Abstract:
The patent covers a reciprocating drive mechanism for a striker in a hammer, a rotary hammer, or a power drill having a hammer action, which utilise a sinusoidal cam channel formed on a drive member and a cam follower, in the form of a ball bearing, attached to a driven member which, due to the interaction of the cam and cam follower, results in a reciprocating movement of the driven member. Both the drive member and driven member can be rotatingly driven by a motor, their relative speeds resulting in the reciprocating movement of the driven member. The driven member is connected to the striker either via a mechanical helical spring or an air spring.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to powered hammers, to powered rotary hammers, and to power drills having a hammer action.  
       BACKGROUND OF THE INVENTION  
       [0002]     Rotary hammers are known in which a motor drives a spindle supporting a hammer bit, while at the same time causing a piston tightly fitted within the spindle to execute linear reciprocating motion within the spindle. This motion causes repeated compression of an air cushion between the piston and a ram slidably mounted within the spindle, which causes the ram in turn to execute reciprocating linear motion within the spindle and apply impacts to the hammer bit via a beat piece.  
         [0003]     In know designs of rotary hammer, the piston is reciprocatingly driven by the motor via a wobble bearing or crank. However, such designs typical require a large amount of space for such drive systems in relation to the amount of reciprocating movement of the piston.  
         [0004]     Further, rotary hammers of this type suffer from the drawback that in order to generate an air cushion between the piston and the ram, the external dimensions of the piston and ram must be closely matched to the internal dimensions of the spindle, which increases the cost and complexity of manufacture of the hammer.  
         [0005]     The present invention seeks to overcome or at least mitigate some or all of the above disadvantage of the prior art whilst producing a compact design.  
         [0006]     US6199640 is a relevant piece of prior art known to the applicant.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     Accordingly, there is provided a power tool comprising:  
         [0008]     a housing;  
         [0009]     a motor mounted within the housing;  
         [0010]     a tool holder rotatably mounted on the housing for holding a cutting tool;  
         [0011]     a striker mounted in a freely slideable manner within the housing, for repetitively striking an end of a cutting tool when a cutting tool is held by the tool holder, which striker is reciprocatingly driven by the motor, when the motor is activated, via a drive mechanism;  
         [0012]     characterised in that the drive mechanism comprises two parts,  
         [0013]     a first part comprising a drive member which is capable of being rotatingly driven by the motor;  
         [0014]     a second part comprising a driven member which is connected to the drive member by at least one cam and cam follower, and to the striker via a spring;  
         [0015]     one part comprising the cam;  
         [0016]     the other part comprising the cam follower which is engagement with the cam;  
         [0017]     wherein rotation of the drive member relative to the driven member results in a reciprocating motion of the driven member which in turn reciprocatingly drives the striker via the spring. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     Three embodiments of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:  
         [0019]      FIG. 1  is a perspective partially cut away view of a rotary hammer of a first embodiment of the present invention;  
         [0020]      FIG. 2  is a perspective partially cut away close up view of the hammer mechanism of the rotary hammer of  FIG. 1 ;  
         [0021]      FIGS. 3A  to  3 D are schematic diagrams of cross sectional side views of the gear mechanism of the rotary hammer of  FIG. 1 .  
         [0022]      FIG. 4  is a perspective partially cut away view of a rotary hammer of a second embodiment of the present invention;  
         [0023]      FIG. 5  is a perspective partially cut away view of a rotary hammer of a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     The first embodiment of the present invention will now be described with reference to FIGS.  1  to  3 .  
         [0025]     Referring to  FIGS. 1 and 2 , a rotary hammer  2  has a housing  4  formed from a pair of mating clam shells  6 ,  8  of durable plastics material and a removable rechargeable battery  10  removably mounted to a lower part of the housing  4  below a handle  12 . The housing  4  defines the handle  12 , having a trigger switch  14 , and an upper part  16  containing an electric motor  18  actuated by means of trigger switch  14 , at a rear part thereof. The electric motor  18  has a rotor which rotates in well known manner when the motor  18  is activated. A chuck  20  is provided at a forward part of the upper part  16  of housing  4  and has an aperture  22  for receiving a drill bit (not shown). The chuck  20  has a gripping ring  21  axially slidably mounted to a hollow spindle  24  for enabling the drill bit to be disengaged from the chuck  20  by rearward displacement of gripping ring  21  relative to the spindle  24  against the action of compression spring  26 , to allow ball bearings  25  (of which only one is shown in  FIGS. 1 and 2 ) to move radially outwards to release a shank of the drill bit in well known manner.  
