Patent Publication Number: US-7210543-B1

Title: Reversible power takeoff driven post hole digger

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of applicant&#39;s provisional application Ser. No. 60/580,482, filed Jun. 17, 2004. 

   FIELD OF THE INVENTION 
   This invention relates to motorized post hole diggers, and more particularly to post hole diggers driven by a power takeoff and provided with a capability for reversing the direction of rotation of an auger used to dig the hole. 
   BACKGROUND OF THE INVENTION 
   Post hole diggers mounted on a three-point hitch of a tractor and connected to the tractor power takeoff are highly effective in digging post holes, but inclusion of a mechanism to reverse rotation of the auger is needed in case underground obstacles such as strong roots or rocks are encountered. Various approaches have been taken, including use of a kit or adapter including a gear transmission providing forward and reverse capability, with this mechanism being placed outside of the power head of the system. It is desired to include a reversing mechanism within the power head, with this mechanism being self-contained in a common housing or case, so that such capability is provided for in initial design and manufacturing steps. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a self-contained, reversible post hole digger apparatus providing for forward and reverse action of the digging auger, effective for augers propelled by a power takeoff of a tractor or other power source. The apparatus includes a power head disposed between a main shaft connected to a power takeoff of a tractor, a supporting boom and an output shaft connected to an auger. A gear box is located within the power head, the gear box comprising a case carrying the main shaft, which extends across and is supported by antifriction bearings on each side of the case. A central portion of the main shaft is provided with splines. Forward and reverse pinion gears are mounted for rotation on the main shaft on each side of the splined portion, each of the pinions provided with an external splined region. The pinions in turn simultaneously and permanently engage an upper ring gear and a lower ring gear. This arrangement compensates for thrust developed between a pinion gear and a single ring gear that tends to wear out bearings of a shaft to which the pinion is mounted. A slide having an internal splined region matching the splines of the central portion of the main shaft is slidably fitted on the splined portion of the main shaft, the slide being movable on the main shaft from a neutral position in the center to a position bridging the splines of the main shaft and the splines of a selected pinion, the selected, bridged pinion determining a forward or reverse direction of the auger. Movement of the slide is carried out by engagement with a fork actuated with a rack and pinion subassembly controlled by a gear shift lever. The lower ring gear is coupled to the output shaft which is driven either forward or in reverse, depending on which end of the slide has been engaged with the respective pinion. Bearings and seals are provided at each end of the shafts and elsewhere as required. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a rear view showing a power head equipped with a gear box and driven by a power takeoff of a tractor. 
       FIG. 2  is an external view of a power head containing a gear box. 
       FIG. 3   a  is a cut-away view taken from a point above and to a power takeoff side of a power head portion of my new reversible post hole digger and showing construction details thereof. 
       FIG. 3   b  is a partial view showing construction details of my new reversible post hole digger. 
       FIG. 3   c  is a partial view showing construction details of my new reversible post hole digger. 
       FIG. 4  is an exploded view showing component parts of the gear box disposed in alignment. 
       FIG. 5  is a front view of the gearbox, with cover removed, showing placement of ring gears and pinions. 
       FIGS. 6 ,  7  and  8  are top, front and side external views of the power head/gear box. 
       FIG. 9  is a cut-away view taken from a point above and to a side of the power head portion of my new reversible post hole digger showing engagement of the central shaft with a leftmost pinion gear. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1  of the drawings, there is shown a power head/gear box case  21  having a top cover  8  and mounted on a boom  53  which is connected to a three point hitch  60 ,  61 ,  62  of a tractor. An input shaft  38  is connected to a power takeoff shaft  54  provided by the tractor. A gear shift handle  30  controls the direction of rotation of the output shaft  16   a , which drives auger  56 . 
   External features of the gear box are shown in  FIG. 2 . The case has a top cover  8  and a dust cover  1  at the center of the top cover. Bolts  7  secure the top in place. Input shaft  38  extends outward through a front cover  51 . An oil fill plug  6  is disposed at the top, and an oil check plug  19  is at a side location. Output shaft  16  extends downward from the bottom of supporting gussets  21 . 
     FIG. 3  shows placement of a rack and pinion subassembly by means of which shifting of gears is carried out. Fork  44  ( FIG. 4 ) operates to move slide  39  to engage internal spline slots  55  provided inside the slide with mating external ridges  63  of a pinion gear  37  or  40 . As noted above, a central portion  52  of input or main shaft  38  is splined, this splined portion  57  meshing with internal splines  55  of slide  39 , providing a neutral position of the auger when the slide is engaged at this central portion of the main shaft. As shown in  FIG. 4 , the length of slide  39  is approximately the same length as the splined region  57  on main shaft  38 . Fork  44  is connected to rack  45 , which is intermeshed with pinion gear  46  controlled by gear shift lever  30 . A rack gear guide rail  48  is provided to control movement of the rack. A set screw  34 , spring  33  and detent ball  32  connected to shifter shaft  26  cooperate to form a detent mechanism that locks a selected pinion gear in place. As shown in  FIG. 9 , shift handle  30  is moved to the right, which in turn rotates pinion gear  46  clockwise. This rotation of pinion gear  46  moves rack gear  45  to the left, causing shift fork  44  to move slide  39  to the left. In this position, slide  39  bridges the splines of the left-most pinion gear  40  and splines  57  of input shaft  38 , locking pinion  40  and shaft  38  together. 
     FIG. 4  is an exploded view showing internal components of the gearbox disposed in alignment. A list of these components and a brief description is as follows: 
   
     
       
         
             
             
           
             
                 
             
             
               Number 
               Item 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
          
