DRILL SHOT OF AN EARTH DRILL

Description

[0001] The invention relates to a rod section of an earth drill string, an earth drill tool, the use of a rod section or an earth drill tool, and a method for drilling an earth borehole in the ground.

[0002] In rod-based drilling in the ground, particularly for creating so-called horizontal boreholes, which can run essentially parallel to or at a relatively shallow angle to the earth's surface, a drill head or drilling tool is advanced by means of a drill string from a drive device located at the earth's surface or in an excavation. The drill strings used typically consist of individual, interconnected sections that are successively attached to the rear end of the already completed drill string and connected to it, following the drilling path.

[0003] Various designs are known for connecting the rod sections to each other. The rod sections can be connected using a threaded connection and / or a plug connection.

[0004] From DE 10 2011 010 958 A1, it is known to specify a method for connecting two drill string sections that combines the advantages of threaded connections and axial plug connections known from the prior art. A plug connection is described which – similar to a threaded connection – is based on spiral projections / grooves extending on a threaded plug with a circular cross-section or in a corresponding threaded bushing, wherein the projections / grooves are designed in such a way that the self-locking characteristic of a threaded connection does not occur.

[0005] DE 200 12 524 U1 discloses a linkage coupling with a cross-section in the form of a rounded polygon nipple with different radii or a corresponding polygon sleeve.

[0006] Based on this prior art, the invention was founded on the objective of providing an improved plug connection for an earth drill string, in particular for a drill string section or earth drilling tool, and a corresponding use and method. In particular, increased strength and / or reduced susceptibility to wear compared to other plug connections can be achieved when drilling in soil.

[0007] This problem is solved by the subject matter of the dependent claims. Advantageous embodiments are the subject matter of the respective dependent claims and / or will become apparent from the following description of the invention.

[0008] One (first) aspect of the invention, which in itself may be grounds for invention or patentability, relates to the design of the connector plug and / or connector socket of a plug connection for an earth drill string. According to this aspect, the outer cross-section of the connector plug or the inner cross-section of the connector socket has at least one circular section and at least one more straight-edged section. Surprisingly, such a shape is suitable for earth drilling with the high loads involved and can exhibit corresponding strength and / or reduced wear, whereby, in particular, the circular section(s) need not be involved in torque transmission. Torque transmission can occur via the more straight-edged section(s).Although not the entire length or circumference of the cross-section is available for torque transmission due to at least one more straight-edged section, the connector can surprisingly meet the high demands of earth drilling in terms of load, wear, and / or service life. The surprisingly suitable shape allows for a design with a relatively small (conceptual) deviation from a perfect circle. For example, compared to a purely square design, additional space can be created—for instance, in the corners, which would otherwise be absent, by incorporating a circular section—and this space can be used for other purposes, such as routing or creating one or more channels for drilling fluid, a data cable, and / or a power cable within the drill string. The cross-section is easily created.The scope of the connector or connector element can be reduced because the cross-section or circumference can be of low complexity and manufactured using simple production machines, especially CNC machines. This allows for a simple design for the user.

[0009] A rod section of an earth drill string is proposed which is designed at its end to form a plug connection and has at least one end (a) a connector plug or (b) a connector socket, wherein the connector plug has on the outside or the connector socket has on the inside at least one circular section and at least one more straight-like section in cross-section.

[0010] A further (second) aspect of the invention, not covered by the claims, relates to the design of the connector and / or socket of a plug connection for an earth drill string, wherein the outer cross-section of the connector or the inner cross-section of the socket has at least one section on which a contact surface for a locking element of the plug connection is provided. In this aspect, the invention departs from the otherwise conventional approach of providing a locking element in a solid section or core, or of arranging the locking pin such that it extends substantially through a center point of the earth drill string in order to obtain the largest possible contact surface. It has been found that the arrangement of the locking element(s) described here is sufficient for many applications.

[0011] A rod section of an earth drill string is proposed which is designed at its end to form a plug connection and has at least one end (a) a connector plug or (b) a connector socket, and the connector plug has a cross-section on the outside or the connector socket on the inside, wherein the cross-section has at least one section on which a contact surface for a locking element of the plug connection is provided.

