Patent Publication Number: US-2020281108-A1

Title: Arrangement for attaching a working tool to a working machine

Description:
FIELD OF THE INVENTION 
     The invention relates to an arrangement for attaching a working tool to a working machine as defined in the preamble of claim  1 . 
     Preferably, the solution according to the invention also comprises a quick hitch suitable for use as a universal quick hitch between a three-point hitch of a working machine, such as a tractor, and an implement, hereafter referred to as a working tool, to be attached to the tractor. Thus, the quick hitch preferably acts as an adapter. The arrangement of the invention also makes it easier to attach the quick hitch to the three-point hitch of the working machine. Similarly, it also makes it easier to directly attach a working tool to the three-point hitch of the working machine when no quick hitch is needed between the working tool and the working machine. The solution according to the invention is useful in agriculture and any other operation where a working tool attached to a working machine needs to be changed repeatedly. 
     The universal quick hitch for a working machine used in the arrangement according to the invention makes it easier and faster to attach a working tool to the working machine. When the working machine is a tractor, the working tool is often attached to a rear linkage of the tractor, often called a tractor three-point hitch. 
     The tractor three-point hitch is a widely used type of linkage between a tractor and a working tool. An ordinary tractor three-point hitch comprises two lower pulling arms, one upper pushing arm as well as one or more lift cylinders which usually are hydraulically driven. The lower pulling arms may also be called draw links or lift arms, and the upper pushing arm may also be called a top link. 
     The position of the coupling elements of the working tools to be attached to the tractor may vary between different working tools. The attaching points of the coupling elements of the working tools often are provided at different heights and widths from each other. The tractor three-point hitch must be adjustable in different ways and easy-to-use to allow a variety of working tools to be attached thereto. The widths and other dimensions of the coupling elements of the implements and working tools to be attached to the three-point hitch, positioned at the rear, and sometimes at the front, of the tractor, are not always standardized, and, there are many different standard sizes as well. Therefore, when attaching a tractor three-point hitch to implements, the coupling elements often need to be adjusted to each other before they can be connected together. In prior-art solutions, the operator of the tractor usually has to get out of the tractor to be able adjust the coupling elements of the three-point hitch of the tractor to match the coupling elements of the working tools. 
     The connecting dimensions according to the different categories result, for example, in that a working tool of Category 2 cannot be attached to a working machine of Category 1 or Category 3. Besides, especially larger working machines often have a robust and heavy three-point hitch pushing arm, possibly making it hard and dangerous, or even impossible, to manually lift and lower it in order to connect a quick hitch or a working tool to the pushing arm. The solution according to the invention aims at eliminating the need of the operator to get out of the working machine in order to adjust the position of the coupling elements of the three-point hitch to match, both in the height direction and in the horizontal direction, with the coupling elements of the working tool or the quick hitch. According to the solution of the invention, the operator of the working machine is able to adjust the positions of the coupling elements of the three-point hitch, manually from the cabin, without leaving his seat, thereby not only making the work easier but also safer. 
     Background of the Invention and Problems Related to the Prior Art 
     As is known, often the problem is that, so far, the dimensions of working tools intended for working machines generally have not been standardized, and, therefore, the manufacturers have each used their own dimensions for layout and positioning of the coupling elements. This has been enabled by the wide adjustability of the three-point hitch of the tractor to match various implements and working tools, but, a drawback encountered has been the need of the operator to get out of the tractor in order to adjust the position of the coupling elements of the three-point hitch to match the coupling elements of the working tool. It can be hard to get out of the working machine for the adjustment if the operator constantly needs to change the implement of his working machine. This has also shown to be a security risk because the operator, or his assistant, needs to move between the working machine and the implement to be attached thereto while the engine of the working machine is running. 
     Solutions for attaching a three-point hitch to a quick hitch, having a fixed structure and not allowing the distance between the fastening elements to be adjusted in the width direction, are known. A quick hitch like this only can accommodate matching implements which follow its dimensions. A more advanced design than this is known from the U.S. Pat. No. 3,312,478. 
     This solution allows the horizontal distance between the lower hooks of the quick hitch to be adjusted to match the attaching points of the working tool. This solutions suffers from the drawback that the adjustment is manual, the adjustment handle being located down on the quick hitch, far away from the operator, making it impossible for the operator to reach the adjustment handle from the cabin, and, consequently, the operator has to step down to the ground between the working machine and the working tool for the width adjustment. This is a difficult task, possibly involving a security risk, as mentioned above. 
     A more contemporary solution is known from the European patent application No. EP3138373A1. A drawback of this solution is that the structure has a fixed width, not allowing for any adjustment of the mutual horizontal distance of the lower hooks or the coupling hooks of the quick hitch. No other than implements and working tools having a matching width can be attached to this quick hitch. Besides, in this solution, the lower hooks or the couplings only can be seen to a restricted extent. This can be a major disadvantage when attaching a working machine to an implement by driving. 
     There are some other known solutions which also suffer from the problem that the lower hooks of the legs of the quick hitch are poorly visible for the operator. The visibility of the lower hooks is substantially important when attaching a working machine to an implement by driving. Attaching the working machine to the implement requires driving accuracy from the operator of the working machine because the alignment of the lower hooks with the coupling elements of the implement can be a matter of centimeters. The lower hooks of the three-point hitch of the working machine are coupled to the coupling elements of the implement after an appropriate approach and accurate driving lines. When approaching the implement, the driving lines of the working machine must be within the range of the coupling elements as the implements, because of their heaviness, rarely are movable by human power. The solution according to the invention avoids the visibility problem by designing the structure to incline forward so as not to hide the lower hooks in the field of view of the operator. 
     The current prior-art quick hitch solutions do not allow working tools having attaching points with varying widths to be attached to a three-point hitch of a working machine, such as a tractor. 
     OBJECTIVE OF THE INVENTION 
     This invention aims at overcoming the above-mentioned drawbacks and providing a flexible, efficient, fast and unnoticeable as well as easy-to-use arrangement for connecting a working tool or a universal quick hitch between a working machine, such as a tractor, and the working tool or the universal quick hitch. The solution according to the invention also aims at making the work of the operator of the working machine, such as the operator of the tractor, easier, at increasing work safety by mechanizing the adjustment of the coupling elements of the three-point hitch and by making it easier to attach the working machine, such as the tractor, to the working tool. 
     DESCRIPTION OF THE INVENTION 
     The quick hitch employed by the solution according to the invention can be regarded as a type of adjustable adapter, enabling various implements and working tools attachable to working machines, such as a tractor, to be attached to the tractor without getting out of the tractor. Besides, the arrangement assists the operator of the working machine in attaching the heavy pushing arm of the three-point hitch to the working tool or the quick hitch. The arrangement according to the invention is characterized in what is set forth in claim  1 . The other embodiments of the invention are characterized in what is set forth in the rest of the claims. 
     A typical arrangement according to the invention for attaching a working tool to a working machine, preferably to a three-point hitch of the working machine, comprising a pushing arm articulated, at one end, to the working machine and two pulling arms articulated, at one end, to the working machine comprises a coupling mechanism for attaching the three-point hitch, from the cabin of the working machine, to the working tool, or, to a quick hitch positioned between the working tool and the working machine. 
