Patent Description:
Conventional down-the-hole hammers and fluid-operated percussion drill tools typically comprise an external cylinder or outer wear sleeve, within which is mounted an inner cylinder which in turn engages with a backhead assembly. A sliding reciprocating piston co-operates with the inner cylinder and backhead assembly, so that when pressure fluid is supplied through the backhead assembly, the piston acts with a percussive effect on a drill bit retained within a drive chuck on the outer wear sleeve.

The drill bit is typically formed with an axially extending shank. Axially extending splines on the shank are slideably engageable with complementary splines formed internally on the drive chuck to transmit rotational drive from the drive chuck to the bit shank. Bit retaining means, such as a bit retaining ring, engages with a shoulder at an upper end of the bit shank to retain the bit in the drill bit assembly.

For large drill bits, such as those with diameters of the order of <NUM>, the combined weight of the bit shank and bit head can be in excess of <NUM>. Such large bits are expensive to produce and their weight can lead to lower speed and efficiency of drilling. One way to reduce the weight of the bit is to reduce the length of the bit shank. However, reducing the length of the bit shank in such conventional arrangements is difficult because the length of the shank is related to the length of the chuck, which must be of a sufficient length to include a screw thread portion at an upper end thereof, for engagement with the wear sleeve, and sufficient splined length to transmit rotational drive effectively.

It is therefore desirable to provide a drive assembly for drill bits, particularly large diameter drill bits, that allows the bit shank to be reduced in length or eliminated.

United States Patent Application Publication No <CIT> relates to down-the-hole drill drive coupling.

According to an aspect of the present invention, there is provided a drill bit assembly for fluid-operated percussion drill tools comprising:.

An advantage of this arrangement is that, because the engagement means are provided at the head portion of the bit, the length of the bit may be reduced, thereby reducing the overall weight of the bit, enabling faster and more efficient drilling. For example, for a <NUM> diameter drill bit, the weight may be reduced to about <NUM>. Furthermore, because the drive ring is provided as a plurality of drive-dog segments that can be assembled around the bit, the bit retaining means may be provided by the drive dog segments themselves, thereby obviating the need for a separate bit retaining ring.

The complementary engagement means, for engagement with the engagement means on the head portion of the bit, may be provided at a forward end of the drive ring. The complementary engagement means, for engagement with the engagement means on the head portion of the bit, may be provided on at least two of the drive dog segments. These may be the same two drive dog segments on which the bit retaining means are provided, or two different segments.

The bit retaining portion of the percussion bit may comprise a retaining shoulder. The bit retaining means may comprise a shoulder formed internally of the drive ring for engagement with the bit retaining portion of the percussion bit to retain the bit in the assembly. An advantage of this arrangement is that a separate bit retaining ring is not required. The bit retaining means, such as the shoulder, may be integrally formed with the drive ring. A shoulder portion may be formed on two or more of the drive dog segments. In a preferred embodiment, a shoulder portion is formed on each of the drive dog segments, such that when the drive ring is assembled in the assembly, a continuous shoulder is formed internally of the drive ring. Alternatively, the shoulder portion may be formed on only some of the drive dog segments, so that the shoulder is discontinuous. Preferably, the shoulder portions are positioned around the bit such that they engage the retaining shoulder of the bit in a balanced fashion.

In an embodiment, the engagement means on the head portion comprises a plurality of recesses and the complementary engagement means on the drive ring comprises a corresponding plurality of protrusions at a forward end thereof, whereby each protrusion is received within a corresponding recess to transmit rotational drive from the drive ring to the percussion bit. The protrusions may be provided in a radially spaced-apart arrangement at a forward end of the drive ring. Similarly, the recesses may be provided in a radially spaced-apart arrangement in a rearwardly-directed face of the head portion of the bit. Because the protrusions are formed at the forward end of the drive ring, and the recesses are formed on the head portion of the bit, the bit is driven as close to the cutting face as possible, thereby allowing the bit shank to be shortened or eliminated.

