Abstract:
A hitch for a work vehicle includes a plurality of links pivotally coupled to a vehicle body and to an implement, either directly or indirectly via a hitch frame or quick coupler. The hitch preferably includes at least one upper link, two lower links and two longitudinally adjustable lift links for raising and lowering the hitch. Each lift link is coupled to an associated lower link near an aft end thereof. The hitch may selectively comprise both rigid and longitudinally adjustable links. The functionality of the hitch can be changed by replacing, adding or removing links. The hitch can be converted between a simple three-point hitch and a “hexapod” type hitch.

Description:
BACKGROUND  
         [0001]    The present invention relates to a hitch for coupling an implement to a work vehicle.  
           [0002]    Vehicle/implement hitches are used to couple various implements to a work vehicle, such as to couple a farm implements to a tractor. A known hitch, such as described in standard ISO 730, has an upper link or upper rod, two lower links, and two lift cylinders which are coupled to a central area of the lower links. Such a hitch is known as a three-point implement hitch. However, the functionality of such a three-point hitch is limited since only a raising and a lowering of the lower links is possible with the lifting cylinders. Other motions cannot be executed by controlling the lifting cylinders.  
           [0003]    It has been proposed that a hydraulic cylinder be used as an upper link so that the hitched implement can be tilted about a horizontal axis running transversely to the longitudinal axis of the vehicle. It is also known to control the lateral deflection of the lower links with lateral struts. The lateral struts can be longitudinally adjustable and activated hydraulically. In addition to a lateral stabilizing of the lower links the lateral struts can serve to influence the lateral alignment of the working implement. However, the functionality of the hitch remains limited even with these measures.  
           [0004]    U.S. Pat. No. 6,321,851 describes a hitch with six longitudinally adjustable links connected between the vehicle and the implement in the a hexapod system. Such a hitch permit motion of the hitched implement with six degrees of freedom. However, such freedom of motion is not always required in practice, such as when an implement is merely being pulled by the vehicle. On the other hand, it is desirable to have a simple hitch with improved functionality and improved comfort.  
         SUMMARY  
         [0005]    Accordingly, an object of this invention is to provide a simple hitch with improved functionality and improved comfort.  
           [0006]    This and other objects are achieved by the present invention, wherein hitch lift links are coupled to lower or draft links near to the aft ends thereof, rather than the central portions thereof. The hitch links may selectively be rigid and longitudinally adjustable so that the functionality of the hitch can be varied by replacing, adding or removing the links of the hitch. The rigid links are manually mechanically adjustable. The length of the longitudinally adjustable links can be automatically adjusted by a control mechanism.  
           [0007]    With such links, the end user may construct a hitch or implement interface as desired for particular requirements. The hitch may be converted as needed by replacing, adding and removing structural links. In particular, it would be possible to rapidly modify a standard simple three-point hitch in a step-by-step manner to achieve the versatile functionality of a hexapod hitch. The hitch can consist of a few types of similar links, preferably, six substantially identical, longitudinally adjustable links with associated control means, two rigid lower links and one rigid upper link whose length can optionally be mechanically adjusted. If needed, other components can be added, such as a hitch frame and rigid or longitudinally adjustable lateral stabilizers. Such a simple hitch may be supplemented as needed by purchasing other components.  
           [0008]    Preferably, the longitudinally adjustable links, especially the upper and the lower links and the lift links are substantially identical. This permits use of a simpler control mechanism. The great number of identical parts can keep the manufacturing cost and the storage cost of the structural unit low.  
           [0009]    Each longitudinally adjustable link can include a hydraulic or electric drive for automatically adjusting its length. It is advantageous to use hydraulic cylinders, such as double-acting hydraulic cylinders. Preferably, the links are coupled and arranged to form closed, kinematic structures so that it is possible to arrange the links in a hexapod such as described in EP-A-1,095,549.  
           [0010]    Preferably, the links are coupled to the frame or implement in a manner which permits relative motion in at least two degrees of freedom. For example, universal joints with pivot axes arranged at 90 degrees to each other and making two degrees of rotational freedom available, or ball-and-socket joints that additionally offer a degree of rotational freedom are suitable.  
           [0011]    In a first preferred embodiment, the hitch includes a conventional upper, central link and two conventional rigid lower links. Lift links are coupled near the free ends of the lower links. If the upper link is a rigid or a mechanically adjustable link, the resulting hitch functions as a customary three-point hitch, and an implement can be automatically raised and lowered by the lift links. If the rigid upper link is replaced by an adjustable link, then the implement also can be automatically tilted about a transverse horizontal axis.  
           [0012]    In the embodiments with only one upper link, the rigid lower links behave substantially as in a customary three-point hitch. In this instance it is advantageous to use known lateral stabilizers that act on a central area of the lower links.  
