BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a power tool and more particularly, to a motor support structure of a power tool.  
         [0003]     2. Description of the Related Art  
         [0004]     Japanese non-examined laid-open Patent Publication No. 2004-106136 discloses an electric hammer drill used for drilling a workpiece such as a concrete. In the known electric hammer drill, a motor for driving a drill bit is disposed in the tip end (front end) region of the hammer drill and housed within a motor housing such that axial direction of the motor is parallel to the axial direction of the drill bit. A front portion on the tool bit side and a rear portion on the grip side of a rotating shaft of the motor are rotatably supported by respective bearings. A grip side bearing housing for housing the rear grip side bearing extends toward the grip and is covered by a grip cover disposed on the rear end portion of the motor housing.  
         [0005]     According to the known art, the grip side bearing housing for the rear bearing extends toward the grip, the extending end of the grip side bearing housing is free and as a result, vibration may be caused in the free end when the motor is driven. As a measure against such vibration, it is conceivable for example to provide an enforcing rib extending from the rear wall of the motor housing in order to increase the rigidity of the grip side bearing housing. However, on the other hand, the known hammer drill generally has a ring-like member operated by a user of the hammer drill to change the direction of rotation of the motor and such ring-like member is generally disposed in the outer peripheral region of the grip side bearing housing. Therefore, due to the ring-like member on the peripheral region of the grip side bearing housing, the enforcing rib cannot be provided as a measure to increase the rigidity of the grip side bearing housing.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, it is an object of the invention to provide an effective technique for a motor support structure of a power tool to reduce vibration.  
         [0007]     The object as described above can be achieved by the claimed invention. According to the representative invention, a representative reciprocating power tool may include a tool body, a tool bit, a grip, a motor, a tool bit side bearing, a grip side bearing, a tool bit side bearing housing, a grip and an elastic element. The tool bit is disposed in a tip end region of the tool body to perform a predetermined operation on a workpiece. The grip is mounted on the tool body on the side opposite to the tool bit. The motor is housed within the tool body to drive the tool bit. The motor may have a rotatable shaft and the tool bit side bearing and the grip side bearing rotatably support the rotating shaft of the motor. The tool bit side bearing housing houses the tool bit side bearing, while the grip side bearing housing houses the grip side bearing. The elastic element is disposed between the grip side bearing housing and the grip wherein the grip side bearing housing is elastically supported by the grip via the elastic element.  
         [0008]     The “power tool” according to the invention typically includes not only impact power tools such as an electric hammer and a hammer drill, but also power tools in which a grip side bearing housing extends from a tool body toward a grip. The “grip” according to the invention suitably includes both a grip that extends in a direction crossing the axial direction of the motor and a grip that extends in a direction substantially parallel to the axial direction of the motor. The “elastic element” may include a shock-absorbing material such as a rubber or a flexible synthetic resin.  
         [0009]     According to the invention, because the grip is adapted to support the grip side bearing housing via the elastic element and the rigidity of the grip side bearing housing can be increased and vibration of the grip side bearing housing can be reduced. Further, the elastic element can absorb manufacturing errors caused between the tool body and the grip when the grip is mounted to the tool body. Thus, the assembling ease can be enhanced.  
         [0010]     The representative power tool may preferably include a ring-like member disposed on an outer surface of the grip side bearing housing. Such ring-like member is manually operated by a user of the power tool to change the driving mode of the tool bit. In such case, the elastic element may be disposed on the grip side bearing housing in a region other than the region where the ring-like member is disposed. For example, when the ring-like member is disposed around an outer circumferential surface of the grip side bearing housing at a predetermined longitudinal region of the grip side bearing housing, the elastic element may preferably be disposed at an longitudinal end region of the grip side bearing housing toward the grip. Further, the elastic element may preferably be integrated with a rubber cover that is disposed on an outer periphery of the grip to contact with the palm and/or fingers of the user of the power tool.  
         [0011]     Other objects, features and advantages of the invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a sectional side view showing an entire hammer drill according to an embodiment of the invention.  
         [0013]      FIG. 2  is a side view showing a motor housing and a grip.  
         [0014]      FIG. 3  is an enlarged view of circled part A in  FIG. 1 .  
         [0015]      FIG. 4  is a sectional view taken along line B-B in  FIG. 3 .  
         [0016]      FIG. 5  is a sectional view showing a modification of a support structure of a cylindrical rear bearing housing of a driving motor.  
         [0017]      FIG. 6  is a sectional view showing another modification of the support structure of the cylindrical rear-bearing housing of the driving motor. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     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 power tools and method for using such power tools and devices utilized therein. Representative examples of the 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.  