     A typical universal quick hitch, intended for a working machine, for attaching working tools to a three-point hitch of the working machine, and employed in the arrangement according to the invention comprises a frame, two legs with a lower hook, an upper hook as well as a width adjustment mechanism for adjusting, from the cabin of the working machine, the mutual distance between the lower hooks in the width direction. 
     Advantages of the Invention 
     The invention makes it easier to attach a working machine, such as a tractor, to various working tools and provides better circumstances for work safety, by allowing the attaching to be carried out from the cabin, without the need of the operator, or his assistant, to step into the unsafe area between the working machine, such as the tractor, and the implement or the working tool. 
     The quick hitch preferably included in the arrangement according to the invention is a universal, preferably mechanically operable quick hitch acting as an adapter, enabling implements and working tools, having their coupling elements positioned in different ways, to be safely attached, from the cabin of a working machine, to the three-point hitch of the working machine. 
     Compared to the above-mentioned known solutions, the adjustability of the width of the fastening elements of the employed quick hitch, without having to get out of the working machine, and the mechanical implementation of the adjustment, can also be seen as an advantage. Besides, the quick hitch included in the arrangement according to the invention is laterally movable, resulting in a better alignment with the coupling elements, such as fastening pins, of the working tool. 
     Another advantage is that the pushing arm of the three-point hitch is safe and easy to mount, from the cabin of the working machine, to the fastening element of the working tool or the quick hitch. 
    
    
     
       LIST OF FIGURES 
       In the following, the invention will be explained in more detail with reference to the accompanying simplified drawings wherein 
         FIG. 1  is a schematic and simplified as well as oblique top view of a working machine with a three-point hitch wherein a quick hitch according to the invention can be used, 
         FIG. 1 a    is a simplified and oblique lateral view of a quick hitch according to the invention, with one leg in partial cross-section, 
         FIG. 2  is a simplified and oblique lateral view of the quick hitch of  FIG. 1 a   , with one leg in partial cross-section, and attached to the three-point hitch of the working machine, which is only partially shown, 
         FIG. 3  is a simplified and oblique top and lateral view of the quick hitch of  FIG. 1 a   , attached as shown in  FIG. 2  and with one leg in partial cross-section, and with essential parts separated from each other, 
         FIG. 4  is a simplified and oblique top and lateral view of a second preferable quick hitch according to the invention, attached as shown in  FIG. 2  and with one leg in partial cross-section, 
         FIG. 5  is a simplified and top view of a third quick hitch according to the invention, attached as shown in  FIG. 2 , 
         FIG. 6  is a simplified and lateral view of the quick hitch of  FIG. 5 , 
         FIG. 7  is an oblique bottom and lateral and simplified view of an upper hook structure and a locking device of the quick hitch of  FIG. 5 , also showing the main parts of the locking device as separated, 
         FIG. 8  is an oblique and lateral view of a length-adjustable lateral stopper of the three-point hitch, affecting the operation of the quick hitch, in a disassembled state and in an assembled state, 
         FIG. 9  is a schematic, simplified and lateral view of still another quick hitch according to the invention, 
         FIG. 10  is a schematic, simplified and lateral view of still another quick hitch according to the invention, 
         FIG. 11  is a schematic, simplified and lateral view of still another quick hitch according to the invention, 
         FIG. 12  is a schematic, simplified and lateral view of still another quick hitch according to the invention, 
         FIG. 13  is a simplified and top view of a preferable width adjustment solution for the quick hitch according to the invention, 
         FIG. 14  is a simplified and top view of another preferable width adjustment solution for the quick hitch according to the invention, 
         FIG. 15  is a simplified and clarified front view of a preferable width adjustment solution and positioning of the lower hooks for the quick hitch according to the invention, 
         FIG. 16  is a simplified and clarified front view of another preferable width adjustment solution for the quick hitch according to the invention, 
         FIG. 17  is an oblique simplified and clarified exploded top view of a preferable width adjustment mechanism for the quick hitch according to the invention, manually operable from the cabin of the working machine, 
         FIG. 18  is an oblique simplified and clarified top view of a preferable upper hook and upper latch mechanism for the quick hitch according to the invention, manually operable from the cabin of the working machine, 
         FIG. 19  is an oblique simplified and clarified top view of a manual version corresponding to the quick hitch shown in  FIG. 4 , 
         FIG. 20  is a lateral simplified and clarified view of a preferable lifting and lowering mechanism for the pushing arm of the three-point hitch in the arrangement according to the invention, manually operable from the cabin of the working machine, 
         FIG. 21  is a lateral simplified and clarified enlarged view of the lifting and lowering mechanism of the pushing arm of the three-point hitch shown in  FIG. 20 , 
         FIG. 22  is a lateral simplified, clarified and partially cross-sectioned view of an advantageous locking and opening mechanism of a pushing arm of a three-point hitch according to the invention in the situation where the locking latch of the pushing arm is in a locked position, 
         FIG. 23  is a lateral simplified and clarified view of the locking and opening mechanism according to  FIG. 22  in an unlocked position, 
         FIG. 24  is a lateral simplified, clarified, enlarged and partially cross-sectioned view of the free end of the pushing arm according to  FIG. 22  in a locked position, 
         FIG. 25  is a lateral simplified, clarified, enlarged and partially cross-sectioned view of the free end of a pulling arm of the three-point hitch according to the invention in the situation where the locking latch of the pulling arm is in a locked position, 
         FIG. 26  is a lateral simplified and clarified view of an advantageous locking and opening mechanism of the pulling arm of a three-point hitch in the arrangement according to the invention, manually operable from the cabin of the working machine, and 
         FIG. 27  is a lateral simplified, clarified and partially cross-sectioned view of another advantageous locking and opening mechanism of the pushing arm of a three-point hitch in the arrangement according to the invention, manually operable from the cabin of the working machine. 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLES SHOWN IN THE FIGURES 
       FIG. 1  is a schematic and simplified oblique top view of a working machine which is provided with a three-point hitch  1   a  and on which a quick hitch included in the arrangement according to the invention can be used. In this example, the working machine is a tractor and the three-point hitch  1   a  is situated at the rear of the tractor. Preferably, the arrangement according to the invention comprises a coupling mechanism for attaching, from the cabin of the working machine, the three-point hitch  1   a  to a working tool, or, to a quick hitch positioned between the working tool and the working machine. A portion of the coupling mechanism can be located in the quick hitch while another portion of it can be located in the three-point hitch  1   a.    
       FIGS. 1 a    to  3  are oblique lateral views, in partial cross-section, of a quick hitch  1  according to a preferable embodiment of the invention. In  FIG. 1 a    the quick hitch  1  is separated while in  FIGS. 2 and 3  the quick hitch  1  is attached to the three-point hitch  1   a  of the working machine, only shown with two pulling arms  21 , a hydraulic pushing arm  23  as well as lateral stoppers  22  and  24 . The first lateral stopper  22  is a hydraulic cylinder, acting as a driving element, and the second lateral stopper  24  is either a fixed or a length-adjustable lateral stopper. The second, length adjustable lateral stopper  24  can be a hydraulic cylinder identical to the first lateral stopper  22 , or mechanically lockable at a certain length. In case both the lateral stoppers  22  and  24  are hydraulic cylinders the pulling arms  21  are easy to be guided laterally to the fasteners of the quick hitch  1   a  or the working tool. 
