Patent Publication Number: US-6907943-B2

Title: Electric hammer

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electric hammer, and more particularly, to a technique of reducing and alleviating vibration in an electric hammer that drives a hammer bit at a predetermined cycle, such as a hammer and a hammer drill. 
   2. Description of the Related Art 
   Japanese unexamined laid-open Utility Model Publication No. 51-6583 discloses a hammer with a vibration reducing device. According to the known hammer, a counter weight is provided on a crank arm mechanism and driven by the crank arm mechanism. The crank arm mechanism is designed to reciprocate the striker that applies a striking force to the hammer bit. The counter weight reciprocates within a gear housing in a direction opposite to the direction of the striker being driven by the crank arm mechanism. Such movement of the counter weight in the opposite direction can effectively reduce and alleviate vibration in the axial direction of the hammer bit during the operation of the hammer. 
   Such a counter weight requires considerable dimensions in order to appropriately reduce strong vibration during the operation of the hammer. Accordingly, the space for receiving such a dynamic vibration reducer also requires considerable spaces within the hammer. Further, in some cases, no need does exist to mount the counter weight in the hammer, depending on the operating conditions, user needs, etc. Therefore, a further improvement is desired in the rational design of the counter weight in the electric hammer. 
   SUMMARY OF THE INVENTION 
   It is, accordingly, an object of the present invention to provide an electric hammer with improved construction, while ensuring the vibration reduction performance. 
   According to the present invention, a representative electric hammer may include a hammer bit, a driving motor, a crank mechanism and a counter weight. The crank mechanism drives a striker by converting a rotating output of the driving motor to linear motion in the axial direction of the hammer bit. The counter weight is detachably mounted to the crank mechanism and serves to reduce vibration of the striker. 
   According to the representative hammer, because the counter weight is detachably mounted to the crank mechanism, it is possible to switch between the mode in which the counter weight is mounted on the hammer body in order to reduce and alleviate vibration and the mode in which the counter weight is removed from the hammer so that the operation can be performed with the hammer having a lighter weight and slimmer appearance. Thus, utility of the electric hammer can be improved. 
   Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view showing an entire hammer  100  according to the first representative embodiment of the invention. 
       FIG. 2  is a sectional view showing an entire hammer  101  according to the representative embodiment of the invention. In  FIG. 2 , a dynamic vibration reducer  301  is detachably mounted to the hammer  101  in comparison with the hammer  100  as shown in FIG.  1 . 
       FIG. 3  is a partially sectional view showing an essential part of the representative hammer  101 . 
       FIG. 4  is a schematic view showing the construction of the counter weight driving device. 
       FIG. 5  is a partially sectional view showing the construction of the modified hammer  102 . 
   

   DETAILED DESCRIPTION OF THE REPRESENTATIVE EMBODIMENT OF INVENTION 
   According to the present invention, a representative electric hammer may include a hammer bit, a driving motor, a crank mechanism and a counter weight. The electric hammer may suitably embrace not only a hammer of the type which performs a hammering function by reciprocating motion of the hammer bit in the axial direction, but a hammer of the drill-hammer type which performs a drilling function by rotation of the hammer bit, as well as the hammering function. The crank mechanism drives a striker by converting a rotating output of the driving motor to linear motion in the axial direction of the hammer bit. The counter weight serves to reduce vibration of the striker. Specifically, the counter weight reciprocates in a direction opposite to the direction of the striker being linearly driven by the crank mechanism. As a result, the kinetic energy (momentum) of the counter weight and the striker is offset against each other, so that the vibration of the entire hammer is effectively reduced. 
   In the present invention, the counter weight having such function is detachably mounted to the crank mechanism. Therefore, it is possible to switch as appropriate between the mode in which the counter weight is mounted on the hammer body in order to reduce and alleviate vibration and the mode in which the counter weight is removed from the hammer so that the operation can be performed with the hammer having a lighter weight and slimmer appearance, in relation to the operating manners, the need for dynamic vibration reduction or other similar conditions. Further, whether the counter weight is mounted or not is left to the user&#39;s discretion, while the hammer is designed such that the counter weight can be mounted. In this manner, the cost and convenience of the electric hammer can be advantageously controlled. Preferably, the counter weight may be mounted and removed through the opening formed over the crank cap or the crank mechanism. 
