Abstract:
It is an object of the present invention to provide an effective technique to improve ease of operation of the power impact tool. The power tool of the present invention includes a tool body, a tool bit, a motor, first and second switches and a mode changing mechanism. The motor is driven only when both switches are in an on position. The first switch is biased in the off position. The second switch is biased in the last position operated. The mode changing mechanism switches between hammer operation modes such that in the first hammer mode, the user actuates the first switch while the second switch is locked in the on position and in the second hammer mode, the first switch is locked in the on position while the second switch is actuated. In the second hammer mode, actuating the second switch similar to a toggle switch operates the tool.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a power impact tool capable of performing a hammering operation on a workpiece by the striking movement of a tool bit, and more particularly, to a technique of switching between operation modes of the tool bit. 
   2. Description of the Related Art 
   Japanese non-examined laid-open Patent Publication No. 2001-62756 discloses a power impact tool capable of performing a hammering operation on a workpiece. The known power impact tool includes a tool bit, a motor for driving the tool bit, an on-off power switch for the motor, a trigger for operating the power switch, and a mode-changing member for switching between respective operation modes of the tool bit. Specifically, the mode-changing member can switch between a hammer mode in which the hammer bit is caused to perform a striking movement and a hammer drill mode in which the hammer bit is caused to perform a combined movement of striking and rotating. The power impact tool further includes an engaging member that can releasably lock the trigger in a depressed position. In order to drive the hammer bit with the mode-changing member in the hammer mode, the trigger is depressed to turn on the power switch and then locked in the depressed position by the engaging member. Thus, in the hammer mode, the tool bit can be caused to perform continuous striking movement without needs of operating the trigger when the trigger is locked in the depressed position by the engaging member. When the lock of the trigger by the engaging member is released, the trigger is allowed to be operated to turn the power switch on and off, so that the tool bit can be caused to perform intermittent striking movement. 
   However, according to the known power impact tool, in order to effect continuous hammering operation by the tool bit, the user must depress the trigger and then operate the engaging member to lock the trigger in the depressed position every time when trying to drive the hammer bit. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an effective technique to improve ease of operation of the power impact tool. 
   The representative power impact tool according to the present invention includes a tool body, a tool bit, a motor, first and second switches and a mode changing mechanism. The tool bit performs a striking movement. The motor drives the tool bit. The motor is driven only when both of the switches are turned on. The first switch is urged from the on position side to the off position side and normally held in the off position. Typically and preferably, the first switch may be defined by a trigger provided on a hand-grip of the power impact tool. On the other hand, the second switch is turned between the on position and the off position and held in one of the on and off positions unless operated to be turned to the opposite position. Typically and preferably, the second switch may be defined by a toggle switch. The mode changing mechanism switches between hammer operation modes of the tool bit. According to the first hammer mode, the user is allowed to actuate the first switch while the second switch is locked in the on position. Further, according to the second hammer mode, the first switch is locked in the on position while the user is allowed to actuate the second switch. 
   According to the invention, when the power impact tool is operated in the second hammer mode, the first switch such like a trigger is locked in the on-position while the user is allowed to actuate the second switch such like a toggle switch to drive the motor. Therefore, while the first switch is normally urged and held in the off position, the user is not required to keep the first switch in the on-position by hand in the second hammer mode. As a result, ease of operation of the power impact tool is enhanced compared with the known art. Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view schematically showing an entire electric hammer drill according to an embodiment of the invention. 
       FIG. 2  is a sectional view of an essential part of the representative electric hammer drill, including a clutch operating mechanism, with clutches in engagement with each other. 
       FIG. 3  is a sectional view of an essential part of the representative electric hammer drill including a clutch operating mechanism, with clutches in disengagement from each other. 
       FIG. 4  is an enlarged sectional view showing a mode-changing mechanism. 
       FIG. 5  shows the wiring of a driving motor. 
       FIG. 6  is a sectional view showing a sub-switch and a switch actuating member. 
       FIG. 7  is a plan view showing a mode-changing mechanism in the hammer drill mode position. 
       FIG. 8  is a sectional plan view showing a switch actuating member, a trigger and a switch actuating member with the mode-changing mechanism in the hammer drill mode position. 
       FIG. 9  is a plan view showing the mode-changing mechanism in the first hammer mode position. 
       FIG. 10  is a sectional plan view showing the switch actuating member, the trigger and the switch actuating member with the mode-changing mechanism in the first hammer mode position. 