     As mentioned previously, the pulling arms  21  or lower pulling arms may also be called draw links or lift arms, and the hydraulic pushing arm  23  or upper pushing arm may also be called a top link. In addition, the lateral stoppers  22  and  24  may also be called stabilizer arms. 
       FIG. 3  also shows the essential parts of the quick hitch  1  as separated from each other. 
     The quick hitch  1  of the preferable embodiment shown in  FIGS. 1 to 3  comprises a width-adjustable frame  3 , two legs  31 , two lower hooks  32 , two lower latches  43  and a latch mechanism  4  for moving them, an upper hook  41  with a support arm, an upper latch  42  and a width adjustment mechanism  5  for adjusting the mutual horizontal distance between the lower hooks  32  and for locking them in the adjusted position. 
     Preferably, the frame  3  is a rectangular tube, for example, having a rectangular but smaller tube  31   a , located at the upper end of the legs  31  and similar in cross-section, inserted into its both ends, the rectangular tube  31   a  of the legs  31  being movable, in a controlled manner, back and forth inside the frame  3  so as to simultaneously move the legs  31  towards or away from each other. The rectangular tubes  31   a  of the legs  31  can best be seen in  FIGS. 5 and 15 . The frame  3  also comprises a support structure  3   a  for connecting the upper hook  41 , at its support arms  41   c , to the frame  3 . In structures where the upper hook  41  travels along a curved path, the support arms  41   c  are connected to the support structure  3   a  by a joint  40 . To move the upper hook  41 , the quick hitch  1  comprises a driving element or actuator  27 , such as a hydraulic cylinder connected to the hydraulic system of the working machine and preferably fitted between the frame  3  and the support arms  41   c.    
     The latch mechanism  4  of the quick hitch  1  comprises the upper latch  42  connected to the upper hook  41  and moving jointly with the upper hook  41 , with a disengaging mechanism  41   a  adapted to be operated by using a pulling means  41   b , such as a chain, rope or rod, the pulling means  41   b  extending to the cabin, or to close proximity thereof, in order to allow the operator of the working machine to release the upper latch  42 , from the cabin of the working machine. The disengaging mechanism  41   a  of the upper latch  42  is articulated to the upper hooks  41 , the upper latch  42  being adapted to be engaged by a spring force and to be disengaged by means of a lever included in the disengaging mechanism  41   a , and of the pulling means  41   b , against the spring force. 
     The latch mechanism  4  also comprises two lower latches  43  for locking the quick hitch  1  to the lower fasteners of the working tool, a length-adjustable latch releaser  44 , a disengaging rod  45  provided inside each leg  31  for each lower latch  43 , and a release mechanism  46  for the lower latches  43 , positioned between the upper hook  41  and the latch releaser  44 , to transmit the movement of the upper hook  41  to the lower hooks  43  for the purpose of engaging and disengaging the lower latches  43 . The latch mechanism  4  comprises locking springs  45   a  for locking the lower latches  43  to the lower fasteners of the working tool. The release mechanism  46  of the lower latches  43  is adapted to pull the latch releaser  44  and the disengaging rods  45 , which are connected thereto, upwards when the upper hook  41  is turned to its upper position. This disengages the lower latches  43 , against the spring force. 
     The width adjustment mechanism  5  of the lower hooks  32  comprises a first lever mechanism  51 ,  52  and a locking element  53  for locking the mutual horizontal distance between the lower hooks  32  in the width direction. The width adjustment mechanism  5  is adapted to move the legs, through the first lever mechanism  51 ,  52 , and, at the same time, the lower hooks  32 , in a mutually synchronized manner in the width direction of the quick hitch  1 , either simultaneously farther away from each other, or simultaneously closer to each other, and at an identical speed with respect to each other, as well as over an equally long distance. The width adjustment mechanism  5  is adapted to be operated from the cabin of the working machine and is preferably connected to the hydraulic system of the working machine but it may as well be connected to the transmission system of the working machine or to the electrical system of the working machine. Alternatively, the quick hitch  1  may comprise a manual actuation means operable from the cabin of the working machine. 
     The locking element  53  for the width adjustment comprises a locking arm  54  and a locking counterpart  55  provided with locking apertures, the locking head of the locking arm being adapted to be locked, at the locking phase of the width adjustment, into these apertures. The locking counterpart  55  is fastened to the first leg  31  of the quick hitch  1 , to be jointly movable with the leg  31 . The locking arm  54  is articulated, at its first end, to the first lever mechanism  51 ,  52 , the locking arm  54  thus moving in the width direction of the quick hitch  1  as the mutual distance between the legs  31  is adjusted, and the locking portion of the locking head, provided in the second end of the locking arm  54 , being insertable, at the locking phase, into the apertures of the locking counterpart  55  aligned to the locking portion of the locking head. For clarity, the actuator for engaging and disengaging the locking arm  54  is not shown in the Figures. 
     The locking element  53  is adapted to lock the structure at a desired grip width. The locking portion of the locking element  53  is adapted to be pressed down into the slot-like apertures of the locking counterpart  55  and, thereby, to prevent any unintentional change of the grip width. 
     The grip width of the quick hitch  1 , i.e. the horizontal distance between the lower hooks  32 , is adapted to be adjusted by means of the motive power of the hydraulic first lateral stopper  22  and the counteracting second locked lateral stopper  24 . The second lateral stopper is a metal rod, for example, fixed at its first end and its second end to the frame of the working machine and to the pulling arm  21 , respectively. 
     The lateral movement of the first lateral stopper  22  at the first leg  31  of the quick hitch  1  is adapted to be transmitted, through the first lever mechanism  51 ,  52 , into a movement changing the distance between the both legs  31 , and thereby, also the distance between the lower hooks  32 , when the second lateral stopper  24  is connected to the second pulling arm  21  to provide counterforce to the first lateral stopper  22 . The first width adjustment element  52 , such as the upper spreading arm herein, is connected at its first end to the first leg  31  of the quick hitch  1  and its second end to the first end of the rocker arm  51 . The second, the lower width adjustment element  52 , such as the lower spreading arm herein, is connected at its first end to the second leg  31  of the quick hitch  1  and its second end to the second end of the rocker arm  51 . The rocker arm  51  is articulated, between its ends, to the frame  3  to turn around its joint. 
     The movement of the first lateral stopper  22  at the second leg  31  of the quick hitch  1  is also adapted to move the entire quick hitch  1  in the lateral direction. This operation is enabled by locking the locking element  53  and by unlocking the second lateral stopper  24 , for example by disconnecting the second lateral stopper  24  from the pulling arm  21  with the result that the counterforce of the second lateral stopper  24  does not restrict the lateral movement of the quick hitch  1 . 