         [0026]     The spindle  24  is rotatably mounted in the upper part  16  of the housing  4  by means of forward rollers  28  and rear bearings  30 , and is provided at a rear end thereof with an integral end cap  32  of generally circular cross section. The integral end cap  32  comprises teeth  34  located on an outer periphery thereof for engaging an annular gear  36  and three equiangularly spaced apertures for receiving shafts  38  of planet gears  40 .  
         [0027]     A ram  42  is slidably mounted within hollow spindle  24  and is connected via a mechanical spring  44  to a support cylinder  48 . Mounted co-axially within the support cylinder  48  is a cam cylinder  46 . The support cylinder  48  is capable of axially sliding within the spindle  24  over a limited range of movement. The support cylinder  48  is provided with at least one axial groove  50  containing a ball bearing  52  for preventing rotation of the support cylinder  48  relative to the hollow spindle  24 . The ball bearing  52  achieves this by also being located within an axial groove  51  formed in the inner wall of the spindle  24 . The ball bearing is allowed to travel along the length of the two axial grooves  50 ,  51  but is prevented from exiting them. The axial grooves  50 ,  51  allow the support cylinder  48  to freely slide in the spindle  24 . The cam cylinder  46  is provided with a sinusoidal cam groove  54  receiving ball bearing  56  located in an aperture in support cylinder  48  such that rotation of cam cylinder  46  relative to support cylinder  48  causes oscillatory axial movement of support cylinder  48  in the hollow spindle  24  in such a manner that one complete rotation of cam cylinder  46  relative to the support cylinder  48  causes one complete axial oscillation of support cylinder  48  relative to cam cylinder  46 .  
         [0028]     The cam cylinder  46  is driven by means of a shaft  57  to which it is attached at its rear end and which is co-axial with the cam cylinder. On the shaft  57  is mounted a central sun gear  58  meshing with planet gears  40 . Rigidly attached, in a co-axial manner, to the end of the shaft is a second cap  59  by which the shaft  57  is rotatingly driven. Teeth  63  are formed around the periphery of the second end cap  59 . The mechanism by which the second cap  59  and hence the shaft  57  is rotatingly driven is described below. However, activation of the motor  18  always results in rotation of the shaft  57 .  
         [0029]     A mode change knob  60  provided on the exterior of the housing  4  is slidable forwards and backwards relative to the housing  4  to cause a lever  62  to move the annular gear  36  between a drill mode (as shown in  FIGS. 3A and 3B ), a hammer drill mode (as shown in  FIG. 3C ) and a chisel mode (as shown in  FIG. 3D ).  
         [0030]     In the drill mode, the annular gear  36  is moved rearwardly as shown in  FIGS. 3A and 3B  to the position shown.  FIGS. 3A and 3B  both show the gears in the drill mode but with the amount of gear reduction between the motor  18  and the shaft  57  set to two different values.  
         [0031]     When the annular gear in this position, it is capable of freely rotating within the housing  6 . The inwardly facing teeth of the annular gear  36  mesh with both of the teeth  41  of the planet gears  40  and the teeth  63  around the periphery of the second end cap  59 . Thus, rotation of the second end cap  57 , and hence shaft  57  and central sun gear  58 , results in the rotation of the annular gear  36  at the same rate as the second end cap  57 . As the planet gears  40  mesh both with the central sun gear  58  and the annular gear  36 , and as the annular gear  36  and central sun gear  58  are rotating at the same speed, the planet gears  40  are prevented from rotating about their shafts  38  thus causing the shafts and in turn the integral end cap  32  to rotate at the same speed as the shaft  57  around the axis of the shaft  57 . The cam cylinder  46  is connected to the shaft  57  and thus rotates with it. The support cylinder  48  is connect to the integral end cap  32  via the spindle  24  and ball bearing  52  and thus rotates with it. As such, the cam cylinder  46  and the support cylinder  48  rotate at the same rate. As there is no relative movement between the cam cylinder  46  and support cylinder  48 , no oscillatory movement is generated as the ball bearing does not travel along the sinusoidal cam groove  54 . However, as the spindle  24  is rotating, the chuck  20  also rotates. Thus, when the annular gear  36  is located in the position shown in  FIGS. 3A and 3B , the rotary hammer drills only.  
