Abstract:
An agricultural harvesting machine comprises a coupling for connecting a shaft  50  to a driving element  14  mounted for rotation about the shaft  50 . The coupling provides a torque path between the shaft  50  and the driving element  14  which passes through both a lost motion connection ( 52,54,58 ) and a shear bolt ( 60,62 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a coupling mechanism for a pickup system of an agricultural harvesting machine, and can be used with round and square balers or any other harvester having a rotor type in-feed system. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a baler, straw, hay or other crop material is picked up from the ground by a pickup system and supplied to a feeder system, e.g., a rotor, which propels the straw into the baling chamber, where it is compacted and formed into bales. The pickup system and the feeder may alternatively be part of an in-feed or transport element for other crop processing means. The feeder and pickup system are connected to rotate in the forward direction at the same time as one another. Typically, a shaft of the rotor which is driven by way of first sprocket by, for example, a tractor PTO (power take-off) shaft, carries a second sprocket which is connected to drive the pickup system. The present invention is particularly concerned with the construction of the coupling mechanism that is suitable for coupling the rotor to the second sprocket driving the pickup system. 
         [0003]    A requirement of the coupling between the feeder drive and the pickup system is that it must be disengaged automatically in the event of an obstruction in the pickup system. 
         [0004]    A coupling is known which comprises discs rotatable with the rotor shaft and disposed adjacent the pickup system drive sprocket. The disc and the sprocket are connected to one another by a shear bolt inserted through bushings affixed to the disc and sprocket. The bolt shears when the torque transmitted through the coupling exceeds a preset maximum and thereby automatically disengages the drive to the pickup system when a serious obstruction is encountered. 
         [0005]    A problem that is experienced with this form of coupling is that after the bolt has sheared it is necessary to realign the bushings in which it fits before it can be replaced by a new shear bolt. As the disc rotates with the feeder and the other with the pickup system, one of these two has to be rotated to achieve the required accurate alignment of the holes and having regard to the size and mass of these two items, this is a task that requires the use of large wrenches or levers. Such means are not readily available when operating the baler in the field. 
       OBJECT OF THE INVENTION 
       [0006]    The present invention seeks therefore to provide a coupling that incorporates a shear bolt which disengages the coupling automatically when a maximum torque is exceeded yet which permits a sheared bolt to be replaced simply by a new one. 
       SUMMARY OF THE INVENTION 
       [0007]    According to the present invention, there is provided an agricultural harvesting machine comprising a coupling for connecting a shaft to a driving element mounted for rotation about the shaft, wherein the coupling provides a torque path between the shaft and the driving element which passes through both a lost motion connection and a shear bolt. 
         [0008]    A lost motion connection is one that transmits force or torque in opposite directions but provides free play when the direction of the force or torque is reversed before a driving connection is re-established. 
         [0009]    Because of the provision of such lost motion within the coupling of the present invention, after the bolt has sheared, there is no requirement to reposition the shaft or the driving element to allow the shear bolt to be replaced. Instead, the lost motion allows a wide range of relative phases between the shaft and the driving element within which the shear bolt can be replaced. 
         [0010]    In a baler, in order to remove blockages that may develop from irregular crop feed, the feeder rotor is commonly provided with a reversing mechanism. Clearing a blockage may require the rotor to be turned in the opposite sense but the pickup system could be damaged if rotated in the wrong sense. The lost motion connection in a coupling of the present invention also mitigates this problem by acting as a limited overrun clutch allowing the rotor to be reversed without any corresponding movement of the pickup system until the lost motion in the coupling is fully taken up in the reverse direction, thereby avoiding damage to the tines of the pickup system. 
         [0011]    In a preferred embodiment of the invention, the coupling further comprises a disc that is rotatable relative to the shaft and connected to the driving element by means of the shear bolt, the lost motion connection being arranged between the shaft and the disc. 
         [0012]    The lost motion connection may conveniently be achieved by means of engagement between a radial arm that is fast in rotation with the shaft and an abutment projecting axially from the side of the disc facing away from the driving element. Such a connection allows a range of free play which approaches one complete revolution. 
     
     
       BRIEF OF THE DRAWINGS 
         [0013]    The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1  is a perspective view of a reversing mechanism of a baler. 
           [0015]      FIG. 2  is a side view of the mechanism shown in  FIG. 1 . 
           [0016]      FIG. 3  is a plan view from above of the mechanism shown in  FIG. 1 . 
           [0017]      FIG. 4  is a section through a detail of the reversing mechanism of  FIG. 1 . 
           [0018]      FIG. 5  is a section taken along the line V-V in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    In the drawings, the sprocket  10  is used to drive the rotor of a baler, the rotor not being shown in the drawings. A ratchet  12  is mounted on the same axis for rotation with the rotor as is a second sprocket  14  which is used to transmit drive to a pickup system. As earlier explained, blockages develop from time to time within the baler and these are freed by rotating the rotor in the reverse direction. 
         [0020]    The reversing mechanism comprises a reversing arm  16  rotatable about the axis of the rotor and carrying a head  18  which is shown in section in  FIG. 4 . The head  18  can pivot relative to the reversing arm  16  about a pivot bolt  20  and it carries a pawl  22  which engages the teeth of the ratchet  12 . At a point  24  above the pivot  20 , the head  18  is pivotably connected to the end of the rod  30  of a double acting hydraulic jack  32  of which the cylinder is pivotably mounted about a fixed pivot bolt  34 . 