       FIG. 11  is a plan view showing the mode-changing mechanism in the second hammer mode position. 
       FIG. 12  is a sectional plan view showing the switch actuating member, the trigger and the switch actuating member with the mode-changing mechanism in the second hammer mode position. 
       FIG. 13  is an enlarged view showing a sub-switch actuating cam groove of a switch actuating member. 
   

   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 impact tools and method for using such power impact 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 13 .  FIG. 1  shows an entire electric hammer drill  101  as a representative embodiment of the power impact tool according to the present invention.  FIGS. 2 and 3  show the essential part of the hammer drill  101 .  FIG. 4  shows a mode changing mechanism  161  in an enlarged view.  FIG. 5  shows the wiring of a driving motor  111 .  FIG. 6  shows a sub-switch  127  and a switch actuating member  129 .  FIGS. 7 to 12  show the mode changing mechanism  161  and the manner of switching between respective modes.  FIG. 13  shows a sub-switch actuating cam groove  167  of a switch actuating member  165 , in enlarged view. As shown in  FIG. 1 , the hammer drill  101  of this embodiment includes a body  103 , a tool holder  113  connected to the tip end region of the body  103 , and a hammer bit  115  detachably coupled to the tool holder  113 . The hammer bit  115  is held in the tool holder  113  such that it is allowed to slide with respect to the tool holder  113  in its longitudinal direction and prevented from rotating with respect to the tool holder  113  in its circumferential direction. The hammer bit  115  is a feature that corresponds to the “tool bit” according to the present invention. 
   The body  103  includes a motor housing  105  that houses a driving motor  111 , a gear housing  107  that houses a motion converting mechanism  131  and a striking mechanism  115 , and a handgrip  109 . The driving motor  111  is mounted such that a rotating shaft  111   a  of the driving motor runs generally perpendicularly to the longitudinal direction of the body  103  (vertically as viewed in  FIG. 1 ). The motion converting mechanism  131  is adapted to convert the rotating output of the driving motor  111  to linear motion and then to transmit it to the striking mechanism  117 . As a result, an impact force is generated in the axial direction of the hammer bit  115  via the striking mechanism  117 . The motion converting mechanism  131  includes a crank mechanism driven by the driving motor  111  via a plurality of gears  132 ,  134 . The crank mechanism includes a crank shaft  133 , a crank pin  135  mounted on the crank shaft  133 , a piston  137 , and a connecting rod  139  that connects the piston  137  and the crank pin  135 . The piston  137  is adapted to drive the striking mechanism  117  and can slide within a cylinder  121  in the axial direction of the hammer bit  115 . The motor  111  and the cylinder  121  are arranged such that their axes run generally perpendicularly to each other. 
   The striking mechanism  117  includes a striker  118  and an impact bolt  119 . The striker  118  is slidably disposed within the bore of the cylinder  121  together with the piston  137 . The impact bolt  119  is slidably disposed within the tool holder  113  and is adapted to transmit the kinetic energy of the striker  118  to the hammer bit  115 . 
   The tool holder  113  is rotated by the driving motor  111  via a power transmitting mechanism  141  having a gear train. A clutch mechanism  151  is disposed in the power transmitting mechanism  141  and is adapted to enable or disable the power transmitting mechanism  141  to transmit rotation of the motor  111  to the tool holder  113  via the clutch mechanism  151 . 
   As shown in  FIGS. 2 and 3 , the power transmitting mechanism  141  includes an intermediate gear  143  driven by the motor  111 , an intermediate shaft  145 , a first bevel gear  147  and a second bevel gear  149 . Rotation of the intermediate gear  143  is transmitted to the intermediate shaft  145  via the clutch mechanism  151 . Rotation of the intermediate shaft  145  is in turn transmitted to the tool holder  113  via the first bevel gear  147  and the second bevel gear  149 . The intermediate shaft  145  is arranged parallel to the rotating shaft  111   a  of the motor  111  and perpendicularly to the axial direction of the hammer bit  115 . The clutch mechanism  151  includes engaging claw clutches, i.e. a driving clutch  153  and a driven clutch  155 . The driving clutch  153  is loosely fitted on the intermediate shaft  145 . The driven clutch  155  is fitted on the intermediate shaft  145  by spline engagement such that the driven clutch  155  can slide with respect to the intermediate shaft  145  in its axial direction and rotate together with the intermediate shaft  145  in its circumferential direction. The driven clutch  155  is urged toward the driving clutch  153  by the biasing force of a biasing member in the form of a clutch spring  157 . The driven clutch  155  transmits the rotation to the intermediate shaft  145  when the driven clutch  155  is in engagement with the driving clutch  153 . When the driven clutch  155  is disengaged from the driving clutch  153  against the biasing force of the clutch spring  157 , the driven clutch  155  is prevented from transmitting the rotation. Switching control of the clutch mechanism  151  will be explained below. 
