United States Patent 3680412

A remotely controlled breakout mechanism grips and loosens threadably joined connections between sections of a drill string. The mechanism is coaxial with and movable along the drill string and includes stationary and rotatable gripping assemblies which are independently operable for interengagement with splines formed about the adjacent ends of adjoining string sections. The stationary gripping assembly holds one section against rotation and axial movement while the rotatable gripping assembly applies a thread-loosening torque to the adjoining section. A pressure fluid power system for the breakout mechanism includes a control which prevents rotation of the rotatable gripping assembly unless the jaws thereof have been operated for positive interengagement with the splines on a section. Another control is responsive to engagement of the jaws of the stationary gripping assembly for limiting the joint retightening torque output of a fluid motor which normally rotates the drill string with full torque output during drilling operations. The breakout mechanism also serves as a centralizer for the drill string and as a support for temporarily suspending the drill string off the hole bottom. The number and shape of the splines on the end surfaces of the sections are preselected to provide substantial circumferential engagement with the jaws of the mechanism and to provide a sufficiently great number of opportunities for the gripping assemblies to interengage the splines so that a short-stroke power cylinder can be employed to operate the rotatable gripping assembly.

Mayer, James R. (Dallas, TX)
Tipton, Joe D. (Garland, TX)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
81/57.16, 81/57.19, 81/57.21, 173/147, 173/159, 173/164, 175/85
International Classes:
E21B19/16; E21B19/20; (IPC1-7): B25B13/50; B25B17/00
Field of Search:
View Patent Images:
US Patent References:
3246547Drill string suspension arrangement1966-04-19O'Neill et al.
3203284Power wrench and power slip1965-08-31Norrick
3041901Make-up and break-out mechanism for drill pipe joints1962-07-03Knights

Primary Examiner:
Jones Jr., James L.
What we claim is

1. A fluid actuated breakout mechanism operable for loosening a threaded joint between a rotatable drill member and a drill string section from an initially tight condition;

2. The invention defined in claim 1, wherein:

3. The invention defined in claim 2, wherein:

4. Threadably joinable drill string sections each having external splines formed adjacent opposite ends thereof and a breakout mechanism for loosening threaded joints between sections of a drill string, comprising:

5. The invention defined in claim 4, wherein:

6. The invention defined in claim 4, together with:

7. The invention defined in claim 4, wherein:

8. The invention defined in claim 4, wherein:

9. The invention defined in claim 4, together with:

10. The invention defined in claim 9, wherein:

11. The invention defined in claim 4, together with:


Remotely controlled mechanisms have been developed heretofore for making up and breaking out threaded connections between sections of pipe or rod joined together to form a drill string. Ordinarily the drill bit is rotated by a drill motor as it is fed into the ground, consequently, the joints between sections become extremely tight and substantial forces are required to loosen or break out such joints as the string is disassembled.

Self-reacting breakout mechanisms which simulate the gripping and turning actions of a pair of human hands have been disclosed in U.S. Pat. No. 3,158,213 issued to O'Neill et al and in U.S. Pat. No. 3,463,037 issued to Johnson.

The Johnson breakout is hinged and openable to receive laterally the ends of two pipe sections. The adjacent ends of the joined sections have six circumferentially spaced slots for receiving single spring applied pawls carried by stationary and rotary portions of the mechanism. An extendable power cylinder mounted on the stationary portion is operable to rotate the rotary portion to loosen the threads.

The breakout disclosed by O'Neill et al is operationally similar to the Johnson device and is incorporated in a semi-automatic drill rig as part of a more comprehensive system intended to reduce human intervention and effort in the drilling operation. Thus O'Neill et al show a portable drill rig having a tiltable mast which slidably supports a rotary drill motor, a breakout mechanism carried by the mast, a suspension means for temporarily supporting the string off the bottom of the hole, and a pipe transfer and storage device for swinging pipe sections to and from alignment with the drill string. The O'Neill breakout includes a stationary jaw assembly, a rotatable jaw assembly and a guiding jaw assembly for guiding the upper pipe into the lower pipe during make-up operations. It is believed that the stationary jaws and rotatable jaws either frictionally engage with or bite into the walls of the pipe sections.

