Abstract:
It is an object of the invention to provide a power tool having a rational structure. A representative power tool is provided to have a tool bit a power tool body, a motion converting mechanism housing chamber, a motion converting mechanism and a clutch mechanism. The power tool further includes a switching member, an opening, a rotating member, a switching operation transmitting mechanism and an actuating member. The switching member is disposed on an upper surface of the power tool body and can be manually operated by a user. The opening is provided to connect the motion converting mechanism housing chamber and the outside. The rotating member can rotate while closing the opening. The switching operation transmitting mechanism is disposed outside the motion converting mechanism housing chamber to connect the switching member to the rotating member and to transmit the switching operation effected by the user&#39;s manual operation of the switching member to the rotating member. The rotating member includes the actuating member that extends into the motion converting mechanism housing chamber to switch the clutch mechanism between the power transmission state and the power transmission interrupted state.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates to a power tool having a tool bit that performs a predetermined operation by linearly moving in its axial direction.  
         [0003]     2. Description of the Related Art  
         [0004]     German Patent Publication No. 19716976 discloses a hammer drill including a crank mechanism and a clutch mechanism within a motion converting mechanism housing chamber. The clutch mechanism is switched between a power transmission state to activate the crank mechanism and a power transmission interrupted state not to activate the crank mechanism by manually operating a clutch switching member. The clutch switching member is disposed on the upper surface of the power tool body in order to enhance an operability of the power tool.  
         [0005]     As to the motion converting mechanism housing chamber, lubrication is necessarily required for the crank mechanism and the clutch mechanism. In this connection, the total volume of the motion converting mechanism housing chamber should preferably be minimized in order to enhance the efficiency of the lubrication. Thus, it is necessary to take both the disposition of the clutch switching member and the structure of the motion converting mechanism housing chamber into account when designing the inner structure of the power tool.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, it is an object of the present invention to provide a power tool having a rational structure.  
         [0007]     The above-described problem can be solved by the features of claimed invention. According to the invention, a representative power tool is provided to have a tool bit that performs a predetermined operation by linearly moving in its axial direction. The “power tool” according to this invention typically includes an impact tool such as an electric hammer in which a tool bit performs axial striking movement or a hammer drill in which a tool bit performs axial striking movement and rotation on the axis. The power tool also suitably includes any power tool of the type in which a tool bit linearly moves in the axial direction.  
         [0008]     The power tool of the present invention includes a power tool body, a motion converting mechanism housing chamber, a motion converting mechanism and a clutch mechanism for the motion converting mechanism. The motion converting mechanism housing chamber is formed within the power tool body. Preferably, the motion converting mechanism housing chamber is hermetically closed and filled with lubricant for lubricating the mechanisms disposed within the motion converting mechanism housing chamber. The motion converting mechanism is disposed within the motion converting mechanism housing chamber and linearly moves the tool bit. The clutch mechanism for the motion converting mechanism is disposed within the motion converting mechanism housing chamber and switched between a power transmission state in which a driving force is transmitted to the motion converting mechanism and a power transmission interrupted state in which transmission of the driving force is interrupted.  
         [0009]     The power tool of this invention includes a switching member, an opening, a rotating member, a switching operation transmitting mechanism and an actuating member. The switching member is disposed on an upper surface of the power tool body and can be manually operated by a user to switch the operating state of the clutch mechanism. The opening is provided to connect the motion converting mechanism housing chamber and the outside. The rotating member can rotate while closing the opening. The switching operation transmitting mechanism is disposed outside the motion converting mechanism housing chamber to connect the switching member to the rotating member and to transmit the switching operation effected by the user&#39;s manual operation of the switching member to the rotating member. The rotating member includes the actuating member that extends into the motion converting mechanism housing chamber, and the actuating member switches the clutch mechanism between the power transmission state and the power transmission interrupted state by utilizing rotation of the rotating member.  
         [0010]     According to this invention, with the construction in which the switching member is disposed on the upper surface of the power tool body, the switching member can be easily operated by the user whether right-handed or left-handed. Further, with the construction in which the switching operation transmitting member is disposed outside the motion converting mechanism housing chamber, the capacity of the motion converting mechanism housing chamber can be reduced by the capacity for housing the switching operation transmitting mechanism. As a result, lubricant can be more readily supplied to the mechanisms disposed within the motion converting mechanism housing chamber, so that the lubricating effect can be enhanced.  
         [0011]     Further, with the construction in which the clutch mechanism is switched by utilizing rotation of the rotating member, the opening can be held closed by the rotating member. Therefore, even in the construction in which the switching operation transmitting mechanism is disposed outside the motion converting mechanism housing chamber, switching of the clutch mechanism can be efficiently effected while avoiding the lubricant from leaking out of the motion converting mechanism housing chamber through the opening.  
         [0012]     Thus, according to this invention, utilizing the advantage of placement of the switching member on the upper surface of the power tool body, the capacity of the motion converting mechanism housing chamber can be reduced while preventing lubricant from leaking out of the motion converting mechanism housing chamber, so that the lubricity of the mechanisms within the motion converting mechanism housing chamber can be enhanced.  
         [0013]     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  
       [0014]      FIG. 1  is a sectional side view schematically showing an entire hammer drill according to a first representative embodiment of the invention.  
         [0015]      FIG. 2  is a sectional side view of an essential part of the hammer drill in hammer mode.  
         [0016]      FIG. 3  is a sectional side view of the essential part of the hammer drill in hammer drill mode.  
         [0017]      FIG. 4  is a sectional side view of the essential part of the hammer drill in drill mode.  
         [0018]      FIG. 5  is a plan view showing a mode switching member in the hammer mode.  
         [0019]      FIG. 6  is a plan view showing the mode switching member in the hammer drill mode.  
