Abstract:
A disc cutterbar having a two-piece mounting hub, one piece rotatably driven and the other supporting a knife for severing standing crop material, with spring-mounted ball and detent devices holding the two pieces members together and forming a shear device therebetween is disclosed. A specially threaded retaining bolt is associated with the knife-supporting piece whereby, upon failure of the shear device, the knife-supporting piece is rotated out of the cutting plane and away from the operational cutterheads.

Description:
FIELD OF THE INVENTION 
     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 
     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, 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. 
     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 that will “fail” upon a predetermined overload being imposed on the device. 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 in U.S. Pat. Nos. 4,999,981, 4,497,161 and 5,715,662. 
     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  that 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. While this structure may in fact eliminate the input of further kinetic energy, it does not stop rotation of the cutterhead or prevent the damage that continued rotation would generate. 
     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, 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 reestablished by continuing to rotate disc  3  with respect to the disc  27  so that the balls  30  again snap into the recesses  31 . The embodiments set forth in this patent exhibit the same shortcomings as seen in the &#39;981 patent, i.e., standard shear mechanisms do not stop rotation of the cutterhead, and thus do not prevent additional damage thereby encountered. 
     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 downwardly 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 t 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. 
     Similar to the devices discussed above, the embodiments of the &#39;662 patent do not stop the cutterhead from rotating, even after power is cut off by a shear device. The third embodiment shown in this patent exhibits an additional shortcoming in that upon failure of the shearable splines, the broken pieces tend to become temporarily “jammed” in among the other parts and components, resulting in even further, though short lived, torque to be transferred, and the resultant additional damage to the cutterheads. 
     Particularly in its preferred embodiment, the instant invention overcomes the drawbacks and shortcomings of the prior art. A two-piece hub design, with a spring mounted ball and detent as a shear mechanism therebetween will fail with substantially no residual transfer of torque. The use of this unique shear mechanism results in no broken pieces to become “jammed” in among the other parts and components, and can be easily repaired by simply realigning the top and bottom hubs so that the spring-loaded ball in the top disc hub fits into the detent in the lower disc hub. Upon failure, the two-piece hub, one of which is driven directly by the drive shaft, separates and the upper disc hub is driven up a specially threaded retaining bolt and separates from the lower hub and drive shaft. This upward movement separates the upper disc hub from the drive train and removes the affected cutting implement from the path of the other cutterheads on the cutterbar. The upper disc hub continues to rotate upward until it reaches a threadless portion of the retaining bolt. There, the upper disc hub is permitted to rotate freely until the absence of drive train inertia causes it to stop. 
     Clearly, the concept of a shear mechanism is not new, however the use of a spring-mounted ball and detent instead of a pin, lug, or bolt, as well as the utilization of a specially threaded retaining bolt, provides advantages in overcoming the problems and shortcomings of the prior art as discussed above. In order to limit the damage to a cutterbar in an overload situation, two characteristics are pursued—a quick, clean disengagement of the driven elements, and the prevention of damage to adjacent discs on the cutterbar by rapid removal of the affected disc from the cutting plane. For non-traditional shear mechanisms, attention is directed to U.S. Pat. No. 2,056,785 (rubber), U.S. Pat. No. 3,064,454 (solder, glass, and other fracturable and fusible materials), and U.S. Pat. No. 3,521,464 (plastic). 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a specially threaded retaining bolt, operating in conjunction with a shear mechanism, in a mechanical drive train for an agricultural cutterbar that will not only stop the transfer of power along the drive train in the event of overload, but also remove the affected disc hub from the path of other cutterheads on the cutterbar. 
     It is another object of the present invention is to provide a novel shear device between hub components of a cutterhead. 
     It is a further object of the present invention is to provide a disc cutterbar with multiple cutterheads, each comprising a drive shaft connected to an inner hub which is connected to an outer hub via a shear mechanism. Upon failure of the shear mechanism, the upper hub and blades are rotated to a position above the cutting plane and out of the path of other cutterheads on the cutterbar. 
     It is yet a further object of this invention to provide an improved disc cutterbar 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. 
     These and other objects, features and advantages are accomplished according to the instant invention by providing a disc cutterbar having a two-piece mounting hub, one piece rotatably driven and the other supporting a knife for severing standing crop material, with spring-mounted ball and detent devices holding the two pieces members together and forming a shear device therebetween. A specially threaded retaining bolt is associated with the knife-supporting piece whereby, upon failure of said shear device, the knife-supporting piece is rotated out of the cutting plane and away from the operational cutterheads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     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 cutterbar 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 cutterbar of the instant invention can be utilized; 
     FIG. 2 is a cross-sectional view of the cutterhead module taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged view of a portion of FIG. 2; 
     FIG. 4 is a top plan view of the lower locking block taken along line  3 — 3  of FIG. 3; 
     FIG. 5 is a view similar to FIG. 3, showing a cross-sectional view of the cutterhead module taken along line  2 — 2  of FIG. 1 after the shear mechanism has failed and the upper disc hub  42  and lower disc hub  43  have separated. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
     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. 
     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 also 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. 
