Abstract:
The subject matter of this invention is an underground directional drilling tool which is particularly effective in drilling rock and highly compacted soil formations. This tool is an improvement upon the tool developed by Applicants and patented in U.S. Pat. No. 6,050,350. The current invention utilizes ball bearings contained within subassemblies positioned at each end of the steering tool. This allows the steering tool to float upon the subassemblies as the inner core and drive shaft rotate within the subassemblies and steering tool, thereby reducing rotational torque transfer from the drill string, subassemblies and drive shaft to the housing of the directional drilling tool. The use of the ball bearing containing subassemblies improves underground stability and, thus, steerability during the forward drilling operation. Further, these improved features reduce wear thereby increasing durability of the tool which is used in the harsh underground environment.

Description:
BACKGROUND OF INVENTION 
     The use of directional horizontal underground drilling has become increasingly effective and more widely accepted for the installation of water and gas pipes, underground utilities, telephone lines, and cables. Prior to the use of these horizontal drilling techniques, open trenches were generally required to place pipes, cables and wires underground. With such trenches, particular difficulties were encountered in crossing bodies of water, roads, driveways, improved areas, or existing underground utility installations. Accordingly, horizontal directional drilling techniques have allowed for the elimination of open trenches in many situations, particularly when encountering obstacles at or near the surface. 
     With the development of these horizontal drilling techniques, there has been an historic need to develop a more precise and cost effective system to effectively control the route of travel, depth of travel, and point of emergence for the drilling apparatus. In response to these needs, a drill radio-transmitting unit was developed and incorporated into the underground directional drilling apparatus to broadcast a remote signal to aid in identifying the direction of travel, depth of the drilling apparatus, orientation within the borehole of the drilling apparatus, and inclination of the drilling apparatus. The development of drill transmitting units, in turn, created a demand for resilient housing to contain and protect transmitting equipment which was located near the leading or cutting end of an underground directional drilling tool. Further, greater demand was created for more precise directional control of the boring operation. 
     When in use, the area of underground drilling is an extremely hostile environment. As such, a desirable underground directional drilling tool should be sufficiently durable to operate within this hostile environment over an extended period of use and an extended product life. Additionally, there remains a continuing need to improve the efficiency of the tool in stabilizing, positioning and controlling the drill bit in downhole operations. It is therefore an object of the present invention to provide a tool for use with directional drills, which tool is efficient in stabilizing, positioning and controlling the direction, depth, orientation and inclination of the drilling operation. 
     The applicant has previously developed and patented an improved underground directional drilling tool having an improved method for control. As discussed in the inventor&#39;s U.S. Pat. No. 6,050,350, which is incorporated herein by reference, there has been and continues to be a need for durable, steerable underground drilling apparatus of simple construction. Simple construction is important to allow for ease of repair, reduction of downtime associated with repair, and minimization of repeated removal of the apparatus from the down hole work area in order to implement repairs. The &#39;350 patent describes an underground directional drilling tool wherein the drive shaft is offset from the centerline of a transmitter housing thus causing the rotation of the drill bit to cut an arcuate path. An overall travel path that is generally straight or that lies in a generally desired route may be formed through periodic rotation of the tool housing, thus changing the immediate arcuate path. As explained in the &#39;350 patent, this design includes a jaw clutch and simple engagement of the housing when the drill string is pulled back. When the housing is so engaged, it may be conveniently rotated through manipulation of the drill string. In this manner, the invention of the &#39;350 patent provides for a simple, reliable, and durable construction that eliminates the need for complex steering devices, motors, and controls. The invention of the &#39;350 patent therefore serves the objective not only of providing a resilient transmitter housing, but it provides a multi-purpose tool that effectively accomplished the objectives of simplicity, durability, and longevity that are important in the hostile, underground environment. The tool also provides a method for steering the tool. In order to pass the torque of the drill string through the tool housing to the drill bit, the &#39;350 housing incorporates a cylindrical bearing in each end of the housing and a cylindrical thrust bearing at the rear. In the &#39;350 housing, the cylindrical thrust bearing and cylindrical bearings carry rotational torque from the driveshaft to the transmitter housing. This creates significant wear on the bearings requiring frequent maintenance and replacement. Further, the rotational torque carried by these bearings to the tool housing creates instability in downhole use that makes directional control more difficult. 
