"IMPROVEMENTS TO RC HAMMER BIT LUBRICATION ^'

This invention relates to providing a lubrication means for a spline and in particular to providing lubrication between the working faces of an engaged spline set.

PRIORITY

This patent application claims priority from:

Australian Provisional Patent Application 201 902055, titled "IMPROVEMENTS TO RC HAMMER BIT LUBRICATION", and filed on 26 May 201 1.

The entire content of this application is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Splines are used in numerous applications to provide a drive coupling while at the same time allowing longitudinal movement along the axis of rotation. The invention will have general application in relation to splines regardless of the field of use, however for the purpose of description, the invention will be described in relation to its use in down hole percussive hammers. A drill bit of a percussive down hole hammer (be it normal and reverse circulation) is conventionally provided with a splined shank. This shank locates within a splined drive sub, which in turn is threadably engaged to an end of a hammer barrel. The use of the spline between the drill bit and drive sub enables rotation of the drill bit with the hammer, while at the same time allowing longitudinal movement of the drill bit with respect to the hammer.

There is generally significant clearance between the drive sub spline and the spline on the shank of the drill bit. This clearance allows a small amount of rotation of the drill bit with respect to the drive sub. As a result, when the hammer rotates in any given direction, contact will be between one side of each individual spline of the drive sub and a single corresponding side of a drive sub spline.

Driving forces including relative movement between the drive sub and the drill bit can be considerable so that damage resulting from high contact loads may be a significant problem.

This damage can be reduced, and therefore the life of a drill bit and drive sub extended, if adequate lubrication is provided between the contacting surfaces of the splines. However, because of the close fit normally provided between these contacting surfaces, it is very difficult to maintain effective lubrication, particularly when the drill bit is operated continuously over an extended period. One solution for ensuring adequate lubrication is to stop the drilling process and to lift the hammer off of the bottom of the hole, which will result in disengagement of the spline surfaces to allow coating with lubricant that is entrained within the compressed air supply that drives the hammer. However, this practice is time consuming and results in a loss to the driller through reduced drilling rates.

It is against this background that the present invention has been developed.

Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

SUMMARY OF THE INVENTION

In one aspect, the invention may be said to reside in a lubrication means for a pair of splines, each spline having a pair of side faces, at least one of which will serve as a working face, where at least portions of the working faces for the pair of splines are abutting, and wherein said means comprises a conduit for providing lubricating fluid supplied at or near a non-working face and/or a non-abutting portion of the working face of at least one of the pair of splines, to the abutting working face portions. In one form, the conduit extends from the non-abutting portion of the working face to the abutting working face portions.

In one form the conduit extends from a non-working face to the abutting working face portions.

In one form, the conduit extends between the side faces of the spline.

In one form, the conduit passes through the spline. In an alternative, the conduit passes over the spline. In a further alternative, the conduit passes beneath the spline.

In one form, the conduit passes through the spline and breaks through a tip of the spline. In an alternative, the conduit does not break through the tip of the spline.

In one form, the lubrication means comprises a plurality of conduits at spaced apart locations along the length of the spline. In one form, a first of the pair of splines is a driving spline, and the second is a driven spline, and the or each conduit extends between the side faces of the driving spline. In an alternative, the or each conduit extends between the side faces of the driven spline. In one form, conduits extend between the side faces of each of the pair of splines.

In a further aspect the invention may be said to reside in a percussive down hole hammer comprising a splined drive sub comprising driving splines abutting driven splines on a drill bit, and where at least one of the driving and/or driven splines comprise a conduit extending between a pair of side faces thereof so that a lubricating fluid can be passed to abutting side faces of the driving and driven splines.

In one form, there is a channel defined between adjacent pairs of abutting splines. In one form, lubricating fluid can be supplied to the or each conduit via this channel.

In one form, the lubricating fluid comprises a lubricant entrained in an air stream.

In yet a further aspect the invention may be said to reside in a drive-sub for a percussive down hole hammer comprising an annular body and an inwardly directed spline comprising a pair of side faces, either of which may serve as a working face, and a conduit extending between the side faces of the spline to provide lubricating fluid to the working face.

In yet a further aspect the invention may be said to reside in a drill bit for a percussive down hole hammer comprising a shank from which there depends at least one outwardly directed spline comprising a pair of side faces, and a conduit for providing lubricating fluid supplied at or near a non- working face and/or a non-abutting portion of a working face of the or each spline, to an abutting working face portion thereof. In one form, the or each conduit is a slot.

In one form, the or each slot extends transversely across the spline.