A protrusion may be provided on at least two of the drive dog segments. Preferably, each drive dog segment comprises one of the plurality of protrusions. Each drive dog segment may also comprise connection means for connecting the drive dog segment to a drive means of the fluid-operated percussion drill tool. Preferably, the protrusions are positioned around the bit such that they engage the recesses on the bit in a balanced fashion.

In one embodiment of the invention, the bit retaining means comprises a shoulder formed on at least two of the protrusions on the drive ring and the bit retaining portion of the percussion bit comprises a retaining shoulder formed at an opening of the corresponding recesses in the head portion of the bit. Ideally, the shoulder is formed around three sides of each of the at least two protrusions and the retaining shoulder is formed around three sides of the corresponding recesses. However, the shoulder may be formed on only one side of the protrusions and the retaining shoulder formed on a corresponding side of the recesses.

In one embodiment of the invention, the head portion of the bit comprises a main body and a plurality of bit inserts engaged therewith, wherein the engagement means is provided by the bit inserts. Preferably, the bit inserts are slidably engageable with the main body of the head portion of the bit. In other embodiments, the bit inserts may be fastened to the bit using suitable fasteners, such as bolts. The bit inserts may be provided in a radially spaced-apart arrangement at a forward end of the main body of the head portion of the percussion bit.

The engagement means on the head portion may comprise a recess provided in a rearwardly-directed face of at least two of the plurality of bit inserts and the complementary engagement means on the drive ring may comprise a corresponding plurality of protrusions at a forward end thereof, whereby each protrusion is received within a corresponding recess to transmit rotational drive from the drive ring to the percussion bit.

An advantage of this arrangement is that the inserts may be replaced as they become worn, multiple times during the lifetime of the bit, without requiring replacement of the entire bit. This is particularly advantageous for large-diameter drill bits.

In one embodiment, a recess is provided in a rearwardly-directed face of at least two of the plurality of bit inserts and a corresponding plurality of protrusions is provided at a forward end of the drive ring, wherein each of the bit inserts, recesses and protrusions is shaped such that, when the insert is engaged with the main body of the head portion of the bit, the insert is rotatable relative to the main body of the head portion of the bit. For example, at least one of the inserts, as well as the recess provided therein and the corresponding protrusion, may be substantially cylindrical in shape.

An advantage of this arrangement is that, during operation of the tool, the inserts will rotate due to rotation of the tool, thereby distributing wear over the entire surface of each insert, so that the lifetime of the inserts is increased.

According to another aspect of the invention, there is provided a down-the-hole hammer comprising an external cylindrical outer wear sleeve, a sliding piston mounted for reciprocating movement within the outer wear sleeve to strike a percussion bit of a drill bit assembly located at the forward end of the outer wear sleeve wherein the drill bit assembly is an assembly as described above.

Referring to <FIG> of the drawings, there is illustrated a drill bit assembly <NUM> of a fluid-operated percussion drill tool according to a first embodiment of the present invention. The assembly comprises a percussion bit <NUM> having a head portion <NUM> and a bit retaining portion <NUM>. The head portion <NUM> of the bit assembly is provided with tungsten carbide buttons <NUM>, in a well-known manner. The bit retaining portion <NUM> of the percussion bit comprises a retaining shoulder <NUM>.

The assembly further comprises a drive ring <NUM> for transmission of rotational drive to the percussion bit. As shown in <FIG>, in this embodiment, the drive ring <NUM> comprises a plurality of separable drive dog segments <NUM> which together form an annular drive ring. The drive ring <NUM> is bolted via holes <NUM> in each segment <NUM> to an outer wear sleeve <NUM> of the percussion drill tool to enable rotational torque to be transmitted from the wear sleeve through the drive ring <NUM> to the bit <NUM>. Each of the drive dog segments is formed with an internal shoulder portion <NUM> which, when the drive ring is assembled, together form a continuous shoulder that engages with the retaining shoulder <NUM> of the percussion bit to retain the bit in the assembly. In alternate embodiments, the shoulder portions <NUM> may be formed only on some of the drive dog segments, which may be positioned around the bit such that they engage the retaining shoulder <NUM> in a balanced fashion.