     The present invention, generally referred to herein as the underground directional drilling tool, seeks to improve in these areas by maintaining simplicity in design, while eliminating the cylindrical bearings in each end of the housing and, further, eliminating the thrust bearing positioned at the rear of the housing. As with the invention of the &#39;350 patent, the housing is offset from the centerline of the drill bit. The new design represented by the present invention reduces the rotational torque transferred from the drive shaft to the offset transmitter housing. Effective use of subassembly bearings allows the drive shaft and rotational components of the subassemblies to operate independently of the direction-controlling, offset transmitter housing as the offset transmitter housing floats on the non-rotating outer sleeve of the subassemblies. It is therefore an object of the present invention to eliminate the bearings in each end of the offset transmitter housing and eliminate the cylindrical thrust bearing that pushes the offset transmitter housing by positioning bearings in the subassemblies located at each end of the housing. These subassemblies are threadably connected to each end of the drive shaft passing through the offset transmitter housing. The housing then floats on the non-rotating outer sleeve of each of the subassemblies independent from the rotating drive shaft. 
     SUMMARY OF INVENTION 
     The underground directional drilling tool includes-a rear subassembly and a front subassembly that allow an offset transmitter housing to float on the non-rotating outer sleeves of each of the subassemblies without the use of bearings in or on the housing. Rather, the subassemblies are composite elements. Rear radial bearings and radial thrust bearings are constrained between the rear inner core and the rear outer sleeve of the rear subassembly. This eliminates the cylindrical bearings and cylindrical thrust bearings that were subjected to high wear. Also, the rear subassembly accommodates the drill string and the drive shaft, and provides for the transmission of drilling fluid and torque there between while maintaining a non-rotating rear outer sleeve for advancing the housing as the drilling progresses. Since the rear outer sleeve does not rotate as it advances the offset transmitter housing, it does not transfer significant torque to the housing. 
     The front subassembly includes a front inner core having a jaw clutch, which core is adapted to couple the drive shaft and a drill bit. Forward radial bearings are constrained between the front inner core and a front outer sleeve to, again, provide a front subassembly with an outer sleeve that is rotationally independent of the drive shaft and that is able to engage and disengage the offset transmitter housing. In both subassemblies, the bearings are better sealed and longer wearing as compared to the use of thrust bearings or cylindrical bearings positioned directly upon the offset transmitter housing in the tool represented by the &#39;350 patent. 
     The offset transmitter housing has a seal affixed to the front and a seal affixed to the rear that slide over the exterior of the front and rear subassemblies to prevent drill cuttings and other debris from entering the tool. Longitudinal manipulation of the drill string may be used to engage and disengage the jaw clutch. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a cut-away side perspective view of the underground directional drilling tool. 
     FIG. 2 is a cross-section view of the line AA in FIG.  1 . 
     FIG. 3 is a cross-section view of the line BB in FIG.  1 . 
     FIG. 4 is a cut-away view of the rear subassembly. 
     FIG. 5 is an angled side view of the rear outer sleeve. 
     FIG. 6 is a cut-away view of the rear outer sleeve. 
     FIG. 7 is an angled side view of the rear inner core. 
     FIG. 8 is a cut-away view of the rear inner core. 
     FIG. 9 is an angled side view of the rear seal nut. 
     FIG. 10 is a cut-away view of the rear seal nut. 
     FIG. 11 is a cut-away view of the front subassembly. 
     FIG. 12 is an angled side view of the front outer sleeve. 
     FIG. 13 is a cut-away view of the front outer sleeve. 
     FIG. 14 is an angled side view of the front inner core. 
     FIG. 15 is a cut-away view of the front inner core. 
    
    
     DETAILED DESCRIPTION 
     In its preferred embodiment, and referring first to FIG. 1, the present invention, an underground directional drilling tool, is comprised of a drive shaft  4 , a offset transmitter housing  3 , a rear subassembly  40 , and a front subassembly  60 . The drill string  2  runs from the surface power unit down hole to the underground directional drilling tool  1 . The drill string  2  is generally hollow and rotatable, and delivers torque and drilling fluid to the down hole operation. The drill string  2  connects to the rear subassembly  40  which, in turn, is connected to the drive shaft  4  passing through the offset transmitter housing  3 . The drive shaft  4  is next connected to the front subassembly  60  which, in turn, is connected to the drill bit  10 . The rotational energy is transferred from drill string  2  through the offset transmitter housing  3  by way of the drive shaft  4  to the drill bit  10  to allow for down hole drilling operations. 