         [0019]     A representative embodiment of the invention is described with reference to FIGS.  1  to  4 .  FIG. 1  is a sectional side view of an entire electric hammer drill  101  as a representative embodiment of a power tool according to the invention.  FIG. 2  is a side view showing a motor housing and a grip.  FIG. 3  is an enlarged view of circled part “A” in  FIG. 1 .  FIG. 4  is a sectional view taken along line B-B in  FIG. 3 . As shown in  FIG. 1 , the electric hammer drill  101  includes a body  103 , a drill bit  119  detachably coupled to the tip end region (on the left side as viewed in  FIG. 1 ) of the body  103  via a tool holder  137 , and a grip  109  held by a user and connected to a region of the body  103  on the opposite side of the drill bit  119 . The body  103  is a feature that corresponds to the “tool body” according to the invention. The drill bit  119  is mounted such that it is allowed to reciprocate with respect to the tool holder  137  in an axial direction and rotate together with the tool holder  137  in a circumferential direction. The drill bit  119  is a feature that corresponds to the “tool bit” according to the invention. In the following description, for the sake of convenience of explanation, the side of the drill bit  119  is taken as the front side and the side of the grip  109  as the rear side.  
         [0020]     The body  103  includes a motor housing  105  that houses a driving motor  111 , and a gear housing  107  that houses a motion converting mechanism  113 , a power transmitting mechanism  114  and a striking mechanism  115 . The motor housing  105  and the gear housing  107  are connected to each other by screws or other similar devices (not shown in the drawings). The motion converting mechanism  113 , the power transmitting mechanism  114  and the striking mechanism  115  form a driving mechanism of the drill bit  119 . An inner housing  106  is disposed within the gear housing  107  on the side adjacent to the joint with the motor housing  105  and separates an inner space of the gear housing  107  and an inner space of the motor housing  105 .  
         [0021]     The motion converting mechanism  113  appropriately converts the rotating output of the driving motor  111  to linear motion and then to transmit it to the striking mechanism  115 . As a result, an impact force is generated in the axial direction of the drill bit  119  via the striking mechanism  115 . Further, the power transmitting mechanism  114  appropriately reduces the speed of the rotating output of the driving motor  111  and transmits the rotating output as rotation to the drill bit  119 . Thus, the drill bit  119  is caused to rotate in the circumferential direction. Here, the driving motor  111  is driven by depressing a trigger  117  mounted on a handgrip  109 .  
         [0022]     The motion converting mechanism  113  includes a driving gear  121  mounted on the end (front end) of an armature shaft  112  of the driving motor  111  and is caused to rotate in a vertical plane, a driven gear  123  that engages with the driving gear  121 , a rotating element  127  that rotates together with the driven gear  123  via an intermediate shaft  125 , a swash plate  129  caused to swing in the axial direction of the drill bit  119  by rotation of the rotating element  127 , and a cylinder  141  caused to reciprocate by swinging movement of the swash plate  129 . The armature shaft  112  is a feature that corresponds to the “shaft of the motor” according to this invention. The intermediate shaft  125  is disposed parallel (horizontally) to the axial direction of the drill bit  119 . The outer surface of the rotating element  127  that is fitted onto the intermediate shaft  125  is inclined at a predetermined angle with respect to the axis of the intermediate shaft  125 . The swash plate  129  is fitted on the inclined outer surface of the rotating element  127  via a ball bearing  126  such that it can rotate with respect to the rotating element  127 . The swash plate  129  is caused to swing in the axial direction of the drill bit  119  by rotation of the rotating element  127 . Further, the swash plate  129  has a swinging rod  128  extending upward (in the radial direction) from the swash plate  129 . The swinging rod  128  is loosely fitted in an engaging member  124  formed in the rear end portion of the cylinder  141 . The rotating element  127 , the swash plate  129  and the cylinder  141  forms a swinging mechanism.  
         [0023]     As shown in  FIG. 1 , the power transmitting mechanism  114  includes a first transmission gear  131  that is caused to rotate in a vertical plane by the driving motor  111  via the driving gear  121  and the intermediate shaft  125 , a second transmission gear  133  that engages with the first transmission gear  131 , a sleeve  135  that is caused to rotate together with the second transmission gear  133 , and a tool holder  137  that is caused to rotate together with the sleeve  135  in a vertical plane.  
         [0024]     As shown in  FIG. 1 , the striking mechanism  115  includes a striker  143  slidably disposed within the bore of the cylinder  141 , and an impact bolt  145  that is slidably disposed within the tool holder  137  and is adapted to transmit the kinetic energy of the striker  143  to the drill bit  119 .  