While the desirability of employing a remotely controlled, self-contained breakout mechanism in a semiautomatic drill rig has been generally recognized by O'Neill et al, substantial problems remain to be solved in the following areas:

1. Provision of interengaging means formed on the breakout jaws and on the drill string sections which will assure rapid and positive engagement between the breakout jaws and the sections without damaging the sections;

2. Provision of powerful, yet compact drive means for rotating the rotary jaws for breakout;

3. Provision of a control system which will provide driving engagement between the rotary breakout jaws and a drill string section before the rotary jaws are powered for breakout;

4. Provision of remotely controlled means for moving the breakout mechanism along the entire length of a drill string section to enable the breakout of connections between the drill motor and a string section in case a string section is advanced only part way into the ground;

5. Provision of a control system which will, as a drill string is being disassembled, automatically coordinate the operation of the drill motor and the breakout mechanism to provide a snug-tight connection between the drill motor and the top of that section joined to the drill motor which will not uncouple when the drill motor is reversely rotated to spin out a preloosened connection at the bottom of that section;

6. Provision of a mechanism which will not only serve its intended breakout purpose, but will also function as a drill string centralizer during the drilling operation and as a temporary support for suspending the drill string off bottom as string sections are removed.


The broad object of this invention is to provide a drill string breakout mechanism for a drill rig which coacts with splined drill string sections and with improved control systems to permit drill strings to be made up and broken down in a manner which is more rapid, foolproof, and safe than any heretofore known. More specifically, this invention is intended to provide structures, mechanisms and controls for drill string handling which meet the several above-enumerated shortcomings of the prior art.


FIG. 1 is a front elevational view of a mobile, track-type drill rig which incorporates the present invention;

FIG. 2 is a partial sectional view of an improved breakout mechanism shown in FIG. 1;

FIG. 3 is a partial sectional view generally taken along lines 3--3 of FIG. 2;

FIG. 4 is a partial sectional view of a connection between threadably joined drill string sections;

FIG. 5 is a diagrammatic illustration of the teeth on the drill string sections and the pistons of the breakout mechanism shown in FIGS. 2 and 3;

FIG. 6 is a schematic illustration of a fluid power and control system for the drill rig shown in FIG. 1; and,

FIGS. 7 through 15 are diagrammatic illustrations of a sequence of operations which may be performed by remote control in the drill rig shown in FIG. 1.


Referring to FIG. 1 of the drawings, the drill rig, generally designated by numeral 20, is of the track type and is movable from place to place by powered tracks 22 which support the rig frame 24. Pivotably supported on the frame 24 is an elongated mast 26 which in the upright position has a foot 28 which rests on the ground surface 30. The mast is generally square in transverse cross section and is fabricated by welding or the like. A pair of transversely spaced guide channels 32 are secured to the front of mast 26 and extend the full length of the mast for retaining and guiding a drill motor, generally shown at 34, and a breakout mechanism, generally shown at 36. The drill motor 34 is moved up and down the mast 26 by a fluid operated motor 38 which drives a chain 40 secured to the drill motor 34 and trained over drive sprocket 42 and idler sprocket 44. The breakout mechanism 36 is powered up and down the mast by a fluid operated motor 46 which drives a chain 48 in a path parallel to the path of chain 40. Chain 48 is trained over drive sprocket 50 and idler sprocket 52 and is secured to the breakout mechanism 36 by a lug 54 as shown in FIG. 3. A rack, generally shown at 56, for transferring and storing sections of a drill string is attached to the side of the mast 26 and is powered for lateral movement by a fluid operated motor 58.

In FIG. 1, many conventional components of the rig 20 as well as fluid supply lines have not been shown since they are not part of this invention. An operator's control panel 60 is shown on the rig with handles for operating certain components of the power and control system of the rig which are illustrated schematically in FIG. 6.

In order to facilitate the description of the operation of this invention for assembling and disassembling a multiple section drill string, the identically constructed pipe or rod sections are designated by letters A, B, C and D. In FIG. 1, section A projects from a bore hole 62 and is connected to adjoining section B which is in turn connected to the projecting shank 64 of the drill motor 34. Sections C and D are stored in the rack 56.

From the foregoing brief description of the drill rig 20, it will be understood that this rig includes these components:

1. Drill motor 34;

2. Transfer and storage rack 56;

3. Breakout mechanism 36;

4. Drill string sections A-D;

5. power and control system shown in FIG. 6.

These components will be discussed in detail under separate headings.


