Abstract:
A length adjustable lifting strut ( 1 ) for a hitch linkage of a tractor has two connection elements ( 11, 12 ) for connecting the lifting strut ( 1 ) to components ( 43, 44 ) of the hitch linkage. A fine adjustment mechanism  17  is provided on the lifting strut ( 1 ) to finely adjust the length of the lifting strut  1.  A quick adjustment mechanism ( 21 ) is provided to adjust the lifting strut ( 1 ) length and is retainable in at least two discrete positions.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102011052461.4 filed Aug. 8, 2011. The entire disclosure of the above application is incorporated herein by reference. 
       FIELD 
       [0002]    The disclosure relates to a length adjustable lifting strut for a lower link of a hitch linkage of a tractor that can be lifted and lowered via a power drive. Two connection elements connect the lifting strut to the power drive of the tractor and to a lower link. Furthermore, an adjustment element is provided with threads arranged on two ends of the adjustment element that extend in opposite directions. One of the connection elements is screwed, by a thread, to the adjustment element. 
       BACKGROUND 
       [0003]    A lifting strut is known from DE 39 38 418 C1. The adjustment element can be pivoted via a gripping sleeve. The two connection elements are non-rotationally connected to the power drive of the tractor or to the lower link. Thus, by turning the adjustment element, the length of the lifting strut can be adapted to the to be used implement. Comparable lifting struts are also known from DE 1 096 102 B as well as DE 40 22 343 C2. 
         [0004]    Today&#39;s tractors, besides having a three-point hitch also include towing hitches, in the form of Piton couplings or ball couplings, by which trailers are towed. When coupling a trailer, which is to be towed via a low towing hitch (low hitch arrangement), the lower links of the three-point hitch are often arranged in the collision area of the drawbar of the trailer. Therefore, the lower links have to be pivoted out of the movement area of the drawbar or have to be completely removed. The known solutions of lifting struts can, however, only be shortened in a limited manner and do not achieve a minimal length, at which the lower links are pivoted out of the potential collision area of the trailer drawbar. 
       SUMMARY 
       [0005]    Thus, it is an object of the present disclosure to provide a lifting strut that has a larger displacement path. 
         [0006]    The object is solved by a length adjustable lifting strut for a hitch linkage of a tractor that comprises two connection elements to connect the lifting strut to the components of the hitch linkage. A fine adjustment mechanism finely adjusts the length of the lifting strut. A quick adjustment mechanism adjusts the lifting strut length and is retainable in at least two discrete positions. 
         [0007]    Thus, the length of the lifting strut, according to the disclosure, can be precisely adjusted via the fine adjustment mechanism. Besides this adjustment, the quick adjustment mechanism is provided to enable an additional adjustment path. Thus, the lifting strut is adjustable to a shorter length. Further, the lifting strut can be transferred quickly into a parking position without a long drawn-out adjustment of the fine adjustment mechanism. Here the lower link is no longer arranged in the collision area of the trailer drawbar. 
         [0008]    Preferably, the fine adjustment mechanism includes an adjustment element with threads arranged on two ends and extending in opposite directions. In this case, the connection elements have, respectively, a thread, that the connection elements are screwed to the threads of the adjustment element. 
         [0009]    For fine adjustment, the fine adjustment mechanism can be adjusted continuously (free of steps) or in smaller steps than the quick adjustment mechanism. 
         [0010]    In an embodiment of the disclosure, the quick adjustment mechanism includes a hinge that displaces the lifting strut between an aligned position and an angled position. By angling the lifting strut, the length of the lifting strut can be significantly shortened. 
         [0011]    Such a hinge can naturally be provided in at least one of the two connection elements. 
         [0012]    The first connection element has an attachment mechanism to connect the first connection element to a power drive of the hitch linkage. The second connection element has an attachment mechanism that connects the lifting strut to a lower link of the hitch linkage. 
         [0013]    The hinge includes a first hinge element and a second hinge element. The first and second hinge elements are pivotably connected to each other around a hinge axis. The first hinge element is connected to a first part of the adjustment element. The second hinge element is connected to a second part of the adjustment element. 
         [0014]    In this case, the first part of the adjustment element has a thread. The adjustment element is then threadably connected to the first connection element. The second part of the adjustment element has a thread. Likewise, the adjustment element is threadably connected to the second connection element. 