The head portion <NUM> of the bit comprises a main body <NUM> and a plurality of bit inserts <NUM> slidably engaged therewith. The bit inserts <NUM> are retained in the main body <NUM> by way of lips <NUM> on the inserts, which engage with complementary shoulders <NUM> on the main body <NUM>. As best shown in <FIG>, the bit inserts <NUM> are provided in a radially spaced-apart arrangement at a forward end of the main body <NUM> of the head portion <NUM> of the percussion bit <NUM>. Together, a central portion of the main body <NUM> and the bit inserts <NUM> make up a cutting face of the bit <NUM>.

As shown in <FIG>, a recess <NUM> is provided in a rearwardly-directed face <NUM> of each of the plurality of bit inserts <NUM>. The drive ring <NUM> is provided with a corresponding plurality of protrusions <NUM> at a forward end thereof. Each drive dog segment <NUM> comprises one of the plurality of protrusions. When the assembly is assembled, each protrusion <NUM> is received within a corresponding recess <NUM> to transmit rotational drive from the drive ring to the percussion bit.

To assemble the drill bit assembly of the first embodiment, the drill bit <NUM> is positioned relative to the wear sleeve <NUM> in the drop-out position as shown in <FIG> and <FIG>. A single drive dog segment <NUM> and a single bit insert <NUM> are assembled together and slid into the main body of the head portion <NUM> of the bit, such that a lip <NUM> of the insert engages with a shoulder <NUM> of the main body <NUM> and shoulder portion <NUM> on the drive dog segment engages with retaining shoulder <NUM> on the bit. The drive dog segment <NUM> is then bolted to the wear sleeve <NUM> via holes <NUM> which can be accessed externally as shown in <FIG>. An alternate embodiment is shown in <FIG>, in which large bolts <NUM> are screwed in from the top of the wear sleeve down into the drive dogs to retain the drive dogs in the assembly.

Each pair of drive dog segment and bit insert is added in the same way. Once all of the drive dog segments have been added, the drive dog segments form a continuous annular drive ring <NUM>. The drive ring is retained in the assembly by way of the bolts and the drive ring in turn retains the percussion bit <NUM> in the assembly. The inserts are engaged with the main body of the bit by way of lips <NUM> and shoulders <NUM>. Rotational drive is transmitted from the drive ring <NUM> to the bit <NUM> by engagement of the protrusions <NUM> with the recesses <NUM> in the bit inserts.

A drill bit assembly according to an example useful for understanding the invention is shown in <FIG>. This example differs from the embodiment shown in <FIG> in that the drive ring <NUM> is formed as a single piece and a bit retaining ring <NUM> is provided between the outer wear sleeve <NUM> and a shoulder <NUM> formed internally of the drive ring <NUM> to retain the bit <NUM> in the assembly. The bit retaining ring is provided as a plurality of part-annular portions, to allow it to be inserted into the assembly. To assemble the assembly of <FIG>, the inserts <NUM> are first slideably engaged with the main body <NUM> of the bit. The drive ring is then set on top of the bit and the part annular-portions of the bit retaining ring <NUM> are inserted between the bit and the drive ring, such that the bit retaining ring <NUM> sits on shoulder <NUM> of the drive ring. Similar to the embodiment shown in <FIG>, large bolts <NUM> are screwed in from the top of the wear sleeve down into the drive ring to retain the drive ring in the assembly. The bit retaining ring is retained in the assembly between a lower end <NUM> of the wear sleeve and shoulder <NUM> of the drive ring. In an alternate example, in place of the bolts <NUM>, the wear sleeve and the drive ring may be clamped together temporarily, and the bit allowed to drop out so that the drive ring may be bolted in from a forward end thereof, as in <FIG>.

