus, regardless of where the reservoir installation opening is located.

Again referring to

FIG. 9

, the reservoir system

60

may be also configured to relieve the expansion, or excess volume, of lubricant contained therein. Any suitable technique or pressure relief device 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 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

.

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.

Referring again 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 backtun 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

.

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

.

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.

In prior art bits l

0

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.

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

.

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 its 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

.

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.

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

.

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 reservoir

62

as 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

.

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

(

FIGS. 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).

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