Abstract:
It is an object of the invention to provide an effective technique for enhancing the effect of reducing vibration of a grip of a reciprocating power tool. According to the present invention, a representative reciprocating power tool may comprise a tool bit, a tool body and a grip. The grip is connected to the tool body via an elastic element and a vibration damping part. The elastic element is resiliently disposed between the tool body and the grip and serves to absorb vibration transmitted from the tool body to the grip during operation. The vibration damping part is disposed between the tool body and the grip and serves to damp and/or attenuate the vibration. According to the invention, the spring constant of the elastic element can be made smaller due to vibration damping part.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a reciprocating power tool and more particularly, to a mounting structure of a grip of a hand-held reciprocating power tool such as an electric hammer and hammer drill reciprocating a tool bit at a certain cycle. 
   2. Description of the Related Art 
   Japanese non-examined laid-open Utility Model Publication No. 1-18306 (D1) discloses an electric hammer having a vibration-proof grip. In the known electric hammer, the grip that the user holds is connected via an elastic element made of rubber to a body of the hammer in which vibration is caused. 
   With such construction, vibration transmitted from the hammer body to the grip can be absorbed via the elastic element. In order to maximize the effect of absorbing vibration, the spring constant of the elastic element must be small. However, if the spring constant is small, the grip and the hammer body are held unsteady with respect to each other and therefore, the spring constant of the elastic element must be set large enough to avoid such unsteadiness. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the invention to provide an effective technique for enhancing the effect of reducing vibration of a grip of a reciprocating power tool. 
   According to the present invention, a representative reciprocating power tool may comprise a tool bit that performs an operation by reciprocating in the axial direction, a tool body that houses an actuating mechanism for driving the tool bit, and a grip mounted on the rear end of the body on the side opposite to the tool bit. The “reciprocating power tool” typically comprises any tool of the type which performs an operation while the user holds the grip and applies a pressing force on the grip in the direction of the tool body. Specifically, the “reciprocating power tool” includes impact power tools such as an electric hammer and a hammer drill, which performs fracturing or drilling operation on a workpiece by causing a tool bit to perform only hammering movement in the axial direction or the hammering movement and rotation in the circumferential direction in combination. In addition to such impact power tools, it may include cutting tools such as a reciprocating saw or a jig saw, which performs a cutting operation on a workpiece by causing a blade to perform a reciprocating movement. 
   According to the invention, the grip is connected to the tool body via an elastic element and a vibration damping part. The elastic element is resiliently disposed between the tool body and the grip and serves to absorb vibration transmitted from the tool body to the grip ring operation. The vibration damping part is also disposed between the tool body and the grip and serves to damp and/or attenuate the vibration. Preferably, the direction of input of the biasing force of the elastic element and the direction of damping action of the vibration damping part may generally coincide with the direction of input of vibration or the axial direction of the tool bit. The “elastic element” may comprise a rubber or a spring. 
   Further, the manner of “damping vibration” typically includes the manner of damping vibration by utilizing frictional resistance that acts on the sliding parts when two elements move in contact with each other. Otherwise, the manner of damping vibration by utilizing resistance produced when fluid passes though an orifice within a space of which capacity varies by the relative movement of the two elements. According to the invention, because the vibration during the operation of the power too is reduced by the elastic element in association with the vibration damping part, the spring constant of the elastic element can be made smaller without causing unstable connection between the tool body and the grip. Therefore, vibration transmitted from the tool body to the grip during operation by the reciprocating power tool is effectively reduced by the vibration absorbing action caused by the elastic deformation of the elastic body and by the damping action of the vibration damping part. 
   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 side view showing an entire electric hammer according to an embodiment of the invention. 
       FIG. 2  is a side sectional view, showing the construction for mounting the upper end portion of a handgrip to the body. 
       FIG. 3  is a partial plan sectional view of the handgrip. 
       FIG. 4  is a sectional view taken along line IV-IV in  FIG. 3 . 