         [0032]     In the hammer drill mode, the annular gear  36  is moved to a middle position as shown in  FIGS. 3C .  
         [0033]     When the annular gear in this position, it is prevented from rotation. The annular gear  36  has a second set of outer teeth formed on its outer periphery in addition to the inwardly facing teeth of the annular gear  36 . These teeth  65  face outwardly. When the annular ring is in the middle position as shown in  FIG. 3C , the out teeth  65  mesh with teeth  67  formed on the inner wall of part  69  of the housing. As such it is prevented from rotation. The inwardly facing set of teeth mesh with the teeth of planet gears  40  only. As the central sun gear  58  rotates due to the shaft  57  rotating, it causes the planet gears  40  to rotate about their shafts  38  as the planet gears are both meshed with the central sun gear  58  and the stationary annular gear  36 . As such, the planet gears  40  roll around the inner surface of the annular gear  36 . This results in their shafts and the end cap  32  rotating. This in turn causes the spindle  24  and the support cylinder  48  to rotate. The cam cylinder rotates as it is connected to the shaft  57 . However, even though the cam cylinder  46  and support cylinder  48  are rotating, the rate of rotation of the support cylinder  48  is different to that the cam cylinder  46  due to the gearing ratio cause by the action of transferring the rotary movement from the central sun gear  58  to the annular gear  36  using the planet gears  40 . This results in a relative movement between the two.  
         [0034]     The relative movement causes the support cylinder  48  to oscillate as the ball bearing mounted in the support cylinder rolls along the sinusoidal track. As the support cylinder is connected to the ram  42  via the spring  44 , the oscillating movement is transferred to the ram  42 . The ram  42  comprises a striker  41  which, when a tool bits is held in the chuck  20 , strikes the end of the tool bit to cause a hammering action in the normal manner.  
         [0035]     As the spindle  24  is rotating, the chuck  20  also rotates. Thus, when the annular gear  36  is located in the position shown in  FIG. 3C , the rotary hammer hammers and drills.  
         [0036]     In the chisel mode, the annular gear  36  is moved to its most forward position as shown in  FIGS. 3D .  
         [0037]     When the annular gear  36  in this position, it is prevented from rotation. The second set of outer teeth of the annular gear  36  mesh with teeth  67  formed on the inner wall of part  69  of the housing. As such it is prevented from rotation. The inwardly facing set of teeth mesh with teeth formed on the integral end cap  32  only. As such the spindle  24 , is prevented from rotating by the annular gear  36 .  
         [0038]     As the inner teeth on the annular ring  36  now no longer mesh with the planet gears  40 , when the shaft  57  and hence the central sun gear  57  rotates, the planet gears  40 , meshed with the central sun gear  58 , rotate about their shafts  38 . As the planet gears  40  are no longer meshed with the annular gear  36 , no force is applied to them to urge them to rotate around the axis of the shaft  57 . However, as the spindle 24  is prevented from movement due to the integral end cap  32 , the shafts  38  of the planet gears  40  are held stationary. As such, the planet gears  40  simply rotate about their shafts  38  only.  
         [0039]     As the spindle  24  is stationary, the chuck  20  is held stationary.  
         [0040]     As the spindle  24  is stationary, the support cylinder  48  is held stationary. As the shaft  57  rotates, so the cam cylinder  46  rotates. As there is relative movement between the cam cylinder  46  and the support cylinder  48 , the support cylinder  48  is caused to oscillate which in turn causes the ram  42  connected to it via the spring to oscillate. If a drill bit is located within the chuck  20 , the striker of the ram  42  would hit the end of the drill bit. As such the hammer drill acts in chisel mode only when the annular gear  36  is in the position shown in  FIG. 3D .  
         [0041]     The shaft  57  and second end cap  59  is driven by the motor  18  via three sets of planet gears  91 , and a speed change switch  64  is movable relative to the housing  4  (between positions  FIGS. 3A and 3B ) to selectively engage or isolate one set of planet gears  91 . The use of such gears to reduce the output speed of a hammer is well know and the readers attention is drawn to EPO which provides one example of the use of planet gears.  
         [0042]     The second embodiment will now be described with reference to  FIG. 4 .  
         [0043]     The second embodiment is similar in design to the first embodiment. Where the same features have been used in the second embodiment as the first, the same reference numbers have been used.  
