Abstract:
It is an object of the invention to provide a technique in a power tool having a detachable bit holder for preventing a bit holder from being detached from the tool body even if unexpected external force is exerted on an operating member for lock release. A representative power tool includes a tool body, a single holder mounting portion. The holder mounting portion removably holds a bit holder selected from multiple kinds of bit holders for holding multiple kinds of tool bits in different manners. Each bit holder includes a cylindrical portion, a through hole formed through the cylindrical portion, an engaging member disposed within the through hole, a cylindrical operating member axially movably fitted on the cylindrical portion between a movement prevented position and a movement allowed position. The operating member is moved to the tool body side in order to be switched from the movement prevented position to the movement allowed position so that the holder mounting portion is allowed to be pulled out of the fitting hole.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique for removably attaching multiple kinds of bit holders to a power tool in a manner of replacing with each other. 
     2. Description of the Related Art 
     Japanese laid-open patent publication No. 10-58352 discloses a technique for removably attaching multiple kinds of bit holders which hold tool bits in different manners and in a manner of being replaced with each other. The known bit holders each have an adapter which can be inserted into a spindle sleeve on the tool body side. When the adapter is inserted into the bore of the spindle sleeve, a locking member in the form of a ball which is held by the spindle sleeve and can move in the radial direction engages (locks) in a recess formed in the outer surface of the adapter. Thus engagement is maintained by a fixing member disposed on the outside of the adapter. Thus, the bit holder is attached to the slide sleeve and prevented from becoming detached from the slide sleeve. Further, the fixing member can move together with an operating sleeve for lock release which is axially movably disposed on the outside of the adapter. When the operating sleeve is moved away from the tool body (forward) against the biasing force of a compression coil spring, the fixing member releases the engagement of the ball with respect to the recess and allows the adapter to be pulled out of the spindle sleeve. 
     The known bit holder can be detached from the spindle sleeve when an operating force is applied to the operating sleeve in the direction of moving the operating sleeve away from the tool body. Therefore, during operation, when an external force is exerted by some chance on the opting sleeve in the direction of moving the operating sleeve away from the tool body, the bit holder may become detached from the spindle sleeve. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to provide a technique in a power tool having a detachable bit holder to prevent a bit holder from being detached from the tool body even if unexpected external force is exerted on an operating member for lock release. 
     The above-described problem can be solved by the features of the claimed invention. According to the invention, a representative power tool is provided to have a tool body, a single holder mounting portion and a recess. The holder mounting portion is disposed in the tip end region of the tool body. The holder mounting portion removably holds a bit holder. The bit holder is selected from multiple kinds of bit holders which hold multiple kinds of tool bits in different manners. The holder mounting portion holds the selected bit holder by replacing the other bit holder attached to the holder mounting portion. 
     The multiple kinds of tool bits according to this invention may typically include a drill bit, a chisel, a rammer, etc. Further, according to the invention, the multiple kinds of bit holders which hold in different manners may typically include bit holder that allows only hammering operation, bit holder that allows only drilling operation and bit holder that allows hammering and drilling operation. 
     The recess is formed in an outer surface of the holder mounting portion. Each of the bit holders include a cylindrical portion, a through hole, an engaging member, cylindrical operating member and a biasing member. The cylindrical portion has a fitting hole. The fitting hole is fitted on the holder mounting portion and can be pulled out. The through hole is formed through the cylindrical portion. One end of the through hole is open to an outer surface of the cylindrical portion and the other end is open to the fitting hole. 
     The engaging member is disposed within the through hole and can move between a locked position and a lock released position. In the locked position, the engaging member protrudes from the one open end of the through hole on the fitting hole side and engages with the recess of the holder mounting portion fitted in the fitting hole. Thus, the holder mounting portion is prevented from being pulled out of the fitting hole. On the other hand, in the lock released position, the engaging member protrudes from the other open end of the through hole on the outer surface side and is disengaged from the recess. Thus, the holder mounting portion is allowed to be pulled out of the fitting hole. 