     FIG. 5  shows the wiring of a driving motor  111 . As shown in  FIG. 5 , the motor  111  is started when both a main switch  125  and a sub-switch  127  are turned to their respective ON positions, while the motor  111  is stopped when either one or both of the main switch  121  and the sub-switch  127  are turned to the OFF positions. The main switch  125  is an automatic-reset type switch that is turned to the ON position by depressing a trigger  123  and returned to the OFF position by the biasing force of a spring (not shown) by releasing the trigger  123 . The main switch  125  is disposed within the handgrip  109 . The sub-switch  127  is a toggle switch that is toggled between the ON and OFF positions by means of a switch actuating member  129  and held in that position until it is toggled to the opposite position. The main switch  125  and the trigger  123  correspond to the “first switch” in this invention. The sub-switch  127  and the switch actuating member  129  correspond to the “second switch” in this invention. 
   The trigger  123  is mounted on the handgrip  109  such that it can rotate about a pivot  123   a . When the user depresses the trigger  123 , the trigger  123  is turned to a position that places the main switch  125  in the ON position. When the user releases the trigger  123 , the trigger  123  is returned to its initial position as the main switch  125  returns to the OFF position. 
   As shown in  FIG. 6 , the switch actuating member  129  extends through the motor housing  105  such that either of its ends protrudes through the side surface of the motor housing  105  when the user pushes the switch actuating member  129  laterally to slide. Specifically, the switch actuating member  129  is mounted such that it can slide in a direction of extending through the side surfaces of the motor housing  105 , i.e. in a direction perpendicular to the longitudinal direction of the body  103 . Further, the switch actuating member  129  is engaged with a knob  127   a  of the sub-switch  127 . Thus, the sub-switch  127  is toggled to the ON position when the user pushes in the switch actuating member  129  from one or the other side surface of the motor housing  105 , while the sub-switch  127  is toggled to the OFF position when the user pushes in the switch actuating member  129  in the opposite direction. 
   The hammer drill  101  includes a mode changing mechanism  161 . The mode changing mechanism  161  can change between a hammer-drill mode, a first hammer mode and a second hammer mode. In the hammer-drill mode, the hammer bit  115  is caused to perform a combined movement of striking and rotation. In the first hammer mode, the hammer bit  115  is caused to perform a striking movement by the operation of the trigger  123 . In the second hammer mode, the hammer bit  115  is caused to perform a striking movement by the actuation of the switch actuating member  129 . 
     FIGS. 7 and 8  show the mode changing mechanism  161  in the hammer-drill mode;  FIGS. 9 and 10  show it in the first hammer mode; and  FIGS. 11 and 12  show it in the second hammer mode. Further,  FIG. 2  shows the state in the hammer-drill mode in which the clutch mechanism  151  is engaged and the hammer bit  115  performs a combined movement of striking and rotation.  FIG. 3  shows the state in the first and second hammer modes in which the clutch mechanism  151  is disengaged and the hammer bit  115  performs a striking movement. 
