Abstract:
A coupling for quickly and easily attaching and detaching stakes from the drive head of a horizontal directional drill. The coupling includes an upper coupler member and a lower coupler member. The lower coupler member slides into the upper coupler member, and a pin in the upper coupler member rotates into opposed, horizontal slots in the lower coupler member.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to horizontal directional drill machines. It relates particularly to the stakedown assembly for a horizontal directional drill machine. 
     BACKGROUND OF THE INVENTION 
     A horizontal directional drill machine is commonly employed for installing pipes beneath the ground and generally parallel to the surface. These machines are used in many different applications and are available in a wide range of sizes. Typical applications where a horizontal directional drill machine might be used include the installation of fiber optic cables, electrical cables, gas lines, water systems, or sewer systems. Horizontal directional drill machines are commonly rated in terms of pull-back capacity. Some machines for smaller applications have as little as five thousand pounds of pull-back capacity. Other machines are available with a pull-back capacity of as much as one million pounds. 
     One alternative to a horizontal directional drill machine is the traditional trencher machine. A trencher machine simply digs a trench into the ground, and after (for example) pipe is laid down in the bottom of the trench, the trench is filled and the pipe is buried. The advantage of a horizontal directional drill machine over a trenching machine is that a pipe can be buried in the ground over long distances without digging a trench. Thus, a horizontal directional drill is particularly desirable when a trench would be difficult or too costly to dig. For example, a horizontal directional drill machine finds particularly advantageous application for installing pipes under roadways, where destruction of the road is expensive and inconvenient to travelers, or under a waterway like a river, where trenching would be impossible. 
     A unique aspect of a horizontal directional drill machine is the special drill head that is attached to the front end of a pipe to be laid. The drill head has an angled shape which allows the operator to change the direction of the pipe after it has entered the ground. Direction changes are achieved by stopping the pipe and drill head rotation and orienting the drill head at a desired angle. Then, by pushing on the drill pipe without rotating it, the drill head and attached pipe will veer in the desired direction. Thus, by effecting directional changes to pipe travel, a pipe might enter the ground at one angle, travel horizontally over a long distance, and exit the ground at another angle. This ability to change the direction of pipe travel also allows the operator to steer the pipe around underground obstacles like boulders. 
     In addition to pushing forces which must be applied to the pipe as it is inserted, it is often necessary to pull back on the pipe. This may be necessary when a direction change is not completely successful on the first attempt, or when an underground obstacle like a boulder is encountered. The machine then pulls the pipe and drill head back to permit a direction change. 
     The push and pull forces that a horizontal directional drill machine must apply to the drill pipe frequently exceed the weight of the machine itself. Therefore, a system is required to anchor the machine and resist these forces. The most common system for anchoring the drill machine comprises the use of stakes mounted on the machine body which are screwed into the ground. The stakes have flighting on their tips and are driven into the ground by applying simultaneous rotational and vertical driving forces to each stake. To drive and remove these stakes, a stakedown assembly is conventionally provided on the end of the drill machine where the drill head enters the ground. 
     A common stakedown assembly in the prior art includes a single drive head which is fixed in one position. This type of stakedown assembly provides a single location, predetermined by the manufacturer, at which a stake can be driven. Other stakedown assemblies, also in the prior art, have two drive heads so that two stakes can be installed into the ground for extra holding strength, or a single stake can be installed in either of the two available locations. Depending on the push-pull forces required and the texture of the ground material, however, a single stake may not be adequate to securely hold the machine in place. Several stakes may be required. The subsurface of the underlying ground may contain obstacles such as large rocks or previously buried pipes or lines which limit the locations where a stake may be installed. So, the two drive head assembly is frequently inadequate. Furthermore, the two drive head assembly is limited in the number of possible stake installation locations and suffers from the higher cost and added complexity associated with the use of dual components. 
     In a recently developed stakedown assembly, however, a single drive head can drive stakes into a variety of locations. This stakedown assembly is described and illustrated in Draney et al. U.S. patent application Ser. No. 09/495,136. This type of stakedown assembly reduces cost by requiring only a single drive head, but also provides added flexibility by allowing multiple stakes to be installed in varying locations. This added flexibility allows the stakes to be optimally placed to avoid underground obstacles and to gain maximum holding strength. 