In one form, the slot is deeper than the overlap between the abutting surfaces (ie. the working depth) of the driving splines and driven splines.

In yet a further aspect the invention may be said to reside in a method for supplying lubricating fluid to a percussive down hole hammer comprised of a drive sub comprising driving splines abutting driven splines on a drill bit, and a channel defined between adjacent pairs of abutting splines, and where at least one of the driving and/or driven splines comprise a conduit extending between a pair of side faces thereof, the method comprising the step of supplying a lubricating fluid though the or each channel to the or each conduit and via the or each conduit to abutting side faces of the driving and driven splines.

In yet a further aspect the invention may be said to reside in a lubrication means for a pair of splines, the pair of splines comprising a male spline and a female spline, the male spline comprising a pair of side faces separated by a top land, and the female spline comprising a pair of side faces separated by a bottom land, where at least one side face of each of the male and female splines will serve as a working face so that the pair of splines have abutting working faces, and where there is a top clearance above the top land of the male spline, and a bottom clearance below a top land of the female spline, and wherein said lubrication means comprises a conduit providing a fluid passageway between the top clearance and the bottom clearance to provide lubricating fluid to the abutting working faces.

In one form, the conduit is a channel formed in the working face of the spline. In an alternative, the conduit passes through the spline.

In one form, the conduit is defined by the female spline. In an alternative, the conduit is defined by the male spline. In a further alternative, the conduit is defined by the male and female splines in combination. In one form, the conduit extends along the working face of the spline. In an alternative, a conduit extends along both faces of the spline.

In one form, the lubrication means comprises a plurality of conduits at spaced apart locations along the length of the spline.

In one form, the female spline is wider than the male spline creating a backlash space between a pair of non-working side faces.

In one form, this backlash space provides a channel between adjacent pairs of abutting splines, via which channel lubricating fluid can be supplied to the or each conduit and the working faces in turn.

In one form, the female spline is a driving spline and the male spline is a driven spline, and the or each conduit is formed in the driving spline. A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications and equivalents. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention.

The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of this invention it will now be described with respect to one or more exemplary embodiments, which shall be described herein with the assistance of drawings wherein:

Figure 1 is a perspective view of a drive-sub for a percussive down hole hammer;

Figure 2 is a cross-sectional view through the drive-sub illustrated in Figure 1 , this being taken lengthwise along A-A;

Figures 3 through 5 are cross-sectional views, taken lengthwise, through the drive-sub of Figures 1 and 2, and a drill bit;

Figure 6 is a cross-sectional view, taken crosswise, through the drive-sub and drill bit of Figures 3 through 5; Figure 7 is a partial cross-sectional view, taken crosswise, through a drive-sub and drill bit according to a further embodiment; and

Figure 8 is a perspective view of the drive-sub of Figure 7. In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to Figure 1 , where there is illustrated drive-sub 10 for a pneumatically operated percussive down hole hammer that combines the hammer (or hitting) action with the turning action of rotary drilling. This drive sub 10 comprises an annular sleeve 12 with an array of spaced apart, inwardly directed driving splines 14. Referring now to Figures 3 through 5, where there is further illustrated a drill bit 20 (without carbide inserts in the face of the drill bit) comprising a shank 22 and a drill bit head 23. The shank 22 has a number of outwardly directed driven splines 24, which are so spaced and numbered as to form, with the driving splines 14, pairs of splines having abutting working faces when the bit 20 is inserted into the drive sub 10 (see Figure 6). A channel 25 is defined between adjacent pairs of abutting splines 14 and 24.

In use, the driving splines 14 act against the driven splines 24 to drive rotation of the drill bit 20 while permitting the drill bit 20 to move longitudinally (under the effect of the hammer), with respect to the drive-sub 10.

Each driving 14 and driven spline 24 comprises a pair of side faces 14a and 14b in one case, and 24a and 24b in the other, either of which may serve as a working face depending on the direction of rotation of the drive sub 10.

Down hole hammers of this type rely on a supply of clean lubricated air (ie. oil entrained in air, or an oil mist) to operate reliably. This lubricated air is supplied via the channels 25. In practice though, it has been found that it is friction between the driving 14 and driven splines 24 that causes changes in the metallurgy of the bit's 10 working faces which results in bit 10 failure.

In the present invention then, the driving splines 14 comprise lubrication means for each pair of driving 14 and driven splines 24 having abutting working faces, said lubrication means comprising, in one embodiment, a conduit 50 extending through the driving spline 14 from face 14a to face 14b to provide lubricating fluid from the channel 25 to each of the abutting working faces.

