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This application claims the benefit of U.S Provisional Application No. 60/144,545, filed Jul. 16, 1999. 
    
    
     TECHNICAL FIELD 
     The present invention relates to directional drilling, particularly to a sonde housing structure for use with a directional drilling bit. 
     BACKGROUND OF THE INVENTION 
     Directional drilling is used for boring under or through obstructions such as roadways, concrete lined waterways and large underground utilities to provide a passageway for utility lines without the need for trenching through or excavating around the particular obstruction. This need has been met by the development of a variety of systems for the installation of underground conduits and pipe bursting/replacement systems. 
     Directional boring apparatus for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed though the soil by means of a powerful device such as a hydraulic cylinder. The drill string ends in a bit having a sloped front face that causes the bit and drill string to deviate in the direction of the sloped face in order to steer. The bit may be pushed and rotated and the same time in order to drill straight. See McDonald U.S. Pat. No. 4,694,913, issued Sep. 22, 1987. A spade, bit or head configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water to assist in boring. 
     Accurate directional boring necessarily requires information regarding the orientation and depth of a cutting or boring tool. Consequently, a sensor and transmitting device (“sonde”) attached to the cutting tool is normally required to prevent mis-boring and re-boring. See, for example, Mercer U.S. Pat. Nos. 5,155,442 and 5,633,589. The sonde includes electronic and electromagnetic components that are sensitive to vibration and may fail if subjected to excessive vibrational shock in service. Since the sonde needs to be positioned adjacent to the cutting or boring head in a drill string in order to provide accurate information regarding the orientation of the cutting head, any vibrations or shock may result in premature failure of the sonde. Additionally, a sonde used in directional boring needs to be housed in a manner that facilitates easy access while simultaneously providing adequate protection to the device. 
     Sondes have been located inside of a bit assembly, such as shown in Stangl U.S. Pat. No. 4,907,658. More typically, however, the sonde is located in a tubular housing that can be connected and disconnected from the housing. The sonde itself is loaded into a compartment that is isolated from compressed fluid that is supplied to the bit through a separate passage in the sonde housing. See Wentworth PCT Publication No. WO 00/11303, published Mar. 2, 2000, and Cox U.S. Pat. Nos. 5,950,743, 5,934,391, 5,931,240 and 5,899,283 for side load sonde housings wherein a door or cover for the sonde compartment is provided. 
     End load sonde housings are also known wherein the sonde is loaded into a blind hole at the rear end of the sonde housing, which is then coupled to a trailing component such as a starter rod. A spacer is inserted behind the sonde to hold it in place. These designs avoid the possibility of breakage of a side load door, but replacing the sonde requires disassembly of drill head. 
     One known side loading sonde housing design is described in commonly-assigned U.S. Pat. No. 6,148,935 and U.S. Pat. No. 6,260,634, the entire contents of which are incorporated for all purposes by reference herein. These patents describes a coupling system known commercially as Splinelok™ wherein the starter rod is connected to the rear end of the sonde housing by a series of interlocking splines that pass torque from the drill string to the sonde housing and bit attached to the front end of the sonde housing. 
     All sonde housing designs must provide sufficient space for the sonde cavity and for a fluid passage to pass drilling fluid up to the bit, which fluid passage is isolated from the sonde compartment, while maximizing the strength of the housing. The sonde is either battery powered or connected to the surface by a wire which runs through the drill string (“wireline”). 
     A need persists for a sonde housing that provides for increased security and protection of the sonde while simultaneously affording convenient and rapid access to the sonde. The present invention provides an end load sonde housing system that is easier to access than known end load systems. 
     SUMMARY OF THE INVENTION 
     According to the invention, an apparatus for mounting an electronic device therein for use in an underground boring machine includes an elongated housing having an elongated, lengthwise central cavity opening at one end thereof. A cartridge containing a sonde fits in the cavity. A keying mechanism is provided on the cartridge and sonde, and also between the cartridge and the housing, for securing the cartridge and sonde in a predetermined orientation relative to the sonde housing when the cartridge is inserted into the cavity through the opening. The sonde housing also preferably includes a lengthwise fluid passage therein which is isolated from the cavity containing the cartridge. According to preferred forms of the invention, an end cap or plug is also provided which holds the sonde cartridge in its installed position and isolates it from contact with the pressure fluid in configurations where the fluid passage and cavity branch from a common end opening of the housing. 