       FIG. 5  is an enlarged view of the circled part A in  FIG. 4 . 
       FIG. 6  schematically shows the construction for mounting the handgrip to the body. 
       FIG. 7  schematically shows a modification of a vibration damping mechanism. 
       FIG. 8  schematically shows a modification of the vibration damping mechanism. 
       FIG. 9  schematically shows a modification of the vibration damping mechanism. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   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 and manufacture improved reciprocating power tools and method for using such reciprocating power tools 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 representative embodiment of the present invention will now be described with reference to the drawings.  FIG. 1  is a side view of an entire electric hammer  101  as a representative embodiment of a reciprocating power tool according to the invention. As shown in  FIG. 1 , the electric hammer  101  includes a body  103 . The body  103  is a feature that corresponds to the “tool body” according to the invention. The body  103  includes a motor housing  105 , a gear housing  107  and a tool holder  109  in the tip end (front end) region of the gear housing  107 . A hammer bit  111  is mounted in the tool holder  109  such that the hammer bit  111  can move in the axial direction with respect to the tool holder  109  and can rotate in the circumferential direction together with the tool holder  109 . The hammer bit  111  is a feature that corresponds to the “tool bit” according to the invention. Further, a handgrip  113  held by the user during operation is mounted on the rear end of the body  103 . In the embodiment, for the sake of convenience of explanation, the side of the hammer bit  11  is taken as the front side and the side of the handgrip  113  as the rear side. 
   An impact driving mechanism (not shown) is disposed within the body  103  and serves to transmit a striking movement to the hammer bit  111  retained by the tool holder  109 . The impact driving mechanism is know in the art and therefore will be explained only briefly. A driving motor as a source is disposed within the motor housing  105 . The rotating output of the driving motor is converted into reciprocating motion of a piston via a crank mechanism disposed within the gear housing  107 . When the piston linearly moves, a striker linearly moves toward the tip end (forward) at high speed by the action of a so-called air spring caused within the cylinder by the linear movement of the pistol. The striker then collides with an impact bolt as an intermediate element. The impact bolt, in turn, linearly moves forward at high speed and collides with the hammer bit  111 . The hammer bit  11  then linearly moves in the axial direction (forward) at high speed. Thus, the hammer bit  11  performs a striking (hammering) movement and as a result, hammering operation such as chipping is performed on a workpiece (not shown). The driving motor  113  is stud or stopped by operating a trigger  115  on the handgrip  113  to turn a power switch to the “ON” or “OFF” position. 
   The striker and the impact bolt form a striking mechanism which transmits a striking movement to the hammer bit  111 . The striking mechanism and the hammer bit  111  move linearly substantially along the same line. Upon striking movement of the hammer bit  111 , vibration is caused in the body  103  in the axial direction of the hammer bit  111 . In order to reduce transmission of such vibration to the handgrip  113 , the handgrip  113  is mounted to the body  103  in the following manner. The construction for mounting the handgrip  113  to the body  103  will now be explained with reference to  FIGS. 1 to 6 .  FIG. 2  is a partial side sectional view showing the construction for mounting the upper end portion of the handgrip  113  to the body  103 .  FIG. 3  is a partial plan sectional view also showing the mounting construction of the upper end portion of the handgrip  113 .  FIG. 4  is a sectional view taken along line IV-IV in  FIG. 3 .  FIG. 5  is an enlarged view of the circled part A in  FIG. 4 .  FIG. 6  schematically shows the construction for mounting the handgrip  113  to the body  103 . 
   The handgrip  113  comprises a synthetic resin covering  121  and a grip  123 . The covering  121  is arranged to cover the rear portion of the body  103 . The grip  123  comprises a metal portion and a synthetic resin potion joined together and is mounted to the covering  121 . The covering  121  is fastened to the rear portions of the gear housing  107  and motor housing  105  which form the body  103 , by screws (not shown) at predetermined several points. Therefore, the covering  121  is secured to the body  103  and substantially defined as a member on the body  103  side. 
