Abstract:
A portable power drill ( 11 ) is disclosed having a chuck or drill collar ( 14 ) at one end and a substantially cylindrical (or frusto-conical) twist throttle handle ( 25, 125, 225 ) at the other end. Rotation of the handle in the direction of forward rotation of the chuck decreases the drill speed and, conversely, rotation of the handle in the direction of reverse rotation of the chuck increases the drill speed. Consequently, in the event of an auger locked in the chuck becoming jammed, the reaction forces experienced by the drill unit rotate the drill unit in a direction such that throttle decreases the drill speed. In addition, the drill unit is provided with forward ( 44 ) and reverse gears ( 45 ) and a forward/reverse selection mechanism ( 48, 50, 51 ) which is actuated by a forward force, or a withdrawing force respectively being applied to the drill unit via an operator who holds the handles ( 20, 25 ) of the drill unit.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to portable powered drills and, in particular, to such drills which are powered by internal combustion engines. Such drills are predominantly used in rural activities such as fencing, building stockyards and general construction work utilising wood. Such drills are also used in the construction of wharfs, for example. 
       BACKGROUND ART 
       [0002]    One type of drill used hitherto has been a chainsaw which is modified so as to remove the cutting blade and chain and attach an auger attachment. Essentially the engine of the chainsaw provides the power and the auger attachment creates the drill. Such modified chainsaws have been known for over 30 years. 
         [0003]    More recently, dedicated drills had been produced by a range of manufacturers including Tanaka, Stihl and Echo. Such drills comprise a chuck to hold an auger bit, a gearbox and a small internal combustion engine. One of the handles by which the drill is held by an operator in use, is a substantially vertical handle which is at the rear of the machine. Typically an unbalanced second handle is provided which extends substantially horizontally and to the left (and occasionally selectively either the left or right) of the machine and is located towards the middle of machine. Thus in operation such prior art machines are held by the operator with the operator&#39;s left-hand on the second handle with the palm of the left hand horizontal, and with the operator&#39;s right hand on the first handle with the palm of the right hand vertical. The first handle generally also contains a throttle control lever or trigger. 
         [0004]    Typically the gasoline engines of such prior art drills have an operational speed of approximately 7000-9000 rpm and the gearboxes have gear reduction ratios between approximately 15:1 to 30:1. 
         [0005]    In rural fencing, it is common to use hardwood fence posts in which multiple holes for spaced apart multiple wires are drilled using a wood auger having a diameter of approximately 1¼ inch (32 mm) since this is a convenient size to receive a single strand of the barbed wire which is almost universally used in rural fencing. A wood auger of this diameter produces a very strong reactive torque in the drill which tends to move the drill unit in the opposite direction of rotation to that of the drill auger. This reactive torque must be counteracted by the operator who must maintain a strong grip on both handles. 
         [0006]    Many fence posts, particularly fence posts used for corners and fence posts used for gates and stockyards, have a large cross-sectional size, typically with a transverse dimension of approximately 10-15 inches (250 mm-375 mm) In order to drill a hole 10-15 inches in length, it is typically necessary to reverse the auger rotation every 2-3 inches (50-75 mm) of drilling (depending on the timber variety) to clear the drilled hole of wood chips, and also prevent the auger from binding up and thereby severely jamming. 
         [0007]    Some prior art drill units are provided with a reverse gear. When drilling with these prior art units, in order to clear a drilled hole of woodchips, for example, it is necessary to undertake the following procedure:
       1. De-accelerate the throttle so as to reduce the engine speed to idle speed,   2. Remove left hand from left handle whilst balancing the drill with the right hand,   3. Using the left hand, manually engage the reverse gear lever and, if necessary, juggle the gear teeth so that they mesh and thus engage the reverse gear,   4. Return left hand to left handle,   5. Accelerate the engine with the reverse gear engaged so as to extract the auger,   6. Repeat step 1,   7. Repeat step 2,   8. Using the left hand, manually engage the forward gear lever and, if necessary, juggle the gear teeth so that they mesh and thus engage the forward gear,   9. Repeat step 4, and   10. Accelerate the engine with the forward gear engaged so as to rotate and advance the auger.       
