Rod coupler and coupled rod assembly

Abstract

A coupled rod assembly includes a first drill rod assembly (106) including an outer tubular drill rod (114) and an inner drill rod (116), and a second drill rod assembly including an outer tubular drill rod and an inner drill rod. Threaded portions (114A, 114B) of the outer drill rods are joined. A torque carrying connection is established between the inner drill rods with a coupler (118). A pair of complementary torque transmitting profiles (138) are provided by the inner drill rod of the first drill rod assembly and the coupler. An end of one of the profiles includes sharp ends, and an end of the other profile includes bevel surfaces that self-guide the profiles into a meshed relationship before the threaded joint is completed by the threaded portions of the outer tubular drill rods of the first and second drill rod assemblies.

Description

Attorney Docket No. 489825-0023-W001ROD COUPLER AND COUPLED ROD ASSEMBLY CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of priority to co-pending U.S. Provisional Patent Application No. 63 / 748,807, filed January 23, 2025, the entire contents of which are incorporated by reference herein.BACKGROUND

[0002] The present invention relates to the coupling together of rods in a torque transmitting relation. The present invention further relates to an assembly of coupled rods, which in some embodiments, can be used in horizontal directional drilling systems.

[0003] Dual drill rod drilling systems for use in directional drilling, and having an inner rod and an outer rod, are known. A typical dual rod drilling system is generally configured to drive into the ground a series of drill rods joined end-to-end to form a drill string. At the end of the drill string is a rotating drilling tool or drill bit. A dual rod drilling system typically includes a first drive mechanism that controls rotation of a drill bit and a second drive mechanism that controls rotation of a steering element.

[0003] There are concerns around the longevity and ability to join or makeup inner rod systems, and in particular a hex-shaped inner rod that is blind mated to a hollow tubular coupler to render a torque transmitting inner rod joint. Complementary torque transmitting profiles can be difficult to connect or mesh when brought axially together. If forced together, damage of one or both of the mating parts may occur.SUMMARY

[0004] In one aspect, the present disclosure provides a coupled rod assembly for a horizontal directional drilling machine. A first drill rod assembly includes an outer tubular drill rod and an inner drill rod inside the outer tubular drill rod. A second drill rod assembly includes an outer tubular drill rod and an inner drill rod inside the outer tubular drill rod. A threaded joint is provided by respective threaded portions of the outer tubular drill rods of the first and second drill rod assemblies. A torque carrying connection is established between the inner drill rods ofAttorney Docket No. 489825-0023-W001the first and second drill rod assemblies with a coupler and including a pair of complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler, respectively. An end of one of the pair of complementary torque transmitting profiles includes a plurality of sharp ends, and an end of the other one of the pair of complementary torque transmitting profiles includes a plurality of bevel surfaces configured to self-guide the pair of complementary torque transmitting profiles into a meshed relationship before the threaded joint is completed by the threaded portions of the outer tubular drill rods of the first and second drill rod assemblies.

[0005] In another aspect, the present disclosure provides a method of making a coupled rod assembly for a horizontal directional drilling machine. A first drill rod assembly and a second drill rod assembly are provided in an end-to-end relationship, each of the first and second drill rod assemblies including an outer tubular drill rod and an inner drill rod inside the outer tubular drill rod. The outer tubular drill rods of the first and second drill rod assemblies are coupled by engagement of cooperating threads. Prior to completing the coupling of the outer tubular drill rods of the first and second drill rod assemblies, a torque carrying connection is established between the inner drill rods of the first and second drill rod assemblies by making an axial joint with a coupler, including axially joining a pair of complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler, respectively.Axially joining the pair of complementary torque transmitting profiles includes introducing a plurality of sharp ends at an end of one of the pair of complementary torque transmitting profiles to a plurality of bevel surfaces at an end of the other one of the pair of complementary torque transmitting profiles to self-guide the pair of complementary torque transmitting profiles into a meshed relationship. The pair of complementary torque transmitting profiles are further axially joined while completing the engagement of the cooperating threads to couple the outer tubular drill rods of the first and second drill rod assemblies.

[0006] Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSAttorney Docket No. 489825-0023-W001

[0007] FIG. 1 is a schematic side view of a horizontal directional drilling machine and a drill string.

[0008] FIG. 2 is a perspective view of a horizontal directional drilling machine and a drill string including a coupled rod assembly, according to one embodiment of the present disclosure.

[0009] FIG. 3 is another perspective view of the horizontal directional drilling machine of FIG. 2.

[0010] FIG. 4 is an exploded perspective view of the coupled rod assembly, including two drill rod assemblies, according to one embodiment of the present disclosure.

[0011] FIG. 5 is a detail view of mating ends of the two drill rod assemblies of FIG. 4.

[0012] FIG. 6 is a perspective view of a coupling end of a first inner drill rod of a first one of the drill rod assemblies of FIGS. 4 and 5.

[0013] FIG. 7 is a perspective view of an end of a coupler configured to receive the coupling end of the first inner drill rod of FIG. 6.

