FIELD OF THE INVENTION 
     The present invention relates to rotary cutterbars and, more particularly, relates to a relationship between the cutterbar gear housing and gearing contained therein. 
     BACKGROUND OF THE INVENTION 
     The cutterbar of a rotary disk mower includes an elongate flat housing containing a spur gear train which is lubricated by oil contained in the housing and drives the respective pinions of the individual cutting disk units. The pinion gears of the cutting units are each integral with a vertical shaft and form a pinion assembly mounted to a top wall of the housing by a bearing assembly. 
     These bearing assemblies may be caused to fail due to the cutting knives impacting rocks, low oil level in the cutterbar, seal damage, bearing fatigue, and other failure modes. When the pinion gear bearing fails, the pinion gear can tilt or drop down in the cutterbar housing allowing rolling elements of the bearing to fall into the housing. These loose pieces can get into the pinion and idler gears and cause major secondary damage to the gear teeth. 
     U.S. Pat. No. 5,012,635, granted 7 May, 1991, discloses a rotary cutterbar of the above-described type. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided an improved rotary cutterbar constructed so as to overcome the above-noted drawback of secondary damage to the gears when a pinion shaft support bearing fails. 
     An object of the invention is to provide a support located for preventing any substantial downward movement of the pinion shaft permitted by a bearing failure. 
     A more specific object of the invention is to provide a support, as set forth in the preceding object, which is formed as an integral part with the gear housing. 
     These and other objects will become apparent from a reading of the ensuing description together with the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a rotary cutterbar module set up as an end cutting unit of the cutterbar, but being shown with the cutting disk removed for the sake of clarity. 
     FIG. 2 is a rear view of the cutterbar module of FIG.  1 . 
     FIG. 3 is a vertical sectional view taken along lines  3 — 3  through the cutterbar module of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, there is shown a cutting unit module  10  of a rotary cutterbar, which may be formed by connecting a plurality of modules in side-by-side relationship to each other so as to result in a flat or low profile tube. The arrow F indicates the forward direction of operation, and terms such as “right-hand” and “left-hand” are considered from the perspective of a viewer standing behind the cutterbar and facing in the direction of forward operation. The module  10  includes a housing  12  having top, bottom, front, and rear walls  14 ,  16 ,  18 , and  20 , respectively. Right- and left-hand ends of the housing  12  define respective planar surfaces  22  and  24  which are parallel to each other and are inclined to the left from top to bottom. The right-hand surface  22  is adapted for having a complementary shaped left-hand surface of a second module (not shown) to be bolted in sealed, face-to-face engagement therewith through the agency of stud bolts inserted through mounting holes provided in the second module and aligned with front and rear threaded openings  26  and  28 , respectively, of the module  10 . The module  10  is set up for being used as a leftmost module of the cutterbar and would have a left-hand end cap (not shown) having a mounting surface shaped complementary to and adapted for being clamped into sealing engagement with the left-hand planar surface  24  of the module  10  through the agency of a pair of stud bolts inserted through front and rear mounting holes  30  and  32 , respectively, of the module  10  and received in aligned threaded holes provided in the end-cap. 
     A forward central location of the top wall  14  is provided with a raised cylindrical pad  34  containing a cylindrical opening  36 , and provided in the top wall  14  at respective locations to the rear of, and on opposite sides of, a fore-and-aft centerline extending through the opening  36 , are right- and left-hand openings  38  and  40 . 
     Referring now also to FIG. 3, it can be seen that a bearing housing  42  includes a cylindrical flange  44  having a flat, circular mounting surface bolted against a complementary surface provided at the top of the cylindrical pad  34  by a plurality of stud bolts  46 . The bearing housing  42  defines a central, cylindrical bore  48  receiving an outer race of each of upper and lower ball bearings  50  separated by a snap ring (not shown), with the lower ball bearing  50  having a lower end surface engaged with a shoulder provided at a lower end of the bore  48 . A snap ring  52  is located in an annular groove provided in the bore  48  at a location which results in the ring  52  engaging a top end of the outer bearing race of the upper ball bearing  50 . A cutting disk drive shaft  54  is integral with, and projects upwardly from, a disk drive pinion gear  56 , the shaft  54  tightly engaging an inner race of each of the bearings  50 . Splined onto the top of the shaft  54  is a hub  58  including a substantially square plate  60  containing holes  62  adjacent its four corners provided for having an input drive shaft as well as a cutting knife support disk secured to it by mounting bolts. This input drive shaft would be driven in a direction so as to cause a clockwise rotation to the pinion gear  56 , and the attached cutting disk (not shown), as indicated by the direction arrow R so that cut crop material is delivered inwardly along the cutterbar. Extending axially from an upper end of the shaft  54  is a threaded bore which receives a hub-mounting cap screw  64  having a head that acts against a washer  66  engaged with a shoulder provided at the lower end of a cylindrical receptacle  68  surrounding the bolt head. 