 
         [0018]    This operational procedure is very cumbersome and time-consuming. Furthermore, because the quickly rotating auger can hit a hidden knot, or a similarly hidden split in the wood, the auger is liable to suddenly jam without any warning. Such a jam causes a sudden reactive torque of severe magnitude which often causes the operator to lose his grip with his left hand. The consequence is that the drill unit suddenly spins out of control whilst the operator&#39;s right hand is still holding the trigger throttle control at a position near to, or at, its full rpm setting. This can cause injuries to the operator&#39;s hand, wrist or fingers, and broken bones are by no means unknown. The fundamental problem is that the suddenness with which a jam occurs does not give the operator sufficient time to release the trigger throttle of the engine, and thereby increase the operator&#39;s chance of avoiding injury. 
       GENESIS OF THE INVENTION 
       [0019]    The genesis of the present invention is a desire to produce a portable powered drill, preferably with an internal combustion engine, which has a much reduced likelihood of operator injury in the event of a jam. 
       SUMMARY OF THE INVENTION 
       [0020]    In accordance with a first aspect of the present invention there is disclosed a portable power drill unit comprising an operational axis having a chuck means at one end and a substantially cylindrical or frusto-conical twist throttle handle at the other end, and wherein rotation of the handle in the direction of forward rotation of the chuck means decreases the drill speed, and rotation of the handle in the direction of reverse rotation of the chuck means increases the drill speed, whereby reaction forces created by a jammed auger rotated by said chuck means decrease the drill speed. 
         [0021]    In accordance with a second aspect of the present invention there is disclosed a portable power drill unit having an operational axis defined by a chuck means at one end and a substantially cylindrical or frusto-conical twist throttle handle at the other end, a motor located intermediate said chuck means and twist throttle handle, and a second handle located above said motor and extending transversely to said operational axis. 
         [0022]    Preferably the second handle extends between a pair of uprights extending one to either side of the drill unit. Preferably the motor is an internal combustion engine. 
         [0023]    According to a still further aspect of the present invention there is provided a portable drill unit having an internal combustion engine, a pair of handles able to be held by an operator, a gearbox including forward and reverse gears, a chuck means, and a forward/reverse selection mechanism connected with said gearbox, said forward/reverse selection mechanism being actuated by a forward force, or a withdrawing force, respectively being applied to said drill unit by an operator holding said handles. 
         [0024]    According to another aspect of the present invention there is provided a method of de-accelerating a portable power drill unit in the event of an auger or drill bit rotated by said drill unit jamming in use, said method comprising the steps of: 
         [0025]    rotating the auger or drill bit in a first direction, 
         [0026]    providing a twist throttle handle having an axis substantially coincident with, or parallel to, the axis of rotation of said auger or drill bit, and 
         [0027]    arranging for rotation of said twist throttle handle in the direction opposite to the direction of rotation of said auger or drill bit, to increase the speed of said drill unit, and vice versa. 
         [0028]    According to a still further aspect of the present invention there is disclosed a gear train for a drill unit having a substantially aligned driven shaft and an output shaft, said output shaft having a chuck means, said gear train being interposed between said shafts and including an intermediate shaft substantially perpendicular to said aligned shafts, a first pinion gear driving said intermediate shaft, and a second pinion gear rotated by said intermediate shaft and meshed with two counter rotating crown gear wheels, each said counter rotating gear wheel including a clutch means connected with said output shaft, and spring means interposed between said chuck means and said counter rotating gear wheels to selectively engage either one of said clutch means to permit corresponding selective rotation of said output shaft in either direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0030]      FIG. 1  is a perspective view from the front of a prior art drill unit, 
           [0031]      FIG. 2  is a perspective view from the rear of the drill unit of the preferred embodiment, 
           [0032]      FIG. 3  is a side elevation of the drill unit of  FIG. 2 , 
           [0033]      FIG. 4  is a plan view of the drill unit of  FIG. 2   
           [0034]      FIG. 5  is a partial longitudinal cross-sectional view of the drill unit of  FIG. 2  but with a different engine, 
           [0035]      FIG. 6  is an enlarged longitudinal cross-sectional view through the gearbox of the drill unit of  FIG. 5  with the forward gear selected, 
           [0036]      FIG. 7  is a view similar to  FIG. 6  but with the reverse gear selected, 
           [0037]      FIG. 8  is a perspective view from the front of the drill unit of  FIG. 5  and with the gearbox illustrated, 
           [0038]      FIG. 9  is a perspective view of a rear handle of a second embodiment having a T-grip, and 
           [0039]      FIG. 10  is a side view of a rear handle of a third embodiment having a pistol grip. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    As seen  FIG. 1 , a prior art drill unit  1  is illustrated, the drill unit being sold under the trade name TANAKA. The drill unit has an internal combustion engine  2 , and a gearbox  3  which drives a chuck  4 . The gearbox has a forward or reverse gear selector lever  5 . The drill unit  1  has a left handle  7  (which is to say a handle held by the left hand of the operator), a right handle  8  (which is to say a handle held by the right hand of the operator), and a trigger throttle control  9  (also operated by the right hand of the operator). The drill unit  1  suffers from all the disadvantages referred to in the introductory portion of the specification, particularly in relation to the danger of injury in the event of the auger (not illustrated) jamming and in relation to the slow procedure to move from forward to reverse gear, and vice versa. 