   Preferably, a dynamic vibration reducer may be detachably mounted to the hammer according to the present invention. The dynamic vibration reducer may have a body, a weight that is housed in the body and an elastic element that connect the weight to the body. The weight is connected to the body at least by an elastic element. In addition, the weight may preferably be connected to the body by an attenuating element. According to the present invention, in addition to the counter weight, the dynamic vibration reducer serves to reduce and alleviate vibration from the reciprocating motion of the crank mechanism. Thus, the vibration which has not been reduced by the counter weight is further alleviated by the dynamic vibration reducer, so that reliable measures can be taken against vibration in the electric hammer. 
   Furthermore, the dynamic vibration reducer functions as a passive vibration reducing mechanism which starts the vibration reducing motion according to the vibration of the vibrating body. Therefore, the dynamic vibration reducer effectively works not only to reduce vibration from the crank mechanism but to reduce vibration when the motion of the counter weight does not offset the motion of the crank mechanism. Further, like the counter weight, the dynamic vibration reducer is detachably mounted to the hammer. Therefore, it is possible to switch as appropriate between the mode in which the dynamic vibration reducer is mounted on the hammer body in order to reduce vibration and the mode in which the dynamic vibration reducer is removed from the hammer so that the operation can be performed with the hammer having a lighter weight and slimmer appearance, according to the operating manners, the need for dynamic vibration reduction or other similar conditions. Further, whether the dynamic vibration reducer is mounted or not is left to the user&#39;s discretion, while the hammer is designed such that the dynamic vibration reducer can be mounted. In this manner, the cost and convenience of the electric hammer can be advantageously controlled. Preferably, the dynamic vibration reducer may be mounted and removed through the opening formed over the crank cap or the crank mechanism. 
   As mentioned above, the counter weight according to the present invention reciprocates in a direction opposite to the reciprocating direction of the striker being driven by the crank mechanism, thereby reducing vibration from the striker. The electric hammer operates either in the mode in which the hammer bit performs a predetermined operation on the workpiece, i.e. the mode in which load is applied to the hammer bit (loaded driving conditions), or, in the mode in which the hammer bid does not operate, i.e. the mode in which load is not applied to the hammer bit (unloaded driving conditions). Therefore, the counter weight, which is essentially provided in order to reduce vibration of the driver under loaded driving conditions, may possibly cause vibration under unloaded driving conditions. 
   In this connection, according to the present invention, the dynamic vibration reducer effectively serves to reduce and alleviate vibration when the counter weight causes vibration under unloaded driving conditions. Specifically, under loaded driving conditions, the dynamic vibration reducer performs vibration reduction of the striker in cooperation with the counter weight of which driving is timed so as to be adapted to the loaded driving conditions. Further, under unloaded driving conditions, the dynamic vibration reducer can perform vibration reduction with respect to the counter weight as well as the striker. 
   Preferably, the crank mechanism may comprise a gear, an eccentric pin and a crank arm. The gear may be drivingly rotated by an output shaft of the driving motor. The eccentric pin may be eccentrically mounted on the gear and revolves with rotation of the gear. One end of the crank arm may be connected to the eccentric pin and the other end may be connected to the hammer bit striking mechanism, so that the crank arm causes the hammer bit striking mechanism to reciprocate and thus drives the striker. Further, the representative hammer may preferably include a counter weight driving mechanism that is removably connected to the eccentric pin and reciprocates in the axial direction of the hammer bit, thereby driving the counter weight to reciprocate. With this construction, the mechanism for driving the counter weight is removably disposed on the mechanism for driving the crank arm by the driving motor via the output shaft and the gear, so that the counter weight can be efficiently driven. 
