Abstract:
A one-piece disc cutterbar shear device that employs frangible structural members between the drive shaft and knives, the frangible members designed to fail before the drive components upon impact with an obstruction.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to mechanisms for protecting mechanical drive components from overloads, and more particularly relates to a shear device coupled between components of an agricultural disc mower that protects the various components of the mower in the event a cutterhead strikes an object and creates an overload condition.  
       BACKGROUND OF THE INVENTION  
       [0002]     Typical disc cutterbars used in agriculture include an elongated housing-containing a train of meshed idler and drive spur gears, or a main power shaft coupled by respective bevel gear sets, for delivering power to respective drive shafts for cutterheads spaced along the length of the cutterbar. The cutterheads each comprise a cutting disc including diametrically opposed cutting blades (though configurations with three or more blades are known) and having a hub coupled to an upper end of a drive shaft, the lower end of the drive shaft carrying a spur gear in the case where a train of meshed spur gears is used for delivering power, and carrying a bevel gear of a given one of the bevel gear sets in the case where a main power shaft is used. In either case, as would be expected, bearings are used to support the various shafts. The cutterheads are rotated at a relatively fast speed making the drive components, such as gears, bearings, and shafts vulnerable to damage in the event that the unit strikes a foreign object. For background information on the structure and operation of some typical disc cutterbars, reference is made to U.S. Pat. No. 4, 815,262 issued to E. E. Koch and F. F. Voler, the descriptive portions thereof being incorporated herein in full by reference.  
         [0003]     In order to minimize the extent of such possible damage to the drive components, it is known to incorporate a shear device somewhere in the drive of each unit which will fail upon the imposition of a predetermined overload. As used herein with reference to shear devices, the terms “fail” or “failing” are intended to cover the actual function of such devices, i.e., shearing, fracturing, breaking and the like. Several different such shear devices and arrangements are shown, for example, in U.S. Pat. Nos. 4,999,981, 4,497,161 and 5,715,662.  
         [0004]     The &#39;981 patent shows a shear mechanism that comprises a shaft with a weakened portion created by a cut groove, or break zone  41  (seen, for example, in  FIG. 3  thereof) in driven shaft  20 . Upon overload, the shaft breaks at zone  41  which is located outside the support bearing such that there is a clean and complete break in the shaft. This structure is intended to eliminate the input of kinetic energy to the cutterhead after failure of the shear mechanism, thereby eliminating damage to the drive system and gearing.  
         [0005]     A somewhat different shear mechanism is disclosed in  FIGS. 2 and 3  of the &#39;161 patent. Cutting disc  3  is connected by a series of shear bolts  26  to the vertical shaft  8 . Upon impact of the cutterhead with an obstruction, one or more of the shear bolts fail, stopping the input of rotational force to the cutterhead.  FIG. 4  shows a slightly different embodiment where a resilient cover plate  28  depresses balls  30  arranged in holes of the disc  3  and fitting into recesses  31  of the disc  27 . An overload impact is intended to cause balls  30  to snap out of the recesses  31  so that the direct rotary joint between shaft  8  and cutting disc  3  is interrupted. It is stated that the connection can be re-established by continuing to rotate disc  3  with respect to the disc  27  so that the balls  30  again snap into the recesses  31 .  
         [0006]     The shear mechanisms shown in the &#39;662 patent each employ shearable splines. In a first embodiment the shear device is in the form of either a collar or clamping member having internal splines received on a splined upper end of the drive shaft and having shearable cylindrical drive lugs engaged with complementary shaped openings provided in an upper surface of a disk hub. Referring more specifically to  FIG. 2  thereof, the upper end of drive shaft  26  has a splined section  86 . Shear collar  88  establishes a drive connection between shaft  26  and hub  80 . The collar  88  includes internal splines  90  engaged with the splined section  86  of shaft  26  just above hub  80 . Shearable cylindrical drive lugs  92  project downwardly from the bottom of collar  88  and are received in complementary holes  94  in hub  80 . An overload situation causes the lugs  92  to shear and the continuing transfer of rotational power to cease.  FIGS. 4 through 6  show another embodiment where shaft  34  has a splined upper end section  110 . Instead of a shear collar, a shear device in the form of a cap-like clamping member  114  is used for transferring torque from shaft  34  to hub  80 . Clamping member  114  has an annular lower portion  116  provided with interior splines  118  engaged with the splined section  110  of shaft  34 . A plurality of shearable lugs  120  extend downward from lower portion  116  and are received in complementary shaped cylindrical openings  94  in hub  80 , whereby torque is transferred from shaft  34  to hub  80 . Again, when an overload occurs, lugs  120  shear, and torque is no longer transmitted. The final embodiment shown in the &#39;662 patent is shown in FIGS.,  7  through  9 . Instead of a disk hub  80 , a disk hub  127  is used which has a central splined opening  128  disposed in spaced concentric relationship to the splined upper end section  110  of shaft  34 . A ring-like shear insert  130  is received on the upper end of the drive shaft  34  and has inner splines  132  engaged with the splined upper end section of the shaft and has outer splines  134  engaged with the splined opening  128  of hub  126 . Splines  132  are designed to shear upon overload. Shearable splines do work; however, shearing splines has the potential of lodging metal fines (small pieces that may accompany the shearing process) into the support bearing(s). Additionally, the splines must be reduced in number or weakened in order to shear properly, thus potentially reducing their longevity.  