     A drill head for use in directional drilling according to the invention includes an elongated housing having an elongated, lengthwise central sonde cavity opening at a front end thereof, a keying mechanism for securing the sonde in a predetermined orientation relative to the housing when the sonde is inserted into the cavity through the opening, a closure device for enclosing the cavity with the sonde therein, and a bit assembly mounted at the front end of the sonde housing, such that upon removal of the bit assembly, the cavity containing the sonde can be accessed. Preferably the sonde is contained within a cartridge as described below. A drill string may be directly connected to a rear end of sonde housing without need for an adapter or starter rod. Preferably fluid passages conduct a pressure fluid through the sonde housing to its front end to further fluid passages in the bit assembly. In this arrangement, the closure device comprises a cap which seals the cavity from the pressure fluid, whether or not the cap forms part of a cartridge for the sonde. 
     A sonde cartridge according to the invention comprises a tube sized to closely receive a cylindrical sonde therein, the tube having alignment openings therein whereby a pin can be used to secure the tube against movement relative to a sonde housing in which the cartridge is to be installed, an end cap which fits into one end of the tube, a keying device which can engage a notch in the sonde so that the sonde may be installed in a predetermined position within the cartridge, and a fastener for securing the end cap to the tube. 
     The present invention provides an improved end load sonde housing that is inherently stronger than conventional side load configurations and which provides a nonthreaded mechanism for indexing and maintaining the sonde in the proper clockwise position, thereby minimizing the possibility of misboring. 
    
    
     DESCRIPTION OF DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a side view of the sonde housing according to the invention; 
     FIG. 2 is a rear end view of the housing shown in FIG. 1; 
     FIG. 3 is a lengthwise section taken along the line B—B in FIG. 2; 
     FIG. 4 is a rear perspective view of the sonde housing of FIG. 1; 
     FIG. 5 is a directional drill head using the sonde housing of the present invention; 
     FIG. 6 is a front view of the drill of FIG. 5; 
     FIG. 7 is a lengthwise section taken along the line A—A in FIG. 6; 
     FIG. 8 is a side view of a sonde cartridge according to the invention; 
     FIG. 9 is a front view of the cartridge of FIG. 8; 
     FIG. 10 is a rear (hook end) view of the cartridge of FIG. 8; 
     FIG. 11 is a lengthwise section taken along line C—C in FIG. 9; 
     FIG. 12 is a perspective view of the cartridge shown in FIG. 8; 
     FIGS. 13-17 are views comparable to FIGS. 8-12, with the cartridge outer tube removed for clarity; 
     FIG. 18 is an exploded view of the cartridge tube, sonde and cap assembly shown previously; 
     FIG. 19 is an exploded view of the cartridge, sonde housing and drill bit; 
     FIG. 20 is a side view of a directional drill employing a second embodiment of the invention wherein the sonde housing functions as a combination of sonde housing and starter rod and wherein the sonde is loaded into the housing from the front end; 
     FIG. 21 is top view of the directional drill of FIG. 20; 
     FIG. 22 is a lengthwise section taken along line A—A of FIG. 21; 
     FIG. 23 is a partial cross section taken along line D—D of FIG. 20; 
     FIG. 24 is a partial cross section taken along line B—B of FIG. 21; 
     FIG. 25 is a partial cross section taken along line C—C of FIG. 21; 
     FIG. 26 is a side view of a sonde cartridge in accordance with the second embodiment of the invention; 
     FIG. 27 is a top view of the sonde cartridge of FIG. 26; 
     FIG. 28 is a cross section taken along line B—B of FIG. 27; 
     FIG. 29 is a lengthwise section taken along line A—A of FIG. 27; and 
     FIG. 30 is a top view of the sonde housing with a threaded male adapter installed. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings wherein like reference numerals denote the same and similar parts throughout and in particular FIGS. 1-7, an improved sonde housing  12  according to the invention is illustrated. Sonde housing  12  comprises a generally cylindrical structure with a longitudinal central cavity and, as illustrated, includes joint ends  13  and  15  of non-threaded couplings suitable for coupling the housing to a drill string and mounting an appropriately designed boring bit  14  or other tool. In one embodiment, the sonde housing  12  is configured in accordance with Splinelok™ joint system described in the foregoing patent applications incorporated by reference herein. As set forth in detail below, the geometry of the sonde housing of the invention is especially suited to protecting the combination sensor and transmitting device that comprises a sonde and allowing for transmission of the information collected to the operator via electromagnetic waves or through a wireline. 
