DRILL HAMMER AND DEPTH DRILLING METHOD

Description

[0001] The invention relates to a rotary hammer with at least one cylinder in which at least one piston is axially displaceable between an upper and a lower end position, the cylinder having at least one lower fluid supply to which a drive fluid can be cyclically supplied. The invention further relates to a method for deep drilling with a rotary hammer having at least one cylinder in which at least one piston is axially displaceable between an upper and a lower end position, the cylinder having at least one lower fluid supply to which a drive fluid is cyclically supplied. Devices and methods of this type are used for deep drilling, for example, to drill hard rock formations economically. Such deep drilling can be used, for example, in oil or gas production, in geothermal energy, or as exploratory drilling in mining.

[0002] From J.-M. Peng, Q.-L. Yin, G.-L. Li, H. Liu and W. Wang: "The effect of actuator parameters on the critical flow velocity of a fluidic amplifier", Applied Mathematical Modelling 37 (2013) 7741, a rotary hammer is known in which a piston slides in a cylinder. The piston movement is transmitted to the drill bit via a connecting rod or a push rod. A drive fluid, for example, the drilling fluid used to remove the drill cuttings, serves to drive the piston. The drive fluid is introduced alternately from below and from above into the cylinder, thus inducing a corresponding piston movement.

[0003] This well-known rotary hammer has the disadvantage that the seals between the piston and cylinder on the one hand, and between the connecting rod and the cylinder base on the other, are subjected to high stress and therefore have a short service life, especially when an abrasive drilling fluid containing particles is used as the drive fluid. Due to this limited service life, the application of this well-known rotary hammer is restricted to a few special cases and / or certain sections of a deep borehole. Thus, while the well-known rotary hammer allows for high drilling rates in hard rock formations, it requires frequent tool changes during larger drilling operations because its service life is limited.

[0004] EP 2 902 154 A1 discloses a striking mechanism in which a striking piston is slidably guided in a housing; the piston is attached to the cylinder by a spring and is pressurized with compressed air.

[0005] Based on the prior art, the invention aims to provide a drilling tool which has longer service life and / or improved performance.

[0006] The problem is solved according to the invention by a device according to claim 1 and a method according to claim 11.

[0007] Advantageous further developments of the invention can be found in the dependent claims.

[0008] According to one aspect of the invention, a rotary hammer is proposed which has at least one cylinder. The cylinder is formed in a housing, which may be made, for example, of a metal or an alloy. Fluid channels may optionally be formed in the cylinder wall, for example, to transport a drive fluid to the underside of the piston or cylinder facing the drilling tool and / or to transport flushing fluid to the drilling tool. In some embodiments of the invention, the housing may be modularly constructed from several individual parts joined together. The cross-section of the housing may be polygonal or round. As a rule, the housing and the cylinder formed within the housing have a greater length than the cylinder's diameter. The outer diameter of the housing may be between approximately 5 cm and approximately 40 cm. The housing may be manufactured by machining or by forming.

[0009] Within the cylinder, at least one piston is accommodated, which is axially displaceable between an upper and a lower end position. The piston can also be made of a metal or an alloy. In some embodiments of the invention, the piston can have stop elements made of a softer material, for example, a ductile metal, a polymer, or an elastomer, at its end face. In other embodiments of the invention, the piston can be provided with a hard coating at its end face to prevent premature wear. The cylindrical surface of a piston can be provided with a wear-resistant layer and / or a friction-reducing coating, which can reduce piston wear. Similarly, the inside of the cylinder can be provided with an optional friction- and / or wear-reducing coating.Such a coating can be selected from TiN or hard chrome or CrN or an oxide or diamond-like carbon (DLC).

[0010] The cylinder has at least one lower fluid inlet to which a drive fluid can be cyclically supplied. During operation of the drill hammer, the drive fluid is supplied at a pressure sufficient to lift the piston within the cylinder against gravity, causing it to fall back down under its own weight. This generates impact energy that can be transferred to a drill bit, resulting in the fragmentation of the rock in the borehole.