The illustrative drill motor 34 is of the percussion type, i.e. a fluid actuated hammer, not shown, impacts a shank 64 which projects from the drill motor front head 66 for threaded engagement with one of the sections A-D. The hammer impacts are transmitted through the shank and the drill string to a bit 212 which cuts into an underlying earth formation to form the bore hole 62 in a well understood manner. To enhance the cutting action of the bit, it is rotated during the drilling operation by a fluid actuated motor 68 comprising a subassembly of the drill motor 34. The rotary output of the rotation motor 68 is coupled to the shank 64 by any suitable means; and, reference may be had to U.S. Pat. No. 3,082,741 for details of one suitable construction. Preferably, the rotation motor 68 may be reversed and operated independently of the drill motor hammer so that the rotation motor is cooperable with the breakout mechanism 36 and the transfer and storage rack 56, as will be hereinafter described, to provide a remotely controlled, semi-automatic means for assembling, disassembling and storing a multisection drill string. Motor 34 is provided with a slide 70 which is restrained within and guided by the spaced channels 32; and, the drive motor 38 and the chain 40 move the drill motor 34 up and down the mast 26 as desired.

While the illustrative drill motor 34 is of the rotary percussive type, the scope of this invention is not limited by a particular drill motor type or construction or by a particular mode of drilling. For example, a so-called "top drive" drill motor which reversibly rotates, but does not impact, a drive spindle could be substituted for motor 34. Moreover, the motive fluid for operating the drill hammer and the rotation motor 68 can be either hydraulic fluid or compressed air as desired, although a hydraulic supply is described hereinafter in connection with FIG. 6.


The remotely controlled rack 56 stores drill string sections not in use and transfers sections to and from coaxial alignment with the drill motor 34 and the breakout mechanism 36. The vertically spaced upper and lower rack assemblies 70, 72 include brackets 74, 76 which are rigidly attached to the side of the mast 26 and T-shaped upper and lower rails 78, 80 which are journaled for lateral movement by roller assemblies 82, 84. The fluid actuated rack motor 58 reversibly rotates an elongated shaft 86 having pinions at its ends which coact with gear racks, not shown, formed on the upper and lower rails 78, 80 whereby rotation of motor 58 and shaft 86 in one direction moves both rails 78, 80 laterally inwardly with respect to the mast 26 and rotation in the other direction moves the rails outwardly. The lower rail 80 carries cuplike receptacles 88 for receiving the threaded lower ends 89 of those sections stored in rack 56. A locking plate 90 attached to the upper rail 78 has an elongated slot, not shown, opening toward the mast 26 in line with the longitudinal axis of the drill string. The slot is dimensioned to receive the reduced diameter neck portion 92 of the sections A-D and the slot is transversely enlarged at spaced intervals to permit the normal diameter upper ends 94 of stored sections to drop down through the locking plate 90. After the lower end 89 of a section has been seated in a receptacle 88 and the upper end 94 of the section is disposed in the slot in the locking plate 90, a power cylinder 96 mounted on the locking plate moves a clamp member 98 with respect to locking plate 90 to grip the upper ends 94 of those sections stored in the rack 56 and secures these sections against rotation for a purpose to be described herein.

Since the transfer and storage rack is only incidentally involved in the operation of the present invention, only a brief description has been set forth. For a detailed description of the structural and functional features of rack 56, reference may be had to copending U.S. Pat. application Ser. No. 757,950 filed Sept. 6, 1968.


The structural details of the breakout mechanism 36 are shown in FIGS. 2 and 3. As viewed in FIG. 2, the breakout mechanism comprises an upper rotatable gripping assembly 100 and a lower stationary gripping assembly 102 which are reversely mounted above and below and intermediate plate 104. The mounting plate 104 is rigidly attached at right angles to a U-shaped slide 106 which carries at either side detachable slide bars 108 which interfit in mast guide channels 32. As hereinbefore explained, the chain 48 is attached to a lug 54 extending rearwardly from the slide 106; and, the chain is powered by motor 46 for raising and lowering the breakout mechanism 36 along the mast 26.

The mounting plate 104 is generally rectangular and extends forwardly from the mast 26 so that an aperture 110 near the center of the plate 104 is aligned with the longitudinal axis of the drill string.