[0012] The two aforementioned aspects can be easily combined, so that the cross-section of the plug connection for connector plugs and / or connector sockets can have the described shape and at least one contact surface for a locking element is provided on a section of the cross-section.

[0013] The term "drilling rod section" as used in the invention comprises an element extending along a longitudinal axis, which may be part of an earth drill string or a drill string for the soil. The drilling rod section may be designed as an element arranged at the front of the drill string with an associated function (e.g., containing a transmitter for location and / or being designed as a front-mounted drilling tool, or similar) or as an element that simply extends the drill string as a "normal" drilling rod section. The drilling rod section may include mechanical channels, for example, for drilling fluid, electrical conductors, electrical components, and / or electronic components. Further (special) functions of the drilling rod section are not excluded.

[0014] A drill string section can have a first end with a described configuration. The drill string section can (especially if it is not configured as a front-facing auger) have a second end spaced apart from the first end, which can be configured for connection with another drill string section or an auger. The drill string section can also have a center line extending from the first end to the second end along its length. The cross-section of the connector or socket under consideration can, in particular, be perpendicular to the center line of the drill string section.

[0015] The drill string system described may, in particular, be a double-pipe drill string system, which includes both an inner and an outer pipe. With such a double-pipe system, a drill head or auger can be driven via the inner pipe by the drive unit located at the surface or in an excavation, which also propels the drill head or auger forward. The inner pipe can be rotatably mounted within the outer pipe of the double-pipe system. The outer pipe of a double-pipe system is typically either not rotated at all or rotated only at a low speed. The rotations of the outer and inner pipes can be independent of each other.A double-tube drill string is particularly suitable for rock drilling rigs, as wear on the drill string can be kept to a minimum. This is because the outer tube, which is in contact with the rocky borehole wall, can be advanced along the rocky borehole wall without rotation or at a low speed, while the inner tube, driven at a higher speed, can be supported within the outer tube in a wear-reducing manner. If the design involves a double-tube drill string section, the inner tube and / or the outer tube of the double-tube drill string section can be designed at at least one end, as described in the description.

[0016] The term "earth drill string" as used in this description refers to a drill string that can be moved through the ground by means of an earth drilling device. In particular, the earth drill string can be moved through the ground by pushing or sliding. The earth drill string can be a rod consisting of sections that can be moved in an existing or newly created channel in the ground to create or enlarge a borehole, especially a horizontal borehole, or to insert pipes or other long objects into the ground. In addition to the pushing force, in particular, the earth drilling device may also provide for a rotary drive of the earth drill string. Specifically, the earth drill string may have an auger at its leading end, which is the first to come into contact with the ground.

[0017] The term "earth drilling device" encompasses, for the purposes of this description, any device capable of moving an earth drill string in an existing or planned channel in the ground to create or enlarge a borehole, particularly a horizontal borehole, or to pull pipes or other long objects into the ground. An earth drilling device may include a drive mechanism that pulls and / or pushes the drill string. It may also be provided that the drive mechanism rotates the drill string.

[0018] The term "horizontal drilling" as used in this description includes in particular any type of existing or to be created, preferably horizontal, channels in a body, especially earth channels including earth boreholes, rock boreholes or underground conduits, as well as underground or aboveground pipelines and water channels that can be produced or installed by using a suitable earth drilling device.

[0019] The term "plug connection" refers specifically to a positive-locking connection between two elements of the auger string or two string sections, particularly between a string section and an auger, formed in the direction of rotation around the center line or longitudinal axis. This connection involves a plug element formed at one end of one auger string element that can be positively inserted into another plug element formed at the other auger string element. The plug elements can be positively engaged, enabling torque transmission between the two auger string elements.

[0020] In a preferred embodiment, the plug connection is aligned coaxially with the drill string or the auger, thus achieving a simple design. The plug connection can be rotationally invariant, particularly if the socket and plug connector exhibit essentially angular symmetry, so that the socket and / or plug connector can be realigned by a rotation of less than 360° around the longitudinal or central axis of the drill string or auger. In particular, a rotational invariance of 180° or 90° can be provided. The design of the socket and / or plug connector is not complex. Handling of the plug connection can be simplified on a construction site and thus under difficult conditions.