     The cylindrical operating member is axially movably fitted on the cylindrical portion and has a movement control region that prevents the engaging member from moving from the locked position to the lock released position, wherein the operating member can move between a movement prevented position in which the movement control region engages with the engaging member and prevents movement of the engaging member and a movement allowed position in which the movement control region is disengaged from the engaging member and allows movement of the engaging member. The biasing member applies a biasing force to the operating member so as normally to hold the operating member in the movement prevented position. 
     The operating member is moved to the tool body side in order to be switched from the movement prevented position to the movement allowed position so that the holder mounting portion is allowed to be pulled out of the fitting hole. Thus, according to the invention, when the operating member is moved toward the tool body, the lock of the engaging member by the movement control region is released. Therefore, during a predetermined operation using the power tool, even if an external force is exerted by chance on the operating member in the direction of moving the operating member away from the tool body, the operating member is prevented from moving to the movement allowed position. Thus, the bit holder is non-detachably secured to the tool body in this state. Further, even if an external force is exerted by chance on the operating member in the direction of moving the operating member toward the tool body and causes the operating member to move to the movement allowed position, the bit holder is non-detachably secured to the tool body due to such movement of the operating member, because the direction of such movement of the operating member is opposite to the direction of detachment of the bit holder. 
     When released from such external force, the operating member is returned to the movement prevented position by the biasing force of the biasing member and can hold the engaging member in the locked position via the movement control region. Therefore, according to the invention, unless the user operates the operating member with the intention of detaching the bit holder from the tool body, the tool holder can be held attached to the tool body. 
     As one aspect of the invention, in order to attach the bit holder to the holder mounting portion, a user grasp the operating member and applies an external force in such a manner as to move the operating member in the axial direction toward the tool body so as to fit the holder mounting portion in the fitting hole. At this time, the operating member and the cylindrical portion move in the axial direction with respect to the tool body against the biasing force of the biasing member, so that the holder mounting portion is fitted in the fitting hole and the engaging member is moved to the locked position. Then, in this state, when the operating member is released from the external axial force, the operating member is moved to the movement prevented position by the biasing force of the biasing member, so that the bit holder is attached to the holder mounting portion. Thus, the user can easily attach the bit holder to the holder mounting portion of the tool body by only one action of applying an external force to the operating member held by the hand in such a manner as to fit the holder mounting portion in the fitting hole of the cylindrical portion. 
     Further, as one aspect of the invention, in order to detach the bit holder from the holder mounting portion, the user gasps the operating member by one hand and applies an external force in such a manner as to move the operating member to the tool body side in the axial direction, thereby moving the operating member to the movement allowed position. As a result, the engaging member is allowed to move from the locked position to the lock released position. Then, while keeping this allowed state, the user grasps the operating member and applies an external force to move the operating member away from the tool body in the axial direction, so that the holder mounting portion is pulled out of the fitting hole. Thus, according to this invention, the bit holder can be detached from the tool body with ease of operation by one hand. 
     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 pay in section, showing a hammer drill according to an embodiment of the invention. 
         FIG. 2  is a sectional view showing a first chuck in the attached state. 
         FIG. 3  is a sectional view showing a position of attachment and detachment of the first chuck. 
         FIG. 4  is a sectional view showing the first chuck in the detached state. 
         FIG. 5  is a sectional view showing the first chuck when a drill bit is attached to or detached from the first chuck. 
         FIG. 6  is a sectional view showing a second chuck in the attached state. 
         FIG. 7  is a sectional view showing the second chuck in the detached state. 
     
    
    
     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 power tools and method for using such 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  FIGS. 1 to 7 .  FIG. 1  is a side view, partly in section, showing an entire electric hammer drill  101  as a representative embodiment of the power tool according to the present invention. In  FIG. 1 , a hammer chuck  151  (hereinafter referred to as a first chuck) for holding a drill bit  119  for hammer drilling is shown attached to the hammer drill.  FIG. 2  is a sectional view showing the first chuck  151  in the attached state.  FIG. 3  is a sectional view showing a position of attachment and detachment of the first chuck  151 ,  FIG. 4  is a sectional view showing the first chuck  151  in the detached state.  FIG. 5  is a sectional view showing the first chuck  151  when the drill bit is attached to or detached from the first chuck. Further,  FIGS. 6 and 7  are sectional views showing a drill chuck  251  (hereinafter referred to as a second chuck) for holding a drill bit  219  for vibration drilling.  FIG. 6  shows the second chuck  251 , instead of the first chuck  151 , attached to the hammer drill  101 .  FIG. 7  shows the second chuck  251  in the detached state. 