     The lower latches  43  of the quick hitch  1  are adapted to be disengaged by the movement of the upper hook  41 . The movement of the upper hook  41  is adapted to be transmitted to the lower latch  43  by means of a movement transmitted by the second release mechanism  46 , the length-adjustable latch releaser  44  and the disengaging rod  45 . The release mechanism  46  of the lower latches  43  connected to the structure of the upper hook  41  is adapted to cause a lifting movement for the latch releaser  44  once the release mechanism  46  has moved to its uppermost extreme position. 
     In this embodiment, the lower latches  43  allow the quick hitch  1  also to be used as a two-point hitch. Since the lower latches  43  lock the lower hooks  32 , a reliable attachment is achieved also when the upper hook  41  is not engaged. 
       FIG. 4  shows a second quick hitch  1  according to the invention where the upper portion of the latch mechanism  4  differs from the above-described structure for the support structure of the upper hook  41 . In this embodiment, the upper hook  41  does not turn around a joint but is provided on the support structure  3   a  which, now, is a substantially straight supporting and guiding post which guides the linear movement of the upper hook  41  and which is provided with sliding and guiding surfaces  50  and along which the upper hook  41  is adapted to move up and down. The movement of the upper hook  41  is adapted to be transmitted to the lower latches  43  by a release mechanism  46  similar to that shown in  FIG. 3 . The spreading of the legs  31  is also adapted to be carried out in a similar way to that described above or below. 
       FIG. 5  shows a third quick hitch  1  according to the invention, also having, for the legs  31 , a width adjustment mechanism differing from that described above. In this solution, the width adjustment mechanism  5  comprises a separate actuator or driving element  22   a , preferably a hydraulic cylinder connected to the hydraulic system of the working machine, for example, and connected at its first end and its second end to the frame  3  of the quick hitch  1  and to the one leg  31  of the quick hitch, respectively. The driving element  22   a  is adapted to change the distance between the lower hooks  32  of the quick hitch  1 . In order to synchronize the width adjustment for both legs  31 , the width adjustment mechanism  5  comprises a first lever mechanism  51 ,  52  and a locking member  53  which are substantially similar to those described above. 
     The driving element  22   a  can also be connected to the legs  31  of the quick hitch  1  at its both ends. 
       FIGS. 6 and 7  are views of the quick hitch  1  of  FIG. 5 .  FIG. 6  is a simplified and lateral view of the quick hitch  1 , with the driving element  22   a  of  FIG. 5  removed.  FIG. 7  is an oblique bottom and lateral as well as simplified view of the structure of the upper hook  41  of the quick hitch  1  of  FIG. 5  and of a locking device  48  thereof, also showing some parts of the locking device  48  as separated.  FIG. 6  also shows parts of the three-point hitch of the working machine, such as the pulling arms  21 , the hydraulic pushing arm  23  and the first lateral stopper  22  as well as the length-adjustable second lateral stopper  24 . With the exception of the structure of the upper hook  41  and the support structure  3   a  thereof, the quick hitch  1  can be and operate in a manner substantially similar to that described above. 
     Thus, the difference from the above is the structure of the upper hook  41 , with the support arms and the locking device  48 , as well as the support structure  3   a  of the upper hook  41 , comprising a substantially straight locking post, provided with guiding surfaces  50  and having a substantially straight locking rail  49  with locking slots  499  disposed above each other in the height direction. 
     The locking device  48  is a separate component of the structure acting as a double locking mechanism and is installed in its place around the support structure  3   a  together with the upper hook  41 . The locking device  48  comprises a locking plate  488 , a stepped wedge  489 , and a frame  48   a  that has an upper part  48   b , a lower part  48   d  and a connection part  48   c  whose upper end is fastened to the upper part  48   b  of the frame  48   a  and whose lower end is fastened to the lower part  48   d  of the frame  48   a . Further, the upper part  48   b  comprises two slots, one for the locking plate  488  and the other for the stepped wedge  489 . The distance between the lower edge of the upper part  48   b  and the upper edge of the lower part  48   d  is greater than the length of the frame part  41   h  of the upper hook  41 . In that case the upper hook  41  with its frame part  41   h  can be movably installed between the upper part  48   b  and the lower part  48   d  of the frame  48   a  of the locking device  48 . 
     The locking plate  488  and stepped wedge  489  are adapted to restrict, by means of a counterpart  487  fastened to the frame part  41   h  of the upper hook  41 , the movement of the upper hook  41  to be shorter than the distance between the locking slots  499 . The stepped wedge  489  and the locking plate  488  are adapted to lock the upper hook  41  in a locking slot  499  of the locking post of the support structure  3   a , at a desired distance from the lower hooks  32 . 
     The locking device  48  is adapted to provide, together with the upper hook  41 , a clamping force for clamping the fastening pins of the working tool, attached to the quick hitch  1 , between the upper hook  41  and the lower hooks  32 . The locking device  48  is adapted to be locked in the locking slot  499  of the locking rail  49  of the locking post by means of the locking plate  488 . The stepped wedge  489  is adapted to adjust the distance between the upper hook  41  and the lower hook  32 , with a sufficient accuracy, to match the fastening elements of the working tool, the quick hitch  1  and the working tool then forming a locked joint. No latch structure  4  is needed in this solution to ensure the attachment of the working tool. 
     The upper hook  41  can move up and down between the locking slots  499  when the stepped wedge  489  is open. The stepped wedge  489  is used to remove the gap between the fastening pin of the working tool and the upper hook  41 . The upper hook  41  can still move the distance equal of two locking slots  499  when the locking plate  488  has already been inserted into one of the locking slots  499  but the stepped wedge  489  is still open, i.e. not yet inserted into its slot. 
       FIG. 8  presents an oblique top and lateral view showing the length-adjustable second lateral stopper  24  of the arrangement according to the invention in a disassembled state and in an assembled state. The length-adjustable lateral stopper  24  comprises a frame  63 , which, in this example, is a tubular, partly hollow rod having, in one end, a fastening hole  70 , and a release handle  61 , which, in this example, is a metal rod. In addition, the frame  63  is provided with a hole  69  for the release handle  61  and with an extended elongated hole  66 . The lateral stopper  24  comprises an arm  62  fittable into the hollow portion of the frame  63  and provided with locking holes  65  and the fastening hole  70 . 
     The second lateral stopper  24  is fixed, at its first and its second end, to the pulling arm  21  and to the frame of the working machine, such as the tractor, respectively. The lateral stopper  24  is adapted to be length-adjustable by means of the release handle  61  of the frame  63  and the locking holes  65  of the arm  62 . The lower end of the release handle  61  locks, by means of the locking holes  65  of the arm  62 , the length of the lateral stopper  24 . An upward pulling of the release handle  61  lifts the lower end of the release handle  61  out of the locking hole to release the length locking between the arm  62  and the frame  63 . The extended hole  66  is adapted to allow for limited variation of the length of the lateral stopper  24 , by means of limiting elements  68  provided in a locking hole  68   a . The variation of the length of the lateral stopper  24  is enabled by the movement of the limiting elements  68  in the extended hole  66 . Preferably, the inner edges of the extended hole  66  are adapted to act as a limiter of the extremities of the limiting element&#39;s  68  travel path. 
