Patent Abstract:
A disc cutterbar with at least one cutterhead having a two-piece mounting hub, one piece rotatably driven and the other supporting a knife for severing standing crop material, with an epoxy layer bonding the two pieces together and forming a shear device therebetween. A brake is associated with the knife-supporting piece whereby upon failure of said shear device, the knife-supporting piece is stopped from rotating within one revolution.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to U.S. patent application Ser. No. 09/845,112 entitled “Overload Protection for a Disc Cutterbar” in the name of Timothy J. Kraus and Imants Ekis, filed on the same date as this application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to mechanisms for protecting mechanical drive components from overloads, and more particularly to a brake coupled between components of an agricultural disc mower that quickly stops rotation of a cutterhead in the event the cutterhead strikes an object with sufficient force to activate a shear mechanism, allowing the cutterhead to rotate freely. 
     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 typical structure and operation of some 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 which 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 such shear devices and arrangements are shown in U.S. Pat. Nos. 4,999,981, 4,497,161 and 5,715,662. 
     A serious drawback of prior art disc cutterbars is that, while they may incorporate a shear device to reduce or eliminate damage to the drive system in the event of an overload, they do not provide means or mechanisms to stop rotation of the cutterhead after failure of the shear device. With multiple cutterheads in line, generating overlapping cutting paths, rotating at high speed and operating in a timed relationship, it is inevitable that when one fails it will lose its timed relationship with adjacent cutterheads, resulting in impacts and damage among the cutterheads comprising the cutterbar. Such damage is often significant not only in repair costs due to parts and labor, but also in lost harvesting time. The instant invention is directed to a brake mechanism that will stop further rotation of the cutterhead after failure of a shear device, thus preventing the damages described. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a brake in the mechanical drive train of a disc cutterbar that will not only stop the transfer of power along the drive train in the event of overload, but also stop rotation of the non-driven components before further damage can occur. 
     Another object of the present invention is to provide a brake and shear mechanism in the drive of a disc cutterbar that will not only cause the cessation of power transfer at a predetermined load, but will also stop the rotation of non-driven components within one rotation. 
     Yet another object of the present invention is to provide a disc cutterbar with multiple cutterheads, each comprising a drive shaft connected to a mounting hub via a shear mechanism. A novel brake mechanism is triggered upon failure of the shear mechanism, stopping rotation of the lower hub and cutterhead. 
     It is yet another 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 with at least one cutterhead having a two-piece mounting hub, one piece rotatably driven and the other supporting a knife for severing standing crop material, with an epoxy layer bonding the two pieces together and forming a shear device therebetween. A brake is associated with the knife-supporting piece whereby upon failure of said shear device, the knife-supporting piece is stopped from rotating within one revolution. 
    
    
     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 cuttterbar of the instant invention can be utilized; 
     FIG. 2 is an enlarged top plan view of a central portion of the assembled modular disc cutterbar depicting two 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; 
     FIG. 3 is a cross-sectional view of the cutterhead module taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is an enlarged view of a portion of FIG. 3; 
     FIG. 5 is a view similar to FIG. 4, showing an exaggerated view of the gap separating inner hub  42  and outer hub  43  after the shear mechanism has failed and the locking blocks have engaged; 
     FIG. 6 is an exploded cross-sectional view of the mounting hub, locking blocks and springs making up significant components of the instant invention; 
     FIG. 7 is a top plan view of the lower locking block taken along line  7 — 7  of FIG. 6; 
     FIG. 8 is a bottom plan view of the outer hub and integral upper locking block taken along line  8 — 8  of FIG. 6; 
     FIG. 9 is an exploded view somewhat rotated showing the relationship between the inner hub, the outer hub and the lower locking block; 
     FIG. 10 is a cross-sectional view of an alternative embodiment of the brake device taken along line  10 — 10  of FIG. 11; and 
     FIG. 11 is a view of an alternative locking block taken along line  11 — 11  of FIG.  10 . 
    
    
     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 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. 1-3, includes a hollow cast housing  41  (FIG. 3) having a shape to retain a low profile and to establish an oil reservoir  84  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 now to FIGS. 2-4, 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  35  of spacer module  32  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  72  that is bent upwardly to engage the corresponding rock guard  65 . 
     Modular drive mechanism  75 , 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. 
