Abstract:
An articulated, modular, track-mounted, self-propelled, remote-controlled drilling apparatus is demountable into several heli-transportable components, including a drilling module and a drill support module, plus separate hydraulically-driven track carriages on which they are removably mountable. The track carriages are demountably coupled in tandem by a tri-axially articulated hitch mechanism incorporating a track steering mechanism. The drilling module carries a rotary drill, a hydraulic pump operatively connected to the track drive mechanisms, and a primary motor, which selectively drives either the drill or the pump. The use of multiple demountable modules reduces the weight of the components to be heli-transported, thus allowing the use of smaller and more economical helicopters. The combination of self-propelled, track-mounted modules with tri-axial articulation and remote controllability enables the assembled apparatus to operate more easily over rough terrain than known seismic drills, reducing or eliminating the need for separate means for transporting the apparatus between borehole locations.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates in general to apparatus for drilling into subsurface soil formations, and in particular relates to drilling apparatus that is transportable by helicopter.  
       BACKGROUND OF THE INVENTION  
       [0002]     Drilling equipment for boring into subsurface formations is used in a variety of industrial applications. One particular application is in seismic drilling, which is commonly used in exploration for oil and gas. In seismic drilling, an explosive charge is detonated inside a borehole, and the resultant wave patterns generated in the soil structure in the vicinity of the borehole are recorded (or “logged”) using special electronic equipment. The seismic logs are interpreted by specialists to identify subsurface zones where crude oil or natural gas may be present.  
         [0003]     It is generally desirable for seismic drills to be self-propelled so that they can easily moved from one borehole site to another without need for separate means of transport. It is also desirable for seismic drills to be adapted for operation on uneven ground surfaces, particularly when used in hilly or mountainous areas. It is further desirable for seismic drills to be comparatively small in physical size so that they will be more easily maneuverable over rough terrain and in forested areas. It is further desirable for seismic drills to be remotely controllable, to eliminate the need for a riding operator who would be exposed to the risk of injury in the event of the drill overturning or other mishaps which are particularly more likely to occur when operating in rough terrain.  
         [0004]     Seismic drilling operations are commonly carried out in remote areas that are not accessible by roads, thus preventing the use of large truck-mounted seismic drilling equipment. It is well known, in such situations, to use drilling rigs that can be flown to the drilling site by helicopter (and therefore may be referred to as “heli-transportable” drills). The cost of transporting equipment by helicopter increases with the weight of the equipment and the size or type of helicopter being used. Accordingly, it is desirable to keep the weight of heli-transportable drilling equipment as low as possible in order for heli-transport to be economically feasible.  
         [0005]     The ideal seismic rig for use in remote locations and rough terrain would incorporate all of the foregoing features, while still having the ability to drill seismic boreholes efficiently and to considerable depths.  
         [0006]     Many of these desirable features can be individually found in the prior art. Examples of heli-transportable drills may be seen in U.S. Pat. No. 3,767,329 (Houck), U.S. Pat No. 3,981,485 (Eddy), U.S. Pat No. 4,192,393 (Womack), and U.S. Pat No. 4,476,940 (Reichert). However, none of these drills are self-propelled. The Houck drill is demountable for heli-transport, but its components weigh as much as 4,000 pounds, necessitating the use of a comparatively large helicopter and entailing correspondingly high helicopter operating costs.  
         [0007]     Self-propelled drill rigs are well known, as are rigs that are articulated and/or track-mounted to facilitate travel over rough terrain. For example, U.S. Pat. No. 3,744,574 (Carley) discloses an articulated, self-propelled, wheel-mounted rock drill. U.S. Pat. No. 6,152,244 (Rokbi) discloses an articulated wheel-mounted drill. Examples of prior art track-mounted drills include U.S. Pat. No. 3,289,779 (Feucht) and U.S. Pat. No. 3,478,832 (Hughes). Each of the foregoing prior art drills is comparatively large and heavy, and neither adapted nor readily adaptable for transport by helicopter.  