[0014] FIG. 8 is a first side view of the coupling end of the first inner drill rod of FIG. 6.

[0015] FIG. 9 is a second side view of the coupling end of the first inner drill rod of FIG. 6.

[0016] FIG. 10 is a first axial end view of the coupler of FIG. 7.

[0017] FIG. 11 is a second axial end view of the coupler of FIG. 7.

[0018] FIG. 12 is a perspective view of a coupler of another embodiment of the present disclosure.

[0019] FIG. 13 is a perspective view of a first coupling end of an inner drill rod of yet another embodiment of the present disclosure having a hex profile.

[0020] FIG. 14 is an axial end view of the first coupling end of the drill rod of FIG. 13.Attorney Docket No. 489825-0023-W001

[0021] FIG. 15 is a perspective view of a coupler configured with a socket for receiving the first coupling end of FIGS. 13 and 14.

[0022] FIG. 16 is an axial end view of the coupler of FIG. 15.

[0023] FIG. 17 is a perspective view of a coupling end of a first inner drill rod according to another embodiment.

[0024] FIG. 18 is a perspective view of an end of a coupler configured to receive the coupling end of the first inner drill rod of FIG. 17.

[0025] FIG. 19 is an axial end view of the coupling end of FIG. 17.

[0026] FIG. 20 is an axial end view of the coupler of FIG. 18.DETAILED DESCRIPTION

[0027] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0028] FIGS. 1-3 show a dual rod drilling system 100. The dual rod drilling system 100 includes a drill string 102 that is directed into the ground 101 by a drilling machine 104. In particular, the drilling machine 104 is a horizontal directional drill. An example drill string 102 is shown in FIG. 1. The drilling machine 104 includes a prime mover 122 (e.g., a diesel engine), gearbox 124, a rack 126, and a break out mechanism 128 (e.g., a vise system, FIG. 3).Optionally, the drilling machine 104 can include a drill rod storage box 130, an operator’s station 132, and a set of tracks or wheels 134. The drill string 102 consists of individual sections of drill rod assemblies 106 that are connected to the drilling machine 104 at an uphole end 108 and a drill head 110 at a downhole end 112.

[0029] Each drill rod assembly 106 (FIG. 4) includes a downhole end 109 and an uphole end 111. The drill rod assemblies 106 are strung together end-to-end along an axis A to form theAttorney Docket No. 489825-0023-W001drill string 102, which can extend significant distances in some drilling applications. Each drill rod assembly 106 is a dual rod assembly that includes an outer tubular drill rod 114 and a smaller, inner drill rod 116 (see the cutaways in FIGS. 2 and 3). The outer drill rod 114 has internal threads 114A on one end and external threads 114B on the opposite end. In some examples, the drill rod assembly 106, and the associated drilling machine 104, is configured so that, when the drill string 102 is constructed, the external threads of the outer drill rod 114 are positioned at the uphole end 111 of the drill rod assembly 106 and the internal threads of the outer drill rod 114 are positioned at the downhole end 109 of the drill rod assembly 106.

[0030] The inner drill rod 116 of each drill rod assembly 106 fits inside the tubular outer drill rod 114. The inner drill rod 116 of each drill rod assembly 106 is interconnected to the next adjacent inner drill rod(s) by an inner rod coupling 118 (hereinafter “coupler”). In some examples, each inner rod coupling 118 is affixed to an inner drill rod 116 at the uphole end 111 thereof. A coupled rod assembly is formed by at least two inner drill rods 116 joined together at the coupler 118 so that the inner drill rods 116 transmit torque and rotate together about the axis A.

[0031] During a drilling operation, the drilling machine 104 individually removes drill rod assemblies 106 from the drill rod storage box 130 and moves each drill rod assembly 106 onto the rack 126. Once positioned on the rack 126, both the breakout mechanism 128 and the gearbox 124 engage the drill rod assembly 106 and couple the drill rod assembly with an immediately preceding downhole drill rod assembly 106. Once coupled, the gearbox 124 is configured to travel longitudinally on the rack 126 toward the breakout mechanism 128, while simultaneously rotating one or both of the outer and inner drill rods 114, 116 of the drill rod assembly 106. When the gearbox 124 reaches the breakout mechanism 128 at the end of the rack 126, the gearbox 124 is de-coupled from the drill rod assembly 106, and thereby the drill string 102, and retracts up the rack 126 so that another drill rod assembly 106 can be added to the drill string 102. This process is repeated until the drilling operation is complete, and then reversed during a pullback operation in which the drilling machine 104 removes the drill rod assemblies 106 from the ground 101.Attorney Docket No. 489825-0023-W001