   As shown in  FIGS. 1 and 2 , the grip  123  extends vertically in a direction crossing the axial direction of the hammer bit  111 . Mounting legs  123   a  and  123   b  extend a predetermined length from the extending ends or the upper and lower ends of the grip  123  in a direction generally parallel to the axial direction of the hammer bit  111  (in a horizontal direction). The grip  123  having the mounting legs  123   a,    123   b  is thus generally U-shaped in side view. As schematically shown in  FIG. 6 , the upper end mounting leg  123   a  is connected to the body  103  via an elastic element in the form of a coil spring  131  and a vibration damping mechanism  141 . The lower end mounting leg  123   b  is connected to tile body  103  via a pivot  127  such that it can pivot with respect to the body  103 . The construction for mounting the mounting legs  123   a,    123   b  will now be explained. 
   As shown in  FIGS. 2 and 3 , the coil spring  131  is resiliently disposed between the mounting leg  123   a  on the upper end of the grip  123  and the gear housing  107  and serves to absorb vibration of the grip  123  during operation. The coil spring  131  is a feature that corresponds to the “elastic element” according to the invention. The coil spring  131  is disposed such that the direction of action of its spring force generally coincides with the axial direction of the hammer bit  111  or the direction of input of vibration. The coil spring  131  is disposed in a position near a line of travel P of the reciprocating hammer bit  111  or in a position slightly above a line of extension of the axis of the hammer bit  111 . One end of the coil spring  131  is supported by a spring receiver  133  on the grip  123  side. The other end of the coil spring  131  extends into the gear housing  107  through the covering  121  and is supported by a spring receiver  135  fixed on the gear housing  107 . The mounting leg  123   a  on the upper end of the grip  123  is thus connected to the body  103  via the coil spring  131 . The spring receiver  133  on the grip  123  side also serves to hold an elastic cover  137  which will be described below. 
   The mounting leg  123   b  on the lower end of the grip  123  is connected to the rear lower end of the covering  121  via the pivot  127  such that it can pivot on the horizontal pivot with respect to the body  103 . The grip  123  is designed such that the direction of the relative pivotal movement via the pivot  127  generally coincides with the axial direction of the hammer bit  111  or the direction of input of vibration. With such construction, the vibration absorbing function of the coil spring  131  is effectively performed with respect to the vibration in the axial direction of the hammer bit  111  transmitted from the body  103  to the grip  123  via the covering  121 . 
   Further, as shown in  FIGS. 3 and 4 , the mounting leg  123   a  on the upper end of the grip  123  is connected to the covering  121  on the body  103  side via the vibration damping mechanism  141  that damps and attenuates vibration by means of friction. The vibration damping mechanism  141  is a feature that corresponds to the “vibration damping part” according to the invention. The vibration damping mechanism  141  comprises a rod-like element  143  and a cylindrical element  145  that move (pivot on the pivot  127 ) with respect to each other. The rod-like element  143  is a feature that corresponds to the “grip-side sliding part” and the “first element”, and the cylindrical element  145  corresponds to the “body-side sliding part” and the “second element” according to the invention. The rod-like element  143  is a linear element that is integrally formed with the mounting leg  123   a  on the upper end of the grip  123 . The rod-like element  143  extends generally parallel to the travel line P of the hammer bit  111  (and thus generally parallel to the coil spring  131 ) from the mounting leg  123   a  toward the gear housing  107 . The rod-like element  143  is inserted into the bore of the cylindrical element  145  integrally formed with the covering  121  such that the rod-like element  143  can move with respect to the cylindrical element  145 . Further, a stopper bolt  149  is screwed into the rod-like element  143  from the covering  121  side and a head  149   a  of the stopper bolt  149  contacts the end surface of the cylindrical element  145 , so that the rod-like element  143  is prevented from coming off. 