         [0025]     In the hammer drill  101  thus constructed, when the user depresses the trigger  117  and the driving motor  111  is driven, the driving gear  121  is caused to rotate in a vertical plane by the rotating output of the driving motor  111 . Then, the rotating element  127  is caused to rotate in a vertical plane via the driven gear  123  that engages with the driving gear  121 , and the intermediate shaft  125 . The swash plate  129  and the swinging rod  128  are then caused to swing in the axial direction of the drill bit  119 , which in turn causes the cylinder  141  to slide linearly. The sliding movement of the cylinder  141  causes the action of an air spring within the cylinder  141 , which causes the striker  143  to linearly move within the cylinder  141 . The striker  143  collides with the impact bolt  145  and transmits the kinetic energy to the drill bit  119 .  
         [0026]     When the first transmission gear  131  rotates together with the intermediate shaft  125 , the sleeve  135  is caused to rotate in a vertical plane via the second transmission gear  133  that engages with the first transmission gear  131 . Further, the tool holder  137  and the drill bit  119  supported by the tool holder  137  rotate together with the sleeve  135 . Thus, the drill bit  119  performs a drilling operation on a workpiece by a hammering movement in the axial direction and a drilling movement in the circumferential direction.  
         [0027]     The hammer drill  101  according to this embodiment can be switched between a hammer drill mode in which the drill bit  119  is caused to perform a hammering movement and a drilling movement as described above and a drill mode in which the drill bit  119  is caused to perform only a drilling movement. A mechanism for such mode changing is not directly related to this invention and therefore will not be described.  
         [0028]     The motor housing  105  has a cylindrical shape having an open front end. The driving motor  111  is disposed within a motor housing such that its axial direction is parallel to the axial direction of the drill bit. A front portion and a rear portion of an armature shaft  112  of the driving motor  111  are rotatably supported by respective bearings (ball bearings)  151 ,  153 . The front bearing  151  is housed within a front bearing housing chamber  152  defined by one part of the inner housing  106 . The front bearing housing chamber  152  is a feature that corresponds to the “tool bit side bearing housing” according to the invention. The rear bearing  153  is housed within a rear bearing housing chamber  155  that is integrally formed with the motor housing  105 . A cylindrical rear bearing housing  157  extends rearward in a bulged form substantially from the central portion in the radial direction of the rear end portion of the motor housing  105 . The cylindrical rear bearing housing  157  defines the rear bearing housing chamber  155 . A plurality of openings  157   a  (see  FIG. 2 ) for ventilation are formed in the cylindrical rear bearing housing  157  at predetermined intervals in the circumferential direction and extend a predetermined length from the proximal end of the rear bearing housing  157 . The rear bearing housing chamber  155  is defined in the extending end portion of the rear bearing housing  157  and surrounded by a wall in its entire region in the circumferential and axial end. The cylindrical rear bearing housing  157  is a feature that corresponds to the “grip side bearing housing” according to the invention.  FIG. 1  shows the cylindrical rear bearing housing  157  in a sectional view taken through the opening  157   a    
         [0029]     Further, as shown in  FIG. 1 , a ring-like operating member  159  for switching the direction of rotation of the driving motor  111  is loosely fitted onto the proximal portion of the cylindrical rear bearing housing  157 . The operating member  159  can be manually operated by the user from outside of the motor housing  105 . The operating member  159  is a feature that corresponds to the “ring-like member” according to this invention.  
         [0030]     As shown in  FIGS. 1 and 2 , the grip  109  includes a grip body  161  integrally formed with the motor housing  105 , and a grip cover  163  mounted to the grip body  161 . The grip body  161  extends downward in a direction crossing the axial direction of the driving motor  111  from the rear end underside region of the motor housing  105 . The grip body  161  has a groove-like shape in section having an open rear end. The grip cover  163  has a groove-like shape in section having an open front end. The open ends of the grip body  161  and the grip cover  163  are butt-joined by appropriate fastening means such as screws, so that a hollow grip  109  is formed. Further, the grip cover  163  has an extending portion  163   a  that extends upward above the upper end of the grip body  161 . An open end of the extending portion  163   a  is butt-joined to the rear end of the motor housing  111 , so that the cylindrical rear bearing housing  157  is housed within the extending portion  163   a.  The extending portion  163   a  is a feature that corresponds to the “covering region” according to this invention. The grip cover  163  is formed of synthetic resin.  
