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This application claims the priority of U.S. Provisional Application No. 60/174,487, filed Jan. 4, 2000 and U.S. Provisional Application No. 60/203,040, filed May 9, 2000. 
     This application is a divisional of U.S. patent application Ser. No. 09/617,189 filed on Jul. 14, 2000 now U.S. Pat. No. 6,349,778. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to horizontal directional drilling and, in particular, to improvements in bottom hole assemblies for such drilling techniques. 
     PRIOR ART 
     Horizontal directional drilling methods are well known and can offer many advantages over traditional open trench digging operations. There remains a need for greater precision in monitoring and guiding the course of the hole as it is being bored. This need is particularly acute in utility easements and like corridors where pre-existing lines are located often without precision in their placement and “as built” records. 
     As used herein, the terms “sonde” and “monitoring/tracking device” are used interchangeably to mean a device known in the trenchless boring industry as a surveying device for the monitoring and tracking of a bore hole. The term “boring device” refers to equipment such as a rock tricone drill bit, a poly-diamond-crystalline (PDC) bit, or any other device known in the art to drill or lengthen a bore hole. Finally, the terms “entrenching powering device” and “mud motor” are used interchangeably for a device generally known in the art used to rotate a boring device, without turning the drill pipe/drill string, by some type of drilling rig to continue a hole or bore. 
     Known horizontal directional drilling bottom hole assemblies typically include a sonde that transmits electromagnetic signals indicating the pitch (from horizontal), the clock (roll about a horizontal axis clockwise or counterclockwise from a reference of say 12 o&#39;clock), and the depth of the sonde. The sonde also enables a person sweeping the corridor with a receiver or detector to locate the horizontal or lateral position of the sonde in the specified corridor. 
     Because of limitations of current tooling, the transmitter/guidance system or sonde is ordinarily located a considerable distance away from the boring device when an entrenching powering device is used. The sonde may only be as close as about 20 feet and as far as about 50 feet from the boring device. This is due to the fact that an entrenching powering device has generally not been designed to integrate a sonde. The distance between the sonde and the boring device is a major concern for drillers in the utility business, especially when they encounter a job with very restrictive parameters in terms of drilling path. 
     The sonde transmits a signal that indicates where the sonde is located which can be 20 feet+behind the boring device. This type of drilling has been described as driving a car forward, from the back seat looking out the rear window. A driller only “sees” where he has already drilled, not where he is currently drilling. This becomes a major problem if the boring device veers off course and begins boring outside a designated corridor. The operator will not know there is a potential problem until the boring device is 20 feet+off course. If the driller waits longer to see if the boring device steers back on course, the boring device may continue even further off course. This causes a risk that the driller may destroy cable lines, gas lines, or the like and if such destruction occurs it is not only expensive but dangerous as well. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved bottom hole assembly for horizontal directional drilling in which the sonde is carried ahead of the power section of the entrenching powering device or mud motor. In a presently preferred embodiment, the sonde is located in a pocket formed in the wall of a housing of the entrenching powering device that surrounds a bearing mandrel or bit driving shaft. More specifically, the sonde receiving pocket is nestled axially between thrust bearings supporting the mandrel and a flex shaft transmission that couples the power section to the mandrel. This forward location of the sonde greatly improves the accuracy of surveying while boring the hole so as to facilitate placement of the hole and ultimate line in the intended path. 
     The disclosed mounting arrangement for the sonde readily allows the sonde to be adjusted for a proper clock orientation and is somewhat resilient to limit vibrational forces transmitted to the sonde during operation. 
     Other mounting structures for the sonde are disclosed. Each of these structures offers improved boring accuracy over prior art constructions by enabling the sonde to be positioned relatively close to the boring device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a bottom hole assembly and a portion of a trailing drill string; 
     FIGS. 2A through 2D is a longitudinal cross sectional view of a mud motor constructed in accordance with the invention; 
     FIG. 3 is a fragmentary perspective exploded view of a portion of the mud motor and the sonde; 
     FIG. 4 is a transverse cross sectional view of the mud motor taken in the plane  4 — 4  indicated in FIG. 2B; 
     FIG. 5 is a side view, partially in section, of a second embodiment of the invention; and 
     FIG. 6 is a side view, partially in section, of a third embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference particularly to FIGS. 1,  2 A- 2 D,  5  and  6 , parts towards the left are sometimes hereafter referred to as forward parts in the sense of the drilling direction, it being understood that in such figures, the drilling direction is to the left; the rearward or trailing end of such parts, conversely, is shown to the right. The forward direction can be equated with a downward direction and the rearward direction can be equated with an upper direction where drilling is vertical. 