[0032] FIG. 5 illustrates in detail the mating downhole and uphole ends 109, 111 of two drill rod assemblies 106. As shown in FIG. 5, the outer drill rods 114 and the coupler 118 are shown in phantom to reveal the inner drill rods 116. An inner drill rod 116 has a first coupling end 116A (e.g., at the downhole end 109) and the next inner drill rod 116 has a second coupling end 116B (e.g., at the uphole end 111). For a set of similar inner drill rods 116, each one may have a first coupling end 116A and a second coupling end 116B opposite the first coupling end 116A. The coupler 118 has a first portion 118A receiving the first coupling end 116A of the first inner drill rod 116 and a second portion 118B receiving the second coupling end 116B of the second inner drill rod 116 such that a torque carrying connection is defined between the first and second inner drill rods 116 through the coupler 118. The coupler 118 can be retained on the second coupling end 116B of the second inner drill rod 116 (e.g., by a pin 120). As shown, the pin 120 extends transversely through the coupler 118 and is situated into a receiving groove or channel in the second inner drill rod 116. In other constructions, the pin 120 may be received into a through hole in the second inner drill rod 116. The coupler 118 and the second coupling end 116B are also connected for co-rotation via torque transmitting profdes (e.g., splines). In a joint with one of the inner drill rods 116, the coupler 118 constitutes a box end member configured to receive the first coupling end 116A as a pin end member. Thus, the first coupling end 116A is configured as a male splined profile, while the coupler 118 has therein a female splined profile configured to receive the male splined profile.

[0033] From the preceding description and corresponding drawings, it will be appreciated that the joint or interface between the inner drill rod coupling ends 116A, 116B and the coupler 118 is not fully exposed or accessible. When the inner rod joint is mated, it is within the outer drill rods 114. Typically, such joints between inner drill rods and couplers may be difficult to align or “clock” properly to allow axial joining. The particular orientations are not easily observable. Moreover, the inner drill rods are configured to establish co-engagement at the same time as the respective outer drill rods are being engaged (e g., threaded) with each other. In some cases, the inner drill rods establish engagement before the outer drill rods, or the outer drill rods establish engagement before the inner drill rods. In other cases, the inner and outer drill rods establish engagement at the same time. Prior solutions to allow mating of the inner drill rods and mating of the outer drill rods have included creating extra rotational clearance (referred to as backlash or “play”) and / or a process of back and forth oscillations with limited axial forceAttorney Docket No. 489825-0023-W001to get the two inner drill rods to find a mate-able orientation, the present disclosure proposes a unique geometric configuration between the first coupling end 116A of an inner drill rod 116 and the corresponding first portion 118A of the coupler 118. The present disclosure can advantageously avoid excessive backlash and retain substantial dimensions (e.g., spline tooth cross-section) to carry large amounts of torque.

[0034] With reference to FIG. 6, the first coupling end 116A of the first inner drill rod 116 includes a torque transmitting profile formed by a plurality of torque transmitting structures 138. In the illustrated construction, the torque transmitting structures 138 are splines. The splines 138 are straight splines that extend parallel to the axis A. There are a total of six splines 138 in the illustrated first coupling end 116A. In other constructions, the number of splines may be more or fewer than six. The splines 138 protrude radially outward from a base surface 140, which is an exterior cylindrical base surface in the illustrated construction. Each spline 138 defines a pair of side surfaces 142, one of which can be engaged with a corresponding structure to transmit torque (e.g., for co-rotation). The side surfaces 142 are separate from respective “top” or radially outboard surfaces 144 of the splines 138. The top surfaces 144 face radially outward and are not configured to drive or receive engagement by corresponding structure during rotation. The base surface 140 and the co-facing side surfaces 142 of two adjacent splines 138 form respective spaced (pockets or recesses) for receiving corresponding splines 148 of the interior of the coupler 118 (FIG. 7).

[0035] With further reference to FIG. 6, the first coupling end 116A of the first inner drill rod 116 terminates at an axial insertion end or end face 150. The splines 138 do not extend all the way to the axial end face 150. Rather, the splines 138 have terminal ends that are offset from the axial end face 150 by a tapered (e.g., conical tapered) section 152. The terminal ends of the splines 138 are tapered to pointed or sharp ends, rather than blunt ends. As described in further detail below, each of the splines 138 can taper down to one straight edge 153 at its terminal end, nearest the axial end face 150. Furthermore, each one of the splines 138 defines a single point 154 (or “leading point” 154) along the edge 153. The leading points 154 lead the respective splines 138 when brought together with the coupler 118 during axial mating. From the leading edge 153, there are two leading surfaces 156 that form a wedge shape. The leading surfaces 156 extend from the leading point 154, radially out toward the top surface 144 and axially backAttorney Docket No. 489825-0023-W001toward the side surfaces 142. The leading surfaces 156 may be flat. Tn other constructions, the leading surfaces 156 may be rounded.

