Abstract:
A belt drive is described for connecting a stationary pulley to a relatively movable pulley. The belt drive comprises a first guide pulley mounted in a fixed position in relation to the stationary pulley and a second guide pulley mounted for movement with the movable pulley. In the invention, the second guide pulley is mounted in such a manner as to be capable of a limited degree of movement relative to the movable pulley and is spring biased in a direction to maintain the belt in tension.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This Patent Application claims priority under 35 U.S.C. § 119 to GB 0423798.8, filed on Oct. 27, 2004 titled, “Belt Drive for a Harvester with a Movable Cutter”, the full disclosure of which is hereby fully incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a belt drive for a harvester with a movable cutter.  
       BACKGROUND OF THE INVENTION  
       [0003]     One type of header that is fitted to combine and forage harvesters comprises a reel that extends transversely to the direction of travel. A scissor-action cutter located beneath the reel cuts the stalks of the crop, spring tines projecting from the rotating reel pick up the cut crop and pushes them on to two augers that advance the crop towards the centre of the harvester. From there, the crop is carried into the processing machinery of the harvester.  
         [0004]     The ideal distance between the cutter and the auger depends on the type of crop being harvested and it is known to mount the cutter in such a manner that it can be moved forwards and backwards relative to the auger. The cutter is formed of two blades, one being movable in a reciprocated movement relative to the other by means of a so-called wobble box, the cutter and its drive mechanism being mounted on a sub-frame that can be moved relative to the main frame of the header by some 50 cms, typically. The wobble box has a drive pulley that is driven by a belt which passes over a stationary powered pulley mounted on the main frame of the header. A belt configuration is therefore required which does not obstruct the movement of the cutter sub-frame, yet which maintains the drive belt under the correct tension to drive the wobble box in all positions of the cutter sub-frame.  
         [0005]     The geometry of the belt drive for a movable cutter of a harvester is further complicated by the magnitude of the permissible movement because it is necessary to ensure that the different runs of the belt never touch one another in any position of the cutter sub-frame. Furthermore, the belt and its various drive, guide and tensioning pulleys must all remain protected within a housing that covers the entire drive mechanism to prevent entanglement of the crop.  
         [0006]     Prior art attempts to meet the above criteria have resulted in belt geometries having as many as eight different pulleys and, despite their complexity, holes were needed in the frame to allow pulleys to be repositioned to achieve the desired belt tension in different positions of the cutter.  
       SUMMARY OF THE INVENTION  
       [0007]     In accordance with a first aspect of the present invention, there is provided a belt drive for connecting a stationary pulley to a relatively movable pulley, comprising a first guide pulley mounted in a fixed position in relation to the stationary pulley and a second guide pulley mounted for movement with the movable pulley, wherein the second guide pulley is mounted in such a manner as to be capable of a limited degree of movement relative to the movable pulley and is spring biased in a direction to maintain the belt in tension.  
         [0008]     In the prior art, the first guide pulley, that is to say the one mounted on the same frame as the stationary pulley, was used as the belt tensioner. To avoid its interfering with components mounted on the same sub-frame as the movable pulley, this necessitated that the movement of the tensioning pulley should be confined to a rectilinear motion. To achieve this, the axle of the tensioning pulley was supported for movement along two parallel guide tracks which made for a complex and costly construction.  
         [0009]     In the present invention, the second guide pulley that is mounted for movement with the movable pulley is the one that is used as the belt tensioning pulley. Such mounting of the tensioning pulley makes for a simpler and more compact construction in that the movement of the tensioning pulley need no longer be rectilinear.  
         [0010]     Conveniently, the second guide pulley is carried on one end of a lever arm that is pivotably mounted on a sub-frame supporting the movable pulley, the opposite end of the lever being acted upon by a spring acting to rotate the lever arm in a direction to increase the belt tension. Since these changes in length of the belt occur during the lifetime of the belt and the tensioning of the belt is done automatically by the spring biased rod, the driver does not need to follow up the stretching of the belt or take care of it.  
         [0011]     The path traced by the belt around the pulleys includes two runs that change in length during displacement of the movable pulley. In a preferred embodiment of the invention, the relative positions of the pulleys are such that while the length of one of these two runs increases the length of the other decreases by a substantially equal amount, whereby the length of the path traced by the belt does not change significantly with the position of the movable pulley relative to the stationary pulley.  
         [0012]     If the length of the path traced by the belt does not vary significantly with movement of the movable pulley, the amount of movement required of the belt tensioner pulley in order to take up the slack in the belt is reduced.  
         [0013]     Because of the extent of possible movement of the cutter, the distance between the stationary and movable pulleys may be too long (when the cutter is moved into its most forward position) to be spanned by a single run of the belt. It is therefore advantageous to provide two support pulleys to contact the opposite sides of the run of the belt that extends from the stationary pulley to the movable pulley.  
         [0014]     In this case, one of the support pulleys may be stationary and the other movable with the movable pulley, the run extending between the two support pulleys being one of the two runs of varying length.  
