Abstract:
The invention contemplates a selectably operable hydraulic means for laterally shifting one end of a non-moving vehicle in order to provide a desired alignment. The present invention is particularly applicable to vehicle-mounted equipment which has an invariant lateral mounting position on the vehicle and which must be laterally aligned with a stationary workpiece axis. An example of such a need occurs with mobile workover rigs used in well maintenance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application, pursuant to 35 U.S.C. 111(b), claims the benefit of the earlier filing date of provisional application Ser. No. 60/730,736 filed Oct. 27, 2005, and entitled “Positioning Mechanism for Placement of a Rig.” 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The field of the present invention is selectably operable hydraulic means for laterally shifting one end of a non-moving vehicle in order to provide a desired alignment. The present invention is particularly applicable to vehicle-mounted equipment which has an invariant lateral mounting position on the vehicle and which must be laterally aligned with a stationary workpiece axis. 
   2. Description of the Related Art 
   The use of vertically acting rigidly mounted corner cylinders, articulated arms, and the like are well known to those engaged in the art of vertically supporting vehicles mounting working equipment. Such vertical supports generally use either a screw jack or hydraulic cylinder to extend an approximately horizontal bearing plate downwardly to bear against the ground surface and thereby provide vertical support and alignment. However, while such devices are designed for providing adjustable corner vertical supports for vehicles, such devices previously have not offered any means to deal with lateral misalignment. 
   Accordingly, lateral alignment of the vehicle with its attendant alignment-sensitive equipment can only be achieved by repeatedly backing up and pulling forward. This procedure can be very time consuming because of the lack of ready visual feedback, since the equipment mounted on the vehicle usually obscures the field of vision of the driver. If the ground surface has soft spots and or ruts, the provision of proper alignment becomes even more difficult. 
   For example, truck or trailer-mounted conventional workover rigs are brought to a well location for workover operations. The driver attempts to back the workover rig so that it is centered over the wellhead. However, it can be very difficult to center the workover rig directly over the wellhead such that the driver has to pull forward and backward a number of times before the workover rig is centered over the wellhead. 
   A need exists for a simple, selectably operable means that can readily provide adjustments in lateral alignment for vehicles such as trucks and truck-trailer rigs. There is a need for a lateral shifting means which can be operated by one man and that does not add significant weight to the vehicle. 
   Furthermore, there is a need for a lateral shifting means that can be set up and retracted rapidly using rig hydraulics to facilitate proper equipment emplacement at a job site. 
   SUMMARY OF THE INVENTION 
   The invention contemplates a vehicular lateral shifting assembly having a selectably extensible hydraulic cylinder mounted on one end of a body of a vehicle, wherein the cylinder is pivotable in a plane transverse to a longitudinal axis of the vehicle, whereby when the cylinder is pivoted and extended the one end of the body of the vehicle is laterally shifted. 
   One aspect of the present invention is a vehicular lateral shifting assembly comprising: (a) a pair of selectably extensible hydraulic cylinders, wherein one cylinder is mounted on a first side of one end of a body of a vehicle and the other cylinder is mounted on a second opposed side of the one end of the body; (b) a mounting means for mounting a proximal end of each cylinder to the one end of the body; (c) a pivotable means for pivoting the cylinders in a plane transverse to a longitudinal axis of the vehicle; (d) a latching means for securing the cylinders in a designated position in the plane transverse to the longitudinal axis of the vehicle; and (e) a swivelable bearing plate mounted on a distal end of each cylinder. 
   Another aspect of the invention is a four-bar linkage vehicular lateral shifting assembly comprising a pair of selectably extensible parallel hydraulic cylinders and two interconnecting links. 
   Yet another aspect of the invention is a vehicular lateral shifting assembly comprising: (a) a pair of selectably extensible hydraulic cylinders, wherein one cylinder is mounted on a first side of one end of a body of a vehicle and the other cylinder is mounted on a second opposed side of the one end of the body; (b) a clevis mount for pivotably mounting a proximal end of each cylinder to the one end of the body; (c) a latching mechanism for securing each cylinder in one of a number of designated positions in the plane transverse to the longitudinal axis of the vehicle; and (d) a swivelable bearing plate mounted on a distal end of each cylinder. 