           [0013]    Currently, a hitch may be automatically laterally aligned within given limits by laterally stabilizing hydraulic cylinders. Instead of these lateral stabilizers, hydraulic lateral stabilization can be performed by two upper longitudinally adjustable links, instead of the only one upper link. The first embodiment can be converted to this configuration by replacing the single upper link with two longitudinally adjustable links.  
           [0014]    Preferably, the two upper links are coupled at the same height and are preferably aligned in a “V” with their first ends spaced farther apart than their second ends. The base of the V can selectively face the vehicle or the implement. However, preferably, the first ends of the upper links are coupled to the vehicle body and the closer second ends are coupled to the implement or to the coupling frame. The V-shaped system adds another controllable degree of freedom since now even the lateral alignment of the implement relative to the vehicle can be automatically adjusted.  
           [0015]    A third embodiment includes two upper, longitudinally adjustable links arranged in a V relative to one another, two lower, lateral, longitudinally adjustable links and two lift links which are coupled to the free ends of the lower links. The third embodiment may be formed by replacing the two rigid lower links of the second embodiment with longitudinally adjustable links. The third embodiment makes possible movement with six degrees of freedom, namely, translatory motions in three directions and rotational motions about three axes. The functionality of a hexapod hitch is therewith achieved.  
           [0016]    In another, especially preferred embodiment, the vehicle-side coupling joints of a lower link and the vehicle-side coupling joints of a lift link are located in a vertical plane. Preferably, the vehicle-side coupling points of the lower link and of the lift link are arranged approximately in a vertically superposed manner. This makes possible a free lateral pivoting out of the hitch, which is necessary in a few applications. In the second and the third embodiments described above, the two upper, longitudinally adjustable links must be shifted to the floating position for a free, lateral pivoting out.  
           [0017]    It is also advantageous to arrange the vehicle-side coupling joint of the lift link near and approximately perpendicular across the vehicle side coupling joint of the upper link.  
           [0018]    It is also advantageous if the upper links and the lift links have a horizontal convergence and if their vehicle coupling joints are closer together than their implement coupling joints. This convergence results in a guide point whose relative position to the work vehicle can be influenced by appropriately controlling the links in an advantageous manner as described in DE-A-10 120 732. Preferably, identical or similar coupling joints are used to reduce cost and complexity.  
           [0019]    To provide a modular unit that is easy to handle, the coupling joints are preferably designed as separate components that can be mounted and dismounted as required on the vehicle body and/or on the implement or on the hitch frame. Threaded bores may be formed in advance on the vehicle body and on the implement or on the coupling frame so that a conversion is possible at all times. This design makes it possible to use only as many coupling points as are actually needed. Superfluous coupling points do not need to be acquired or can be dismounted.  
           [0020]    Each adjustable link is preferably associated with its own separate control system. For example, a separate hydraulic valve system is used for each hydraulic cylinder. The control systems can be designed to be identical or similar so that the number of different components is kept low.  
           [0021]    It is furthermore advantageous to design the control systems in such a manner that they can be readily mounted and dismounted at any time to the vehicle body or implement or coupling frame so that the number of control systems used can be adapted to the particular requirement. In particular, in order to save structural space and assure good accessibility, the controls can be mounted in series close to each other on the vehicle body, e.g., on a differential transmission housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a perspective view of a first embodiment of the hitch of the invention.  
         [0023]    [0023]FIG. 2 is a perspective view of a modification of the hitch of FIG. 1.  
         [0024]    [0024]FIG. 3 is a perspective view of a second embodiment of the hitch of the invention.  
         [0025]    [0025]FIG. 4 is a perspective view of a third embodiment of the hitch of the invention.  
         [0026]    [0026]FIG. 5 is a top view onto the hitch of FIG. 4.  
         [0027]    [0027]FIG. 6 is a side view of the hitch of FIG. 4. 
     
    
     DETAILED DESCRIPTION  
       [0028]    In the following description the same reference numerals are used for identically or similarly designed structural components with the same functionality.  
         [0029]    [0029]FIG. 1 shows a part of a differential transmission housing  10  that is located in the rear of a tractor (not shown) and forms a vehicle body. A power takeoff shaft  12  exits from the central area of transmission housing  10 . A coupling joint  14 ,  16 , each of which serves to articulate a rigid link  18 ,  20 , is located on each side of transmission housing  10  on its lower area. Links  18 ,  20  are customary lower links designed as fixed length, rigid components. Coupling joints  14 ,  16  can also be designed in a customary manner. They include a ball-and-socket joint so that lower links  18 ,  20  can pivot about a horizontally axis in a vertical direction and can be deflected laterally within narrow limits.  