     The construction of the hammer drill  101  according to this embodiment will now be explained with reference to  FIG. 1 . The hammer drill  101  includes a body  103 , the drill bit  119  for hammer drilling which is detachably coupled to the tip end region (on the front end side) of the body  103  via the first chuck  151 , and a handgrip  109  that is provided on the rear end side of the body  103  or on the side opposite to the drill bit  119 . The drill bit  119  is held by the first chuck  151  such that it is allowed to move with respect to the first chuck  151  in its axial direction and prevented from rotating with respect to the first chuck in its circumferential direction. The drill bit  119  and the first chuck  151  are features that correspond to the “tool bit” and the “bit holder”, respectively, according to the present invention. In the present embodiment, 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 handgrip  109  as the rear side. 
     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 striking mechanism  115  and a power transmitting mechanism  117 . The motion converting mechanism  113  is adapted to appropriately convert 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 seed of the rotating output of the driving motor  111  is appropriately reduced by the power transmitting mechanism  117  and then transmitted to the drill bit  19 . As a result, the drill bit  119  is caused to rotate in the circumferential direction. The driving motor  111  is driven when a trigger  109   a  on the handgrip  109  is depressed. 
     The motion converting mechanism  113 , the striking mechanism  115  and the power transmitting mechanism  117  are known in the art, and therefore will be only briefly explained. The motion converting mechanism  131  includes a driven gear  123  that is rotated in a horizontal plane by the driving motor  111 , a crank plate  125 , a crank arm  127  and a driving element in the form of a piston  129 . The crank plate  125 , the crank arm  127  and the piston  129  form a crank mechanism. The piston  129  is slidably disposed within a cylinder (not shown) and reciprocates within the cylinder bore when the driving motor  111  is driven. 
     The striking mechanism  115  includes a striker  143  and an impact bolt  145 . The striker  143  is slidably disposed within the bore of the cylinder. The impact bolt  145  is slidably disposed within the tool holder  137  and serves as an intermediate element to transit the kinetic energy of the striker  143  to the drill bit  119 . An air chamber is formed within the cylinder and partitioned by the radial wall surface of the cylinder, the piston  129  and the striker  143 . The striker  143  is linearly driven via the action of an air spring of the air chamber which is caused by sliding movement of the piston  129 . The striker  143  then collides with (strikes) the impact bolt  145  and transmits the so force to the drill bit  119  via the impact bolt  145 . 
     The power transmitting mechanism  117  includes a transmission gear  131  that is driven to rotate in a horizontal plane by the driving motor  111 , a small bevel gear  133  that is caused to rotate in a horizontal plane together with the transmission gear  131 , a large bevel gear  135  that engages with the small bevel gear  133 , and a tool holder  137  that is caused to rotate in a vertical plane together with the large bevel gear  135 . The rotational driving force of the tool holder  137  is transmitted to the first chuck  151  mounted on the tip end of the tool holder  137  and to the drill bit  119  held by the first chuck  151 . 
     In the hammer drill  101  thus constructed, when the trigger  109   a  is depressed by the user and the driving motor  111  is driven, the piston  129  is caused to linearly slide along the cylinder via the motion converting mechanism  113  that is mainly comprised of the crank mechanism. As a result, the striker  143  reciprocates within the cylinder by the action of the air spring function which is caused within the air chamber by the sliding movement of the piston  129 . The kinetic energy of the striker  143  which is caused by the collision with the impact bolt  145  is transmitted to the drill bit  119 . Meanwhile, the rotating output of the driving motor  111  is transmitted to the tool holder  137  via the power transmitting mechanism  117 . As a result the tool holder  137  is driven to rotate in a vertical plane, and the drill bit  119  is rotated together with the first chuck  151  attached to the tool holder  137 . Thus, the drill bit  119  performs a drilling operation on a workpiece (e.g. concrete) by the hammering movement in the axial direction and the drilling movement in the circumferential direction. 