[0036] The first portion 118A forms an inlet opening for receiving the first coupling end 116A. As shown in FIG. 7, the first portion 118A of the coupler 118 has a complementary profile to the torque transmitting profile formed by the splines 138 of the first coupling end 116A of the first inner drill rod 116. In the illustrated example, the coupler 118 includes splines 148 (e.g., quantity of six) that are configured to fit into the circumferential spaces between the splines 138 on the first coupling end 116A of the first inner drill rod 116. The complementary splines 138, 148 may be sized to keep a relatively small amount of rotational play when engaged (e.g., less than 10 degrees, or less than 5 degrees, or less than 2 degrees). The splines 148 protrude radially inward from a base surface 158, which is an interior cylindrical base surface in the illustrated construction. Each spline 148 defines a pair of side surfaces 160, one of which can be engaged with a corresponding structure to transmit torque (e.g., for co-rotation). The side surfaces 160 are separate from respective “top” or radially inboard surfaces 162 of the splines 148. The top surfaces 162 face radially inward and are not configured to drive or receive engagement by corresponding structure during rotation. The base surface 158 and the side surfaces 160 of two adjacent splines 148 form respective spaces (pockets or recesses) for receiving corresponding splines 138 of the exterior of the first coupling end 116A of FIG. 6.

[0037] With further reference to FIG. 7, the first portion 118A of the coupler 118 terminates at an axial end or end face 166. The splines 148 extend all the way to the axial end face 166. The terminal ends of the splines 148 do not have blunt ends adjacent the axial end face 166. Each of the splines 148 can have a terminal end including two bevel surfaces 170 intersecting at a straight edge 171. The bevel surfaces 170 can be rounded or, more particularly, concave. In other words, the spline ends may be described as being scalloped or cupped on both sides of the edge 171. In some constructions, the bevel surfaces 170 can each be an interior spherical surface segment (e.g., machined by a ball end mill). Furthermore, each one of the splines 148 (along the edge 171 between the bevel surfaces 170) defines a single point 172 of intersection with the axial end face 166 of the coupler 118. The edge 171 that separates the two bevel surfaces 170 can bifurcate the end surface of the spline 148. The two bevel surfaces 170 on the end of the spline 148 can be symmetrical across the edge 171 therebetween. For each spline 148, the edge 171Attorney Docket No. 489825-0023-W001can occupy a plane P that extends axially through the middle of the spline 148 (two exemplary planes P are shown in FIG. 10). Whether the bevel surfaces 170 are concave or another shape (e.g., flat), the bevel surfaces 170 are angled or swept back so as to guide one of the splines 138 of the exterior of the first coupling end 116A of FIG. 6 into the space defined between adjacent side surfaces 160 of adjacent splines 148. In other words, each bevel surface 170 extends further away from the axial end face 166 with increasing distance from the edge 171.

[0038] As can be appreciated from the preceding description of the structure of the splines 138, 148, the axial ends of these splines form a self-guiding interface when initially brought together along the axis A. In any relative rotational relationship where the first and second drill rods are coaxial but the interior splines 148 are not already rotationally aligned (“clocked”) to enter the spaces between the exterior splines 138, the point 154 of the spline 138 will contact one of the bevel surfaces 170 on the end of the interfering spline 148. The only exception is the condition of “perfect misalignment” where the splines 138 are centered on the splines 148. In this condition, which is highly unlikely, the points 154 of all the splines 138 are in exact alignment with the straight edges 171 between the bevel surfaces 170. Practically speaking, any modest axial joining force drives the splines 138, 148 out of the perfect misalignment condition into a regular misaligned condition in which the end geometries of the splines 138, 148 act to self-guide (under axial joining force) into a relative rotational condition where the splines 138, 148 no longer interfere with each other and can be overlapped by axial joining to establish the torque transmitting spline joint. In practice, the axial joining force can be a result of the outer drill rods 114 being threaded together.

[0039] FIG. 8 illustrates the splines 138 of the first coupling end 116A of the first inner drill rod 116 in greater detail. As mentioned above, the point 154 at the end of the spline 138 is the nearest point of the spline 138 to the axial end face 150. In other words, the leading edge 153 that extends from the point 154 to the top surface 144, between the two leading surfaces 156, is inclined at a non-zero angle. From a reference line that is parallel to the axial end face 150 and perpendicular to the axis A, the incline angle a is in a range of 1-89 degrees, and more particularly, a range of 20 degrees to 60 degrees.Attorney Docket No. 489825-0023-W001

[0040] FIG. 9 also illustrates the splines 138 of the first coupling end 116A of the first inner drill rod 116 in detail, although in a different rotational orientation compared to FIG. 8. The view of FIG. 9 looks straight into the top surface 144 of one of the splines 138. In this view, the two leading surfaces 156 of the spline 138 that extend from the point 154, radially out toward the top surface 144 and axially back toward the side surfaces 142, define a wedge angle p. The wedge angle P can be in a range of 20 to 60 degrees).