   As shown in  FIGS. 2 to 4 , the mode changing mechanism  161  includes a mode-changing operating member  163 , a switch actuating member  165  and a clutch operating mechanism  171 . The movement of the switch actuating member  165  is interlocked with the operation of the mode-changing operating member  163  so as to lock the trigger  123  and the switch actuating member  129  in their respective ON positions or to allow them to be operated between the ON position and the OFF position. The clutch operating mechanism  171  controls engagement of the clutch mechanism  151  according to the switching operation of the mode-changing operating member  163 . The mode-changing operating member  163  is mounted externally on the upper surface of the motor housing  105  such that it can be operated by the user. Specifically, the mode-changing operating member  163  is disposed on the side opposite to the clutch mechanism  151  with respect to the cylinder  121 . The mode-changing operating member  163  includes a disc  163   a  with an operating grip  163   b  and is mounted on the motor housing  105  such that it can be turned in a horizontal plane. As shown in  FIG. 7 , the operating grip  163   b  is mounted on the upper surface of the disc  163   a  and extends in the diametrical direction of the disc. One end of the operating grip  163   b  in the diametrical direction is tapered and forms a switching position pointer. The three mode positions, i.e. hammer drill mode position, first hammer mode position and second hammer mode position, are marked on the motor housing  105  in predetermined intervals in the circumferential direction of the disc  163   a . Further, a first eccentric pin  163   c  and a second eccentric pin  163   d  are mounted on the underside of the disc  163   a  of the mode-changing operating member  163  in the respective positions displaced from the center of rotation of the disc  163   a . The first eccentric pin  163   c  and the second eccentric pin  163   d  actuate the switch actuating member  165  and the clutch operating mechanism  171 , respectively. 
   The switch actuating member  165  is defined by a plate member and has a slot  165   a  in one end portion. The first eccentric pin  163   c  is engaged in the slot  165   a . Thus, the switch actuating member  165  is caused to move lineally in the longitudinal direction of the body  103  (or the tool bit  115 ) via the first eccentric pin  163   c  when the mode-changing operating member  163  is operated (turned) to switch between the hammer drill mode, the first hammer mode and the second hammer mode. In other words, the switch actuating member  165  moves in a direction generally perpendicular to the moving direction of the switch actuating member  129  and in the direction of depressing the trigger  123 . The trigger  123  and the switch actuating member  129  are arranged substantially side by side in the moving direction of the switch actuating member  165 . The switch actuating member  165  is disposed within the motor housing  105  and extends generally horizontally toward the trigger  123  over the switch actuating member  129 . The switch actuating member  165  has a cam groove  167  extending in its moving direction. The switch actuating member  129  has a lug  129   a  and the lug  129   a  is engaged with the cam groove  167 . Further, the switch actuating member  165  extends into the handgrip  109  across the connection between the handgrip  109  and the body  103 . An end  165   b  of the switch actuating member  165  in the handgrip  109  faces an end  123   b  of the trigger  123  (which is remote from the pivot  123   a ) and can abut on it. 
   The end  165   b  of the switch actuating member  165  moves away from the end  123   b  of the trigger  123  when the mode-changing operating member  163  is turned to the hammer drill mode position or the first hammer mode position. In this state, the on-off operation of the main switch  125  by the trigger  123 , or the depressing and releasing of the trigger  123  is allowed. When the mode-changing operating member  163  is turned to the second hammer mode position, the end  165   b  of the switch actuating member  165  moves toward the trigger  123  and presses on the end  123   b  of the trigger  123 . As a result, the trigger  123  is moved to a depressed position, or a position that places the main switch  125  in the ON position, and locked in the depressed position. 
   As shown in  FIG. 13  in enlarged view, the cam groove  167  of the switch actuating member  165  has a locking region  167   a  and a switch actuation allowing region  167   b  in the moving direction of the switch actuating member  165 . In the locking region  167   a , the switch actuating member  129  of the sub-switch  127  is locked in the ON position. In the switch actuation allowing region  167   b , the user is allowed to actuate the switch actuating member  129  between the ON position and the OFF position. The cam groove  167  in the locking region  167   a  has such a width as to prevent the lug  129   a  of the switch actuating member  129  from moving in the switching direction of the switch actuating member  129 . Thus, the user is prevented from turning the sub-switch  127  on and off via the switch actuating member  129 . The cam groove  167  in the switch actuation allowing region  167   b  has such a large width in the direction generally perpendicular to the moving direction of the switch actuating member  165  or in the switching direction so as to allow the sub-switch  120  to be switched between the ON and OFF positions. The lug  129   a  of the switch actuating member  129  is located in the locking region  167   a  when the mode-changing operating member  163  is in the hammer drill mode position or the first hammer mode position (see  FIGS. 8 and 10 ). The lug  129   a  of the switch actuating member  129  is located in the switch actuation allowing region  167   b  when the mode-changing operating member  163  is in the second hammer mode position (see  FIG. 12 ). 