         [0020]      FIG. 7  is a plan view showing the mode switching member in the drill mode.  
         [0021]      FIG. 8  is a sectional plan view showing a second switching mechanism in the hammer mode.  
         [0022]      FIG. 9  is a sectional plan view showing the second switching mechanism in the hammer drill mode.  
         [0023]      FIG. 10  is a sectional plan view showing the second switching mechanism in the drill mode.  
         [0024]      FIG. 11  is a sectional side view of an essential part of a hammer drill, in the hammer drill mode according to a second representative embodiment of the invention.  
         [0025]      FIG. 12  is a sectional side view of the essential part of the hammer drill in the drill mode according to the second embodiment of the invention.  
         [0026]      FIG. 13  is a plan view showing a swinging member.  
         [0027]      FIG. 14  is a side view showing the swinging member and a rotating member.  
         [0028]      FIG. 15  is a sectional side view schematically showing an entire hammer drill according to a third representative embodiment of the invention.  
         [0029]      FIG. 16  is a sectional side view of an essential part of the hammer drill.  
         [0030]      FIG. 17  illustrates the construction and method for mounting a first switching mechanism in a gear housing.  
         [0031]      FIG. 18  is an illustration as viewed from the direction of arrow A in  FIG. 17 .  
         [0032]      FIG. 19  is a sectional view taken along line B-B in  FIG. 17 .  
         [0033]      FIG. 20  is an illustration as viewed from the direction of arrow C in  FIG. 17 .  
         [0034]      FIG. 21  is a sectional side view schematically showing an entire hammer drill according to a fourth embodiment of the invention.  
         [0035]      FIG. 22  is a sectional side view of an essential part of the hammer drill in hammer mode.  
         [0036]      FIG. 23  is a sectional side view of an essential part of the hammer drill in drill mode.  
         [0037]      FIG. 24  is a plan view showing the configuration of a dynamic vibration reducer.  
         [0038]      FIG. 25  is a sectional view showing the entire dynamic vibration reducer.  
         [0039]      FIG. 26  is a sectional view taken along line A-A in  FIG. 24 .  
         [0040]      FIG. 27  is a sectional view taken along line B-B in  FIG. 24 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     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.  
       First Representative Embodiment  
       [0042]     A first representative embodiment of the present invention will now be described with reference to FIGS.  1  to  10 .  FIG. 1  is a sectional side view showing an entire electric hammer drill  101  as a representative embodiment of the power impact tool according to the present invention. As shown in  FIG. 1 , the hammer drill  101  of this embodiment includes a body  103 , a hammer bit  119  detachably coupled to the tip end region (on the left side as viewed in  FIG. 1 ) of the body  103  via a hollow tool holder (not shown), and a handgrip  109  that is held by a user and connected to the body  103  on the side opposite to the hammer bit  119 . The hammer bit  119  is held by the tool holder such that it is allowed to reciprocate with respect to the tool holder in its axial direction and prevented from rotating with respect to the tool holder in its circumferential direction. The hammer bit  119  is a feature that corresponds to the “tool bit” according to the present invention. In the present embodiment, for the sake of convenience of explanation, the side of the hammer bit  119  is taken as the front side and the side of the handgrip  109  as the rear side.  
         [0043]     The body  103  includes a motor housing  105  that houses a driving motor  111 , and a gear housing  107  that houses a motion changing mechanism  131 , a striking mechanism  115  and a power transmitting mechanism  117 . The motion changing 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 hammer bit  119  via the striking mechanism  115 . Further, the speed of the rotating output of the driving motor  111  is appropriately reduced by the power to transmitting mechanism  117  and then transmitted to the hammer bit  119 . As a result, the hammer 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.  
         [0044]     FIGS.  2  to  4  show an essential part of the hammer drill  101  in enlarged sectional view. The motion changing mechanism  113  includes a driving gear  121  that is rotated in a horizontal plane by the driving motor  111 , a driven gear  123 , a crank shaft  122 , a crank plate  125 , a crank arm  127  and a driving element in the form of a piston  129 . The crank shaft  122 , the crank plate  125 , the crank arm  127  and the piston  129  form a crank mechanism  114 . The piston  129  is slidably disposed within the cylinder  141  and reciprocates along the cylinder  141  when the driving motor  111  is driven.  
         [0045]     The crank shaft  122  is disposed such that its longitudinal direction is a vertical direction crossing the axial direction of the hammer bit  119 . A clutch member  124  is disposed between the crank shaft  122  and the driven gear  123 . The clutch member  124  has a cylindrical shape and has a flange  124   b  extending outward from one axial end (upper end) of the clutch member  124 . The clutch member  124  is mounted on the crank shaft  122  such that the clutch member  124  can move in the longitudinal direction with respect to the crank shaft  122  and rotate together in the circumferential direction. The clutch member  124  further has clutch teeth  124   a  on the outer periphery. The driven gear  123  has a circular recess and clutch teeth  123   a  are formed in the inner circumferential surface of the circular recess. The teeth  124   a  of the clutch member  124  are engaged with and disengaged from the clutch teeth  123   a  of the driven gear  123  when the clutch member  124  moves on the crank shaft  122  in the longitudinal direction. In other words, the clutch member  124  can be switched between a power transmission state (see  FIGS. 2 and 3 ) in which the driving force of the driven gear  123  is transmitted to the crank shaft  122  and a power transmission interrupted state (see  FIG. 4 ) in which such transmission of the driving force is interrupted. The clutch member  124  is normally biased by a biasing spring  126  in the direction of engagement between the clutch teeth  124   a  and the clutch teeth  123   a  of the driven gear  123 .  