[0041] FIGS. 10 and 11 are detail views of the coupler 118 taken along the axis A, viewing toward the axial end face 166. Representative dimensions are labeled in FIG. 11. In particular, the coupler 118 has an outside diameter DI . In addition, the tooth profile of the splines 148 defines additional major and minor diameters D2, D3. Midway between the major and minor diameters D2, D3 is a pitch diameter D4. Each spline 148 has a minimum tooth thickness T1 (at the minor diameter D3). Each spline 148 has a principal tooth thickness T2 (at the pitch diameter D4). Along the pitch diameter D4, each adjacent set of splines 148 defines therebetween a spline-to-spline space SI to accommodate the tooth thickness of the splines 138. SI is equivalent to the maximum theoretical tooth thickness of the splines 138 (with no clearance between splines 138, 148). Both the principal tooth thickness T2 and the spline-to-spline space SI are at least 20 percent of the pitch diameter D4. The principal tooth thickness T2 can be at least 25 percent of the pitch diameter D4. Spline thickness is an important characteristic for the robustness of the spline joint (e.g., high torque capability and long-term durability). Toothed joints such as the spline joint of the illustrated construction are sometimes preferable to a more common hex-and-socket joint for rod couplings as the side surfaces 142, 160 enable better load handling. A hex-and-socket joint with normal clearance will predominantly load the material around the points of the hex profile, and the absence of dedicated side surfaces in the socket means that the male hex loads the socket surface that extends perpendicular to a radial line. Simply expanding the clearance (e.g., to ease the make-up of the blind joint) only exacerbates the shortcomings of the typical hex-and-socket joint.

[0042] The bevel surfaces 170 on the ends of the interior splines 148 span across the pitch diameter D4 in the radial direction. In other words, each bevel surface 170 lies partially inside the pitch diameter D4 and partially outside the pitch diameter D4. With respect to the corresponding points 154 at the end of the exterior splines 138, these are set on a circle at orAttorney Docket No. 489825-0023-W001inside the minor diameter D3 with the edges 153 extending outward to cross the minor diameter D3 and the pitch diameter D4. In the condition that the central axes of the first coupling end 116A of the inner drill rod 116 and the corresponding coupler 118 are misaligned when being brought together axially, one or more of the leading points 154 may encounter one of the bevel surfaces 170 of one or more of the splines 148. In this circumstance, the surfaces 170 are configured to guide the leading point 154 (and the first coupling end 116A) toward co-axial alignment. In other words, the end shape of the splines 148 of the coupler 118 is configured for centering the first coupling end 116A into the coupler 118 when forced axially together (e.g., by concurrent threading engagement of the corresponding outer drill rods 114). It should be noted that oscillating (i.e., inducing relative clockwise and counterclockwise rotation between the first coupling end 116A and the coupler 118) may be performed to reduce loading during the process of establishing the joint.

[0043] The end shape of the splines 148, via the bevel surfaces 170, is also configured for “clocking” the first coupling end 116A when forced axially together. The “clocking” effect can be provided by a partial rotation of one or both of the first coupling end 116A and the coupler 118 so that the splines 138, 148 are no longer in interference and are instead able to slide past each other. When the pair of complementary torque transmitting profiles (e.g., the splines 138, 148 of the illustrated construction) are joined together to establish a torque transmitting joint, they are said to be in a meshed or coupled relationship. For the dual rod drill assemblies 106 in which the outer drill rods 114 are threaded into engagement, the meshed relationship of the inner drill rods 116 is to be established before the outer drill rods 114 are threaded together. After achieving the meshed relationship, the profiles provided by the splines 138, 148 experience increasing axial overlap as the outer drill rods 114 thread together until the joint therebetween is completed (e.g., a joint torque threshold is reached). This corresponds to a state of maximum penetration of the first coupling end 116A into the coupler 118 - alternately, fully-coupled or fully-meshed. As mentioned above, the joint between the inner drill rods 116 is characterized as “blind” since the components having the torque transmitting profiles is not visible. The proper meshing orientation between the two inner drill rods 116 (one with no interference between the respective splines 138, 148) cannot be guaranteed to be set and maintained when bringing the two drill rod assemblies 106 together for joining.Attorney Docket No. 489825-0023-W001

[0044] Taking the exemplary orientation of the coupler 118 in FIG. 10, there is a receptacle or assembly space between adjacent splines 148 at the 12 o’clock position. Assuming, merely for the exemplary description, that the orientation of the coupler 118 is fixed and that the first coupling end 116A is in the orientation shown in FIG. 9, the first coupling end 116A is not in position to mate and must be rotated. During assembly, axially forcing the first coupling end 116A (in the FIG. 9 orientation) together with the coupler 118 drives a clockwise or counterclockwise rotation that results in reorienting the first coupling end 116A to the orientation of FIG. 8 in which one of the splines 138 is at the 12 o’clock position so that it occupies the complementary receptacle in the coupler 118. During interaction of the self-guiding interface of the first coupling end 116A and the corresponding first portion 118A of the coupler 118, one or more of the leading edges 153 of the splines 138 slide along corresponding ones of the bevel surfaces 170 of the splines 148.