   The rod-like element  143  and the cylindrical element  145  are disposed on the both sides of the coil spring  131 . As shown in  FIG. 4 , the rod-like element  143  and the cylindrical element  145  have a generally oval section having flat side surfaces or width across flats. Specifically, the outer surface of the rod-like element  143  and the inner surface of the cylindrical element  145  have side regions configured as vertical flat surfaces  143   a,    145   a  and upper and lower regions configured as circular arc surfaces  143   b,    145   b.  As shown in  FIG. 5  in enlarged view, a predetermined clearance is provided between the outer surface of the rod-like element  143  and the inner surface of the cylindrical element  145 . Thus, the rod-like element  143  is loosely fitted into the cylindrical element  145 . A projection  147  is formed on one of the flat surface  143   a  or side region of the rod-like element  143  and the flat surface  145   a  or side region of the cylindrical element  145 . In this embodiment, the projection  147  is formed on the flat surface  143   a  of the rod-like element  143  and contacts the flat surface  145   a  of the cylindrical element  145 . The projection  147  causes friction (resistance to the sliding movement) by sliding in contact with the flat surface  145   a  of the cylindrical element  145  when the rod-like element  143  moves with respect to the cylindrical element  145 . By this friction, vibration which is transmitted from the body  103  to the grip  123  during operation is damped. The projection  147  and the flat surface  145   a  of the cylindrical element  145  which contacts the projection  147  are features that correspond to the “sliding part” according to the invention. 
   The relative movement of the rod-like element  143  and the cylindrical element  145  is defined by a pivotal movement around the pivot  127 . Therefore, the clearance between the circular arc surface  143   b  of the rod-like element  143  and the circular arc surface  145   b  of the cylindrical element  145  is designed to be large enough to avoid interference between the rod-like element  143  and the cylindrical element  145 . 
   The coil spring  131  and the vibration damping mechanism  141  are covered with a rubber elastic cover  137  disposed between the mounting leg  123   a  on the upper end of the grip  123  and the covering  121 . The elastic cover  137  has a bellows-like cylindrical shape. One open edge of the elastic cover  137  is fitted on the inner surface of the mounting leg  123   a  and anchored by the spring receiver  133  on the mounting leg  123  side. The other open edge of the elastic cover  137  is fastened by engaging with an annular engaging groove  139  that is formed in the covering  121 . 
   Operation and usage of the electric hammer  101  constructed as described above will now be explained. When the trigger  115  is depressed to turn on the power switch and the driving motor  113  is driven, the rotating output of the driving motor is converted into linear motion via the crank mechanism, as mentioned above. Further, the linear motion is transmitted to the hammer bit  111  as striking movement via the striking mechanism that comprises the striker and the impact bolt. Thus, the hammering operation is performed on the workpiece. The hammering operation by the electric hammer  101  is performed while the user holds the grip  123  and applies a pressing force on the grip  123  in the direction of the body  103 . When the pressing force is applied to the grip  123 , the mounting leg  123   a  on the upper end of the grip  123  rotates toward the body  103  (forward) around the pivot  127 . At this time, the coil spring  131  is compressed and deformed, and the head  149   a  of the stopper bolt  149  is caused to move apart from the cylindrical element  145  together with the rod-like element  143 . Thus, the grip  123  is allowed to pivot in the both directions around the pivot  127  with respect to the body  103 . 
