Abstract:
A torque limiter for a row unit of a harvester has a shell that is threaded on to a limiter base to compress the limiter&#39;s spring.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to agricultural harvesters. More particularly, it relates to harvesting heads for harvesters. Even more particularly, it relates to drive systems for row units of the heads 
       BACKGROUND OF THE INVENTION 
       [0002]    Harvester heads for row crops include several laterally disposed row units. Each row unit is oriented to gather and cut a single row of crops. The row units are driven by one or more elongated rotating drive shafts that extend across the width of the harvesting head. A typical drive shaft may be coupled to and drive ten or twelve different row units simultaneously. 
         [0003]    The row units are located adjacent to the ground so all the crop plant is gathered for processing. The drive shafts extend across the width of the harvesting head, immediately adjacent to the ground. 
         [0004]    In this position, the drive shafts and row units tend to accumulate plant matter lying on the ground. The torque limiters (also known as clutches, jaw clutches or slip clutches) that couple the drive shafts to the row units are particularly prone to being fouled and jammed by this matter due to the several exposed bolts that extend from the torque limiter Furthermore, loosening the torque limiters to remove trash is difficult due to the several bolts that hold the torque limiters together. 
         [0005]    What is needed, therefore, is an improved torque limiter for harvester row units that is protected from extraneous matter and that is easier to loosen, clean, adjust, and tighten. It is an object of this invention to provide such a torque limiter. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with a first aspect of the invention, a torque limiter is provided having a compression spring disposed within a shell that is threaded to a base. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an exploded perspective view of the torque limiter of the present invention. 
           [0008]      FIG. 2  is a partial cutaway view of an assembled torque limiter. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0009]    Referring now to  FIGS. 1 and 2 , a torque limiter (also known as a “slip clutch”)  100  has a base  102  that supports an input plate  104 , an output plate  106 , a washer  108 , a compression spring  110 , and a shell  112 . 
         [0010]    A row unit drive shaft  114  for driving the torque limiter extends though an aperture  116  in the input plate  104  and engages plate  104  to communicate torque to it. The drive shaft  114  has external hexagonal flats  118  that mate with corresponding internal hexagonal flats  120  on the aperture extending through the input plate. 
         [0011]    The input plate  104  is supported on a flat annular surface  122  of the base  102  for rotation with respect to the base  102  about a common longitudinal axis  124 . The input plate  104  is generally formed as a collar  126  that extends around and engages the drive shaft  114 , to which is fixed an outwardly extending flange  128 . The flange  128  has one flat surface  130  that engages the base  102 , and an opposing surface  132  with radially extending corrugations  134 . 
         [0012]    The output plate  106  includes a disk  136  with a central aperture  138 , the disk  136  having one side that defines a similarly corrugated surface  140  that faces and engages the corrugated surface  140  of the input plate  104  and an opposing side that defines a surface  142  that faces and engages the compression spring  110 . The output plate  106  also has two protrusions  144 ,  146  extending from opposite sides of the disk  136  that are disposed in opposing apertures  148 ,  150 , respectively, formed in the base  102 . The apertures  148 ,  150  and the protrusions  144 ,  146  are configured such that the output plate  106  communicates torque about the longitudinal axis  124  to the base  102  yet permits the output plate  106  to move in the longitudinal direction sufficiently to permit the output plate  106  to move from a first position in which the corrugations on the input plate  104  and the output plate  106  are intimately engaged to transmit torque one to the other, to a second position in which the input plate  104  and the output plate  106  are axially separated sufficient to permit them to rotate with respect to each other. 
         [0013]    The spring  110  is a coiled compression spring having a longitudinal axis  124  that is coaxial with the other components of the torque limiter. It has a first end  152  that faces and engages the second surface of the output plate  106  and a second end  154  that faces and engages the inside surface of the shell  112 . 
         [0014]    The shell  112  is a generally bell- or cylindrical-shaped structure with a first end  156  that is generally enclosed. The first end  156  defines an aperture  158  that permits the driveshaft  114  to pass therethrough. The internal surface of the second, opposing end  160  of the shell  112  has threads  162  to engage mating threads  164  on the base  102 . These threads  162 ,  164  have a root diameter greater than the outer diameter of the spring  110  and the spring  110  are disposed radially inside the threads  162 . The threads  162 ,  164  are generally coaxial with the spring  110  and extend about the periphery of the spring  110 , thereby distributing the spring pressure evenly to the threads  162 ,  164 . A pin  166  is provided that extends through the wall of the shell  112  and into a space adjacent to the output plate  106 . The pin  166  is preferably a roll pin and is long enough to engage structures (in this case, the protrusions  144 ,  146 ) in order to prevent the shell from completely unthreading itself. The shell  112  can unthread until the pin  166  abuts a protrusion  144 ,  146 , at which point no further unthreading is possible. Structures  170  are provided on the shell  112  for tightening the shell  112  on the base  102 , such as splines, holes, wrenching flats, protrusions configured to engage e.g. a tightening tool such as a pin, eye or hook spanner; wrench or rod. 
