Abstract:
A front loader arrangement includes a hydraulically sprung lift cylinder arrangement coupled between opposite loader arm sides and respectively mounting masts. In order to permit the masts to pivot freely about their pivotal connections with the loader arm sides to aid the coupling of the masts to respective mounting frames fixed to a carrying vehicle, the hydraulic system in which the lift cylinder arrangement is incorporated includes a device, including a shut-off valve and an accumulator arrangement for establishing a float condition in the lift cylinder arrangement after a source of hydraulic fluid and associated control valve is decoupled by separating a hydraulic quick coupler.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a front loader arrangement with a mounting frame and a mounting mast, wherein the mounting mast can be coupled to the mounting frame and can be decoupled therefrom, with a front loader arm which is connected to the mounting mast for being pivoted vertically by a hydraulic cylinder extending between the front loader arm and the mounting mast, wherein the hydraulic cylinder is formed in a double-acting manner with a rod end chamber and a head end chamber, and with a device for the hydraulic spring suspension of the front loader arm, wherein the device comprises a hydraulic accumulator in conjunction with a control valve controlled by load pressure. 
       BACKGROUND OF THE INVENTION 
       [0002]    Front loader arrangements, i.e., the arrangement of a front loader on a vehicle, in particular on an agricultural vehicle, or else on a different type of utility vehicle, are known. Front loaders can be connected to, o mounted on, a vehicle, for example on a tractor or an agricultural tractor, by means of a mounting frame, in order to carry out loader operations. The mounting frame is customarily screwed to the vehicle frame or fastened to the latter. The front loader itself has a connecting or mounting point or mounting mast which is connected to, or is mounted on, or coupled to, the console. Various possibilities are known in this respect. Some known exemplary embodiments of front loader arrangements have mechanisms which are formed on the console and serve for receiving two bearing bolts formed on the mast arrangement of the front loader, wherein at least one of the catch hooks is locked after receiving the bearing bolts. The bearing bolts are received here by the mounting frame being guided up to, or the vehicle being driven up to, the mounting mast or to the front loader which is in a corresponding parking position or mounting position. After the bearing bolts have been received, the catch hooks can be locked manually or else in a partially automated or fully automated manner or by an external motor or by remote control. In other mechanisms, the console has only one catch hook which serves for receiving a bearing bolt formed on the mast arrangement. For locking purposes, connecting openings are then formed both on the mounting frame and mounting mast, with the connecting openings, when brought into alignment with each other, being connected to each other via a locking bolt, or a locking bolt is guided through the mast. The locking can also take place here manually or else in a partially automated or fully automated manner or by an external motor or by remote control. 
         [0003]    Such a partially automated locking is disclosed in U.S. Pat. No. 7,632,056, granted Dec. 15, 2009 which presents a front loader arrangement which comprises a spring pre-tensioned locking bolt which can be actuated via adjusting elements formed on a mounting mast and on a mounting frame by the adjusting elements, by means of a relative movement with respect to one another, triggering a locking in such a manner that the locking bolt is guided by spring force into connecting openings formed on the mounting mast and on the mounting frame of the front loader arrangement. For unlocking purposes, the locking bolt has to be guided manually out of the connecting openings counter to the spring force and the adjusting elements have to be brought into a corresponding unlocking position. It is disadvantageous in this connection that, in particular, the design and arrangement of the adjusting element formed on the mast arrangement, and also the connection of said adjusting element to the locking bolt require a relatively complex outlay in terms of manufacturing and installation. 
         [0004]    Furthermore, EP 1 774 106 B1 discloses a front loader arrangement, in which the mounting mast is guided via a ramp formed on the mounting fame wherein the mounting frame has catch hooks in which bearing bolts formed on the mounting mast are received. The front loader arrangement can be locked via a spring pre-tensioned spring-loaded locking catch, which engages in a first depression and then a second depression formed on the frame, wherein a pre-locking is formed here, in which the spring-loaded locking catch engages in the first depression and the mounting mast is still movable relative to the mounting frame until the mounting mast reaches the end position thereof, in which the bearing bolts have been fully inserted into the catch hooks. Only then does the spring-loaded locking catch snap into the second depression, at which final locking arises. Disadvantages here include the fact that, firstly, the design and arrangement of the spring-loaded locking catch provided on the mounting mast and, furthermore, the first and second depressions which are formed on the mounting frame and are intended for the pre-locking and final locking require a relatively complex outlay in terms of manufacturing and installation and also a great diversity of components. 