   Additionally, the representative electric hammer may preferably be constructed in which the counter weight driving device has an eccentric pin sliding groove. The eccentric pin may be removably fitted in the eccentric pin sliding groove and allowed to slide with respect to the sliding groove. With this construction, the counter weight driving device for driving the counter weight may engage with the eccentric pin that is mounted on the crank mechanism in order to drive the crank arm, via the eccentric pin sliding groove. The eccentric pin may slide with respect to the counter weight driving device within the sliding groove. When the eccentric pin slides, the counter weight reciprocates via the revolution of the eccentric pin which is caused by rotation of the gear. Further, with the construction in which the eccentric pin is fitted in the sliding groove, the mounting accuracy between the eccentric pin and the sliding groove can be roughly set. Therefore, the cost efficiency in manufacturing and the workability in mounting can be improved. 
   Further, the representative electric hammer may preferably be constructed in which the counter weight driving device includes a second crank arm. One end of the second crank arm may removably be connected to the eccentric pin and the other end may be connected to the counter weight. With this construction, the reciprocating motion of the counter weight can be obtained via the second crank arm, one end of which is removably connected to the eccentric pin that is provided on the crank mechanism in order to drive the crank arm and the other end is connected to the counter weight. Further, the gear and the eccentric pin which form the crank mechanism and the second crank arm which forms the counter weight driving device are arranged as an integral rigid body. Therefore, these elements can be readily supported with stability when drivingly rotated by the output shaft of the driving motor. Furthermore, because the second crank arm is removably connected to the eccentric pin, when it becomes unnecessary, the counter weight can be removed together with the second crank arm, so that the construction of the electric hammer can be readily simplified. In order to removably connect the second crank arm to the eccentric pin, preferably, a screw or bolt may be utilized. 
   Moreover, the representative electric hammer may preferably be constructed in which the counter weight and the counter weight driving device can be mounted and removed through the crank cap that is used to dispose the crank arm in the hammer body or through the opening formed above the crank mechanism. With this construction, the existing crank cap or opening above the crank mechanism can be utilized to mount or remove the counter weight and the counter weight driving device. Thus, an electric hammer having efficient construction can be obtained. Further, like the counter weight, preferably, the dynamic vibration reducer may be configured to be mounted and removed through the crank cap. 
   Each of the additional features and method steps disclosed above and below may be utilized separately or in conjunction with other features and method steps to provide improved electric hammer and method for using such electric hammer and devices utilized therein. Representative examples of the present invention, which examples utilized many of these additional features and method steps in conjunction, will now be described in detail with reference to the drawings. This detailed description is merely intended to teach a person skilled in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed within the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe some representative examples of the invention, which detailed description will now be given with reference to the accompanying drawings. 
   A hammer according to a representative embodiment of the present invention will now be described with reference to the drawings.  FIG. 1  shows a representative hammer  100  with a counter weight  201 .  FIG. 2  shows the representative hammer  101  with a counter weight  201  and a dynamic vibration reducer  301 . The hammers  100  and  101  utilize equivalent elements except for a dynamic vibration reducer  301 . Such elements will be designated by the same numerals in the drawings and the following description. 
   As shown in  FIG. 1 , the representative hammer  100  according to this embodiment comprises a body  103  having a motor housing  105  and a gear housing  107 . A hammer bit coupling portion  111  for coupling a hammer bit  129  to the body  103  is provided in the tip end region of the gear housing  107 . Further, a handgrip  113  is provided on the rear end side of the motor housing  105  and the gear housing  107 . 
   The motor housing  105  houses a driving motor  121 . An opening  110  is formed in the upper surface of the gear housing  7  and a crank cap  109  is disposed within the opening  110 . A counter weight  201  and/or a dynamic vibration reducer  301  (see FIG.  2 ), which is described below in detail, are detachably mounted to the body  103  through the opening  110 . 
   The gear housing  107  houses a motion converting mechanism  123 , a cylinder mechanism  125  and a striking element  127 . The motion converting mechanism  123  is adapted to convert the rotating output of the driving motor  121  to linear motion in the axial direction of the hammer bit  129 . The cylinder mechanism  125  is driven via the motion converting mechanism  123 . The striking element  127  mainly includes a striker  128  that applies an impact force to the hammer bit  129  in the axial direction by a striking force obtained from the cylinder mechanism  125 . 
   The counter weight  201  is detachably mounted on the motion converting mechanism  123  of the hammer  100  and in the region right under the opening  110 . The counter weight  201  is used to reduce vibration in the axial direction of the hammer bit  129 , which vibration is developed in the motion converting mechanism  123 . 
