Abstract:
A hitch device for a working vehicle for coupling a working device to the working vehicle has a lifting shaft unit supported in the frame structure of the working vehicle, and a coupling structure that is operatively connected therewith. The lifting shaft unit includes a lifting shaft, at least one lifting arm that is fixedly connected with the lifting shaft, and at least one reciprocating cylinder, which is hingedly connected with the lifting arm. The coupling structure includes first, upper coupling elements, which are located on the frame structure, second, lower coupling elements, which are hingedly connected to the frame structure, and connecting elements that are hingedly located on lifting arms of the lifting shaft. At least one of the connecting elements is rigid. In this manner, it is ensured that the load on the coupling elements that form the hitch device is balanced, even when a load is introduced asymmetrically.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The invention described and claimed hereinbelow is also described in German Patent Applications DE 10 2007 046 890.5 filed on Sep. 28, 2007. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a hitch device for a working vehicle. 
     Publication WO 2004/056168 makes known a hitch device for a working vehicle designed as a tractor, the coupling structure of which is supported at the top on a frame structure of the tractor via an upper lifting shaft. The lifting shaft is coupled with two reciprocating cylinders that are hingedly located on the frame structure of the tractor via lifting arm systems having a single-piece or multiple-piece design. On the front side, the lifting arm system includes two—or pairs of—coupling elements that are positioned in the vertical direction and whose lengths may be adjusted—and which are hydraulically adjustable reciprocating cylinders in this case—that are hingedly connected at their free ends with lower linkages located in pairs on the underside. 
     The lower linkages are acted upon in a hinged manner on the frame structure of the tractor in a region that is located below the vehicle axis. By applying or releasing pressure to the reciprocating cylinders connected with the lifting shaft, the coupling frame and the hitch device connected thereto may be raised or lowered in the vertical direction. A special position of the coupling frame and the hitch devices attached thereto may also be adjusted by applying pressure to or releasing pressure from the reciprocating cylinders, which are located in a nearly vertical position. Given that the vertically-extending reciprocating cylinders act on the lower linkages in a central region, bending occurs in the lower linkages, the lifting shaft rotates, and pressure is applied to the arresting devices assigned to the free ends of the lower linkages, in particular when a load is introduced asymmetrically. 
     A design of a hitch device that does not include a lifting shaft was made known in EP 1 360 886 in order to optimize the loads that act on the hitch device, and with consideration for the fact that the application of a hitch device of this type must be highly flexible. Depending on the degrees of freedom desired, a hitch device of this type that is composed of six coupling elements includes up to six adjustable-length coupling elements, or two adjustable-length coupling elements and a large number of rigid coupling elements, via which a hitch device is supported and guided on a working vehicle, e.g., a tractor. Given that the coupling elements are located directly on the tractor or a coupling frame, or directly on the working device, only tensile and compression loads occur in the coupling elements. 
     The coupling elements of the hitch device located on the right and left sides are interconnected in a hydraulic manner, however, so that, when loads are introduced into the hitch device in an asymmetrical manner, as takes place, e.g., when working with a plow or when mowing using lateral mowing units, loads are applied to the coupling elements asymmetrically. To prevent damage from occurring to the coupling elements, which are typically designed as reciprocating cylinders, they must therefore be considerably oversized in design. In addition, given that the hitch device is coupled with the tractor exclusively via the coupling elements, the coupling elements must be controlled in a complicated manner so that the particular hitch device performs the desired reciprocating motion in a precise manner. 
     SUMMARY OF THE PRESENT INVENTION 
     The object of the present invention, therefore, is to avoid the described disadvantages of the related art and, in particular, to provide a hitch device that ensures that the load on the coupling elements—which form the hitch device—is balanced, even when loads are introduced asymmetrically. 