     More specifically, the drill string coupling  48  connects the drill string  2  to the rear subassembly  40 . The drill string  2  has a forward end  19 , preferably threaded, that enters a rear inner core  41  of the rear subassembly  40  and engages, preferably through threaded engagement, the rear drill string coupling  48  of the rear subassembly  40 . The rear inner core  41  of the rear subassembly  40  has a rear drive shaft coupling  49  that contains a forward facing enlarged cavity to engage the drive shaft  4  rearward end. Although threaded engagement is preferred, the engagement of the drill string  2  and the drive shaft  4  may be by any convenient means that will allow secure connection of these elements and transmission of torque between the drill string  2  to the drive shaft  4 . Finally, the rear inner core  41  has a central cavity  21  formed therein that is adapted to allow the transmission of drilling fluid between the drill string  2  and the drilling fluid passageway  50  of the drive shaft  4 . The front of the drive shaft  4  connects to the front inner core  61 , preferably by means of threadable engagement, by way of the front drive shaft coupling  67 . The drill bit  10  preferably threadably engages the drill bit coupling  68  positioned at the front of the front inner core  61 . Like the rear inner core  41 , the front inner core has a central cavity  69  formed therein that is adapted to allow the transmission of drilling fluid between the drilling fluid passageway  50  of the drive shaft  4  and the drill bit  10 . 
     The drive shaft  4  is a longitudinally extended member that is housed in an off-center, longitudinal cavity  20  that is formed within the offset transmitter housing  3 . As explained generally in the &#39;350 patent, and as utilized in the current invention and explained herein, an offset transmitter housing  3  provides a variety of functions to the underground directional drilling tool  1 . First, it houses the transmitter  11 , which sends information to the operator pertaining to the direction, depth, orientation, and inclination of the underground directional drilling tool as the down hole drilling operations progress. Secondly, and as explained in the &#39;350 patent, affixed to the exterior of the offset transmitter housing  3  are front stabilizing fins  6  and rear stabilizing fins  7  that function to provide frictional surface areas to prevent the unwanted rotation of the offset transmitter housing  3  and to hold the offset transmitter housing  3  in a stable orientation within the borehole, thus steering the direction of the forward drilling operation. In the present invention, the subassemblies  40 ,  60  serve to minimize rotational torque to the offset transmitter housing  3  due to the rear outer sleeve  42  and the front outer sleeve  62  remaining stationary in relation to the offset transmitter housing  3 . Through relocation of the bearing-housing function from the offset transmitter housing  3  to the subassemblies  40 ,  60 , as explained more fully below, the offset transmitter housing  3  is floating on the rear outer sleeve  42  and the front outer sleeve  62  and is less prone to rotation. 
     The drive shaft  4  may be solid and inflexible. In the preferred embodiment, however, it has a hollow interior forming the drilling fluid passageway  50 , while still maintaining sufficient stiffness to resist flexion or bowing during forward drilling operations. The drilling fluid passageway  50  carries pressurized drilling fluid. Small fluid holes  18  placed in the drive shaft  4  extend to the drilling fluid passageway  50  and allow for the escape of drilling fluid into the drive shaft cavity  20 . This drilling fluid functions to cool, lubricate, and flush the annular space within the drive shaft cavity  20  that separates the drive shaft  4  and the interior of the offset transmitter housing  3 , and to provide a continuous washing action to remove debris from the area of the drive shaft  4 , and jaw clutch  8 . 
     Although preferred to be generally circular in nature, the wide side of the offset transmitter housing  3  retains a cover plate  12  closing off the cavity in which the transmitter  11  is housed, and the narrow side of the offset transmitter housing  3  is the side nearest to the drive shaft  4  passing through it. The function of the transmitter  11  is to transmit information to the operator on the position, direction, orientation and inclination of the underground directional drilling tool  1 . This information is used by the operator to steer the forward drilling operation. Other forms of sending units may be used which include transmission means by way of wires running from the surface to the offset transmitter housing  3 . The cover plate  12  retaining the transmitter within the cavity in the side of the offset transmitter housing  3  in conjunction with the transmitter windows  17  allows the signal to readily pass through the offset transmitter housing  3  to be received at the surface. 