         [0030]    A central upper coupling joint  22  is located above power take-off shaft  12  and pivotally supports rigid upper link  24 . Link  24  can have a length which can be adjusted mechanically by screwing a spindle in or out. Upper coupling joint  22  comprises a universal joint so that the upper link can be pivoted laterally and in a vertical direction relative to transmission housing  10 .  
         [0031]    The free ends of the two lower links  18 ,  20  and of upper link  24  are pivotally coupled by coupling joints  26 ,  28 ,  30  to a coupling frame  32  which has an inverted U-shape. Coupling joints  26 ,  28 ,  30  can be universal joints. Coupling frame  32  includes three coupling hooks  33  for receiving an implement (not shown). Alternatively, it is also possible to pivotally couple the free ends of links  18 ,  20 ,  24  directly to an implement.  
         [0032]    Two longitudinally adjustable lift links  34 ,  36 , each of which comprises a double-acting hydraulic cylinder, are used to raise and lower coupling frame  32  and the hitched implement. The control of the hydraulic cylinders takes place for each via one of hydraulic control systems  37 ,  38 . Control systems  37 ,  38  are mounted adjacent to one another on the top of transmission housing  10  and include conventional control valves.  
         [0033]    The vehicle end of the lift links  34 ,  36  is pivotally coupled to the transmission housing  10  via universal type coupling joints  40 ,  42 . The free end of each lift links  34 ,  36  is not coupled to a central portion of the associated lower link (as is customary in the case of a known three-point hitch), but rather is articulated via coupling joints  44 ,  46  to coupling frame  32 . Alternatively, the free end of lift links  34 ,  36  can also be coupled directly to an implement (not shown). This selection of the action point of the free end of lift link  34 ,  36  provides increased functionality in a simple manner wherein the lift links  34 ,  36  can be retained and arranged in closed kinematic structures, and provides a great number of degrees of freedom of movement for the hitch.  
         [0034]    Coupling joints  44 ,  46  are located near to coupling joints  26 ,  28 , whereas coupling joints  40 ,  42  are spaced farther apart and are located substantially vertically over these positions. Thus, coupling joints  14 ,  40  are located substantially in a vertical plane. As a result, the coupling frame and the implement relative to the vehicle may be deflected laterally.  
         [0035]    In order to limit or adjust the lateral deflection of coupling frame  32 , a mechanical lateral stabilizer  48  acts on a central area of each lower link  18 ,  20  in a customary manner, the other end of which stabilizer is pivotally coupled to transmission housing  10  or to the vehicle chassis with interposition of holder  50 . FIG. 1 shows only one of the two lateral stabilizers  48 . Conventional known passive links acting as a stop can be used as lateral stabilizers.  
         [0036]    The hitch shown in FIG. 1 has substantially the same functionality as a previously customary hitch.  
         [0037]    The hitch of FIG. 2 differs from the hitch of FIG. 1 solely by the design of the upper link. According to FIG. 2, upper link  52  is longitudinally adjustable and includes a hydraulic cylinder. This upper link  52  is structurally the same as the two lift links  34 ,  36 , and is controlled by a separate control system  54  that can be mounted adjacent to the already cited control systems  37 ,  38  on transmission housing  10 . Upper link  52  is articulated by coupling joint  53  to transmission housing  10  and by another coupling joint  55  to coupling frame  32 . Both coupling joints  53 ,  55  are universal joints.  
         [0038]    The hitch of FIG. 2, in addition to the functionality of the hitch of FIG. 1, can tilt about a horizontal pivot axis which extends transversely to the longitudinal axis of the vehicle and substantially through the two implement-side coupling joints  26 ,  28 .  
         [0039]    As best seen in FIG. 3, the second embodiment of the hitch includes two longitudinally adjustable links  56 ,  58  instead of a single upper link, and each link  56 ,  58  is controlled by an associated control system  60 ,  62 . The two upper links  56 ,  58  are substantially structurally the same as the two lift links  34 ,  36 . Also the four control systems  37 ,  38 ,  60 ,  62  are preferably designed to be structurally the same.  
         [0040]    The two upper links  56 ,  58  are arranged in a V-shaped manner. Vehicle coupling joints  64 ,  66  are spaced far apart from one another and are located in the vicinity of and directly above coupling joints  40 ,  42 . The two implement coupling joints  68 ,  70  are located at the same level and spaced closely adjacent to one another. They are coupled to coupling frame  32  or to an implement (not shown).  
         [0041]    In this second embodiment, the stabilizers  48  of FIGS. 1 and 2 can be eliminated, since the upper links  56 ,  58  can assume the function of the lateral shifting of implement frame  32 .  