[0021] A separation of the force-transmitting sections can be achieved at a point in the earth drill string. Compressive forces, for example, can be transmitted via a stop in the connector between the socket and plug. This stop for transmitting compressive forces can be formed by an edge of the socket and / or plug, which, when connected, are at least partially in contact with each other. Torque or rotational forces can be transmitted via the cross-sectional profile formed within the connector between the plug and socket. Tensile forces can be transmitted via a locking element in the connector, for which a contact surface for the locking element can be formed on the respective section of the earth drill string.

[0022] The terms "connecting plug" and "connecting socket" encompass, for the purposes of this description, a configuration as an element of a pair of mechanical coupling elements, one of which ("connecting plug") can be at least partially inserted into the other ("connecting socket") to form the connection. The "connecting plug" need not necessarily comprise a solid or filled element; in particular, it is also intended that the inserted element may have a hollow core. The connecting plug may have a free inner area; the connecting plug may be cylindrical with a casing, the interior of which may contain free space.

[0023] For the purposes of this description, the term "cross-section" refers to a sectional view perpendicular to the longitudinal direction of the connector plug or socket, and perpendicular to the centerline of the drill string or auger. In particular, the cross-section can be viewed at an angle of approximately 90° to the centerline.

[0024] Therefore, the outer cross-section of a connector can be a cross-section that is at least partially designed for torque transmission to the socket. The outer cross-section can be at least partially in contact with an inner cross-section that is at least partially adapted to the outer cross-section.

[0025] The inner cross-section of a connector socket can be a cross-section that is at least partially designed for torque transmission to the connector plug. The inner cross-section can be at least partially in contact with an outer cross-section that is at least partially adapted to the inner cross-section.

[0026] The term "circular section" encompasses a section that can essentially correspond to the shape of a segment of a circle; in particular, the section can be designed in such a way that torque cannot be transmitted, or could only be transmitted to a very limited extent, for example via static friction, in a plug connection via the section's cross-sectional design. The shape of a circular section itself can be designed in such a way that torque transmission cannot occur.

[0027] The term "more straight-line section" refers to a section that essentially has a shape different from the "circular section," whereby the geometric design of the "more straight-line section" allows for torque transmission in a plug connection via the section's cross-sectional shape. The "more straight-line section" can essentially correspond to a straight line, although a slight curvature may be incorporated.

[0028] Regarding the distinction between a "circular section" and a "more straight-line section," one distinction can be made by the difference in the radius of curvature of the two sections, which may be formed on a cross-section or circumference. The "more straight-line section(s)" can, in particular, have a curvature ranging from 0% (not curved, straight) to 50% (only half the curvature) of the circular section. It is possible to refer to the "more straight-line section(s)" as the "torque-transmitting section(s)," since the torque between the elements of the connector is essentially transmitted via the "more straight-line section(s)."

[0029] According to the invention, the cross-section has several circular sections which have an essentially the same radius of curvature with respect to the essentially same point.

[0030] The more straight-line-like sections can be designed as essentially straight sections with low curvature, i.e., a higher radius of curvature with different centers of curvature, wherein all the more straight-line-like sections preferably have the same radius of curvature. It can be provided that the more straight-line-like sections are designed as straight lines, in particular essentially as secants of a circle that forms sections for the circular sections. The cross-section can initially be constructed as a circle in a first step, with sections of the circle forming the circular sections and the more straight-line-like sections being inserted between the sections of the circle (circular sections can be replaced by more straight-line-like sections), thus forming a cross-section for the plug connection.The cross-section is point-symmetric about the center point, through which the longitudinal axis of the connector or the longitudinal axis of the rod section passes, and consists of circular and more straight-line segments. Additionally, the cross-section can be axially symmetric, with the axis of symmetry running perpendicular to the longitudinal axis and intersecting the center point. Multiple axes of symmetry are possible. The number of circular segments and more straight-line segments is specified as equal, and in particular, as 4.