[0011] The cylinder is sealed with an upper and a lower cover, with the piston resting on the inside of the lower cover in its lower end position, or dynamically striking it. In some embodiments of the invention, the lower cover is sealed and, in particular, lacks a passage for a connecting rod or push rod. The impact energy is thus transferred exclusively from the piston to the drilling tool via the lower cover. This eliminates the need for a wear-prone seal for the passage through the lower cover, potentially extending the service life of the rotary hammer, especially when driven by a particulate-containing drive fluid, which can also serve as a flushing fluid, for example. Furthermore, the pressure of the drive fluid can act on the piston over a larger area, thus potentially increasing the efficiency of the rotary hammer.

[0012] In some embodiments of the invention, the rotary hammer can additionally include an upper fluid supply. This allows the piston to be actively moved downwards by applying a drive fluid, thus increasing the impact energy and consequently the drilling progress. In some embodiments of the invention, the drive fluid can be delivered into the cylinder at a higher pressure through the upper fluid supply than through the lower fluid supply. This allows for a gentle lifting of the piston to prepare for the impact and a powerful downward movement with high impact energy. Furthermore, the piston can exert impact energy on the drilling tool even when the bore is horizontal and the piston does not fall due to gravity.

[0013] In some embodiments of the invention, the lower fluid supply can be designed as a first channel that passes through the upper cover, the cylinder wall, and the lower cover. This results in a compact design for the rotary hammer. Integrating the fluid supply within the housing prevents damage to external lines. Due to the modular design, wear parts of the rotary hammer can be replaced quickly and cost-effectively, even on-site.

[0014] In some embodiments of the invention, the upper fluid supply can be designed as a second channel that passes through the upper cover. Integrating the fluid supply within the housing prevents damage to external lines.

[0015] In some embodiments of the invention, the drill hammer further includes a flushing channel through which the drive fluid can be discharged from the cylinder. The drive fluid can then be guided via the flushing channel to the drill bit, so that the resulting drill cuttings can be carried away by the flushing fluid. In some embodiments of the invention, the drive fluid can contain particles that increase the abrasive wear of the rock being drilled and thereby accelerate the drilling progress. The particles can have a diameter of less than approximately 200 µm, or less than approximately 100 µm, or less than approximately 80 µm, or less than approximately 50 µm.

[0016] In some embodiments of the invention, an outer surface of the lower cover can be in contact with a drilling tool. By eliminating connecting rods or push rods, the impact energy generated when the piston strikes the inner surface of the lower cover is transferred directly to the drilling tool via the outer surface of the lower cover. This results in a compact and mechanically simple design of the rotary hammer.

[0017] An annular gap is formed between the entire surface of the piston and the inner wall of the cylinder; that is, the annular gap has a length equal to the length of the piston. The annular gap has a height H, which corresponds to the difference between the inner radius of the cylinder and the outer radius of the piston. The height H of the annular gap is chosen to allow particles within the drive fluid to pass through it. Since a fluid film can thus form between the piston and cylinder, effective lubrication of the piston / cylinder pair is achieved, which reduces wear on the hammer drill and ensures a long service life. Furthermore, the manufacturing of the hammer drill can be simplified because a tightly toleranced fit of the piston / cylinder pair is avoided.

[0018] An annular gap is formed between the piston's outer surface and the cylinder's inner wall, which has a gap height H with H > 2 ⋅ R a , Zylinder + R a , Kolben + 3 ⋅ D Partikel , where R a,cylinder and R a, piston to denote the mean roughness values ​​of the piston's outer surface and the cylinder's inner wall and D particles The maximum particle size in the drive fluid is defined as follows. In some embodiments of the invention, the mean roughness of the piston's outer surface and the cylinder's inner wall can each be between approximately 3 µm and approximately 25 µm. In some embodiments of the invention, the maximum particle size in the drive fluid can be between approximately 50 µm and 200 µm or between approximately 90 µm and approximately 110 µm. The annular gap height, which represents the difference between the cylinder's inner radius and the piston's outer radius, is thus selected such that the flushing fluid particles can pass through the annular gap and / or the fluid film has a sufficient thickness to allow low-wear sliding of the piston / cylinder pair.

[0019] In some embodiments of the invention, an annular gap can be formed between the piston's outer surface and the cylinder's inner wall, with a gap height of approximately 45 µm to approximately 1500 µm. In other embodiments of the invention, the gap height can be selected between approximately 50 µm and approximately 500 µm. In still other embodiments of the invention, the gap height can be between approximately 500 µm and approximately 1000 µm. These gap heights can be produced with minimal manufacturing effort, so the rotary hammer according to the invention can be manufactured more easily than known rotary hammers and remains suitable for long-term use even under harsh operating conditions.