       SUMMARY OF THE INVENTION 
       [0005]    The problem on which the invention is based is considered that of specifying a front loader arrangement of the type mentioned at the beginning, by means of which one or more of the above-mentioned disadvantages are overcome. 
         [0006]    The object is achieved according to the invention by the teaching of claim  1 . Further advantageous refinements and developments of the invention emerge from the dependent claims. 
         [0007]    According to the invention, a front loader arrangement of the type mentioned at the beginning is designed in such a manner that adjusting means, by means of which the hydraulic cylinder can be brought into a floating position when a hydraulic fluid supply and associated control valve carried on the carrying vehicle is decoupled, are provided on the front loader arrangement, wherein the adjusting means comprise a shut-off valve which has a first and a second switching position, wherein, in the first switching position, a fluid connection, which operates via the shut-off valve, can be produced between the head end and rod end chambers. A fluid connection between the head end and the rod end chambers of the hydraulic cylinder ensures that the hydraulic cylinder is brought into a floating position. As a result, the mounting mast can move relatively freely and is not blocked by the hydraulic cylinder, as is otherwise customary during the coupling, since a hydraulic connection between vehicle and front loader arrangement has been disconnected during the decoupling and, during the coupling, can only be actuated by an operator in a further step if the mounting mast has been coupled to the mounting frame. The mounting frame can comprise, for example, a ramp on which the mounting mast is guided for being displaced along the ramp for the coupling and decoupling. By means of the floating position, the mounting mast can be pivoted about the coupling point thereof with respect to the front loader arm, i.e. relative to the loader arm, and, for example during the coupling, can be adapted to a positioning angle with respect to the mounting frame or aligned with respect to the latter. An alignment takes place here by the bearing bolts of the mounting mast sliding over the ramp during the coupling and being guided into the catch hooks, wherein, by means of this interaction, the bearing bolts are brought into the position thereof provided for the coupling. Without the abovementioned floating position of the hydraulic cylinder, the mounting mast would be in a rigid connection with respect to the front loader arm such that the mounting mast cannot carry out any pivoting movements relative to the front loader arm. Therefore, should the geometrical dimensions between vehicle and front loader arrangement have changed during a time in which the front loader arrangement was decoupled from the vehicle, which is entirely possible, for example due to location instabilities (ground unevenness, subsidence of the ground, etc.), change in the filling of the tyres of the vehicle, changes to the tyre size, leakages in the hydraulics of the front loader device or because of other circumstances, then a change in the positioning angle of the mounting mast with respect to the mounting frame is generally also associated therewith, as a result of which the next coupling of the front loader arrangement is made considerably more difficult, since, because of the rigid connection between mounting mast and front loader arm, the entire front loader arrangement (apart from the mounting frame) has to be raised, displaced, lowered, tilted, etc., and therefore also the entire weight of the front loader arrangement has to be moved until the mounting mast has been aligned in a manner corresponding to the mounting frame. The shut-off valve is preferably opened directly after the front loader is decoupled from the vehicle, with a hydraulic supply from the vehicle for the hydraulic cylinder of the front loader arrangement (operating hydraulics) customarily also being interrupted or decoupled, as a result of which the hydraulic cylinder is already held in a floating position and is prepared for the next coupling. Of course, the shut-off valve can also be opened just immediately before the next coupling. Although a manual opening can be provided here, this will only ensure that the floating position for the hydraulic cylinder can be set irrespective of the vehicle hydraulics or of operating hydraulics for the front loader arrangement. It is entirely also conceivable here to provide a mechanical or electric device for opening the shut-off valve if said device can be operated independently of the operating hydraulics of the front loader or ensures the opening of the shut-off valve independently of operating hydraulics, i.e. enables the shut-off valve to open if a connection to the operating hydraulics is interrupted. 