         [0046]     The striking mechanism  115  includes a striker  143  and an impact bolt  145  (see  FIG. 1 ). The striker  143  is slidably disposed within the bore of the cylinder  141 . The impact bolt  145  is slidably disposed within the tool holder and serves as an intermediate element to transmit the kinetic energy of the striker  143  to the hammer bit  119 . The striker  143  is driven via the action of an air spring of an air chamber  141   a  of the cylinder  141  which is caused by sliding movement of the piston  129 . The striker  143  then collides with (strikes) the impact bolt  145  that is slidably disposed within the tool holder, and transmits the striking force to the hammer bit  119  via the impact bolt  145 .  
         [0047]     The power transmitting mechanism  117  includes an intermediate gear  132  that engages with the driving gear  121 , an intermediate shaft  133  that rotates together with the intermediate gear  132 , a small bevel gear  134  that is caused to rotate in a horizontal plane together with the intermediate shaft  133 , a large bevel gear  135  that engages with the small bevel gear  134  and rotates in a vertical plane, and a slide sleeve  147  that engages with the large bevel gear  135  and is caused to rotate. The rotation driving force of the slide sleeve  147  is transmitted to the tool holder via the cylinder  141  which rotates together with the slide sleeve  147 , and then further transmitted to the hammer bit  119  held by the tool holder. The slide sleeve  147  can move with respect to the cylinder  141  in the axial direction of the hammer bit and rotates together with the cylinder  141  in the circumferential direction.  
         [0048]     The slide sleeve  147  forms a clutch mechanism in the power transmitting mechanism  117 . Clutch teeth  147   a  are formed on the outer periphery of one longitudinal end portion of the slide sleeve  147  and engage with clutch teeth  135   a  of the large bevel gear  135  when the slide sleeve  147  moves rearward (toward the handgrip) with respect to the cylinder  141 . Such engagement is released when the slide sleeve  147  moves forward (toward the hammer bit) with respect to the cylinder  141 . In other words, the slide sleeve  147  can be switched between a power transmission state (see  FIGS. 3 and 4 ) in which the rotation driving force of the large bevel gear  135  is transmitted to the cylinder  141  and a power transmission interrupted state (see  FIG. 2 ) in which such transmission of the driving force is interrupted. The slide sleeve  147  is normally biased by a biasing spring  148  in the direction of engagement between the clutch teeth  147   a  and the clutch teeth  135   a  of the large bevel gear  135 .  
         [0049]     Further, rotation locking teeth  147   b  are formed on the other longitudinal end (forward end) of the slide sleeve  147 . When the slide sleeve  147  is caused to move forward and switched to the power transmission interrupted state (when the hammer bit  119  is driven in the hammer mode), the teeth  147   b  of the slide sleeve  147  engage with teeth  149   a  of a lock ring  149  that is locked in the circumferential direction with respect to the gear housing  107 . As a result, the cylinder  141 , the tool holder and the hammer bit  119  can be locked against free movement in the circumferential direction (“variolock”).  
         [0050]     The motion changing mechanic  113  and the power switching mechanism  117  are housed within a crank chamber  151  or the inside space of the gear housing  107 . Sliding parts are lubricated by lubricant (grease) filled in the crank chamber  151 .  
         [0051]     A mode switching mechanism  153  for switching between driving modes of the hammer bit  119  will now be explained with reference to FIGS.  2  to  10 . The mode switching mechanism  153  can be switched among a hammer mode in which the hammer bit  119  is caused to perform only striking movement, a hammer drill mode in which the hammer bit  119  is caused to perform both the striking movement and rotation, and a drill mode in which the hammer bit  119  is caused to perform only rotation.  
         [0052]     As shown in FIGS.  2  to  4 , the mode switching mechanism  153  mainly includes a mode switching member  155 , a first switching mechanism  157  that switches the clutch member  124  of the crank mechanism  114  according to the switching operation of the mode switching member  155 , and a second switching mechanism  159  that switches the slide sleeve  147  of the power transmitting mechanism  117 . The mode switching member  155  is a feature that corresponds to the “switching member” according to this invention. The mode switching member  155  is mounted externally on the upper surface of the gear housing  107 . In other words, the mode switching member  155  is disposed above the crank mechanism  114 . As shown in FIGS.  5  to  7 , the mode switching member  155  includes a disc  155   a  with an operating grip  155   b  and is mounted on the gear housing  107  such that it can be turned in a horizontal plane. The three mode positions, i.e. hammer mode position, hammer drill mode position, and drill mode position, are marked on the gear housing  107  at 120° intervals in the circumferential direction of the disc  155   a . The mode switching member  155  can be switched to a desired mode position by placing the pointer of the operating grip  155   b  on the appropriate mark.  FIG. 5  shows the mode switching member  155  placed in the hammer mode position,  FIG. 6  shows it in the hammer drill mode position, and  FIG. 7  shows it in the drill mode position.  
         [0053]     The first switching mechanism  157  is constructed such that switching of the clutch member  124  of the crank mechanism  114  is effected by revolution (eccentric revolution) of a first eccentric pin  167  on the axis of rotation of a rotating member  166  when the mode switching member  155  is turned for mode change. The first switching mechanism  157  mainly includes a first gear  161 , a second gear  162 , a rotation transmitting shaft  163 , a third gear  164 , a fourth gear  165 , the rotating member  166  and the first eccentric pin  167 .  