   The cam groove  167  further has a switching region  167   c  between the locking region  167   a  and the switch actuation allowing region  167   b . In the switching region  167   c , the switch actuating member  129  is forced to be switched between the ON position and the OFF position according to the movement of the switch actuating member  165 . The cam groove  167  in the switching region  167   c  is inclined a predetermined angle with respect to the moving direction of the switch actuating member  165 . The cam groove  167  in the switching region  167   c  has a V-shaped guide wall  167   d  that guides the lug  129   a  of the switch actuating member  129  from the ON position to the OFF position according to the movement of the switch actuating member  165  and a guide wall  167   e  that guides the lug  129   a  of the switch actuating member  129  from the OFF position to the ON position. The V-shaped guide wall  167   d  has a height H (see  FIG. 13 ) required to turn the sub-switch  127  from the ON position to the OFF position. Specifically, the height H corresponds to the switch stroke. 
   As shown in  FIGS. 2 and 3 , the clutch operating mechanism  171  includes a frame member  173  that is generally U-shaped in plan view, a ring  175  and a wedge-shaped cam  177 . The frame member  173  is caused to move lineally in the longitudinal direction of the cylinder  121  (the axial direction of the hammer bit  115 ) by revolving movement of the second eccentric pin  163   d  of the mode-changing operating member  163 . The ring  175  is coupled to the frame member  173 . The cam  177  is mounted on the ring  175  and adapted to control the engagement of the clutch mechanism  151 . The frame member  173  is disposed generally horizontally within the gear housing  107 . The frame member  173  is generally U-shaped having a base which is engaged with the mode-changing operating member  163  and two legs which extend toward the ring member  175 . Specifically, a slot  173   a  (shown in  FIGS. 2 and 3  in sectional view) is formed in the base of the frame member  173  and engages with the second eccentric pin  163   d . Thus, the frame member  173  can be moved in the longitudinal direction of the cylinder  121  by revolving movement of the second eccentric pin  163   d . The legs of the frame member  173  extend in the longitudinal direction of the cylinder  121  (as shown by dotted line in  FIGS. 2 and 3 ) and are coupled to the ring  175  at their ends. 
   As shown in  FIGS. 2 and 3 , the ring  175  is disposed around the outside of the cylinder  121  and can slide with respect to the gear housing  107  in the longitudinal direction of the body  103 . The cam  177  is secured to the ring  175  and moves together with the ring  175 . The cam  177  lies apart from a clutch control member  159  of the clutch mechanism  151  when the mode-changing operating member  163  is in the hammer drill mode position (see  FIG. 2 ). In this state, the driven clutch  155  is in engagement with the driving clutch  153 . When the mode-changing operating member  163  is turned to the first hammer mode position or the second hammer mode position, a slanted surface  177   a  of the cam  177  presses on the clutch control member  159  (see  FIG. 3 ). As a result, the clutch control member  159  pushes the driven clutch  155  away from the driving clutch  153  against the biasing force of the clutch spring  157 , so that the clutches are disengaged from each other. 
   Operation and usage of the hammer drill  101  constructed as described above will now be explained. 
   As shown in  FIG. 2 , when the user turns the mode-changing operating member  163  to the hammer drill mode position as shown in  FIG. 7 , the frame member  173  is caused to move via the second eccentric pin  163   d  toward the tip end (the hammer bit  115 ) of the hammer drill  101 . Thus, the ring  175  and the cam  177  also move in this direction and the cam  177  moves away from the clutch control member  157 . As a result, the engagement between the driven clutch  155  and the driving clutch  153  is maintained by the biasing force of the clutch spring  157 . Further, by thus turning the mode-changing operating member  163 , as shown in  FIGS. 7 and 8 , the switch actuating member  165  is caused to move toward the tip end of the hammer drill  101  via the first eccentric pin  163   c . Thus, the end  165   b  of the switch actuating member  165  moves away from the end  123   b  of the trigger  123 . As a result, the main switch  125  is held in the OFF position unless the trigger  123  is depressed. At this time, the lug  129   a  of the switch actuating member  129  is located within the locking region  167   a  of the cam groove  167 . Therefore, the sub-switch  127  is held in the ON position. 
   In this state, when the trigger  123  is depressed to turn the main switch  125  to the ON position and the driving motor  111  is driven, the rotation of the driving motor  111  is converted into linear motion via the motion converting mechanism  131 . The piston  137  of the motion converting mechanism  131  then reciprocates within the bore of the cylinder  121 . The linear motion of the piston  137  is transmitted to the hammer bit  111  via the striker  118  and the impact bolt  119  which form the striking mechanism  117 . Further, the rotation of the driving motor  111  is transmitted as rotation to the tool holder  113  and the hammer bit  111  (supported by the tool holder  113  such that the hammer bit  111  is prevented from rotating with respect to the tool holder  113 ) via the power transmitting mechanism  141 . Specifically, the hammer bit  115  is driven with the combined movement of string (hammering) and rotation (drilling). Thus, a predetermined hammer-drill operation can be performed on the workpiece. 