       FIGS. 9 to 15  are schematic and simplified views of different preferable embodiments of quick hitches according to the invention. 
       FIG. 9  shows a preferable quick hitch  1  according to the invention, comprising an upper hook  41  and a fixed support structure  3   a  for the upper hook  41 , the support arms  41   c  of the upper hook  41  being connected thereto by a joint  40 . In addition, the upper hook  41  and the lower hooks  32  comprise an upper latch  42  and lower latches  43 , respectively. The upper hook  41  is adapted to travel along a circular arc, around the horizontal joint  40 , and the latches of the upper hook  41  and of the lower hooks  32  are adapted to be locked to the fastening elements of the working tool. A similar solution is shown above, i.a. in  FIGS. 1 a    to  3 . 
       FIG. 10  shows another preferable quick hitch  1  according to the invention, having an upper hook  41  and a fixed support structure  3   a  for the upper hook  41 , in this solution, a substantially straight supporting and guiding post which guides the linear movement of the upper hook  41  and is provided with sliding and guiding surfaces  50  and along which the upper hook  41  is adapted to move up and down. In addition, the structure comprises an upper latch  42  for the upper hook  41  and lower hooks  32  with lower latches  43 . The upper hook  41  is adapted to move towards the lower hooks  32 , and away therefrom, guided by the linear support structure  3   a  provided with the sliding and guiding surfaces  50 , and the latches of the upper hook  41  and of the lower hooks  32  are adapted to be locked to the fastening elements of the working tool. A similar solution is shown above, i.a. in  FIG. 4 . 
       FIG. 11  shows still another preferable quick hitch  1  according to the invention, having an upper hook  41  and a fixed support structure  3   a  for the upper hook  41 , the support arms  41   c  of the upper hook  41  being connected thereto by a joint  40 . In addition, the structure incorporates a curved locking plate  47 , with locking slots, and a locking device  48 . Preferably, the locking device  48  can be similar to the locking device shown in  FIG. 7  and comprise, i.a. a locking plate and a stepped wedge supported by bearings on a frame positioned on the horizontal joint  40 . The upper hook  41  is adapted to travel along a circular arc, around the horizontal joint  40 , and the distance between the upper hook  41  and the lower hooks  32  is adapted to be kept substantially constant by means of the locking device  48  and the curved lock plate  47 . The locking device  48  unnecessitates any use of upper or lower latches for securing the attachment of the working tool. The other actuators and structures of the quick hitch  1  can be identical to those described above. 
       FIG. 12  shows another preferable quick hitch  1  according to the invention, having an upper hook  41  and a fixed support structure  3   a  for the upper hook  41 , herein a substantially straight supporting and guiding post which guides the linear movement of the upper hook  41  and is provided with sliding and guiding surfaces  50 , as well as with locking slots  499 , and along which the upper hook  41  is adapted to move up and down. In addition, the structure incorporates a locking device  48  and lower hooks  32 . The upper hook  41  is adapted to move towards the lower hooks  32 , and away therefrom, guided by the linear support structure  3   a  provided with the sliding and guiding surfaces  50 , and the distance between the upper hook  41  and the lower hooks  32  is adapted to be kept substantially constant by means of the locking device  48  and the locking slots  499 . The locking device  48  unnecessitates any use of upper or lower latches for securing the attachment of the working tool. The other actuators and structures of the quick hitch  1  can be identical to those described above. A similar solution is shown in  FIGS. 5 to 7 . 
       FIGS. 13 to 16  show width adjustment solutions for the legs  31  of the quick hitch  1  according to the invention. In the solution of  FIG. 13 , a hydraulically driven first lateral stopper  22  is used for the width adjustment, as already described above. Correspondingly, in the solution of  FIG. 14  a separate hydraulic actuator  22   a , preferably attached onto the frame  3 , is used for the width adjustment. This solution has already been explained above in the description of  FIG. 5 . 
       FIGS. 15 and 16  show two separate width adjustment mechanisms with their lever solutions. The solution of  FIG. 15  has already been explained above and is applicable to any quick hitches  1  according to the invention. 
     In the solution of  FIG. 16 , the driving force for the width adjustment of the legs  31  is provided by the actuator  27  moving the upper hook  41 , not shown in  FIG. 16  but explained in more detail in the description of  FIG. 3 . This solution incorporates a lever mechanism for the width adjustment mechanism  5 , with its width adjustment element  52  comprising two spreading arms, the first end of the first spreading arm being articulated to the upper end of the first leg  31  and the first end of the second spreading arm being articulated to the upper end of the second leg  31 , and the second end of the spreading arms being articulated to a preferably plate-shaped, vertically movable position element  56  lateral to the center part of the frame  3  and intended for a locking element  53 . 
     In addition, the locking element  53  comprises a locking plate provided with a vertical groove and locking slots and guiding the position element  56 , the locking plate being laterally attached to the center part of the frame  3 . Further, the locking element  53  comprises a rod-shaped coupling arm  58  suspended by a suspension element  59  from an articulated shaft  60  and articulated to turn in two planes, i.e. in the width direction of the quick hitch  1  and in a direction perpendicular thereto. Preferably, the articulated shaft  60  is mounted in the support arms  41   c  of the upper hook  41 . 
     A spring-loaded locking pin  57  extends through the positioning member  56 , the end of the pin, which is larger than the cross-sectional are thereof, is spaced from the surface of the position element  56 . The locking pin  57  is provided with a spring pressing the locking pin  57  towards the locking slots of the locking plate. The lower end of the coupling arm  58  comprises a laterally open slot adapted to be fitted, by a turning movement of the coupling arm  58 , between the end of the locking pin  57  and the position plate  56 , when the locking pin  57 , for the width adjustment of the legs  31 , must be pulled out of the locking slot of the locking plate. Then, the coupling arm  58  is turned, in the width direction of the quick hitch  1 , around the joint of the coupling arm  58 , provided in the suspension member  59 , thereby positioning the slot of the lower end of the coupling arm  58  laterally to the end of the locking pin. Thereafter, the coupling arm  58  is turned around the articulated shaft  60  to allow the slot of the lower end of the coupling arm  58  to be turned to a position between the end of the locking pin  57  and the position plate  56 , onto the shaft of the locking pin  57 . Now, the locking pin  57  can be pulled out of the locking slot by turning the upper end of the coupling arm  58  around the articulated shaft  60 , towards the working machine. Once the locking pin  57  has been pulled out to an extent that the width locking is released, the height position of the position element  56  is changed by a lifting movement of the upper hook  41 , by means the driving element  27 . The height position of the position plate  56  is changed by the coupling arm  58 . After the change of the height position, the coupling arm  58  is turned aside again, in the width direction of the quick hitch  1 , and the locking pin  57  is pressed, by spring force, into the locking slot aligned thereto. 
     The solution of  FIG. 16  is also applicable to any quick hitches  1  according to the invention. 
       FIGS. 17 to 19  show manual versions of the quick hitch  1  according to the invention, operable from the cabin of the working machine.  FIG. 17  shows a manual width adjustment mechanism  5 , with its main parts separated,  FIG. 18  shows a manually operable structure of the upper hook  41  with its upper latch  42  while  FIG. 19  shows a manually operable version corresponding to the quick hitch  1  of  FIG. 4 . 