         [0044]     The difference between the first and second embodiments of the present invention is that the two ball bearings  52 , 56  in the first embodiment has been replaced by a single ball bearing  100  in the second embodiment. The ball bearing  100  is located within the sinusoidal cam groove  54  of the cam cylinder  46  and the axial groove  51  of the spindle  24  whilst being held within an aperture formed through the wall of the support cylinder  48 . The interaction of the ball bearing  100  following the cam groove  54  causes the reciprocating movement of the support cylinder  48 . The interaction of the ball bearing  100  following the axial groove  51  causes the rotational movement of the support cylinder  48  with the spindle  24 , the axial groove  51  allowing the support cylinder  48  to axially reciprocate relative to the spindle  24 . The ball bearing  100  performs the same function as the two ball bearings  52 ,  56  in the first embodiment. As only one ball bearing  100  is used, the axial groove  50  in the support cylinder of the first embodiment is no longer required and is instead replaced with the aperture in the wall of the support cylinder  48  so that the ball bearing  100  can be located in both the cam groove  54  and the axial groove  51  at the same time whilst its position remains fixed relative to the support cylinder  48 .  
         [0045]     The third embodiment will now be described with reference to  FIG. 5 .  
         [0046]     The third embodiment is similar in design to the first embodiment. Where the same features have been used in the third embodiment as the first, the same reference numbers have been used.  
         [0047]     The first difference between the first and third embodiments of the present invention is that the two ball bearings  52 , 56  in the first embodiment has been replaced by a single ball bearing  200  in the third embodiment (in the same manner as the second embodiment). The ball bearing  200  is located within the sinusoidal cam groove  54  of the cam cylinder  46  and the axial groove  51  of the spindle  24  whilst being held within an aperture formed through the wall of the support cylinder  48 . The interaction of the ball bearing  200  following the cam groove  54  causes the reciprocating movement of the support cylinder  48 . The interaction of the ball bearing  200  following the axial groove  51  causes the rotational movement of the support cylinder  48  with the spindle  24 , the axial groove  51  allowing the support cylinder  48  to axially reciprocate relative to the spindle  24 . The ball bearing  200  performs the same function as the two ball bearings  52 ,  56  in the first embodiment. As only one ball bearing  200  is used, the axial groove  50  in the support cylinder of the first embodiment is no longer required and is instead replaced with the aperture in the wall of the support cylinder  48  so that the ball bearing  200  can be located in both the cam groove  54  and the axial groove  51  at the same time whilst its position remains fixed relative to the support cylinder  48 .  
         [0048]     The second difference is that the mechanical spring  44  in the first embodiment has been replaced by an air spring  206 .  
         [0049]     Located within the support cylinder  48  is a hollow piston  202 . The hollow piston  202  is rigidly attached to the support cylinder  48  via a cir clip  204  which prevents relative movement between the two. The cir clip  204  is located towards the front end of the support cylinder  48  where the support cylinder&#39;s inner diameter is less than that of the support cylinder  48  at its rear end. The rear end of the support cylinder  48  surrounds the cam cylinder  46  and interacts with the cam cylinder via the ball bearing  200  in a manner described previously. However, the outer diameter of the hollow piston  202  remains constant along its length. The rear end of the hollow piston  202  is located within the cam cylinder  46 , the cam cylinder  46  being sandwiched between the rear end of the support cylinder  48  and the rear of the hollow piston  202 . The hollow piston can freely slide within the cam cylinder  46 .  
         [0050]     The ram  42  is located within the hollow piston  202  and comprises a rubber seal  210  which forms an air tight seal between the ram  42  and the inner wall of the hollow piston  202 . Air vents  212  are provided in the piston  202 .  
         [0051]     In use, when the support cylinder  48  is reciprocatingly driven by cam cylinder  46  via ball bearing  200 , the hollow piston  202 , which is attached to the support cylinder  48  is similarly reciprocatingly driven. The hollow piston  202  in turn reciprocatingly drives the ram  42  via the air spring  206 . The operation of the hollow piston  202 , air spring  206  and the ram is standard and as such is well known in the art and therefore will be described no further.  
         [0052]     Additional vents  208  have been added to the cam cylinder  46  to allow free movement of the air which otherwise would be trapped behind the hollow cylinder  202  within the cam cylinder  46 .