         [0041]    Turning now to  FIGS. 2-4 , the drill unit  11  of the preferred embodiment has an internal combustion engine  12 , a gearbox  13 , and a chuck equivalent in the form of a bit holding collar  14  which releasably retains an auger  15 . The drill unit  11  is provided with two handles, namely a dorsal handle  20  supported by two uprights  21 ,  22  and intended to be held by the operator&#39;s left hand, and a cylindrical (or slightly frusto-conical) rear handle  25  intended to be held by the operator&#39;s right hand. The dorsal handle extends transversely to the longitudinal axis of the drill and is located near to the centre of gravity and thus is substantially balanced. The rear handle  25  is rotatable in the direction of arrow A in  FIG. 2  through an arc of 10°-40° so as to increase the speed of the internal combustion engine  12 . In this respect the handle  25  is similar to the accelerator of a conventional motorbike. Preferably the handle  25  has a more limited 15°-20° arc of movement than a conventional motor bike accelerator, but this is not essential. Rotating the rear handle  25  in a clockwise direction opposite to that of the arrow A in  FIG. 2 , reduces the speed of the internal combustion engine  12  until a rest position corresponding to an idle speed is achieved. A cutout switch  26  for the internal combustion engine  12  is mounted at the junction of the handle  25  and the throttle housing  27 . The drill unit  11  has a longitudinal axis  30  as illustrated in  FIG. 2 . 
         [0042]    In view of the above handle arrangement, prior to operation, the drill unit  11  is able to be conveniently held in a substantially balanced position by the handle  20  and carried from place to place. This carrying action can be undertaken by either hand of the operator. However, during drilling, the operator&#39;s left hand holds the handle  20  and assists to provide the forward pull of the auger  15  through the workpiece, whilst the rear handle  25  is held in the operator&#39;s right-hand. By slightly twisting the wrist of the right hand, the operator can control the speed of the internal combustion engine  12  and hence the speed of the auger  15 . 
         [0043]    In the event of the auger  15  suddenly jamming, the entire drill unit  11  rotates about the longitudinal axis  30  of the drill unit  11  so as to move the handle  20  in an anticlockwise direction as seen in  FIG. 2  and as indicated by arrow B in  FIG. 2 . The magnitude of this reaction force is generally greater than the operator is able to resist and as a consequence, the entire drill unit  11  turns in an anticlockwise direction as seen in  FIG. 2 . Since the operator is still holding the handle  25 , the handle  25  is effectively turned in a clockwise direction relative to the drill unit throttle housing  27  (that is to say, in the direction opposite to the direction of the arrow A in  FIG. 2 ). This has the effect of immediately or instantaneously reducing the throttle setting of the internal combustion engine  12 , preferably back to idling speed. 
         [0044]    The consequence of the reduction of the throttle is that the drill unit  11  does not spin round and round in an anticlockwise direction as shown in  FIG. 2  about the stationary auger  15 , as is sometimes the case with some prior art drill units when the auger jams. 