     Sonde  18  transmits radio signals defining the subterranean location of the drill head  14  to an operator and the orientation of the slanted front bit face used for steering. Sonde  18  typically transmits information regarding the position, depth, pitch of the axis relative to gravity and clock position of the apparatus. This information allows the operator to determine which direction bit  14  will go during a steering correction. In order to measure the clock position of bit  14  accurately, sonde  18  must be held in registry relative to particular features on the boring head or bit  14 . 
     Referring to FIGS. 1-7, sonde housing  12  includes an axially extending, rearwardly opening blind hole. This blind hole, henceforth referred to as the cartridge bore or cavity  22 , is configured to receive a sonde cartridge  20  (FIGS. 8-12) encapsulating sonde  18 . A cross-drilled hole  26  is positioned near the blind end  24  of the cartridge bore  22 . A spiral wound roll pin  30  (FIG. 7) is inserted into hole  26 . This transverse pin  30  serves to orient cartridge  20  when the cartridge is installed in the cartridge bore  22 . At the rear of the cartridge bore  22 , there is a profiled, rearwardly facing, generally annular depression  34  surrounding bore  22 . Depression  34  is shallow, for example ⅜ inch, and is designed to accept a flange  36  of a cap  38 , a component of cartridge  20 . Radial slots  40  extend through sonde housing  12  and into cartridge bore  22 . Slots  40  permit transmission of the sonde signal into the surrounding ground. Without slots  40 , the steel of the housing  12  would shield or block the signals. Alternatively, a wireline (not shown) could be utilized to transmit information. Sonde housing  12  also has an axial fluid passage  16  passing lengthwise through the housing  12  and bit  14  to conduct the drilling fluid around the sonde  18 . Fluid is injected through the drill string to a starter rod  56  and then into passage  16  to provide lubrication to the bit and to carry away debris generated during the drilling operation. 
     Referring now to FIGS. 8-19, cartridge  20  includes an outer tube  42  designed to provide a snug slip-fit over the sonde  18 . Preferably, tube  42  is formed from a material such as plastic which allows transmission of the radio signal. A U-shaped guide  44  is provided at front end  43  of tube  42 . Guide  44  includes a pair of relieved edges  48  that snap fit into corresponding lengthwise, opposed grooves  54  in tube  42 , securing the guide in the tube and providing for proper longitudinal and clockwise alignment of the cartridge  20  and sonde  18  within housing  12 . Guide  44  has a small, rearwardly extending tab  46  which fits in a corresponding notch in the end of the sonde  18 , thereby preventing rotation of sonde  18  within the cartridge  20  and keying the sonde to a predetermined position relative to cartridge  20 . 
     Upon installation, roll pin  30  passes through the middle of the “U” of guide  44 . A pair of opposed, frontwardly opening keyhole-shaped slots  50  at the front end  43  of the cartridge extend through the wall of tube  42 . Slots  50  snap over the transverse pin  30  described above, so that the rounded inner ends  52  of slot  50  engage the transverse pin. The mating of the keyhole shaped slots  50  and transverse pin  30  prevent rotation of the cartridge  20  (and therefore of sonde  18 ) within the cartridge bore  22  of housing  12 , maintaining the clockwise orientation of the cartridge within the bore. 
     After cartridge  20  is inserted into cartridge bore  22 , the cartridge is secured in the cartridge bore with an end cap  38 . Cap  38  may be formed from any appropriate material, such as steel, plastic or aluminum, so long as the cap  38  is capable of sealing the cartridge bore against the entry of high pressure (2000 psi) drilling mud or fluid and bearing the applied load of the fluid. As will be appreciated by reference to FIGS. 3 an  7 , drilling mud or fluid is present at the joint between the sonde housing  12  and the starter rod  56  as it moves from the drill string through the starter rod  56  and into a rear end opening  15  which is slightly larger in diameter than cavity  22  and configured to receive the projecting end of the starter rod therein. 
     As shown in FIG. 2, passage  16  and cavity  22  both branch from rear opening  15 . In this configuration, the high pressure drilling fluid present in the joint between starter rod  56  and sonde housing  20  will produce a load on the back of cartridge  20 . For example, at 2000 psi with a bore of 1.62 inches, the applied load will be approximately 4140 lbs. Cap  38  is provided with an annular flange or lip  36  that serves to bear the load upon the rearwardly facing depression  34  in housing  12 , protecting sonde  18  from the load. To further aid in protecting sonde  18  against the incursion of drilling fluid into cartridge bore  22 , cap  38  is provided with a series of annular grooves  35  along its midsection for mounting elastomeric O-rings  37  which further seal any gap between the cap and cartridge bore  22 . Additionally, a rubber nub  39  at the end of cap  38  remote from end flange  36  resiliently engages the rear end of sonde  18 . 
