Abstract:
A hydraulic arrangement for lifting and/or lowering at least one implement carrying arm on an agricultural machine. The arrangement comprises an inlet hydraulic line and an outlet hydraulic line connecting a fluid pump ( 18 ) and a fluid reservoir ( 26 ) respectively to a first valve means ( 12 ), said arrangement comprising at least one dual acting hydraulic cylinder ( 15 ) for lifting/and or lowering the implement carrying arm. The at least one cylinder is connected to the first valve means ( 12 ) allowing the cylinder ( 15 ) to be switched between a single acting mode wherein the arm can be lifted and a double acting mode wherein the arm can be lifted and lowered.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention relates to a hydraulic lifting and lowering arrangement on a self propelled machine. More specifically the invention relates to a lifting and lowering arrangement of an implement carrying arm on an agricultural machine. 
         [0003]    2. Description of Related Art 
         [0004]    Agricultural machines, such as forage harvesters for example may be equipped with implements to be worked over the ground. The implement may carry out processes such as cutting grass, grain, maize or working the soil. Owing to the variety of working processes and terrain conditions a self propelled machine must be capable of carrying and moving a wide range of different implements of varying weights under different working conditions. 
         [0005]    For some processes such as heavy soil tillage, the full weight of the implement rests on the ground. In other working conditions the full weight of the implement will be carried by the machine so that the implement does not touch the ground. This would be the case for example with maize harvesting. In other cases, such as grass harvesting, part of the weight of the implement is carried by the machine and part of the weight is borne by the ground. 
         [0006]    Typical lifting arrangements on agricultural machines comprise one or more carrying arms to which an implement is attached and which can be moved to lift and lower an implement. A carrying arm is movable around one, or more pivot points by one or more hydraulic cylinders. There is therefore mechanical and hydraulic friction with such an arrangement. The amount of friction will depend on the direction of movement of the arms and will be different from the extending and retracting stroke of the cylinders which will lead to hysteresis. 
         [0007]    Some implements which are attached to the machine are to be moved in one direction only (upwards) since to move the implement downwards using the cylinders could damage the ground or implement. Such implements require a single acting hydraulic cylinder or a double acting hydraulic cylinder that can be used in single acting mode. Typically, the hydraulic arrangement is arranged such that pressurisation of the cylinder extends the piston rod which raises a carrying arm and implement. When the cylinder is not pressurised the piston retracts slowly under the weight of the attached implement lowering the carrying arm and implement to the ground. 
         [0008]    Owing to mechanical and hydraulic friction in a hydraulic arrangement, the weight of the attached implement may not be sufficient to contract the cylinder to lower the carrying arm. Such implements will require a double acting hydraulic cylinder so that the implement can be both lifted and lowered to the ground by controlling the pressure exerted on the hydraulic cylinders. 
         [0009]    Also, for maintenance of a forage harvester it is necessary to dismount an intake from the carrying arms to allow maintenance work to the machine to be carried out. This means that there is no weight attached to the carrying arms and therefore if a single acting hydraulic cylinder is used the cylinders cannot be retracted and therefore the carrying arms cannot be lowered unless an external force is applied to the carrying arms. 
         [0010]    It is a known problem to retract a double acting cylinder which is connected to a single acting valve arrangement as it must be pushed in manually. This means the attached carrying arm must be pushed downwards manually if it is to be lowered. 
         [0011]    Alternatively, if the carrying arm has already been detached for maintenance purposes, the attachment rods (to which the carrying arms are mounted) must pushed in manually. It is known that hydraulic cylinders used on medium or large size machines cannot be pushed in manually because the frictional force is so high that it can not be overcome by human force alone. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    It is an aim of the invention to overcome the problem set out above and provide a hydraulic arrangement for moving a carrying arm on an agricultural machine in which the function of the hydraulic cylinders can be easily switched between a single acting mode and a double acting mode using a single valve arrangement. 
         [0013]    It is a further aim of the invention to provide an hydraulic arrangement which is suitable for moving both heavy and light implements attached to a carrying arm in a manner that the pressure required to lift a light implement will be raised artificially to the same level that is required to lift a heavy implement. 
         [0014]    In accordance with the invention there is provided an hydraulic arrangement for lifting and/or lowering at least one implement carrying arm on an agricultural machine having the features of claim  1 . 
         [0015]    In case of maintenance and service it may be necessary for a person to position himself under an implement mounted to a forage harvester. In order to prevent serious injuries due to an operator lifting or lowering the implement, there is legislation stating that it must be possible to lock and hold the at least one hydraulic cylinder so that its movement does not caused injury. 
         [0016]    Preferably, the hydraulic arrangement comprises a blocking valve to prevent unwanted movement of the at least one cylinder. 
         [0017]    Further preferred features of the invention are set out in the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention will now be described by example only, with reference to the following drawings in which: 
           [0019]      FIG. 1  is a circuit diagram of the hydraulic arrangement in accordance with the invention, 
           [0020]      FIG. 2  is a circuit diagram of the hydraulic arrangement of  FIG. 1  in which the circuit is single acting and is suitable for use with a light implement, 
           [0021]      FIG. 3  is a circuit diagram of the hydraulic arrangement of  FIG. 1  in which the circuit is single acting and is suitable for use with a heavy implement, 
           [0022]      FIG. 4  is a is a circuit diagram of the hydraulic arrangement of  FIG. 1  in which the circuit is double acting, 
           [0023]      FIG. 5  is a circuit diagram of the hydraulic arrangement of  FIG. 1  in which the circuit is in a locked position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  is an hydraulic circuit  1  for controlling movement (lifting and/or lowering) of at least one carrying arm on an agricultural machine, for example a forage harvester. A variety of implements such as a mower, plough or crop cutter may be attached to the carrying arm. 