         [0015]    The base  102  of the torque limiter  100  comprises a body  172  having an aperture  174  concentric with the longitudinal axis  124  of the base  102 . The body  172  has a flat annular surface  122  generally normal to the longitudinal axis  124 , and that faces toward the input  104  and output  106  plates and the spring  110 . The washer  108  is disposed between the flat surface  130  of the input plate and the flat surface  122  of the base  102  to reduce friction and wear between the input plate  104  and the base  102 . The base  102  includes a generally cylindrical sidewall  176  that is fixed to and extends from the body  172 . The apertures  148 ,  150  that receive the protrusions  144 ,  146  extending from the output plate  106  are formed in the sidewall  176 . The external threads  164  formed in the outer cylindrical surface of the sidewall engage the internal threads  162  formed on the inner surface of the second end  160  of the shell  112 . 
         [0016]    In use, the shell  112  is threaded onto the base  102 , to compress the spring  110 . The spring  110  is compressed between the inner surface of the shell, and one side of the output plate. This spring compression forces the corrugated surface of the output plate to be compressed against the mating corrugated surface of the input plate. The input plate, is compressed against the washer, which in turn is compressed against the body. The body is fixed to the sidewall, which is threaded to the shell, both the sidewall and the shell being in tension by the spring. 
         [0017]    When a torque less than a predetermined threshold torque is applied to the drive shaft, it tends to rotate the input plate with respect to the output plate. As long as this torque is below the threshold, the two plates will rotate with respect to each other spreading apart and compressing the spring slightly to maintain a torque of equal and opposite value on the input plate. The corrugations will still remain engaged, however, although slightly offset. The torque applied by the input plate through the corrugations to the output plate is then communicated to the two protrusions on the output plate, and thence to sidewalls of the apertures in the base that receive the protrusions. The base then applies the torque through the surface structures of the base to the input gear of the row unit, which is driven thereby. 
         [0018]    When the torque exceeds the predetermined threshold torque, the spring is compressed sufficient to permit the input and output plates to rotate with respect to each other, or “slip”, hence the alternative term for this device: a “slip clutch”. In this mode, the drive shaft can spin while the base and the input gear to the row unit remain stationary, or alternatively spin at a speed less than that of the drive shaft. The torque applied to the row unit is thereby limited to the threshold torque. When the torque drops below the predetermined threshold torque the torque limiter automatically resets, the corrugations re-engage rather slip past each other, the input and output plates again rotate in synchrony, and the row unit is driven that the desired speed. 
         [0019]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims. For example, the shell may have various slots or apertures to permit water to leak out (for example) or to reduce weight. The shell may have external threads on its lower portion that engage internal threads formed on the base. The washer can be removed entirely if wear is not an issue, or replaced with a different structure that reduces wear such as a lubricant or a self lubricating metal. The corrugations can be replaced with any of a variety of different shapes that provide interengagement sufficient to communicate torque while preferably providing the automatic disengagement when torque over a predetermined threshold is applied. The corrugations can even be replaced with friction material, such as the material sued for vehicular brake shoes or brake pads. The protrusion and interengaging aperture arrangement can be reversed by providing apertures on the output plate and protrusions on the base that interengage to prevent the output plate from rotating with respect to the base, thereby communicating torque from the output plate to the base in place of the existing arrangement. Alternatively, the protrusion and interengaging aperture arrangement can be supplemented by providing apertures on the output plate and protrusions on the base that interengage to prevent the output plate from rotating with respect to the base, thereby communicating torque from the output plate to the base. The apertures of the protrusion and aperture pairs can extend completely through the structure in which they are formed, or they can extend only partially into the structure. additional protrusion and aperture pairs can be provided beyond the two illustrated in the figures. The hex flats of the input plate can be replaced with a clamp, splines or other structure that permits the transmission of torque. When the torque converter is used with other input devices that do not need a drive shaft extending through each torque limiter to engage other torque limiters, no aperture passing through the input plate is required, just the provision of mechanical structures of some form that will interengage with a shaft. In some applications, the input plate further comprise a shaft (instead of its illustrated aperture) that extends away from the torque limiter and to which some other shaft such as the drive shaft illustrated herein may be coupled, for example, with a rotary coupling. In another arrangement, the torque limiter may be configured to be disposed inside the row unit itself, rather than, as illustrated here, being disposed adjacent to the row unit and coupled thereto. The spring can be a stack of dished spring washers (often called Belleville washers or disc springs) that are separate or fixed together.