     As previously noted, sonde cartridge  20  receives guide  44  at a position predetermined by slots  54 , and guide  44  in turn is provided with indexing tab or key  46  to position sonde  18  in one orientation within the cartridge. In turn, cartridge  20  has keyhole slots  50  which engage transverse pin  30  to position the cartridge in one of two possible orientations, each 180° apart. However, this arrangement still allows the cartridge  20  and sonde  18  to possibly be inverted 180° upon installation in sonde housing  12 . 
     To prevent the cartridge and sonde from being installed in the inverted position, flange  36  of cap  38  is provided with an alignment feature. In the illustrated embodiment, the alignment feature comprises lateral wings or tabs  60 . Wings  60  fit only into a profiled portion  62  of recess  34  (FIGS.  3  and  6 ), thereby aligning cartridge  20  in the proper orientation relative to housing  12 . This feature provides the assembler with a means of avoiding a situation where the cartridge is accidentally inverted 180° degrees from the correct clockwise orientation during installation. 
     Cap  38  is secured to tube  42  by bolts  70  that are received in apertures  72  through the wall of plastic tube  42  and are tightened into threaded holes  73  against a counterbore  74  in cap  38 . The heads of bolts  70  function as shear pins to keep cap  38  aligned as well as providing a means to extract the outer tube  42  and sonde  18  from the cartridge bore  22 . A hook eye  76  on the outer surface of cap  38  provides means for pulling cartridge  20  out of housing bore  22 . 
     Referring now to FIGS. 20-30, a second embodiment of the sonde housing of the invention is illustrated. In this embodiment, a sonde housing  112  is adapted to be directly connected to the lead end of a drill string (not shown) thereby eliminating the necessity for a starter rod. The elimination of a separate starter rod provides for a simpler construction and assembly. Housing  112  includes a central cavity or bore  122  and, as illustrated incorporates a non-threaded joint  113 , such as the Splinelok™ joint for mounting a downhole tool, such as a bit assembly  114 . Bit assembly  114 , including an interchangeable bit  117  and a bit head  119 , is further described in commonly assigned U.S. patent application Ser. No. 09/393,778, filed Sep. 10, 1999, the contents of which are incorporated by reference herein. 
     Turning to FIGS. 20-25, the sonde housing  112  consists of a generally cylindrical body including a cartridge bore  122  extending rearwardly from a forward end  182 , the forward end  182  being adapted to receive a drill bit  114  or similar tool. As illustrated, sonde housing  112  is incorporates the Splinelok™ joint system described in pending U.S. patent application Ser. No. 09/212,042, filed Dec. 15, 1998, the disclosure of which is incorporated herein for all purposes. As shown in FIG. 30, a threaded adapter  100  may be mounted on sonde housing  112  upon removal of bit assembly  114  to provide for use of other bits or back reamers tools adapted for threaded connection. 
     Sonde housing  112  includes a threaded aperture  180  for receiving a male end of a leading drill rod (not shown) and a passageway  178  for a wireline in case where a wireline-type sonde is used. Passageway  178  is sealed by a plastic or rubber plug, not shown, prior to use to prevent pressure fluid from entering the sonde compartment. Such a plug is either completely solid, or else may be formed around the wire line. As shown in FIG. 24, housing  112  also include a pair of fluid passageways  116  that extend the length of the housing to allow flow of drilling fluid from the drill string through the housing to the bit assembly  114 . Cartridge bore  122  extends longitudinally along a portion of the length of housing  112  from the forward end of housing  112 . As illustrated, cartridge bore  122  terminates in a blind or, in the case of a wire-line type sonde, a semi-blind end  124 . 