         [0007]     Another significant and generally universal problem with shear systems that use mating surfaces, such as shear pins or splines, is that mating surfaces wear during normal cutterbar operation leading to premature failure.  
         [0008]     It would improve the operation of disc cutterbars if the problems identified above could be overcome.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, an object of the present invention is to provide a shear mechanism in a mechanical drive train for an agricultural cutterbar that will stop the transfer of power along the drive train in the event of overload.  
         [0010]     A further object of the present invention is to provide a novel shear device between components of a cutterhead.  
         [0011]     A further object of the present invention is to provide a novel shear device between components of a cutterhead that has no mating surfaces which wear and lead to premature fatigue failure.  
         [0012]     Yet another object of the present invention is to provide a disc cutterbar with multiple cutterheads, each comprising a drive shaft connected via a single-piece shear hub to the knives of the cutterhead.  
         [0013]     It is a still further object of the present invention to provide a shear mechanism in a mechanical drive train for an agricultural cutterbar that can be easily removed and replaced upon failure.  
         [0014]     It is yet a further object of this invention to provide an improved disc cufterbar that is relatively durable in construction, inexpensive of manufacture, carefree of maintenance, easy to assemble, simple and effective in use, and less likely than prior art cutterbars to sustain costly damage upon contact with a fixed object.  
         [0015]     These and other objects, features and advantages are accomplished according to the instant invention by providing a one-piece disc cutterbar shear device that employs frangible structural members between the drive shaft and knives, the frangible members designed to fail before the drive components upon impact with an obstruction. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]     The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:  
         [0017]      FIG. 1  is a top plan view of a disc mower mounted on the three-point hitch of a tractor, the disc mower having a modular disc cufterbar incorporating the principles of the instant invention, the rotational path of the individual disc members being shown in phantom, the disc mower being one of the configurations in which the improved disc cuttterbar of the instant invention can be utilized;  
         [0018]      FIG. 2  is an enlarged top plan view of a central portion of the assembled modular disc cutterbar depicting two adjacent cutterhead modules and an interstitial spacer module, portions of the spacer modules on opposite sides of the cutterhead modules being broken away and the disc members being removed for clarity;  
         [0019]      FIG. 3  is a cross-sectional view of the cutterhead module taken along line  3 - 3  of  FIG. 1 ; and  
         [0020]      FIG. 4  is a perspective view of the shear device of the instant invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Referring now to the drawings and particularly to  FIG. 1 , a modular disc cutterbar incorporating the principles of the instant invention can best be seen in a configuration in which the disc cutterbar is conventionally utilized. For a more detailed description of a conventional modular disc cutterbar and various configurations thereof reference is made to U.S. Pat. No. 5,996,323. The disclosure in that patent is hereby incorporated herein in its entirety by reference.  
         [0022]     Cutterbar  30  is mounted in a disc mower  10  having a support frame  11  connected to the three-point hitch mechanism  3  of a tractor T on which the mower  10  is carried in a conventional manner. The disc mower  10  receives operative power from the conventional tractor power take-off shaft  5 . The mower drive mechanism  15  receives the rotational power from shaft  5  and transfers the rotational power to a gearbox  17 , which in turn transfers the rotational power to the cutterbar drive mechanism.  
         [0023]     An alternative configuration for the disc cutterbar would be to incorporate the cutterbar in a disc mower-conditioner. This well-known configuration is shown in more detail in U.S. Pat. No. 5,761,890, which is hereby incorporated herein in its entirety by reference. One skilled in the art and knowledgeable about commercial applications of disc cutterbars will readily recognize that there are other specific configurations of cutterbars to which the invention to be disclosed herein will be applicable. Such skilled individual will also readily recognize that the cutterbar need not necessarily be modular in construction.  
         [0024]     Modular cutterbar  30  is formed from alternating cutterhead modules  40  and spacer modules  32 . Each cutterhead module  40 , as best seen in  FIGS. 1-3 , includes a hollow cast housing  41  ( FIG. 3 ) having a shape to retain a low profile and to establish an oil reservoir  44  therewithin. Cutterheads  40  are gear driven and assembled in such a manner as to establish a specific timing relationship between adjacent units. More particularly, the cutterheads are arranged such that the knives  74  on adjacent units have overlapping cutting paths, but do not come into contact with each other. Failure to maintain this timed relationship during operation will result in one unit hitting the adjacent unit(s), damaging the cutterheads (and possibly initiating a chain reaction that damages all cutterheads), the drive train of the cutterbar and/or tractor T.  