     Stabilizer fins  6  are located on the side wall furthest from the drive shaft  4  near the front of the offset transmitter housing  3 , and stabilizing fins  7  are also located on the opposing side wall of the offset transmitter housing  3  near the rear. The stabilizing fins  6 ,  7 , operate to center the offset transmitter housing  3  in the borehole and provide a ready pathway for the flow of drilling fluid and cutting debris past the underground directional drilling tool  1 . The cutting debris and the drilling fluid that flows past the stabilizing fins  6 ,  7 , operate to provide a medium with additional frictional resistance to prevent unwanted rotation of the offset transmitter housing  3 , thereby maintaining the offset transmitter housing  3  in a stable position. This stable position is maintained even when drilling through solid rock. Use of the rear stabilizing fins  7  is preferred to assist in centering the offset transmitter housing  3  within the borehole, and helping to maintain the offset transmitter housing  3  in a stable position. 
     The front subassembly  60  of the underground directional drilling tool  1  in combination with the rear subassembly  40  allow the offset transmitter housing  3  to “float” on the rear outer sleeve  42  and the front outer sleeve  62 . This floating positioning aides in the stabilization of the offset transmitter housing  3  through elimination of the positioning of bearings within and against the offset transmitter housing  3 . In prior versions of this tool, the bearings positioned within and against the offset transmitter housing  3  transferred larger amounts of rotational torque to the offset transmitter housing  3  thereby causing the offset transmitter housing  3  to rotate. This new invention allows the rear outer sleeve  42  to remain stationary against the rear seal  15 , and the front outer sleeve  62  to remain stationary against the front seal  14  while the drive shaft  4  rotates. The offset transmitter housing  3  thereby “floats” while drilling and shifting operations are in progress. 
     The offset nature of the drive shaft  4  passing through the offset transmitter housing  3  operates to position the drill bit  10  above the centerline of the offset transmitter housing  3 . As long as the offset transmitter housing  3  remains stationary down hole, the drill bit  10  will cut a pathway with a constant curvature away from the wide side of the offset transmitter housing  3 . The orientation of the underground directional drilling tool is accomplished by use of jaw clutch  8  at the connection between the offset transmitter housing  3  and front subassembly  60 . The jaw clutch  8  utilizes a plurality of teeth and notches. When forward thrust is applied, the jaw clutch  8  is disengaged by the drive shaft  4  sliding forward through the offset transmitter housing  3  until the rear outer sleeve  42  of the rear subassembly  40  comes into contact with the back of the offset transmitter housing  3 . This allows the front inner core  61  and the fixed sleeve  63  of the front subassembly  60 , and the attached drill bit  10 , to spin freely without the transfer of significant rotational torque to the offset transmitter housing  3 , thus allowing the housing to be rotationally independent of the drive shaft  4  when the jaw clutch  8  is disengaged. 
     In order to steer or alter the course of the drill head, the operator merely pulls back on the drill string  2  a short distance so as to engage the jaw clutch  8  and thereby expose the housing to torque transfer from the drill string  2  through the drive shaft  4 . The jaw clutch  8  is comprised of a rearward segment  22  and a forward segment  23 . Each segment  22 ,  23  of the jaw clutch  8  is beveled to facilitate engagement and allow for the ready removal of cuttings and debris from the engaging surfaces. After engagement of the rearward segment  22  and the forward segment  23  of the jaw clutch  8 , the operator rotates the drill string  2  the desired number of degrees so as to reposition the offset transmitter housing  3  within the hole. In this fashion the operator may turn the pathway of drilling in any direction without the need of an external steering sleeve or complex mechanism to cam the drill head. This affords the operator the ability to make quick and precise alterations in the direction of the drilling pathway. 