The jaw or gripping assembly 100 includes a housing 112 having four angularly spaced stepped bores 114 which open radially through the housing body into a center bore 116. A cylinder 118 is removably retained in each of the radial bores 114 by a snap ring 120; and, a piston 122 operates within each of the cylinders 118 between a retracted position, shown in FIGS. 2 and 3, and an extended position wherein the cylindrical rod portion of each piston 122 enters the center bore 116 for a purpose to be explained. The enlarged head 126 of each piston carries an O-ring 128 to provide a fluid seal between the head 126 and the interior wall of the cylinder 118. The pistons 122 are normally biased to the retracted position by surrounding coiled springs 130 seated between a shoulder of the stepped bores 114 and the piston heads 126. Pressure fluid is communicated to and from the rear pressure surfaces of this piston heads from a flexible supply conduit 132 through a fitting 134 which opens into one of four internal passages 136 in housing 112 which interconnect the bores 114. The internal passages 136 open to annular grooves 138 relieved in the external walls of cylinders 118; and, ports 140 connect the grooves 138 to the interior of the cylinders. When pressure fluid is supplied to the cylinders 118, the pistons 122 are simultaneously forced radially inwardly into the central bore 16; and, when pressure fluid is thereafter exhausted from the cylinders 118, the return springs 130 urge the pistons 122 radially outwardly from the central bore 116 to their fully retracted position.

The extreme inner ends of the piston rods 122 are arcuate as viewed in FIG. 3 and are slotted or serrated at 192 for interengagement with the splines 144 formed on the lower end 89 of a drill string section. Splines 145 which are identical to splines 144 are framed on the end of shank 64 which has male threads which join the shank to the upper end 94 of a string section. To maintain proper alignment of the piston splines 192 with either the section splines 144 or the shank splines 145, the piston rods are held against rotation with respect to the stepped bores 114 by a slot and key arrangement designated at 146. Further discussion of the piston rod splines 192 is presented hereinafter in connection with the detailed description of the sections A-D.

A centralizer bushing 148 of hard, wear-resistant material is mounted on the housing 112 concentrically with the center bore 116 by means of a flanged retainer ring 150 which is removably secured to the housing by a plurality of angularly spaced fasteners 152. The interior diameter of the bushing is smaller than the diameter of the center bore 116 and is selected to provide a loose running fit with the exterior surface of a drill string section.

As thus far described, the structural and operational details of the rotatable jaw assembly 100 and the stationary jaw assembly 102 are identical; therefore, to avoid needless duplication of the description of the stationary jaw assembly, the suffix letter "a" will be added to those numerals denoting identical structure elements incorporated in the stationary jaw assembly 102.

The center bores 116, 116a of the housings 112, 112a are concentrically piloted with respect to the mounting plate aperture 110 by the interfitting of annular bosses 154, 154a within the counterbores formed in opposite openings of the aperture 110. The stationary jaw assembly 102 is fixed against rotation with respect to plate 104 by means of a plurality of cap screws 156 which clamp a radially projecting annular flange 158a of the lower housing 112a to the underside of plate 104. The flange 158 of the upper housing 112 is held in bearing relation against the upper surface of the plate 104 by an annular retaining ring 160. While the retaining ring is fixed to the plate 104 by plural cap screws 162, it will be understood that the housing 114 of the rotatable gripping assembly 100 is free to rotate about the axis of its center bore 116 relative to the retaining ring 160, the plate 104 and the stationary gripping assembly 102.

The jaw assembly 100 is rotatable with respect to the stationary jaw assembly 102 through an angle Z from the full line position to the broken line position as depicted in FIG. 3. Such rotation of jaw assembly 100 is provided by a double acting power cylinder 164 having a cylinder body 166 pivotally attached to the mounting plate 104 at 168 and having an extendable and retractable piston rod 170 pivotally attached to a lever arm 172 by a clevis and pin arrangement 174. The inner end of the lever arm 172 is threaded into a boss 176 projecting from the housing 112. Pressure fluid for actuating the piston of the power cylinder 164 is communicated to opposite ends of the cylinder body 166 by flexible conduits 178 and 180. It will be noted that the power cylinder 164 has a short stroke and is, therefore, relatively small and mountable on the support plate 104 in a very compact manner without adding appreciably to the overall size or weight of the breakout mechanism 36.


When having reference to FIGS. 2 through 5, numerals indicating common structural features of all of the string sections A--D will not include a suffix letter. However, in connection with the description of the operation of the drill rig 20, as shown in FIGS. 1 and 7 through 15, the sections will be generally designated by letters A, B, C, and D and numerical references to structural features of a particular section will be followed by a letter suffix. For example, see FIG. 1 where the upper end segment of section B is indicated as 94B.