   In the hammer  101  as shown in  FIG. 2 , in addition to the above-mentioned construction of the hammer  100 , the dynamic vibration reducer  301  is detachably mounted on the counter weight  201  and in the region right above the opening  110 . During loaded driving operation of the hammer  101 , the dynamic vibration reducer  301  serves to reduce and alleviate vibration in the axial direction of the hammer bit  129  which is developed in the motion converting mechanism  123 , by cooperation with the counter weight  201 . Further, during unloaded driving operation of the hammer  101 , the dynamic vibration reducer  301  is adapted to reduce and alleviate vibration caused by the counter weight  201  as well as vibration developed in the motion converting mechanism  123 . 
     FIG. 3  shows an essential part of the hammer  101  including the counter weight  201  and the dynamic vibration reducer  301 . The hammer  100  as shown in  FIG. 1  has the same construction as the hammer  101  shown in  FIG. 2  except for whether the dynamic vibration reducer  301  is mounted or not. Therefore, in order to avoid duplication of explanation, as for description and illustration of the detailed construction of the essential parts of the hammer  100 , description and illustration relating to the hammer  101  will also be utilized. 
   As shown in  FIG. 3 , the motion converting mechanism  123  of the hammer  101  includes a speed change gear  135 , a gear shaft  137 , an upper bearing  138   a  and a lower bearing  138   b , an eccentric pin  139  and a crank arm  143 . The speed change gear  135  is rotated by engaging a gear portion  133  of the output shaft  131  of the driving motor  121 . The gear shaft  143  integrally rotates with the speed change gear  135 . The upper and lower bearings  138   a  and  138   b  rotatably support the gear shaft  137 . The eccentric pin  139  is eccentrically disposed in a position displaced from the center of rotation of the speed change gear  135  (or the center of rotation of the gear shaft  137 ). One end of the crank arm  143  is connected to the eccentric pin  139  via an eccentric pin bearing  141 , and the other end of the crank arm  143  is connected to a driver  145  that is disposed within a cylinder  147 . The driver  145  slides within the cylinder  147  so as to linearly drive a striker, which is not shown for the sake of convenience, by a so-called air spring function. As a result, the driver  145  generates impact loads upon the hammer bit  129  shown in FIG.  2 . 
   Further, in the present embodiment, the counter weight  201  and a counter weight driving device  203  are provided on the motion converting mechanism  123 . The counter weight driving device  203  includes a counter weight driving crank  205  and a crank pin  207 . The counter weight driving crank  205  has an eccentric pin guide groove  209 . The eccentric pin  139  engages the guide groove  209  and is thus connected to the counter weight driving crank  205 . The crank pin  207  is integrally formed with the counter weight driving crank  205  on its front end region (left end region as viewed in FIG.  3 ). The counter weight driving crank  205  is rotatably supported by the inner peripheral surface of the crank cap  109  via a bearing  206  and can rotate within the horizontal plane. 
   The dynamic vibration reducer  301  is disposed on the counter weight  201  and the counter weight driving device  203 . The dynamic vibration reducer  301  has an elongated hollow cylindrical body  303 . The cylindrical body  303  is a feature that corresponds to the “body” of the dynamic vibration reducer according to the present invention. A weight  305  is disposed within the cylindrical body  303  and extends in the axial direction of the body  303 . The weight  305  has a large-diameter portion  313  and a small-diameter portion  315 . A biasing spring  317  is mounted on the right and left sides of the large-diameter portion  313 . The biasing spring  317  is a feature that corresponds to the “elastic element” according to the present invention. The biasing spring  317  exerts an elastic force on the weight  305  between the spring and the body  303  while moving in the axial direction of the body  303 . 
   The counter weight  201  and the counter weight driving device  203  are mounted in the opening  110  of the hammer  101 , and the dynamic vibration reducer  301  is mounted right on the opening  110 . The counter weight  201 , the counter weight driving device  203  and the dynamic vibration reducer  301  can be readily mounted to and removed from the hammer  101 . The counter weight driving device  203  can be removed above the opening  110  together with the crank cap  109  as mentioned above. Thus, efficiency in the mounting and dismounting operation can be ensured. The eccentric pin  139  of the speed change gear  135  is only loosely and removably fitted from below in the eccentric pin guide groove  209  of the counter weight driving crank  205 . Thus, the eccentric pin  139  does not impair the removability of the counter weight driving device  203 . 
