Patent Description:
Piston actuated drilling tools, such as rotary percussion tools (RTP) employ the efficient application of compressed air energy in combination with rotary drilling forces to achieve a high rate of penetration and drilling performance.

Known rotary percussion tools contain a retaining system, for example, in the form of a split retaining ring to prevent the mandrel and the bit from disengaging from the remaining components of the percussion tool, such as the casing.

In some percussion tools there is also a guide bushing provided or a foot valve, to co-operate with the piston nose and regulate the flow around it.

The retaining system and the guide bushing have completely different functions, but are often placed in close proximity to one another, this is shown for example in patent applications <CIT> and <CIT>.

<CIT> discloses a fluid operated drilling device and a method for drilling a hole using a fluid operated drilling device. <CIT> discloses a fluid actuated impact drilling tool for use in rotary drilling in a string of drilling pipe. <CIT> discloses a down-the-hole hammer wherein the lift force in maximized.

The problem with this is that to ensure proper assembly and to maintain their position during operation, it is necessary to very tightly and carefully control the tolerances of the parts, which requires complex machining, which adds further costs and time to achieve the required dimensions.

It is an objective of this invention to provide a novel and improved assembly for a piston actuated drilling tool for down the hole drilling.

The objective is achieved by providing a piston actuated drilling tool comprising a housing, a top sub, a piston and a drive sub; the piston having a nose at its forward end that is slidably mounted for reciprocating movement within the housing and which strikes a mandrel located at the forward end of the housing; wherein there is an integrated retaining and bushing system that comprises a retaining ring for preventing the mandrel from detaching from the rest of the tool encasing a bushing for co-operation with the piston nose to stabilise and guide the piston and provide a timing event for the percussion.

The integration of the retaining ring and the bushing means that it is not necessary to maintain such tight tolerances to achieve proper assembly and to maintain the correct positioning of the parts during operation, therefore easing and reducing the cost of the manufacturing process. The integration means that there is no longer the need for complex machining of the housing or the retaining rings. Further, the internal air volume is controlled and so the efficiency of the drilling assembly is improved.

Optionally, the retaining ring is split into at least two parts. This makes it easier to replace the bushing as the retaining ring can just be split apart to remove a worn or damaged bushing and then a new bushing of standard geometry can be inserted.

Preferably, one or more O-rings are used to hold the multiple sections of the retaining ring together. This provides a simple and reliable method of holding the retaining ring together if it has been split into multiple sections. It is important that the retaining ring is securely held together to prevent the leakage of air which would result in a loss of power or misalignment which would result in excessive wear or broken components.

Alternatively, the retaining ring is a one-piece body. If the retaining ring is a one-piece body, it is easier to manufacture.

Preferably, the retainer ring is made of a different material than the bushing. Typically, the retaining ring is made of a stronger material compared to the bushing. Advantageously, this adds structural strength to the integrated retaining and bushing system.

Preferably, the bushing is made a polymer, a glass filled polymer, non-ferrous metal, a heat treated or coated steel. These materials provide a low friction surface, therefore allowing the piston to be able to freely slide in and out of the bushing whilst minimising wear.

Optionally, at a mating surface within the integrated retaining and bushing system, a radially inner surface of the retaining ring and a radially outer surface of the bushing are both cylindrically flat and parallel to one another. Advantageously, this enables ease of construction.

Alternatively, at a mating surface within the integrated retaining and bushing system, a radially inner surface of the retaining ring and a radially outer surface of the bushing each comprise one of at least one notch and at least one protrusion to form a retention lock within the system. Advantageously, the interlocking geometries means that the two parts of the integrated system are securely held together.

Optionally, the top half and the bottom half of the bushing is asymmetrical, so that the same bushing can be inserted into the retaining ring in a first position for normal operation modes and in a second position for altered timing characteristics, wherein the bushing extends further towards the piston nose in the second position compared the first position. Advantageously, the same bushing can be used in either operational position thus making it is easy and convenient to swap between the two modes, without the need to have to have a second different type of bushing available.