         [0008]    In the first switching position, a fluid connection, which at the same time also operates via the shut-off valve, can be produced between the head end chamber, the rod end chamber and the hydraulic accumulator. The hydraulic accumulator which is provided in any case for the hydraulic spring suspension of the front loader arrangement can therefore be fluidly connected to the head end and rod end chambers by opening of the shut-off valve, wherein the volume differences or the cross-sectional differences between the two chambers are compensated for by the hydraulic accumulator. 
         [0009]    In the second position, a fluid connection, which operates via the shut-off valve, between the head end chamber, the rod end chamber and the hydraulic accumulator is interrupted. In this position, the hydraulic spring suspension is fully functional, i.e. the hydraulic accumulator can be operated solely via the load-pressure-controllable control valve and also the hydraulic cylinder is ready for use for lifting and lowering the front loader arrangement. 
         [0010]    In an alternative embodiment, a further hydraulic accumulator is provided, and, in the first switching position, a fluid connection, which operates via the shut-off valve, is produced between the head end chamber, the rod end chamber and the further hydraulic accumulator. The manner of operation here is unchanged with respect to the manner of operation described above, except that use is made of, for example, a smaller hydraulic accumulator, and therefore, in the floating position, the freedom of movement can be improved because of smaller accumulator pressures. The further hydraulic accumulator is used here solely for producing the floating position of the hydraulic cylinder. The hydraulic accumulator provided for the hydraulic spring suspension is not used in this case. This is expedient in particular if high spring rates are provided for the hydraulic spring suspension such that the hydraulic accumulator provided for the hydraulic spring suspension has a relatively high spring pressure number which is disproportionately high for use for the floating position function. 
         [0011]    In the second switching position, a fluid connection, which operates via the shut-off valve, between the head end chamber, the rod end chamber and the further hydraulic accumulator is interrupted. In this position, the hydraulic spring suspension is fully functional, and the further hydraulic accumulator is isolated, i.e. the hydraulic accumulator can be operated solely via the load-pressure-controllable control valve and also the hydraulic cylinder is ready for use for lifting and lowering the front loader arrangement. 
         [0012]    A bypass line which is provided with a check valve is arranged between the further hydraulic accumulator and the head end chamber, wherein the check valve closes in the direction of the further hydraulic accumulator. It is thereby ensured that the further hydraulic accumulator, in an isolated state, can be relieved of pressure via the bypass line, for example if the hydraulic accumulator is heated by solar irradiation. 
         [0013]    The above-described front loader arrangement can be used on various carrier vehicles, but in particular on agricultural vehicles, such as tractors. 
         [0014]    The invention and further advantages and advantageous developments and refinements of the invention will be described and explained in more detail below with reference to the drawing which shows two exemplary embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the drawing: 
           [0016]      FIG. 1  is a schematic side view of an agricultural vehicle with a front loader arrangement; 
           [0017]      FIG. 2  is a schematic side view of a mounting mast in cross section and of a mounting frame of the front loader arrangement from  FIG. 1  in a decoupled state; 
           [0018]      FIG. 3  is a further schematic side view of the mounting mast and of the mounting frame from  FIG. 2  in a first coupling state; 
           [0019]      FIG. 4  is a further schematic side view of the mounting mast and of the mounting frame from  FIGS. 2 and 3  in a further coupling state; 
           [0020]      FIG. 5  is a further schematic side view of the mounting mast of the mounting frame from  FIGS. 2 to 4  in a coupled state; 
           [0021]      FIG. 6  is a further schematic side view of the mounting mast and of the mounting frame from  FIGS. 2 to 5  in a first coupling state; 