         [0031]     A rubber cover  165  covers the regions of the outer surface of the grip body  161  and the grip cover  163  which contact the user&#39;s palm and/or fingers when the user holds the grip. As shown in  FIGS. 1 and 3 , an elastic cylindrical portion  167  is integrally formed with the rubber cover  165  on the grip cover  163  side and located to face with the extending end of the cylindrical rear bearing housing  157  of the motor housing  105 . The elastic cylindrical portion  167  extends from the outer surface side to the inner surface side of the grip cover  163  and has an open front end. The elastic cylindrical portion  167  supports the extending end portion of the cylindrical rear bearing housing  157  that extends from the motor housing  105 . The elastic cylindrical portion  167  has a tapered bore that is concentric with the armature shaft  112  of the driving motor  111 . A conical projection  157   b  is formed on the axially-extending end surface of the cylindrical rear bearing housing  157 . The projection  157   b  is closely fitted into the bore of the elastic cylindrical portion  167 , so that the outer region of the projection  157   b  is supported. The rubber cover  165  of the grip cover  163  and the elastic cylindrical portion  167  are features that respectively correspond to the “elastic element” in this invention.  
         [0032]     Further, as shown in  FIG. 4 , the grip cover  163  has a cylindrical portion  163   b  closely fitted onto the elastic cylindrical portion  167 . The cylindrical portion  163   b  serves to restrain the elastic cylindrical portion  167  from moving in the radial direction, or in a direction crossing the extending direction of the cylindrical rear bearing housing  157 . The cylindrical portion  163   b  is a feature that corresponds to the “rigid region” according to this invention. Further, spline-like grooves  167   a  are formed in the inner surface of the bore of the elastic cylindrical portion  167 . Crests  167   b  is defined between the grooves  167   a  contact to support the outer peripheral surface of the projection  157   b  partially in the circumferential direction. Preferably, three or more than three crests  167   b  may be provided to stably support the outer peripheral portion  167 . Each crest  167   b  corresponds to the feature of “contacting portion” in the invention.  
         [0033]     As described above, in the hammer drill  101  according to this embodiment, the cylindrical rear bearing housing  157  is provided on the rear end region of the motor housing  105  and extends rearward from the central portion in the radial direction of the rear end region. The bearing  153  housed within the cylindrical rear bearing housing  157  supports the rear portion of the armature shaft  112 . In such a motor support structure, the axially extending end region of the cylindrical rear bearing housing  157  is supported via the elastic cylindrical portion  167  of the grip  109 . Further, the ring-like operating member  159  is fitted on the cylindrical rear bearing housing  157 . With such construction, the rigidity of the cylindrical rear bearing housing  157  can be increased, and vibration of the cylindrical rear bearing housing  157  can be reduced which is caused by run-outs developed when the driving motor  111  is rotated. Further, with the construction in which the grip cover  163  supports the cylindrical rear bearing housing  157  via the elastic cylindrical portion  167 , the elastic cylindrical portion  167  can absorb manufacturing errors which are caused between the motor housing  105  and the grip cover  163  when the grip cover  163  is mounted to the motor housing  105 . Thus, the assembling ease can be enhanced.  
         [0034]     Further, in this embodiment, the elastic cylindrical portion  167  is integrally formed with the rubber cover  165  that covers the outer surface of the grip cover  163 . Further, as shown in  FIG. 4 , the cylindrical portion  163   b  of the grip cover  163  supports the periphery of the elastic cylindrical portion  167  and thereby restrains the elastic cylindrical portion  167  from moving radially outward. Therefore, elastic deformation of the elastic cylindrical portion  167  can be prevented, so that the effect of reducing vibration of the cylindrical rear bearing housing  157  can be enhanced. Further, the elastic cylindrical portion  167  is configured to support the outer peripheral surface of the projection  157   b  via the crests  167   b  of the spline-like grooves  167   a.  Therefore, the crests  167   b  can be easily deformed. As a result, the projection  157   b  can be easily fitted into the bore of the elastic cylindrical portion  167  when the grip cover  163  is mounted to the grip body  161 .  