     The hammer drill  101  can be switched not only to the above-mentioned hammer drill mode in which the drill bit  119  is caused to perform both the hammering movement in the axial direction and the drilling movement in the circumferential direction, but to drill mode in which the drill bit  1119  is caused to perform only the drilling movement or to hammer mode in which the drill bit  119  is caused to perform only the hammering movement. A mode switching mechanism is not directly related to the present invention and therefore will not be described. 
     The first chuck  151  will now be explained with reference to  FIGS. 2 to 5 . The first chuck  151  includes a cylindrical chuck body  153 , a plurality of steel balls  155  and a tool sleeve  157 . The chuck body  153  has a bit insertion hole  153   a  having a circular section into which the drill bit  119  is removably inserted. The steel balls  155  serve to prevent or allow removal of the drill bit  119  from the bit insertion hole  153   a . The tool sleeve  157  serves to switch the steel balls  155  between a bit removal prevented position and a bit removal allowed position. A plurality of slots  153   b  are formed in the chuck body  153  at predetermined intervals in the circumferential direction and extend in the axial direction of the chuck body  153 . The steel balls  155  are disposed in the slots  153   b . The steel balls  155  can move in the axial direction within the associated slots  153   b  and can be displaced in the radial direction of the chuck body  153 . 
     The tool sleeve  157  is fitted on the chuck body  153  such that it can move in the axial direction. A control ring  159  is disposed on the inner periphery of the tool sleeve  157  and prevents radially outward displacement of the steel balls  155 . Further, a control plate  161  is disposed on the rear side of the control zing  159 . The control plate  161  can move in the axial direction of the tool sleeve  157  with respect to the tool sleeve  157 . The control plate  161  is pressed against the rear surface of the control ring  159  by a biasing spring  163  disposed between the control plate  161  and the chuck body  153 . The biasing force of the biasing spring  163  acts as a force of pressing the tool sleeve  157  forward. Therefore, the front end of the tool sleeve  157  contacts a cap  165  attached to the front end of the chuck body  153 , so that the tool sleeve  157  holds the steel balls  155  in the bit removal prevented position. 
     In order to attach or detach the drill bit  119  with respect to the first chuck  151 , the user grasps the tool sleeve  157  and moves the tool sleeve  157  rearward against the biasing force of the biasing spring  163 . In this state, the drill bit  119  is allowed to be attached or detached. This state is shown in  FIG. 5 . When the user moves the tool sleeve  157  rearward, the steel balls  155  are released from the control ring  159  and allowed to move radially outward. In this state, when the drill bit  119  is inserted into the bit insertion hole  153   a , the steel balls  155  are pressed by the end of the drill bit  119  and once moved radially outward. Thereafter, the steel balls  155  engage with engagement grooves  119   a  formed in the outer periphery of the shank of the drill bit  119 . In this state, when the user releases the tool sleeve  157 , the tool sleeve  157  is moved forward by the biasing force of the biasing spring  163 , and the control ring  159  holds the steel balls  155  engaged with the associated engagement grooves  119   a . Thus, the drill bit  119  is prevented from slipping out. The engagement groves  119   a  of the drill bit  119  extend to a predetermined length in the axial direction. Therefore, the drill bit  119  is allowed to move a predetermined distance in the axial direction with respect to the chuck body  153 . Further, when the drill bit  119  is pulled forward in the state in which the tool sleeve  157  is moved rearward, the drill bit  119  can be detached from the first chuck  151  while pushing the steel balls  155  radially outward. 
     Further, a plurality of radially protruding torque transmitting parts in the form of protrusions  153   c  are formed on the inner peripheral surface of the bit insertion hole  153   a  of the chuck body  153  at predetermined intervals in the circumferential direction. The torque transmitting protrusions  153   c  extend to a predetermined length in the axial direction of the chuck body  153 . Torque transmission grooves  119   b  are formed in the outer periphery of the shank of the drill bit  119  and engage with the protrusions  153   c  when the drill bit  119  is inserted into the bit insertion hole  153   a . In this engagement, the rotating force of the chuck body  153  is transmitted to the drill bit  119 . Further, each of the torque transmission grooves  119   b  is open at its shank end such that the drill bit  119  is positioned in the circumferential direction when the drill bit  119  is inserted into the bit insertion hole  153   a . Thus, the drill bit  119  is held by the first chuck  151  such that it is allowed to move in its axial direction. 