             
               1 
               dust cap-prevents dust from entering housing 
             
             
               2 
               cotter pin-locks castle nut in place 
             
             
               3 
               castle nut-secures upper shaft segment in place 
             
             
               4 
               spindle washer-distributes pressure from castle nut 
             
             
               5 
               upper bearing-upper antifriction bearing for shaft segment 
             
             
               6 
               fill plug-oil fill plug 
             
             
               7 
               top cover bolts-secure top cover to housing 
             
             
               8 
               top cover-rotatably holds upper shaft segment and covers 
             
             
                 
               housing 
             
             
               9 
               lower bearing-lower antifriction bearing for shaft segment 
             
             
               10 
               shim-thickness adjusts lower bearing running clearance 
             
             
               11 
               ring gear bolts-secures upper ring gear to upper ring gear plate 
             
             
               12 
               upper ring gear plate-fixed to upper shaft segment, holds ring 
             
             
                 
               gear in place 
             
             
               12a 
               upper shaft segment-rotatably supports upper ring gear 
             
             
               13 
               upper ring gear-distributes pinion loads 
             
             
               14 
               lower ring gear-driven by forward and reverse pinion gears, 
             
             
                 
               attached to output shaft 
             
             
               15 
               lower ring gear bolts-attaches lower ring gear to lower ring gear 
             
             
                 
               plate 
             
             
               16 
               lower ring gear plate-interfaces output shaft with lower ring gear 
             
             
               16a 
               lower output shaft portion-holds post hole auger, driven by lower 
             
             
                 
               ring gear 
             
             
               17 
               output shaft bearing-antifriction bearing for output shaft 
             
             
               18 
               check plug seal-gasket seal for oil check plug 
             
             
               19 
               check plug-oil check plug 
             
             
               20 
               drain plug-oil drain plug 
             
             
               21 
               case-housing for gear train 
             
             
               22 
               output shaft bearing-antifriction bearing for output shaft 
             
             
               23 
               spindle washer-distributes pressure from spindle nut 
             
             
               24 
               spindle nut-secures output shaft in place 
             
             
               25 
               oil seal-prevents oil leakage through antifriction bearings 
             
             
               26 
               shifter shaft-interfaces shift lever with gear shift pinion gear 
             
             
               27 
               oil seal-prevents oil leakage at shifter shaft 
             
             
               28 
               guide rail bolt-holds rack gear guide rail in place 
             
             
               29 
               guide rail bolt-holds rack gear guide rail in place 
             
             
               30 
               shift handle-rotates shifter shaft to shift into forward/reverse 
             
             
               31 
               shift handle bolt-secures shifter handle to shifter shaft 
             
             
               32 
               detent ball-temporarily locks shifter shaft in selected gear 
             
             
               33 
               spring-biases detent ball 
             
             
               34 
               set screw-adjusts detent force 
             
             
               35 
               input shaft bearing-antifriction bearing for driven input shaft 
             
             
               36 
               shim-thickness adjusts running clearance for input shaft bearing 
             
             
               37 
               pinion-forward-drives lower ring gear and output shaft holding 
             
             
                 
               auger in digging direction 
             
             
               38 
               input shaft-receives rotational force and transmits to ring gear 
             
             
                 
               via pinion-forward gear 
             
             
               39 
               slide-couples power from input shaft to selected pinion 
             
             
               40 
               pinion-reverse-drives lower ring gear and output shaft holding 
             
             
                 
               auger in reverse 
             
             
               41 
               shim-thickness adjusts running clearance for input shaft bearing 
             
             
               42 
               input shaft bearing-antifriction bearing for driven input shaft 
             
             
               43 
               C-clip-prevents input shaft from moving longitudinally 
             
             
               44 
               shift fork-interfaces rack gear with slide 
             
             
               45 
               rack gear-interfaces shift fork with pinion gear 
             
             
               46 
               pinion gear-moves rack gear to select forward/reverse 
             
             
               47 
               set screw-fixes shifter shaft to pinion gear 
             
             
               48 
               rack gear guide rail-guides motion of rack gear 
             
             
               49 
               front oil seal-prevents oil leakage through front cover 
             
             
               50 
               front cover bolts-secure front cover to case 
             
             
               51 
               front cover-provides access to input shaft and bearings 
             
             
                 
             
          
         
       
     
   
     FIG. 5  shows upper ring gear  13 , lower ring gear  14 , forward pinion  37  and reverse pinion gear  40  in a neutral position owing to shift handle  30  being placed in an upright position. Upon moving the handle to the left or right, the selected pinion gear  37  or  40  would be moved to bridge the splines between the splines of the main shaft and splines of a selected pinion, causing the output shaft ad auger to be rotated in a forward or reverse direction. This view also shows rack gear guide rail  48 , partly broken away to show rack gear  45  which is engaged by pinion  46 . 
     FIGS. 6 ,  7  and  8  respectively provide external views of the power head/gear box assembly from the top, front and side.  FIG. 6  shows a top cover  8  having a dust cap  1  in the center. An outer end of input shaft  38  extends outward for connection with a power takeoff shaft  54  which drives an auger  56 . 
   A reversible post hole digger designed from the start for being carried in a single housing provides significant advantages over approaches in which reversibility is obtained by connecting an existing one-way digger with external components of an after-market kit. Inclusion of a second ring gear integrated into a single transmission enables a stronger and simpler apparatus by compensating for thrust developed by a single ring and pinion gear such as currently found in the prior art. 
   While the invention is described above in terms of a preferred embodiment, it is not to be understood as being limited to such an embodiment, but is limited only as indicated by the appended claims.