     In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a hitch device for a working vehicle for coupling a working device to the working vehicle, that includes a lifting shaft unit supported in the frame structure of the working vehicle, and a coupling structure that is operatively connected therewith, the lifting shaft unit including a lifting shaft, at least one lifting arm that is fixedly connected with the lifting shaft, and at least one reciprocating cylinder, which is hingedly connected with the lifting arm, wherein the coupling structure includes first, upper coupling elements, which are located on the frame structure, second, lower coupling elements, which are hingedly connected to the frame structure, and connecting elements that are hingedly located on lifting arms of the lifting shaft, at least one of the connecting elements being rigid in design. 
     Given that the hitch device for a working vehicle for coupling a working device to the working vehicle includes a lifting shaft unit supported in the frame structure of the working vehicle and a coupling structure that is operatively connected therewith, and the coupling structure includes first, upper coupling elements that are hingedly located on the frame structure, second, lower coupling elements that are hingedly located on the frame structure, and connecting elements that are hingedly located on lifting arms of the lifting shaft—with at least one of the connecting elements being rigid in design—it is ensured that the coupling and connecting elements located on the right and left sides are coupled mechanically via the lifting shaft. As a result, when a load is introduced asymmetrically into the hitch device, a nearly balanced load distribution within the coupling structure is attained, thereby eliminating the need to oversize the coupling elements as a safeguard against asymmetrical introductions of loads. 
     By integrating the lifting shaft unit and at least one rigid connecting brace in the coupling structure, it is also ensured that the hitch device may be operated in a passive floating position, in which none of the adjustable-length coupling elements needs to be actively controlled. The floating position allows the coupling device to compensate for uneven ground surfaces solely via the natural weight of the working devices, without using the hydraulic circuit. When in a floating position of this type, the working device—which is preferably a ground-working device—is retained on the hitch device in a self-guiding manner solely via the action of process forces. 
     Great flexibility in terms of procurement costs, realizable degrees of freedom, and the use of the hitch device for highly diverse applications results when one or more of the coupling and connecting elements is/are rigid in design, and the remaining coupling elements and connecting elements are designed such that their lengths may be adjusted. 
     An optimized introduction of load into the coupling structure and, ultimately, into the hitch device is made possible in an advantageous embodiment of the present invention by the fact that the upper and lower coupling elements and the connecting elements of the coupling structure are located in pairs. 
     Given that, in an advantageous refinement of the present invention, the coupling and connecting elements are rigid in design and, by activating the at least one reciprocating cylinder of the lifting shaft unit, the working device that is adapted to the coupling structure may perform a vertical swivel motion, a cost-favorable basic configuration of the inventive hitch device is provided that is usable in a large number of general applications of the tractor. 
     In an advantageous refinement of the present invention, the upper coupling elements are designed such that their lengths may be adjusted, and the connecting elements and the lower coupling elements are rigid in design, so that, by activating the at least one reciprocating cylinder of the lifting shaft unit and/or the adjustable-length upper coupling elements, the working device—which is adapted to the coupling structure—is capable of carrying out a translatory motion along the vertical axis, a rotary motion around the transverse axis, and/or a controlled lateral motion composed of the rotation about a vertical axis and a superimposed translatory motion along the transverse axis. In addition to the cost-favorable use of a large number of identical parts, a design of the hitch device of this type has the advantage in particular that the hitch device is suitable in particular for coupling with working devices that require a vertical floating position, e.g., ground-working devices. 
     When, in a further advantageous embodiment of the present invention, the upper coupling elements and a connecting element are designed such that their lengths may be adjusted, and the further connecting element and the lower coupling elements are rigid in design, it is possible—by activating the at least one reciprocating cylinder of the lifting shaft unit and/or the adjustable-length coupling elements, and/or the adjustable-length connecting element—for the working device, which is adapted to the coupling structure—to carry out a translatory motion along a vertical axis, a rotary motion around the transverse axis, a rotary motion around the vehicle longitudinal axis, and a superimposed translatory motion along the transverse axis. In addition to easily compensating for hilly terrain, e.g., with working machines with a large working width, it is possible using a configuration of this type to greatly shorten the set-up of a plow, since controlling the adjustable-length coupling elements is easier and more comfortable as compared with conventional systems. 