     Because a variable position drive head assembly, as previously described, must be able to drive several different stakes, the stakes can not be rigidly attached to the drive shaft, but instead must be releasably connected to the drive shaft. It is therefore desirable to have a coupling that will allow quick and easy attachment and detachment of the stakes from the drive head. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a new and improved releasable coupler for coupling stakes and the drive shaft of a stake assembly drive motor. 
     It is another object to provide a coupler which facilitates simple and rapid coupling and decoupling from the stake. 
     According to the invention, the coupler includes an upper coupler member and a lower coupler member. The upper coupler member includes a cylindrical fitting having a cylindrical attachment pocket formed upwardly into its lower end. A pin is installed transversely through the socket and extends. 
     The lower coupler member comprises a cylindrical fitting having an outer diameter which is slightly smaller than the inner diameter of the socket, so as to permit a sliding fit between the two members. 
     The lower coupler fitting has a transverse, vertical slot that extends through, and longitudinally downward, from the top of the member. It has two circumferential horizontal slots which each extend around a portion of the circumference of the lower fitting coupler. The vertical slot intersects the horizontal slots at about the midpoint of the fitting. 
     The lower coupler fitting is fastened to a stake. Its fitting is slidably received upwardly into the upper fitting until the pin in the upper coupler fitting is seated in the bottom of the vertical slot. Then, the upper fitting is rotated on its axis in its driving direction and the fittings are interlocked. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     The invention, including its construction and method of operation, is illustrated more or less diagrammatically in the drawings, in which: 
     FIG. 1 is a side elevational view of a horizontal directional drill, showing the drill in its operating mode; 
     FIG. 2 is a perspective view of a stakedown assembly, with one stake installed into the ground and a second stake positioned under the drive head for installation; and 
     FIG. 3 is a perspective view of the coupling, in a disconnected position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and particularly to FIG. 1, a horizontal directional drill machine is shown generally at  10 . The drill machine  10  includes a frame  12  supported by driven tracks  14  for moving the drill machine  10  from place to place. 
     The drill machine  10  includes a longitudinally elongated boom  16  pivotally mounted on the front end of the frame  12 , as at  17 . A conventional pipe drill assembly  18  is mounted on the boom  16 , extending coextensively therewith. The drill assembly  18  is designed to drill a series of pipe sections P 1 , P 2 , P 3 , et seq., into the ground, in sequence. 
     In the operating mode of the drill machine  10 , the boom  16  is pivoted upward away from the frame  12  so that pipe section P 1  extends from the drill assembly  18  and intersects the ground at an angle. A special drill head (not shown) is attached to the front end of the first drill pipe section P 1 . In order to drill the pipe section P 1  into the ground and make any desired directional changes in its path, a variety of push, pull, and rotational forces are applied to the pipe section P 1  by the drill assembly  18 . The manner in which the drill assembly  18  applies these forces to the drill pipe section P 1  are not described, but are well known to those skilled in the art. 
     As the first pipe section P 1  is drilled into the ground, new pipe sections P 2 , P 3 , et seq., are successively attached to the rear end of the preceding pipe sections. A cartridge  22  of pipe sections P 2 , P 3 , et seq. is provided on the boom  16  for storing these additional pipe sections, and a semi-automatic or fully automatic loader (not shown) may be provided for attaching them to the preceding pipe sections. 
     A stakedown assembly  24  is connected to the front end of the drill machine  10 . The stakedown assembly  24  is connected to the forward end of the boom  16  at a pivot connection  26 , which allows the stakedown assembly to be oriented level with the ground surface when the boom is tilted. 
     Turning now to FIG. 2, a stakedown assembly  24  is shown in greater detail. The stakedown assembly  24  includes a tower  27  mounted on a base plate  32  at a connection  31  which permits the tower  27  to rotate about its vertical axis. A drive head  28  is attached to the tower  27  through a sleeve  30  which permits longitudinal sliding along the tower  27 , and a cantilevered arm  29  on which the drive head  28  is mounted. 