           [0022]      FIG. 7  is a further schematic side view of the mounting mast and the mounting frame from  FIGS. 2 to 6  in a further decoupling state; 
           [0023]      FIG. 8  is a further schematic side view of the mounting mast and the mounting frame from  FIGS. 2 to 7  in a decoupled state; 
           [0024]      FIG. 9  is a perspective side view of the pivoting lever of the mounting mast from  FIGS. 2 to 8 ; 
           [0025]      FIG. 10  is a perspective side view of the actuating device for the pivoting locking bar of the mounting mast from  FIGS. 2 to 8 ; 
           [0026]      FIG. 11  is a schematic hydraulic circuit diagram for a first embodiment of a front loader arrangement with a hydraulic spring suspension and adjusting means for producing a floating position for the hydraulic cylinders; and 
           [0027]      FIG. 12  is a schematic hydraulic diagram of a further embodiment for a front loader arrangement with a hydraulic spring suspension and adjusting means for producing a floating position for the hydraulic cylinders. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]      FIG. 1  illustrates an agricultural vehicle in the form of a tractor  10  (carrier vehicle). The tractor  10  has a mounted front loader arrangement  12 . The front loader arrangement  12  comprises a front loader  13  and mounting frame  16 , which are mounted on a vehicle frame  14  of the tractor  10  on both sides of the tractor  10 , for the coupling of the front loader  13 . The front loader  13  has a mounting mast  18 , likewise on both sides of the tractor, by means of which the front loader  13  is coupled to the mounting frame  16  of the front loader arrangement  12  and therefore to the tractor  10 . 
         [0029]    The front loader arrangement  12  or the front loader  13  has a front loader arm  20  which has a rear end pivotally fastened to the mounting mast  18  and has a forward end to which a front loader tool  22  is pivotally connected. The front loader arm  20  comprises a pair of parallel carriers  21  which run in parallel on the opposite sides of the tractor  10  and are connected to each other via one or more transverse carriers (not shown). The front loader tool  22  is designed, by way of example, in the form of a loading shovel, wherein the front loader tool  22  could also be designed as loading forks, grippers, etc. The front loader arm  20  is pivoted relative to the mounting mast  18  via a pair of hydraulic lifting cylinders  24  which respectively extend at opposite sides of the tractor  10  between an adjacent one of the pair of mounting masts  18  and an adjacent one of the pair of carriers  21  of the front loader arm  20 . A tilting linkage  26 , which serves for the parallel guidance of the front loader tool  22 , extends in each case between links  25 , which are pivotally connected to the carriers  21  of the front loader arm provided on the opposite sides of the tractor  10 , and the respective mounting masts  18 . The front loader tool  22  is pivotally connected to front ends of the carriers at both sides of the front loader arm  20  via a pivoting linkage  27 , which is connected between a front region of the loader arm  20  and to backside locations of the front loader tool  22 , and also via a hydraulic pivoting cylinder  28  which is connected to the respective pivoting linkage  27  and to the respective link  25 . 
         [0030]    The mounting frame  16  has a receiving region  32  for receiving or for the coupling of the mounting mast  18 , and a fastening region  34  for fastening the mounting frame  16  to the vehicle frame  14 . At the fastening region  34 , the mounting frame  16  is screwed to the vehicle frame  14  via screw connections (not shown). The mounting frame  16  has a first (front) catch hook  36  on a lower front region of the receiving region  32  and a second (rear) catch hook  38  on an upper rear region of the receiving region  32 , or hook-shaped bearing points in each case. 
         [0031]      FIGS. 2 to 8  illustrate a respective combination of the mounting mast  18  and mounting frame  16  at the right side of the front loader arrangement  12  in enlarged form in a plurality of side views and in a plurality of cross-sectional views, in which further individual details of the front loader arrangement  12  are illustrated in detail. 
         [0032]    The mounting frame  16  has a ramp  40  or ramp-shaped configuration which extends between the front and rear catch hooks  36  and  38 , and, in the lower region of the ramp, a depression or notch  32  is defined directly to the rear of the lower or front catch hook  36 . 