     Broadly, within each cutterhead unit there is a two-piece hub, one inner hub and one outer hub, normally held together by a shear mechanism. The inner hub is connected to a drive shaft, and the outer hub, including an integral upper locking block, is connected to a rotatable knife support member. Spaced below the outer hub is a fixed lower locking block. These components are arranged such that when a knife engages a solid or fixed object and a shear force generated adequate to cause the shear mechanism to fail, the outer hub rotates freely and drops (preferably under the influence of a downward biased spring) causing the upper and lower locking blocks to engage and the knife support member to cease rotation. By thus preventing the knives from rotating further, damage is prevented to the drive train of the cutterbar and between adjacent cutterhead units. Ideally, the brake will stop rotation in one revolution or less. 
     Now, and more specifically, attention is directed to FIG. 9 which shows an exploded perspective view of the inner hub  42 , the outer hub  43  and the lower locking block  44 . In the preferred embodiment, inner hub  42  is affixed to outer hub  43  by means of a layer of epoxy bonding surfaces  45  and  46  of the two hubs, respectively. By controlling the size of the bonded surface area of the two hubs, and knowing the shear strength of the epoxy, a specific shear point or force can be calculated so that failure will occur at the desired point and upon a specific impact. Outer hub  43  includes an upper locking block made up of spaced apart teeth  47  and  48  set within a circular recess  49 . Lower locking block  44  comprises protruding cylindrical member  50  with surface spaced apart teeth  51  and  52 . When assembled, as best seen in FIG. 4, protruding cylindrical member  50  fits rotatably part way into cylindrical recess  49 . Also as best seen in FIG. 4, before failure of the layer  53  cap  56 , inner hub  42  and outer hub  43  are fixed to and rotate with drive shaft  86 . After failure of layer  53 , outer hub  43  is free to rotate about drive shaft  86 , at least until the locking blocks engage. When engaged as discussed further below, the teeth on the respective locking blocks loosely fit together to prevent relative rotational movement between the two locking blocks. 
     Surfaces  45  and  46  may have generally any configuration or slope, so long as the outer hub can move into the locking position upon failure of layer  53 . The configuration shown has proven to be quite successful and functional. 
     One of skill in the art will recognize that there are many types of epoxy available that will work in this environment. By way of example, successful operation has been experienced with an epoxy known as “HP-120” by Loctight. A useful characteristic of epoxy, as used in the instant invention is that only a very thin layer is required to hold the hubs together, and when it fails, the material all but disappears. This feature is quite valuable and important from a practical point of view in that the cleanliness of shear failure promotes quick operation of the brake. Devices such as that shown in the &#39;662 patent listed above would, upon failure of the shear device, present metallic debris that would interfere with, and “jam” up the brake disclosed herein. 
     While epoxy is disclosed as the preferred bonding or shear medium, there are other alternatives. For example, rubber, plastic, solder, brazing and the like could all be used. It is worthwhile to note that in the environment of a cutterhead, mechanical shear pins or similar fitted shear mechanisms tend to fail prematurely due to the fatigue experienced from the vibration and alternating stress inherent in the application. 
     FIG. 6 is an exploded cross-sectional view of the primary elements making up the preferred embodiment of the invention and is included herein for further clarity. The Belleville washers (springs)  54  and  55  are mounted in an opposing manner and shown here in their compressed state, but it can be clearly seen that when assembled the washers will exert a downward bias on outer hub  43 . Thus, if the epoxy bond between the inner and outer hubs  42 ,  43  is broken, outer hub  43  will be biased to move downwardly. 
     FIGS. 7 and 8 are also presented for additional clarity. FIG. 7 is a top plan view of lower locking block  44  taken along line  7 — 7  of FIG.  6 . Looking at this view and FIG. 9 it can be seen that there are raised areas, or teeth,  51  and  52  extending partially around the circumference of the protruding cylindrically shaped portion  50 , forming lower interstitial areas  57 . FIG. 8 shows that outer hub  43  includes a portion  59  which is referred to as the upper locking block. Upper locking block  59  can be either integral with outer hub  43 , as shown here, or formed as a separate piece and affixed to outer hub  43 . Teeth  47  and  48  are spaced apart, forming lower interstitial areas  58 . Interstitial areas  57  and  58  are larger circumferentially than the respective teeth that are to be engaged therein. This difference in size is to allow time and space for the full engagement of the locking blocks upon failure of the shear layer. When assembled, the teeth of the two locking blocks are separated; however, if the epoxy bond fails, i.e., the shear mechanism fractures, outer hub  43  (and because they are integral, upper locking hub  59 ) drops into lower locking block  44 —teeth  51  and  52  drop into spaces  58 , and teeth  47  and  48  go into spaces  57 . The two locking blocks are thus “locked” together, stopping the rotation of outer hub  43  (and thus disc member  80  and knives  82 ). Lower locking block  44  is fixed in place, i.e., does not rotate and thus provides solid support for the locking function. 