     A structure for removably attaching the first chuck  151  to the tool holder  137  will now be explained. A chuck mounting part  139  is formed on the tip end portion (front end portion) of the tool holder  137 . A spline shaft  139   a  and engagement recesses  139   b  are formed in the outer peripheral surface of the chuck mounting part  139 . The chuck mounting part  139  is a feature that corresponds to the “holder mounting portion” according to this invention. 
     The first chuck  151  has a cylindrical mounting portion  167  integrally formed on the rear end of the chuck body  153  such that the first chuck  151  is removably attached to the chuck mounting part  139 . The cylindrical mounting portion  167  is a feature that corresponds to the “cylindrical portion” according to this invention. The cylindrical mounting portion  167  has a spline hole  167   b  and a plurality of locking steel balls  169 . The spline hole  167   b  can be fitted onto the spline shaft  139   a  of the chuck mounting portion  139  and can be pulled out. The steel balls  169  can engage with the engagement recesses  139   b  of the chuck mounting part  139  and thereby serve to prevent the cylindrical mounting portion  167  from slipping out in the axial direction. The chuck body  153  can be rotated together with the tool holder  137  by spline engagement of the cylindrical mounting portion  167  with the chuck mounting portion  139 . The steel balls  169  and the spline hole  167   b  are features that correspond to the “engaging member” and the “fitting hole”, respectively, according to this invention. 
     A plurality of through holes  167   a  are formed in the cylindrical mounting portion  167  at predetermined intervals in the circumferential direction of the cylindrical mounting portion  167  and extend radially through the cylindrical mounting portion  167 . The steel balls  169  are radially movably disposed in the trough holes  167   a . The steel balls  169  can move between an engagement position in which the steel balls engage with the engagement recesses  139   b  of the chuck mounting part  139  and a disengagement position in which such engagement is released. The engagement position and the disengagement position of the steel balls  169  are features that correspond to the “locked position” and the “lock released position”, respectively, according to this invention. 
     A lock releasing slide sleeve  171  is fitted on the cylindrical mounting portion  167  and is manually operated by the user. The slide sleeve  171  is a feature that corresponds to the “operating member” according to this invention. The slide sleeve  171  can be moved in the axial direction of the chuck body  153  (the axial direction of the drill bit  119 ). A lock ring  173  is mounted to the slide sleeve  171  such that it can move together with the slide sleeve  171 . The lock ring  173  locks the steel balls  169  in the engagement position when the lock ring  173  is located on the outer side of the steel balls  169 , while the lock ring  173  releases the lock of the steel balls  169  when the lock ring  173  is moved rearward away from the steel balls  169 . The lock ring  173  is a feature that corresponds to the “movement control region” according to this invention. 
     The slide sleeve  171  is biased forward (to the drill bit  119  side) by a compression coil spring  175 . The compression coil spring  175  is a feature that corresponds to the “biasing member” according to this invention. The compression coil spring  175  is disposed on the outside of the lock ring  173  and between a spring receiving ring  177  fixed to the cylindrical mounting portion  167  and a spring receiving ring  179  fixed to the slide sleeve  171 . The slide sleeve  171  is pushed forward by the biasing force of the compression coil spring  175  and contacts a stopper  167   c  that is formed on the outer diameter side of the cylindrical mounting portion  167 . Thus, the end of the forward movement of the slide sleeve  171  is defined by such contact with the stopper  167   c . When the slide sleeve  171  is placed in the forward position, the lock ring  173  is located on the outer side of the steel balls  169  and prevents the steel balls  169  from moving radially outward. When the slide sleeve  171  is moved rearward (to the body  103  side) against the biasing force of the compression coil spring  175 , the lock ring  173  is moved away from the steel balls  169  and allows the steel balls  169  to move radially outward. The forward position and the rearward position of the slide sleeve  171  are features that correspond to the “movement prevented position” and the “movement allowed position”, respectively, according to this invention. 