     In a further advantageous embodiment of the present invention, the working vehicle includes articulated driving axles, which enable a “dog walk” function to be carried out, and with which one of the upper and lower coupling elements and one connecting element of the pairs of coupling and connecting elements are rigid, and the further ones are designed such that their lengths may be adjusted, and, by activating at least the adjustable-length lower and upper coupling elements and the adjustable-length connecting element, the motion of the working device that is adapted to the coupling structure may be coupled to the steering motion of the driving axles. It is therefore possible to always maintain the working device in the direction of travel of the working vehicle nearly precisely, even when working in the “dog walk” mode. In this manner, it is also ensured that the adapted working device does not collide, e.g., with the land wheels of the working vehicle. The multi-functionality of a design of this type is enhanced further in that, by activating the at least one reciprocating cylinder of the lifting shaft unit, and/or the adjustable-length upper and lower coupling elements, and the one adjustable-length connecting element, the working device that is adapted to the coupling structure may carry out a translatory motion in the vertical direction and a rotary motion around a longitudinal axis. An optimal implementation of the various courses of motion of the coupling structure is attained when, in an advantageous embodiment of the present invention, the adjustable-length coupling and connecting elements, and the rigid coupling and connecting elements are assigned to the hitch device on the right or left sides. 
     Similar effects are attained when, in a further advantageous embodiment of the present invention, the working vehicle also includes articulated driving axles, which enable a “dog walk” function to be carried out, and with which the upper and one of the lower coupling elements and one connecting element of the paired coupling and connecting elements are designed such that their lengths may be adjusted, and the remaining coupling and connecting elements are rigid in design, and, by activating the adjustable-length coupling elements and the adjustable-length connecting element, the motion of the working device that is adapted to the coupling structure may be coupled to the steering motion of the driving axles. In addition, with a structure of the hitch device of this type, it is possible, by activating the at least one reciprocating cylinder and/or the adjustable-length coupling elements and the adjustable-length connecting element of the coupling structure, for the working device that is adapted to the coupling structure to carry out a translatory motion in the vertical direction, a rotary motion around the transverse axis, a rotary motion around a longitudinal axis, and/or a controlled lateral motion. In addition to the effects described above, the number of realizable degrees of freedom of the motion of the hitch device is therefore increased further. 
     The greatest number of degrees of freedom in the motion of the hitch device results, in an advantageous refinement of the present invention, when the upper and lower coupling elements and one connecting element are designed such that their lengths may be adjusted, and the further connecting element is rigid in design, and, by activating the at least one reciprocating cylinder of the lifting shaft unit and the adjustable-length coupling and connecting elements, the working device that is adapted to the coupling structure carries out translatory motions along—and rotary motions around—an axis of motion that is oriented in the vehicle longitudinal direction, transversely to the vehicle longitudinal direction, and in the vertical direction. 
     In an advantageous embodiment of the present invention, the translatory motion may be carried out in and opposite to an axis of motion that is oriented in the vehicle longitudinal direction in order to compensate for oscillations between the working vehicle and the adapted working device. This is very interesting, in particular, when the working device is a piston press, and the motion of the coupling structure in and opposite to the vehicle longitudinal direction is carried out to compensate for vibrations of the working vehicle that are caused by the piston press. 
     In an advantageous refinement of the present invention, the length of the adjustable-length coupling elements and connecting elements may be adjusted hydraulically, mechanically, and/or electrically. In this context, it is also advantageous when the rigid coupling element(s) or the at least one rigid connecting element include means for manually changing their length. In this manner it is possible to tailor the basic dimensions of the coupling structure and, therefore, the hitch device, to the particular application. 
     Low reaction forces in the lifting shaft support are also ensured by the fact that the bearing of the lifting shaft on the frame structure of the working vehicle and the bearing of the lower coupling elements on the frame structure of the working vehicle are located close to each other. 