         [0021]    When the rotor is to be reversed for the purpose of clearing a blockage, the rod  30  of the hydraulic jack  32  is retracted from the park position shown in  FIG. 2 . Pulling on the pivot point  24  causes the head  18  to pivot about the bolt  20  so that the pawl  22  engages in the teeth of the ratchet  12 . This locks the reversing arm  16  to the rotor and as the rod  30  is retracted the rotor is caused to rotate in the reverse direction. To continue to turn the rotor after the rod of  30  has reached the limits of its stroke, the rod  30  is first extended towards the illustrated position in  FIG. 2 . While doing so, the pawl  22  will ride over the teeth of the ratchet  12  against the action of a spring  44  which biases the pawl  22  in a direction to engage with the ratchet teeth. Several cycles of operation of the hydraulic jack  32  may be carried out until the rotor has been turned sufficiently for the blockage to be cleared. 
         [0022]    Once the blockage has been cleared, it is essential for the pawl  22  to be disengaged from the teeth of the ratchet  12  before the drive to the rotor through the sprocket  10  is re-engaged. This is effected by extending the rod  30  to the position shown in  FIG. 2  in which the reversing arm  16  abuts an adjustable stop  42 . Further extension of the rod  30  will now cause the head  18  to pivot clockwise, as viewed, about the bolt  20  and thereby disengage the pawl  22  from the teeth of the ratchet  12 . This is the position which is referred to herein as the park position. 
         [0023]    To ensure that the head  18  of the reversing arm  16  always returns to the parking position, it is additionally pivotably connected at the point  24  to a lever system  26  biased by a spring  40  which together urge the reversing arm  16  towards the park position. The construction and operation of the lever system and necessary modifications to the circuit of the hydraulic jack  32  are described in detail in GB Patent Application No. 0607557.6 but such a detailed explanation is not required in the present context. It suffices for an understanding of the present invention to know that the rotor shaft  50  which is coupled to the sprocket  14  driving the pickup system normally turns continuously in one direction but it occasionally needs to be turned a small amount in the opposite direction to free a blockage. 
         [0024]    The mechanism coupling the shaft  50  to the sprocket  14  comprises a collar  52  that is keyed onto the shaft  50  and has a radially projecting arm  54 . A disc  56  freely mounted for rotation about the collar  52  has an abutment block  58  that projects into the path of the radial arm  54  from the side of the disc  56  facing away from the sprocket  14 . The sprocket  14  which serves to drive the pickup system is also freely rotatable about the collar  52  and is coupled for rotation with the disc  56  by means of a shear bolt (not shown). The bolt is passed through two hardened bushings  60  and  62  that are welded to the disc  56  and the sprocket  14 , respectively. The head of the bolt rests on the bushing  60  and its nut is received in, and prevented from rotating by, the bushing  62  (see  FIG. 5 ) that is welded to the sprocket  14 . 
         [0025]      FIGS. 3 and 5  also show a bearing support for the shaft  50  which is generally designated  70 . This is one of the bearings used to support the rotor shaft  50  in the frame of the agricultural machine but it is drawn in dotted lines and will not be described herein in detail as it is not concerned with the operation of the coupling driving the pickup system. 
         [0026]    Under normal operating, because of the keying of the collar  52  to the rotor shaft  50 , rotation of the rotor shaft  50  rotates the arm  54  clockwise as viewed in  FIG. 2  until it comes into contact with the abutment block  58 . Once abutment occurs, the disc  56  is made to rotate with the shaft  50  and this then drives the sprocket  14  through the shear bolt causing the pickup system to operate. Of course, such an abutment block  58  would be superfluous if the bushing  60  were made sufficiently strong to fulfil the same task. 
         [0027]    Should a blockage occur, it is freed by rotating the shaft  50  counter clockwise using the previously described reversing mechanism. Rotation of the arm  54  counter clockwise causes it to move away from the abutment  58  so that no torque is transmitted to the pickup system for nearly one complete revolution, after which it will come into contact with the bushing  60 . This amount of lost motion, which is preferably at least half a turn and more preferably three quarters of a turn, is normally sufficient to allow the rotor blockage to be cleared. 
         [0028]    If, for any reason, excessive resistance is encountered when driving the pickup system the shear bolt will shear automatically to disconnect the sprocket  14  from the shaft  50 . After the obstruction in the pickup system has been cleared, a new shear bolt has to be inserted in the bushings  60  and  62  to reconnect the sprocket  14  for rotation with the rotor shaft. 
         [0029]    Before a shear bolt can be replaced it is necessary first to align accurately the bushings in which it is to be inserted. In the prior art, when a shear bolt was used, it was mounted in elements that were fast in rotation with the rotor shaft  50  and the sprocket  14 , respectively. Because of the large rotating masses in both the rotor and the pickup system, such realignment was very difficult to achieve, especially when working in the field. 
         [0030]    This problem is circumvented in the illustrated embodiment of the invention in that the disc  56  can be rotated freely through nearly one complete revolution relative to the shaft  50 . It is only necessary to rotate the rotor shaft  50 , using either the power take off or the reversing mechanism, to a position in which the arm does not obstruct the position in which the bushings  60  and  62  are aligned. The disc  56  can then be rotated manually to align the bushings  60  and  62 . Remounting of the shear bolt is simplified by the fact that its nut cannot turn in the bushing  62 , so that it can be replaced simply using a single spanner to engage the head of the bolt, which remains readily accessible. The task of replacement of a shear bolt is thereby simplified to the extent that it can be carried out quickly in the field by an unassisted operator.