         [0008]     What is needed, therefore, is a self-propelled seismic drill that is adapted for efficient operation over rough or uneven terrain, and that can be transported by smaller helicopters than known heli-transportable drills. The present invention is directed to these needs.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0009]     In general terms, the present invention is an articulated, modular, track-mounted, self-propelled, remote-controlled drilling apparatus demountable into separate components to facilitate transport by helicopter. These components include front and rear track carriages, which are connected in tandem by an articulated hitch means that provides for articulation about all three axes. The articulated hitch means also incorporates track carriage steering means. The track carriages are constructed in accordance with known technology, with each carriage having a pair of crawler tracks which provide enhanced traction and maneuverability over rough or uneven surfaces. The track carriages have separate hydraulic drive systems of known type, adapted for cooperative operation. The track drive systems and track carriage steering mechanism are remotely controlled, using known remote control technology, thus eliminating the need to provide an operator&#39;s seat and operator&#39;s drive and steering controls, with corresponding savings in equipment weight.  
         [0010]     The rear track carriage is adapted for demountably carrying a drilling module, the main sub-components of which are a rotary drill mechanism, a primary motor, and a hydraulic pump. The primary motor (preferably a 4-cylinder diesel motor) is adapted to provide power to both the rotary drill and the hydraulic pump, which in turn serves the hydraulic drive systems of the track carriers. Means are provided whereby the motor can be selectively switched between drill drive mode and pump drive mode.  
         [0011]     The front track carrier is adapted demountably carrying a drill support module, the sub-components of which may vary depending on the nature of the drilling operations to be conducted. Seismic drilling is commonly carried out using either water or compressed air. When boreholes are being drilled in cohesive soils such as clay and shale, water is introduced into the borehole (typically via the drill stem) to lubricate the drill bit and to assist in removal of drill cuttings. However, this is less effective (or not effective at all) when drilling in non-cohesive soils such as gravel, in which case demountably carrying it may be necessary or desirable to inject compressed air (via the drill stem) to blow cuttings out of the borehole via the annulus between the drill stem and the borehole. Compressed air is also commonly used when drilling through rock formations or large boulders, which typically entails the use of air hammers to break up the rock.  
         [0012]     Accordingly, the drill support module in one embodiment of the invention will primarily comprise a water storage tank, which preferably will have a storage capacity in the range of 200 Imperial gallons. In an alternative embodiment, the drill support module will comprise an air compressor with a dedicated power unit (preferably a small diesel motor). The drill support module in this embodiment may also have a small water tank to provide for situations where drilling will be primarily air-assisted but may require the use of water to drill through localized zones of cohesive material. Flexible water hoses or air hoses are provided, as appropriate, to convey water or compressed air to the drill.  
         [0013]     The use of multiple demountable modules, as described above, makes it possible to reduce the weight of individual components of the apparatus to approximately 1,850 pounds or less, thus allowing the use of helicopters than are considerably smaller and more economical to operate than those typically required for known heli-transportable drills. As well, the use of a pair of track carriages reduces the necessary physical size of each carriage, thus enhancing maneuverability. The combination of self-propelled, track-mounted modules with tri-axial articulation and remote controllability enables the assembled apparatus to traverse rough and steep terrain more easily and with greater stability than known self-propelled seismic drill units such as the four-wheel-drive quad units and six-wheeled or eight-wheeled “argos” commonly used in seismic operations. The drilling apparatus of the present invention thus can readily move on its own power between borehole locations, considerably reducing or eliminating the need for separate means (such as a helicopter) for transporting the apparatus between borehole locations.  
         [0014]     Accordingly, in a first aspect the present invention is a modular, self-propelled, articulated drilling apparatus comprising: 
        (a) a front track carriage having a front end, a rear end, a longitudinal axis, and a hydraulic drive system;     (b) a rear track carriage having a front end, a rear end, a longitudinal axis, and a hydraulic drive system;     (c) a drill support module removably mountable on the front carriage;     (d) a drilling module removably mountable on the rear carriage;     (e) tri-axially articulated hitch means for demountably coupling the front and rear track carriages; and     (f) steering means associated with the articulated hitch means; 
 
 wherein the drilling module comprises: 
    (g) rotary drill apparatus;     (h) a hydraulic pump, for driving the hydraulic drive systems of the front and rear track carriages;     (i) a primary motor; and     (j) motor control means, for selectively switching the primary motor between a first mode in which the primary motor drives the rotary drill apparatus, and a second mode in which the primary motor drives the hydraulic pump.        