The sections A-D are identically constructed and, as shown in FIG. 4, comprise an upper end segment 94 and a lower end segment 89 which are preferably attached at opposite ends of an elongated body segment 182 by some suitable welding operation such as friction welding. The body segment 182 generally comprises a hardened thin-walled metal tube having inner and outer diameters uniform from end to end. The interior of the upper end segment 92 is provided with female threads 184 which receive mating male threads 186 formed exteriorly on the lower end segment 89. The threads engage for their full length and the extreme upper end surface of the upper end segment 94 abuts with an annular shoulder 188 of the lower end segment 89. A reduced diameter neck portion 92 is provided to permit the upper segments 94 to be received in the aforedescribed slot in the locking plate 90 of the transfer and storage rack 56. Since other types of racking devices could be used with the rig 20, the neck 90 may not be necessary and represents only one possible embodiment.

An important feature of this invention is the provision of serrations or splines 144 and 190 respectively located adjacent the ends of the lower end segment 89 and the upper end segment 94. The basic function of these splines is to provide an improved surface means on the drill string sections whereby the jaw assemblies 100 and 102 can quickly and positively grip the adjacent end segments of joined drill string section.

The prior art suggests that drill pipes and rods be provided with flat surfaces relieved in their outer wall which are engageable by opposed jaws of a wrench. Usually two, four or six flats are provided for this purpose; and, unless the wrench can be moved substantially about the perimeter of a string section and can be easily manipulated with respect to the flats, extreme difficulty is experienced in engaging the wrench with the flats. This poor situation is worsened if the wrench is capable of only very limited angular movement relative to the flats since the angular opportunities for engaging a six flatted section, for example, are 60° apart. Thus a wrench adapted for gripping a six flatted section must be capable of rotating 60° with respect to the section to insure an opportunity for the wrench to fit onto the flats. An additional increment of wrench rotation must be provided which at least equals the rotation needed to break out the threads between sections. The amount of breakout rotation will depend upon the configuration of the threads and the properties of the thread material. It is believed that wrench rotation on the order of 60° is unacceptable where the wrench comprises a part of a self-contained breakout device for a portable drill rig because the power cylinder must have a relatively long stroke to turn the lever arm of the wrench through a 60° arc. The restraints imposed on the physical dimensions and weight of a power cylinder suitable for use on a breakout mechanism such as that disclosed in this specification require that the stroke of the power cylinder be as short as possible.

Several solutions to theproblems noted above in the use of a short stroke cylinder for rotational power in a breakout mechanism have been proposed but found unacceptable. One solution involves the substitution of a rotary drive motor for the power cylinder 164 so that unlimited wrench rotation is available to align the wrench jaws with flats or slots as taught by the prior art. It has been found, however, that sufficiently high starting torque for breaking out tight joints encountered in a typical drill string cannot be provided by a rotary drive motor which meets the size and weight requirements of the application under consideration. It has also been suggested that the jaws of the wrench have sharp edges which bite into the outer wall of the drill string sections thereby eliminating flats altogether. Such biting action will severely shorten the useful life of a thin-walled section such as sections A-D if the section material is soft enough to deform. If the sections are hardened, as is the usual case with percussive drill strings, the jaws will not bite into the section sufficiently to hold when loosening torque is applied to the wrench. Still another solution has been advanced whereby the number of wrench flats on the sections is substantially increased to increase correspondingly the opportunities for the wrench to come into alignment with a pair of flats. In practice any improvement has been severely limited since increasing the number of flats produces a decrease in the area of each flat hence a decrease in the effective area of driving contact between the wrench jaws and the flats.

The present invention effectively uses a short stroke cylinder 164 to rotate the rotatable jaw assembly 100 through an angle Z, shown in FIG. 3, to achieve assured engagement of the splines 144 on the lower end segments 89 and splines 145 on the shank 64 with complementary splines 192 on the end surfaces of the pistons 122. In the development of the breakout mechanism 36, it has been discovered that three factors must be considered if a splined or serrated construction is to be successfully employed with drill string sections, namely:

1. The size of the angle of rotation Z of the rotatable jaw assembly 100 as provided by a power cylinder having a short stroke length applied to a lever arm also of the shortest practical length.

2. The size of the angle of rotation Y needed to loosen the threads 184, 186 which join adjacent drill string sections. The angle Y may be referred to as the thread breakout angle and can be calculated or measured for any given type of threaded joint.