     Modular cutterbar  30  is formed from alternating cutterhead modules  40  and spacer modules  32 . Each cutterhead module  40 , as best seen in FIGS. 1 and 2, includes a hollow cast housing  41  (FIG. 2) having a shape to retain a low profile and to establish an oil reservoir  89  therewithin. As will be discussed in more detail below, the 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  82  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. In such case, the damage is usually significant. 
     Referring particularly to FIG. 2, it can be seen that each cutterhead module  40  is provided with a forwardly positioned rock guard  65  and a skid shoe  70  that passes beneath cutterhead module  40  for engagement with the surface of the ground. The rock guard  65  has a conventional semi-circular configuration and is mounted to opposing forward mounting arms of the spacer modules  32  in known manner adjacent to the corresponding cutterhead module  40 . 
     One skid shoe  70  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  71  with a mounting tab  73  affixed thereto and projecting upwardly. The body portion  71  is also formed with a forward end that is bent upwardly to engage the corresponding rock guard  65 . 
     Modular drive mechanism  75 , best seen in FIG. 2, is fully disclosed in the &#39;323 patent and reference is made thereto for a more complete description. 
     Broadly, within each cutterhead unit there is a two-piece hub, one upper disc hub and one lower disc hub, normally held together by a shear mechanism. The lower hub is connected to a drive shaft, and the upper hub is connected to a rotatable knife support member and positioned on a specially threaded retaining bolt. At the top of the retaining bolt is an area that remains threadless. When a knife engages a solid or fixed object and a shear force generated adequate to cause the shear mechanism to fail, the upper disc hub rotates upward along the threads of the retaining bolt to the threadless area of the bolt where it is permitted to rotate freely. By thus preventing the knives from rotating further, damage is prevented to the drive train of the cutterbar and between adjacent cutterhead units. 
     Attention is now directed to FIGS. 3-5. In the preferred embodiment, upper disc hub  42  is affixed to lower disc hub  43  by means of multiple spring-mounted balls and detents  50  (only one shown in FIGS.  3  and  5 ). Bore hole  51  through upper disc hub  42  contains a spring  52  and ball  53 . Detent  54  in lower disc hub  43  is aligned with the spring-mounted ball  53  to affix the two hubs. By controlling the compression force of spring  51  on ball  52  (and that of any others used), a specific shear point or force can be calculated so that failure will occur at the desired point and upon a specific impact. After failure of the shear device  50 , upper disc hub  42  is free to rotate upward on threads  61  about specially threaded retaining bolt  60  until it reaches the threadless point of the bolt  62 . At threadless point  62 , the upper disc hub  42  ends its upward rotation, rotates freely, and eventually comes to a stop on its own. 
     Retaining bolt  60  has a nut at the tope end thereof, a threaded portion  63  at the opposing end thereof for tightening in a centrally threaded bore in driven shaft  86 . Driven shaft  86  is splined at  82  and thus affixed to lower disc hub  43 . The intermediate portion of retaining bolt  60  is reverse threaded at  61  and to upper disc hub  42 . Bolts  81  hold cover  84  and cover, or “turtle”,  80  in place on upper disc hub  42 , but do not extend into lower hub  43 . 
     A useful characteristic of the shear mechanism of the instant invention is that the ball and detent design allows for shear pin failure without any byproducts that could affect the other operations of the cutterbar. Devices such as that shown in the &#39;662 patent listed above would, upon failure of the shear device, present metallic debris that would likely interfere with, and “jam” up the brake disclosed herein. 
     As can be seen in FIGS. 2 and 3, upper disc hub  42  is detachably splined onto driven shaft  86 . Upper disc hub  42  is affixed to lower disc hub  43  by multiple spring-mounted ball and detent devices that, as described above, serve as a shear device. Turtle  80 , and thus knives  82 , rotates with lower hub  43 . The driven shaft  86  is rotatably supported by a bearing block detachably mounted to the cutterhead module housing  41  by bolts. The bearing block seals an opening in the top of the housing  41  through which the drive gears can be extracted from the oil reservoir  89 . 
     As most clearly seen in FIG. 5, when the cutterhead engages a fixed object of sufficient mass or rigidity to generate a shearing force on the spring-mounted balls and detents  50  adequate to cause failure thereof, the upper and lower disc hubs  42 ,  43  will separate and upper disc hub  42  will rotate upwardly via threads  36 . 
     As taught in the incorporated patents, the drive mechanism  75  in each cutterhead module  40  is coupled to the other cutterhead module drive assemblies by a transfer shaft that passes through a spacer module. A transfer shaft is splined at each opposing end thereof to be finally received within either of the hubs to transfer rotational power thereto. 
     Referring again to the configurations of utilization of the cutterbar  30  as depicted in FIG. 1, it can be seen that the drive mechanism  75  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. 
     As seen in FIG. 4, four shear devices, i.e., balls and detents, are used in the preferred embodiment. Any reasonable number can be used, so long as together the shear forces can be adjusted within useful limits. The shear force may be adjusted or established by the selection of springs, the sizes of the balls, the depth of the detents, and the number and location of shear devices used. The balls and detents are space equally around the rotational axis of the hubs, but this is not necessarily done in all possible embodiments. Additionally, it is possible to use balls and detents of different sizes to establish the required shear force. 
     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.