 
         [0025]     In a second aspect, the invention is a tri-axially articulated hitch mechanism for demountably coupling a first mobile equipment unit to a second mobile equipment unit, said hitch mechanism comprising: 
        (a) first and second hitch sections, each having an inner end and an outer end, said first and second hitch sections being swivellably connected near their inner ends about a swivel axis;     (b) first axle-mounting means mounted to the outer end of the first hitch section; and     (c) second axle-mounting means mounted to the outer end of the second hitch section so as to be pivotable relative to the second hitch section about a pivot axis intercepting the swivel axis; 
 
 wherein: 
    (d) the first axle means is hingeingly mountable to a first equipment unit such that the first equipment unit is hingeable relative to the first axle means about a hinge axis transverse to the longitudinal axis of the first equipment unit; and     (e) the second axle means is hingeingly mountable to a second equipment unit such that the second equipment unit is hingeable relative to the second axle means about a hinge axis transverse to the longitudinal axis of the second equipment unit.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     Embodiments of the invention will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which:  
         [0032]      FIG. 1  is an elevation of a modular drilling apparatus in accordance with one embodiment of the invention.  
         [0033]      FIG. 2  is a plan view of the articulated hitch mechanism of the drilling apparatus in accordance with the preferred embodiment.  
         [0034]      FIG. 3  is a side view of the articulated hitch mechanism of  FIG. 2 .  
         [0035]      FIG. 4A  is an exploded side view of a pivot block assembly for use with the hitch mechanism of  FIG. 2 .  
         [0036]      FIG. 4B  is an exploded end view of a pivot block assembly for use with the hitch mechanism of  FIG. 2 .  
         [0037]      FIG. 5  is a side view of a pivot pin for use with the hitch mechanism of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0038]     Referring to  FIG. 1 , the drilling apparatus of the present invention (generally indicated by reference number  10 ) comprises a front track carriage  20 , a rear track carriage  30 , an articulated hitch mechanism  40  (by means of which front track carriage  20  and rear track carriage  30  may be demountably coupled), a drill support module  80  which is removably mountable upon front carriage  20 , and a drilling module  90  which is removably mountable upon rear carriage  30 . It should be noted that the reference to the track carriages as “front” and “rear” carriages is for convenience only, and is not intended to be limiting in terms of the configuration or direction of travel or in any other way (although it will perhaps be usual for rear carriage  30  to trail front carriage  20  when drilling apparatus  10  is in self-propelled transit). Front carriage  20  and rear carriage  30  have individual hydraulic drive systems, which may be of any suitable known type. Front carriage  20  and rear carriage  30  are cooperatively engageable by means of the hitch mechanism  40 , which allows for tri-axial articulation as will be described in further detail herein.  
         [0039]     Drilling module  90  includes a structural frame  92  adapted to support a rotary drill apparatus  94 , and to carry ancillary equipment (conceptually represented by block  96  in  FIG. 1 ) including a primary motor and a hydraulic pump. Structural frame  92  is adapted so as to be removably mountable to rear track carriage  30 . Structural frame  92  of drilling module  90  is conceptually shown in  FIG. 1  as an open framework, but this for exemplary illustrative purposes only; structural frame  92  may be of any suitable construction and configuration.  
         [0040]     The primary motor is adapted to selectively drive the drill apparatus  94  or the hydraulic pump, which in turn is operatively engageable with the hydraulic drive systems of the front track carriage  20  and the rear track carriage  30 . The primary motor may be of any suitable type (for example, a 4-cylinder diesel motor). Ancillary equipment  96  includes motor control means (not shown) whereby the output of the primary motor can be selectively directed to driving drill apparatus  94  when a borehole is being drilled, or to driving the hydraulic pump so as to power the hydraulic drive systems of track carriages  20  and  30  when the apparatus  10  is in transit between borehole locations. Persons skilled in the art of the invention will readily appreciate that various types or configurations of motor control means suitable for this purpose may be devised in accordance with technology well known in the field. Preferably, the motor control means is electronically controlled.  
         [0041]     Drill support module  80  includes a structural frame  82  adapted to carry ancillary equipment (conceptually represented by block  84  in  FIG. 1 ) needed or desired to support the operation of drill apparatus  94 . Structural frame  82  of drill support module  80  is conceptually shown in  FIG. 1  as an open framework, but this for exemplary illustrative purposes only; structural frame  82  may be of any suitable construction and configuration.  