         [0054]     The first gear  161  rotates in a horizontal plane together with the mode switching member  155  when the mode switching member  155  is turned in a horizontal plane. The second gear  162  is integrally formed on one longitudinal end portion (upper end portion) of the rotation transmitting shaft  163  and engages with the first gear  161 . The rotation transmitting shaft  163  is disposed vertically such that its longitudinal direction is parallel to the longitudinal direction of the crank shaft  122 . The third gear  164  is integrally formed on the other longitudinal end portion (lower end portion) of the rotation transmitting shaft  163  and engages with the fourth gear  165 . The fourth gear  165  is integrally formed on the rotating member  166 . The rotating member  166  is horizontally disposed below the rotation transmitting shaft  163  such that its longitudinal direction is perpendicular to the rotation transmitting shaft  163 . Each of third and fourth gears  164 ,  165  comprises a bevel gear and engages with the other.  
         [0055]     When the mode switching member  155  is turned, the rotation transmitting shaft  163  rotates in a horizontal plane via the first and second gears  161 ,  162 . The rotation of the rotation transmitting shaft  163  is further transmitted as rotation in a vertical plane to the rotating member  166  via the third and fourth gears  164 ,  165 . The first eccentric pin  167  is provided on the axial end surface of the rotating member  166  and disposed in a position displaced a predetermined distance from the axis of rotation of the rotating member  166 . The first eccentric pin  167  is disposed to face the underside of the flange  124   b  of the clutch member  124 . Therefore, when the rotating member  166  rotates in a vertical plane and thus the first eccentric pin  167  eccentrically revolves on the axis of rotation of the rotating member  166 , the first eccentric pin  167  vertically moves the clutch member  124  along the crank shaft  122  while engaging with the flange  124   b  of the clutch member  124  by its vertical components (components in the longitudinal direction of the crank shaft  122 ) of the revolving movement. In this manner, the first eccentric pin  167  moves the clutch member  124  between the power transmission position and the power transmission interrupted position. The first gear  161 , the second gear  162 , the rotation transmitting shaft  163 , the third gear  164  and the fourth gear  165  form a switching operation transmitting mechanism  169 . The first eccentric pin  167  is a feature that corresponds to the “actuating member” according to this invention.  
         [0056]     The first and second gears  161 ,  162  of the first switching mechanism  157  are disposed within the crank chamber  151 , while the rotation transmitting shaft  163 , the third gear  164 , the fourth gear  165  and the rotating member  166  of the first switching mechanism  157  are disposed outside the crank chamber  151 . Specifically, a housing space  152  for housing the switching operation transmitting mechanism  169  is provided within the gear housing  107  and houses the rotation transmitting shaft  163 , the third gear  164 , the fourth gear  165  and the rotating member  166 . The housing space  152  is a feature that corresponds to the “outside” according to this invention. The housing space  152  communicates with the crank chamber  151  via a circular opening  168 . The rotating member  166  is disposed such that a circular periphery of the rotating member  166  is closely fitted in the opening  168  in such a manner as to close the opening  168  and the rotating member  166  can rotate in this state. The first eccentric pin  167  is disposed to generally horizontally extend into the crank chamber  151  via the opening  168  and to face the underside of the flange  124   b  of the clutch member  124 .  
         [0057]     When the mode switching member  155  is turned to the hammer mode position or the hammer drill mode position, as shown in  FIGS. 2 and 3 , the first eccentric pin  167  is moved to a position on the same level as or below the axis of rotation of the rotating member  166  in the vertical direction. At this time, the clutch member  124  is moved downward by the biasing spring  126  and the clutch teeth  124   a  engage with the clutch teeth  123   a  of the driven gear  123 . Thus, the clutch member  124  is switched to the power transmission state. On the other hand, when the mode switching member  155  is turned to the drill mode position, as shown in  FIG. 4 , the first eccentric pin  167  is moved to a position higher than the axis of rotation of the rotating member  166  in the vertical direction. At this time, the clutch member  124  is moved upward by the first eccentric pin  167  against the biasing force of the biasing spring  126  and thus the engagement between the teeth  124   a ,  123   a  is released. Thus, the clutch member  124  is switched to the power transmission interrupted state.  
         [0058]     The second switching mechanism  159  will now be explained with reference to FIGS.  8  to  10 . The second switching mechanism  159  is constructed such that switching of the slide sleeve  147  of the power transmitting mechanism  117  is effected by linear motion of a generally U-shaped frame member  173  in the longitudinal direction of the cylinder  141 . The second switching mechanism  159  mainly includes the frame member  173  that is generally U-shape in plan view and disposed within the crank chamber  151 . The frame member  173  is a feature that corresponds to the “clutch switching mechanism” according to this invention.  
         [0059]     As shown in FIGS.  8  to  10 , the frame member  173  includes a base  173   a  which extends horizontally in a direction crossing the longitudinal direction of the cylinder  141 , and two legs  173   b  which extend horizontally in the longitudinal direction of the cylinder  141  through the space outside the large bevel gear  135 . The base  173   a  has connecting pins  173   c  on the both ends in the extending direction, and the connecting pins  173   c  are engaged in recesses of the legs  173   b . Thus, the base  173   a  and the legs  173   b  moves together in the longitudinal direction of the cylinder  141 . An oblong hole  173   d  is formed in the base  173   a  of the frame member  173  and engages with a second eccentric pin  175  (shown in cross section in FIGS.  8  to  10 ). The second eccentric pin  175  is provided on the underside of the first gear  161  of the first switching mechanism  157  and disposed in a position displaced a predetermined distance from the axis of rotation of the first gear  161 . Therefore, when the second eccentric pin  175  revolves on the axis of rotation of the first gear  161 , the second eccentric pin  175  moves the frame member  173  in the longitudinal direction of the cylinder  141  by its longitudinal components (components in the longitudinal direction of the cylinder  141 ) of the revolving movement.  