     Operation of attaching and detaching the first chuck  151  having the above-mentioned construction with respect to the chuck mounting portion  139  will now be explained. As shown in  FIG. 4 , in the state in which the first chuck  151  is detached from the chuck mounting portion  139 , the slide sleeve  171  is pushed forward by the biasing force of the compression coil spring  175  and placed in the forward position defined by the stopper  167   c . Further, the lock ring  173  is located on the outer-side position to prevent movement of the steel balls  169 , so that the steel balls  169  protrude to the spline hole  167   b  side. 
     In this state, in order to attach the first chuck  151  to the chuck mounting portion  139 , with the slide sleeve  171  in the hand, the user linearly moves the slide sleeve  171  toward the body  103  and fits the spline hole  167   a  of the cylindrical mounting portion  167  of the chuck body  153  onto the spline shaft  139   a  of the chuck mounting portion  139 . During this process, the steel balls  169  contact the shank end (the front end) of the spline shaft  139   a  and thereby prevents the cylindrical mounting portion  167  from moving rearward to the body  103  side. This state is shown in  FIG. 3 . In this state of contact when the user applies a force to the slide sleeve  171  in order to further move the slide sleeve  171  rearward, the slide sleeve  171  and the lock ring  173  are moved rearward while compressing the compression coil spring  175 . Thus, the lock ring  173  is moved rearward from the outer-side position on the outer side of the steel balls  169  and allows the steel balls  169  to move radially outward within the associated through holes  167   a . Therefore, the steel balls  169  move onto the outer diameter part of the spline shaft  139   a  over the shank end of the spline shaft  139   a , so that the cylindrical mounting portion  167  is allowed to move. In this state, when the cylindrical mounting portion  167  is moved to a predetermined rearward position, the spline hole  167   b  is fitted onto the spline shaft  139   a , and the steel balls  169  engage with the associated engagement recesses  139   b . In this state, when the force exerted upon the slide sleeve  171  is released, the slide sleeve  171  is moved to the forward position by the biasing force of the compression coil spring  175 , and the lock ring  173  is placed on the outer side of the steel balls  169 . Thus, the steel balls  169  are locked in engagement with the engagement recesses  139   b.    
     As mentioned above, the user can easily attach the first chuck  153  to the chuck mounting portion  139  by only one action of linearly moving the slide sleeve  171  toward the body  103 , with the slide sleeve  171  in the hand, in such a manner as to fit the spline hole  167   b  of the cylindrical mounting portion  167  onto the spline shaft  139   a  of the chuck mounting portion  139 . The relative positions of the engagement recesses  139   b  and the steel balls  169  in the circumferential direction may be marked on the body  103  and the first chuck  151 , respectively. Such marking facilitates positioning the first chuck  151  with respect to the body  103  in the circumferential direction when the user attaches the first chuck  151  to the chuck mounting portion  139 . 
     In order to detach the first chuck  151  from the chuck mounting portion  139 , the user grasps the slide sleeve  171  and moves it rearward (to the body  103  side). Thus the locking  173  is also moved rearward so that the lock of the steel balls  169  is released. Therefore, while keeping this state (the relative positional relationship), the user moves the chuck body  153  forward, or substantially holds the tool sleeve  157  and moves it forward, so that the cylindrical mounting portion  167  is slipped off the chuck mounting portion  139 . Thus, according to this embodiment, the first chuck  151  can be detached from the chuck mounting portion  139  with ease of operation by one hand. 
     According to this embodiment, the steel balls  169  are disengaged thorn the engagement recesses  139   b  when the lock ring  173  is moved rearward together with the slide sleeve  171 . In other words, the lock of the steel balls  169  is released when the slide sleeve  171  is moved toward the body  103 . Therefore, during operation using the hammer drill  101 , even if an external force is exerted by some chance on the slide sleeve  171  in the direction of moving the slide sleeve  171  away from the body  103 , the slide sleeve  171  and the lock ring  173  are prevented from moving in such direction and held in the locked position. Thus, the lock of the steel balls  169  is not released, so that the first chuck  151  never becomes detached from the chuck mounting portion  139 . 