3. The size of the angle X between the splines.

In relating these angles to the design of the breakout mechanism and the drill string and shank splines, the angle Z must be at least equal to the sum of angles X and Y if the teeth 196 of the piston splines 192 are to be provided enough rotative movement to insure that they will come into engaging alignment with the splines 144 and 145 under the worst conditions of initial misalignment and will thereafter be rotated through the breakout angle of the joint threads. As an example, if the angle Z is fixed at 15° by the design of the breakout mechanism and if the breakout angle of the threads 184, 186 is known to be 6° , the angular spacing of the splines 144, 145 and 192 can be no more than 9°. Under these conditions 40 splines could be provided. It will be understood that for any given breakout angle Y the number of splines will vary directly as the rotation angle Z is changed. From a knowledge of this relationship and fixing what has been found to be a practical design limit on angle Z of 30°, the minimum number of splines for drill strings having a breakout angle of 6° would be 15.

The maximum number of splines has been found to be established by practical limits on the circumferential spacing between adjacent splines. If an excessive number of splines are formed on a string section of a given diameter and wall thickness, the teeth of the splines are not of sufficient cross section and strength to withstand the turning forces applied thereto to break out a joint. Moreover, if the splines are too closely spaced, they will tend to become clogged with dirt and mud while in the bore hole and the piston splines 192 cannot interengage. A minimum critical circumferential spacing between splines has been established as being .125 inch.

Another feature of the splined string sections and shank disclosed herein is the slope of the walls of spline teeth. Referring to FIG. 5 it will be seen that the sides of an individual tooth 194 on a string section slope toward one another and if projected, intersect to define an included angle R. The teeth 196 of the piston splines 192 are sloped at the same angle R for interfitting engagement with the splines 144. In order to maximize the engagement between the teeth 194 and 196, the number of teeth 196 which will engage upon linear movement of the piston 122 should be made as great as possible. The limitation on the number of teeth 196 is the maximum possible size of the angle S which, in turn, can be no greater than the included angle R defined by the slope of the teeth 194. Thus the slope of the walls of the teeth on the string section and the piston surface 142 determines the maximum number of engageable teeth, the diameter of the pistons 122 and, therefore, the total area of clamping engagement of the rotation assembly 100 and the stationary assembly 102 with the drill string sections engaged thereby. A practical upper limit on the size of angles R and S occurs when the tooth slope is so great that a tangential rotating force applied by the teeth 196 of the pistons 122 to the teeth 194 creates a reactance force acting upon the piston teeth 196 which has a radial force component greater than the opposed force imparted to the teeth 196 by the pressure fluid acting on the head 128 of each piston 122. If this condition should occur, the teeth 194 and 196 will not stay in rotary driving engagement; and, it is possible to severely damage these teeth. In a preferred embodiment of the splines 144, 190 on the pipe sections and the pistons 122, 122a, the included angle R is 60°.


In the preferred embodiment of the drill rig 20, the hereinbefore described components and assemblies are powered by and controlled by a hydraulic system comprised of conventionally constructed pumps, motors and valves. The pumps P1, P2 and P3 are are mounted on the rig frame and are powered by a suitable prime mover also carried on the rig frame

The pump P1 supplies the reversible motor 38 which moves the drill 34 up and down the mast under the control of the rig operator by means of a suitable motor control valve, not shown. The pump P2 supplies the reversible drill rotation motor 68 which is remotely controllable by the rig operator by valve means, not shown. A pilot controlled relief valve V1 is connected in parallel with the drill rotation motor 68; and, when opened, V1 bypasses fluid around motor 68. V1 only operates as a bypass for fluid flow which produces rotation of the motor 68 in the forward direction i.e., the direction of rotation of the shank 64 which tends to tighten a threaded joint between the shank and string sections and between sections. The relief valve V1 opens at a preset fluid pressure, less than the full pressure of the pump P2, only when a two-way pressure operated valve V2 is opened to connect the pilot portion of V1 to a fluid reservoir by means of conduit 198. Thus it will be understood that valves V1 and V2 coact to reduce the torque output of the drill rotation motor only in the forward direction to limit the tightness of threaded joints while the reverse or thread disconnecting torque output is unchanged. In a preferred embodiment of this control feature of the invention the joint connecting torque output of the motor 68 is cut to from one fourth to one third of the joint disconnecting torque output. The purpose of this control feature will be more clearly understood from the following description of the operation of the invention.