   Still yet another aspect of the present invention is a method for laterally shifting an end of a stationary vehicle having the vehicular lateral shifting assembly of claim  16 , the method comprising the steps of: (a) selectably tilting the distal end of the hydraulic cylinders in an opposed direction to the direction in which lateral displacement is desired; (b) activating the latching mechanism to secure each tilted hydraulic cylinder into one of the designated positions; and (c) extending the hydraulic cylinders to urge the bearing plates against a supporting surface thereby laterally displacing the one end of the vehicular body in the desired direction. 
   The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is an oblique profile view of a semitrailer towed by a tractor rig with a workover rig positioned on the trailer, wherein one embodiment of the lateral shifting means is mounted at the rear of the vehicle. 
       FIG. 2  is a side profile view of the embodiment of  FIG. 1 . 
       FIG. 3  is an oblique view of the rear of the lateral shifting means shown in  FIG. 1 , wherein the lateral shifting means mechanism is shown in an exploded state. 
       FIG. 4  is a rear profile view of the vehicle and the first embodiment of the lateral shifting means, wherein the shifting means is retracted in its traveling position and the rear of the vehicle is laterally displaced from a wellhead upon which work is to be performed using vehicle-mounted equipment. 
       FIG. 5  is a view corresponding to  FIG. 4 , wherein the cylinders of the lateral shifting means are pinned in an inclined position to urge the rear end of the vehicle laterally toward the wellhead. 
       FIG. 6  is a view corresponding to  FIGS. 4 and 5 , wherein the rear end of the vehicle has been shifted laterally to be in transverse alignment with the wellhead and the lateral shifting means returned to an alignment with vertical cylinders extended to enhance the stability of the rear end of the vehicle. 
       FIG. 7  is a rear profile view of the vehicle and the second embodiment of the lateral shifting means, wherein the shifting means is retracted in its traveling position and the rear of the vehicle is laterally placed from a wellhead upon which work is to be performed using the vehicle-mounted equipment. 
       FIG. 8  is a view corresponding to  FIG. 7 , wherein the cylinders of the lateral shifting means are pinned in an inclined position to urge the rear end of the vehicle laterally toward the wellhead. 
       FIG. 9  is a view corresponding to  FIGS. 7 and 8 , wherein the rear end of the vehicle has been shifted laterally to be in transverse alignment with the wellhead and the lateral shifting means returned to an alignment with vertical cylinders extended to enhance the stability of the rear end of the vehicle. 
       FIG. 10  is a rear profile view of the vehicle and the third embodiment of the lateral shifting means, wherein the shifting means is retracted in its traveling position and the rear of the vehicle is laterally displaced from a wellhead upon which work is to be performed using the vehicle-mounted equipment. 
       FIG. 11  is a view corresponding to  FIG. 10 , wherein the cylinders of the lateral shifting means are pinned in an inclined position to urge the rear end of the vehicle laterally toward the wellhead. 
       FIG. 12  is a view corresponding to  FIGS. 10 and 11 , wherein the rear end of the vehicle has been shifted laterally to be in transverse alignment with the wellhead and the lateral shifting means returned to an alignment with vertical cylinders extended to enhance the stability of the rear end of the vehicle. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The lateral rig shifter of the present invention provides a means of quickly, safely, and effectively producing a desired transverse alignment for the end of a vehicle on which a piece of working equipment is mounted. The lateral rig shifter employs a pair of conventional corner jacking cylinders that are conventionally used for rig vertical stabilization. However, by mounting them in a latchable transversely movable four-bar linkage, a single man can readily adjust the orientation of the jacking cylinders to not only support the rig vertically, but also to selectably realign the end of the vehicle to either side in a controllable manner. 
   The materials of construction of the vehicle frame and working deck are typically steel rolled sections and plate assembled by welding. Although it is not shown in all the Figures, the rear of the deck of the vehicle is assumed to mount an item of working equipment, such as a workover rig, which has a fixed vertical longitudinal plane in which it works and which is fixed against lateral movement by its mountings. The vehicle is normally supported at its rear by a sprung suspension system and one or more axles on which pneumatic tires are mounted. Where the vehicle is a trailer, as shown herein, a towing tractor will normally support the front end of the vehicle. The lateral shifting mechanism, which includes a pair of hydraulic cylinders, is generally fabricated from steel bars, tubes, and weldments utilizing rolled plate. 
   The lateral rig shifter of the present invention is operated by utilizing the hydraulic system of the vehicle-mounted equipment as a power supply. The details of the available hydraulic systems of the vehicle-mounted equipment vary considerably and so are not shown here. If single-acting spring-return hydraulic cylinders are used for the present invention, they are easily controlled by a manual two-position three-way valve connected to the piston end of the lift cylinders. Pressure is selectably applied to the rod end of the cylinders with the valve in one position, while the cylinders are vented to the tank of the hydraulic system with the valve its other position. 
   First Embodiment  10   
   Referring now to the drawings, it is pointed out that like reference characters designate like or similar parts throughout the drawings. The Figures or drawings are not intended to be to scale. As seen in  FIGS. 1 and 2 , the first embodiment  10  of the present invention utilizes a semitrailer  11  as the vehicle upon which a piece of working equipment is generally mounted. Such working equipment, as for example a drilling rig or workover rig may be utilized for the boring and servicing of wells. In general, such equipment is mounted on the vehicle in a manner that does not permit the equipment to be laterally shifted on the vehicle to alter its alignment with a work site on the surface of the ground  13 . The trailer  11  is towed to its working location by a tractor rig  18  and backed up to its desired location. Longitudinal alignment typically is easily managed when backing up to a work site, but lateral alignment is more difficult to obtain, particularly if a location has an irregular surface. 
   The trailer  11  typically has a working deck of steel plate supported by longitudinal and transverse beams and upon which is mounted working equipment having a vertical axis of operation  20  located on the longitudinal vertical centerline of the trailer and offset to the rear of the trailer. As seen in  FIG. 1 , a workover rig  90  consisting of a pivotable mast  91 , mast elevating cylinders  92 , a drawworks  95 , a crown block  96 , and a traveling block  97  is mounted at the rear of the trailer  11 . The workover rig  90  requires that the vertical axis  20  for travel of its traveling block  97  and its attached hook  98  be aligned with the axis  71  of the wellhead  70 . For clarity, only the axis of operation  20  is shown herein for the Figures following  FIG. 1 . 
   The trailer  11  is attached to a tractor rig  18  for transport and is normally left coupled to the tractor rig. However, for clarity in the Figures following  FIG. 2 , the trailer  11  is shown without its attached tractor rig  18 . When decoupled from the tractor rig  18 , the forward end of the trailer  11  may be supported on vertically extensible support legs  12  that bear on the ground surface  13 . A vertically downwardly extending king pin  14 , used to connect the trailer  11  to the fifth wheel of the tractor rig  18  for towing, is positioned on the longitudinal vertical midplane of the underside of the forward end of the trailer  11 . The king pin  14  and the fifth wheel of the tractor rig  18  have a common vertical axis of rotation  19  when coupled as shown in  FIGS. 1 and 2 . 
   As shown in  FIGS. 1 ,  2 , and  4 , the rear of the trailer  11  is supported by a conventional sprung suspension mounting one or more rear axle assemblies  15  which in turn mount pneumatic tires  16  which support the trailer during travel and setup or when parked. 
   As seen best in  FIG. 3 , at the rear of the trailer  11 , a reinforced plate transverse rear bulkhead  17  serves as a mounting for the lateral shifting assembly  21 . Bulkhead  17  is penetrated by two similar sets of latch pin holes. Although any number or shape of latch pin holes can make up a set, the example described herein uses a set of three pin holes  37 ,  38 , and  39 . The two pin hole sets are symmetrically placed about the longitudinal vertical axis of the trailer and all of the pin holes are parallel to the longitudinal horizontal axis of the trailer  11 . Typically, each set of latch pin holes  37 ,  38 , and  39  is located on a common circular arc and at uniform angular spacings. 
   On each side of the lateral shifting assembly  21  is a pair of lift cylinder brackets  22  with each cylinder bracket  22  mounting a lift cylinder  26  with a swivelable bearing foot  50  on the outer end of the cylinder rod  29 . The two lift cylinders  26  are interconnected with a tie bar  60 . The lateral shifting assembly  21  is mounted to the transverse rear bulkhead  17  of the trailer  11  and is contained in a plane that is transverse to the trailer horizontal longitudinal axis. The plane of the lateral shifting assembly  21  is forward of the vertical axis  20  of the trailer mounted equipment, and is slightly offset to the rear from the bulkhead  17 . 
   The downwardly opening clevis-type lift cylinder brackets  22  are mounted at the outer upper corners of the rear face of bulkhead  17 . Each cylinder bracket  22  has a swivel pin hole  23  extending coaxially through both of its clevis plates, with the swivel pin holes parallel to the horizontal longitudinal axis of the trailer  11 . A main cylinder pivot pin  24  of headed right circular cylindrical construction is mounted in each swivel pin hole  23 , where it serves to support the piston end of a lift cylinder  26 . The lift cylinders  26  are preferably single-acting spring-return hydraulic cylinders with single end piston rods  29  projecting generally downwardly through rod glands on their lower ends and having end swivel plates  27  at their upper ends. The distal ends of the piston rods  29  are helically threaded. Each symmetrically positioned end swivel plate  27  is penetrated by a centrally located right circular cylindrical cylinder swivel pin hole  28  which has a rotational fit with the main cylinder pivot pin  24  in the bracket  22  on its side of the bulkhead  17 . This arrangement permits each cylinder to pivot about the swivel pin hole  28  at its upper end and in the transverse plane of the lateral shifting assembly  21 . 
   At an intermediate position in the length of each cylindrical cylinder body below midlength is positioned a latching sleeve  32 . The latching sleeve  32  is a right circular cylindrical sleeve fixed to the body of the lift cylinder  26  and having an integral, tangentially projecting latch plate  33  extending generally toward the middle horizontal axis of the trailer  11 . The latch plates  33  are parallel to but offset to the forward side of the end swivel plates  27  so that they are coplanar and are in sliding contact with the transverse rear bulkhead  17  of the trailer  11 . Each latch plate  33  is penetrated by a centrally located right circular cylindrical latch pin hole  34  which is parallel to the horizontal longitudinal axis of the trailer  11 . 
   When the lift cylinder  26  on either side of the trailer  11  is swiveled about its pivot pin  24 , the path of the center of its latch pin hole  34  is both coradial and concentric with the circular arc on which are positioned the first  37 , second  38 , and third latch pin hole  39  on that side of the bulkhead  17 . On either side of the trailer  11 , a headed right circular cylindrical latch pin  36  which is a close fit to both the latch pin hole  34  of the latch plate  33  of the latching sleeve  32  and to any of the latch pin holes  37 ,  38 ,  39  in the bulkhead  17  is used to lock the lift cylinder on that side in a fixed orientation. With the latch pin  36  engaged in the second latch pin hole  38  in the bulkhead which is in the middle of the set of latch pin holes  37 ,  38 , and  39 , the lift cylinder  26  is positioned parallel to the vertical midplane of the trailer  11 . 
   Threadedly attached to the lower end of the rod  29  of each lift cylinder  26  is a rod end fitting  45 . The rod end fitting  45  has a right circular cylindrical shank portion with a coaxial tapped hole in its upper end, a reduced diameter neck at the lower side of the shank portion, and a spherical ball end  46  coaxially located on the bottom end of the neck. A pair of diametrically opposed radially extending short right circular cylindrical tie bar pins  47  extend from the shank portion of each rod end fitting  45  at approximately midheight of the shank. The tie bar pins  47  of the rod end  45  are oriented so that they are parallel to the horizontal longitudinal axis of the trailer  11 . The rotational axes created by the tie bar pins  47  intersect the longitudinal axes of their respective lift cylinders  26 . 
   Mounted to the ball end  46  of each rod end  45  is a bearing foot  50 . The bearing foot  50  is a rectangular plate structure having a flat central portion and with a short length of the outer portion of two opposed sides bent slightly upwardly. Centrally located on the upper surface of the bearing foot  50  is an upwardly projecting ball socket  51  which has a spherical internal cup which engages and has a slip fit with the ball end  46  of the rod end  45 . The exterior of the ball socket  51  is a short right circular cylindrical section. While the bearing feet  50  are able to freely swivel about the ball end  46  of the rod end  45 , the bearing feet are normally oriented so that the planes of symmetry extending through both bent sections of the feet are in the transverse plane of the trailer  11 . This orientation more readily permits the bearing feet  50  to conform to a soft or irregular ground surface  13 . 
   As best seen in  FIGS. 1 and 3 , a tie bar  60  consists of an elongated tubular midbody supporting two antisymmetrically mounted tie bar devises  61  at its outer ends. A pair of coaxial right circular cylindrical clevis pin holes  62  which are engagable with the tie bar pins  47  of the rod ends  45  penetrate the jaw plates of each tie bar clevis  61 . The distance between the pairs of clevis pin holes  62  is equal to the distance between the pairs of swivel pin holes  23  of the lift cylinder brackets  22 . The tie bar pins  47  and the tie bar clevis pin holes  62  have a rotational slip fit. The clevis pin holes  62  at each end of the tie bar  60  are connected to the tie bar pins  47  of the rod ends  45  of the lift cylinders  26 . 
   The lateral shifting assembly  21  constitutes a four-bar linkage lying in the transverse plane at the rear of the trailer  11 . The links of the four-bar linkage are the tie bar  60 , the lift cylinders  26  with their rods and rod ends, and the transverse rear bulkhead  17  of the trailer. The pins of the linkage are the main cylinder pivot pins  24  and the tie bar pins  47  of the rod ends  45  of the cylinders  26 . For this first embodiment, the opposed sides of the four-bar linkage are maintained parallel. 
   Second Embodiment  100   
   A second embodiment  100  of the laterally shiftable vehicle is shown in  FIGS. 7 ,  8 , and  9 . For clarity in illustrating the second embodiment the tractor rig  18  is not shown in  FIGS. 7 ,  8  and  9 , although it is assumed that the tractor rig  18  is attached to the trailer  11  while at the work location. 
   The second embodiment  100  is configured identically with the first embodiment  10 , with the exception that the tie bar  60  is eliminated and the tie bar pins  47  of the rod end  145  are omitted in the lateral shifting assembly  121 . Otherwise, the construction of the rod end  145  and adjoining ball end  146  is identical with that of the rod end  45  and ball end  46  of the first embodiment  10  of the present invention. 
   These modifications make the positioning of the lift cylinders  26  independent and the lateral shifting assembly  121  of the second embodiment is no longer a four-bar linkage. However, in operation the lift cylinders  26  are always pinned by means of their latch pins  36  and the two sets of latch pin holes  37 ,  38 , and  39  in bulkhead  17  so that the axes of the cylinders are parallel. This arrangement is particularly suitable for an uneven ground surface  13 , as it permits the rods  29  of the lift cylinders  26  to be extended unequally. For such an arrangement, the two lift cylinders  26  can be independently valved. 
   Third Embodiment  200   
   The third embodiment  200  of the laterally shiftable vehicle is shown in  FIGS. 10 ,  11 , and  12 . For clarity in illustrating the third embodiment  200 , the tractor rig  18  is not shown in  FIGS. 10 ,  11  and  12 . The third embodiment  200  is very similar to the first  10  and the second  100  embodiments and uses the same trailer  11  and tractor rig  18 , but the lateral shifting assembly  221  of the third embodiment  200  has the following differences in structure. The lateral shifting assembly  221  uses the same cylinder rod end  145  without an integral tie bar pin as is used for the lateral shifting assembly  121  of the second laterally shiftable vehicle embodiment  100 . 
   Lateral shifting assembly  221  does utilize a tie bar  260  to interconnect the two sides of the lateral shifting assembly, but the tie bar is pivotably attached to each of the bearing feet  50 , rather than to the rod end  45  as in the first embodiment  10 . For each end of the tie bar  260 , the attachment of the tie bar is to a tie bar pin plate  253  positioned on the transverse plane of the lateral shifting assembly  221  and welded on the inboard side of the each of the bearing feet  50 . The tie bar pin plates  253  are penetrated by right circular cylindrical pin holes that are parallel to the horizontal longitudinal axis of the trailer  11 . The tie bar  260  is structurally similar to the tie bar  60  of the first embodiment  10 , but it is shorter. Additionally, the tie bar devises  261 , penetrated by clevis pin holes, are narrower. The tie bar pins  247  are substantially identical to the tie bar pins  47  of the first embodiment  10 . The tie bar pins  247  are engaged in both the clevis pin holes of the tie bar  260  and in the pin holes in the tie bar pin plates  253 . The locations of the installed tie bar pins  247  are such that the axes of the pins are offset inwardly from the centerline of the lift cylinders  26 . 
   OPERATION OF THE INVENTION 
   First Embodiment  10   
   The first embodiment of the laterally shiftable vehicle  10  operates in the following manner. The tractor rig  18  backs the trailer  11  up to the wellhead  70  until the transverse plane of the trailer containing the vertical axis  20  of the trailer-mounted equipment is aligned with the vertical axis  71  of the wellhead  70 . For clarity, the tractor rig  18  is not shown in the Figures herein and the front end of the trailer  11  is assumed to be supported pivotably about the vertical axis  19  of the king pin  14  and the fifth wheel by the tractor rig  18 . It also is assumed herein for the sake of illustration that the axis  20  of the trailer-mounted equipment will be laterally misaligned so that it is offset to the left of the wellhead, as shown in  FIG. 4 . 
   In order to correct this lateral misalignment, the person operating the lateral shifting mechanism  21  will manually swing the dependent portion of the four-bar linkage, consisting of the lift cylinders  26  with attachments and the tie bar  60 , to the left as seen in  FIG. 5 . The lateral shifting mechanism  21  is locked in its leftward position by engaging the lefthand latch pin  36  both through the latch pin hole  34  of the latching sleeve  32  on the lefthand lift cylinder  26  and in the third latch pin hole  39  on the lefthand side of the transverse rear bulkhead  17  of the trailer  11 . Likewise, the righthand latch pin  36  is engaged both in the righthand latch pin hole  34  of the latching sleeve  32  of the lift cylinder  26  and in the first latch pin hole  37  on the righthand side of the transverse rear bulkhead  17 . This engagement of the latch pins  36  locks the cylinders  26  in a parallel, leftwardly inclined position. The tie bar  60  aids in the alignment of the final of the two pinnings of the latch pins  36 , since pinning one latch pin causes the latch pin hole  34  on the other side to align with its target latch pin hole  37 ,  38 , or  39  in the transverse rear bulkhead  17  of the trailer  11 . 
   Following this pinning of the lift cylinders  26  in the position shown in  FIG. 5 , the rods  29  of the cylinders are extended to engage the ground surface  13  with the bearing feet  50 . Because the lift cylinders  26  are locked in a parallel position and the tie bar  60  has a fixed length, the rods  29  of the lift cylinders must be extended substantially equally unless one of the latch pins  36  is not in pinned engagement. As the rods  29  of the lift cylinders  26  are extended beyond their initial engagement with the ground surface  13 , a portion of the vertical load of the trailer weight is transferred to the cylinders from the tires  16  and suspensions of the rear axles  15  of the trailer  11 . 
   This load transfer partially unloads the suspension of the trailer  11 , so that the suspension extends and the tires  16  still contact the ground surface  13 . Simultaneously, the lift cylinders  26  are exerting a rightward lateral load on the trailer  11 . This rightward load causes the rear end of the trailer  11  to displace rightwardly, with the tires  16  dragging across the ground surface. At the same time, the forward end of the trailer  11  is restrained against lateral movement by the tractor rig  18 , so that the trailer  11  pivots about the vertical axis  19  of the king pin  14  and the fifth wheel of the tractor rig. During this time, the presence of the tie bar  60  aids in stabilizing the ends of the piston rods  29  in the event of lateral slippage of one of the bearing feet  50 . This stabilization is produced by lateral load sharing through the tie bar. 
   By metering the extension of the rods  29  of the lift cylinders  26  by means of the hydraulic controls (not shown) for the cylinders, the rightward travel of the rear end of the trailer  11  can be selectably controlled. When the desired orientation of the vertical axis  20  of the trailer mounted equipment with the vertical axis  71  of the wellhead  70  is achieved, the hydraulic pressure on the piston ends of the lift cylinders  26  is vented, causing the lift cylinders to support only minor loads attendant with hydraulic flow losses between the piston end of the cylinders and the hydraulic tank. The rods  29  of the single-acting spring-return lift cylinders  26  are returned to their retracted positions when extension pressure is removed by the reaction of the bearing feet  50  with the ground surface and the return springs. As a result, the weight of the trailer  11  supported by the lift cylinders  26  is transferred back fully to the tires  16  and the suspension of the rear axles  15  of the trailer and the trailer is lowered with its rear end substantially in alignment with the wellhead  70 . The frictional resistance of the tires  16  to lateral movement aids in preventing the return of the rear end of the trailer  11  to its original position during this lowering. 
   In the event that the residual piston end pressure during retraction of the lift cylinders  26  causes a nontrivial leftward lateral load component to be applied to the trailer  11  while it is being lowered, some minor rebound to the left of the trailer will occur. Experienced operators of the lateral shifting assembly  21  can compensate for this hysteresis rebound by providing selectably determined overtravel to the right during the extension of the piston rods  29 . In the event to shifting the trailer  11  too far to the right during the lifting operation, the four-bar linkage can be unpinned and then repinned in a rightwardly inclined position for repositioning leftwardly. 
   When the desired transverse alignment of the vertical axis  20  of the trailer-counted equipment and the vertical axis  71  of the wellhead  70  is obtained, the latch pins  36  are withdrawn and repinned in the second latch pin holes  38  on both sides of the bulkhead  17 . The lift cylinders  26  can then have their rods  29  extended so that the trailer  11  is leveled and stabilized as shown in  FIG. 6  by transferring load from the tires  16  and suspension of the rear axles  15  to the cylinders and their attached bearing feet  50 . In the event that the ground is uneven, it is possible to disengage one of the latch pins  36  so that the rods  29  of the lift cylinders  26  can be extended unequally. When work is completed, then pressure is vented from the piston end of the lift cylinders  26  and the rods  29  are fully retracted to their traveling positions shown in  FIG. 4  by the action of the return springs. 
   It should be noted that, if the lift cylinders  26  are to be extended by different amounts, side loads could be induced on the rods  29  and damage could result. For this reason, one of the latch pins  26  should not be engaged in such an instance. An alternative measure to avoid unequal extension of the rods  29  would be to use a hydraulic flow divider to ensure that both lift cylinders  26  receive the same flow during extension and hence will extend equally. 
   Second Embodiment  100   
   The operation of the lateral shifting assembly  121  of the second embodiment  100  of the laterally shiftable vehicle is very similar to that of the first embodiment  10 . For the second embodiment,  100 , the lack of a tie bar means that the operator must individually incline and pin the lift cylinders  26 . The lift cylinders  26  are always placed in parallel positions and pinned using their respective latch pins  36  before cylinder extension and lifting are initiated. The lack of a tie bar eliminates the need for matching the extensions of the rods  29  for the pair of lift cylinders  26  for the second embodiment  100 . Otherwise, the basic operations of the first  10  and second  100  embodiments are identical. 
   Third Embodiment  200   
   The operation of the lateral shifting assembly  221  of the third embodiment  200  of the laterally shiftable vehicle is very similar to that of the first two embodiments  10  and  100 . As shown in  FIGS. 10 ,  11 , and  12 , it may be seen that the tiebar  260  is parallel to the deck of the trailer  11  and the lift cylinders  26  are mutually parallel when the lift cylinders are in any position, as long as the cylinder rod  29  extensions are equal and the bearing plates  50  are also parallel to the trailer deck. When this is not the case, then the lift cylinders  26  are no longer parallel. For this reason, one of the latch pins  36  is not inserted whenever the lift cylinders  26  are extended in order to avoid side loads on the rods  29  or other overstress conditions. 
   ADVANTAGES OF THE INVENTION 
   The present invention permits achieving proper lateral alignment of a vehicle such as a truck or tractor/trailer with a fixed axis by a much simpler method than previously available. Repeatedly backing up, inspecting alignment, and pulling forward to permit backing up again to correct the alignment is very time consuming, particularly on uneven ground. The present invention is operable by one operator and requires only converting the mounting of the leveling lift cylinders normally on the rear of a working vehicle to a pivotable mounting, the provision of latch pins and receptacles, and a tie bar if desired. The lateral shifting assemblies of the present invention are safe to use, only marginally heavier than conventional corner lift cylinders, and inexpensive. Because the present invention can achieve lateral alignment much faster than conventional methods, it permits much quicker setups at work locations with attendant cost savings. 
   Various details of the present invention may be modified without departing from the spirit of the invention. For instance, double acting hydraulic cylinders could be used, latch pin positions moved, the geometry of the latching sleeve varied, and the location of the tie bar pins could be moved in the event that a tie bar is used. Likewise, a conventional truck could replace the trailer/tractor rig combination. In such a case, the vertical axis of rotation for the movement of the vehicle would be a vertical axis centrally located between the front wheels of the truck. However, these and other modifications do not alter the basic spirit of the invention.