     Further, even if an external force is exerted by some chance on the slide sleeve  171  in the direction of moving the slide sleeve  171  toward the body  103  and causes the slide sleeve  171  and the lock ring  173  to move toward the body  103 , the first chuck  151  never becomes detached from the chuck mounting portion  139 , because the direction of such movement of the slide sleeve  171  is opposite to the direction of detachment of the first chuck  151  from the chuck mounting portion  139 . When released from such external force, the slide sleeve  171  and the lock ring  173  are returned to the original ford position by the biasing force of the compression coil spring  175 . Thus, the steel balls  169  can be locked. Therefore, according to this embodiment, unless the user operates the slide sleeve  171  with the intention of detaching the first chuck  151  from the chuck mounting portion  139 , the first chuck  151  can be held attached to the chuck mounting portion  139 . 
     Next, the construction of a second chuck  251  which can be attached, instead of the first chuck  151 , to the chuck mounting portion  139  will now be explained with reference to  FIGS. 6 and 7 . The second chuck  251  is a claw chuck of the type which holds a drill bit  219  for vibration drills such that the drill bit  219  is prevented from moving in the axial direction and rotating on its axis with respect to the second chuck  251 . The drill bit  219  for vibration drills and the second chuck  251  are features that correspond to the “tool bit” and the “bit holder”, respectively, according to this invention. The second chuck  251  includes a chuck body  253 . The chuck body  253  has a bit insertion hole having a circular section into which the drill bit  219  is inserted, and a plurality of (e.g. this) holding claws  255  for holding the drill bit  219  inserted into the bit insertion hole. The holding claws  255  can be opened and closed by turning an adjusting ring  257  that is rotatably fitted on the chuck body  253 . Such opening and closing of the holding claws  255  allow attachment and detachment of the drill bit  219 . 
     A cylindrical chuck holder  267  is coaxially connected to the rear end of the chuck body  253  via a fastening bolt  268 . As an alternative to this construction of this embodiment, the chuck body  253  and the chuck holder  267  may be integrally formed with each other. The chuck holder  267  is a feature that corresponds to the “cylindrical portion” according to this invention. The chuck holder  267  corresponds to the above-described cylindrical mounting portion  167  of the first chuck  151  and can be removably mounted on the chuck mounting part  139  of the tool holder  137 . The mounting structure of the chuck holder  267  is exactly the same as in the case of the first chuck  151 . 
     Specifically, the chuck holder  267  has a spline hole  267   b  and a plurality of steel balls  269 . The spline hole  267   b  can be fitted onto the spline shaft  139   a  of the chuck mounting portion  139 . The steel balls  269  engage with the engagement recesses  139   b  of the chuck mounting part  139  when the chuck holder  267  is splint fitted on the chuck mounting part  139 . The spline hole  267   b  and the steel balls  269  are features that correspond to the “fitting hole” and the “engaging member”, respectively, according to this invention. A plurality of through holes  267   a  are formed in the chuck holder  267  and extend radially through the chuck holder  267 . The steel balls  269  are disposed in the through holes  267   a  and can move between an engagement position in which the steel balls engage with the engagement recesses  139   b  of the chuck mounting part  139  and a disengagement position in which such engagement is released. The engagement position and the disengagement position of the steel balls  269  are features that correspond to the “locked position” and the “lock released position”, respectively, according to this invention. 
     A lock releasing slide sleeve  271  is designed to be manually operated by the user and fitted on the chuck holder  267  such that the slide sleeve  271  can be moved in the axial direction of the chuck holder  267 . A lock ring  273  is mounted to the slide sleeve  271  such that it can move together with the slide sleeve  271 . The slide sleeve  271  and the lock ring  273  are features that correspond to the “operating member” and the “movement control region”, respectively, according to this invention. The lock ring  273  locks the steel balls  269  in the engagement position when the lock ring  273  is located on the outer side of the steel balls  269 , while the lock ring  273  releases the lock when the lock ring  273  is moved rearward away from the steel balls  269 . 
     The slide sleeve  271  is biased forward (to the drill bit  219  side) by a compression coil spring  275 . The compression coil spring  275  is a feature that corresponds to the “biasing member” according to this invention. The compression coil spring  275  is disposed between a spring receiving ring  277  fixed to the chuck holder  267  and a spring receiving ring  279  fixed to the slide sleeve  271 . A stopper  267   c  is formed on the chuck holder  267  and defines the end of the forward movement of the slide sleeve  271  by contact with the slide sleeve  271  which is biased forward by the biasing force of the compression coil spring  275 . When the slide sleeve  271  is placed in the forward position, the lock ring  273  is located on the outer side of the steel balls  269  and prevents the steel balls  269  from moving radially outward when the slide sleeve  271  is moved rearward (to the body  103  side) against the biasing force of the compression coil spring  275 , the lock ring  273  is moved away from the steel balls  269  and allows the steel balls  269  to move radially outward. The forward position and the rearward position of the slide sleeve  271  are features that correspond to the “movement prevented position” and the “movement allowed position”, respectively, according to this invention. 