[0031] In a preferred embodiment, the circular section and the more straight-line-like section are continuously or smoothly connected. For the purposes of this description, the term "continuous" or "smooth" describes a property of the cross-section such that the cross-section has essentially no discontinuities; that is, the change in the function values ​​describing the cross-section can be arbitrarily restricted by limiting oneself to sufficiently small changes in the argument, for example, in the polar angle. The term "continuous" or "smooth" refers to a macroscopic view, in which minor discontinuities, particularly microscopic ones, may be present, but in particular a radially extending macroscopic section or several radially extending macroscopic sections can be excluded or may not be present. "Continuous" or "smooth" can mean a cross-section without edges or...Describe or designate a cross-section designed without edges.

[0032] In a preferred embodiment, the more straight-line section has a radius of curvature that is more than 1.5 times, and in particular more than 2 times, larger than the radius of the circular section. This allows for a separation of torque-transmitting and non-torque-transmitting sections, which can be easily designed and manufactured using simple means.

[0033] In a preferred embodiment, the more straight-line section intersects a circular section having a radius smaller than that of the circular section. A simple design of the connector or its components is possible.

[0034] In a particularly preferred embodiment, the cross-section is at least partially P4C-shaped.

[0035] The term "P4C-shaped" for a cross-section, as described, encompasses the well-known P4C polygon profile, although deviations from the pure shape are possible, particularly those caused by manufacturing tolerances. Insofar as it is described that the cross-section "at least partially" exhibits the described shape in essence, this includes the possibility that (circumferential) sections of the cross-section may be present that are not P4C-shaped. It is essential that P4C-shaped sections of the cross-section are present, but other sections may also be present. In particular, a P4C-shaped cross-section may be characterized by the fact that torque-transmitting sections of the cross-section may be P4C-shaped. A P4C-shaped cross-section may also have torque-non-transmitting sections or several such sections, which...which, without impairing the function of torque transmission, may be designed differently than specified by the P4C shape.

[0036] The described cross-sectional design allows for the creation of a plug-in connection capable of transmitting very high torque. This design ensures that the two connecting elements of the earth drill string make contact across their entire cross-sectional area, resulting in significantly reduced surface pressure. Notch effects are thus avoided.

[0037] The cross-sectional design as at least partially P4C-shaped in the circumferential direction at the connector socket and / or connector is not necessarily present over the entire length of the connector socket and / or connector, but can extend over the entire length.

[0038] The term "contact surface" as used in this description encompasses an area for which an element, at least partially adapted to the shape of the contact surface, in particular the securing element, may be present. A connection can be established by placing the element or securing element against the contact surface. The contact surface may include an area that runs perpendicular to the longitudinal direction of the drill string or earth auger.

[0039] The term "locking element" as used in this description encompasses a component that secures two elements to each other, in which the locking element rests against a contact surface of one of the two elements, or specifically against a contact surface of each of the two elements. The locking element can be inserted into the designed plug connection to rest against the contact surface(s). The locking element can extend through or be inserted into a bore passing through the connector socket and plug. The locking element can be an elongated or rod-shaped element that can be inserted into the connector socket and plug. The locking element can form at least a partial force-fit, form-fit, and / or material connection with the contact surfaces, so that the locking element can secure the plug connection in the longitudinal direction of the connection.The locking element can be screwed, inserted, slid, pressed, and / or glued into or onto the contact surface(s). The locking element can be designed as a spring pin, the diameter of which is selected so that it can be compressed to a desired extent when installed. The spring pin can be inserted into a bore of a connector and socket that are aligned with each other. The contact surface(s) described can be created by means of a bore. A spring pin can be easily installed and removed. Furthermore, a contact surface or surfaces for the spring pin can be easily designed and manufactured. A spring pin allows for installation / removal without special tools.