The pump P3 supplies valves V3, V4, V5 and V6 which are also connected to a reservoir for the pump P3.

V3 is a three-position spring centered valve shown in the neutral position. V3 is operated to supply pressure fluid from pump P3 to the transfer and storage rack motor 58 for forward and reverse rotation to effect lateral movement of the rack 56 as described above.

V4 is a two-position detented valve shown in the disengaged position wherein conduits 200 and 202 are connected to the reservoir of pump P3. When V4 is operated to connect conduits 200 and 202 to the pump P3, pressure fluid is supplied to the stationary jaw assembly 102 to force the pistons 122a radially inwardly into gripping engagement with the splines 190. At the same time, pressure fluid is supplied to V2 which opens the bypass valve V1 in the manner described above. When V4 is returned to the position shown in FIG. 6, the conduits 100 and 102 are exhausted to the reservoir whereby the springs 130a return the pistons to their retracted position and valve V2 is depressurized thereby blocking the bypassing fluid flow through V1.

V5 is a three-position, spring centered valve shown in the neutral position. V5 supplies pressure fluid from pump P3 to actuate the piston jaws 122 of the rotary jaw assembly 100 and to extend and retract the double acting cylinder 164 for effecting rotation of the rotary jaw assembly 100. Conduit 132 communicates V5 to the fitting 134 on the housing 112 and has a branch conduit 180 connected to one end of the cylinder 164. Interposed in branch conduit 180 is a pressure sensing sequence valve V7 which is operated to its open position by a build-up of fluid pressure in the conduit 132 as the pistons 122 of the rotary jaw assembly engage with shank 64 or with a drill string section. The conduit 178 connects the other end of the cylinder 164 with V5. The sequence valve V7 provides an important control feature of this invention by assuring that the pistons 122 have been extended so that the piston teeth 196 are biased for interengagement with splines 144 or 145 before pressure fluid is admitted to the power cylinder 164 to rotate the pistons 122. This sequence of operations gives the piston teeth 196 their best chance for engagement with splines 144 or 145 with a very minimum degree of relative rotation and reduces the chance of damage to these splines or malfunction of the rotary breakout assembly due to a failure of the spline teeth to engage prior to actuation of the power cylinder 164.

V6 is a three-position, spring centered valve shown in the neutral position for supplying pressure fluid from pump P3 to the reversible motor 46 which powers the breakout mechanism 36 up and down the rig mast 26.

The manual control handles for valves V3, V4, V5 and V6, as well as the handles for control valves, not shown, for the drill rotation motor 68 and the drill pull-down motor 38, may be conveniently grouped on the operator's control panel 60. In FIGS. 1 and 7-15 the pressure fluid conduits for the rig components described above have not been shown since their location and manner of installation are merely a matter of design and convenience.


The preferred mode of operation of the drill rig 20 is as follows. The rig 20 is moved into position at the drilling site and the mast 26 is elevated to the desired angle with respect to the ground surface 30. As shown in FIG. 7, string section A is initially stored in the mast 26 with its upper end 94A joined to the drill motor shank 64 and with its lower end 89A extended through the breakout mechanism 36 which has been lowered by motor 46 to its lowermost position for bearing up on the plate 210 of the mast foot 28. The threaded lower end 89A of section A is joined to a drill bit 212 which is advanced into the ground by the hammering and rotating action of the drill motor 34 and by the pull-down force applied to the drill string by the motor 38. The pistons 122, 122a of the breakout mechanism 36 are retracted and the centralizer bushings 148, 148a closely surround the body 182A of section A. The sections B, C, and D are stored in the rack 56 which has been moved to its outermost lateral position by motor 58.