   During such hammering operation by the electric hammer  101 , impulsive and cyclic vibration is caused in the body  103  when the hammer bit  111  is driven. The input of such vibration from the body  103  to the grip  123  is reduced and attenuated by the vibration absorbing action caused by elastic deformation of the coil spring  131  and by the vibration damping action caused by friction of the vibration damping mechanism  141 . Specifically, in the vibration damping mechanism  141 , friction (force of inhibiting relative movement) acts upon the contact part between the projection  147  of the rod-like element  143  and the flat surface  145   a  of the cylindrical element  145  which produce sliding friction in contact with each other. By this friction, the vibration damping mechanism  141  damps vibration which is to be transmitted to the grip  123  via the coil spring  131 . The coil spring  131  has a property of keeping rocking once it starts to rock. According to this embodiment, however, the rock of the coil spring  131  is controlled by friction of the vibration damping mechanism  141 . Thus, the input of vibration from the body  103  to the grip  123  can be effectively reduced by the vibration absorbing action of the coil spring  131  and by the damping action caused by friction of the vibration damping mechanism  141 . The degree of damping of the vibration damping mechanism  141  can be adjusted by changing the magnitude of friction that acts upon the contact part between the projection  147  and the flat surface  145   a  during sliding contact. Specifically, the magnitude of friction can be changed, for example, by changing the surface roughness, materials or area of the contact part or by changing the force acting upon the contact part in the direction perpendicular to the direction of movement. 
   Further, in this embodiment, the grip  123  is connected to the body  103  in a position near the source of vibration (near the travel line P of the hammer bit  111 ) via the coil spring  131  and the vibration damping mechanism  141 . The grip  123  is also connected to the body  103  in a position remote from the source of vibration via the pivot  127  such that it can pivot in the direction of input of vibration with respect to the body  103 . Thus, the vibration absorbing function of the coil spring  131  and the vibration damping function of the vibration damping mechanism  141  can be effectively performed. Further, the vibration damping mechanism  141  is disposed on the both sides of the coil spring  131  or on the both sides of the travel line P of the hammer bit  111 . Therefore, movements are produced on the both sides around an axis perpendicular to the travel line P of the hammer bit  111  by the sliding contact between the projection  147  of the rod-like element  143  and the flat surface  145   a  of the cylindrical element  145 , and such moments act in a manner of canceling each other out. As a result, undesired generation of moments due to provision of the vibration damping mechanism  141  is avoided. 
   Further, by the combined use of the coil spring  131  and the vibration damping mechanism  141 , the spring constant of the coil spring  131  can be freely and easily chosen without need of considering the “unsteadiness” which may be caused between the grip  123  and the body  103  if the grip  123  is connected to the body  103  only by the coil spring  131 . 
   Further, in this embodiment, with the construction in which the body  103  and the grip  123  are joined to each other via the pivot  127 , they are prevented from relative movement except for the pivotal movement around the pivot  127 . Therefore, the contact between the projection  147  of the rod-like element  143  and the flat surface  145   a  of the cylindrical element  145  can be held in a constant state, so that the friction in the sliding part can be stabilized. Further, the sliding part that comprises the projection  147  and the flat surface  145   a  is provided on the side regions of the rod-like element  143  and the cylindrical element  145 . Thus, the sliding part can be linearly configured on the rod-like element  143  and the cylindrical element  145  that pivot on the pivot  127  with respect to each other. Therefore, the sliding contact part can be easily provided while maintaining stable friction. 
   Now, modifications of the vibration damping mechanism  141  will be explained with reference to  FIGS. 7 to 9 . 
   In the above-mentioned embodiment, the cylindrical element  145  made of synthetic resin is in frictional contact with the rod-like element  143  made of metal. However, in the modification shown in  FIG. 7 , the rubber elastic cover  137  is in frictional contact with the metal rod-like element  143 . Specifically, an arm  151  is integrally formed with the elastic cover  137  and extends toward the rod-like element  143 . The end of the arm  151  is pressed against the rod-like element  143  by a predetermined pressing force from a direction crossing the direction of movement of the rod-like element  143 . In this state, the arm  151  slides with respect to the rod-like element  143 . In another modification shown in  FIG. 8 , an O-ring  153  is additionally disposed on the engaging surface between the rod-like element  143  and the cylindrical element  145  in the above-mentioned embodiment. According to the modifications shown in  FIGS. 7 and 8 , by utilizing the elastic deformation of the arm  151  and the O-ring  153 , a required biasing force can be applied to the sliding surface in a direction crossing the sliding direction. Further, the pivotal movement of the rod-like element  143  around the pivot  127  can be accommodated by the elastic deformation. Therefore, the rod-like element  143  may have, for example, a simple circular shape in section in order to enhance the manufacturability. 