     The preferred rear subassembly  40  is illustrated in FIG. 4, with the preferred components thereof illustrated in FIG. 5 through 10. The rear subassembly  40  is comprised of a rear outer sleeve  42 , a rear inner core  41 , and a rear seal nut  43 . In the preferred embodiment the rear seal nut  43  is threadably engaged to the exterior of the rear inner core  41 , which threadable connection facilitates disassembly in the event of the need for maintenance. As shown in cut-away fashion by FIG. 4, the rear outer sleeve  42  and rear inner core  41  are mated so that the rear inner core  41  rotates inside the rear outer sleeve  42  on a plurality of radial bearings  46  positioned within bearing races  24  located within the outer wall of the rear inner core  41  and the inner wall of the rear outer sleeve  42 . In the preferred embodiment, ball bearings are employed for both the radial bearings  46  and radial thrust bearings  47 . In this manner, when the drill string  2  is threadably engaged in the drill string coupling  48  of the rear subassembly  40 , rotation of the drill string  2  causes the rear inner core  41  to rotate upon the bearings  46 ,  47  held between the rear inner core  41  and the rear outer sleeve  42 , thus allowing the rear outer sleeve  42  to remain stationary. In the preferred embodiment, grease fittings are provided in the rear subassembly  40  to allow lubrication of the bearings  46 ,  47  and the annular space that exists between the components of the rear subassembly  40 . Also, located on the forward portion of the interior wall of the rear seal nut  43  is the nut seal  44 , while the rear driveshaft seal  45  is located on the forward portion of the interior wall of the rear outer sleeve  42 . The nut seal  44  and the rear driveshaft seal  45  operate to prevent the infusion of drilling fluid and debris into the bearing races  24 . In further examination of FIG. 1, it may be observed that the rear portion of the offset transmitter housing  3  has a rear seal cover  13  which is a circumferential cover into which the rear outer sleeve  42  of the rear subassembly  40  is positioned. The rear seal cover  13  is affixed to the rear of the offset transmitter housing  3 . This is usually accomplished by either machining the rear seal cover  13  as an integral part of the offset transmitter housing  3  or by having the rear seal cover  13  made separately and affixed by welding or bolting the rear seal cover  13  into position at the rear of the offset transmitter housing  3 . The welding method is preferred for ease of manufacture. Near the rearward inner wall of the rear seal cover  13  is positioned the rear seal  15 . The rear seal  15  is made of elastic material of sufficient stiffness so as to frictionally prevent undesired rotation of the rear outer sleeve  42  during actual downhole drilling operations, and it also serves to prevent cuttings and debris from entering into the drive shaft cavity  20 . Small amounts of unwanted rotational torque play upon the rear outer sleeve  42  as a result of its contact with the bearing assemblies  46 ,  47 , the nut seal  44 , and the rear driveshaft seal  45 . In actual operation, when the operator retracts the drill string  2  to engage the jaw clutch  8  for purposes of orienting or reorienting the offset transmitter housing  3 , the forward portion of the rear outer sleeve  42  does not pass rearwardly past the location of the rear seal  15 . When forward drilling is progressing, the rear outer sleeve  42  remains stationary and is positioned approximately as shown in FIG. 1, and the forward portion of the rear outer sleeve  42  pushes the offset transmitter housing  3  forward as drilling progresses. As forward drilling operations proceed, the primary forward thrust is transferred directly from the drill string  2  to the drive shaft  4  by way of the drill string coupling  48 . 
     With reference now to FIG. 11, the front subassembly  60  is illustrated. The front subassembly  60  is comprised of a front inner core  61 , front outer sleeve  62 , and fixed sleeve  63 . The rearward portion of the front inner core  61  contains the notches or teeth of the forward segment  23  of the jaw clutch  8 . Also at the rear side of the front inner core  61  is an enlarged cavity that is adapted to receive a forward end of the drive shaft  4  and serve as a front drive shaft coupling  67 . As with the rear subassembly  40 , the means for engagement of the drive shaft  4  may be any convenient engagement means that may maintain a secure engagement during rotation of the drive shaft  4 , but threaded engagement is preferred. The front side of the front inner core  61  also contains an enlarged cavity that is adapted to receive the rearward portion of the drill bit  10  and serve as a drill bit coupling  68 . The drill bit coupling  68  preferably employs threaded means for engaging the drill bit  10 . A front subassembly fluid cavity  69  is formed between the front drive shaft coupling  67  and the drill bit coupling  68  to provide for the transmission of drilling fluid from the drilling fluid passageway  50  to the drill bit  10 . The exterior wall of the front inner core  61  has a plurality of bearing races  24  integrally formed therein, and corresponding bearing races  24  are integrally formed in the inner wall of the front outer sleeve  62 . The front outer sleeve  62  is disposed around the front inner core  61  beginning at the rearward portion of the front inner core  61 , but does not extend the entire length of the front inner core to completely cover it. A fixed sleeve  63  is positioned forward of the front outer sleeve  62  and is securely fastened by welding or other means to front inner core  61 . As a result of this configuration, the front outer sleeve  62  may spin freely about the front inner core  61  on the plurality of radial bearings  65  positioned in the bearing races  24  correspondingly formed in each component. As with the rear subassembly  40 , ball bearings are preferred. Bearing seals  64  are located near the front and rear inner wall of the front outer sleeve  62  to retain grease and prevent the infusion of drilling fluid and debris into the bearing races. In the preferred embodiment grease fittings are provided in the front subassembly  60  to allow lubrication of the radial bearings  65 . 
