Abstract:
A hammer drill is equipped with a connector shaft, which is rotationally driven by a motor, a spindle that transmits the rotation through a connector shaft, and a percussive impact means that applies a percussive force in the axial direction to a drill bit held by the spindle through performing a reciprocating motion, in the axial direction, relative to a spindle that receives the rotation of the connector shaft through a motion converter mechanism. The hammer drill is provided with a percussive force converter means from the percussive impact means by changing the speed reduction ratio between the motor and the connector shaft. This makes it possible to adjust the percussive force according to the drill bit used.

Description:
BACKGROUND OF INVENTION  
         [0001]    The present invention relates to hammer drills used for, for example, boring concrete.  
           [0002]    A hammer drill is a tool that applies a percussive impact to a drill bit in the axial direction while rotating the drill bit about its axis. The motion of a reciprocating piston propagates to a hammer, which is supported through an air spring, as the mechanism by which to provide the percussive impact. However, it is difficult to adjust the percussive force in hammer drills using this type of mechanism for providing the percussive impact, resulting in bent or broken drill bits when small drill bits are used. Conversely, when drill bits with larger diameters are used, with hammer drills with relatively small percussive forces, it is difficult to maintain the speed of the boring operations, causing the boring operations to be too time-consuming.  
         SUMMARY OF INVENTION  
         [0003]    The present invention is a hammer drill comprising a connecting shaft driven rotationally by a motor, a spindle, to which the rotation is transmitted through the connector shaft, a percussive impact mechanism that applies a percussive force in the axial direction to a drill bit that is held by the spindle, and that reciprocates in the axial direction relative to the spindle, and that is rotated by the connector shaft via a motion converter mechanism, and a percussive force modification mechanism that modifies the percussive force from the percussive impact mechanism through modifying the reduction ratio between the motor and the connecting shaft. This makes it possible to adjust the percussive force according to the drill bit used.  
           [0004]    The percussive force conversion mechanism is a transmission mechanism interposed between the motor and the connecting shaft where, in the transmission mechanism, preferably multiple gears that have mutually differing numbers of gear teeth, that can move freely in the axial direction of the connecting shaft, and that are rotated by receiving a rotational force from the motor, are preferably meshed selectively by the force of a spring, with the gear teeth equipped on the connecting shaft side, where the mating teeth of the, gear of that meshes with the teeth on the connecting shaft side are, preferably, equipped with a side wall on one side in the axial direction.  
           [0005]    Furthermore, preferably the teeth on the connecting shaft side, or the mating teeth of the gear of that meshes with the gear teeth, have a different length in the axial direction for every other tooth, or, preferably, either the gear teeth on the connecting shaft side, or the mating teeth that mesh with the teeth, are equipped for every second tooth.  
           [0006]    A sleeve is affixed to the connecting shaft, where the sleeve may be equipped with a gear and with a spring that applies a force to the gear.  
           [0007]    Furthermore, the gear transmission mechanism is equipped with a shifting shaft for shifting between pairs of gears, making it possible to use, as appropriate, a mechanism wherein the shifting shaft is moved in the axial direction of the connecting shaft to separate one gear from the teeth on the connecting shaft side, pushing against the force of a spring, while another gear is moved by the force of the spring to a position wherein the gear meshes with the teeth on the connecting shaft side.  
           [0008]    In one embodiment, this shifting shaft is equipped in a position that is off-center relative to the center of rotation of the shifting switch on the axis of the connecting shaft, and the position on the axis of the connecting shaft is changed by the shifting shaft rotating, for example, by 180°.  
           [0009]    The pair of gears is not only equipped with a specific gap therebetween in the axial direction of the connecting shaft, but, preferably, there should be a space between the gears for obtaining a neutral state wherein neither gear meshes with the connecting shaft, and, more preferably, the equilibrium positions of the springs that exert forces on each of the gears in the pair, should be at the position of said neutral state. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a partial cross-sectional drawing of a hammer drill according to an embodiment of the present invention.  
         [0011]    [0011]FIG. 2 is a cross-sectional drawing of a hammer drill according to an embodiment of the present invention.  
         [0012]    [0012]FIG. 3A is a partial cross-sectional drawing of a hammer drill in the state wherein the reduction ratio is small.  
         [0013]    [0013]FIG. 3B is a drawing showing the state of the shifting switch in the state wherein the reduction ratio is low.  
         [0014]    [0014]FIG. 4A is a partial cross-sectional drawing of a hammer drill in the neutral state.  
         [0015]    [0015]FIG. 4B is a drawing showing the state of the shifting switch in the neutral state.  