       Modification of the Representative Embodiment  
       [0035]      FIGS. 5 and 6  show modifications of the support structure of the grip  109  that support the extending end region of the cylindrical rear bearing housing  157 . In the modification as shown in  FIG. 5 , an elastic portion  168  is provided and configured to be butted in facial contact with the axially extending end surface of the cylindrical rear bearing housing  157  in order to support the cylindrical rear bearing housing  157 . The elastic portion  168  is a feature that corresponds to the “elastic element” according to this invention. The elastic portion  168  is adapted to be butted in an appropriately elastically deformed state against the axially extending end surface of the cylindrical rear bearing housing  157  when the grip cover  163  is attached to the grip body  161  and the housing cover  105 . Further, the cylindrical portion  163   b  integrally formed with the grip cover  163  supports the outer peripheral surface of the elastic portion  168  and thereby restrains the radial movement of the elastic cylindrical portion  167 . With such construction of the support structure, like in the above-mentioned embodiment, the cylindrical rear bearing housing  157  can increase in rigidity, and vibration of the cylindrical rear bearing housing  157  can be reduced which is caused when the driving motor  111  is rotated.  
         [0036]     In addition to the support structure by butted facial contact as shown in  FIG. 5 , the modification as shown in  FIG. 6  provides a support structure in which the outer peripheral region of the extending end portion of the cylindrical rear bearing housing  157  is also supported. Specifically, an elastic cylindrical portion  169  is provided and configured to support both the outer peripheral region and the axial end surface region of the extending end portion of the cylindrical rear bearing housing  157 . The elastic cylindrical portion  169  is a feature that corresponds to the “elastic element” according to this invention. Further, the cylindrical portion  163   b  integrally formed with the grip cover  163  supports the outer peripheral surface of the elastic cylindrical portion  169  and thereby restrains the radial movement of the elastic cylindrical portion  169 . With such construction of the support structure, the cylindrical rear bearing housing  157  can further increase in rigidity, and the effect of reducing vibration of the cylindrical rear bearing housing  157  can be further enhanced.  
         [0037]     Although, in the above-mentioned embodiment, the elastic cylindrical portions  167 ,  169  and the elastic portion  168  is described as being integrally formed with the rubber cover  165 , they may be separately formed. Further, in this embodiment, the grip  109  is described as being connected to the motor housing  105  in such a manner as to extend in a direction crossing the axial direction of the driving motor  111 . However, this invention may also be applied to a power tool such as an electric grinder having a grip extending parallel to the axial direction of a driving motor. Further, the hammer drill  101  is described as a representative example of the power tool, but this invention is not limited thereto. This invention can be applied to any power tool in which the grip  109  is connected to the rear end region of the handle  105  and the cylindrical rear bearing housing  157  for housing the rear bearing  153  of the driving motor  111  extends toward the grip  109 .  
       DESCRIPTION OF NUMERALS  
       [0000]    
       
           101  hammer drill (power tool)  
           103  body (tool body)  
           105  motor housing  
           106  inner housing  
           107  gear housing  
           109  grip  
           111  driving motor (motor)  
           112  armature shaft (rotating shaft)  
           113  motion converting mechanism  
           114  power transmitting mechanism  
           115  striking mechanism  
           117  trigger  
           119  drill bit (tool bit)  
           121  driving gear  
           123  driven gear  
           124  engaging member  
           125  intermediate shaft  
           126  ball bearing  
           127  rotating element  
           128  swinging rod  
           129  swash plate  
           131  first transmission gear  
           133  second transmission gear  
           135  sleeve  
           137  tool holder  
           141  cylinder  
           143  striker  
           145  impact bolt  
           151  front bearing  
           152  front bearing housing chamber (tool bit side bearing housing)  
           153  rear bearing  
           155  rear bearing housing chamber  
           157  cylindrical rear bearing housing (grip side bearing housing)  
           157   a  opening  
           157   b  projection  
           159  ring-like operating member (ring-like member)  
           161  grip body  
           163  grip cover  
           163   a  extending portion (covering region)  
           163   b  cylindrical portion (rigid region)  
           165  rubber cover  
           167  elastic cylindrical portion (elastic element)  
           167   a  groove  
           167   b  crest  
           168  elastic portion (elastic element)  
           169  elastic cylindrical portion (elastic element)
It is an object of the invention to provide an effective technique for a motor support structure of a power tool to reduce vibration. A representative reciprocating power tool may include a tool body, a tool bit, a grip, a motor, a tool bit side bearing, a grip side bearing, a tool bit side bearing housing, a grip and an elastic element. The tool bit side bearing housing houses the tool bit side bearing, while the grip side bearing housing houses the grip side bearing. The elastic element is disposed between the grip side bearing housing and the grip wherein the grip side bearing housing is elastically supported by the grip via the elastic element. According to the invention, because the grip is adapted to support the grip side bearing housing via the elastic element and the rigidity of the grip side bearing housing can be increased and vibration of the grip side bearing housing can be reduced. Further, the elastic element can absorb manufacturing errors caused between the tool body and the grip when the grip is mounted to the tool body.