     The universal usability of the hitch device is also increased by the fact that the free ends of the coupling elements and connecting elements facing away from the working vehicle are directly adaptable to the particular working device or a coupling frame. A rapid adaptation of the working device to the hitch device is also supported when the coupling frame is designed essentially as a type of single-phase coupler, and the particular free end of the coupling and connecting elements located on the working-device side are attached thereto. A technically proven design of the coupling points results when the articulation points—on the working-device side—of the upper and lower coupling elements and the connecting elements are designed as coupling hooks, and, together with the corresponding articulation points of the working device or a coupling frame, form a hinged connection. 
     In an advantageous refinement of the present invention, the working-vehicle side articulation points of the pairs of lower and upper coupling elements and the connecting elements are separated from each other, thereby making it possible to position at least one power take-off transmission and/or a pulling device between them. 
     In a further advantageous embodiment of the present invention, the working-vehicle side and the working-device side articulation points of the coupling elements and the connecting elements including bearing points with two or three degrees of freedom. In a preferred embodiment, these may be designed as ball joints. The number of coupling points required may also be reduced when one coupling element and one connecting element in each case have—on the working-vehicle side and/or the working-device side—a common articulated point that is designed as a ball joint. 
     Given that the coupling structure includes at least one rigid connecting element, it is also ensured that the hitch device may be operated in a passive floating position. 
     A lateral pendulum motion of the inventive hitch device may be initiated precisely and rapidly when, in an advantageous refinement, the paired upper coupling elements are designed as dual-action, reciprocating cylinders, and the pressure chambers—located on the piston-rod side and the piston-surface side—of the reciprocating cylinders are interconnected so that the hydraulic medium may be exchanged. 
     A reduction in the torque that acts on the lifting shaft decreases when the same load is introduced and as the distance between the vehicle-side articulation points of the lower coupling elements of the coupling structure decreases. It is therefore advantageous when the working-vehicle side articulation points of the lower coupling elements are separated by an adjustable, horizontal expansion distance. 
     In an advantageous refinement of the present invention, the hitch device may be located on the front and/or back side(s), depending on the application. 
     In an advantageous embodiment of the present invention, the coupling structure defines the horizontal and vertical instantaneous centers, the position of the instantaneous centers being adjustable, thereby enabling the courses of motion and the trajectories of motion followed by the coupling structure to be adapted in a highly variable manner to highly diverse conditions of use. 
     In addition, the inventive hitch device is designed such that the motion of the coupling structure in the vertical direction ( 34 ,  38 ) is brought about solely by pressure acting on or being released from the reciprocating cylinder that actuates the lifting shaft unit. In this manner it is ensured that, even in the technically simplest design, the coupling structure at least allows an adapted hitch device to be raised and lowered. 
     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective illustration of a first structure of the hitch device 
         FIG. 2  shows a perspective illustration of a further structure of the hitch device with working vehicles with a “dog walk” function 
         FIG. 3  shows a perspective illustration of a further structure of the hitch device 
         FIG. 4  shows a perspective illustration of a further structure of the hitch device 
         FIG. 5  shows a perspective illustration of the hitch device exclusively with rigid coupling elements 
         FIG. 6  shows a perspective illustration of a detail of the hitch device 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a working vehicle  1  designed as a tractor  2 , to which hitch device  3 —which will be described in greater detail—is assigned, at the rear. It is within the scope of the present invention for hitch device  3 ,  3 ′ to be assigned to the front of tractor  2 , as an alternative or in addition thereto. In a known manner, tractor  2  includes a front axle  6  with land wheels  4 ,  5 , and a rear axle  7 . In the exemplary embodiment shown, rear axle  7  is accommodated by a frame structure  8 , which is assigned to working vehicle  1  that is designed as a tractor  2 . In a region assigned to rear axle  7  on the underside, bearing flanges  9  are integrally formed with frame structure  8 , which accommodate bearing seats  10  of a lifting shaft  11  in a manner such that rotation axis  12  of lifting shaft  11  extends nearly perpendicularly to vehicle longitudinal axis  13  of tractor  2 . 