[0040] The term "bore" as used in this description encompasses a depression or opening, which may have a round cross-section. The term "bore" also includes a depression and / or opening that is not completely surrounded by material. In particular, there may be no material present in a direction that does not impair the locking function. The term "bore" also includes a recess in a direction transverse to the longitudinal direction of the connector socket or plug, such that the bore or recess has a contact surface that interacts with the locking element under tensile load. The bore or recess may bear against the locking element with its contact surface.The term bore is not limited to a recess, depression or hole produced by means of a rotating tool with corresponding mechanical removal of chips or fragments, but also includes production by electrical discharge machining, vibration lapping and / or laser machining.

[0041] In a preferred embodiment, the plug connection of the drill string section can be implemented using a connecting bushing that has a through-hole for inserting the locking element. This allows for easy access, as the locking element can extend through the connecting bushing. For example, the locking element can be inserted on one side of the through-hole and ejected on the other. In a preferred embodiment, the through-hole is arranged such that its longitudinal axis forms an angle with a line passing through the centerline of a cross-section. The through-hole can be positioned such that its longitudinal axis does not intersect the centerline of the drill string section or the auger. The through-hole can be formed circumferentially on the inner cross-section.Preferably, several through-holes are formed circumferentially around the inner cross-section, which can be substantially equidistant from one another. The (through-)hole can be a secant of the cross-section. In a particularly preferred embodiment, more than one through-hole is provided. For example, a through-hole can be provided for each locking element. In particular, the through-hole can be formed in a region of the cross-sectional profile that does not serve the torque-transmitting function of the inner cross-section of the connector. For example, two through-holes can be provided for two locking elements, three through-holes for three locking elements, and in particular, four through-holes for four locking elements. The locking elements can be spaced apart around the circumference of the inner cross-section of the connector bushing; the through-holes or...The locking elements are distributed circumferentially around the cross-section. In a particularly preferred embodiment, four through-holes are provided, especially in the case of a P4C-shaped cross-section, which may be provided particularly in areas not intended for torque transmission.

[0042] In a preferred embodiment, the drill string section includes a transmitter, which in particular enables the location of the drill string. A drill string section with a transmitter is usually arranged in the front section of the drill string. Most often, the drill string section with a transmitter is used as a section located behind the drill bit.

[0043] In a preferred embodiment, the drill string or earth auger has a different connection at its other end, which is spaced apart from the other end, for connecting to another drill string. This allows switching to a different type of connection on the other side of the drill string.

[0044] In a preferred embodiment, the rod section is designed as a double-tube rod section. In a particularly preferred embodiment, the plug connection is located on the outer rod section of the double-tube rod section. This allows for greater variability and flexibility. The inner rod section can be connected to the plug connection in a different way than in the present embodiment. This allows for adaptation to various applications and requirements.

[0045] The described design with regard to the cross-sectional shape is not limited to a section of an earth drill string usually referred to as a drill bit, but can also relate to the design of an earth drill tool, so that, according to an aspect that justifies the invention, it can relate to an earth drill tool that can have a connector plug and / or a connector socket for forming a plug connection of an earth drill string. According to this aspect, the outer cross-section of the connector plug or the inner cross-section of the connector socket of the earth drill tool is at least partially P4C-shaped.

[0046] The term "earth auger" refers to a drill head located at the front end of the auger string or drill bit, which may include moving parts. However, the earth auger may also have a fixed or rigid, or largely fixed or rigid, outer contour.

[0047] An earth drilling tool is described which is designed at its end to form a plug connection and has (a) a connector plug or (b) a connector socket, wherein the connector plug has at least one circular section on the outside or the connector socket has at least one straight-like section on the inside.

[0048] The described design with regard to the contact surface on at least one section of a cross-section is not limited to a rod section itself, but can also relate to the design of an earth drilling tool, so that, according to an aspect justifying the invention, an earth drilling tool can have a connector plug and / or a connector socket for forming a plug connection of an earth drilling rod, wherein a contact surface for a locking element of the plug connection is designed on at least one section of the outer cross-section of the connector plug or on the inner cross-section of the connector socket.

[0049] An earth drilling tool is described which is designed at its end to form a plug connection and has (a) a connector plug or (b) a connector socket, and the connector plug has a cross-section on the outside or the connector socket has a cross-section on the inside, wherein the cross-section has at least one section on which a contact surface for a locking element of the plug connection is provided.