<FIG> shows a piston actuated drilling tool <NUM> for downhole drilling that comprises a housing <NUM> (otherwise known as a cylinder or a casing), a top sub <NUM> threadedly coupled the top end of the housing <NUM> and a drive sub <NUM> threadedly mounted to the opposing end (the bottom / drive end) of the housing <NUM>. The tool further comprises an annularly shaped piston <NUM> moveably positioned within the housing <NUM>. The piston <NUM>, which is typically a cylinder although other configurations could be envisaged, optionally includes an air distributor tube <NUM> extending substantially centrally therethrough for providing air flow to drive the piston <NUM> and regulate the timing event. Once the tool <NUM> is assembled, a top pressure fluid chamber <NUM> and a bottom pressure fluid chamber <NUM> are formed within the housing <NUM>. The drive sub <NUM> houses one or more annularly shaped drive lugs <NUM> that are stacked on top of one another and a portion of a mandrel <NUM>. The mandrel <NUM> is a substantially solid component to which a drill bit (not shown), that is provided with a plurality of inserts which are typically made from tungsten carbide, can be attached to. The mandrel <NUM> is axially moveable with respect to both the housing <NUM> and the drive sub <NUM>, a portion of the mandrel <NUM> being inserted and housed within the housing <NUM>. The top sub <NUM> is threadedly connected to a drill string (not shown), which is connected to a rotation motor on a drilling rig at the surface. Rotational torque is then applied through the rotating assembly including housing <NUM>, drive sub <NUM>, drive lugs <NUM>, and mandrel <NUM>. For DTH hammers the drive lugs <NUM> are normally replaced by interlocking splines for the transmission of torque. The drive lugs <NUM> could also be replaced by low friction drive pins to prevent galling.

As the piston <NUM> slidably moves upward towards the top sub <NUM>, the volume of the top pressure fluid chamber <NUM> decreases, while the volume of the bottom pressure fluid chamber <NUM> increases. Conversely, as the piston <NUM> slidably moves downward towards the mandrel <NUM>, the volume in the top pressure fluid chamber <NUM> increases and the volume in the bottom fluid chamber <NUM> decreases. The piston <NUM> is used to deliver a downward force to onto the mandrel <NUM> when the bottom end of the piston <NUM> contacts the mandrel <NUM>. The piston <NUM> is then forced back up and then the cycle continues. <FIG> shows the mandrel in the closed position. <FIG> shows the same drilling tool <NUM> as shown in <FIG> but with the mandrel in the open position and so that the retaining ring <NUM> can be seen retaining mandrel <NUM>. <FIG> shows the same drilling tool <NUM> as shown in <FIG> and <FIG> but with the mandrel <NUM> closed and piston <NUM> positioned on the mandrel <NUM>.

<FIG> shows a perspective view and <FIG> shows an exploded view of an integrated retaining and bushing system <NUM> for an annular bushing <NUM> (otherwise known as an aligner) and a retaining ring <NUM>. The bushing <NUM> is typically made from a polymer, a glass filled polymer, non-ferrous metal, a heat treated or coated steel and is a standard part that is readily available and does not need to be formed to a specific tight tolerance. The bushing <NUM> is encased inside the retaining ring <NUM>, which is also annularly shaped. The retaining ring <NUM> is typically made from stronger material than the bushing <NUM>, for example a ferrous metal.

The integrated retaining and bushing system <NUM> are stacked on top of the drive sub <NUM> and has a dual function.

It should be appreciated that the bushing <NUM> described in the present application performs a similar function as an exhauster used in a RPS system or a foot valve used in a DTH drill or the geometry of a valveless DTH hammer.

Firstly, the retaining ring <NUM> part of the system <NUM> functions to prevent the mandrel <NUM> and the bit (not shown) from disengaging from the remaining components of the piston actuated drilling tool <NUM>, such as the housing <NUM>. This is achieved through engagement cooperation between a radial protrusion <NUM> of the upper end of the mandrel <NUM> and a shoulder <NUM> on the lower end of the retaining ring <NUM>. The mandrel <NUM> slidably engages with the retaining ring <NUM> part of the system <NUM>. When an upward force is placed onto the bottom of the bit, the mandrel <NUM> slidably moves toward the top sub <NUM> such that the top portion of the mandrel <NUM> and the retaining ring <NUM> are not adjacent and/or in contact with one another. Conversely, when an upward force is not placed onto the bottom of the bit, the mandrel <NUM> slidably moves away the top sub <NUM> such that the top portion of the mandrel <NUM> and the retaining ring <NUM> are adjacent and/or in contact with one another.

The retaining ring <NUM> is optionally split as shown in the <FIG>, for example, it could be formed in two half annular parts for ease of assembly, but it could also be split further into more than two parts. If the retaining ring <NUM> is split, an O-ring <NUM> is used as an assembly aid and also provides the benefit of reducing the bypass of air between the retaining ring <NUM> and the housing <NUM>. Alternatively, the split sections of the retaining ring <NUM> could be held together using a different method, such as locking bands or through-bolts.