[0045] Although the construction of the preceding description features the sharp spline ends (e.g., where the wedge surfaces 156 come together at the leading edges 153 and leading points 154) on the first coupling end 116A of the drill rod 116 and features the bevel surfaces 170 on the coupler splines 148, this relationship may be effectively reversed within the scope of the present disclosure. In such a construction, the pointed shape at the ends of the splines 138 is provided on the ends of the splines on the inside of the coupler, and the bevel surfaces 170 at the ends of the splines 148 are provided on the ends of the external rod splines 138. An example coupler 218 according to this construction is shown with sharp-ended splines 248 in FIG. 12.

[0046] As can be appreciated from the preceding description of the structure of the splines 138, 148, the axial ends of these splines form a self-guiding interface when initially brought together along the axis A. In any relative rotational relationship where the first and second drill rods are coaxial but the interior splines 148 are not already rotationally aligned (“clocked”) to enter the spaces between the exterior splines 138, the point 154 of the spline 138 will contact one of the bevel surfaces 170 on the end of the interfering spline 148. The only exception is the condition of “perfect misalignment” where the splines 138 are centered on the splines 148. In this condition, which is highly unlikely, the points 154 of all the splines 138 are in exact alignment with the straight edges 171 between the bevel surfaces 170. Practically speaking, any modest axial joining force drives the splines 138, 148 out of the perfect misalignment conditionAttorney Docket No. 489825-0023-W001into a regular misaligned condition in which the end geometries of the splines 138, 148 act to self-guide (under axial joining force) into a relative rotational condition where the splines 138, 148 no longer interfere with each other and can be overlapped by axial joining to establish the torque transmitting spline joint. In practice, the axial joining force can be a result of the outer drill rods 114 being threaded together.

[0047] Although there are advantages in providing an inner rod joint with a splined coupler and splined rod ends, the present disclosure also contemplates similar self-guiding end shaping between a coupler and rod end in which one or both are not splined. One such construction is shown and described with reference to FIGS. 13-17. Like parts follow the reference numbers of the preceding embodiment, with the exception of a leading “3” and is should be understood that the preceding description applies to the parts of FIGS. 13-17, except for the variations noted explicitly below. Rather than a spline outer profile, the rod end or first coupling end 316A (e.g., at the downhole end) of the first inner drill rod has a non-circular exterior profile (e.g., polygonal profile) as shown in FIGS. 13 and 14. The exterior profile can include a plurality of torque transmitting surfaces or “flats” 342. Around the central axis A, the flats 342 intersect with adjacent flats 342 at respective edges 343. Each edge 343 has a terminal edge or point 354, which is the nearest point to the axial insertion end or end face 350 along the edge 343 (which can also be referred to as the leading end or leading point of the edge 343). The distal ends of the edges 343 with the respective edges or points 354 constitute sharp ends of the torque transmitting profile of the first coupling end 316A. In terms of the polygonal profile, the flats 342 are the polygon sides, and the edges 343 are the vertices. The terminal edges or points 354 can be offset from the axial end face 350 by a tapered section 352.

[0048] As shown in FIGS. 15 and 16, the coupler 318 at the second coupling end 316B of the next inner drill rod (e.g., at the uphole end) has a corresponding interior profile that cooperates with the outer profile of the rod end 316A to establish a torque transmitting joint. For example, the interior profile of the coupler 318 can be a non-circular profile (e.g., polygonal profile) that is fully or partially complementary to the exterior profile of the rod end 316A. The coupler 318 has a first portion 318A configured to receive the first coupling end 316A and including hexagonal socket profile (absent spline teeth) including six equal-length flat sides or “flats” 360 provided around the central axis A. Around the central axis A, the flats 360 intersect with adjacent flatsAttorney Docket No. 489825-0023-W001360 at respective comers or valleys 358. In terms of the polygonal profile, the flats 360 are the polygon sides, and the valleys 358 are the vertices. Opposite the first portion 318A, the coupler 318 includes a second portion 318B receiving the second coupling end of the second inner drill rod to define a torque carrying connection. Similar to the second portion 118B and the second coupling end 116B, the coupler 318 can be axially retained to the second inner drill rod (not shown) via a pin 120 (FIG. 5).

[0049] At the inlet end of the coupler 318 where the corresponding rod end 316A is initially met, the coupler 318 has bevel surfaces 370 (in the form of concave or rounded portions). There may be two bevel surfaces 370 provided at the end of each flat 360. The bevel surfaces 370 can be rounded or, more particularly, concave. In other words, the ends of the flats 360 may be described as being scalloped or cupped. In some constructions, the bevel surfaces 370 can each be an interior spherical surface segment (e.g., machined by a ball end mill). Each one of the flats 360 defines a single point 372 of intersection with the axial end face 366 of the coupler 318. The points 372 can be located centrally along the respective flats 360 in axial end view. The two bevel surfaces 370 that meet at a corresponding point 372 can be symmetrical across a line through the central axis A and the point 372 in axial end view (FIG. 16). Whether the bevel surfaces 370 are concave or another shape (e.g., flat), the bevel surfaces 370 are angled or swept back so as to guide one of the edges 353 of the exterior of the first coupling end 316A of FIGS.13 and 14 into the nearest valley 358. In other words, each bevel surface 370 extends further away from the axial end face 366 with increasing distance from the point 372.