   When the user turns the mode-changing operating member  163  from the hammer drill mode position as shown in  FIG. 7  to the first hammer mode position as shown in  FIG. 9 , the frame member  173  is caused to move via the second eccentric pin  163   d  toward the rear (the handgrip  109 ) of the hammer drill  101 . Thus, the ring  175  and the cam  177  also move in this direction and the slanted surface  177   a  of the cam  177  presses on the clutch control member  159 . As a result, the clutch control member  159  pushes the driven clutch  155  away from the driving clutch  153  against the biasing force of the clutch spring  157 , so that the clutches are disengaged from each other. Therefore, the hammer bit  115  does not rotate in the first hammer mode (see  FIG. 3 ). 
   Further, as shown in  FIGS. 9 and 10 , by thus turning the mode-changing operating member  163 , the switch actuating member  165  is caused to move toward the rear of the hammer drill  101  via the first eccentric pin  163   c . However, with this travel of the switch actuating member  165 , the end  165   b  of the switch actuating member  165  comes near but still stays apart from the end  123   b  of the trigger  123 . Therefore, like in the above-mentioned hammer drill mode, the trigger  123  is held in the OFF position and allowed to be depressed to the ON position. Further, the lug  129   a  of the switch actuating member  129  is also located within the locking region  167   a  of the cam groove  167  of the switch actuating member  165 . Therefore, the sub-switch  127  is held in the ON position. Specifically, when the mode-changing operating member  163  is turned to the first hammer mode position, the switch actuating member  165  is caused to move so as to allow operation of the trigger  123  and to lock the switch actuating member  129  of the sub-switch  127  in the ON position. 
   In this state, when the trigger  123  is depressed to turn the main switch  125  to the ON position and the driving motor  111  is driven, the rotation of the driving motor  111  is converted into linear motion via the motion converting mechanism  131 . Then, the linear motion is transmitted to the hammer bit  111  via the striker  118  and the impact bolt  119  which form the striking mechanism  117 . At this time, the clutch mechanism  151  of the power transmitting mechanism  141  is in the disengaged state, so that rotation is not transmitted to the hammer bit  115 . Therefore, in the first hammer mode, the user can perform a predetermined hammering operation solely by the striking movement (hammering) of the hammer bit  115  by depressing the trigger  123  to turn the main switch  125  to the ON position. In the first hammer mode, the hammer bit  115  can be readily driven and stopped by depressing and releasing the trigger  123 . Therefore, this mode is particularly useful for a hammering operation in which the hammer bit  115  is driven on an on-again off-again basis. 
   When the mode-changing operating member  163  is turned from the first hammer mode position shown in  FIG. 9  to the second hammer mode position shown in  FIG. 11 , as shown in  FIG. 3 , the frame member  173  is caused to move via the second eccentric pin  163   d  farther toward the rear (the handgrip  109 ) of the hammer drill  101  than in the first hammer mode. Thus, the ring  175  and the cam  177  also move in this direction. At this time, a flat surface of the cam  177  slides on the upper surface of the clutch control member  159 , which does not cause to move the clutch control member  159 . Therefore, the clutches of the clutch mechanism  151  are held disengaged from each other. 
   Further, as shown in  FIGS. 11 and 12 , by thus turning the mode-changing operating member  163 , the switch actuating member  165  is caused to move farther toward the rear of the hammer drill  101  via the first eccentric pin  163   c . By this movement, the end  165   b  of the switch actuating member  165  presses on the end  123   b  of the trigger  123 . As a result, the trigger  123  is turned to a depressed position, so that the main switch  125  is turned to and locked in the ON position. Further, the lug  129   a  of the switch actuating member  129  moves from the locking region  167   a  to the switch actuation allowing region  167   b  via the switching region  167   c  in the cam groove  167  as the switch actuating member  165  moves. At this time, in the switching region  167   c , the V-shaped guide wall  167   d  guides the lug  129   a  of the switch actuating member  129  to move in a direction perpendicular to the moving direction of the switch actuating member  165 . As a result, the sub-switch  127  is turned from the ON position to the OFF position (downward as viewed in  FIG. 12 ). 