         [0016]    [0016]FIG. 5A is a partial cross-sectional drawing of a hammer drill in the state wherein the reduction ratio is large.  
         [0017]    [0017]FIG. 5B is a drawing for explaining the state of the shifting switch in the state wherein the reduction ratio is large.  
         [0018]    [0018]FIG. 6 is an oblique view of the sleeve and gear.  
         [0019]    [0019]FIG. 7 is a cross-sectional drawing of the assembly block for changing speeds.  
         [0020]    [0020]FIG. 8A to  8 C are figures showing the meshing operations of the gears and sleeve.  
         [0021]    [0021]FIG. 9 is an oblique view of the sleeve and gears in an embodiment of the present invention.  
         [0022]    [0022]FIG. 10 is a cross-section of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]    An embodiment of the present invention will be explained in detail below, referencing the attached drawings. In the hammer drill shown in the figures, the rotation of the motor  2 , as the motive source, equipped in a housing  1  is transmitted to a connecting shaft  60 . As the rotation of the connecting shaft  60  is transmitted to an output shaft through a spindle  7 , a piston  8 , which is equipped so as to rotate freely on the axis thereof and which can slide freely in the axial direction relative to the spindle  7 , is caused to undergo reciprocating motion by a motion converter mechanism equipped on the connecting shaft. The hammer  80 , equipped within the piston  8 , moves backward and forward in the space enclosed by the piston  8  and the spindle  7 . The hammer  80  strikes against the back edge of the output shaft according to the reciprocating motion of the piston  8 . Air chambers are formed in the forward and backward directions of the hammer  80 , and act as springs.  
         [0024]    The motion converter mechanism  6  comprises an inner race  61 , which rotates as a unit with the connecting shaft  60 , an outer race  63 , which is equipped so as to rotate freely relative to the inner race  61 , with ball bearings  62  interposed therebetween, and a rod  64 , which protrudes from the outer race  63 . The rod  64  is connected to the back end of the piston  8  through a universal joint, and the rotating surface of the outer race  63  that is a surface that is tilted relative to the axis of the connecting shaft  60 . Consequently, when the connecting shaft  60  and the inner race  61  rotate, the outer race  63  and the rod  64  undergo reciprocating motion in the axial direction of the piston  8 .  
         [0025]    The front end of the output shaft  9  is equipped with a chuck  10  for housing a drill bit (not shown). The chuck  10  secures the drill bit. When the motor  2  rotates, at the same time as the drill bit is rotating due to the rotational forces transmitted to the output shaft through the spindle  7 , there is also a percussive impact applied in the axial direction by the hammer  80 .  
         [0026]    The transmission of the rotational forces from the motor  2  to the connection shaft  9  in this embodiment is done through a two-stage transmission, as explained below. As is shown in FIG. 1, a pinion  22  equipped with a large diameter part  23  and a small diameter part  24  is attached to the axle  21  of a motor  2 . Additionally, a gear  3 , which meshes with the large diameter part  23  of the pinion  22 , and the gear  4 , which meshes with a small diameter part  24  of the pinion  22 , are equipped on the connecting shaft  60  via a sleeve  5 .  
         [0027]    The sleeve  5  is secured on the connecting shaft  60 . On the other hand, the gears  3  and  4  equipped with a specific gap in the axial direction are equipped so as to be able to slide freely in the axial direction of the sleeve, and equipped so as to be able to rotate freely relative to the sleeve  5 . There is a ring-shaped collar  15  equipped between the gears  3  and  4 , and there is a stop ring  51  equipped on one end of the sleeve  5 . Furthermore, a stop ring  56  is equipped at the other end of the sleeve  5 . Between a spring bearing  55  and the gear  4 , there is a spring  54 , which provides a force on the gear  4  towards the gear  3 .  
         [0028]    Gear teeth  50  are equipped on the outer peripheral surface of the sleeve  5  in the region near the center in the actual direction. The inner peripheral part of the gear  3  on the gear  4  side is equipped with mating teeth  32  that mesh with the gear teeth  50 , and the inner peripheral part of the gears  4  on the gear  3  side are equipped with mating teeth  42 , which mesh with the gear teeth  50 .  
         [0029]    The mating teeth  32  of the gear  3  and the mating teeth  42  of the gear  4  can mesh, selectively, with the gear teeth  50 . At the position wherein the spring forces of the springs  53  and  54  are at equilibrium (see FIG. 4), the gear teeth  50  are at a position between the gears  3  and  4 , and neither the gear  3  nor the gear  4  mesh with the gear teeth  50 . When the gears  3  and  4  are moved in the backwards direction (towards the motor  2 ), then, as shown in FIG. 3, the mating teeth  42  of the gear  4  mesh with the gear teeth  50 , and, conversely, when the gears  3  and  4  are moved in the forward direction (towards the motion converter mechanism  6 ), then, as shown in FIG. 1 and FIG. 5, the mating teeth  32  of the gear  3  mesh with the gear teeth  50 .  