[0050] As can be appreciated from the preceding description of the structure in FIGS. 13-16, the axial ends of the rod end 316A and the inlet end of the coupler 318 form a self-guiding interface when initially brought together along the axis A. In any relative rotational relationship where the first and second drill rods are coaxial but the respective flats 342, 360 are not already rotationally aligned (“clocked”), the point 354 of the edge 343 contacts one of the bevel surfaces 370. The only exception is the condition of “perfect misalignment” where the edges 343 are perfectly centered on the flats 360 to contact the points 372. Practically speaking, any modest axial joining force drives the mating structures out of the perfect misalignment condition into a regular misaligned condition in which the end geometries including the points 354 and the bevel surfaces 370 act to self-guide (under axial joining force) into a relative rotational conditionAttorney Docket No. 489825-0023-W001where the edges 343 no longer interfere with the flats 360, but align with the valleys 358, and can be overlapped by axial joining to establish the torque transmitting joint. In practice, the axial joining force can be a result of the outer drill rods being threaded together. Although the construction of the preceding description features the sharp ends (e.g., the ends of the edges 343 where the edges or points 354 are located) on the first coupling end 316A of the drill rod and features the bevel surfaces 370 on the coupler 318, this relationship may be effectively reversed within the scope of the present disclosure.

[0051] Returning to splined constructions, additional embodiments of the first coupling end 416A and the complementary first portion 418A of the coupler 418 are shown and described with reference to FIGS. 17-20. The reference numbers in FIGS. 17-20 mirror those of the preceding embodiments, with the exception of a leading “4” and it should be understood that the preceding description applies to the parts of FIGS. 17-20, except for the variations noted explicitly below. Although the first coupling end 416A is externally splined like the first coupling end 116A, the splines 438 of FIGS. 17 and 19 may be wider than the splines 138. The splines 438 are straight splines that extend parallel to the axis A, like the splines 138. However, the splines 438 are undercut toward the base surface 440. As such, the side surfaces 442 of a given spline 438 converge at an angle 0 as shown in FIG. 19. This results in the side surfaces 442 of two adjacent splines 438 being parallel to each other.

[0052] Similar to the preceding embodiment, the first coupling end 416A of the first inner drill rod 416 terminates at an axial insertion end or end face 450. The splines 438 have terminal ends that are offset from the axial end face 450 by a tapered section 452. The terminal ends of each of the splines 438 is tapered to a pointed or sharp end, including one straight edge 453 and a single point 454 (or “leading point” 454) along the edge 453. From the leading edge 453, there are two leading surfaces 456 that form a wedge shape.

[0053] As shown in FIGS. 18 and 20, the first portion 418A forms an inlet opening for receiving the first coupling end 416A, and the first portion 418A of the coupler 418 has a complementary profile to the torque transmitting profile formed by the splines 438 of the first coupling end 416A of the first inner drill rod 416. As such, each spline 448 defines a pair of side surfaces 460 that are parallel to each other. The configuration of the side surfaces 460 results inAttorney Docket No. 489825-0023-W001the spline 448 having a single tooth thickness, rather than different tooth thicknesses at different diameters. However, the side surfaces 460 of two adjacent splines 448 converge toward the central axis A. The space between adjacent splines 448 is therefore complementary to the undercut splines 438 (i.e., the facing side surfaces 460 converging at the angle 0).

[0054] Similar to the preceding embodiment, the first portion 418A of the coupler 418 terminates at an axial end or end face 466, and the splines 448 extend all the way to the axial end face 466. Each of the splines 448 has a terminal end including two bevel surfaces 470 intersecting at a straight edge 471. Each one of the splines 448 (along the edge 471 between the bevel surfaces 470) defines a single point 472 of intersection with the axial end face 466.Whether the bevel surfaces 170 are concave or another shape (e.g., flat), the bevel surfaces 170 are angled or swept back so as to guide one of the splines 438 of the exterior of the first coupling end 416A into the space defined between adjacent side surfaces 460.

[0055] Various features and aspects of the invention are set forth in the following claims.

Claims

1. Attorney Docket No. 489825-0023-W001CLAIMSWhat is claimed is:

1. A coupled rod assembly for a horizontal directional drilling machine, the drill string comprising:a first drill rod assembly including an outer tubular drill rod and an inner drill rod inside the outer tubular drill rod;a second drill rod assembly including an outer tubular drill rod and an inner drill rod inside the outer tubular drill rod;a threaded joint provided by respective threaded portions of the outer tubular drill rods of the first and second drill rod assemblies;a torque carrying connection established between the inner drill rods of the first and second drill rod assemblies with a coupler and including a pair of complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler, respectively,wherein an end of one of the pair of complementary torque transmitting profiles includes a plurality of sharp ends, and an end of the other one of the pair of complementary torque transmitting profiles includes a plurality of bevel surfaces configured to self-guide the pair of complementary torque transmitting profiles into a meshed relationship before the threaded joint is completed by the threaded portions of the outer tubular drill rods of the first and second drill rod assemblies.