     Formed on the bottom wall  16  of the housing  12  in axial alignment with each of the holes  34  and  36  is a cylindrical pad  70  in which is located a threaded bore  72 . An idler gear support shaft  74 , having an enlarged head sized for closing the holes  38  and  40  and a threaded lower end, is screwed into each of the threaded bores  72 . Located between the head and threaded lower end is an intermediate cylindrical section having a lower shoulder engaged with a top surface of a respective one of the pads  70 . Because the module  10  is set up as the leftmost module, only the shaft  74  located in the right-hand hole  34  is used to support an idler gear. Specifically, the inner race of a ball bearing  76  is received on the intermediate cylindrical section of the shaft  74  located in the right-hand hole  38 , and mounted for rotating about this shaft  74  is an idler gear  78  containing a central bore receiving an outer race of the bearing  76 . The idler gear  78  is meshed with the drive pinion gear  56  and is adapted for being mounted in mesh with a similar idler gear mounted in the left side of a second module and meshed with a further idler gear located in the right side of the second module, which would be bolted to the right side of the module  10  as described above. Thus, power is input to the pinion gear  56  by a drive shaft coupled to the hub  58 , and this power is transmitted to the next adjacent module and similarly serially through further modules, through intermeshed idler gears along the remainder of the cutterbar. Pinion gears of the various modules are driven through a selected one of the pair of idlers located within a given module, this selection being made by an eccentric mounting of the bearing housings  42  for supporting the pinion drive shafts in a manner known in the art. 
     To this point, the structure described is conventional. 
     The present invention resides in a pinion assembly support pad  80  formed on the bottom wall  16  at a location directly below the drive pinion gear  56  in approximate centered relationship to an axis of rotation of the pinion gear. The pad  80  is approximately triangular in top view, but with rounded corners. For reasons explained below, only a small clearance c exists between the pad  80  and the bottom of the gear  56 . The surface area of the top of the pad  80  is quite small and it has been found that it is adequate if the area is no greater than about 10% of the area of a bottom surface of the pinion assembly, and preferably about 5% of the bottom surface of the pinion assembly. 
     In operation, assuming the cap screw  64  and bearings  50  to respectively be properly tightened and in good condition, the pinion gear  56  will operate spaced from the support pad  80  by the clearance c. Then, if the bearings  50  should wear to the point that the shaft  54  and gear  56  begin to wobble, the support pad  80  will contact the bottom surface of the gear  56  and restrain it from tipping far enough to allow the balls of the bearings  50  to escape into the cutterbar housing  12 . Likewise, if the cap screw  60  would become loose and the bearings  50  become worn at the same time to the extent that the shaft  54  falls, the support pad  80  will again engage the bottom of the gear  56  and once again prevent it from lowering far enough to permit the balls of the bearings  50  to escape into the cutterbar housing  12 . Because the size of the support pad  80  is small and located centrally below the gear, the velocity of that part of the gear  56  in contact with the support pad  80  is small, and consequently the relative velocity between the gear  56  and the pad  80  is small. The oil in the cutterbar is thus able to provide sufficient lubrication to prevent excessive wear and to dissipate heat. 
     By eliminating the possibility of the gear  56  from dropping and the bearings  50  from coming apart, internal damage to the cutterbar is greatly reduced. This reduces the time and cost to fix the failed pinion bearings. 
     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.
The pinion gears of a rotary cutterbar equipped with a parallel-series arrangement of idler gears and pinion gears includes a pinion gear support pad formed integrally with the bottom wall of the gear housing and located in close relationship to a bottom surface of the pinion gear so as to prevent the latter from moving, once bearing wear or loosening of mounting hardware has occurred, to the extent that rolling elements of a bearing arrangement supporting the pinion drive shaft are permitted to fall out into the gear housing and cause additional damage to the gearing located in the housing.