The drill motor is then actuated to impact and rotate section A and bit 212 to start the hole 62. The centralizer bushings 148, 148a serve to restrain section A and the bit 212 from lateral bending and wandering as the hole is started. The incorporation of this centralizing function in the breakout mechanism itself is particularly advantageous since it eliminates the need for a separate centralizer assembly on the rig. As the drill motor is advanced by the feed motor 38, the rotation motor 68 may be operated up to full torque output. When the extreme lower position of the drill motor 34 is reached, as shown in FIG. 8, the front head 66 of the drill motor abuts with the retainer ring 150 of the breakout mechanism 36; and, the shank 64 and upper section end 94A are automatically aligned for engagement with the breakout pistons 122 and 122a, respectively. The stationary jaw assembly 102 is then actuated by valve V4 to cause the piston teeth 196a to engage with the string section splines 190A whereby section A is held against rotation and longitudinal movement. When V4 is operated to actuate the stationary jaw assembly 102, the valve V2 is simultaneously operated to place the bypass valve V1 in parallel with the drill rotation motor 68. Valve V5 is then operated first to supply pressure fluid behind the piston jaws 122 of the rotary jaw assembly 100 causing jaws 122 to contact the shank serrations 145 and thereafter to extend the piston rod 170 of the cylinder 164 causing the jaws 122 to rotate the shank 64 through the angle Z, as shown in FIG. 3. As soon as the jaw teeth 196 and shank splines 145 interengage, the cylinder 164 imparts thread breakout rotation to the shank relative to the nonrotatably held section A. The valve V5 is then operated to release the pistons 122 and to retract the piston rod 170 of the rotation cylinder 164. The drill rotation motor 68 is then reversed at full power to completely disconnect or spin out the shank from section A. The motor 38 then raises the drill motor 34 to the top of the mast 26 as shown in FIG. 14 so that the rack 56 may be moved in to the position shown in FIG. 9 whereby the section B is aligned with the drill motor 34 and the breakout mechanism 36. Drill motor 34 is then lowered to thread the shank 64 into the upper end 94B of section B and is then raised again to lift section B so that the lower end 89B clears the receptacle 88 and the neck 92B is aligned with the slot in the locking plate 90 whereby the rack 56 can be laterally retracted to the position shown in FIG. 10. The drill motor 34 is then lowered and operated to rotate section B to connect its male threads 186B with female threads 184A of section A. Valve V4 is then operated to release the stationary piston jaws 122a and to take the bypass valve V1 out of circuit with the drill rotation motor 68.

The cycle of operations described above is repeated until a sufficient number of sections have been added to the drill string to advance the bit 212 to the desired depth.

Not all of the length of a string section need be employed; therefore, holes may be drilled to depths which are not even multiples of a section length. In such a case the joint between the shank 64 and the uppermost section, section B in this case, is stopped short of the lowermost position of the breakout mechanism 36 as shown in FIG. 10. To disassemble sections A and B, valve V6 is operated to actuate the motor 46 to raise the breakout mechanism 36 up the mast into abutting engagement with the drill motor 34 as shown in FIG. 11. The stationary breakout assembly 102 is actuated by valve V4 and the rotary breakout assembly is then actuated by valve V5 to loosen the joint between sections A and B. The rotation motor 68 is then operated in the forward direction, but at reduced torque output because the bypass valve V1 is in circuit with the rotation motor, to retighten the shank 64 to a snug relation with the upper end 94B of section B. Thus snug-tight connection between the shank and section B is for a purpose to be explained hereafter. The breakout mechanism 36 is lowered against the foot plate 210 and the drill motor raised to position the joint between sections A and B in proper alignment with the breakout mechanism, as shown in FIG. 12. The breakout mechanism is operated to break out the joint between sections A and B in the manner described above. With the rotatable jaws 122 retracted and the stationary jaws 122a engaged to support section A off the hole bottom, the rotation motor is reversed to spin out the joint between sections A and B. This step in the string disassembly cycle can be performed with complete confidence that the shank will not uncouple from the top of section B since this joint has previously been retightened to a snug condition by the reduced forward torque output of the drill rotation motor 68 while, on the other hand, the joint between sections A and B has not been retightened at all from its loosened condition. This feature of the invention provides a foolproof method of drill string disassembly which increases the speed and efficiency of drilling operations and eliminates a heretofore hazardous working condition for the rig operator. Section B is then raised by the drill motor 34 to align the neck 92B with the slot in the locking plate 90 of the rack 56. The rack is moved laterally to receive the section B and the drill motor 34 is then lowered to seat it lower end 89B in receptacle 88 and to align its upper end 94B with the clamp member 98. Cylinder 96 is then actuated to clamp section B against rotation; and, the drill rotation motor 6B is reversed at full torque output to disconnect completely the snug-tight joint between the shank 64 and the top of section B. Rack 56 is then retracted, as shown in FIG. 14, and the drill motor 34 is lowered to connect the shank 64 with the upper end 94A of section A which is supported by the breakout mechanism 36, as shown in FIG. 15. Section A is then withdrawn from the hole 62 to its stored position in the mast 26, shown in FIG. 7, to complete the drilling cycle.