         [0042]    [0042]FIG. 4 shows a third embodiment of the hitch, wherein the two rigid lower links  18 ,  20  of FIGS.  1  to  3  are replaced by lower, longitudinally adjustable links  72 ,  74 . Vehicle-side coupling joints  76 ,  78  of the lower links  72 ,  74  and their implement-side coupling joints  80 ,  82  comprise universal joints. The hitch frame  32  is connected to the vehicle body or transmission housing  10  via six identical or similar longitudinally adjustable links  34 ,  36 ,  56 ,  58 ,  72 ,  74 . Links  34 ,  36 ,  56 ,  58 ,  72 ,  74  are arranged in closed, kinematic structures, and form a hexapod system. Each of the six links  34 ,  36 ,  56 ,  58 ,  72 ,  74  is associated with its own control system  37 ,  38 ,  60 ,  62 ,  84 ,  86 . Control systems  37 ,  38 ,  60 ,  62 ,  84 ,  86  are mounted adjacent to each other on transmission housing  10 .  
         [0043]    Coupling joints  68 ,  70  are located close to one another in the middle of upper transverse beam  88  of implement frame  32 . Coupling joints  44 ,  80  and  46 ,  82  are located on each lower free end  90 ,  92  of implement frame  32 . Thus, the implement-side coupling joints of the six links  34 ,  36 ,  56 ,  58 ,  72 ,  74  are located substantially in the corner points of an isosceles triangle.  
         [0044]    Lower links  72 ,  74  run substantially horizontally and are articulated by coupling joints  76 ,  78  to lateral lower areas of transmission housing  10 . The two closely adjacent coupling joints  40 ,  64  and  42 ,  66  of each of the two lift links  34  and  36  as well as of each of the upper links  56  and  58  are located approximately vertically above these coupling joints  76 ,  78 .  
         [0045]    As FIG. 5 shows, the two lower links  72 ,  74  and the two lift links  34 ,  36  do not run parallel to each other. Rather, they converge horizontally so that their axes  94 ,  96  intersect at horizontal guide point  98 . Furthermore, coupling joints  76 ,  78 ,  40 ,  42 ,  80 ,  82 ,  44 ,  46  are selected in such a manner that lift links  34 ,  36  are located vertically above lower links  72 ,  74 . Thus, vehicle-side coupling joints  76 ,  40  are also located here substantially in vertical plane.  
         [0046]    As FIG. 6 shows, the two lower links  72 ,  74  and the two upper links  56 ,  58  are not parallel to each other, but rather they converge vertically so that their axes  100 ,  102  intersect in a vertical guide point  104 . Vertical guide point  104  and horizontal guide point  98  normally do not occupy the same spatial position. Preferably, the components of the hitch are standardized so that a small number of different components are required. In order to be able to perform any desired conversions between the three embodiments a hitch “kit” would include the following components:  
         [0047]    six identical, longitudinally adjustable links  34 ,  36 ,  56 ,  58 ,  72 ,  74  with hydraulic cylinders and with coupling joints  40 ,  42 ,  44 ,  46 ,  64 ,  66 ,  68 ,  70 ,  76 ,  78 ,  80 ,  82  designed as universal joints;  
         [0048]    six identical control systems  37 ,  38 ,  60 ,  62 ,  84 ,  86  with control valves and the hydraulic lines (not shown) for supplying longitudinally adjustable links  34 ,  36 ,  56 ,  58 ,  72 ,  74 ;  
         [0049]    two similar, rigid lower links  18 ,  20 , with associated coupling joints  14 ,  16 ,  26 ,  28  comprising ball-and-socket joints;  
         [0050]    one upper link  24  with coupling joints  22 ,  30 ;  
         [0051]    two mechanical lateral stabilizers  48 ; and  
         [0052]    a coupling frame  32 .  
         [0053]    Mounting devices, such as threaded bores, are formed in transmission housing  10  and optionally on coupling frame  32  so that the coupling joints can be selectively coupled to the transmission housing  10  and to coupling frame  32 . Preferably, the same mounting devices can be used for both rigid and longitudinally adjustable links, so that either the coupling joint  14  of a rigid lower link  18  or the coupling joint  76  of a lower, adjustable link  72  can be mounted to the same position on the transmission housing  10 .  
         [0054]    Preferably, coupling joints are mounted only for the links which are used in the selected embodiment. For example, in the first embodiment, not two, but rather only one lateral upper link is used, and threaded bores  99  for the corresponding links remain unused. The number of control systems  37 ,  38 ,  60 ,  62 ,  84 ,  86  used and mounted on transmission housing  10  corresponds to the number of longitudinally adjustable links used. The coupling joints of the longitudinally adjustable links are preferably universal joints. In contrast thereto, the coupling joints of the rigid lower links comprise either a ball-and-socket joint customary for lower links or also comprise universal joints that resemble the ball-and-socket joints already described for the hydraulic cylinders.  
         [0055]    While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.