A drill bit assembly according to another example useful for understanding the invention is shown in <FIG>. In this example, an upper part <NUM> of the single-piece drive ring <NUM> is internally screw threaded. An external screw-thread <NUM> is provided on a lower portion of the wear sleeve <NUM>. The drive ring <NUM> is screwed onto the lower end of the wear sleeve so that the retaining ring <NUM> is held in place between shoulder <NUM> on the drive ring <NUM> and a lower end <NUM> of the wear sleeve. The screw-threaded engagement of the drive ring <NUM> with the wear sleeve enables rotational torque to be transmitted from the wear sleeve through the drive ring to the bit <NUM>.

A drill bit assembly according to another example useful for understanding the invention is shown in <FIG>. In this example, an upper part <NUM> of the single-piece drive ring <NUM> is provided with an external screw thread <NUM>. An internal screw-thread <NUM> is provided on a lower portion of the wear sleeve <NUM>. The drive ring <NUM> is screwed into the lower end of the wear sleeve so that the retaining ring <NUM> is held in place between shoulder <NUM> on the wear sleeve <NUM> and an upper end <NUM> of the drive ring. The screw-threaded engagement of the drive ring <NUM> with the wear sleeve enables rotational torque to be transmitted from the wear sleeve through the drive ring to the bit <NUM>.

A drill bit assembly according to a third embodiment of the invention is shown in <FIG>. As shown in <FIG> and <FIG>, the percussion bit <NUM> is generally cylindrical and is formed with a bit head portion <NUM> at a forward end thereof and a bit retaining portion <NUM> at a rear end thereof. The bit <NUM> is formed as a single piece having a plurality of recesses <NUM> provided in a radially spaced-apart arrangement at a rear end of the bit. Each recess has an opening <NUM> in a rear face of the bit <NUM> and an opening <NUM> in a curved face of the bit <NUM>. A retaining shoulder or lip <NUM> is formed at the opening <NUM> of each recess in the rear face of the bit, and the shoulders <NUM> form the bit retaining portion <NUM> of the bit <NUM>. The shoulder <NUM> associated with each recess extends towards the centre of that recess. In the embodiment shown, each shoulder <NUM> extends around three sides of each recess. In alternate embodiments, the shoulder may be provided only at one side of the recess, such as the innermost side, opposite the opening <NUM>.

The assembly further comprises a drive ring <NUM> for transmission of rotational drive from to the percussion bit. As shown in <FIG>, the drive ring <NUM> comprises a plurality of part-annular drive dog segments <NUM> which together form an annular drive ring. The drive ring <NUM> is bolted via holes <NUM> in each segment <NUM> to an outer wear sleeve <NUM> of the percussion drill tool to enable rotational torque to be transmitted from the wear sleeve through the drive ring <NUM> to the bit <NUM>.

The drive ring <NUM> is provided with a plurality of protrusions <NUM> at a forward end thereof, the protrusions corresponding in number and dimension to the recesses <NUM> in the percussion bit. Each drive dog segment <NUM> comprises one of the plurality of protrusions. When the assembly is assembled, each protrusion <NUM> is received within a corresponding recess <NUM> to transmit rotational drive from the drive ring to the percussion bit. Each protrusion <NUM> is formed with a shoulder <NUM> at a free end thereof. In the embodiment shown, the shoulder <NUM> extends around three sides of the protrusion <NUM>. In alternate embodiments, the shoulder <NUM> may be provided only at one side of the protrusion, such as the innermost side of the protrusion. As shown in <FIG>, when the drive dog segments are assembled with the bit <NUM>, the shoulders <NUM> engage with the retaining shoulders <NUM> of the percussion bit to retain the bit in the assembly.

To assemble the drill bit assembly according to the third embodiment of the invention, the drill bit <NUM> is positioned relative to the wear sleeve <NUM> in the drop-out position. A single drive dog segment <NUM> is slid into one of the recesses <NUM> in the bit, such that shoulder <NUM> on the drive dog segment engages with retaining shoulder <NUM> on the bit. The drive dog segment <NUM> is then bolted to the wear sleeve <NUM> via holes <NUM> which can be accessed externally. Alternatively, large bolts are screwed in from the top of the wear sleeve down into the drive dogs to retain the drive dogs in the assembly.