         [0060]     When the mode switching member  155  is actuated, the frame member  173  is linearly moved in the longitudinal direction of the cylinder  141  by the second eccentric pin  175  engaged with the oblong hole  173   c . The legs  173   b  extend through the region outside the large bevel gear  135 , and ends of the legs  173   b  in the extending direction reach the outside of the slide sleeve  147 . An engagement end  173   e  is formed on the end of each of the legs  173   b  in the extending direction and can engage with a stepped portion  147   c  of the slide sleeve  147  in the extending direction. The engagement end  173   e  is formed by bending the end of the leg  173   b  inward (toward the slide sleeve  147 ).  
         [0061]     When the mode switching member  155  is turned to the hammer mode position, as shown in  FIGS. 2 and 8 , the frame member  173  is moved forward (leftward as viewed in the drawing) by the second eccentric pin  175  and pushes the stepped portion  147   c  of the slide sleeve  147  forward against the biasing spring  148  by the leg engagement ends  173   e . As a result, the slide sleeve  147  is moved forward away from the large bevel gear  135 , and the clutch teeth  147   a  of the slide sleeve  147  are disengaged from the clutch teeth  135   a  of the large bevel gear  135 . Thus, the slide sleeve  147  is switched to the power transmission interrupted state. On the other hand, when the mode switching member  155  is tuned to the hammer drill mode position or the drill mode position, as shown in  FIGS. 3 and 9  or  FIGS. 4 and 10 , the frame member  173  is moved rearward (rightward as viewed in the drawings) by the second eccentric pin  175 , and the engagement ends  173   e  on the leg ends are disengaged from the stepped portion  147   c  of the slide sleeve  147 . Then the slide sleeve  147  is moved rearward toward the large bevel gear  135  by the biasing force of the biasing spring  148 , and the clutch teeth  147   a  of the slide sleeve  147  engage with the clutch teeth  135   a  of the large bevel gear  135 . Thus, the slide sleeve  147  is switched to the power transmission state.  
         [0062]     Further, when the mode switching member  155  is turned to the hammer mode position, the instant when the slide sleeve  147  is placed in the power transmission interrupted state, the rotation locking teeth  147   b  of the slide sleeve  147  engage with the teeth  149   a  of the lock ring  149  and thus the slide sleeve  147  is locked against movement in the circumferential direction (“variolock” is effected).  
         [0063]     Operation and usage of the hammer drill  101  constructed as described above will now be explained. When the user turns the mode-switching member  155  from the hammer drill mode position or the drill mode position to the hammer mode position shown in  FIG. 5 , in the first switching mechanism  157 , the rotating member  166  is caused to rotate via the rotation transmitting shaft  163  and the third and fourth gears  164 ,  165 . At this time, as shown in  FIG. 2 , the first eccentric pin  167  is caused to revolve downward about 120° on the axis of rotation of the rotating member  166  from its position in the hammer drill mode or the drill mode and is thus disengaged from the flange  124   b  of the clutch member  124 . As a result, the clutch member  124  is moved downward toward the driven gear  123  by the biasing spring  126 , and the clutch teeth  124   a  of the clutch member  124  engage with the clutch teeth  123   a  of the driven gear  123 . Thus, the clutch member  124  is switched to the power transmission state.  
         [0064]     Meanwhile, in the second switching mechanism  159 , the second eccentric pin  175  is caused to revolve about 120° on the axis of rotation of the first gear  161  from its position in the hammer drill mode or the drill mode and moves the frame member  173  forward (toward the hammer bit  115 ). At this time, as shown in  FIGS. 2 and 8 , the forward moving frame member  173  pushes the slide sleeve  147  forward by the engagement ends  173   e  of the legs  173   b , and thus the clutch teeth  147   a  of the slide sleeve  147  are disengaged from the clutch teeth  135   a  of the large bevel gear  135 . Thus, the slide sleeve  147  is switched to the power transmission interrupted state. Further, the rotation locking teeth  147   b  of the slide sleeve  147  engage with the teeth  149   a  of the lock ring  149  and thus the slide sleeve  147  is locked against movement in the circumferential direction (“variolock”).  
         [0065]     In order to drive the hammer bit  119  in the hammer mode, the hammer bit  119  is adjusted (positioned) to a predetermined orientation in the circumferential direction. This adjustment can be made in the state in which the mode switching member  155  is turned to an intermediate position (neural position), which is not shown, between the hammer mode position and the hammer drill mode position, or between the hammer mode position and the drill mode position. Specifically, in this intermediate position, the clutch teeth  147   a  of the slide sleeve  147  are disengaged from the clutch teeth  135   a  of the large bevel gear  135 , and the rotation locking teeth  147   b  of the slide sleeve  147  are disengaged from the teeth  149   a  of the lock ring  149 . In this neutral state, the hammer bit  119  is adjusted in orientation. Thereafter, when the mode switching member  155  is turned to the hammer mode position, the above-mentioned “variolock” can be effected and the hammeing operation can be performed with the hammer bit  119  held in fixed orientation.  
         [0066]     In this state in which the mode switching member  155  is in the hammer mode position, when the trigger  109   a  is depressed to drive the driving motor  111 , the rotation of the driving motor  111  is converted into linear motion by the crank mechanism  114 . The piston  129  then linearly slides along the cylinder  141 . The striker  143  is caused to reciprocate within the cylinder  141  via the action of an air spring or pressure fluctuation of air within the air chamber  141   a  of the cylinder  141  which is caused by sliding movement of the piston  129 . The striker  143  then collides with the impact bolt  145  and transmits the kinetic energy to the hammer bit  119 . At this time, the slide sleeve  147  of the power transmitting mechanism  117  is in the power transmission interrupted state. Therefore, the hammer bit  119  does not rotate. Thus, in the hammer mode, a predetermined hammering operation can be performed solely by the striking movement (hammering movement) of the hammer bit  119 .  