     As best illustrated in FIGS. 20-22,  23  and  25 , bit assembly  114  is retained on the forward end of sonde housing with two pairs of solid steel anchor pins  184  that pass through apertures  188  in housing  112 . Anchor pins  184  pass through holes in the male end  186  of bit assembly  114  to secure the bit to the housing  112 . Anchor pins  184  are formed with a pair of rounded, circumferential grooves  187  that are spaced for alignment with a retainer hole  192  that passes through housing  112  and is substantially perpendicular to apertures  188 . Retainer holes  192  are aligned to intersect the grooves  187  of anchor pins  184  so that a retainer  190  inserted in retainer hole  192  fits into grooves  186  of anchor pins  184 , locking the anchor pins in position. Preferably, retainers  190  are roll pins, i.e. a flat sheet of steel rolled into a tube. Resilient engagement between retainers  190  and the walls of retainer holes  192  and/or interference with anchor pins  184  maintain retainers  190  in place upon installation. However, other engagement mechanisms between the bit assembly and sonde housing, such as the splined connections shown in the above-cited PCT publication, or even a threaded connection, may also be employed. A threaded connection is, however, more difficult to use and is not preferred. Similarly, bit assembly  114  may be replaced by the bit  14  discussed in connection with the first embodiment above. 
     Referring now to FIGS. 26-29, a sonde cartridge  120  for use in connection with the front loading sonde housing of the invention includes an outer plastic tube  142  and an end cap  138  generally similar to cap  38  and tube  42  discussed above. A retainer  130  such as a roll pin passes through tube  142  and a transverse hole in sleeve  147  adjacent to a rear end  143  of cartridge  120  to secure cartridge  120  in the sonde housing. Sleeve  147  may be formed from an elastomeric material to provide a resilient cushion for sonde  18 . 
     Cap  138  includes an annular flange  136  designed to fit into a shallow depression  134  (FIG. 22) formed at the forward end of cartridge bore  122 . Cap  138  also includes a key or tab  146  at its rear end that indexes against the notch in sonde  18  to position the sonde at the proper clockwise orientation within the tube  142 . Sonde housing  112  includes a cross-drilled hole  126  that passes through the housing and cartridge bore  122 . A transverse retainer, such as a roll pin  130  is inserted through the cross-drilled hole  126 . 
     Tube  142  includes an aperture  172  that extends through the wall of plastic tube  142  for receiving a bolts or screws  170  in order to secure cap  138  onto the tube. Bolt  170  is tightened into one or more holes  174  in cap  138  to secure the cap  138  and sonde  18  in cartridge  122 . The front end of cap  138  may include a recessed crossbar  135  that serves as a handle for pulling cartridge  120  from bore  122 . Flange  136  is provided with wings  160  that engage profiled recess  162  of cartridge bore  122 . As previously discussed, wings  160  in conjunction with profiled section  162  prevent the cartridge  120  from being accidentally inverted from the proper clockwise orientation when installed in cartridge bore  122 . Although guide  44  is absent in this embodiment, keying of the sonde position is still accomplished because the tab  146  and holes  174  are in a predetermined alignment, and a similar keyed connection is maintained between wings  160  and profiled recess  162 . Upon installation of cartridge  22 , keyholes grooves  150  fit over and stop against transverse pin  130 . 
     Fluid passages  116  terminate at a rear end opening  201  in the bit assembly, which communicates with fluid channels  216  in the bit assembly. The arrangement of the first embodiment is thus reversed, with cap  138  performing the same functions but now facing frontwardly at the joint between the bit assembly and the sonde housing. As such, upon removal of the bit, which occurs frequently, this embodiment of the invention allows ready access to the sonde and the same time. 
     As will be appreciated by those skilled in the art the sonde housing of the invention provides for securing a sonde in an indexed position with a combination of orienting features that require the installation of the sonde in the proper orientation. Furthermore, as opposed to other end load design, the sonde housing described herein, in combination with the Splinelok™ joint maintains a bit or tool in a known clockwise orientation with the sonde. Thus, as opposed to designs that utilize thread-on type tool joints, the orientation of the tool relative to the sonde is not dependent upon the orientation of a threaded tool connection. This feature represents a substantial advantage over prior art designs that are susceptible to mis-orientation due to the use of a threaded tool connection. 
     Additionally, the sonde housing described above provides proper sonde orientation in an end loading housing that structurally superior to side load configurations that by design weaken the torsional and bending strength of a housing, require complicated closure mechanisms, and/or are more likely to fail. 
     While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art, such changes being embodied within the scope and spirit of the present invention as defined in the appended claims.

Summary:
An apparatus for mounting an electronic device therein for use in an underground boring machine includes an elongated housing having an elongated, lengthwise central cavity opening at one end thereof, a cartridge containing a sonde therein, which cartridge fits in the cavity; and a keying mechanism for securing the cartridge and sonde in a predetermined orientation relative to the housing when the cartridge is inserted into the cavity through the opening. One or more lengthwise fluid passages isolated from the cavity extend through the housing. A sonde housing of the invention may be used with a drill string and bit assembly in directional boring.