Each drive dog segment is added in the same way. Once all of the drive dog segments have been added, the drive dog segments form a continuous annular drive ring <NUM>. The drive ring is retained in the assembly by way of the bolts and the drive ring in turn retains the percussion bit <NUM> in the assembly by engagement of shoulders <NUM> with shoulders <NUM> on the bit. Rotational drive is transmitted from the drive ring <NUM> to the bit <NUM> by engagement of the protrusions <NUM> with the recesses <NUM> in the bit.

A drill bit assembly according to another example useful for understanding the invention is shown in <FIG> and <FIG>. As shown in these figures, the percussion bit <NUM> is formed with a bit head portion <NUM> at a forward end thereof and a bit retaining portion <NUM> at a rear end thereof. The bit retaining portion <NUM> of the percussion bit comprises a retaining shoulder <NUM>. The bit <NUM> is formed as a single piece having a plurality of recesses <NUM> provided in a radially spaced-apart arrangement at a rear end of the bit. Each recess has an opening <NUM> in a rear face of the bit <NUM> and an opening <NUM> in a curved face of the bit <NUM>.

The assembly further comprises a drive ring <NUM> for transmission of rotational drive to the percussion bit. The drive ring <NUM> is provided with plurality of protrusions <NUM> at a forward end thereof, corresponding to the recesses <NUM> in the bit <NUM>. As in the example shown in <FIG>, the drive ring <NUM> is formed as a single piece and a bit retaining ring <NUM> is provided between the outer wear sleeve <NUM> and a shoulder <NUM> formed internally of the drive ring <NUM> to retain the bit <NUM> in the assembly. The bit retaining ring is provided as a plurality of part-annular portions, to allow it to be inserted into the assembly.

To assemble the assembly of <FIG>, the drive ring is set on top of the bit such that each protrusion <NUM> on the drive ring is received in a recess <NUM> formed in the bit and the part annular-portions of the bit retaining ring <NUM> are inserted between the bit and the drive ring, such that the bit retaining ring <NUM> sits on shoulder <NUM> of the drive ring. An upper part <NUM> of the single-piece drive ring <NUM> is internally screw threaded. An external screw-thread <NUM> is provided on a lower portion of the wear sleeve <NUM>. The drive ring <NUM> is screwed onto the lower end of the wear sleeve so that the retaining ring <NUM> is held in place between shoulder <NUM> on the drive ring <NUM> and a lower end <NUM> of the wear sleeve. The screw-threaded engagement of the drive ring <NUM> with the wear sleeve enables rotational torque to be transmitted from the wear sleeve through the drive ring to the bit <NUM>.

Referring to <FIG> of the drawings, there is illustrated a drill bit assembly <NUM> of a fluid-operated percussion drill tool according to a fourth embodiment of the present invention. The assembly comprises a percussion bit <NUM> having a head portion <NUM> and a bit retaining portion <NUM>. The bit retaining portion <NUM> of the percussion bit comprises a retaining shoulder <NUM>.

The assembly further comprises a drive ring <NUM> for transmission of rotational drive to the percussion bit. As shown in <FIG>, in this embodiment, the drive ring <NUM> comprises a plurality of separable drive dog segments <NUM> which together form an annular drive ring.

The drive ring <NUM> is bolted via holes <NUM> in each segment <NUM> to an outer wear sleeve <NUM> of the percussion drill tool to enable rotational torque to be transmitted from the wear sleeve through the drive ring <NUM> to the bit <NUM>. Each of the drive dog segments is formed with an internal shoulder portion <NUM> which, when the drive ring is assembled, together form a continuous shoulder that engages with the retaining shoulder <NUM> of the percussion bit to retain the bit in the assembly. In alternate embodiments, the shoulder portions <NUM> may be formed only on some of the drive dog segments, which may be positioned around the bit such that they engage the retaining shoulder <NUM> in a balanced fashion.