         [0033]    The mounting mast  18  comprises an upper bearing point and a lower bearing point respectively in the form of an upper bearing bolt  44  and a lower bearing bolt  46 . It is conceivable here for the combination of catch hooks  36 ,  38  and bearing bolts  44 ,  46  also to be able to be realized in a manner the other way around, such that the bearing bolts  44 ,  46  are formed on the mounting frame  16  and the catch hooks  36 ,  38  are formed on the mounting mast  18 . Furthermore, an upper pivoting bolt  48 , a central pivoting bolt  50  and a lower pivoting bolt  52  are arranged on the mounting mast  18 , with the pivoting bolts respectively pivotally connecting the tilt linkage  26 , the front loader arm  20  and the hydraulic cylinder  24  to the mounting mast  18 . 
         [0034]    The mounting mast  18  furthermore comprises a pivoting locking bar  54  (also see  FIG. 9 ) which has a first and second arms  56  and  58 , respectively, joined together and mounted for pivoting about a pivot axis  60 . An adjusting means in the form of a supporting means  62 , which is designed in the form of a supporting hinge, is arranged at a free end of the first pivoting arm  56 . The supporting means  62  is hinged or pivotally coupled to a free end of the first pivoting arm  56  by means of a joint  63  and is pre-tensioned by means of a spiral spring  64  in such a manner that said supporting means is pressed or pushed against the end of the first pivoting arm  56  and, in an extreme position, comes to bear against an end surface  66  formed at the free end of the end of the pivoting arm  56 . The lower side of the first pivoting arm  56 , i.e., that side of the pivoting arm  56  which faces the ramp  40 , has a step  68  which is formed in a complementary manner to the depression  42  formed on the ramp  40 . 
         [0035]    The second pivoting arm  58  of the pivoting locking bar  54  is designed to be shorter and is arranged above the first pivoting arm  56 , offset at an angle of approximately 70° (counterclockwise in the figures) and forms a further lever arm about the pivot axis  60  of the pivoting locking bar  54 . The second pivoting arm  58  is connected to a frame part  72  of the mounting mast  18  via a tension spring  70 , and therefore the pivoting locking bar  54  is pre-tensioned in the direction of the ramp  40 . 
         [0036]    An actuating element  74  (see  FIG. 10 ), via which the pivoting locking bar  54  can be actuated, is arranged between the first and second arms  56  and  58 . The actuating element  74  includes an actuating lever  76  which is accessible on the outside of the mounting mast  18  and extends radially from a shaft  78 . The shaft  78  is mounted for rotation in the mounting mast  18  at a location between the first and second arms  56  and  58 . An adjusting arm  80  is formed in a central region of the shaft  78 , the adjusting arm extending radially from the shaft  78  and being formed and arranged in such a manner that it can be brought into engagement with the second arm  58  of the pivoting locking bar  54  upon rotation of the shaft  78 , this rotation causing the locking bar  54  to be set into a pivoting movement. The shaft here is set into rotation by pivoting the actuating lever  76  from a basic position ( FIGS. 2 to 5 ,  7  and  8 ), into an engagement position (corresponding to  FIG. 6 ), whereupon the adjusting arm  80  likewise pivots and is brought into engagement with the upper pivoting arm  58  and therefore with the pivoting locking bar  54 , and the pivoting locking bar  54  can be moved from a locking position (see  FIG. 5 ) into an unlocking position (see  FIG. 6 ). The pivoting arm  58 , and therefore also the pivoting locking bar  54 , is released again by pivoting the shaft  78  in the reverse direction. 