   Further, according to a different modification as shown in  FIG. 9 , the vibration damping mechanism  141  comprises a fluid damper  155 . The fluid damper  155  includes a cylinder  156  mounted on the body  103  and a piston  157  mounted on the grip  123 . The piston  157  moves within the cylinder  156  when the body  103  and the grip  123  move with respect with each other. At this time, fluid resistance of the fluid passing through an orifice  158  within the cylinder  156  is utilized as a vibration damping force. Further different constructions other than the above-mentioned modifications can also be applied. For example, a plate spring or a resin spring may be provided and engaged with the friction sliding surface of the rod-like element  143  while applying the biasing force in a direction perpendicular to the direction of movement of the rod-like element  143 . 
   Instead of utilizing the coil spring  131  as an elastic element, a rubber may be used. Further, as to the mounting leg  123   b  on the lower end of the grip  123  rotatably connected to the body via the pivot  127 , it may be connected to the body via the coil spring  131  and the vibration damping mechanism  141  in the same manner as the mounting leg  123   a  on the upper end 
   Further, the friction sliding part is formed by the projection  147  and the flat surface  145   a  in this embodiment, but it may be formed by opposed flat surfaces. As for the projection  147  provided between the rod-like element  143  and the cylindrical element  145 , one or more projections  147  may be provided between each paw of the opposed flat surfaces  147 , or the projections  147  may continuously extend in the direction of the relative movement. In this case, the surface of the projecting end of the projection  147  which contacts the opposed flat surface  145   a  may comprise a flat surface or a spherical surface. 
   Further, in this embodiment, the electric hammer is described as a representative example of the reciprocating power tool. However, the invention may also be applied to a hammer drill which performs a drilling operation on a workpiece by causing a tool bit or a hammer bit to perform hammering movement in the axial direction and rotation in the circumferential direction. In addition to the impact power tools such as an electric hammer and a hammer drill, the invention may also be applied to cutting tools such as a reciprocating saw or a jig saw which perform a cutting operation on a workpiece by causing a tool bit or a blade to perform a reciprocating movement. 
   Further, the vibration damping part may be disposed on the both sides of a travel line of the tool bit. With such construction, moments produced on the both sides around an axis perpendicular to the travel line of the tool bit by the vibration damping action of the vibration damping part are canceled out to each other. As a result, undesired generation of moments due to provision of the vibration damping mechanism is avoided. Further, the vibration damping part may be disposed on the both sides of the travel line of the tool bit typically in such a manner that the sliding surfaces on the both sides of the travel line extend parallel to each other. 
   It is explicitly stated that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure as well as for the purpose of restricting the claimed invention independent of the composition of the features in the embodiments and/or the claims. It is explicitly stated that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure as well as for the purpose of restricting the claimed invention, in particular as limits of value ranges. 
   DESCRIPTION OF NUMERALS 
   
       
         101  electric hammer (reciprocating power tool) 
         103  body (tool body) 
         105  motor housing 
         107  gear housing 
         109  tool holder 
         111  hammer bit (tool bit) 
         113  handgrip 
         115  trigger 
         121  covering 
         123  grip 
         123   a  mounting leg on the upper end 
         123   b  mounting leg on the lower end 
         127  pivot 
         131  coil spring 
         133  spring receiver 
         135  spring receiver 
         137  elastic cover 
         139  engaging groove 
         141  vibration damping mechanism (vibration damping part) 
         143  rod-like element 
         143   a  flat surface 
         143   b  circular arc surface 
         145  cylindrical element 
         145   a  flat surface 
         145   b  circular arc surface 
         147  projection (sliding part) 
         149  stopper bolt 
         149   a  head 
         151  arm 
         153  O-ring 
         155  fluid damper 
         156  cylinder 
         157  piston 
         158  orifice