         [0067]     Next, when the user turns the mode switching member  155  from the hammer mode position to the hammer drill mode position shown in  FIG. 6 , as shown in  FIG. 3 , the first eccentric pin  167  of the first switching mechanism  157  is caused to revolve about 120° on the axis of rotation of the rotating member  166  from its position in the hammer mode and comes close to the flange  124   b  of the clutch member  124 . The first eccentric pin  167  only comes into contact with or faces the flange  124   b  with a slight clearance therebetween, and falls short of pushing up the flange  124   b . Therefore, the clutch member  124  is held in the power transmission state. Meanwhile, the second eccentric pin  175  of the second switching mechanism  159  is caused to revolve about 120° on the axis of rotation of the first gear  161  from its position in the hammer mode and moves the frame member  173  rearward as shown in  FIG. 9 . Thus, the engagement ends  173   e  of the frame member  173  are disengaged from the slide sleeve  147 , and then the slide sleeve  147  is moved toward the large bevel gear  135  by the biasing force of the biasing spring  148 . As a result, the clutch teeth  147   a  engage with the clutch teeth  135   a  of large bevel gear  135 . Thus, the slide sleeve  147  is switched to the power transmission state.  
         [0068]     In this state, when the trigger  109   a  of the handgrip  109  is depressed to drive the driving motor  111 , like in the hammer mode, the crank mechanism  114  is driven, and kinetic energy is transmitted to the hammer bit  119  via the striker  143  and the impact bolt  145  which form the striking mechanism  115 . Meanwhile, the rotating output of the driving motor  111  is transmitted as rotation to the cylinder  141  via the power transmitting mechanism  117  and further transmitted as rotation to the tool holder connected to the cylinder  141  and to the hammer bit  119  held by the tool holder in such a manner as to be locked against relative rotation. Specifically, in the hammer drill mode, the hammer bit  119  is driven in the combined movement of striking (hammering) and rotation (drilling), so that a predetermined hammer-drill operation can be performed on a workpiece.  
         [0069]     Next when the mode switching member  155  is turned from the hammer drill mode position to the drill mode position shown in  FIG. 7 , as shown in  FIG. 4 , the first eccentric pin  167  of the first switching mechanism  157  is caused to revolve about 120° on the axis of rotation of the rotating member  166  from its position in the hammer drill mode to the uppermost position in the vertical direction and pushes up the flange  124   b  of the clutch member  124 . In other words, the clutch member  124  is moved upward away from the driven gear  123 , so that the clutch teeth  124   a  of the clutch member  124  are disengaged from the clutch teeth  123   a  of the driven gear  123 . Thus, the clutch member  124  is switched to the power transmission interrupted state. Meanwhile, the second eccentric pin  175  of the second switching mechanism  159  is caused to revolve about 120° on the axis of rotation of the first gear  161  from its position in the hammer drill mode. At this time, as shown in  FIG. 10 , the second eccentric pin  175  moves through a circular arc region of the oblong hole  173   d  of the base  173   a  of the frame member  173 , so that the longitudinal components of the revolving movement of the second eccentric pin  175  are not transmitted to the frame member  173 . Therefore, the frame member  173  is held in the same position as in the hammer drill mode, and the slide sleeve  147  is held in the power transmission state.  
         [0070]     In this state, when the trigger  109   a  of the handgrip  109  is depressed to drive the driving motor  111 , because the clutch member  124  is held in the power transmission interrupted state, the crank mechanism  114  is not driven and the hammer bit  119  does not perform the striking movement. Meanwhile, in the power transmitting mechanism  117 , the slide sleeve  147  is held in the power transmission state, so that the rotating output of the driving motor  111  is transmitted as rotation to the hammer bit  119 . Specifically, in the drill mode, the hammer bit  119  is driven solely by rotation (drilling movement), so that a predetermined drill operation can be performed on a workpiece.  
         [0071]     In the electric hammer drill  101  according to this embodiment, the mode switching member  155  is disposed externally on the upper surface of the gear housing  107  or on the upper surface of the body  103 . With this construction, the mode switching member  155  can be easily operated with one hand, whether right or left, while holding the handgrip  109  with the other hand.  
         [0072]     Further, the rotation transmitting shaft  163 , third gear  164 , the fourth gear  165  and the rotating member  166  for transmitting the switching operation of the mode switching member  155  to the rotating member  166  are disposed outside the crank chamber  151 . Therefore, the capacity (volume) of the crank chamber  151  can be reduced by the capacity (volume) for housing these components. Thus, the lubricant filled in the crank chamber  151  can be readily supplied to the sliding parts of the crank mechanism  114  and the power transmitting mechanism  117  which are housed within the crank chamber  151 , so that these mechanisms improve in lubricity. Further, by reduction of the capacity of the crank chamber  151 , the required amount of lubricant to be filled in the crank chamber  151  can be reduced.  
         [0073]     Further, with the construction in which switching of the clutch member  124  is effected by utilizing rotation of the rotating member  166 , the opening  168  connecting the crank chamber  151  and the housing space  152  can be closed all the time by the rotating member  166 . Thus, even in the construction in which the switching operation transmitting mechanism  169  is disposed outside the crank chamber  151 , switching of the clutch member  124  can be efficiently effected while avoiding the lubricant from leaking out of the crank chamber  151 .  
         [0074]     Further, according to this embodiment, in the construction in which the mode switching member  155  and the clutch member  124  are disposed on the opposite sides of the crank mechanism  114  in the vertical direction, an efficient switching arrangement is realized by utilizing the vertically extending rotation transmitting shaft  163  and the rotating member  166  having the eccentric pin  167  and extending in the direction crossing the rotation transmitting shaft  163 . Such switching arrangement allows the clutch member  124  to be switched between the power transmission state and the power transmission interrupted state, while avoiding interference with the crank mechanism  114 . In this case, rotation transmitting shaft  163  and the rotating member  166  rotate in the installed position and are connected to each other by the bevel gears in the form of the third and fourth gears  164 ,  165 , so that the rotation transmitting shaft  163  and the rotating member  166  can be installed in a smaller space.  