         [0045]    Turning now to  FIGS. 5-8 , the internal mechanisms of the drill unit  11  will now be described. The internal combustion engine  12  is connected to a substantially conventional centrifugal clutch which drives a clutch drum  32  mounted on a horizontal shaft  33 . A helix gear  34  is mounted on the shaft and meshes with another helix gear  35  mounted on a second horizontal shaft  36 . The forward end of the shaft  36  carries a first pinion gear  37  which drives an intermediate vertical shaft  38  by means of a crown gear  39 . 
         [0046]    As seen in  FIG. 6 , the vertical shaft  38  carries a pinion crown gear  42  which meshes with two permanently rotating final crown gear wheels  44  and  45  respectively. The gear wheels  44  and  45  rotate in opposite directions and have recesses on their non-gear faces to receive the projections of dog clutches. Slidably mounted within the crown gear wheels  44 ,  45  is the driveshaft  46  which carries the collar  14  to lock the auger  15 . In the situation where the driveshaft  46  is driven forwardly (that is the auger  15  rotates in a clockwise direction as seen in  FIG. 2 ) the driveshaft  46  is moved rearwardly by means of a spring  48  which is compressed between a bearing  49  and a (forward) dog clutch  50 . The dog clutch  50  engages the recesses of the crown wheel  44  and thereby rotates the drive shaft  46  in the clockwise direction (as seen in  FIG. 2 ). 
         [0047]    In the reverse drive configuration, as shown in  FIG. 7 , the driveshaft  46  is moved forwardly by the operator pulling the drill unit towards the operator whilst the auger  15  is engaged in the workpiece, thereby further compressing the spring  48  so as to disengage the forward dog clutch  50  from the recesses of the crown gear wheel  44  and simultaneously engaging a reverse dog clutch  51  with the recesses of the crown gear wheel  45 . This has the effect of rotating the drive shaft  46  in the opposite, or reverse, direction so as to extract the auger  15  from the workpiece. 
         [0048]    The strength of the spring  48  is selected so that the driveshaft  46  is driven towards the rear of the drill unit  11  thereby engaging the forward dog clutch  50  and forward crown gear wheel  44 . Thus when the auger  15  not engaged in any workpiece, the drill unit is always in forward gear. However, with the auger  15  engaged in the workpiece, the drill unit  11  can be moved rearwardly by the operator pulling on the handle  20 . This moves the driveshaft  46  forwardly so as to disengage the recesses of the forward crown gear wheel  44  with the forward clutch  50 , and engage the recesses of the reverse crown gear wheel  45  with the reverse dog clutch  51 . 
         [0049]    The operational consequence of this construction is that during drilling, the auger  15  can be easily and quickly reversed by the operator merely by pulling backwardly on the drill unit via the handle  20 . This means that the auger  15  immediately reverses direction and clears the hole being drilled of wood chips and similar debris. Thus, unlike in the prior art arrangement described above, there is no need to reduce the speed of the internal combustion engine to idle to change gears, and the clearing of wood chips can take place momentarily and drilling can be resumed immediately thereafter by pushing the handle  20  forwardly. 
         [0050]    Turning now to  FIG. 9 , the rear handle  25  can be replaced and a handle  125  of a second embodiment including a T-grip  126 . The handle  125  has a shorter cylindrical body than the handle  25  which is not grasped since the operator grasps the T-grip  126  instead. However, the T-grip  126  can enable the operator&#39;s right hand to apply either a forward force, or a rearward force, to the drill unit  11 . 
         [0051]    In addition, the T-grip  126  is rotated about the axis  30  in the direction of arrow A to increase the engine speed, and in the opposite direction to decreases the engine speed. 
         [0052]    In a third embodiment illustrated in  FIG. 10 , the rear handle  25  is replaced by a handle  225  which incorporates a pistol grip  226 . The handle  225  also has a shorter cylindrical body than the handle  25 . The pistol grip  226 , like the T-grip  126 , can enable the operator&#39;s right hand to apply either a forward force, or a rearward force, to the drill unit  11 . The pistol grip  226  is similarly rotatable about the axis  30  in opposite directions to increase or decrease the engine speed. 
         [0053]    The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the portable powered drill arts, can be made thereto without departing from the scope of the present invention. 
         [0054]    The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “including” or “having” and not in the exclusive sense of “consisting only of”.