TECHNICAL AREA

The present invention concerns a fluid-driven down-the-hole drill comprising a housing, a drill bit mounted in a driver chuck in a manner that does not allow it to rotate, a hammer piston arranged to impact on a neck of the drill bit and a fluid-driven vane motor arranged at the housing for rotation of the drill bit.

BACKGROUND

Fluid-driven down-the-hole drills of this type are often used with drill rods that are joined together. The fluid that drives the impacts and the rotation is led through the rods. Another manner to lead the driving fluid is through what is known as "coiled tubing", a flexible drill tubing that is unreeled from a roll. The advantage of using flexible tubing is that the direction of the drilling can be controlled, and that the drilling proceeds more rapidly, due to the fact that the tube does not require joining. The disadvantage of this type of fluid-driven down-the-hole drill is that the fluid is led first to the part that is closest to the end of the drill rod, such as a motor that drives the rotation. The pressure and flow that are not used for rotation are led onwards to the second part, such as the hammer. This means that the part that has access only to the excess flow is difficult to monitor, since the pressure can vary, depending on how much pressure is used by the first part. This means that the rotation motor will stop if the drill bit becomes stuck, whereby no flow will arrive at the hammer.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide in a simple manner, for fluid-driven down- the-hole drills of the type that has a separate rotation motor and a hammer, both parts access to full fluid pressure and fluid flow. A second purpose is to achieve a fluid-driven down-the-hole drill that is easier to control during guided drilling.

These purposes are achieved through the rotation motor and the hammer being connected in parallel to the flow. The invention is defined by the attached patent claims. DESCRIPTION OF DRAWINGS

Figure 1 shows a summary of a down-the-hole drill with impact mechanism and rotation motor,

Figure 2 shows a rotation motor in a cut-through view. DESCRIPTION OF EMBODIMENTS

The fluid-driven down-the-hole drill 1 shown in Figure 1 has a machine housing 2 with a conventional impact mechanism or impact hammer 3. Thus, during drilling, the complete machine housing is introduced into a borehole in the rock with the impact hammer directed towards the bottom of the borehole and the drill string extending from the borehole connected to a source, not shown in the drawings, of a fluid under pressure through a connection A.

Even if the present embodiment will be described based on a liquid-driven impact hammer, it should be realised that the arrangement according to the invention is not limited to use with hammers of this type, but can be arranged for an impact hammer that is driven by any suitable pressurised medium at all, such as air or what is known as "mud". The machine housing 2 comprises a tubular machine pipe 4, and a drill bit 6 protrudes into the end of the machine pipe by its neck 7. An impact mechanism 5 with a hammer piston 8 that demonstrates a piston surface Y is mounted in the machine pipe 4 and is arranged to impact in an axially displaceable manner onto the neck 7 of the drill bit 6. The hammer piston 8 is connected to a fluid flow that alternately fills and empties through a valve V one or several pressure chambers 9, 9a for fluid under pressure that impacts the piston 8 onto the neck 7 of the drill bit 6 through the piston surface Y. The valve may comprise a slide valve, but may comprise also other types of valve. When the hammer piston 8 has completed its impact, the pressure chamber 9b is placed under low pressure, whereby the hammer piston is caused to carry out its return motion.

The neck H of the drill bit 6 has a sp lined connection 10 with a drill bit chuck 1 1, which gives a guided reciprocating motion to the drill bit as shown by the arrow in Figure 1. The drill bit chuck 11 is fixed screwed, fixed pressed or fixed attached in another manner at the machine pipe 4. The neck 7 of the drill bit 6 is mounted in the drill bit chuck 11 after which a stop ring 13 is mounted onto the neck 7 of the drill bit 6 in order to prevent the drill bit 6 being able to fall out from the chuck 11. The drill bit chuck 11 is subsequently mounted at the end 4a of the machine pipe 4. The drill bit 6 may, in another embodiment, be equipped with only one slot 14 to guide the reciprocating motion.