<FIG> shows that alternatively the retaining ring <NUM> is formed as a one-piece body. If a one piece body retaining ring <NUM> is used it may have an internal catch <NUM> to retain it in place, alternatively a circlip or pin or other suitable retainment method could be used. <FIG> and <FIG> show the perspective view and cross sectional view of the retaining ring <NUM> as a one-piece body respectively. <FIG> shows one possible interlock between the integrated retaining and bushing system <NUM> and the mandrel <NUM> having an internal catch <NUM> when the one piece body retaining ring <NUM> is employed, this is more likely to be used on a DTH hammer wherein a traditional spline system is used. The retaining ring <NUM>, whether split or a one-piece body, is typically made from a ferrous steel.

Secondly, the bushing <NUM>, which is used in place of a foot valve, is arranged to co-operate with a nose <NUM> of the piston <NUM>. A purpose of the bushing <NUM> is to align the top of the mandrel <NUM> with the piston nose <NUM> to help stabilise and guide and provide a timing event for the piston <NUM>. A lower annular volume is formed between the piston <NUM> and the bushing <NUM> in the bottom pressure fluid chamber <NUM>. When the piston <NUM> rises out of the bushing <NUM>, the piston <NUM> exhausts the volume of air. Further, the bushing <NUM> acts as a seal to prevent the lower annular volume of air that pushes the piston <NUM> from escaping. This is important because any loss of air volume would reduce the efficiency of the tool <NUM>. The bushing <NUM> is typically a one-piece body, i.e. not split. Further, the bushing <NUM> can be made from a low friction material such as a polymer, a glass filled or reinforced polymer, non-ferrous metal, a heat treated or coated steel.

Optionally, the mating surfaces between a radially inner surface <NUM> of the retaining ring <NUM> a radially outer surface <NUM> of the bushing <NUM> are both cylindrically flat and parallel to one another. Alternatively (as shown in <FIG>), the mating surfaces between the radially inner surface <NUM> of the retaining ring <NUM> and the radially outer surface <NUM> of the bushing <NUM> each comprise one of at least one notch <NUM> and at least one protrusion <NUM> to form a retention lock within the system <NUM>. The one or more notches <NUM> could be in the retaining ring <NUM> and the one or more protrusions <NUM> could be in the bushing <NUM> as shown or the one or more protrusions <NUM> could be in the retaining ring <NUM> and the one or more notches <NUM> could be in the bushing <NUM> or any other combination so that the mating surface between the radially inner surface <NUM> of the retaining ring <NUM> a radially outer surface <NUM> of the bushing <NUM> forms an interlock. Alternatively, the radially inner surface <NUM> of the retaining ring <NUM> a radially outer surface <NUM> of the bushing <NUM> could have a tapered geometry, a mechanical fastener, be coated with an adhesive, dimensions for a press fit, have a textured surface or have any other suitable interface. Any type of mating surface geometry, i.e. flat and parallel or interlocking or otherwise, can be combined with the retaining ring <NUM> being split or being a one-piece body.

<FIG> show that optionally, the bushing <NUM> could have an asymmetric geometry, wherein there is at least one notch <NUM> or at least one protrusion <NUM> positioned on the radially outer surface <NUM>, such that a top half <NUM> of the bushing <NUM> and a bottom half <NUM> of the bushing <NUM> are asymmetrical. This means that when the bushing <NUM> is inserted in a first position, as shown in <FIG>, the bushing <NUM> does not extend as close to the nose <NUM> of the piston <NUM> as does when the bushing is flipped over and reinserted in a second position, as shown in <FIG> illustrates how the bushing would be installed for use under a first operational mode. <FIG> illustrates how the bushing would be installed for a second, alternative operational mode. When the bushing is installed for the second operational mode the bushing <NUM> extends closer to the nose <NUM> of the piston <NUM>, and thus changes the operational characteristics according the environmental or input variations or restrictions thereof. The distance above a line <NUM> shown on <FIG> illustrates the additional distance that the bushing <NUM> extends towards the nose <NUM> of the piston <NUM> in second operational mode compared to the first operational mode.

Claim 1:
A piston actuated drilling tool (<NUM>) comprising a housing (<NUM>), a top sub (<NUM>), a piston (<NUM>) and a drive sub (<NUM>);
the piston (<NUM>) having a nose (<NUM>) at its forward end that is slidably mounted for reciprocating movement within the housing (<NUM>) and which strikes a mandrel (<NUM>) located at the forward end of the housing (<NUM>);
a retaining ring (<NUM>) for preventing the mandrel (<NUM>) from detaching from the rest of the tool (<NUM>);
a bushing (<NUM>); wherein the purpose of the bushing (<NUM>) is for co-operation with the piston nose (<NUM>) to stabilise and guide the piston (<NUM>) and provide a timing event for the percussion;
wherein the retaining ring (<NUM>) encases the bushing (<NUM>) to form an integrated retaining and bushing system (<NUM>).