The head portion <NUM> of the bit comprises a main body <NUM> and a plurality of bit inserts <NUM> slidably engaged therewith. In this embodiment, the bit inserts are substantially cylindrical in shape, with a disc-shaped cutting face <NUM> at a forward end. Each bit insert <NUM> is retained in the main body <NUM> by way of a lip <NUM> around the circumference of the insert, which engages with a complementary shoulder <NUM> on the main body <NUM>. As best shown in <FIG> and <FIG>, the bit inserts <NUM> are provided in a radially spaced-apart arrangement at a forward end of the main body <NUM> of the head portion <NUM> of the percussion bit <NUM>. A central portion of the main body <NUM>, together with the bit inserts <NUM>, makes up a cutting face of the bit <NUM>.

As shown in <FIG> and <FIG>, a recess <NUM> is provided in a rearwardly-directed face <NUM> of each of the plurality of bit inserts <NUM>. The drive ring <NUM> is provided with a corresponding plurality of protrusions <NUM> at a forward end thereof. In this embodiment, the protrusions <NUM> are substantially cylindrical in shape and the recesses <NUM> are correspondingly shaped. Each drive dog segment <NUM> comprises one of the plurality of protrusions. When the assembly is assembled, each protrusion <NUM> is received within a corresponding recess <NUM> to transmit rotational drive from the drive ring to the percussion bit.

To assemble the drill bit assembly of the fourth embodiment, the drill bit <NUM> is positioned relative to the wear sleeve <NUM> in the drop-out position as shown in <FIG>. A single drive dog segment <NUM> and a single bit insert <NUM> are assembled together by inserting protrusion <NUM> into recess <NUM> and slid into the main body of the head portion <NUM> of the bit, such that a lip <NUM> of the insert engages with a shoulder <NUM> of the main body <NUM> and shoulder portion <NUM> on the drive dog segment engages with retaining shoulder <NUM> on the bit. The drive dog segment <NUM> is then bolted to the wear sleeve <NUM> via holes <NUM> which can be accessed externally. In an alternate embodiment, large bolts may be are screwed in from the top of the wear sleeve down into the drive dogs to retain the drive dogs in the assembly.

Each pair of drive dog segment and bit insert is added in the same way. Once all of the drive dog segments have been added, the drive dog segments form a continuous annular drive ring <NUM>. The drive ring is retained in the assembly by way of the bolts and the drive ring in turn retains the percussion bit <NUM> in the assembly. The inserts are engaged with the main body of the bit by way of lips <NUM> and shoulders <NUM>. Rotational drive is transmitted from the drive ring <NUM> to the bit <NUM> by engagement of the protrusions <NUM> with the recesses <NUM> in the bit inserts. In this embodiment, the shape of the bit inserts and the protrusions is such that each of the inserts is rotatable relative to the bit head. During operation of the tool, the inserts will rotate due to the rotational torque of the tool. This increases the lifetime of the bit inserts by distributing wear over the whole of the cutting face of each insert as they rotate in the bit head.

The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claim 1:
A drill bit assembly (<NUM>) for fluid-operated percussion drill tools comprising:
a drive ring (<NUM>);
a percussion bit (<NUM>) having a head portion (<NUM>) and a bit retaining portion (<NUM>);
engagement means (<NUM>) on the head portion engageable with complementary engagement means (<NUM>) on the drive ring (<NUM>) whereby rotational drive from the drive ring is transmittable to the percussion bit;
bit retaining means (<NUM>) adapted for engagement with the bit retaining portion of the percussion bit to retain the percussion bit in the drill bit assembly; and
connection means on the drive ring adapted for connecting the drive ring to a drive means of the fluid-operated percussion drill tool;
wherein the drive ring comprises a plurality of separable part-annular drive dog segments (<NUM>), wherein the bit retaining means are provided on at least two of the drive dog segments, and characterised in that each drive dog segment receives a bolt for individually connecting the drive dog segment to the drive means of the fluid-operated percussion drill tool.