     Lifting arms  14  are integrally formed with lifting shaft  11  in the region of bearing seats  10 , with which supporting flanges  15  are integrally formed in their top-side region assigned to rear axle  7 , with which piston rod-side ends  16  of reciprocating cylinders  18  engage in a pivoting manner, piston rod-side ends  16  being accommodated by frame structure  8  on the cylinder side  17  in a pivoting manner. By applying pressure to or releasing pressure from reciprocating cylinders  18 , lifting arms  14  and, therefore, the lifting shaft are swiveled around rotational axis  12  of lifting shaft  11  in arrow direction  19 . 
     To articulate coupling structure  20 , which will be described in greater detail, supporting flanges  21  are integrally formed with frame structure  8  of tractor  2  in a top-side region at the same horizontal level in order to accommodate—in a pivotable manner—first, paired, upper coupling elements  22 . Supporting flanges  23  are integrally formed with frame structure  8  of tractor  2  in an underside region, which is preferably located in the region of bearing flange  9  of lifting shaft  11 , at the same horizontal level in order to accommodate—in a pivotable manner—second, paired, lower coupling elements  24 . Lifting arms  14  of lifting shaft  11  also include—in a top-side region facing away from rear axle  7 —further supporting flanges  25 , which accommodate paired connecting elements  26  in a pivoting manner. Articulation points  27 —which will be described in greater detail below—are located on the free ends—facing away from rear axle  7 —of upper coupling elements  22 , lower coupling elements  24 , and connecting elements  26 , the articulation points  27  being connectable in a pivoting manner with coupling points  28  of a coupling frame  29 , or directly with coupling points  30  of a working device  31  to be adapted to working vehicle  1 , e.g., a plow. 
     For simplicity, further aspects of the present invention will be described with reference to an embodiment with coupling frame  29 , even though the interrelationships described apply similarly for hitch devices  3  that are directly connected to particular working device  31  without the use of a coupling frame  29 .  FIG. 1  shows the design of coupling structure  20 , with which hitch device  3  may be operated with six degrees of freedom. To this end, it is necessary for the upper and lower coupling segments  22 ,  24  and one of the connecting elements  26  that connects lifting shaft  11  with coupling frame  29  to be designed such that their lengths are adjustable, i.e., as hydraulic cylinders in the simplest case. According to the present invention, the further one of the paired connecting elements  26  is designed as a rigid connecting brace  32 . 
     By either applying pressure to or releasing pressure from—separately or in a coordinated manner—reciprocating cylinders  18  that actuate lifting shaft unit  33 , or adjustable-length, upper and lower coupling elements  22 ,  24 , and adjustable-length connecting brace  26 , it is possible for coupling frame  29 —and, therefore, working device  31  adapted thereto—to carry out translatory motions (arrow directions  36  through  38 ) along—and rotary motions (arrow directions  39  through  41 ) around—an axis of motion that is oriented in vehicle longitudinal direction  13 , transversely to vehicle longitudinal direction  35 , and in vertical direction  34 . In addition to the completely free motion of coupling frame  29  in three dimensions, translatory motion  36 , e.g., of coupling frame  29  along vehicle longitudinal axis  13  may be used to compensate for vibrations between adapted working device  31  and working vehicle  1 . An application of this type is helpful, in particular, when adapted working device  31  is designed as a piston press—which is not shown but which is known per se—whose circumferential plunger—which performs a working stroke and a return stroke—introduces considerable vibrations into working vehicle  1  when conventional hitch devices  3  are used. 
     Given that one of the connecting elements  26  is designed as a rigid connecting brace  32 , coupling structure  20  is also designed such that hitch device  3  may be operated in a passive floating position, in which a working device that has been adapted to hitch device  3  may glide over the ground without any need to actively control adjustable-length coupling and connecting elements  22 ,  24 ,  26 . 