         [0025]     Referring again to  FIGS. 2 and 3 , it can be seen that each cutterhead module  40  is provided with a forwardly positioned rock guard  50  and a skid shoe  52  that passes beneath cutterhead module  40  for engagement with the surface of the ground. The rock guard  50  has a conventional semi-circular configuration and is mounted to opposing forward mounting arms of spacer module  32  adjacent to the corresponding cutterhead module  40 .  
         [0026]     One skid shoe  52  is mounted beneath each cutterhead module  40  to protect the cutterhead module from wear due to engagement with the surface of the ground. Each skid shoe is formed as a generally planar body portion  54  with a mounting tab  56  affixed thereto and projecting upwardly. The body portion  54  is also formed with a forward end  58  that is bent upwardly to engage the corresponding rock guard  50 .  
         [0027]     Modular drive mechanism  59 , best seen in  FIGS. 2 and 3 , is fully disclosed in the &#39;323 patent and reference is made thereto for a more complete description.  
         [0028]     In a simplified manner the drive structure for the cutterhead will now be described in reference to  FIG. 3 . The horizontal drive shaft  60  transfers rotational power along the length of the cutterbar  30 . Shaft  60  is either one long shaft or a series of smaller interconnected shafts extending between adjacent cutterheads  40 . Bevel gear pairs  62 ,  64  convert the horizontal rotational power in shaft  60  to vertical rotational power in drive shaft  66 . The top end portion of drive shaft  66  has splines  68  cut therein, making a male splined shaft, for attaching hub  78  as will be explained further below.  
         [0029]     Cutterhead cover  72  is either pressure formed or fabricated in a bowl-like configuration to provide protection to the underlying components and a support for knives  74 . The number and means for attachment of knives may vary, but are well-known features of such mechanisms. Affixed by to a central opening in cover  72  is splined hub  78 .  
         [0030]     Hub  78  is, as can best be seen in  FIG. 4 , a disk-like member symmetrical about its central vertical axis, and includes a central splined through opening  80  contained within a generally cylindrically-shaped collar-like portion  82 . A generally ring-like outer portion  84  of hub  78  contains a plurality of annularly-space bolts  76 , threaded into holes  77  in hub  78 , and additionally fix movement of the outer portion  84  of hub  78  with cover  72  and knives  74 . Collar-like inner portion  82  is fixed relative to, and supported by, outer portion  84  by a plurality of web members  81 . Web members  81  are made of a frangible material, such as, for example, powdered metal, and designed with such dimensions as are necessary to cause the webs to fail at a specified torque or impact force. The failure forces required to cause the web to fail are, obviously, determined to cause minimum damage to the drive components, yet adequate to allow the effective operation of the cutterhead. Hub  78  may be fabricated in several different ways to achieve the required characteristics and elements. It may, for instance, be cast of a single material with the dimensions of the web members being such that the required failure point is met. Additionally, the inner collar-like portion  82  may be totally supported by web members  81 , or, portion  82  may be supported by web members  81  and a relatively thin flat inward continuation of the outer portion  84  (that does not cover opening  80 ). Such a structure, while functional, would result in additional debris at the time of failure.  
         [0031]     The hub  78  can be located on the underside of the cover  72  or on the upper side, depending upon the cutterhead profile desired. The hub is affixed to cover  72  by bolts  76  which may also attach a smaller cover  94  to prevent bolts  76  from unnecessary or premature wear. Hub  78  is affixed to drive shaft  66  by bolt and cap washer  92  that tightens vertically into the end of shaft  66  to hold the hub in place to rotate with the drive shaft.  
         [0032]     When the cutterhead engages a fixed object of sufficient mass or rigidity to generate a shearing force on web members  81 , adequate to cause failure thereof, the outer portion  84  of hub  78  and the drive shaft  66  will separate and power will cease to be transferred to the knives  74 , thus preventing further damage.  
         [0033]     The drive mechanism  59  in each cutterhead module  40  is coupled to the other cutterhead module drive assemblies by a transfer shaft  60  that passes through the spacer module  32 , as best depicted in  FIG. 2 .  
         [0034]     Referring now to the configurations of utilization of the cutterbar  30  as depicted in  FIG. 1 , it can be seen that the drive mechanism  59  in a disc mower  10  receives rotational power from a gearbox  17  that is supported adjacent the inboardmost cutterhead module  40 . Accordingly, the drive assembly is connected directly to the output shaft (not shown) of the gearbox  17 . The transfer of rotational power to the remaining cutterhead modules  40  proceeds as described above.  
         [0035]     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.