         [0042]     The ancillary equipment  84  carried by drill support module  80  may vary depending on the nature of the drilling operations involved, and the subsurface soil conditions at the drilling site. In one embodiment of drill support module  80 , ancillary equipment  84  includes a water storage tank, which preferably will have a storage capacity in the range of 200 Imperial gallons. This configuration of drill support module  80  may be desirable when drilling through cohesive soils, as previously described. Flexible water hoses (not shown) are also provided, to convey water from the storage tank to drill apparatus  94 .  
         [0043]     In an alternative embodiment, ancillary equipment  84  of drill support module  80  includes an air compressor with a dedicated power unit (for example, a small diesel motor). This alternative configuration of drill support module  80  may be desirable when drilling through non-cohesive soils, such as gravel, or when drilling through rock formations or large boulders. Flexible air hoses (not shown) are provided for delivering compressed air from the compressor to drill apparatus  94 . The drill support module  80  in this alternative embodiment may also have a small water tank (conceptually indicated in  FIG. 1  by reference number  84 A) to provide for situations where drilling conditions in which the use of both compressed air and water may be beneficial.  
         [0044]     Hitch mechanism  40  couples front track carriage  20  and rear track carriage  30  such that they can articulate relative to each other about three axes. This articulation capability can be best understood from  FIGS. 2 and 3 , which illustrate a preferred embodiment of the articulating hitch mechanism  40 . Hitch mechanism  40  comprises a a first hitch section  42  and a second hitch section  44 , each of which has an inner end ( 42 A,  44 A) and an outer end ( 42 B,  44 B). In the preferred embodiment, first hitch section  42  comprises an upper plate  43 U and a lower plate  43 L, and second hitch section  44  comprises an upper plate  45 U and a lower plate  45 L, said upper and lower plates of each hitch section being spaced apart from each other. As shown in  FIG. 2 , plates  43 U,  43 L,  45 U, and  45 L are of generally triangular configuration in the preferred embodiment, but this is not essential to the invention. Nor is it essential that either first hitch section  42  or second hitch section  44  be fabricated with plates; the hitch sections may take various other forms of construction (such as an open structural framework, to give only one example) without departing from the concept of the invention.  
         [0045]     Hitch sections  42  and  44  are swivellably connected about a swivel axis XS in the vicinity of their respective inner ends  42 A and  44 A, using a swivel pin  46  of any suitable type. Hitch mechanism  40  includes steering means, for controlling articulation about swivel axis XS and thus effectively controlling the direction of travel of the drilling apparatus  10  when in transit under its own power. In the preferred embodiment of the invention, the steering means comprises a pair of hydraulic cylinders  48  disposed one on either side of swivel axis XS, each cylinder  48  being rotatably connected at one end to hitch section  42  near its outer end  42 B and at the other end to hitch section  44  near its outer end  44 B, all as illustrated in  FIG. 2 . As shown in  FIGS. 2 and 3 , hitch sections  42  and  44  may be provided with cylinder bosses  47  to facilitate mounting of hydraulic cylinders  48 .  
         [0046]     Hydraulic cylinders  48  are operably connected in well-known fashion to the hydraulic pump of drilling module  90  (or, in alternative embodiments, to a dedicated steering pump) by means of suitable flexible hydraulic fluid conduits (not shown). Hydraulic cylinders  48  preferably will be double-acting cylinders, but single-acting cylinders may be used in alternative embodiments.  
         [0047]     In the preferred embodiment of the invention, the operation of the primary motor and hydraulic pump of drilling apparatus  10  are remotely and electronically controlled with respect to both track-drive functions and steering functions. The remote control function may be provided using a remote control station linked to drilling apparatus  10  by means of a control cable or by a wireless communication link, in accordance with methods and technology well known to persons skilled in the field of the invention.  