     In a further embodiment of the present invention as shown in  FIG. 2 , working vehicle  1  is capable of performing a “dog walk” function. This means that land wheels  4 ,  5  of front and rear axles  6 ,  7  may be controlled individually or in an axle-wise manner. It is therefore possible for working vehicle  1  to be driven over ground  42  such that each land wheel  4 ,  5  runs along a separate track, which minimizes damage to the ground that results when it is rolled over repeatedly. In this variant of the embodiment, inventive coupling structure  20  of hitch device  3  includes adjustable-length, upper coupling elements  22 , an adjustable-length, lower coupling element  24 , and an adjustable-length connecting brace  26  of paired coupling elements  22 ,  24  and connecting braces  26 . In the simplest case, the length may be adjusted via reciprocating cylinders. Remaining connecting brace  26  and one of the lower coupling elements  24  are designed as rigid connecting brace  32 . 
     By applying pressure to or releasing pressure from adjustable-length coupling elements  22 ,  24  designed as reciprocating cylinders, and one connecting element  26 , it is possible to couple the motion of coupling frame  29  and working device  31  adapted thereto to steering motion  43  of land wheels  4 ,  5 , thereby ensuring that the orientation of working device  31  relative to the orientation of land wheels  4 ,  5  and, therefore, to direction of travel FR of working vehicle  1 , remain nearly unchanged. In a preferred embodiment, the steering angle of land wheels  4 ,  5  described by steering motion  43  is measured and converted in an evaluation unit  44  into a pivot motion  45  of coupling structure  20 . Finally, pressure is applied to or released from adjustable-length coupling elements  22 ,  24  and adjustable-length connecting element  26  in a manner such that coupling structure  20  carries out pivot motion  45  that has been ascertained. 
     By applying pressure to or releasing pressure from—separately or in a coordinated manner—reciprocating cylinders  18  that actuate lifting shaft unit  33 , or to/from adjustable-length, upper and lower coupling elements  22 ,  24 , and one adjustable-length connecting brace  26 , it is possible for coupling frame  29 , and therefore, working device  31  adapted thereto, to carry out a translatory motion  38  in vertical direction  34 , a rotary motion  40  around transverse axis  35 , a rotary motion  39  around a longitudinal axis  13 , and/or a controlled lateral motion composed of rotation  41  about a vertical pivot axis  34  and a translatory motion  37  along transverse axis  35 . With a design of this type, coupling frame  29  does not perform a translatory motion along vehicle longitudinal axis  13 . 
     The “dog walk” function of working vehicle  1  may be added subsequently to working device  31  when, e.g., for reasons of cost, only one of the pairs of upper and lower coupling elements  22 ,  24  and connecting braces  26  is designed such that its length may be adjusted, and adjustable-length coupling elements  22 ,  24  and adjustable-length connecting element  26  are assigned to hitch device  3  and, therefore to coupling structure  20 , on either the left or right side. The number of possible degrees of freedom is reduced in this case, however. In the present case, there is no rotary motion around transverse axis  35 , nor is there a lateral pendulum motion due to blocked rotary motion  41  around vertical pivot axis  34 . 
     In a further embodiment of the present invention as shown in  FIG. 3 , upper coupling elements  22  and a connecting element  26  are designed such that their lengths may be adjusted, and further connecting element  26  and lower coupling elements  24  are designed as rigid connecting braces  32 . By activating reciprocating cylinders  18  of lifting shaft unit  33 , and/or adjustable-length coupling elements  22 , and/or adjustable-length connecting element  26 , it is possible for working device  31  that is adapted to coupling structure  20  to carry out a translatory motion  38  along a vertical axis  34 , a rotary motion  40  around transverse axis  35 , a rotary motion  39  around vehicle longitudinal axis  13 , and/or a controlled lateral motion, i.e., rotation  41  about a vertical pivot axis  34 , and a superimposed translatory motion  37  along transverse axis  35 . 
     Given that, in  FIG. 4 , upper coupling elements  22  are designed such that their lengths may be adjusted, and connecting elements  26  and lower coupling elements  24  are designed as rigid coupling braces  32 , the costs to manufacture coupling structure  20  and, therefore, hitch device  3 , are reduced further. The number of degrees of freedom are further reduced with a structure of hitch device  3  of this type. By activating reciprocating cylinders  18  of lifting shaft unit  33 , and/or adjustable-length, upper coupling elements  22 , working device  31  that is adapted to coupling structure  20  carries out a translatory motion  38  along vertical pivot axis  34 , a rotary motion  40  around transverse axis  35 , and/or a controlled lateral motion, which is composed—as described above—of rotation  41  about a vertical axis  34  and a superimposed translatory motion  37  along transverse axis  35 . 