         [0025]    The carrying arm, or carrying arms (not shown) are connected to one or more dual acting cylinders  15 . In  FIG. 1 , two dual acting cylinders are shown for use with two carrying arms. Both the piston end  15   a  and cap end  15   b  of the cylinders are connected to a first valve means  12  which is a 4/3 directional valve. Directional valve  12  is connected by hydraulic line  25  to a blocking valve  13  and a second valve means  14 . Second valve means  14  is a 4/4 directional control valve. Valve  14  is connected to a pump  18 . Valves  12 ,  13 ,  14  are also connected to fluid reservoirs  26  by hydraulic line  27 . Valves  12  and  13  are shown as being manually operable by an operator pushing them, however other valves such as mechanically, electrically or pneumatically operated valves could also be used, Valve  14  is electrically operable by means of signal from an ECU  22  (explained below). 
         [0026]    When an implement is fitted to the carrying arms and the machine is travelling over undulating surface conditions the weight distribution between the ground and the machine is kept constant by a control system. The control system comprises a pressure transducer  21 , an ECU unit  22  and a control panel  23 . The transducer  21  constantly measures the pressure in hydraulic line  24  and the ECU continually compares this value with a pressure entered into the control panel  23  by the operator. If the pressure in hydraulic line  24  is too high, control valve  14  can be activated to lower the implement. If the pressure is too low, control valve  14  can be activated to lift the implement. Such a control system is well known and does not form part of the invention and is therefore excluded from  FIGS. 2 to 5 . 
         [0027]      FIG. 2  shows valve  12  in a first position  12   a  for when a light implement, such as a grass cutting implement is attached to the carrying arms. Valve  13  is in the open position  13   a.  When valve  14  is moved from the closed position  14   b  into the open position  14   a,  fluid is pumped through line  25 . With valve  12  in position  12   a  both the piston end  15   a  and cap end  15   b  of cylinders  15  are connected to line  25  and the pressure in cap end  15   b  can be increased pushing the piston out and raising the carrying arm and attached implement. This results in quick movement and high pressure facilitating easier control because the distance between the pressure level that needs to be controlled and the pressure level that is caused by hysteresis has been increased. The system is single acting. By moving valve  14  into position  14   c,  the weight of the implement will cause the cylinders  15  to retract, moving fluid from the cap ends  15   b  through line  25  to the reservoir  26 . Also the piston ends of the cylinders will be filled. The actual lowering speed can be adjusted easily as valve  14  is a proportional valve. 
         [0028]    The accumulator  16  serves to absorb vibrations caused by the machine running over undulating ground and can be connected and disconnected by valve  17  in order to react to different operating conditions. It also supports the pressure control system described above because the hydraulic accumulator in conjunction with the cylinder acts similar to a mechanical spring. If the valve is connected any changes in pressure will fed directly to the accumulator. If the valve  17  is disconnected constriction  20  serves as a pressure balance. For example, if the accumulator is switched off and a new heavier implement is attached, constriction  20  prevents carrying arm crashing down. Likewise, if a lighter implement is attached it prevents the carrying arm lifting. 
         [0029]      FIG. 3  shows the hydraulic arrangement when valve  12  is moved into position  12   c  for when a heavy attachment, such as a corn header is attached to the carrying arms. In position  12   c  cylinder piston ends  15   a  are connected to hydraulic line  27  and the hydraulic line  25  is connected to the cylinder cap ends  15   b.  Valve  13  is in the open position  13   a.  This arrangement is single acting. When valve  14  is moved to open position  14   a  pressure only acts on the cap end sides  15   b  of the pistons allowing a large force to be exerted on the pistons, to extend it, thus raising the arm. At the same time pressure on the piston side  15   a  is released through line  27  to reservoirs  26 . When valve  14  is moved to position  14   c  the cylinders can retract under the weight of the attached implement and the carrying arms lower as fluid flows from the cylinders through line  27  to the reservoir  26 . 
         [0030]      FIG. 4  shows the hydraulic arrangement when valve  12  is moved into position  12   b  so that line  27  is connected to the piston ends  15   a  of the cylinders  15  and line  25  is connected to the cap ends  15   b  of the cylinders. Valve  13  is in the open position  13   a.  With this arrangement the cylinders  15  are double acting. When valve  14  is moved to open position  14   a  fluid can flow through line  25  to the cap ends  15   b  exerting a pressure on the piston and extending the pistons lifting the carrying arms and an attached implement. Fluid in piston ends  15   a  can flow through line  27  to reservoir  16 . If the valve  14  is then moved to position  14   b,  the weight of the attached implement will cause pistons  15  to retract and fluid will flow from the cap ends  15   b  to reservoir  26 . If, however, there is no implement attached to the carrying arms the weight of the arms alone will not provide a strong enough force to retract the cylinders and the carry arms will remain in a lifted position. It may be necessary to lower the arms to allow maintenance work to be done to the machine. In order to lower the arms, the hydraulic arrangement can be used to provide a force on the piston to retract the pistons. 
         [0031]    With the valve  12  in position  12   c  and valve  14  in position  14   b,  the pump  18  can be used to pump fluid through line  27  to the piston ends  15   a  of the cylinders to provide a force on the piston to retract the piston and thus lower the carrying arms. 
         [0032]      FIG. 5  shows the case where blocking valve  13  is in the closed position  13   b.  Valve  13  can be manually pushed by the operator into the closed position. Essentially the cylinders  15  are locked in position so that the carrying arms cannot move. This is a safety measure so that it is safe for a person to carry out maintenance, or checks close to the carrying arms without there being any danger of movement of the arms.