         [0048]     Hitch mechanism  40  also includes first axle-mounting means  70 A which is mounted to first hitch section  42  at the outer end  42 B thereof, generally as shown in  FIGS. 2 and 3 . First axle-mounting means  70 A is adapted to connect to a first axle means (conceptually indicated by reference number  72 A) which in turn is mounted to first track carriage  20  such that first track carriage  20  is hingeingly rotatable about a hinge axis XH-A transverse to the longitudinal axis of first track carriage  20 . As shown in  FIGS. 2 and 3 , first axle means  72 A may comprise a square (or round) tubular member, which has the benefit of providing torsional strength while being comparatively light in weight. The tubular member may be rotatably connected to first track carriage  20  by means of suitable shafts and bearings (not shown) in accordance with well-known methods. However, this preferred arrangement for first axle means  72 A is not essential to the invention; persons skilled in the field of the invention will readily appreciate that first axle means  72 A and its hingeing connection to first track carriage  20  may take a variety of other forms in accordance with known technology.  
         [0049]     As illustrated in  FIGS. 2 and 3 , first axle-mounting means  70 A may be provided in the form of a clamp plate  74 A by which first axle means  72 A may clamped to outer end  42 B of first hitch section  42  using clamp bolts  76 A that engage an end plate  42 C provided at outer end  42 B of first hitch section  42 . However, this arrangement is exemplary only, and various other configurations of first axle-mounting means  70 A may be devised without departing from the present invention.  
         [0050]     Second hitch section  44  includes a pivot pin housing  50  disposed between the upper and lower plates  44 U and  44 L of second hitch section  44 . Pivot pin housing  50  has a cylindrical pivot pin bore  51  for receiving a pivot pin. As shown in  FIG. 3 , pivot pin housing  50  may be in the form of a round pipe  52  with spacers  54  as necessary to facilitate connection to upper and lower plates  44 U and  44 L (such as by welding). Pivot pin housing  50  is oriented such that the axis of pivot pin bore  51  (which may be referred to as pivot axis XP) is preferably (but not necessarily) substantially perpendicular to swivel axis XS and intercepts swivel axis XS. It is preferable if pivot axis XP and intercepts swivel axis XS with close to geometrical precision, but this is not critical. The desirability of having pivot axis XP intercept swivel axis XS lies in avoiding eccentricity in the transfer, of longitudinal forces between front track carriage  20  and rear track carriage  30 , but drilling apparatus  10  can function satisfactorily even if hitch mechanism  40  incorporates some amount of longitudinal eccentricity. Accordingly, the phrase “intercepts the swivel axis” and contextually similar phrases in this patent document are not intended to be restricted to the case where pivot axis XP intercepts swivel axis XS with geometrical precision, but also cover cases where pivot axis XP passes to one side of, but reasonably close to, swivel axis XS.  
         [0051]     Hitch mechanism  40  also includes a second axle-mounting means  70 B for receiving a second axle means  72 B mounted to second track carriage  30  such that second track carriage  30  is hingeingly rotatable about a hinge axis XH-B transverse to the longitudinal axis of second track carriage  30 . The details of second axle-mounting means  70 B and its connection to second track carriage  30  are generally as described previously with respect to first axle means  72 A, with the exception that second axle-mounting means  70 B is mounted to second hitch section  44  so as to be pivotable about pivot axis XP. This feature is provided in the preferred embodiment by means of a split pivot block  60  comprising a first pivot block section  62  and a second pivot block section  64 , which are illustrated in  FIGS. 4A and 4B . First pivot block section  62  defines a semi-cylindrical cavity  62 A, and second pivot block section  64  defines a semi-cylindrical cavity  64 A having the same diameter as cavity  62 A.  
         [0052]     Second pivot block section  64  is matingly engageable with first pivot block section  62  such that semi-cylindrical cavities  62 A and  64 A combine to form a cylindrical pivot block passage  65 . First pivot block section  62  and second pivot block section  64  are provided with means for releasably securing second pivot block section  64  to first pivot block section  62 . In the embodiment illustrated in  FIGS. 2, 3 ,  4 A, and  4 B, this securing means is provided in the form of fastener holes  66  for receiving fasteners  68 . Fastener holes  66  may be straight holes passing fully through pivot block sections  62  and  64  for receiving through-bolts, or they may incorporate threaded sections  66 A for receiving machine screws. Other suitable means of releasably securing second pivot block section  64  to first pivot block section  62  will be readily apparent to persons skilled in the art.  