[0020] In some embodiments of the invention, the piston can have a length of approximately 10 cm to approximately 60 cm, or approximately 20 cm to approximately 40 cm, or approximately 40 cm to approximately 60 cm. The piston is thus significantly longer than in known rotary hammers. The length of the piston increases the flow resistance within the annular gap, thereby reducing pressure losses and enabling the piston to be driven by the drive fluid despite the increased gap height compared to the prior art.

[0021] In some embodiments of the invention, there is no sealing element between the piston and the cylinder wall. This can increase the service life because a component subject to wear can be omitted.

[0022] In some embodiments of the invention, the pressure loss dP gap The force of the drive fluid in the annular gap during operation of the drill hammer must be greater than the quotient of the weight force. F gof the piston and the cross-sectional area A of the piston, i.e. dP Spalt > F g A . The force acting on the piston results from the pressure of the circulating fluid and the piston's face area. At least in the case of bottom fluid intake, this face area must be large enough to overcome the piston's weight and move it upwards. Since the circulating fluid can flow past the piston through the annular gap, the pressure below the piston does not exceed the pressure drop in the annular gap. According to the Darcy-Weissbach formula, this pressure drop is proportional to the aspect ratio of piston length to gap height, the coefficient of flow friction, the density of the circulating fluid, and the square of the circulating fluid velocity.

[0023] In some embodiments of the invention, the rotary hammer further includes at least one hydraulic pump, which is configured to deliver the drive fluid into the cylinder. A hydraulic pump can be coupled to the upper and lower fluid inlets of the cylinder via a hydraulic changeover switch, so that the drive fluid is supplied alternately above and below the piston, moving the piston accordingly.

[0024] The hydraulic pump can be part of the drill hammer and lowered into the borehole together with it. In some embodiments of the invention, the hydraulic pump can remain on the surface and be connected to the drill hammer via a pipe or hose.

[0025] In some embodiments of the invention, the hydraulic pump itself can be hydraulically driven by a flushing fluid. This allows for the use of different fluids for the flushing fluid and the drive fluid of the hammer drill. For example, the flushing fluid can be water containing abrasive particles. The drive fluid of the hammer drill can be, for example, particle-free, clear water, an alcohol, and / or an oil. In this case, a centrifugal pump, a gear pump, or a piston pump can be used as the hydraulic pump. A turbine or a reverse-acting gear pump can be used to drive this pump. The flushing fluid flows through the turbine, and in this way, the flow energy of the flushing fluid generates mechanical drive power for the hydraulic pump of the drive fluid, similar to an exhaust gas turbocharger in an internal combustion engine.

[0026] In some embodiments of the invention, the drill hammer can further include a switching element that interrupts the supply of the drive fluid to the cylinder when the drill hammer, with its attached drill bit, is not engaged with a rock layer. As soon as the drill hammer is subjected to axial load, the switching element can release the drive fluid, thus activating the drill hammer. This allows the drill hammer to be lowered into the borehole while a drilling fluid is supplied to it.

[0027] In some embodiments of the invention, the switching element comprises a cylindrical housing with a control piston slidably mounted therein, the housing having an inlet on its upper side. The housing further comprises a first outlet on a side wall, through which the flushing fluid is directed via a flushing channel to the front of the rotary hammer or to the drilling tool. In addition, the switching element comprises a second outlet, which is arranged within the control piston and through which the drive fluid is supplied to the rotary hammer. The control piston is mounted in the housing by a compression spring, so that it opens the first outlet. When the switching element is subjected to axial load, the control piston retracts against the spring force, so that the first outlet is closed by the piston. The flushing fluid is then guided through the rotary hammer and engages the impact mechanism.

[0028] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention. This will show Figure 1 shows a known rotary hammer. Figure 2 shows the operating principle of a rotary hammer according to the invention. Figure 3 schematically shows the construction of a rotary hammer according to the invention in a first embodiment. Figure 4 schematically shows the construction of a rotary hammer according to the invention in a second embodiment. Figure 5 schematically shows the construction of a rotary hammer according to the invention in a third embodiment. Figure 6 shows a possible embodiment of a switching element.