         [0037]    The front loader  13  or the mounting mast  18  is coupled to, or decoupled from, the mounting frame  16  as described below with reference to  FIGS. 2 to 8 . The mounting frame  16  is moved from a decoupled state, in which the front loader  13  is set down and is separated hydraulically and mechanically from the tractor, in the direction of the mounting mast  18  corresponding to the movement indicated by the arrow V ( FIG. 2 ). The upper bearing bolt  44  begins to enter into engagement with the ramp  40  and slides up along the inclined plane of the ramp  40  and along the ramp surface until the bearing bolt enters into engagement with the upper catch hook  38  ( FIGS. 3 and 4 ). At this same time, the lower bearing bolt  46  enters into engagement with the lower catch hook  36  ( FIGS. 3 and 4 ). Approximately at the time at which the bearing bolts  44 ,  46  enter into engagement with the catch hooks  38 ,  36  ( FIG. 3 ), the lower catch hook  36 , or a lower end of the ramp  40 , abuts against the supporting means  62  and begins to pivot the latter counter to the pre-tensioning thereof from the position thereof, which is oriented substantially perpendicularly to the ramp surface and in which the supporting means takes up the supporting position, into an increasingly deflected position (see  FIGS. 3 to 5 ). When the supporting position of the supporting means  62  is cancelled, the spring  70  on the pivoting locking bar  54  causes the latter to move with the lower pivoting arm  56  thereof in the direction of the ramp surface  40  such that, finally, the step  68  of the lower pivoting arm  56  comes to bear against the ramp  40  and slides up along the ramp ( FIGS. 3 and 4 ). As can best be seen in  FIG. 5 , the mounting mast  18  reaches an end position relative to the mounting frame  16 , in which end position the bearing bolts  44 ,  46  come to bear completely in the catch hooks  38 ,  36 . At the same time, the spring pre-tensioned pivoting locking bar  54  takes up the locking position thereof and latches with the step  68  formed on the first pivoting arm  56  in the depression  42  such that the mounting mast  18  is locked to the mounting frame  16 , since relative movement between mounting mast  18  and mounting frame  16  is now blocked firstly by the catch hooks and secondly by the step  68  which has come to bear in the depression  2 . The front loader is now in the operating position and can be put into operation.  FIGS. 6 to 8  show the unlocking of the front loader, i.e., the decoupling of the mounting mast  18  from the mounting frame  16 . The pivoting locking bar  54  is brought here from the locking position thereof into an unlocking position by means of the actuating element  74 , as described above ( FIG. 6 ). At the same time, the spring pre-tensioned supporting means  62  can thereby take up the supporting position thereof and the pivoting locking bar  54  can be released again from the actuating element  74  by the actuating lever being brought again into the basic position thereof. The pivoting locking bar  54  is now held in the unlocking position by the supporting means  62 . In this state, the mounting mast  18  is unlocked from the mounting frame  16 , and therefore the mounting frame  16  can be removed from the mounting mast  18 , as indicated by the arrow R in  FIGS. 7 and 8 . By means of the relative movement between mounting mast  18  and mounting frame  16  and the sliding of the supporting means  62  along the ramp surface, the supporting means  62  is pushed against the end surface  66  of the pivoting arm  56 , as a result of which the supporting means maintains the supporting position thereof and the pivoting locking bar  54  cannot snap back into the depression ( FIG. 7 ). By moving the mounting frame  16  away, i.e., by backing the tractor  10 , the mounting frame  16  can now be removed from the mounting mast  18 , i.e., from the front loader  13 , so that the decoupling of the mounting mast  18  from the mounting frame  16  is finished ( FIG. 8 ). So that the front loader  13  can be completely separated and removed from the tractor  10 , first the hydraulic supply of the lifting cylinder  24  has to be decoupled. The operator can undertake this in parallel with the unlocking of the pivoting locking bar  54 , i.e., in a working sequence wherein the pivoting locking bar  54  is unlocked and the hydraulic supply disconnected. 
         [0038]    The front loader  13  furthermore has a device for the hydraulic spring suspension of the front loader arm  20 , wherein the device comprises a hydraulic accumulator  82  in conjunction with a control valve  84  that is controlled by load pressure, the control valve  84  being depicted in  FIGS. 11 and 12 , in which a part of a hydraulic system  85  respectively for the hydraulic supply of two double-acting lifting cylinders  24  is depicted, the lifting cylinders having a piston  86  and being hydraulically supplied via a hydraulic supply line  87  and a hydraulic supply line  88 , the supply lines both emanating from a coupling part  92  of a quick coupler (not shown) . The hydraulic accumulator  82  can be used via the control valve  84  for the spring suspension of the lifting cylinders  24 , with reference being made here to a conventional spring suspension which, since it is known, does not require a more detailed description. 