         [0015]    A retaining mechanism is provided to retain the lifting strut in the aligned position. Further, a retaining mechanism can be provided to retain the lifting strut in the angled position. The retaining mechanisms can, respectively, be separate retaining mechanisms or identical retaining mechanisms. 
         [0016]    Preferably, the retaining mechanism has a retaining pin that is insertable in the aligned position in retaining bores of the two hinge elements. Thus, the two hinge elements are supported via the retaining pin on each other. In this case, the retaining pin is arranged parallel to the hinge axis. 
         [0017]    The retaining mechanism that retains the lifting strut in the angled position can also include a retaining pin. The retaining pin is the same retaining pin that is used to retain the lifting strut in the aligned position. The pin is insertable in the angled position into at least one retaining bore of one of the two hinge elements. The other hinge element can then be supported in a pivot direction on the retaining pin, so that the first connection element cannot be moved from the angled position in a direction to the aligned position. 
         [0018]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0019]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0020]      FIG. 1  is a side elevation view of a lifting strut according to the disclosure in an aligned position on a hitch linkage in form of a three-point hitch of a tractor; 
           [0021]      FIG. 2  is a view like  FIG. 1  of the lifting strut in an angled position forming a knee; 
           [0022]      FIG. 3  is an enlarged perspective view of the hinge; 
           [0023]      FIG. 4  is an exploded perspective view of the area of the hinge of the lifting strut according to  FIG. 1 ; and 
           [0024]      FIG. 5  is a longitudinal sectional view of the lifting strut according to  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0026]      FIGS. 1 to 5  illustrate a lifting strut  1  in different views and are described in the following together. The lifting strut  1  extends along a longitudinal axis L and has at an upper end, relative to the installation position, with a first attachment mechanism  2 . A lower end has second attachment mechanism  3 . The first attachment mechanism  2  includes an attachment element  9 , with a bore  10 , which extension axis intersects the longitudinal axis L. The attachment element  9 , via the bore  10 , as shown in  FIG. 1 , can be connected to a power drive  43  to lift and lower the lower links  44  of a three-point hitch at the rear  45  of a tractor. To also enable a lateral pivoting of the lower links  44 , the attachment element  9  is pivotably arranged around a pivot axis V in relation to the remaining part of the lifting strut  1 . The pivot axis V intersects the longitudinal axis L at a right angle. In  FIG. 1  an attachment bracket  46  is shown. The attachment bracket  46  is arranged between the two lower links  44  and has a trailer coupling  47  (here a ball coupling) to tow a trailer via a drawbar  48 . 
         [0027]    The second attachment mechanism  3  includes a fork  4  with two fork arms  5 ,  6 . For the assembly, the fork arms  5 ,  6  embrace the lower link  44 . Elongated holes  7  are provided in the fork arms  5 ,  6  for passage of a pin  8  to attach the fork arms  5 ,  6  with the lower link  44 . The pin  8  is also passed in the assembled condition through an attachment bore  49  in the lower link, so that the lifting strut  1  is connected to the lower link  44 . 
         [0028]    The lifting strut  1  includes a first connection element  11 , connected with the first attachment mechanism  2 , as well as a second connection element  12 , connected with the second attachment mechanism  3 . The two connection elements  11 ,  12  are displaceable relative to each other along the longitudinal axis L. The first connection element  11  has a trunnion  13  with an outer thread  14 . The second connection element  12  also has a trunnion  15  with an outer thread  16 . A fine adjustment mechanism is provided with an adjustment element  17  that has at a first end with an inner thread  18  and a second end with an inner thread  19 . The first and second ends extend in opposite directions. The outer thread  14  of the first connection element  11  is screwed into one of the inner threads  18  of the adjustment element  17 . The outer thread  16  of the second connection element  12  is screwed into the other inner thread  19  of the adjustment element  17 . Thus, by means of turning the adjustment element  17  the two connection elements  11 ,  12  can be moved towards each other or away from each other. A gripping element  20 , which is non-rotationally connected to the adjustment element  17 , serves to adjust the adjustment element  17 . 