   Hammer  101  according to this embodiment is constructed as described above. Operation and usage of the hammer  101  will now be explained. When the driving motor  121  is driven, the torque of the driving motor  117  is transmitted to the speed change gear  135  via the output shaft  131  and the gear portion  133  of the output shaft  131 . Thus, the speed change gear  135  is rotated together with the gear shaft  137 . When the speed change gear  135  rotate, the eccentric pin  139  revolves around the axis of rotation of the gear shaft  137 , which in turn causes the crank arm  143  to reciprocate rightward and leftward as viewed in the drawings. Then, the driver  145  reciprocates within the bore of the cylinder  147 . 
   When the driver  145  reciprocates, a striker (not shown) collides with an impact bolt (not shown) at a speed higher than the driver  145  by the action of the air spring function as a result of the compression of the air within the cylinder  147  between the striker and the impact bolt. As a result, the hammer bit  129  (see  FIG. 2 ) reciprocates at a higher speed by the kinetic energy caused by the collision. Thus, the hammering operation is performed on a workpiece (not shown). 
   In this embodiment, the counter weight  201  is driven by using the revolution of the eccentric pin  139  of the motion converting mechanism  123  as shown in FIG.  3 . With respect to the manner of driving the counter weight  201 , the relationship of the eccentric pin  139 , the counter weight driving crank  205 , the eccentric pin guide groove  209 , the crank pin  207  and the counter weight  201  is schematically shown in FIG.  4 . As described above, when the eccentric pin  139  revolves around the axis of rotation of the gear shaft  137 , the eccentric pin guide groove  209  receives the revolution of the eccentric pin  139 , which causes the counter weight driving crank  205  to rotate. Then, the crank pin  207  eccentrically disposed on the counter weight driving crank  205  revolves in a position diametrically opposed to the eccentric pin  139 . 
   Further, due to the construction in which the eccentric pin  139  is loosely fitted in the eccentric pin guide groove  209 , it is not necessary to mount it with high accuracy. Therefore, the cost effectiveness and mountability can be improved in such a hammer. 
   A crank pin guide slot  211  is formed in the counter weight  201  and extends in a direction crossing the longitudinal direction of the counter weight  201  (in a vertical direction as viewed in FIG.  4 ). The revolving motion of the crank pin  207  has a linear motion component in the longitudinal direction of the counter weight  201 . Solely this linear motion component is transmitted to the counter weight  201 . Thus, the counter weight  201  reciprocates in a direction opposite to the direction of the revolution of the eccentric pin  139  or to the reciprocating direction of the striker  128 . 
   Thus, when the striker is caused to reciprocate by the crank arm  143  reciprocating in the longitudinal direction of the hammer  101  (rightward and leftward as viewed in FIG.  3 ), the counter weight  201  reciprocates in a direction opposite to the reciprocating direction of the striker. As a result, the dynamic vibration of the striker is efficiently reduced. Further, in the present embodiment, in addition to the vibration reducing function of the counter weight  201 , the dynamic vibration reducer  301  also serves to reduce dynamic vibration of the striker  128 . Therefore, vibration which will be developed during operation of the hammer  101  can be considerably reduced, so that ease of use and the quietness of the hammer  101  can be improved. 
   The counter weight  201  of the present embodiment is configured to perform the vibration reducing function by reciprocating in a direction opposite to the reciprocating direction of the striker  128  under loaded driving conditions. Therefore, the counter weight  201  effectively performs the vibration reducing function under loaded driving conditions. However, to the contrary, under unloaded driving conditions, the counter weight  201  may possibly become a source of vibration because counter weight  201  is driven while the object of vibration reduction for the counter weight  201  does not move. 