     In  FIG. 17  shown width adjustment mechanism  5 , which is operable by hand, i.e. manually, comprises a first handle  51   a  fastened to the first end of the rocker arm  51  of the first lever mechanism, and, a second handle  54   a  fastened to the locking arm  54  of the width adjustment locking element  53 . Both handles  51   a  and  54   a  are positioned to be reachable for the operator of the working machine, from the cabin of the working machine. The horizontal distance between the legs  31  of the quick hitch  1  is adjusted by turning the first handle  51   a  in the width direction of the quick hitch  1 , and the width position is locked by turning the locking arm  54  to its locking position, by means the second handle  54   a . The overall structure and lever arrangement of the width adjustment mechanism of  FIG. 17  is mainly similar to the width adjustment mechanism  5  presented in  FIG. 3 . 
     The manually operable upper hook structure shown in  FIG. 18  comprises, in addition to the above-mentioned upper hook structure, a third handle  41   d  having, at its first end, inside the upper hook  41 , an upper latch  42 , and, at its second end, a grab handle  41   e  positioned to be easily reachable from the cabin of the working machine. The upper latch  42  is released by turning the third handle  41   d  around its joint provided in the upper hook, the third handle  41   d  also being used for lifting the upper hook  41  into a vertical position. 
     The main difference between the supporting and guiding structure of the upper hook  41  shown in  FIG. 19  and the structure shown in  FIG. 4  is that the structure now comprises a lever mechanism  41   f  for manually releasing the upper latch  42  from the cabin of the working machine. The lever mechanism  41   f  also comprises a handle  41   g  positioned to be easily reachable from the cabin of the working machine. 
     The manual versions shown in  FIGS. 17 to 19  can also be connected to a driving element or actuator, such as a hydraulic cylinder, allowing them to be actuated by either manual or machine power. 
       FIGS. 20 and 21  are lateral simplified and clarified views of a preferable lifting and lowering mechanism  6  of the pushing arm  23  of the three-point hitch  1   a  in the arrangement according to the invention, manually operable from the cabin of the working machine and forming part of the coupling mechanism of the arrangement according to the invention when said lifting and lowering mechanism  6  is installed on the working machine. For clarity,  FIGS. 20 and 21  are simplified and they do not show all the structural parts. 
     A joint  11  connects the pushing arm  23  of the three-point hitch  1   a , at the first end thereof, to the rear part  1   b  of the working machine, for example. Likewise, the pulling arms  21  are articulated, at their first ends, to the rear part  1   b  of the working machine. In many, especially larger working machines, the pushing arm  23  can be very heavy, making it difficult and dangerous, or even impossible, to move it, by hand, in the vertical plane. Therefore, accurate positioning of the free end, i.e. the second end, of the pushing arm  23  into the fastening element  23   a  of the working tool, or the quick hitch  1 , can be a complicated task. Preferably, the arrangement according to the invention comprises said separate lifting and lowering mechanism  6  for moving the pushing arm  23 , substantially in the vertical plane. 
     The lifting and lowering mechanism  6  comprises a hydraulic cylinder  7  acting as a driving element or actuator and connected, at the first end of the cylinder part, by means of a joint  12 , to the rear part  1   b  of the working machine, above the pushing arm  23  and preferably in the same vertical plane as the longitudinal vertical plane of the pushing arm  23 . Preferably, the hydraulic cylinder  7  can be smaller, more lightweight and shorter than the pushing arm  23 . The free end of the piston rod of the hydraulic cylinder  7  is provided with a first gripping member  8 , preferably an annular member forming a closed loop and extending, from the end of the piston rod, down towards the pushing arm  23 . 
     Correspondingly, the upper surface of the pushing arm  23  is provided with a second gripping member  23   b  adapted to act as a counterpart of the first gripping member  8 . Preferably, the second gripping member  23   b  has a substantially round cross-section and is adapted to be curved, from the upper surface of the pushing arm towards the hydraulic cylinder  7 , and, at the same time, away from the rear part  1   b  of the working machine. The second gripping member  23   b  is adapted to fit through the loop of the first gripping member  8  as the lifting and lowering mechanism  6  is connected to the pushing arm  23 . 
     The joint  11  of the pushing arm  23  at the rear part  1   b  of the working machine is positioned lower and, with respect to the longitudinal direction of the pushing arm  23 , further outwards than the joint  12  of the hydraulic cylinder  7  of the lifting and lowering mechanism  6 . Thus, the mutual positioning of the joints  11  and  12  is geometrically chosen so that, as the piston rod of the hydraulic cylinder  7 , which is connected to the gripping member  23   b  of the pushing arm, is pulled inwards, the pulling force causes a force component directed substantially upwards and forcing the pushing arm  23  to turn, around its joint  11 , towards the above hydraulic cylinder  7 , which, in turn, at the same time turns around its joint  12 , substantially upwards. Correspondingly, as the piston rod of the hydraulic cylinder  7 , which is connected to the gripping member  23   b  of the pushing arm  23 , is pushed outwards, the gravity pulls the pushing arm  23  to turn around its joint  11 , substantially downwards. At the same time, the hydraulic cylinder  7  connected to the gripping member  23   b  turns around its joint  12 , substantially downwards. 
     The lifting and lowering mechanism  6  is also provided with a spring element  10 , or a similar element, adapted to lift the hydraulic cylinder  7  upwards, away from top of the pushing arm  23 , when the hydraulic cylinder  7  is not connected to the gripping member  23   b  of the pushing arm. The spring element  10  can be an extension spring, for example, connected between the hydraulic cylinder  7  and the rear part  1   b  of the working machine. 
     Preferably, the lifting and lowering mechanism  6  is also provided with a handle  9  allowing the hydraulic cylinder  7  to be laterally moved when connecting the first gripping member  8  with respect to the second gripping member  23   b . When the hydraulic cylinder  7  is connected to the pushing arm  23 , the handle also allows the pushing arm  23  to be laterally moved. This is helpful especially when the pushing arm  23  is connected to the quick hitch  1 , or to a working tool without the quick hitch  1 . 
       FIGS. 22-24  present in a lateral view an advantageous locking and opening mechanism of the hook  23   d  of the pushing arm  23  of the three-point hitch  1   a  according to the invention. The pushing arm  23  is articulated at its second end by a joint  11  for instance to the rear part  1   b  of the working machine. In addition, the pushing arm  23  is suspended by a spring  26  to lighten the handling of the pushing arm  23 . 
       FIG. 22  is a lateral simplified, clarified and partially cross-sectioned view of an advantageous locking and opening mechanism of the pushing arm  23  of the three-point hitch  1   a  according to the invention in the situation where the pushing arm  23  is in a locked position, whereas  FIG. 23  presents the same pushing arm  23  in an unlocked position, and  FIG. 24  presents the hook  23   d  of the same pushing arm  23  in an enlarged and partially cross-sectioned view so that a spring-loaded locking latch  23   e  placed movably inside the hook  23   d  is clearly seen. A spring  23   g  is arranged to press the locking latch  23   e  to close the throat opening of the hook  23   d.    