The second end 4b of the machine housing is arranged with a rotation motor 15 according to Figure 2. The rotation motor 15 comprises a generally known vane motor of the type that comprises a housing H with radially displaceable vanes 16 arranged on a rotor shaft 17 surrounded by a pressure chamber 18. It is an advantage that the pressure chamber be formed by the inner surface of the housing H and the jacket surface of the rotor shaft 17. The rotation axis comprises a central passage 21 to lead the flow to the impact hammer 3. The pressure chamber 18 is so designed that the volume increases at the start of the rotation, and subsequently decreases at the end of the rotation. Due to the fact that the vanes 16 are radially displaceable, the vanes 16 follow the form of the pressure chamber 18 and obtain in this way an area that increases, and subsequently obtain an area that decreases at the end of the rotation. When the fluid under pressure is led into the pressure chamber 18, it presses the vane 16 in front of it, whereby the rotation is achieved. During the rotation, the drill bit 6 is caused to rotate in that it accompanies the rotation of the vane motor 15.

The rotation motor 15 mounted at the drill string in a manner that allows it to rotate in such a manner that the drill string remains stationary, i.e. it does not rotate, while the hammer 3 is mounted at the rotation motor 15 in a manner that does not allow it to rotate. This means that what is known as a "coil" can be used to lead fluid to the machine housing 2, as shown in Figure 2, whereby the hammer 3 and the rotation motor 15 rotate when fluid is led through the coil or drill string to the machine housing 2.

The pressurised fluid is led into the machine housing 2 through the drill rod or drill string through a connection A at the end 4b of the machine pipe at which the rotation motor 15 is placed. When the fluid enters the machine housing 2 it arrives initially at a flow distributor 19. The flow distributor 19 leads the flow from the passage of the drill string to flow pathways 20 integral to the body of the connection A.

The flow pathways 20 in the body of the connection lead the flow of fluid not only to the pressure chamber 18 of the rotation motor 15 but also to the central passage 21 of the motor, which passage connects the flow with the pressure chamber 9 of the hammer 3.

When the flow from the drill string arrives at the rotation motor 15, the motor starts to rotate, and takes with it the machine housing in the rotation. The flow at the same time is in constant connection with the impact hammer 3 through the central passage 21. Due to the arrangement with a flow distributor 19 and the connection between the rotation motor 15 and the hammer 3, both the hammer 3 and the rotation motor 15 obtain access to full pressure. The pressure across the hammer 3 can in this way be monitored and controlled in an advantageous manner, by adapting the flow with which the fluid is led through the drill string.

If the resistance with which the drill bit 6 comes into contact with the rock at the bottom of the borehole becomes too low, there is a risk that the rotation motor 15 will start to rotate too rapidly. In order to avoid this, the inlet into the machine housing 2 can be arranged with a flow- regulation valve 22. The valve 22 is adjusted before the drilling operation to the maximum flow that the current drilling operation is intended to use. If the resistance at the drill bit 6 becomes too low, the rotation motor 15 is thus prevented from rotating at a speed that is higher than the speed that the flow allows. The flow valve 22 may be so designed, in another embodiment, that the flow limitation can be regulated during ongoing drilling.

When the pressurised fluid in the pressure chambers 9, 18 has caused the motor 15 to rotate and the hammer 3 to impact onto the drill bit 6, the flow is led onwards to outlets 23, 24 that open outside the machine pipe 4. The motor 15 and the hammer 3 have separate outlets, the outlet 23 of the hammer farthest into the borehole through a passage through the neck of the drill bit and a passage K that extends through the hammer piston, and the outlet 24 of the rotation motor closer to the opening of the hole. This gives the advantage that drilling cuttings are displaced away from the region of the drill bit 6 efficiently. While the return flow with drilling cuttings is being displaced through the borehole towards the opening of the borehole, the flow decreases. When the return flow reaches the outlet of the rotation motor 15, the outlet fluid is given an addition of both flow and pressure, whereby the borehole is cleaned in an efficient manner. A passage, not shown in the drawings, leads a part of the return flow through the drill bit, and opens out into the centre of the drill bit 6 in order to rinse the drill bit 6 clean.

The present invention is not limited to what has been described above: it can be changed and modified in several different ways within the scope of the innovative concept defined by the attached patent claims.