         [0053]     First pivot block section  62  is securely connected to second axle-mounting means  70 B (such as by welding), with the axis of pivot block passage  65  oriented substantially perpendicular to hinge axis XH-B. Second axle-mounting means  70 B may now be pivotably mounted to second hitch section  44  using a pivot pin  67  disposed within both pivot pin bore  51  of pivot pin housing  50  and pivot block passage  65  of assembled pivot block  60 , so as to be rotatable about pivot axis XP while at the same time being retained longitudinally within pivot pin housing  50  and the assembled pivot block  60 .  
         [0054]     In the illustrated preferred embodiment of the invention, the diameters of pivot pin bore  51  and pivot block passage  65  are equal, and pivot pin  67  comprises a round shaft  69  having a diameter slightly smaller than that of pivot pin bore  51  and pivot block passage  65 , such that pivot pin  67  will be freely rotatable within pivot pin bore  51  and pivot block passage  65 . Round shaft  69  has an inner end  69 A and an outer end  69 B, and has a stop member  67 A (such as an annular ring as in  FIG. 5 , or any other suitable appurtenance or attachment accomplishing the desired function) at or near inner end  69 A. An annular groove  69 C is formed in shaft  69  near outer end  69 B.  
         [0055]     As best seen in  FIGS. 2 and 3 , pivot pin  67  may be inserted through pivot pin bore  51  such that outer end  69 B of shaft  69  projects beyond outer end  44 B of second hitch section  44 . The projecting outer end  69 B of shaft  69  may then be disposed within semi-cylindrical cavity  62 A of first pivot block section  62 , whereupon second pivot block section  64  may be engaged with and fastened to first pivot block section  62  as previously described. As a result of this assembly, the axis of pivot pin  67  will coincide with pivot axis XP. In the illustrated embodiment, fastener holes  66  of first and second pivot block sections  62  and  64  are configured such that fasteners  68 , when inserted through fastener holes  66 , will at least partly intercept annular groove  69 C of shaft  69  when said annular groove  69 C is longitudinally aligned with fastener holes  66 . By means of this arrangement, fasteners  68  will retain pivot pin  67  longitudinally within pivot block passage  65  while still allowing pivot pin  67  to rotate about pivot axis XP within pivot block passage  65 . Pivot pin  67  is longitudinally retained within pivot pin housing  50  by means of stop member  67 A, abuts the inner end of pivot pin housing  50  as seen in  FIGS. 2 and 3 .  
         [0056]     Although pivot pin  67  has been described and illustrated in the simple form of a round bar of uniform diameter with an annular groove for retention within pivot block  60 , persons skilled will recognize that pivot pin  67  may take other forms and configurations while still having the functional features described herein. For example, pivot pin  67  could have sections of different diameters, with pivot pin bore  51  and pivot block passage  65  having correspondingly different diameters. Longitudinal retention of pivot pin  67  within pivot pin housing  50  and pivot block  60  may be provided by other means as well. For example, semi-cylindrical cavities  62 A and  64 A could be formed with annular ridges that are matingly engageable with annular groove  69 C of pivot pin  67 . In an analogous alternative embodiment, pivot pin  67  could be formed with an annular ridge matingly engageable with annular grooves formed into semi-cylindrical cavities  62 A and  64 A. These exemplary alternative embodiments would eliminate the need for fasteners  68  to serve as longitudinal retention means, thus providing additional options with respect to the releasable connection of first pivot block section  62 , to second pivot block section  64 .  
         [0057]     In the preferred embodiment, hitch mechanism  40  is provided with limiting means (not shown) for limiting the range of swivelling, pivoting, and hingeing movement about the swivel, pivot, and hinge axes respectively. The limiting means may be provided in the form of stop members, straps, cables, or suitable appurtenances of other types which may be readily devised by persons skilled in the field of the invention.  
         [0058]     It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the essential concept of the invention, and all such modifications are intended to be included in the scope of the claims appended hereto. By way of example (and without intending to limit the foregoing statement), first axle-mounting means  70 A could be pivotably mounted to first hitch section  42  in addition to or instead of second axle-mounting means  70 B being pivotably mounted to second hitch section  44 . In another exemplary variant of the invention, the pivot pin may be non-rotatably connected to first hitch section  42  or second hitch section  44 , such that it only rotates within pivot block passage  65 .  
         [0059]     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following that word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element.