         [0039]    In order to make coupling easier, it is expedient, as has been previously described, that during the coupling, the mounting masts  18  can be moved and adapted as freely as possible to the position of the mounting frame  16  so that the bearing bolts  44 ,  46  are guided as exactly and precisely as possible into the catch hooks  36 ,  38 . This is achieved by cancelling the rigid connection between the mounting mast  18  and the front loader arm  20 , which results when the hydraulic fluid supply and associated control valve is disconnected at the quick coupler (not shown) causing the lifting cylinders  24  to remain fixed in the position which they have last taken up thereby holding the mounting masts  18  rigidly with respect to the front loader arm  20 . The mounting masts  18  are thereby brought into a movable state in which the mounting masts can be pivoted relative to the front loader arm  20 . For this purpose, as  FIGS. 11 and 12  schematically show, a shut-off valve  90  is provided, wherein,  FIG. 11  depicts a first exemplary embodiment, and  FIG. 12  depicts a second exemplary embodiment, of a hydraulic system  85  for double-acting lifting cylinders with a device for the hydraulic spring suspension of the mounting masts  18 . 
         [0040]    In both cases, the shut-off valve  90  is designed to be actuated manually and can be operated by an operator, during the coupling and decoupling of the front loader  13 , when the hydraulic fluid supply and associated control valve (not shown) is connected or disconnected from the hydraulic system  85 . 
         [0041]    With regard to  FIG. 11 , part of the hydraulic system  85  for supplying hydraulic fluid to the two double-acting lifting cylinders  24  is depicted, the lifting cylinders each having a piston  86  and having fluid supplied via the fluid supply line  87  and via the fluid supply line  88 . The supply line  87  extends from a coupling part  92  of a quick coupler (not shown) to head end chambers  94  of lifting cylinders  24 , while the supply line  88  extends from the coupling part  92  to rod end chambers  96 . As can be seen in  FIG. 1 , the head end of the right lifting cylinder  24  is connected to the front loader arm  20  and the rod end is connected to the right mounting mast  18 , with it being noted that the left lifting cylinder  24  is similarly connected between the loader arm  20  and the left mounting mast  18 . Therefore, the front loader arm  20  can be raised and lowered by respectively directing hydraulic fluid to, and draining hydraulic fluid from, the rod end chambers  96 , wherein a control valve (not shown) of the hydraulic system  85  is correspondingly activated in a known manner in order to lift and lower the front loader arm  20 . The head end chambers  94  of the two lifting cylinders  24  are connected to each other by a connecting line  98  that is connected to the supply line  87 . Furthermore, the rod end chambers  96  of the lifting cylinders  24  are connected to each other by a connecting line  100  which is connected to the fluid supply line  88 . As a result, the two hydraulic cylinders  24  are pressurized uniformly. The hydraulic accumulator  82  makes a first connection with the shut-off valve  90  by a connecting line  102 . Furthermore, a connecting line  104  leads from the fluid supply line  87  to a second connection with the shut-off valve  90 , and a further connecting line  106  leads from the supply line  88  to a third connection with the side of the shut-off valve  90 . The shut-off valve  90  has a first or off switching position  108 , that shown in  FIG. 11 ) in which all of the connections are closed, and therefore a fluid connection is not produced between the connecting lines  102 ,  104  and  106 . Furthermore, the shut-off valve  98  has a second or open switching position  110  in which three connecting lines  102 ,  104  and  106  are brought into fluid connection. By opening the shut-off valve  90 , i.e., by switching the shut-off valve  90  into the open switching position  110 , it can be ensured that when the hydraulic fluid supply is decoupled, hydraulic fluid is not trapped in the chambers  94 ,  96 , but rather can escape into the hydraulic accumulator  82  and into the respective other chamber  94 ,  96 , and vice versa. As a result, the lifting cylinders  24  can take up a floating position in which the pistons  86  are freely movable, wherein volume differences between the head end chambers  94  and the rod end chambers  96  are compensated for by the hydraulic accumulator  82 . This state, in turn, permits a relatively free movement of the mounting masts  18  in relation to the front loader arm  20 , and therefore, when the shut-off valve  90  is open, each mounting mast  18  can be aligned for connection with a respective mounting frame  16  in a freely pivoted manner during the coupling. The opening of the shut-off valve  90  during the decoupling of the front loader  13  can be carried out here by an operator in one working sequence together with an unlocking of the pivoting locking bar  54  and the separating of the hydraulic fluid supply and associated control valve (separating of the quick coupler). Owing to the fact that the opening of the shut-off valve  90  already takes place during the decoupling of the front loader  13 , the shut-off valve  90  is also already prepared here for the next coupling operation, and therefore an operator can couple the front loader  13  to the freely movable mounting masts  18  without leaving the tractor  10 . After the coupling of the front loader  13 , the shut-off valve  90  has to be closed for the starting up of the hydraulic function (connecting of the hydraulic fluid supply) in order to ensure a hydraulic operation of the front loader  13 . However, this can likewise take place in one working sequence together with the connection of the quick coupler. 