         [0029]    Besides ensuring fine adjustment, via the adjustment element  17 , the device also provides a quick length adjustment along the largest possible adjustment path, via a quick adjustment mechanism with a hinge  21 . The hinge  21  separates the adjustment element  17  into two components. It includes a first part  22  that has one of the inner threads  18 , as well as a second part  23 , that has the other of the two inner threads  19 . Via the hinge  21 , the two parts  22 ,  23  can be displaced between the aligned position, shown in  FIG. 1 , and the angled position, shown in  FIG. 1 . 
         [0030]      FIG. 3  shows in an enlarged perspective view of the hinge  21 . The hinge  21  includes a first hinge element  24  that is connected to the first part  22  of the adjustment element  17 . The hinge  21  has a second hinge element  25  that is connected to the second part  23  of the adjustment element  17 . The first hinge element  24  has a central lug  26 . The second hinge element  25  is formed fork-like with a first fork arm  27  and a second fork arm  28 . The two fork arms  27 ,  28  enclose the central lug  26  of the first hinge element  24 . A hinge bore  29  is provided in the central lug  26 . A hinge bore  30 ,  31 , aligned with the hinge bore  29  of the central lug  26 , is provided in each of the fork arms  27 ,  28 . Through the hinge bores  29 ,  30 ,  31 , a hinge pin  32  is passed and axially secured. The hinge pin  32 , as well as the hinge bores  29 ,  30 ,  31 , coaxially align with the hinge axis S. The hinge axis S intersects the longitudinal axis L at a distance. Principally however, it can also intersect the longitudinal axis L. 
         [0031]    A retaining bore  33  is provided in the central lug  26 . The retaining bore  33  is arranged parallel to the hinge bore  29 . The fork arms  27 ,  28  include retaining bores  34 ,  35 , that are arranged parallel to the hinge bores  30 ,  31  of the fork arms  27 ,  28 . In the aligned position of the lifting strut  1  according to  FIG. 1 , all retaining bores  33 ,  34 ,  35  are aligned. A retaining pin  36  is passed through the retaining bores  33 ,  34 ,  35 , so that the lifting strut  1  is secured in the aligned position. The parallel arrangement of the hinge bores  29 ,  30 ,  31  relative to the retaining bores  33 ,  34 ,  35  and the arrangement of all bores with a distance to the longitudinal axis L, ensure the most favorable support against buckling moments. 
         [0032]    The retaining pin  36  has a pin head  37 , which has a larger diameter than the retaining bores  33 ,  34 ,  35 . Thus, in an insertion direction an axial abutment is provided. On an end facing away from the pin head  37 , the retaining pin  36  has a securing bore  38 . The securing bore  38  extends transversally through the retaining pin  36 . A securing pin  39  is passed through the securing bore  38  to prevent an unintentional pulling-out of the retaining pin  36 . 
         [0033]    In order to angle the lifting strut  1 , the retaining pin  36  is pulled out of the retaining bores  33 ,  34 ,  35 . The first part  22  of the adjustment element  17  is angled relative to the second part  23  of the adjustment element  17  around the pivot axis S. In the angled position, shown in  FIG. 2 , the central lug  26  is partially pivoted out of the intermediate space between the fork arms  27 ,  28 . Thus, the retaining bore  33  is not enclosed anymore by the fork arms  27 ,  28 . In this position, the retaining pin  36  can be passed through the retaining bore  33  of the central lug  26 . When pivoting the lifting strut  1  back in the direction towards the aligned position, the retaining pin  36  abuts externally the fork arms  27 ,  28  and prevents a transfer of the lifting strut  1  in the direction to the aligned position. 
         [0034]    A head plate  40  is additionally arranged on the pin head  37  of the retaining pin  36 . The head plate  40  extends vertically to the retaining pin  36 . A securing bore  41  is provided in the head plate  40 . The securing bore  41  extends parallel to the retaining pin  36 . In the angled position, the head plate  40  can be pushed onto a projecting end of the hinge pin  32 . A securing bore  42 , extending transversally to the hinge pin  32 , is provided in the projecting end of the hinge pin  32 . The securing pin  39  can be inserted into the securing bore  42  so that a pulling-out of the retaining pin  36  from the retaining bore  33  of the central lug  26  is prevented. 
         [0035]    The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.