     Given that—as shown in FIG.  5 —upper coupling elements  22  are designed as rigid connecting braces  32 , a coupling structure  20  results that is composed exclusively of rigid connecting braces  32 . With a structure of this type, an exclusive vertical pivot motion of hitch device  3  in arrow direction  46  may be realized by applying pressure to or releasing pressure from reciprocating cylinders  18  that are coupled with lifting shaft unit  33 . A lateral pendulum motion of hitch device  3  in arrow direction  47  depends on the bearing play in various articulation points  27  and may not be influenced in a specific manner. 
     It is also within the framework of the present invention for the adjustable-length lower and upper coupling elements  22 ,  24  and adjustable-length connecting element  26  to be adjustable in terms of length in a hydraulic, mechanical, or electrical manner. In addition, rigid connecting braces  32  shown in  FIG. 4  may include means for manually changing the length of particular connecting brace  32 , e.g., a threaded spindle system. Regardless of whether particular coupling and connecting elements  22 ,  24 ,  26  are designed such that they are rigid or that their lengths may be adjusted, a load-optimized design of hitch device  3  results when vehicle-side articulation points  27  of lower coupling elements  24  are positioned on frame structure  8  such that they are close to bearing seats  10  of lifting shaft  4  on frame structure  8 . 
     According to  FIG. 6 , coupling frame  29  may be designed as a single-phase coupler. Articulation points  27  assigned to coupling frame  29  are designed as peg-shaped segments  49 . The free ends—located on the coupling-frame side—of coupling elements  22 ,  24  and connecting elements  26  accommodate self-closing coupling hooks  50 , which may snap into peg-shaped segments  49  of coupling frame  29  in a self-closing manner. Coupling frame  29  includes—on the working-device side—receiving hooks, which may ultimately be brought into engagement with corresponding coupling points  30  of working device  31 . It is within the scope of the present invention for coupling and connecting elements  22 ,  24 ,  26  to also be located directly on a working device  31  without a coupling frame  29  between them. In addition, articulation points  21 —on the working-device side—of the pairs of lower and upper coupling elements  22 ,  24 , and connecting elements  26  are separated by a distance S 1  through S 3 , which makes it possible to position at least one not-shown power take-off transmission and/or a pulling device between them. 
     Distance S 1 —which is also referred to as the expansion distance—between articulation points  27  of lower coupling elements  24  may also be adjustable, thereby making it possible to further optimize the loads that act on hitch device  3 . Bearing points  51  with two or three degrees of freedom may be created, depending on the state of the bearings—which are positioned in working vehicle-side and working device-side articulation points  27 —of coupling elements  22 ,  24  and connecting elements  26 . It is within the scope of the present invention for articulation points  27  to be designed as ball joints  52 , and for articulation points  27  of various coupling and connecting elements  22 ,  24 ,  26  to be combined into a single ball joint  52 . 
     If, as shown in  FIG. 4 , paired, upper coupling elements  22  are designed as reciprocating cylinders, the horizontal pendulum motion of hitch device  3  and, therefore, that of the working device may be realized in a simple manner by connecting the piston-rod side and piston-surface side pressure chambers of the reciprocating cylinders such that they may exchange hydraulic medium via line systems and related switching valves  53 . 
     In a manner known per se, coupling elements  22 ,  24 , which are integrated in coupling structure  20  in a pivotable manner, form a horizontal and vertical instantaneous center M 1 , M 2 , respectively, for pivoting coupling structure  20  in a horizontal and vertical plane, as shown in  FIG. 1 , it being possible to change the horizontal and vertical instantaneous center M 1 , M 2  depending on the adjustable geometry of the coupling structure. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in a hitch device for a working vehicle, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.