[0029] Based on the Figure 1A known drilling hammer 1 is described in more detail. The drilling hammer 1 is designed and intended for drilling a deep borehole in the Earth's crust 45. The deep borehole can be, for example, a mining or scientific exploration borehole, or a borehole for exploiting mineral resources such as petroleum or natural gas. In some embodiments of the invention, the deep borehole can serve for geothermal energy production. The deep borehole can be approximately vertical, inclined, or horizontal.

[0030] For the production of the deep borehole 46, a drilling tool 4 is provided, which may optionally be equipped with cutting edges on its end face 465. The drilling tool 4 can be set in rotation by means of a drive (not shown). In addition, it has proven advantageous, particularly when drilling hard rock, to exert impacts on the drilling tool 4 in an axial direction, so that the hard rock is crushed and can be removed as drilling dust together with a drilling fluid.

[0031] A cylinder 2, in which a piston 10 is axially displaceable, serves to generate the impact energy. The cylinder 2 has a lower fluid supply 21 and an upper fluid supply 22. Furthermore, the cylinder 2 is closed on the side facing the drilling tool 4 by a lower cover 23. An upper cover 24 is located on the side opposite the drilling tool.

[0032] To generate an impact, a pressurized drive fluid is introduced into the space between the piston and the lower cover 23 via the lower fluid supply 21, causing the piston to move towards the upper cover 24. When the piston reaches its upper reversal point, a drive fluid is supplied to the upper fluid supply 22, which moves the piston 10 downwards within the cylinder 2. The impact energy thus generated is transferred to the drilling tool 4 via a connecting rod 101. For this purpose, a bore 235 is provided in the lower cover 23, in which the connecting rod 101 is axially displaceable and sealed. The piston length of the known drill hammer 1 is approximately 4 cm.

[0033] A hydraulic changeover switch 3 is provided to supply the cylinder 2 with drive fluid alternately via the lower fluid supply 21 and the upper fluid supply 22. The drive fluid is supplied to the hydraulic changeover switch at increased pressure via a pump (not shown), so that it exits alternately via a first outlet 31 and a second outlet 32 ​​of the hydraulic changeover switch 3, which are each connected to the lower fluid supply 21 and the upper fluid supply 22, respectively. A flushing fluid, which essentially contains water in which abrasive particles are dispersed, is preferably used as the drive fluid.The flushing fluid can be partially routed past the hydraulic changeover switch 3 via flushing channels (not shown) to cool the drill bit 4 directly in the borehole 46, remove the resulting drill cuttings, and accelerate drilling progress through the abrasive wear caused by the particles. Furthermore, the flushing fluid can be used completely or partially to drive the drill hammer, as described above. The drive fluid ejected from the cylinder 2 can also be ejected via flushing channels (not shown) towards the drill bit 4 or returned directly to the surface.

[0034] The in Figure 1The known rotary hammer shown has the disadvantage that a tightly toleranced fit must be manufactured between the piston 10 and the cylinder 2 to allow the piston 10 to slide smoothly within the cylinder 2 and to achieve sufficient sealing between the two components. Sealing elements are typically used in addition, for example, in the form of a metallic gasket made of ductile material or an elastomer seal. However, if a flushing fluid containing particles is used as the drive fluid, the high-precision piston / cylinder pairing is quickly destroyed by abrasive wear. The frequent replacement of the rotary hammer 1 after only a short period of operation makes its use uneconomical for many applications and necessitates frequent interruptions of the drilling process, during which the rotary hammer must be brought to the surface for replacement or maintenance.

[0035] The same problem arises at the feedthrough 235 in the lower cover 23. There, too, tightly toleranced fits and additional sealing elements must ensure that the pressure introduced via the lower fluid supply 21 actually acts on the piston 10 and does not escape from the cylinder 2 through the opening 235. This fit, or rather the sealing element inserted therein, must also be manufactured with high precision and is subject to severe abrasive wear from the flushing fluid used as the drive fluid. Finally, the Figure 1 The depicted rotary hammer has the disadvantage that, due to the double bearing in the cylinder 2 and the lower cover 23, the piston 10 and the connecting rod 101 tend to jam when the drilling tool is subjected to lateral stress. In this case, too, the work must be interrupted and the rotary hammer 1 brought to the surface.