         [0030]    Regardless of the direction of movement of the gears  3  and  4 , they always mesh with the pinion  22 , and are always driven by the rotation of the motor  2 .  
         [0031]    The aforementioned movement of the gears  3  and  4  in the axial direction is done through the operation of the shifting switch  11 , equipped on the outer surface of the housing  1 . This shifting switch  11  is equipped with a shifting shaft  12  at a position that is off-center from the center of rotation thereof. The tip of the shifting shaft  12  is linked to a collar  15 . When the shifting shaft  12  is moved by a rotating operation relative to the shifting switch  11 , one of the gears  3  ( 4 ) is pushed by the collar  15  to move against the spring  53  ( 42 ), while the other gear  4  ( 3 ) is moved following the other gear  3  ( 4 ), due to the force of the spring  54  ( 32 ) so that the mating teeth  42  ( 32 ) thereof or mesh with the gear teeth  50 . In other words, the structure is such that the gear  3  ( 4 ), which is moved by the operation of the shifting switch  11 , ceases to mesh with the gear teeth  50 , and the force of the spring  54  ( 32 ) causes the gear  4  ( 3 ) to mesh with the gear teeth  50 . In addition, the respective mating teeth  32  and  42  are equipped on the inside wall on the opposite wall side from the gear teeth  50 . Because of this, when the mating teeth  32  or  42  mesh with the gear teeth  50 , the same mating position in the axial direction is always maintained.  
         [0032]    When, as a shown in FIG. 1 (or FIG. 5), when the mating teeth  32  of the gear  3 , which meshes with the large diameter part  23  of the pinion  22 , mesh with the gear teeth  50  of the sleeve  5 , the rotation of the motor  2  is transmitted to the sleeve  5 , and to the connecting shaft  60 , at a low speed ratio. On the other hand, as is shown in FIG. 3, when the mating teeth  42  of the gear  4 , which meshes with the small diameter part  24  of the pinion  22 , mesh with the gear teeth  50  of the sleeve  5 , the revolution of the motor  2  is sent to the sleeve  5 , and to the connecting shaft  60 , at a large transmission ratio. In this way, the modification of the state of rotation of the connecting shaft  60  changes the number of percussive impacts per unit time of the hammering that is performed by the receipt of the revolving motion of this connecting shaft  60  by the motion converter mechanism  6 . Furthermore, because the maximum speed also changes when the piston  8  undergoes reciprocating motion, the acceleration that moves the hammer  80  is also changed, changing not only the number of percussive impacts, but changing the impact forces as well.  
         [0033]    Because of this, when a drill bit with a large diameter is used, a large percussive force can be obtained through the rotation of the connecting shaft  60  at a high-speed by reducing the transmission ratio applied to the connecting shaft  60 , while, on the other hand, when a drill bit with a small diameter is used, the percussive force can be reduced through reducing the state of rotation of the connecting shaft  60 , through increasing the reduction ratio arriving at the connecting shaft  60 . Consequently, even if a drill bit with a small diameter is used, it is possible to avoid problems with the drill bit bending or breaking.  
         [0034]    As is clear from FIGS.  3  to  5 , not only does the center of rotation of the shifting switch  11  pass-through the center axle of the sleeve  5 , but the shifting shaft  12 , where having either gear  3  or the gear  4  of meshes with the gear teeth  50  of the sleeve  5  positioned on the central axis of the sleeve  5  is to prevent the effects of component forces that tend to rotate the shifting switch  11 .  
         [0035]    Furthermore, the fact that these forces off the springs  53  and  54  are in equilibrium at the neutral position shown in FIG. 4 and FIG. 7 not only improves the transmission characteristics, but also reduces the amount of force required for operating the shifting switch  11 , ensuring that there is no disparity in the forces that must be applied in the operating direction.  
         [0036]    The mating teeth  32  of the gear  3  (as shown in FIG. 6) are structured from the mating teeth  32 A, which are long in the axial direction, and mating teeth  32 B, wherein a portion is cut away for the gear teeth  50 , and so are short in the axial direction. The mating teeth  42  of the gear  4  also comprise the mating teeth  42 A, which are long in the axial direction, and the mating teeth  42 B, wherein a part is cut away for the gear teeth  50 , and thus are short in the axial direction. Furthermore, there are half as many gear teeth  50  equipped on the outer peripheral surface of the sleeve  5  as there are mating teeth  32  or  42 , so as to be placed in pairs therewith.  