         [0015]     In accordance with a second aspect of the invention, there is provided a belt drive for connecting a stationary pulley to a relatively movable pulley, comprising a first guide pulley mounted in a fixed position in relation to the stationary pulley and a second guide pulley mounted for movement with the movable pulley, wherein the path traced by the belt around the pulleys includes two runs that change in length during displacement of the movable pulley, and wherein the relative positions of the pulleys are such that while the length of one of the two runs increases, the length of the other decreases by a substantially equal amount, whereby the length of the path traced by the belt does not change significantly with the position of the movable pulley relative to the stationary pulley. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:  
         [0017]      FIG. 1  is a schematic representation of a known belt drive for a harvester header having a movable cutter;  
         [0018]      FIG. 2  shows the belt drive of  FIG. 1  when the cutter is moved forwards;  
         [0019]      FIG. 3  is a similar schematic representation of a belt drive of the present invention;  
         [0020]      FIG. 4  is a view of parts of the belt drive shown in  FIG. 3 , drawn to an enlarged scale, showing the configuration of the belt drive in different positions of the movable pulley; and  
         [0021]      FIG. 5  is a view of parts of the belt drive shown in  FIG. 3 , drawn to an enlarged scale, showing the configuration of the belt drive in different positions of the movable pulley are views of parts of the belt drive shown in  FIG. 3 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     In  FIGS. 1 and 2 , a drive pulley  10  is mounted on the frame of the header of a harvester and is connected by a chain and sprocket transmission (not shown) for rotation with the auger of the header. A driven pulley  12  is mounted on a sub-frame  15 , which is movable relative to the frame of the header. The pulley  12  is fitted to the input shaft  12   a  of a wobble box (not shown) that reciprocates one of the blades of the cutter (also not shown). A first guide pulley  14  is mounted on the frame of the header and a second guide pulley  16  is mounted on the movable sub-frame  15 . The belt  18 , if passing only around the four pulleys mentioned above, would include two long runs  18   a  and  18   b  from the pulley  12  to the pulleys  10  and  16 . To avoid excessive transverse movement of the belt  18  along these two runs  18   a  and  18   b , they are each guided over a respective pair of support pulleys  20  and  22 . The pulleys  20  and  22  supporting the run  18   a  of the belt  18  between the pulleys  12  and  16  are mounted on the movable sub-frame  15 . In the situation of the two pulleys  24  and  26 , which support the run  18   b  of the belt  18 , and which extend between the pulleys  12  and  10 , the pulley  24  is mounted on the sub-frame  15  and the pulley  26  is stationarily mounted on the frame (not shown) of the header.  
         [0023]     The guide pulley  14  acts as a tensioning pulley and its axle  28  is guided for movement along slots  30  in a bracket  34  that is secured to the frame of the header. The axle  28  of the pulley  14  is received in a clevis that slides along the slots  30  and is connected to a rod  36  that applies a spring bias  37  to the axle  28  to maintain the belt  18  in tension in all positions of the pulley  12 .  
         [0024]     A comparison of  FIGS. 1 and 2  will show that when the sub-frame  15  and the various pulleys mounted on it are moved, only two runs of the belt change in length, namely the run  18   a  that extends between the pulleys  14  and  16  and the run  18   b  that extends between the pulleys  24  and  26 . Because of the geometry of the pulleys, these two runs  18   a  and  18   b  do not change in length by equal amounts and the length of the path traced by the belt changes significantly as the sub-frame  15  moves. The guide pulley  14  needs therefore a considerable degree of travel to take up the slack created in the belt  18 . This is in addition to the movement of the tensioning pulley  16  that is required to compensate for stretching of the belt  18  as it ages. For this reason, in the prior art, in addition to providing long slots  30  for the movement of pulley  14 , holes (not shown) were provided into the sub-frame  15  to allow the pulley  16  to be repositioned when necessary.  
         [0025]     It will also be noted, from  FIG. 1  in particular, that the space in which one can accommodate a tensioning pulley capable of a large degree of travel is severely limited and consequently, the tensioning pulley  14  needs to be guided for linear movement.  
         [0026]     In the embodiment of the invention now to be described with reference to FIGS.  3  to  5 , in order to avoid unnecessary repetition, items that serve the same function as described with reference to  FIGS. 1 and 2  have been allocated the same reference numerals in the one hundred series (i.e. 100 has been added to the numerical values of each reference numeral).  
         [0027]     The embodiment of the invention differs from the prior art belt drive shown in  FIGS. 1 and 2  in that the run  118   a  that extends between the pulleys  112  and  116  does not require the addition of a support pulley as it does not risk to interfere with any other part of the belt drive in any position of the sub-frame  115 . All the remaining pulleys do however have counterparts in the embodiment of FIGS.  3  to  5 .  
         [0028]     An important difference between the embodiment of the present invention and the prior art is that in this case the pulley  114  is directly mounted on the frame (not shown) of the header and it is the pulley  116  that acts as the tensioning pulley for the belt  118 . Furthermore, the pulley  116  is not guided for rectilinear motion but is instead carried by a lever arm  140  which is pivoted at its center on the sub-frame  115 . The axle of the pulley  116  is mounted on one end of the lever arm  140  and the other end of the lever arm  140  is connected to a clevis  142  on one end of a spring biased rod  144  which biases the lever arm  140  in a clockwise direction to maintain the belt  118  under tension.  
         [0029]     A further important difference resides in the geometry of the pulleys. If the runs  118   a  and  118   b  were to lie parallel to one another and parallel to the direction of movement of the pulley  112 , there would be no change in the length of the path traced by the belt  118  in the different positions of the sub-frame  115 . Because this is difficult to achieve (on account of the need to support the run of the belt between the pulley  110  and  112 ), the two variable length runs  118   a  and  118   b  are instead inclined at the same shallow angle as one another to the direction of movement to direction movement of the sub-frame. Consequently, during movement of the sub-frame  115 , these two runs  118   a  and  118   b  change length by substantially equal amounts, with the one being lengthened as the other is shortened. The little variation in the attitude of these runs  118   a  and  118   b  in the different positions of the sub-frame  115  shown in FIGS.  3  to  5  is to be contrasted with the significant variation that occurs between  FIGS. 1 and 2  in the prior art. As a result of this design, the movement of the pulley  116  to tension the belt  118  is required predominantly to compensate for stretching of the belt  118  with age, not for the slack that is created and taken up as the sub-frame  115  moves.