[0036] Based on the prior art, the invention is thus based on the objective of providing a rotary hammer that can be operated more reliably, thereby accelerating the drilling progress. Furthermore, the rotary hammer 1 should exhibit greater stability. The solution found for this purpose is described by means of the Figures 2 to 6 explained in more detail. This shows Figure 2 the operating principle. Figures 3 to 6 Three embodiments of the invention are explained in more detail.

[0037] Figure 2 Figure 1 illustrates the operating principle of the rotary hammer according to one aspect of the invention. Identical components of the invention are identified by the same reference numerals. The rotary hammer 1 is also shown according to Figure 1. Figure 2The system comprises a drilling tool 4, which is designed and intended to crush and / or chip the rock and remove it as drill cuttings along with a drilling fluid. The drilling tool 4 can have a diameter of approximately 5 cm to approximately 40 cm. Optionally, the drilling tool can be a hollow cylinder or contain a hollow cylinder, so that the material from the borehole 46 can be extracted as a core sample.

[0038] Furthermore, the rotary hammer 1 includes a cylinder 2 in which a piston 10 is axially displaceable. The cylinder 2 can be formed in a housing, which may be made of a metal or an alloy. The housing can be provided with a wear- or friction-reducing coating on the outside and / or on the inner wall 26 of the cylinder 2. In some embodiments, the coating may be selected from hard chrome plating and / or an oxide and / or a nitride and / or a carbide and / or diamond-like carbon (DLC). Similarly, the outer surface 106 of the piston 10 may be at least partially coated.

[0039] The cylinder 2 is closed on its side facing the drilling tool 4 by a lower cover 23. On the side facing away from the drilling tool 4, the cylinder 2 is closed by an upper cover 24. An upper fluid supply 22 is located in the upper cover 24. A lower fluid supply 21 is located in the lower cover 23.

[0040] Unlike the prior art, the lower cover 23 does not have an opening 235. The piston 10 also lacks a connecting rod. There is no direct mechanical connection between the piston 10 and the drilling tool 4. When the hammer drill 1 is operated, the piston periodically strikes the inside of the closed lower cover 23, which transfers the impact energy to the drilling tool.

[0041] Furthermore, the rotary hammer can have a hydraulic changeover switch 3. In the schematic diagram of the Figure 1The hydraulic switch 3 is an integral part of the cylinder housing. In other embodiments of the invention, the hydraulic changeover switch 3 can also be arranged outside the cylinder housing and connected to the upper and lower fluid inlets 21 and 22 via hoses.

[0042] The drive fluid is supplied to cylinder 2 or the hydraulic changeover switch 3 via a high-pressure pump 65.

[0043] As with the familiar rotary hammer, the drive fluid is initially supplied to the lower fluid supply 21 via the hydraulic changeover switch 3. This displaces the drive fluid located between the piston 10 and the upper cover 24, expelling it from the cylinder chamber as the piston 10 moves upwards. Upon reaching the upper end position, the further supply of drive fluid via the lower fluid supply 21 is interrupted. The drive fluid is then supplied to the cylinder 2 via the upper fluid supply 22 through the second outlet 32 ​​of the hydraulic changeover switch 3. This causes the piston 10 to move downwards, expelling the drive fluid from the lower part of the cylinder 2. In the lower end position, the piston 10 strikes the inner surface 231 of the lower cover 23.The deceleration of the piston 10 generates an impact force, which is transmitted via the outer surface 232 of the lower cover 23 to the drilling tool 4. The drive fluid is then supplied again via the hydraulic changeover switch 3 and its first outlet 31 to the lower fluid supply 21, and the process repeats cyclically. The drive fluid ejected from the cylinder 2 during each working cycle can be conveyed via flushing channels 35, which are formed in the housing of the drill hammer 1, to the end face 465 or to the engagement surface of the drilling tool 4 in order to cool and / or lubricate the drilling tool 4 and / or to remove the resulting drilling dust.

[0044] Furthermore, the hydraulic changeover switch 3 can have an optional third outlet 33. This can serve, on the one hand, to direct the drive fluid discharged from the cylinder 2 into the flushing channel 35. In some embodiments of the invention, however, in a third switching position of the changeover switch 3, the drive fluid can also be supplied wholly or partially directly to the third outlet 33 in order to supply the drive fluid as flushing fluid to the drilling tool 4 without the impact mechanism of the drill hammer 1 being in operation.