     The locking and opening mechanism presented in  FIGS. 22-24  comprises a lever mechanism  25  which can be operated from the cabin of the working machine. The lever mechanism  25  comprises a first lever  25   a , a second lever  25   b , a third lever  25   c , a fourth lever  25   d  and a fifth lever  25   e  which are articulated to each other with joints. All the levers comprise a first end and a second end. The hook  23   d  comprises an inner space  23   f  for the first end of the second lever  25   b , fifth lever  25   e  and spring-loaded locking latch  23   e.    
     The first lever  25   a  is articulated at its second end by a joint  28   a  with the second end of the second lever  25   b  which is further articulated by a joint  28   c  to the piston of the pushing arm  23 , more precisely to the hook  23   b  at the piston end of the pushing arm  23 . The joint  28   c  is placed from a short distance from the first end of the second lever  25   b . Further, the first end of the second lever  25   b  is articulated by a lower joint at the second end of the fifth lever  25   e  to the fifth lever  25   e . The upper joint at the first end of the fifth lever  25   e  is articulated to the first end of the locking latch  23   e  of the pushing arm hook  23   d.    
     In addition, the third lever  25   c  is articulated at its second end by a joint  28   b  to the first lever  25   a , close to the second end of the first lever  25   a , and at its first end to the lower joint at or close to the second end of the fourth lever  25   d  which fourth lever  25   d  is further articulated at its first end by an upper joint to the second lever  25   b , which upper joint is placed at a distance from the joint  28   c  towards the second end of the second lever  25   b . The second end of the fourth lever  25   d  rests against the upper surface of the piston rod of the pushing arm  23 , and thus locks and keeps the lever mechanism  25  steady in its position when the first lever  25   a  is not turned. 
       FIG. 23  presents the pushing arm hook  23   d  in an unlocked position. In order to unlock the hook  23   d  the first lever  25   a  is turned upwards around the joint  28   a . In that case the third lever  25   c  draws the fourth lever  25   d  at its second end so that the fourth lever  25   d  turns around its upper joint and at the same time allows the second lever  25   b  to turn around the joint  28   c  so that the first end of the second lever  25   b  moves upwards and at the same time draws the locking latch  23   e  upwards through the fifth lever  25   e . This unlocks the hook  23   d  and the pushing arm  23  can be turned upwards around the joint  11 . 
       FIGS. 25 and 26  present in a lateral view an advantageous locking and opening mechanism  30  of the hook  21   a  of each pulling arm  21  of the three-point hitch  1   a  according to the invention.  FIG. 25  is a lateral simplified, clarified, enlarged and partially cross-sectioned view of the free end of the pulling arm  21  in the situation where the locking latch  21   b  of the hook  21   a  of the pulling arm  21  is in a locked position, and  FIG. 26  presents in a lateral view said locking and opening mechanism  30  of the pulling arm hook  21   a , which locking and opening mechanism  30  is manually operable from the cabin of the working machine. 
     The locking and opening mechanism  30  is a lever mechanism that comprises at least a joint assembly  30   a , a first lever member  30   b , a second lever member  30   c , a third lever member  30   d  and a grip handle  30   e , which lever members are suitably articulated by joints to each other. In addition, locking and opening mechanism  30  comprises a support element  35  to keep the upper end of the third lever member  30   d  substantially steady in a horizontal direction. The locking and opening mechanism  30  also comprises a substantially transversal connection bar  36  to connect the locking and opening mechanisms  30  of each pulling arm  21  to each other so that both the locking and opening mechanisms  30  can be simultaneously operated by the grip handle  30   e.    
     The joint assembly  30   a  comprises three joints  21   e ,  21   f  and  21   g . A locking latch  21   e  is articulated by the joint  21   e  to the joint assembly  30   a , and the first end of the first lever member  30   b  is articulated by the joint  21   f  to the joint assembly  30   a . Further, the joint assembly  30   a  itself is articulated by the joint  21   g  to the hook  21   a  of the pulling arm  21 . The locations of the joints  21   e ,  21   f  and  21   g  are selected so that when the first lever member  30   b  is drawn away from the hook  21   a  the joint assembly  30   a  turns around the joint  21   g  and joint  21   e  draws the locking latch  21   b  obliquely upwards away from the throat opening of the hook  21   a . This unlocks the hook  21   a , and the pulling arm  21  can be turned downwards around its joint. 
     As mentioned previously, the first end of the first lever member  30   b  is articulated by the joint  21   f  to the joint assembly  30   a . The first lever member  30   b  is a substantially thin rod that is substantially parallel with the pulling arm  21  and extends from the joint assembly  30   a  towards the rear part  1   b  of the working machine. The first lever member  30   b  is articulated at its second end by a joint  33  to the first end of the second lever member  30   c  that is further articulated at its second end by a joint  34  to the pulling arm  21 . Further, the second end or lower end of the third lever member  30   d  is articulated by the already mentioned joint  33  to the first end of the second lever member  30   c.    
     The locations of the joints  33  and  34  at the both ends of the second lever member  30   c  are selected so that the joint  33  is upper and closer to the hook  21   a  than the joint  34 . In that case, in the locking position of the hook  21   a , the second lever member  30   c  is in an inclined position where its first end is upper than its second end and closer to the hook  21   a  than its second end. That makes the locking and unlocking the hook  21   a  easy, and it can be done from the cabin of the working machine. When the hook  21   a  is unlocked the grip handle  30   e  is drawn upwards in which case the second lever member  30   c  turns around its joint  34  so that its first end turns away from the hook  21   a  and at the same time draws the first lever member  30   b  away from the hook  21   a . This unlocks the hook  21   a  and the pulling arm  21  can be turned downwards around its joint as has been previously mentioned. 
       FIG. 27  presents in a lateral simplified, clarified and partially cross-sectioned view another advantageous locking and opening mechanism of the hook  23   d  of the pushing arm  23  of the three-point hitch  1   a  in the arrangement according to the invention. Though it is not presented in  FIG. 27  the pushing arm  23  may also be suspended by a similar spring  26  as shown in  FIG. 26  to lighten the handling of the pushing arm  23 . The locking and opening mechanism presented in  FIG. 27  comprises a lever mechanism  37  which can be operated from the cabin of the working machine. The lever mechanism  37  comprises a first lever  37   a , a second lever  37   b , a third lever  37   c , a fourth lever  37   d  and a fifth lever  37   e  which are articulated by joints to each other. All the levers comprise a first end and a second end. In addition, the locking and opening mechanism comprises a support member  37   f  close to the upper end of the substantially vertical fifth lever  37   e  that also has a grip handle  37   g  at its upper end for operating the locking and opening mechanism from the cabin of the working machine. The hook  23   d  also comprises an inner space for the first lever  37   a , second lever  37   b  and spring-loaded locking latch  23   e.    