     Referring now to FIG. 1, a bottom hole assembly  10  comprises a boring device or bit  11  and an entrenching powering device or mud motor  12  having its forward end carrying the bit  11 . A drill string  13  is coupled to a trailing end  14  of the mud motor  12  in a conventional fashion. 
     The mud motor  12 , as shown in FIGS. 2A-2D includes a hollow cylindrical bearing mandrel  18  having a central through bore  19 . The bit  11  is coupled to a bit box  21  formed in the forward end of the bearing mandrel  18 . Thus, the bearing mandrel  18  is enabled to drive the bit  11  in rotation and to transmit thrust from the drill string  13 . 
     Adjacent its forward end  22 , the bearing mandrel  18  is rotationally supported in a lower tubular cylindrical housing  23  by a set of radial bearings  24 . A conical shoulder  28  of the bearing mandrel  18  is received in a conical bore  29  of a radial ring  31 . A radial face of the ring  31  is arranged to abut an adjacent one of the set of radial bearings  24 . Male threads  36  of the lower or forward housing  23  couple with female threads  38  in a forward end  39  of an elongated hollow circular outer housing  41 . 
     Sets of thrust bearings  44 ,  46  are assembled on a carrier nut  47  at opposite sides of an annular flange  48 . The carrier nut  47  is threaded onto an externally threaded part  49  of the bearing mandrel  18 . The carrier nut  47  is locked in position on the bearing mandrel  18  by set screws  51  spaced about the periphery of the flange  48 . 
     Sleeve bearings  53 , of suitable self-lubricating material such as the material marketed under the registered trademark DU® are received in counterbores  54  formed in the outer housing  41  and serve to rotationally support the mid and trailing length of the bearing mandrel  18 . A longitudinal bore  56  in the surrounding outer housing  41  provides clearance for the main length of the bearing mandrel  18 . 
     An annular piston  59  floats on a rearward part of the mandrel  18  in a counterbore  61  in the outer housing  41 . The piston  59  retains lubricant in the annular zones of the bearings  53 ,  44  and  46 . A circular bearing adapter  62  is threaded onto the rear end of the bearing mandrel  18 . A plurality of holes  63  distributed about the circumference of the adapter  62  are angularly drilled or otherwise formed in the adapter to provide mud flow from its exterior to a central bore  64  of the adapter. As shown, the central bore  64  communicates directly with the bore  19  of the bearing mandrel  18 . The bearing adapter  62  is radially supported for rotation in a sleeve-type marine bearing  66  assembled in a counter bore  67  in a rear portion of the outer housing  41 . Ports  68  allow flow of mud through the marine bearing  66  for cooling purposes. 
     A flex shaft  71  rotationally couples a rotor adapter  72  to the bearing adapter  62 . At each end of the flex shaft  71  is a constant velocity universal joint  73  comprising a series of circumferentially spaced balls  74  seated in dimples in the flex shaft and in axially extending grooves in a skirt portion  76  of the bearing adapter  62  or skirt portion  77  of the rotor adapter  72 . Each coupling or universal joint  73  also includes a ball  78  on the axis of the flex shaft and a ball seat  79  received in the respective bearing adapter  62  or rotor adapter  72 . Each universal joint  73  includes a bonnet  81  threaded into each of the skirts  76  or  77  to retain the joints or couplings  73  in assembly. Cylindrical elastomeric sleeves  82  are disposed within each of the bonnets  81  to retain grease in the area of the balls  74 ,  78  and to exclude contamination from this area. A cylindrical tubular flex housing  84  surrounds the flex shaft  71  and is fixed to the rear end of the outer housing  41  by threading it into the latter at a joint  86 . The flex housing  84  is bent at a mid plane  87  such that the central axis at its rear end is out of alignment with its central axis at its forward end by a small angle of, for example, 2°. At its rearward end, the flex housing  84  is fixed to the stator or housing  88  of a power section  89  of the mud motor  12  by a threaded joint  91 . The stator  88  is a hollow internally fluted member in which operates an externally fluted rotor  92 . The power section  89  formed by the stator  88  and rotor  92  are of generally known construction and operation. The rotor adapter  72  is threaded into the forward end of the rotor  92  to rotationally couple these members together. The drill string  13  is threaded on the rear end of the stator with or without the use of an adapter. The flex shaft  71  converts the rotational and orbital motion of the rotor  92  into plain rotation of the bearing mandrel  18 . 
     Referring particularly to FIGS. 3 and 4, the outer housing  41  is formed with a pocket or elongated recess  101  rearward of the thrust bearing units  44 ,  46 . The pocket  101  is milled or otherwise cut out of the wall of the outer housing  41  with an included angle of 90° in the plane of FIG. 4 transverse to the longitudinal axis of the housing  41 . Surrounding the pocket  101  is a relatively shallow seat or recess  102  similarly cut into the wall of the housing  41 . When viewed in the plane of FIG. 4, this seat has a cylindrical arcuate surface area  103  concentric with the axis of the housing  41  and radially extending surfaces  104 . 
     An elastomeric sarcophagus  106  of polyurethane or other suitable material has exterior surfaces generally conforming to the surfaces of the pocket  101 . The sarcophagus  106  is configured with a round bottom slot  107  for receiving a sonde  108 . More specifically, the slot  107  is proportioned to receive a standard commercially available sonde of a size which, for example, can be 1¼″ diameter by 19″ long. It is understood that the sarcophagus may be configured with a slot to fit sondes of other standard sizes such as 1″ diameter by 8″ long or a secondary sarcophagus may be provided to increase the effective size of a smaller sonde to that of the larger size. An arcuate cover plate  109  of steel or other suitable material is proportioned to fit into the area of the seat  102  to cover and otherwise protect the sonde  108  from damage during drilling operations. The cover  109  is proportioned, when installed in the seat  102 , to provide an outer cylindrical surface  111  that lies on the same radius as that of the outer cylindrical surface of the housing  41  surrounding the pocket or slot  101 . The cover  109 , is provided with a plurality of longitudinal through slots  112 , to allow passage of electromagnetic signals transmitted from the sonde  108 . The slots  112  are filled with non-metallic material such as epoxy to exclude contaminates from passing into the pocket  101  or otherwise reaching the sonde  108 . Additionally, for purposes of allowing the sonde to transmit signals over a wide angle, the body of the housing  41  is drilled with holes  113  which are filled with epoxy or other non-metallic sealant. A shallow groove  114  is cut in a generally rectangular pattern in the surface  103  around the pocket  101  to receive an O-ring seal  116 . 
     The round bottom slot or groove  107  in the sarcophagus is dimensioned to provide a friction fit with the sonde  108 . This permits the sonde  108  to be rotated or rolled on its longitudinal axis to “clock” it by registering its angular orientation relative to the plane of the bend in the flex housing  84  as is known in the art. 
     The cover or plate  109  is retained in position over the sonde  108  by a plurality of screws  117  assembled through holes  118  in the cover and aligned with threaded holes  119  formed in the outer housing  41 . The screw holes  118 ,  119  are distributed around the periphery of the cover  109 . The O-ring  116  seals against the inside surface of the cover  109  to exclude contaminates from entering the pocket  101  during drilling operations. 
     The sarcophagus  106  is proportioned so that it is compressed by the cover  109  around the sonde  108  when the screws  117  draw the cover tight against the seat surface  103 . This compression of the sarcophagus  106  increases its grip on the sonde  108  so that the sonde is locked in its adjusted “clocked” position. The elastomeric property of the sarcophagus  106 , besides enabling it to resiliently grip the sonde when compressed by the cover  109 , can serve to cushion the sonde  108  from excessive shock forces during drilling operation. 
     Other resilient mounting structures for the sonde  108  are contemplated. For example, the sonde  108  can be retained in the pocket  101  by resilient steel straps arranged to overlie the sonde as it lies in the pocket  101 . The straps can be retained in place by suitable screws or other elements. 
     When the mud motor  12  is operated, mud or water passing between the stator  88  and rotor  92  travels through the transmission and bearing sections of the mud motor bounded by the flex housing  84 , outer housing  41 , and lower housing  23  and is delivered to the bit  11 . More specifically, the mud flows through the annulus between the flex shaft  71  and an inner bore  120  of the flex housing  84 . From this annulus, the mud enters the central bore  64  of the bearing adapter through the angularly drilled holes  63 . The mud flows from this bore  64  through the axial bore  19  in the bearing mandrel  18 . 
     From the foregoing description, it can be seen that the disclosed arrangement in which the sonde is received in the wall of a main housing part, namely the outer housing  41 , the sonde can be disposed quite close to the bit  11  with minimal hardware and without complexity. As seen, the flow of mud from the power section  89  to the bit  11  is unrestricted and the diameter of the transmission section is not unnecessarily enlarged beyond that which is already required for the necessary bearings and other componentry. By locating the sonde  108  close to the bit  11 , much greater accuracy in monitoring and tracking the progress of the boring process over that possible with the prior art is achieved. 
     Operation of the mud motor to steer the pipe string along its desired path will be evident to those skilled in the art. Typically, to adjust the direction of the bore, the drill string is rotated to point the bit in the direction of the needed adjustment. The orientation of the bit is transmitted to a surface receiver by the sonde. The drill string is held against rotation while the mud motor rotates the bit and the drill string is thrust forward to redirect the direction of the bore. The disclosed mud motor provides a unique function that is enabled by the provision of the forward set of thrust bearings  44 . These bearings  44  allow the mud motor to operate to rotate the bit  11  when the drill string is being pulled out of the hole so that during this withdrawal process the hole is conveniently reamed or enlarged with a hole opening device. 
     FIGS. 5 and 6 illustrate additional embodiments of the invention. Parts like those described in connection with the embodiment of FIGS. 1-4 are designated with the same numerals. In FIG. 5, a tubular cylindrical collar  126  housing the sonde  108  is assembled around a housing  127  that corresponds to the outer housing  41  of the embodiment of FIGS. 1-4. The collar  126  is formed of steel or other suitable material. The collar  126  is fixed longitudinally and angularly relative to the housing  127  by set screws  128  threaded into the wall of the collar  126  and received in blind holes  129  drilled in the wall of the housing  127 . The sonde  108  is received in the sarcophagus  106  and protected by the cover  109  as previously described. Various other techniques, besides the set screws  128 , can be used to fix the collar  126  on the housing  127 . The collar  127  can be threaded onto the housing  127  where the housing, for example, is provided with external threads and a stop shoulder. Another technique is to weld the collar  126  to the housing  127 . If desired or necessary, the sonde  108  can be assembled in a hole aligned with the axis of the collar  126  and open at one end. The opening can be plugged with a suitable closure during use. 
     FIG. 6 illustrates another embodiment of the invention. A coupler  131  is disposed between the bearing mandrel  18  and the bit  11 . The coupler  131  has external threads mated with the bit box  21  and internal threads receiving the bit  11 . The coupler  131  is formed with the pocket  101  for receiving the sonde  108 . The coupler  131  has a central bore for conveying mud from the bearing mandrel  18  to the bit  11 . If desired, an axially oriented hole can be used instead of the open face pocket  101  to receive the sonde  108  and the hole can be plugged by a suitable closure. Still further, if it is desired to locate the sonde  108  at the center of the coupler  131 , water corsets or passages can be drilled or otherwise formed axially through the coupler and circumferentially spaced about the sonde to allow mud to pass through the coupler. 
     While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.

Summary:
A bottom hole assembly for horizontal directional drilling that improves the accuracy of surveying while boring by enabling the progress of the bore to be monitored and tracked with the aid of a sonde. In one embodiment the sonde is received in the wall of a housing area of a mud motor surrounding the bearing mandrel, in another embodiment the sonde is carried in the wall of a collar surrounding the bearing mandrel housing, and in an additional embodiment the sonde is carried in an adapter between the bearing mandrel and the bit.