[0045] An annular gap 5 is formed between the inner wall 26 of the cylinder 2 and the outer surface 106 of the piston 10. The gap height H of this annular gap 5 is defined as the difference between the inner radius of the cylinder 2 and the outer radius of the piston 10. The following applies to the gap height H: H > 2 ⋅ R a , Zylinder + R a , Kolben + 3 ⋅ D Partikel , where R a,cylinder and R a, pistondenote the mean roughness values ​​of the outer surface 106 of the piston 10 and the inner wall 26 of the cylinder 2. D particlesThis refers to the maximum particle size in the drive fluid. The average roughness values ​​are typically between approximately 4 µm and approximately 25 µm, depending on the manufacturing process of the piston on the one hand and the cylinder on the other. The maximum particle size results from the requirements for the flushing fluid, but is often less than approximately 100 µm or less than 80 µm. Accordingly, in some embodiments of the invention, the annular gap has a gap height of approximately 45 µm to approximately 1500 µm. In other embodiments of the invention, the gap height is between approximately 50 µm and approximately 500 µm. In still other embodiments of the invention, the gap height is approximately 500 µm to approximately 1000 µm. The annular gap can extend over the entire length of the piston.This eliminates the need for both tight tolerances between the piston and cylinder and an additional sealing element, provided the piston is larger than in conventional rotary hammers and, for example, has a length of approximately 10 cm to approximately 60 cm. In these cases, the pressure loss of the drive fluid flowing in the annular gap is so significant that the piston can be moved by the drive fluid at a sufficient frequency and speed, despite the lack of a seal between the outer surface 106 and the inner wall 26. Surprisingly, it has been shown that this rotary hammer offers an advantage of approximately 30% in terms of pressure loss and impact frequency compared to conventional rotary hammers, thus enabling significantly faster work progress in conjunction with the extended maintenance intervals.

[0046] Based on the Figure 3A first embodiment of the present invention is explained in more detail. Identical components of the invention are designated with the same reference numerals, so the following description is limited to the essential differences. As can be seen from Figure 3As can be seen, the hydraulic changeover switch 3 is not part of the cylinder 2 or its housing, but is connected to the hammer drill 1 as a separate component via pipes or hoses. Furthermore, the housing of the hammer drill 1 is made up of three parts: an upper cover 24, a lower cover 23, and a cylinder housing located between them, in which the cylinder 2 is machined as a through-bore. After inserting the piston 10, the housing of the hammer drill 1 can be completed by screwing and / or riveting and / or welding the upper cover 24, the middle section, and the lower cover 23 together. First channels 215 and second channels 225 are formed in the upper cover 24 and the lower cover 23, through which the lower fluid supply 21 and the upper fluid supply 22 are realized. Channels for the flushing channel 35 and the lower fluid supply 21 are also provided in the cylinder wall 25.

[0047] Based on the Figure 4 A second embodiment of the present invention is explained in more detail below. Identical components of the invention are again provided with the same reference numerals. Figure 4 Cylinder 2 is shown only schematically. Piston 10, which is also part of the second embodiment, is not shown for clarity. Furthermore, the embodiment according to Figure 4 shall be provided with a multi-part housing, as explained above with reference to the first embodiment.

[0048] The second embodiment according to Figure 4This embodiment differs from the previous embodiments essentially in that it includes a hydraulic pump 6, which allows the drive fluid to be circulated in a closed loop. Thus, during the upward movement of the piston, the drive fluid is supplied via the lower fluid inlet 21. The drive fluid, simultaneously expelled from the upper part of the cylinder 2, is discharged via the upper fluid inlet 22 and fed into a sump or reservoir. Upon reaching the upper reversal point, the hydraulic pump 6 draws the drive fluid from the reservoir and returns it to the cylinder 2 via the upper fluid inlet 22. Since the drive fluid circuit is therefore closed and the drive fluid does not escape into the environment, it can be different from the flushing fluid. For example, water without dispersed particles can be used as the drive fluid.In other embodiments of the invention, an alcohol, a water / alcohol mixture, or hydraulic oil can be used as the drive fluid. This can reduce the abrasive wear of the piston / cylinder pairing or improve cooling.