     The first lever  37   a  with its joints and functions is similar to the fifth lever  25   e  in  FIGS. 22 and 24 . The second lever  37   b  is articulated by a joint  28   c  to the piston of the pushing arm  23 , more precisely to the hook  23   b  at the piston end of the pushing arm  23 . The joint  28   c  is placed from a short distance from the first end of the second lever  37   b . Further, the first end of the second lever  37   b  is articulated by a lower joint at the second or lower end of the first lever  37   a . The second end of the second lever  37   b  beyond the joint  28   c  is bent upwards and is articulated by a joint to the first end of the third lever  37   c.    
     The third lever  37   c  may be a substantially thin rod that is substantially parallel with the pushing arm  23  and extends from the second lever  37   b  towards the rear part  1   b  of the working machine. Further, the third lever  37   c  is articulated at its second end by a joint  38  to the first end of the fourth lever  37   d  that is further articulated at its second end by a joint  39  to the second end of a measure rod  23   j . The first end of the measure rod  23   j  is fastened to the piston rod  23   c  so that the measure rod  23   j  moves with the piston rod  23   c . Further, the second end or lower end of the fifth lever  37   e  is articulated by the already mentioned joint  38  to the first end of the fourth lever  37   d.    
     The locations of the joints  38  and  39  at the both ends of the fourth lever  37   d  are selected so that the joint  38  is upper than the joint  39  and closer to the hook  23   d  than the joint  39 . In that case, in the locking position of the hook  23   d , the fourth lever  37   d  is in an inclined position where its first end is closer to the hook  23   d  than its second end. That makes the locking and unlocking the hook  23   d  easy, and it can be done from the cabin of the working machine. When the hook  23   d  is unlocked the grip handle  37   g  is drawn upwards in which case the fourth lever  37   d  turns around its joint  39  so that its first end turns away from the hook  23   d  and at the same time draws the third lever  37   c  away from the hook  23   d . In that case the second lever  37   b  turns around the joint  28   c  so that the first end of the first lever  37   a  moves upwards and at the same time draws the locking latch  23   e  upwards. This unlocks the hook  23   d  and the pushing arm  23  can be turned upwards around the joint  11 . 
     The structures of the locking and opening mechanisms of the hooks  21   a  and  23   d  can also be different from those presented above. Advantageously, a part of the levers and rods or all the levers and rods of the locking and opening mechanism may be replaced by wires or other flexible means and, when needed, properly placed deflection or diverting pulleys. Also wires with jackets, such as accelerator cables or alike may be used instead of the lever mechanisms presented above. 
     Preferably, the three-point hitch  1   a  comprises a hydraulic levelling assembly  131  which is useful in many operations of the hitch. Locking latches  21   b  and  23   e  may also be self-locking. For that purpose, the solution of the invention comprises locking stoppers  34   a  and  39   a , shown in  FIGS. 26 and 27 . The automatic locking of the locking latch  21   b  of the pulling arm  21  is activated by pushing the third lever member  30   d  downwards as far as the first end of the lever  30   c  stops against the locking stopper  34   a . Correspondingly, the locking of the locking latch  23   e  of the pushing arm  23  is activated by pushing the fifth lever  37   e  downwards as far as the first end of the lever  37   d  stops against the locking stopper  39   a . The dimensions of the levers of the locking and opening mechanisms and positions of the joints in the structure have been selected so that the locking latches  21   b  and  23   e  keep locked as long as the grip handles  30   e  and  37   g  are kept in their lowermost position. When the grip handles  30   e  and  37   g  are drawn upwards the locking latches  21   b  and  23   e  are drawn in the unlocked position. 
     The principal idea of the invention is to make it faster, and in general, possible to safely attach various implements and working tools to a three-point hitch of a working machine, such as a tractor. Thus, one of the main ideas is to allow the three-point hitch and its hooks to be easily and safely operated from the cabin of the working machine in order to accurately lower the pushing arm of the three-point hitch, even if it is heavy, by means of the coupling mechanism, to the right position on a fastening element of the a working tool, or of a quick hitch serving as an adapter, and in order to lift it away therefrom. Besides, in a preferred arrangement, the coupling mechanism comprises pulling and transmission means, such as flexible ropes or chains or appropriately designed rods and/or lever mechanisms, allowing the attaching of the three-point hitch to the working tool or to the quick hitch to be managed in a controlled way, for instance by unlocking the quick coupling hooks of the three-point hitch. Preferably, the pushing, pulling and transmission means are adapted to be operated from the cabin of the working machine. 
     Further, a preferred idea is to facilitate an arrangement allowing the grip width of the quick hitch  1  to be changed from the cabin of the working machine. The width adjustment mechanism  5  according to the invention and the locking element  53 , as well as the actuators of the width adjustment mechanism  5 , such as the hydraulic cylinders  22  and  22   a  and/or, the manual actuators, such as the handles  51   a ,  54   a ,  41   e  and  41   g , with their lever mechanisms, constitute means for adjusting the mutual horizontal distance between the lower hooks  32 , from the cabin of the working machine, and, at the same, form part of the coupling mechanism of the arrangement according to the invention. 
     The structure and actuators of the coupling mechanism of the arrangement according to the invention, as well as the number thereof, are adapted to vary case by case. For instance, some of the actuators of the coupling mechanism, such as the above-mentioned width adjustment mechanism  5  of the quick hitch  1 , with its actuators, are incorporated in the quick hitch  1 , thus only forming part of the coupling mechanism when the quick hitch  1  is used. Correspondingly, the above-mentioned lifting and lowering mechanism  6  of the pushing arm  23  only forms part of the coupling mechanism of the arrangement according to the invention when the lifting and lowering mechanism  6  is installed on the working machine. 
     In the solution according to the invention, in common to all the locking and opening or unlocking mechanisms for locking latches of the hooks of the pushing arm and the pulling arms is the fact that the lever mechanisms and/or wire mechanisms are guided and/or shielded so that they are secure, safe and reliable to use from the cabin of the working machine, and that they do not get entangled with other structures of the working machine, three-point hitch or working tools causing damages to itself or to other components. 
     It is obvious to a person skilled in the art that different embodiments of the invention are not solely restricted to the above-described examples but may vary within the accompanying claims. Besides, the solutions described in the different examples may vary between the different exemplary solutions. 
     It is also obvious to the person skilled in the art that the structure of the release mechanism of the lower latches may differ from that described above. Instead of a lever mechanism, the release mechanism may comprise a chain, rope or any other structure resilient in another direction and only transmitting a force in the pulling direction when the upper hook is lifted. 
     It is also obvious to the person skilled in the art that the arrangement may comprise a separate rack which can hold the quick hitch and from which it can easily be lifted away, by means of the three-point hitch, and to which it also can be lowered back when no longer needed. The rack allows the quick hitch to be held at an appropriate height off the ground, thus making it easier to fasten the pulling arms of the three-point hitch to the pins of the fastening elements of the three-point hitch, for example. 
     It is also obvious to the person skilled in the art that the structure of the lifting and lowering mechanism of the pushing arm may differ from that described above. As an example, the first gripping member of the hydraulic cylinder of the lifting and lowering mechanism can be a hook-shaped, almost straight pin, and, correspondingly, the second gripping member of the pushing arm can be an annular member allowing the hook-shaped pin of the first gripping member to be inserted through it.