         [0075]     Further, in this embodiment, the eccentric pin  167  disposed in a position displaced from the axis of rotation of the rotating member  166  is designed as an actuating member for switching the clutch member  124  between the power transmission state and the power transmission interrupted state. Thus, switching of the state of the clutch member  124  can be realized with a simple construction, which is effective in simplification in structure and cost reduction.  
       Second Representative Embodiment  
       [0076]     A second representative embodiment of the present invention is explained with reference to FIGS.  11  to  14 . This embodiment relates to a modification to the switching arrangement for switching the clutch member  124  of the crank mechanism  114  between the power transmission state and the power transmission interrupted state. Therefore, components which are substantially identical to those in the first embodiment are given like numerals as in the first embodiment and will not be described.  
         [0077]      FIGS. 11 and 12  are sectional views showing an essential part of the hammer drill  101  having a first switching mechanism  181  according to this embodiment.  FIG. 13  is a plan view showing the first switching mechanism  181  and  FIG. 14  is a side view of the first switching mechanism  181 . The first switching mechanism  181  according to this embodiment mainly includes a swinging member  183  and a rotating member  185 . The swinging member  183  forms a switching operation transmitting mechanism for transmitting the switching operation of the mode switching member  155  to the rotating member  185 . The swinging member  183  includes a plate-like member having a generally L-shaped section including a horizontal plate portion  183   a  and a vertical plate portion  183   b . The horizontal plate portion  183   a  is disposed under the mode switching member  155 , and the front end portion (on the hammer bit side) of the horizontal plate portion  183   a  is connected to the gear housing  107  via a pin  107   a  formed on the gear housing  107  such that the horizontal plate portion  183   a  can swing on the pin  107   a  in a horizontal plane. Further, the horizontal plate portion  183   a  has a slot  183   c  extending in the longitudinal direction of the cylinder  141 . An eccentric portion  155   c  of the mode switching member  155  is engaged with the slot  183   c . Therefore, when the mode switching member  155  is turned, the swinging member  183  swings horizontally on the pin  107   a . Further, the slot  183   c  may be formed in the mode switching member  155 , and the eccentric portion  155   c  may be provided on the horizontal plate portion  183   a.    
         [0078]     The vertical plate portion  183   b  of the swinging member  183  is disposed outside the crank chamber  151  or in the housing space  152  of the gear housing  107 . The vertical plate portion  183   b  has a circular arc shape having its center on the pin  107   a  and extends downward from a connection with the horizontal plate portion  183   a . A gear  183   d  is formed in the lower end of the vertical plate portion  183   b  and extends in the swinging direction. The gear  183   d  is engaged with a circular gear  185   a  formed in the rotating member  185 . The rotating member  185  has a first eccentric pin  187 . The first eccentric pin  187  extends into the crank chamber  151  through an opening  188  and can engage with the underside of the flange  124   b  of the clutch member  124 , like in the first embodiment. Further, the vertical plate portion  183   b  has a guide groove  183   e  extending in the swinging direction, and the guide groove  183   e  engages with a guide pin  107   b  extending horizontally from the gear housing  107 . Therefore, the swinging member  183  swings while being guided by the guide pin  107   b , so that the swinging movement is stabilized.  
         [0079]     The first switching mechanism  181  according to this embodiment is thus constructed. Therefore, when the mode switching member  155  is turned for a mode change, the swinging member  183  is caused to swing clockwise or counterclockwise on the pin  107   a  by the eccentric portion  155   c  of the mode switching member  155 . Then the rotating member  185  is caused to rotate via the gears  183   d ,  185   a . When the rotating member  185  rotates, the first eccentric pin  187  revolves on the axis of rotation of the rotating member  185  and thus, the vertical position of the first eccentric pin  187  changes. As a result, the clutch member  124  is moved in the longitudinal direction of the crank shaft  122  and thus switched to the power transmission state or the power transmission interrupted state, like in the first embodiment.  FIG. 12  shows the state in which the mode switching member  155  is turned to the hammer drill mode position and the clutch member  124  is switched to the power transmission state.  FIG. 13  shows the state in which the mode switching member  155  is turned to the drill mode position and the clutch member  124  is switched to the power transmission interrupted state.  
         [0080]     According to this embodiment, the rotating member  185  having the first eccentric pin  187  for switching the operating state of the clutch member  124  and the swinging member  183  for transmitting the switching operation of the mode switching member  155  to the rotating member  185  are disposed outside the crank chamber  151 . Therefore, like in the first embodiment, the capacity of the crank chamber  151  can be reduced while avoiding the lubricant from leaking out of the crank chamber  151 , so that the effect of the lubricant lubricating the crank mechanism  114  or the power transmitting mechanism  117  can be enhanced.  
         [0081]     Further, with the construction in which the rotating member  185  is caused to rotate by utilizing the swinging movement of the swinging member  183 , the swinging member  183  can be reduced in thickness in the longitudinal direction crossing the direction of the swinging movement. Therefore, the housing space  152  within the gear housing  107  can be reduced in the longitudinal direction, so that the body  103  can be reduced in size in the longitudinal direction.  
       Third Representative Embodiment  
       [0082]     A third representative embodiment of the present invention is explained with reference to FIGS.  15  to  20 . This embodiment relates to a mounting structure mounting operation of the first switching mechanism  157  according to the above-described mode switching mechanism  153 . Therefore, components which are substantially identical to those in the first embodiment are given like numerals as in the first embodiment and will not be described.  