     The lower end of a hydraulic cylinder  36  is pivotally attached to the tower  27 , while the upper end is pivotally attached to the arm  29 . Thus, the arm  29  and drive head  28  can be driven in a vertical direction by the hydraulic cylinder  36 . 
     The base plate  32  has a series of stake locator ports  34  extending vertically through it, for receiving stakes S when they are installed. These ports  34  are arranged in a semi-circular pattern at equal distances from the tower&#39;s  27  axis of rotation. The cantilevered arm  29  extends outwardly over the path of the ports  34  so that the drive head  28  can be positioned over any one of them as the tower  27  is rotated. 
     A drive motor  38  with a vertical output shaft  39  is mounted in the drive head  28  on the free end of the cantilevered arm  29 . By rotating the tower  27 , the output shaft  39  of the motor  38  can be positioned over any one of the guide ports  34 . The tower is rotated manually by the operator. 
     To operate the multiple position stakedown assembly  24 , the desired number of stakes S to be installed, and their placement, is first determined by testing soil conditions and locating any underground obstacles. The drive head  28  is rotated until its cantilevered arm  29  is over a desired guide port  34 , and then locked into position. The bottom end of a stake S is positioned in the desired guide hole  34 , and the top end of the stake S is attached to the drive shaft  39  of the motor  38  with a coupling  48  embodying features of the present invention. 
     Turning now to FIG.  3  and the present invention, the coupling  48  includes the lower coupler member  60  and an upper coupler member  50 . The lower coupler member  60  is mounted on the top end  42  of the stake  30 . The upper coupler member  50  is mounted on the lower end of the drive shaft  39  from the drive motor  38 . 
     The upper coupler member  50  comprises a cylindrical fitting  52 . The cylindrical fitting  52  has an attachment bore  53  formed coaxially in its upper end. A large diameter coupling socket  54  is formed coaxially in its lower end. A coupling pin  55  is mounted in the socket  54 , extending transversely through the fitting  52 . 
     The lower coupler member  60  comprises a cylindrical fitting  62  having a body  63  with an outer diameter slightly smaller than the inner diameter of the socket  54 , so as to provide a sliding fit between the two coupler members  50 ,  60 . A coaxial clearance fore  64  is in the fitting body  63  provided with an inner diameter of immaterial size. A transverse, vertical slot  66  extends through the body  63 , downward from the top end  68  of the fitting body. Two circumferential, horizontal slots  69  extend around opposite sides of the fitting body  63 , at a location displaced from its top end, each extending through an arc of about 160°, i.e., about 80° to each side of the center line of the vertical slot  66 . 
     The coupling  48  is engaged by placing a stake S with an attached lower coupler member  60  directly below the upper coupler member  50 . The drive shaft  39  of the drive motor  38  is then rotated so that the pin  54  in the upper coupler member  50  is aligned with the vertical slot  66  of the lower coupler member  60 . Next, the drive head  28  is lowered, without drive shaft  39  rotation, so that the pin  55  slides into the slot  66 . When the pin  55  has been lowered sufficiently so that it is aligned with the horizontal slot  69 , the drive shaft  39  is rotated until opposite ends of the pin  55  contact the ends of the slot  69 . The stake  30  and the coupling  48  are then ready for the simultaneous rotational and vertical forces necessary to drive the stake  30  into the ground. 
     The driven stake S is then clamped to the base plate  32 . To this end, a cap  40  is installed on each of the stakes S. The cap  40  has an inner diameter clearance hole through its center which is large enough to provide a sliding fit between the cap  40  and the stake S, but is smaller than the lower coupler member  60  which is fixedly attached to the top end of the stake S. Because its outer diameter is larger than that of the guide ports  34 , the cap  40  is sandwiched between the base plate  32  and the lower coupler member  60  when the stake S is fully driven into the ground. 
     After disconnecting the first installed stake S from the drive shaft  39 , additional stakes S can be installed. To do so, the drive head  28  is rotated to a new position and the stake installation process is repeated. 
     While a preferred embodiment of the invention has been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.