In this illustrative embodiment, each conduit 50 is a slot machined into the spline 14, which is deeper than the overlap between the abutting working faces (ie. the working depth) of the driving splines 14 and driven splines 24, and which breaks through a tip of the spline so as to divide the spline 14 into segments.

Moreover, there is a plurality or array of these slots 50 at spaced apart locations along the length of the driving spline 14. While the slots 50 could be machined into either the driven 24 or driving splines 14, or both, its is preferred that they are machined ^' into the driving splines 14 of the drive sub 10 only, as this component simply rotates, and is not subject to the reciprocation or impact stresses of the bit 20. Since the bit 20 is already prone to fatigue stress, the addition of stress raising features within its driven splines 24 is undesirable.

A pumping effect is created through the down hole hammer by the pulsating pressures produced by the cyclic exhausting of the hammer's (not shown) top and bottom chambers, which drive its

reciprocation. This effect will thereby assist delivery of the oil mist to the surfaces of the slot 50.

Segmenting the driving splines 14 with conduits 50 improves the ratio of perimeter to surface area of the working face, thereby reducing the mean distance from the perimeter of the working face (or contact) area, where oil is present, to the centroid of the area, thereby enabling better penetration of the oil to the centroid of the working face of each discreet spline segment.

The number and size of slots 50 must be carefully selected because if the slots are too large and/or too numerous this can reduce the contact area of the working faces (ie. the working face portions) to such an extent as to render the segmented spline or splines prone to failure. Conversely, if the slots 50 are too few slot and/or too small, insufficient lubrication of the working faces may result, similarly resulting in failure.

Since the slot 50 volume comprises a cavity through which the main flow streamlines of the oil entraining air flowing in channel 25 do not pass, there are no significant shear forces present that would otherwise tend to strip the oil from the major spline surfaces 14a and 14b in one case, and 24a and 24b in the other. This enables a thicker boundary layer to be present and results in higher deposition of oil where required. The relative motion of the driving 14 and driven splines 24 will promote a smearing action, whereby the lubricant is transported to where it is required between the splines 14 and 24.

The movement of air in and out of the slots 50 will also improve the ventilation and cooling of the splines 14 and 24 in general, as well as the contact areas and thereby reduce the peak temperatures arising from the friction.

By machining the slots 50 to a depth greater than the width of the overlap between the driving and driven splines (i.e. the working face portions) one can create a conduit from one side of the driving spline 14 to the other, thereby enabling the passage of air (and oil mist) through the slot 50 should conducive pressure gradients exist, this providing an additional transport mechanism to that of pumping. Careful selection of the shape of the areas available for flow along either side of the splines enables one to bias flow to either side and thereby create a static pressure differential. This will produce a net flow through the slot 50 and thereby provide more lubricant to the splines 14 and 24. Formation of slots 50 as described with high velocity air and oil travelling tangentially to the opening of the slot 50 is likely, providing the slot 50 is above a critical value in width, to produce a trapped vortex that also may assist in the entrainment of oil in addition to that of the pumping action and the static pressure differential produced by the aforementioned means. Referring now to Figures 7 and 8, where there is illustrated a male spline 24 (the driven spline in this case) and a female spline 14 (the driving spline in this case), the male spline 24 comprising a pair of side faces 24a separated by a top land 24b, and the female spline 14 comprising a pair of side faces 14a separated by a bottom land 14b, where at least one side face of each of the male and female splines will serve as a working face so that the pair of splines have abutting working faces. There is a top clearance 100 above the top land 24b of the male spline 24, and a bottom clearance 1 10 below a top land of the female spline 14, and wherein said lubrication means comprises a conduit 120 providing a fluid passageway between the top clearance 100 and the bottom clearance 120 to provide lubricating fluid to the abutting working faces. The conduit 120 is a channel formed in the working face of the female (or driven) spline 24, and there is a plurality of conduits 120 at spaced apart locations along the length of the spline 24. The female spline 14 is wider than the male spline 24 creating a backlash space 130 between a pair of non- working side faces. This backlash space 130 provides a channel between adjacent pairs of abutting splines, via which channel 130 lubricating fluid can be supplied to the or each conduit 120 and the working faces in turn, as discussed above.

In conclusion, it can be seen that the above described lubrication means promotes and improves the delivery of lubricant to abutting working faces of each pair of splines, thereby reducing the friction between the driving and driven splines which causes changes in the metallurgy of the bit surface that lead to failure and shankage.

Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that, various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope.