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BACKGROUND OF THE INVENTION 
     The subject matter of this application relates to agricultural implements. 
     In order to maximize yields of certain crops while minimizing water usage, it is desirable to prepare the soil of the field or planting area so that the surface of the soil within the planting area has an optimum topography. Typically, such preparation is performed using an agricultural scraper, which may comprise a blade that is supported in a generally horizontal disposition on a frame provided with ground-engaging wheels and a tongue for attachment to a tractor or other towing vehicle. Global positioning system (GPS) receivers may be mounted at the two opposite ends of the blade for measuring difference in height between the two ends of the blade and the frame may be movable vertically relative to the wheel axles by use of hydraulic cylinders or other actuators in order to adjust the height of one or both ends of the blade. By drawing the scraper over the soil, variations in height of the surface of the soil may be reduced or eliminated. 
     The blade of a conventional agricultural scraper may be as much as 20 feet long. The length of the blade presents a substantial challenge when moving a scraper from field to field of a farming operation and an even greater challenge when it is necessary to move the scraper over public roads and highways. One conventional scraper meets this challenge by employing two separate sets of wheels, for scraping and for road transportation respectively. At least one set of wheels is movable between a storage position and deployed position. Such an arrangement is complex and expensive and is prone to breakdown. 
     In operation of a conventional agricultural scraper, the blade extends perpendicular to the direction of travel of the frame. Thus, the soil that is moved by the scraper moves generally in the direction of travel of the frame. However, it may be desirable when using a scraper to feed the soil to left or right of the direction of travel. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention there is provided an agricultural implement comprising a traction structure at a forward end of the implement, a tool beam rearward of the traction structure and extending transverse to a longitudinal axis of the traction structure in a substantially horizontal disposition, first and second wheeled support structures supporting the tool beam at opposite respective ends of the tool beam, first and second linkages each having a forward portion connected to the traction structure and having rearward portions connected to the first and second support structures respectively, and an actuator effective between the traction structure and the first linkage for selectively adjusting an angular position of the first linkage relative to the longitudinal axis of the traction structure, and wherein the tool beam provides a force transmitting connection between the rearward portions of the first and second linkages whereby angular movement of the first linkage relative to the traction structure is accompanied by angular movement of the second linkage relative to the traction structure. 
     In accordance with a second aspect of the present invention there is provided an agricultural scraper comprising a traction structure at a forward end of the scraper, and a scraper blade rearward of the traction structure and extending transverse to a longitudinal axis of the traction structure in a substantially horizontal disposition, first and second wheeled support structures supporting the scraper blade at opposite respective ends of the scraper blade, and wherein the scraper blade comprises first and second segments each having an outer end and an inner end, the outer ends of the first and second segments are supported by the first and second support structures respectively, the inner ends of the first and second segments are connected together by a hinge that allows the scraper blade to be folded about a substantially vertical axis, whereby the first and second segments can be brought selectively to an aligned disposition or to a folded disposition, and the first and second segments are brought from the aligned disposition to the folded disposition by moving the inner ends of the first and segments forward relative to the outer ends of the first and second segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an agricultural scraper embodying subject matter disclosed in this application, 
         FIG. 2  is a right side elevation of the scraper, 
         FIG. 3  is an enlarged side elevation of a blade support structure in a lowered position, 
         FIG. 4  is a similar view of the blade support structure in an elevated position, 
         FIG. 5  is a top plan view of the scraper, showing the scraper blade disposed perpendicular to the path of movement of the scraper, 
         FIG. 6  is a top plan view of the scraper showing the scraper blade disposed oblique to the path of movement of the scraper, 
         FIG. 7  is a top plan view of the scraper showing the blade in a folded disposition, 
         FIG. 8  is a perspective view of the scraper showing the blade in the folded disposition, and 
         FIG. 9  is a schematic view illustrating a hydraulic control system of the scraper. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, the suffix L or R may be used to designate left or right. The suffix may be omitted when the description pertains equally to left and right. 
     The illustrated agricultural scraper comprises a tongue  2  provided at a forward end with a coupler  6  for attachment to a tractor  4  or other towing vehicle. Two beams  8 L,  8 R are connected at respective proximal ends to the rear end of the tongue in a manner allowing pivotal movement of the beams about a vertical axis  10  that is directly to the rear of the coupler  6 . The two beams  8 L,  8 R are supported at their distal ends by wheel assemblies  12 L,  12 R respectively. Each wheel assembly  12  comprises a generally C-shaped blade support structure  16  including a cylindrical bearing post  20  mounted between the top arm of the C-shaped structure and a mounting point  22 . The bearing post  20  is fitted in a bearing (not shown) at the distal end of the respective beam  8  so that beam is turnable relative to the wheel assembly about an axis  24  perpendicular to the longitudinal axis of the beam. 
     A wheel carrier link  28  is pivotally attached to the blade support structure  16  near the lower end thereof and a wheel truck  32  is pivotally attached to the wheel carrier link  28  at a rear end thereof. The wheel truck  32  comprises a rocker  38  and fore and aft wheels  40  mounted on axles projecting from the rocker. A hydraulic cylinder  36  is effective between the wheel carrier link  28  and an attachment point near the upper end of the blade support structure  16 , whereby the blade support structure may be selectively raised ( FIG. 4 ) and lowered ( FIG. 3 ) relative to the wheels, raising and lowering the bearing post  20  and the distal end of the beam  8 . Pivotal movement of the rocker  38  relative to the wheel carrier link allows the wheels to remain in contact with the ground surface under changes in topography of the ground surface and changes in angular position of the wheel carrier link when the blade support structure  16  is raised and lowered. 
     A scraper blade  42  having two opposite (right and left) ends is supported between the two blade support structures  16 . At each end of the scraper blade, a lower edge of the scraper blade is pivotally supported at the lower end of the blade support structures by a pivot pin engaging in a sleeve bearing and an upper edge of the scraper blade is connected to the blade support structure by a double-acting hydraulic cylinder  46  engaging a mounting bracket  48  attached to the scraper blade. By extending and retracting the hydraulic cylinders  46 L,  46 R, the blade  42  can be tilted about its lower edge relative to the wheel trucks. 
     A lever arm  52  projects laterally of each scraper support structure  16  at about 60° to the axles of the wheels  40 . As shown in  FIG. 4 , the lever arm  52  is at about 90° to the beam  8 . The distal end of the lever arm is pivotally connected to one end of a bar  56 , the opposite end of which is pivotally attached to the tongue at a point that is spaced from the pivot axis  10  by a distance that is substantially equal to the length of the lever arm. The beam  8 , lever arm  52 , connecting bar  56  and tongue  2  form a four-bar linkage. 
     The tongue  2  may be considered to have a longitudinal axis that intersects the axis  10  and the axis about which the tongue turns relative to the towing tractor when the tractor is steered to left or right. In the disposition shown in  FIGS. 1 and 5 , the blade is perpendicular to the longitudinal axis of the tongue and the wheel axles are parallel to the blade and to the longitudinal axis of the tongue. As the tractor tows the scraper over a surface, a hydraulic controller  58  ( FIG. 9 ) controls supply of hydraulic fluid to the cylinders  36  to place the blade at a suitable height relative to the wheels  40  and at a suitable inclination to horizontal to move soil so as to achieve a desired topography. 
     When the towing tractor is towing the scraper straight ahead, the tracking path of the wheels (i.e. the path perpendicular to the axles on which the wheels are mounted) is parallel to the longitudinal axis of the tongue. In the event that the tractor is steered to left or right, the tongue tends to turn about the axis  10  and the four-bar linkages transmit the turning movement of the tongue to the wheel assemblies  12 , which also turn to left or right following the tongue. 
     A double-acting hydraulic cylinder  60  is effective between the tongue  2  and the beam  8 R. When the cylinder is retracted from the disposition shown in  FIG. 1 , the beam  8 R is forced to turn counterclockwise relative to the tongue (as seen in  FIG. 1 ) about the pivot axis  10  and the distal end of the beam  8 R is forced forward. Since the blade  42  rigidly connects the distal end of the beam  8 L to the distal end of the beam  8 R, the beam  8 L also turns counterclockwise relative to the tongue about the pivot axis  10  and the distal end of the beam  8 L is forced rearward. As the beams  8  turn, the four-bar linkages constrain the lever arms  52  to remain at a constant angular position relative to the tongue and consequently the blade support structures do not turn and the wheel axles remain perpendicular to the longitudinal axis of the tongue. Correspondingly, when the cylinder is extended from the disposition shown in  FIG. 1 , the beam  8 R turns clockwise relative to the tongue and the distal end of the beam  8 R is forced rearward. The beam  8 L also turns clockwise relative to the tongue and the distal end of the beam  8 L is forced forward. The four-bar linkages constrain the lever arms  52  to remain at a constant orientation relative to the tongue and the wheel axles remain perpendicular to the longitudinal axis of the tongue. The scraper shown in the drawings is therefore adjustable between a position in which the blade is perpendicular to the direction of travel of the scraper and a position in which either the left end or the right end of the blade is forward of the other end, allowing the scraper to feed material to either side. 
     In some cases it may be desired to discharge the material to one side of the path of the scraper but in other cases it may be desired to displace the material to left or right of the path of the scraper without discharging the material. Accordingly, the blade is provided at each end with a detachable retaining fence  64  that is hinged to the end of the blade and is pivotally connected to one end of a rod  68 , the opposite end of which is pivotally connected to the forward end of the mounting bracket  48 . The locations of the points of pivotal connection of the fence  64  and rod  68  to the blade  42  and bracket  48  are such relative to the axis  24  that the bracket  48 , rod  68 , fence  64  and blade  42  form a parallelogram linkage and accordingly the fence  64  remains parallel with the tracking path of the wheels, even though the scraper blade may not be perpendicular to the tracking path of the wheels. 
     Referring again to  FIG. 1 , the scraper blade  42  is composed of two wings  70 L and  70 R that are connected by a hinge comprising bracket structures  74  welded to the two wings and a hinge pin  76  that engages the bracket structures and defines a pivot axis that is parallel to the axis  24 . The two bracket structures  74  are provided with respective force transmitting bar structures  80 , which are pivotally connected by a pin  82  that is to the rear of the hinge pin  76 , and double-acting hydraulic cylinders  86  are effective between the bracket structures  74  and the bar structures  80 . When the cylinders  86  are retracted, the pin  76  and the pin  82  are drawn together and the two wings are held in a mutually aligned disposition. The blade is then straight and is configured for use. Conversely, when the cylinders are extended the pin  76  is forced forward relative to the pin  82  and the wings are brought to a disposition, as shown in  FIGS. 7 and 8 , in which the blade  42  is folded. Whereas the wheel trucks  32  may be as much as 30 feet or more apart when the wings  70  are in the aligned disposition, when the blade is in the folded disposition the wheel trucks may be less than eight feet apart. By lifting the scraper blade above the ground surface and bringing the blade to the folded disposition, the scraper is suitably configured for transporting between fields of a farming operation or on a public road. Moreover, when the blade is in the folded disposition the scraper is suitably dimensioned for placing in a standard ISO shipping container, facilitating long distance transportation. 
     Because the pin  76  moves forward relative to the wheel assemblies  12  when the cylinders  86  are expanded to change the blade from its straight configuration to its folded configuration, the force that is exerted on the blade when the scraper is being used to move soil, rock or other material to achieve a desired topography tends urge the blade toward its straight configuration. Thus, it is not necessary to supply significant effort through the cylinders  86  to retain the blade in its straight configuration. 
     Referring again to  FIG. 6 , the hydraulic controller supplies hydraulic fluid under pressure to the cylinders  36 ,  46 ,  60  and  86  in response to various input signals, including operator signals and, optionally, signals generated by GPS receivers  88 L,  88 R mounted on the support structures  12 L,  12 R respectively for detecting differences in height of the two ends of the scraper blade. 
     It will be appreciated that the invention is not restricted to the particular embodiment that has been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims, as interpreted in accordance with principles of prevailing law, including the doctrine of equivalents or any other principle that enlarges the enforceable scope of a claim beyond its literal scope. For example, although the invention has been described in the context of a detachable implement that is towed by a tractor, the scraper may be self-propelled. In addition, although the fences  64  are illustrated as being attached directly to the wings  74 , the fences  64  may alternatively be attached to extension wings that are aligned with the wings  74  and extend outward beyond the wheel assemblies  12 . The blade may be in the form of a box structure and the extension wings may be withdrawn into the box structure when not needed. Unless the context indicates otherwise, a reference in a claim to the number of instances of an element, be it a reference to one instance or more than one instance, requires at least the stated number of instances of the element but is not intended to exclude from the scope of the claim a structure or method having more instances of that element than stated. The word “comprise” or a derivative thereof, when used in a claim, is used in a nonexclusive sense that is not intended to exclude the presence of other elements or steps in a claimed structure or method.

Summary:
An agricultural implement includes a traction structure and a tool beam rearward of the traction structure. First and second wheeled support structures support the tool beam at opposite respective ends of the tool beam. First and second linkages each have a forward portion connected to the traction structure and rearward portions connected to the first and second support structures respectively. An actuator is effective between the traction structure and the first linkage for selectively adjusting an angular position of the first linkage relative to the longitudinal axis of the traction structure. The tool beam provides a force transmitting connection between the rearward portions of the first and second linkages whereby angular movement of the first linkage relative to the traction structure is accompanied by angular movement of the second linkage relative to the traction structure.