[0050] In a preferred embodiment, the earth drilling tool is suitable for drilling a pilot bore, particularly a rock bore. This eliminates the need for earth drilling tools that are typically driven through the soil by pushing or pushing. When drilling into rock or drilling a pilot bore, slight tensile forces may occur; these can then be transferred by means of the securing element(s) and the corresponding contact surfaces.

[0051] The invention also relates to a drill string section of an earth drill string, in which a rod section designed in accordance with the description is connected to an earth drill tool designed in accordance with the description.

[0052] The invention also proposes the use of a rod or an earth drilling tool, wherein the rod or earth drilling tool is designed at its end to form a plug connection and has at least one end (a) a connector plug or (b) a connector socket, wherein the connector plug has at least one circular section on the outside or the connector socket has at least one more straight section on the inside.

[0053] The invention also proposes the use of a rod section or an earth drilling tool, wherein the rod section or the earth drilling tool is designed at its end to form a plug connection and has at least one end (a) a connector plug or (b) a connector socket, and wherein the connector plug has a cross-section on the outside or the connector socket has a cross-section on the inside, wherein a cross-section is used which has at least one section on which a contact surface for a locking element of the plug connection is provided.

[0054] The two aforementioned uses can be freely combined, so that the cross-section of the plug connection for connector plugs and / or connector sockets can have the described shape and at least one contact surface for a locking element is provided on a section of the cross-section.

[0055] The invention also proposes a method for drilling an earth borehole in the ground, wherein a drill string or an earth drilling tool is provided, wherein the drill string or the earth drilling tool is designed at its end to form a plug connection and has at one end (a) a connector plug or (b) a connector socket, and the cross-section of the connector plug on the outside or of the connector socket on the inside has at least one circular section and at least one more straight-edged section.

[0056] The invention also proposes a method for drilling an earth borehole in soil, wherein a drill string or an earth drilling tool is provided, wherein the drill string or the earth drilling tool is designed at its end to form a plug connection and has at least one end (a) a connector plug or (b) a connector socket, and wherein the connector plug has a cross-section on the outside or the connector socket has a cross-section on the inside, wherein a cross-section is provided which has at least one section on which a contact surface for a locking element of the plug connection is provided.

[0057] The two aforementioned methods can be easily combined so that the cross-section of the plug connection for connector plugs and / or sockets can have the described shape and at least one contact surface for a locking element is provided on a section of the cross-section.

[0058] If the description includes a device, particularly in the form of a rod assembly or an earth drilling tool, a method, and a use, the descriptions of the individual aspects complement each other. In particular, the descriptions of the operation, especially with regard to its characteristics, also apply to the method and the use.

[0059] Numerical specifications as used in this description are specifications that may be subject to a tolerance of + / - 10%, so that the numerical specification describes not only a single value, but a range of values, in order to take account of tolerance ranges that may be due to manufacturing processes.

[0060] The foregoing statements, as well as the following description of an exemplary embodiment, do not constitute a waiver of certain embodiments or features.

[0061] The invention is explained in more detail below with reference to an embodiment shown in the drawings.

[0062] The drawings show: Fig. 1 an isometric view of a connector; Fig. 2 a view of a connector socket in the direction of the center line of the connector socket; Fig. 3 an isometric view of the connector socket of Fig 2 ; Fig. 4 a side view of an interlocking plug connection according to Fig.1 and connection socket of Fig. 2 and 3 ; Fig. 5 a front section of a double-pipe earth drill string in a partially cutaway view; and Fig. 6 a detailed view of the Fig. 5 .

[0063] Fig. 1 Figure 1 schematically shows, in an isometric view, a connector 1 as it can be formed at the end of a drill string or an auger. The end of the drill string or auger is designed to form a plug connection. In the illustrated embodiment, the connector 1 is part of a pair which also includes a socket 2, as is particularly common in connection with Fig 2 and 3 as described, exhibits.

[0064] The Fig. 1 The connector shows an outer cross-section 3 over a length Q, which is adapted to an inner cross-section 4 of the connection socket 2.