         [0042]    In the alternative exemplary embodiment illustrated in  FIG. 12 , there is a further (second) hydraulic accumulator  112  which is connected to the shut-off valve  90  via a connecting line  114 , wherein the connecting line  102  from  FIG. 11  is dispensed with here, and the further hydraulic accumulator  112 , instead of the connecting line  102  from  FIG. 11 , is connected to the shut-off valve  98 . Furthermore, a further connecting line  116  which extends between the supply line  87  and the connecting line  114  is provided. A check valve  118  closing in the direction of the further hydraulic accumulator  112  is arranged in the connecting line  116 . In the exemplary embodiment with respect to  FIG. 12 , the first hydraulic accumulator  82 , in contrast to the exemplary embodiment in  FIG. 11 , is used only for the hydraulic spring suspension of the lifting cylinders  24  and is not used for equalizing the volume between the chambers  94 ,  96  when switching on the floating position. In the first switching position  108 , the shut-off valve  90  closes all of the connections, and therefore a fluid connection is not produced between the connecting lines  104 ,  106  and  114 . By contrast, in the second switching position  110 , a fluid connection is produced between the connecting lines  104 ,  106  and  114 . The remaining configuration of the hydraulic circuit is comparable to the manner of operation illustrated in  FIG. 11 , except that here the connecting line  116  is also provided in conjunction with the check valve  118  in order to relieve the further hydraulic accumulator  112  of pressure. By opening of the shut-off valve  90 , i.e., by switching the shut-off valve  90  into the opened switching position  110 , the connecting lines  104 ,  106  and  114  are brought into fluid connection, as a result of which it can be ensured that, when the hydraulic fluid supply is decoupled, the hydraulic fluid is not trapped in the chambers  94 ,  96 , but rather can escape into the further hydraulic accumulator  112  and into the respective other chamber  94 ,  96 , and vice versa. As a result, the lifting cylinders  24  can take up a floating position in which the pistons  86  are freely movable, wherein volume differences between the head end chambers  94  and the rod end chambers  96  are compensated for by the further hydraulic accumulator  112 . This state, in turn, also permits a relatively free movement here of the mounting mast  18  in relation to the front loader arm  20 , and therefore, when the shut-off valve  90  is open, the mounting mast  18  can be freely pivoted into alignment with the associated mounting frame  16  during the coupling. The opening of the shut-off valve  90  during the decoupling of the front loader  13  can be carried out here by an operator in one working sequence together with unlocking of the pivoting locking bar  54  and the separating of the hydraulic supply (separating of the quick coupler). Owing to the fact that the shut-off valve  90  is already opened during the decoupling of the front loader  13 , the latter is also already prepared here for the next coupling operation, and therefore an operator can couple the front loader  13  including the freely movable mounting masts  18  to the mounting frames  16  without leaving the tractor  10 . The shut-off valve  90  has to be closed after the coupling of the front loader  13 , for the starting up of the hydraulic function (connecting of the hydraulic fluid supply), in order to ensure a hydraulic operation of the front loader  13 . However, this can likewise take place in one working sequence together with the connection of the quick coupler. 
         [0043]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.