[0049] The hydraulic pump 6 can, for example, be driven by an electric motor using electrical energy. In some embodiments of the invention, the hydraulic pump 6 can have a hydraulic drive 61. The hydraulic drive 61 can, in turn, be driven by the drilling fluid. The drilling fluid is supplied by a high-pressure pump 65. This pump enters the hydraulic drive via a fourth inlet 34 and exits it via the third outlet 33, and then serves to flush the borehole or to cool the drilling tool 4. The energy extracted by the hydraulic drive 61 from the flow of the drilling fluid can then serve as mechanical power to drive the hydraulic pump 6. The hydraulic pump 6 can, for example, be selected from a gear pump, a centrifugal pump, or a piston pump.In some embodiments of the invention, the hydraulic drive 61 may include a turbine or a reverse-acting gear pump.

[0050] Based on the Figures 5 and 6A third embodiment of the invention will be explained in more detail. This third embodiment differs essentially by a hydraulic switching element 7. The flushing fluid is supplied to the hydraulic switching element 7 from the high-pressure pump 65 via an inlet 703. Depending on the position of the switching element 7, the flushing fluid is discharged from the hydraulic switching element 7 either via the first outlet 701 and / or via the second outlet 702. The first outlet 701 opens into a second flushing channel 36, which passes by the impact mechanism of the drill hammer 1 and directs the flushing fluid directly to the drilling tool 4. The second outlet 702 is connected to the impact mechanism of the drill hammer and drives it either directly via the hydraulic changeover switch 3, as in conjunction with Figures 2 and 3 described, or indirectly via a hydraulic drive 61, as in connection with Figure 4 explained in more detail.

[0051] The hydraulic switching element 7 is specifically designed to switch off the impact mechanism of the drill hammer 1 while the drill hammer is being lowered into the borehole.

[0052] At the same time, the borehole is to be flushed. When the drill bit 4 is placed at the bottom of the borehole 46, the impact mechanism of the rotary hammer 1 switches on automatically.

[0053] The construction of the hydraulic switching element 7 is described using the Figure 6 explained in more detail. As from Figure 6 As can be seen, the switching element 7 comprises a cylindrical housing 70 with a control piston 75 slidably mounted therein. The housing 70 has an inlet 703 on its upper surface 71. Furthermore, the housing 70 has at least one first outlet 701 on a side wall 72. In addition, the control element 7 has at least one second outlet 702, which is arranged inside the control piston 75.

[0054] The control piston 75 can be extended from the housing by means of at least one compression spring 79. Provided the switching element 7 is not axially loaded, the control piston is extended from the housing 70 by the action of the at least one compression spring 79. In this position of the control piston, the first drain 701 is open. A spring-loaded valve or a throttle valve 77 can be arranged in the second drain 702, which creates increased flow resistance at the second drain 702. This causes the flushing fluid to be discharged predominantly or completely through the first drain 701 and directed to the drilling tool 4 via the second flushing line 36.

[0055] When the drilling tool 4 is axially loaded via its end face 465 upon contact with the bottom of the borehole 46, the hydraulic switching element 7 is also axially loaded. This pushes the control piston 75 into the housing 70 until it closes the first outlet 701. The flushing fluid supplied via the inlet 703 then exits exclusively or predominantly through the second outlet 702 and starts the impact mechanism.

[0056] Naturally, the invention is not limited to the embodiments shown. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define "first" and "second" embodiments, this designation serves to distinguish between two similar embodiments without establishing any hierarchy.

[0057] The research that led to these results was funded by the European Union.

Claims

1. Hammer drill (1) comprising at least one cylinder (2), in which at least one piston (10) is mounted such that it can be moved axially between an upper and a lower end position, wherein the cylinder (2) has at least one lower fluid supply (21), which can be cyclically supplied with a drive fluid, and the cylinder (2) is closed with an upper cover (24) and a lower cover (23), wherein the piston (10) in the lower end position is in contact with an inner side (231) of the lower cover (23) and a ring gap (5) is formed between the entire casing surface (106) of the piston (10) and the inner wall (26) of the cylinder (2), which ring gap has a gap height H wherein H > 2 ⋅ R a , cylinder + R a , piston + 3 ⋅ D particle , where Ra,cylinder and Ra,piston denote the center roughness values of the casing surface (106) of the piston (10) and the inner wall (26) of the cylinder (2) and Dparticle denotes the maximum particle size in the drive fluid.