   In this embodiment, under such unloaded driving conditions, even if the vibration is caused by the counter weight  201 , the above-mentioned dynamic vibration reducer  301  effectively performs the vibration reducing function against such vibration. Specifically, in the hammer according to this embodiment, under loaded driving conditions, the dynamic vibration reducer  301  serves to reduce vibration of the striker  128  in cooperation with the counter weight  201  of which phase has been adjusted in relation to the loaded driving conditions. Under unloaded driving conditions, the dynamic vibration reducer  301  serves to reduce vibration of the counter weight  201  as well as the striker  128 . 
   Moreover, in this embodiment, the counter weight  201  and the counter weight driving device  203  can be readily removed from the hammer  101  through the opening  110  above the crank cap  109 . Further, the dynamic vibration reducer  301  can be easily detached from above the opening  110 . Whether each of these vibration reducing elements is mounted or removed can be selected according to the operating manners, the need for dynamic vibration reduction or other similar conditions. Thus, the cost, convenience, outer dimensions, weight or other similar factors of the hammer can be efficiently adjusted. 
   A hammer according to a modification of this embodiment will be explained with reference to FIG.  5 . The hammer  102  is a modification made with respect to the manner of connection between the eccentric pin  139  and the counter weight driving device  203 . Elements having the same effects as in the hammers  100 ,  101  will be designated by the same numerals in the drawings and will not be described below in detail. 
   As shown in  FIG. 5 , the eccentric pin  139  on the speed change gear  135  is removably fixed to the counter weight driving crank  205  via a lock pin  139   a . The counter weight driving crank  205  forms an essential part of the counter weight driving device  203  and can rotate with respect to the crank cap  109  via a bearing  206  in the lower region of the opening  110 . The counter weight  201  reciprocates in the longitudinal direction of the hammer  102  (rightward and leftward as viewed in  FIG. 5 ) as the counter weight driving crank  205  rotates. In this manner, the counter weight  201  serves to reduce vibration from the reciprocating motion of the crank arm  143 . 
   In this modification, because the eccentric pin  139  is fixed to the counter weight driving crank  205  via the lock pin  139   a , the speed change gear  135 , the gear shaft  137 , the eccentric pin  139 , the lock pin  139   a  and the counter weight driving crank  205  are integrally rotated as one rigid body. Therefore, the stability of such driving rotation can be ensured simply by rotatably supporting the upper and lower portions of the integral rigid body in an appropriate manner. In this modification, an upper bearing  206  and a lower bearing  138   a  are used as such supports for rotatably supporting the integral rigid body. Thus, in this modification, it is not necessary to provide a support for the speed change gear  135  and the gear shaft  137  and a support for the counter weight driving crank  205  separately. Simply the integral rigid body having a considerable height needs to be rotatably supported. Therefore, even if the mounting accuracy of each component is roughly set to some reasonable extent, the driving rotation will not be easily impaired. Thus, an effective construction can be achieved in terms of simplification of the internal mechanism and stable support of the rotational elements. 
   Furthermore, these elements can be removed through the opening  110  simply by releasing the lock between the eccentric pin  139  and the counter weight driving crank  205  via the lock pin  139   a . Thus, the removability of the vibration reducing mechanism can be further improved. 
   DESCRIPTION OF NUMERALS 
   
       
         100 ,  101 ,  102  hammer 
         103  body 
         105  motor housing 
         107  gear housing 
         109  crank cap 
         109  hammer bit mounting chuck 
         110  opening 
         111  hammer bit coupling portion 
         113  hand grip 
         121  driving motor 
         123  motion converting mechanism 
         125  cylinder mechanism 
         127  striking element 
         128  striker 
         129  hammer bit 
         131  output shaft 
         133  gear portion 
         135  speed reduction gear 
         137  gear shaft 
         138   a ,  138   b  gear shaft bearing 
         139  eccentric pin 
         141  eccentric pin bearing 
         143  crank arm 
         145  driver 
         147  cylinder 
         201  counter weight 
         203  counter weight driving device 
         205  counter weight driving crank 
         206  crank bearing 
         207  crank pin 
         209  eccentric pin guide groove 
         211  crank pin guide groove 
         301  dynamic vibration reducer 
         303  cylindrical body (body) 
         305  weight 
         313  large-diameter portion 
         315  small-diameter portion 
         317  biasing spring (elastic element)