[0065] The outer cross-section 3 of the connector 1 and the inner cross-section 4 of the socket 2 have four circular sections 17, 17a and four more straight-like sections 18, 18a. The four circular sections 17, 17a and the four more straight-like sections 18, 18a of a circumference or cross-section form a P4C-shaped configuration. Over the length Q, connector 1 and socket 2 interact via the P4C-shaped cross-section to transmit a torque from connector 1 to socket 2 and vice versa.

[0066] A pushing force can be transmitted between connection socket 2 and connection plug 1 by means of contact surfaces 5, 6, which lie against each other when plugged together.

[0067] To create a locking mechanism for the plug connection, holes are provided in connector 1 and connector socket 2, into which a locking element can be inserted.

[0068] The bores are formed in the connecting bushing 2 by means of through bores 7, 8, 9, 10. In the outer edge region, the through bores exit at holes 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b. In the connecting bushing 2, the bores form 4 open recesses in the inner cross-section, one of which, 9c, is located in Fig. 3 is shown.

[0069] On connector 1, the bores lead to recesses 11, 12 with a corresponding contact surface for the locking element.

[0070] The bores or recesses 7, 8, 9, 10, 11, 12 are formed in the cross-sectional section or area in which the P4C-shaped cross-section does not have the function of torque transmission.

[0071] Fig. 5 und 6 Figure 1 shows a double pipe rod section 16, with inner rod section 13 and outer rod section 14. The outer rod section 14 of the double pipe rod section 16 is connected to an earth drilling tool 15 by means of a plug connection as described above.

Claims

1. Rod section or borehole tool (15) of a borehole drill string, wherein the rod section or the borehole tool (15) is designed at the end to form a plug connection and has at at least one end (a) a connecting plug (1) or (b) a connecting socket (2), characterised in that the connecting plug (1) has sections (17, 17a) that are circular in cross-section (3, 4) on the outside or the connecting socket (2) has straighter sections (18, 18a) on the inside, the circular sections (17, 17a) forming sections of a common circle and the straighter sections (18, 18a) being inserted between the circular sections (17a, 17a), the number of the circular sections (17, 17a) and the straighter sections (18, 18a) being the same and 4 each, there being a point-symmetrical formation of the cross-section to the centre point through which the longitudinal axis of the rod section extends.

2. Rod section according to claim 1, wherein the circular sections (17, 17a) and the straighter sections (18, 18a) are connected to one another continuously or smoothly.

3. Rod section according to claim 1 or 2, wherein the straighter sections (18, 18a) have radii of curvature which are more than 1.5 times, in particular more than 2 times, larger than the radius of the circular sections (17, 17a).

4. Rod section according to any of claims 1 to 3, wherein the straighter sections (18, 18a) intersect a circular section having a radius that is smaller than the radius of the circular sections (17, 17a).

5. Rod section according to any of claims 1 to 4, characterised in that the rod section has a transmitter.

6. Rod section according to any of claims 1 to 5, characterised in that the rod section has another connection at the other end spaced apart from the end for connection to another rod section.

7. Rod section according to any of claims 1 to 6, characterised in that the rod section is a double-pipe rod section (16).

8. Rod section according to claim 7, characterised in that the plug connection is present on the outer rod section (14) of the double-pipe rod section (16).

9. Borehole drill string section of a borehole drill string, in which a rod section according to any of claims 1 to 8 and a borehole tool (15) according to any of claims 1 to 8 are connected.

10. Method for drilling a borehole into the ground, wherein a rod section or a borehole tool (15) is provided, wherein the rod section or borehole tool (15) is designed at the end to form a plug connection and has at one end (a) a connecting plug (1) or (b) a connecting socket (2), and the cross-section of the connecting plug (1) having circular sections (17, 17a) on the outside or the connecting socket (2) having straighter sections (18, 18a), the circular sections (17, 17a) forming sections of a common circle and the straighter sections (18, 18a) being inserted between the circular sections (17a, 17a), the number of the circular sections (17, 17a) and the straighter sections (18, 18a) being the same and 4 each, there being a point-symmetrical formation of the cross-section to the centre point through which the longitudinal axis of the rod section extends.