       FIG. 6  shows the state in which the second chuck  251 , instead of the first chuck  151 , is attached to the chuck mounting portion  139  of the hammer drill  101 . In this state, as shown, a bore bottom  267   d  of the chuck holder  267  is opposed to the tip end (front end) of the impact bolt  145  and can contact it. Therefore, when the drilling operation using the drill bit  219  for vibration drills is performed in hammer drill mode by rotation and striking movement of the drill bit  219 , the striking force of the impact bolt  145  is transmitted from the impact bolt  145  to the drill bit  219  via the chuck holder  267  and the chuck body  253 . 
     The second chuck  251  is attached to the chuck mounting portion  139  in exactly the same manner as the first chuck  151 . Further,  FIG. 7  shows the state in which the second chuck  251  is detached from the chuck mounting portion  139 , and the manner of the detachment is also exactly the same as that of the first chuck  151 . Therefore, the second chuck  251  is attached to and detached from the chuck mounting portion  139  in the same manner as the first chuck  151 . Specifically, the user can easily attach and detach the second chuck  251  with respect to the chuck mounting portion  139  by grasping the slide sleeve  271  or grasping the slide sleeve  271  and the chuck body  253  and linearly moving the second chuck  251  in the axial direction. 
     Further, during operation with the second chuck  251  attached to the chuck mounting portion  139 , when an external force is exerted by some chance on the slide sleeve  271  in the direction of moving the slide sleeve  271  away from the body  103 , or when an external force is exerted by some chance on the slide sleeve  271  in the direction of moving the slide sleeve  271  toward the body  103  and causes the slide sleeve  271  and the lock ring  273  to move toward the body  103 , in either case, like the first chuck  151 , the second chuck  251  can be prevented from becoming detached from the chuck mounting portion  139 . 
     Further, in this embodiment, the hammer drill  101  is described as an example of the power tool, but the invention may be applied to a hammer which performs a hammering operation by linear striking movement of the tool bit. 
     DESCRIPTION OF NUMERALS 
     
         
           101  hammer drill 
           103  body 
           105  motor housing 
           107  gear housing 
           109  handgrip 
           109   a  trigger 
           111  driving motor 
           113  motion converting mechanism 
           115  string mechanism 
           117  power transmitting mechanism 
           119  drill bit (tool bit) 
           119   a  engagement groove 
           119   b  torque transmission groove 
           123  driven gear 
           125  crank plate 
           127  crank arm 
           129  piston 
           131  transmission gear 
           133  small bevel gear 
           135  large bevel gear 
           137  tool holder 
           139  chuck mounting portion 
           139   a  spline shaft 
           139   b  engagement recess 
           143  striker 
           145  impact bolt 
           151  first chuck 
           153  chuck body 
           153   a  bit insertion hole 
           153   b  slot 
           153   c  protrusion 
           155  steel ball 
           157  tool sleeve 
           159  control ring 
           161  control plate 
           163  biasing spring 
           165  cap 
           167  cylindrical mounting portion 
           167   a  through hole 
           167   b  spline hole 
           167   c  stopper 
           169  steel ball 
           171  slide sleeve 
           173  lock ring 
           175  compression coil spring 
           177  spring receiving ring 
           179  spring receiving ring 
           251  second chuck 
           253  chuck body 
           255  holding claw 
           257  adjusting ring 
           267  chuck holder 
           267   a  through hole 
           267   b  spline hole 
           267   c  stopper 
           267   d  bore bottom 
           268  fastening bolt 
           269  steel ball 
           271  slide sleeve (operating member) 
           273  lock ring (movement control region) 
           275  compression coil spring (biasing member) 
           277  spring receiving ring 
           279  spring receiving ring