     The number and configuration of teeth on the locking blocks can, of course, vary depending upon several factors such as the harness of the base materials, the speed of rotation, the mass of the cutterhead, and the timing required to stop the relative movement of the components. In addition, for similar reasons, it may be appropriate or beneficial to harden the teeth, add cushioning material to the interfering faces and/or add friction-reducing materials to the contacting surfaces. 
     Referring now to FIGS. 3-5, inner hub  42  is detachably splined onto a drive shaft  86  having an integral driven gear  77  positioned within the oil reservoir  84 . Inner hub  42  is affixed to outer hub  43  by a layer of epoxy  53  which, as described above, serves as a shearing device. A disc member  80  is detachably connected to outer hub  43  by bolts  81  so as to be rotatable therewith (and thus knives  82 ). The drive shaft  86  is rotatably supported by a bearing block  78  detachably mounted to the cutterhead module housing  41  by bolts  79 . The bearing block  78  seals an opening in the top of the housing  41  through which the driven gear can be extracted from the oil reservoir  84 . 
     When the cutterhead engages a fixed object of sufficient mass or rigidity to generate a shearing force on layer  53 , adequate to cause failure thereof, the inner and outer hubs  42 ,  43  will separate and outer hub  43  will drop. In the preferred embodiment, outer hub  43  is biased downwardly by means such as Belleville washers  54  and  55  working between cap  56  and outer hub  43 . FIG. 5 shows this change in position of outer hub  43  (has moved downwardly on shaft  86 ) in exaggerated form for illustrative purposes. 
     The drive mechanism  75  in each cutterhead module  40  is coupled to the other cutterhead module drive assemblies  85  by a transfer shaft  94  that passes through the spacer module  32 , as best depicted in FIG.  2 . The transfer shaft  89  is splined at each opposing end thereof to be finally received within either of the hubs  89 ,  90  to transfer rotational power thereto. 
     Referring now 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  85  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. 
     FIGS. 10 and 11 show an important alternative structure to the brake. In the brake described above, the outer hub drops down to allow the locking blocks to engage. A potential problem with this arrangement is that crop materials and debris can build up on the lower part of the structure and potentially hinder or interfere with the quick engagement of the brake. While one could take steps and develop structure to reduce or prevent the build up of materials, the structure shown in FIGS. 10 and 11 eliminates the potential problem by causing the outer hub to move upward on the drive shaft  86  to engage the brake. 
     Inner hub  110  is connected to outer hub  112  by shear bolt  114 . Of course, instead of a shear bolt(s) a frangible layer as taught above could also be used as the shear device. Between the inner hub  110  and outer hub  112  is a spring  116 , in this embodiment a known wave spring, biasing the outer hub upwardly relative to inner hub  110  which is fixed to shaft  86  by, for example, splines. Annular lip  118  on cap  117  forms a stop against further upward movement of inner hub  110 . Thus, upon failure of the shear device, outer hub  112  moves upwardly away from inner hub  110  under the bias of spring  116  until it engages lip  118  of cap  117 . 
     Though the interlocking configuration of the locking blocks could be essentially the same as that described and shown in earlier Figures this embodiment shows a slight modification. Lower locking block  120  has an annular recess  122  into which flange  124  of outer hub  112  fits. As best seen in FIG. 11, lower locking block  120  has spaced apart annular lips  126  forming annular openings  128  which matingly match teeth (not shown) on flange  124  such that the teeth mate with openings  128  to lock outer hub  112 , when the shear device fails, in the manner described above. The dimensional relationship among the component parts is such that lip  118  stops upward movement of outer hub  112  at the same time the teeth on flange  124  move into openings  128  and engage the edges  130  of openings  128 . 
     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.

Technology Classification (CPC): 0