2. The coupled rod assembly of claim 1, wherein the plurality of bevel surfaces are formed in the coupler.

3. The coupled rod assembly of claim 1, wherein the pair of complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler include an exterior polygonal profile comprising a plurality of flats and a complementary interiorAttorney Docket No. 489825-0023-W001polygonal profile comprising a plurality of flats, and wherein the plurality of bevel surfaces are provided at axial ends of the plurality of flats of the interior polygonal profile.

4. The coupled rod assembly of claim 3, wherein the plurality of bevel surfaces converge to a point located at an axial end face of the one of the inner drill rod and the coupler having the interior polygonal profile.

5. The coupled rod assembly of claim 3, wherein the exterior polygonal profile comprising a plurality of flats is a hex profile consisting of six flats, and the complementary interior polygonal profile comprising a plurality of flats is a hex profile consisting of six flats.

6. The coupled rod assembly of claim 3, wherein the plurality of flats of the exterior polygonal profile intersect with each other at respective edges, and the respective edges have terminal edges or points that define the plurality of sharp ends.

7. The coupled rod assembly of claim 6, wherein the plurality of sharp ends are offset from an axial end face of the one of the inner drill rod and the coupler having the exterior polygonal profile by a tapered section.

8. The coupled rod assembly of claim 2, wherein the plurality of bevel surfaces are provided at ends of spline teeth that extend along an interior surface of the coupler.

9. The coupled rod assembly of claim 1, wherein the plurality of sharp edges are formed in the coupler.

10. The coupled rod assembly of claim 1, wherein each of the plurality of bevel surfaces has the shape of an interior spherical surface segment.

11. The coupled rod assembly of claim 1, wherein the pair of complementary torque transmitting profiles are cooperating male and female splined profiles.

12. The coupled rod assembly of claim 11, wherein each of the cooperating male and female splined profiles has six spline teeth.Attorney Docket No. 489825-0023-W00113. The coupled rod assembly of claim 11 , wherein, on the male splined profile, the plurality of sharp edges are at respective spline tooth terminal ends that are offset from an axial end face of the inner drill rod of the first drill rod assembly by a tapered section.

14. The coupled rod assembly of claim 1, wherein each of the plurality of sharp edges is inclined at a non-zero angle so as to terminate at a single leading point.

15. The coupled rod assembly of claim 1, wherein the plurality of bevel surfaces are grouped in pairs with one pair of bevel surfaces formed in each of a plurality of spline teeth, the bevel surface of each respective pair intersecting at a shared straight edge.

16. The coupled rod assembly of claim 1, wherein one of the pair of complementary torque transmitting profdes is an interior spline profile including a plurality of spline teeth defining a pitch diameter midway between a minor diameter and a major diameter, wherein, at the pitch diameter, both a principal tooth thickness of each of the plurality of spline teeth and a spline-to-spline space between adjacent pairs of the plurality of spline teeth are at least 20 percent of the pitch diameter.

17. The coupled rod assembly of claim 1, wherein the pair of complementary torque transmitting profiles are cooperating male and female polygon profiles.Attorney Docket No. 489825-0023-W00118. A method of making a coupled rod assembly for a drill string on a horizontal directional drilling machine, the method comprising:providing a first drill rod assembly and a second drill rod assembly in an end-to-end relationship, each of the first and second drill rod assemblies including an outer tubular drill rod and an inner drill rod inside the outer tubular drill rod;coupling the outer tubular drill rods of the first and second drill rod assemblies by engagement of cooperating threads;prior to completing the coupling of the outer tubular drill rods of the first and second drill rod assemblies, establishing a torque carrying connection between the inner drill rods of the first and second drill rod assemblies by making an axial joint with a coupler, including axially joining a pair of complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler, respectively,wherein axially joining the pair of complementary torque transmitting profiles includes introducing a plurality of sharp ends at an end of one of the pair of complementary torque transmitting profiles to a plurality of bevel surfaces at an end of the other one of the pair of complementary torque transmitting profiles to self-guide the pair of complementary torque transmitting profiles into a meshed relationship; andfurther axially joining the pair of complementary torque transmitting profiles while completing the engagement of the cooperating threads to couple the outer tubular drill rods of the first and second drill rod assemblies.

19. The method of claim 18, wherein establishing the torque carrying connection includes aligning and meshing respective interior and exterior polygonal profiles of the pair of complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler.

20. The method of claim 18, wherein establishing the torque carrying connection includes aligning and meshing respective interior and exterior spline profiles of the pair ofAttorney Docket No. 489825-0023-W001complementary torque transmitting profiles provided by the inner drill rod of the first drill rod assembly and the coupler.

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