     As observed at the rear of the offset transmitter housing  3 , a seal cover is also located at the front. Like the rear seal cover  13 , the front seal cover  14  is circumferential and may be either machined as an integral part of the offset transmitter housing  3  or made separately and welded or bolted into place. The welded method is, again, preferred. Positioned in the forward portion of the interior wall of the front seal cover  14  is the front seal  16 . The front seal  16  is made of elastic material of sufficient stiffness so as to frictionally prevent unwanted rotation of the front outer sleeve  62  during actual downhole drilling operations, and it also serves to prevent cuttings and debris from entering into the drive shaft cavity  20 . As with the rear assembly  40 , small amounts of unwanted rotational torque play upon the front outer sleeve  62  as a result of its contact with the radial bearings  65  and the bearing seals  64 . In actual operation when engaged in forward drilling, the rearward portion of the front outer sleeve  62  does not pass beyond the front seal  16 . When forward drilling is progressing, the front outer sleeve  62  remains stationary and is positioned approximately as shown in FIG.  1 . As forward drilling operations proceed, the primary forward thrust is transferred directly from the drive shaft  4  to the front inner core  61  by way of the front drive shaft coupling  67  and then transferred to the drill bit  10  by way of the drill bit coupling  68 . 
     In its preferred embodiment, on the inner wall of the front seal cover  14 , immediately rearward of the front seal  16 , there is located a forward flange  70 . As preferred, the forward flange  70  is created upon the machining of the front seal cover  14 , and is positioned so that it is located equal distance from the radial bearings  65  when the front subassembly is forwardly extended during the drilling operation. The forward flange  70  serves to decrease the gap between the interior wall of the front seal cover  14  and the exterior wall of the front outer sleeve  62 . In so doing the forward flange  70  serves four purposes. First, in actual drilling operations, there is constant stress that acts to apply radial load to the drill bit  10  and front subassembly  60 . The forward flange  70  reduces the play of the front subassembly  60  by operating as a ledge against which the front outer sleeve  62  comes into contact as drilling is proceeding. The second function of the forward flange  70  in its positioning in relation to the radial bearings  65  is to extend the life of the radial bearings  65  by acting as a point of contact to center the radial load between the bearing races  24  in which the radial bearings  65  are located. A third function of the forward flange  70  is to aid in positioning the moving parts of the underground directional drilling tool  1  away from the wall of the borehole. The fourth function of the forward flange  70  is to assist the front seal  16  in providing frictional grip on the front outer sleeve  62  to thereby prevent the unwanted rotation of the sleeve. 
     As preferred, a rearward flange  71  is located on the inner wall of the rear seal cover  13 . As with the forward flange  70 , the rearward flange  71  is machined as an integral part of the rear seal cover  13 , and is positioned so as to be centered between the radial bearings  46  when forward drilling is occurring. The rearward flange  71  accomplishes much the same four functions as are accomplished with the forward flange  70 . 
     Having thus described the invention in connection with the preferred embodiments thereof, it will be evident to those skilled in the art that various revisions can be made to the preferred embodiments described herein without departing from the spirit and scope of the invention. It is our intention, however, that all such revisions and modifications that are evident to those skilled in the art will be included within the scope of the following claims.