   Thus, when the mode-changing operating member  163  is turned to the second hammer mode position, the main switch  125  is locked in the ON position. At the same time, the sub-switch  127  is forced to be turned from the ON position to the OFF position, and then in the switch actuation allowing region  167   b , the user is allowed to turn the sub-switch  127  on and off. 
   In this state, when the switch actuating member  129  is pushed to turn the sub-switch  127  from the OFF position to the ON position, the driving motor  111  is driven. The clutch mechanism  151  of the power transmitting mechanism  141  is in the disengaged stat in the second hammer mode, so that the hammer bit  115  only performs a linear motion via the motion converting mechanism  131  and the striking mechanism  117 . In the second hammer mode, once the switch actuating member  129  of the sub-switch  127  is pushed in to the ON position, it is held in the ON position unless pushed in the opposite direction. Further, the trigger  123  of the main switch  125  is also locked in the ON position. Therefore, the user can perform a hammering operation by continuously driving the tool bit  115 . 
   Further, in the second hammer mode, when the mode-changing operating member  163  is turned to the first hammer mode position after the switch actuating member  129  of the sub-switch  127  is pushed in to the OFF position, the end  165   b  of the switch actuating member  165  is moved away from the end  123   b  of the trigger  123 . As a result, the trigger  123  returns to the ON position together with the main switch  125 . Further, by this movement of the switch actuating member  165 , the lug  129   a  of the switch actuating member  129  is pressed by the guide wall  167   e  in the switching region  167   c  of the cam groove  167  from the OFF position to the ON position. Thus, like in the above-mentioned case, the user can perform a predetermined hammering operation by the striking movement of the hammer bit  115  by depressing the trigger  123  to turn the main switch  125  to the ON position. According to this embodiment, in the hammering operation in the second hammer mode, the user can drive and stop the hammer bit  115  by sliding the switch actuating member  129  to turn the sub-switch  127  between the ON position and the OFF position as necessary. 
   On the other hand, according to the prior art, the trigger  123  is locked in the depressed position by an engaging member in order to effect continuous hammering operation. In this case, in order to drive the hammer bit in the hammer mode, the user must depress the trigger  123  and then operate the engaging member to lock the trigger in the depressed position. In other words, the user needs to perform two operations every time when trying to drive the hammer bit. To the contrary, according to this embodiment, the need for any operation of the trigger  123  is eliminated in the second hammer mode. The user only needs to actuate the switch actuating member  129  to toggle the sub-switch on and off. Therefore, ease of operation of the hammer drill  101  is enhanced compared with the prior art. 
   Further, according to this embodiment, when the mode-changing operating member  163  is turned from the first hammer mode position to the second hammer mode position, the sub-switch  127  is forced to be turned from the ON position to the OFF position. Therefore, even if the user changes from the first hammer mode to the second hammer mode with the trigger  123  inadvertently left depressed, the hammer bit  115  is not driven. Further, in this embodiment, when the mode-changing operating member  163  is turned from the second hammer mode position to the first hammer mode position, the sub-switch  127  is forced to be turned from the OFF position to the ON position. Therefore, the user need not operate the sub-switch  127  when operating the mode-changing operating member  163 . 
   Further, according to this embodiment, the trigger  123  and the switch actuating member  129  are linked with the switch actuating member  165 , so that both can be actuated by the switch actuating member  165  as single device. Therefore, the number of parts can be reduced and the structure can be simplified. Further, with the construction in which the actuation of the switch actuating member  129  is controlled by the cam groove  167  of the switch actuating member  165 , inadvertent push of the switch actuating member  129  can be reliably prevented in the hammer drill mode or the first hammer mode. 
   Further, in this embodiment, the switch actuating member  165  moves in the longitudinal direction of the body  103 , and the switch actuating member  129  is actuated in a direction perpendicular to the moving direction of the switch actuating member  165  or in a direction of extending through the side surfaces of the body  103 . With this construction, the switch actuating member  165  is arranged in a position to keep out of the way of the other functional parts, so that effective arrangement of parts can be realized. 
   The above-described invention can be applied to an electric hammer in which the hammer bit  155  only performs a striking movement. Further, the lug may be formed on the switch actuating member  165  and the cam groove in the switch actuating member  129 .