         [0037]    This is for ease in meshing when, as shown in FIG. 8, the force of the spring  53  or spring  54  causes the rotating gear  3  or  4  to move to the gear teeth  50  side, as shown in FIG. 8, and, in order to reduce the chatter in the radial direction after the linkages complete. This structure not only makes it possible to perform the shifting operations smoothly, but also reduces the loss of percussive impact energy, maintaining the percussive performance.  
         [0038]    In addition, as shown in FIG. 9, the gear teeth  50  may instead be equipped alternating between gear teeth  50 A, which are long in the axial direction, and gear teeth  50 B, wherein both ends in the axial direction are cut away so that the gear teeth are short in the axial direction. In this case, the mating teeth  32  and  42  on the gear  3  and gear  4  side are structured from teeth with only a single length.  
         [0039]    Note that each of the components are disposed appropriately in order to prevent the gear  4  from contacting the motion converter mechanism  6  and the piston  8  when an operation on the shifting switch  11  moves the gear  4  to the motion converter mechanism  6  side. Furthermore, the various members are disposed appropriately so that even if the gear  4  moves far enough towards the motion converter member  6  side that the spring  54 , positioned between the gear  4  and the motion converter mechanism  6 , is fully compressed with the coils touching each other, the gear  4  will not come into contact with the motion converter mechanism  6  nor with the piston  8 .  
         [0040]    The provision of the small diameter gear  3  on the motor  2  side, and the provision of the large diameter gear  4  on the motion converter mechanism  6  (piston  8 ) side is to make it possible to have a structure with a shape that balances the pinion  22  well, thus making it possible to maintain the precision of the oscillating movement, and possible to maintain, with ease, the wall thickness of the pressure bearing relative to the axle  21 .  
         [0041]    In the hammer drill according to the form of embodiment, the gears  3  and  4 , which function as the transmission, the sleeve  5 , the springs  53  and  43 , and the spring  15  are structured as a single assembly block, as shown in FIG. 7. Consequently, as a shown in FIG. 10, merely attaching a key  69 , for stopping the rotation relative to the connecting shaft  60 , and stop rings  68  and  68  in order to prevent the axial direction movement, will be efficient in terms of assembly, as well.  
         [0042]    As described above, given embodiments of the present invention, one or more of the benefits described below will be obtained:  
         [0043]    In embodiments of the present invention, it is possible to change the percussive force for the drill bit, producing a small percussive force when using a small-diameter drill bit and producing a large percussive force when using a large diameter drill bit, thereby making it possible to ensure that the boring is always stable. Furthermore, in the present invention, the RPM can also be changed at the same time as changing the percussive force, and thus it is possible to reduce the electric current used when boring. Furthermore, even when the drill bit is clogged with cement dust, boring can still be performed with repeatability.  
         [0044]    Given embodiments of the present invention, excellent gear-to-gear meshing is always maintained, and when the gear shift operations are performed when stopped, even when the gear is not meshed with the gear teeth in contact with the gear teeth on the connector shaft side, the gear teeth on the connector shaft side will mesh with the gear at the start of the rotation, making smooth gear shifting possible.  
         [0045]    Furthermore, in embodiments of the present invention, the positioning of the gear teeth and of the mating gear teeth in the axial direction is simple.  
         [0046]    In addition, in embodiments of the present invention, not only is the meshing operation of the gear with the connector shaft gear teeth done smoothly, but also, chattering in the radial direction is suppressed after meshing.  
         [0047]    Furthermore, in embodiments of the present invention the structuring of the transmission mechanism as a single assembly block makes it easy to perform assembly and greatly suppresses costs.  
         [0048]    Moreover, embodiments of the present invention has the shifting shaft of the shifting switch  11  positioned at an off-center position, and thus is able to avoid any unanticipated movement of the shifting switch due to reactive forces.  
         [0049]    Furthermore, in embodiments of the present invention, a pair of gears is equipped with a specific gap in the axial direction therebetween, and a neutral state is formed wherein the gear teeth on the connector shaft do not meshed with either gear, making it possible to suppress the amount of grease (which is filled into the meshing part) that is thrown off.  
         [0050]    Furthermore, in embodiments of the present invention, not only is it possible to perform the shifting operations and the shifting motion smoothly, but also the shifting operations can be performed through a relatively light operating force, and with the same operating force regardless of the direction of operation.  
         [0051]    While the invention has been described with respect to a limited number of embodiments, those who skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.