2. Hammer drill according to claim 1, characterized in that the lower fluid supply (21) is designed as a first channel (215) which is passed through the upper cover (24) and a cylinder wall (25) and the lower cover (23) and / or in that an upper fluid supply (22) is present, which is designed as a second channel (225) that is passed through the upper cover (24).

3. Hammer drill according to any one of claims 1 to 2, further comprising a flushing channel (35) through which the drive fluid can be removed from the cylinder (2).

4. Hammer drill according to any one of claims 1 to 3, characterized in that an outer side (232) of the lower cover (23) is in contact with a drilling tool (4) and / or in that there is no mechanical connection (101) between the piston (10) and the drilling tool (4).

5. Hammer drill according to any one of claims 1 to 4, characterized in that the ring gap (5) has a gap height of about 45 µm to about 1500 µm or from about 50 µm to about 500 µm or from about 500 µm to about 1000 µm.

6. Hammer drill according to any one of claims 1 to 5, characterized in that the piston (10) has a length from about 10 cm to about 60 cm or from about 20 cm to about 40 cm or from about 40 cm to about 60 cm.

7. Hammer drill according to any one of claims 5 or 6, characterized in that, during the operation of the hammer drill (1), the pressure loss dPgap of the drive fluid in the ring gap (5) is greater than the quotient of the weight force Fg of the piston (10) and the cross-sectional area A of the piston (10), i.e. dP gap > F g A 8. Hammer drill according to any one of claims 1 to 7, further comprising a hydraulic pump (6) which is designed to convey the drive fluid into the cylinder (2) or further comprising a hydraulic pump (6), which is designed to deliver the drive fluid into the cylinder (2) and which is drivable by a flushing fluid.

9. Hammer drill according to any one of claims 1 to 8, further comprising a switching element (7), which has a cylindrical housing (70) with a control piston (75) slidably mounted therein, wherein the housing (70) has an inlet (703) on an upper side (71) of the housing (70) and a first outlet (701) on a side wall (72) of the housing (70), wherein the control piston (75) can be extended from the housing (70) by means of a compression spring (79) so that the first outlet (701) is unblocked and the control piston (75) can be retracted in the case of an axial load against the spring force of the compression spring (79) so that the first outlet (701) is closed by the piston, wherein the control element (7) furthermore has a second outlet (702), which is arranged inside the control piston (75) and which is provided with a spring valve or throttle valve (77).

10. Hammer drill according to claim 9, characterized in that a flushing channel (35) is connected to the first outlet (701) and the second outlet (702) is coupled to the upper and the lower fluid supply (22, 21) via a hydraulic changeover switch (3).

11. Method for deep drilling using a hammer drill (1) with at least one cylinder (2), in which at least one piston (10) is mounted such that it can be moved axially between an upper and a lower end position, wherein the cylinder has at least one lower fluid supply (21) which is cyclically supplied with a drive fluid, and the cylinder is closed with an upper cover (24) and a lower cover (23), wherein the piston in the lower end position is in contact with an inner side (231) of the lower cover (23) and a ring gap (5) is formed between the entire casing surface (106) of the piston (10) and the inner wall (26) of the cylinder (2), which ring gap has a gap height H wherein H > 2 ⋅ R a , cylinder + R a , piston + 3 ⋅ D particle , where Ra,cylinder and Ra,piston denote the center roughness values of the casing surface (106) of the piston (10) and the inner wall (26) of the cylinder (2) and Dparticle denotes the maximum particle size in the drive fluid.

12. Method according to claim 11, characterized in that the drive fluid is supplied alternately via the lower fluid supply (21) and an upper fluid supply (22).

13. Method according to any one of claims 11 or 12, characterized in that the drive fluid is supplied to the cylinder at a pressure dPgap which is greater than the quotient of the weight force of the piston Fg and the cross-sectional area A of the piston, i . e . dP gap > F g A 14. Method according to any one of claims 11 to 13, characterized in that the drive fluid is a flushing fluid which is removed from the cylinder (2) via a flushing channel (35) and / or in that the drive fluid is conveyed by a hydraulic pump (6) which is driven by the flushing fluid.

15. Method according to any one of claims 11 to 14, characterized in that the hammer drill (1) furthermore contains a switching element (7) via which the flushing fluid is supplied, the hammer drill (1) being lowered into a drill hole (46) functionless while flushing fluid is supplied and being switched on when a bottom of the drill hole (465) is reached.