         [0083]      FIG. 17  illustrates the construction and method for mounting the first switching mechanism  157  in the gear housing  107 .  FIG. 18  is an illustration as viewed from the direction of arrow A in  FIG. 17 .  FIG. 19  is a sectional view taken along line B-B in  FIG. 17 .  FIG. 20  is an illustration as viewed from the direction of arrow C in  FIG. 17 .  
         [0084]     As mentioned above, the first switching mechanism  157  includes the first gear  161  integrally formed with the mode switching member  155 , the second gear  162  that engages with the first gear  161 , the rotation transmitting shaft  163  having the second gear  162  as an integral part, the third gear  164  integrally formed with the rotation transmitting shaft  163 , the fourth gear  165  that engages with the third gear  164 , the rotating member  166  having the fourth gear  165  as an integral part, and the first eccentric pin  167  integrally formed with the rotating member  166 . In this construction, the positional relationship between the switching position to which the mode switching member  155  is turned and the operating position to which the first eccentric pin  167  is moved when the mode switching member  155  is turned for mode change is extremely important. In other words, if the positional relationship is not proper, the first eccentric pin  167  fails to move the clutch member  124  by a predetermined amount, which may cause a malfunction. In order to avoid such malfunction, when the above-mentioned members forming the first switching mechanism  157  are mounted in the gear housing  107 , the engagement between the first and second gears  161  and  162  and the engagement between the third and fourth gears  164  and  165  must be made in respective predetermined proper positional relationships with respect to each other in the respective circumferential directions (in the respective directions of rotation).  
         [0085]     The members forming the first switching mechanism  157  are mounted in the gear housing  107  by inserting the rotating member  166  having the first eccentric pin  167  and the fourth gear  165 , the rotation transmitting shaft  163  having the third gear  164  and the second gear  162 , and the mode switching member  155  having the first gear  161 , in this order, into associated mounting holes  107   c ,  107   d ,  107   e  (see  FIG. 16 ) of the gear housing  107 . The inserting order and direction are shown by numerals and arrows in  FIG. 17 . In his insertion mounting process of the first switching mechanism  157 , the fourth gear  165  of the rotating member  166  and the third gear  164  of the rotation transmitting shaft  163  and further the second gear  162  of the rotation transmitting shaft  163  and the first gear  161  of the mode switching member  155  are engaged with each other in respective proper positional relationships with respect to each other in the respective circumferential directions (in the respective directions of rotation). To this end, a positioning member is provided for each engagement in order to define the circumferential positions of the components when inserted.  
         [0086]     A positioning member for the fourth gear  165  of the rotating member  166  and the third gear  164  of the rotation transmitting shaft  163  comprises a positioning pin  191  mounted in the gear housing  107 . The third gear  164 , the fourth gear  165  and the positioning pin  191  are features that correspond to the “driving-side rotating member”, the “driven-side rotating member” and the “positioning member”, respectively, according to this invention. The positioning pin  191  includes a shank  192  and a flange  193  and is mounted in the gear housing  107  such that its axial direction is parallel to the axial direction (longitudinal direction) of the rotating member  166 . The positioning pin  191  mounted in the gear housing  107  is designed such that the flange  193  is exposed to the outside of the gear housing  107  and the end of the shank  192  protrudes a predetermined length into the gear housing  107 .  
         [0087]     The rotating member  166  includes a disc  194  that is fastened by a screw  195  to an axial end of the rotating member on the side opposite to the fourth gear  165 . The rotating member  166  is a feature that corresponds to the “driven shaft” according to this invention. The disc  194  has a diameter slightly larger than the outside diameter of the fourth gear  165 . A recess  194   a  (see  FIG. 18 ) is formed in the periphery of the disc  194  and has a circular shape complementary to the circular shape of the outer edge of the flange  193 . A circular mounting hole  107   c  (see  FIG. 16 ) for mounting the rotating member  166  is formed though the gear housing  107  in the longitudinal direction (in the direction crossing the longitudinal direction of the crank shaft  122 ). The rotating member  166  is inserted into the mounting hole  107   c  from behind in order to be mounted in the gear housing  107 . In this insertion mounting, the disc  194  of the rotating member  166  is allowed to pass the flange  193  without interference with the flange  193  when the recess  194   a  of the disc  194  is aligned with the peripheral edge of the flange  193  of the positioning pin  191 , or when the circular surface of the recess  194   a  is placed in a position (see  FIGS. 17 and 18 ) corresponding to the peripheral edge of the flange  193 . On the other hand, when the recess  194   a  of the disc  194  is not in alignment with the peripheral edge of the flange  193 , the disc  194  interferes with the flange  193  and is thus prevented from being further inserted into the mounting hole  107   c . In other words, the rotating member  166  having the fourth gear  165  is allowed to be mounted in the gear housing  107  only when inserted into the mounting hole  107   c  with proper positioning in a predetermined relative position in the circumferential direction with respect to the positioning pin  191 . Further, the rotating member  166  inserted into the gear housing  107  until the disc  194  passes the flange  193  of the positioning pin  191  and is rotatably supported in the position by the inner wall surface of the mounting hole  107   c . In this state, the first eccentric pin  167  faces the flange  124   b  of the clutch member  124 .  
         [0088]     As shown in  FIGS. 16 and 17 , a shank  166   a  formed in one axial end of the rotating member  166  and a shank hole  194   b  formed in the disc  194  are fitted together, and in this state, the rotating member  166  and the disc  194  are fastened together by a screw  195 . The shank  166   a  and the shank hole  194   b  have circular sections having notched planar surfaces  166   b ,  194   c , respectively, in a part in the circumferential direction and are fitted together in the state fixed in position via the respective planar surfaces  166   b ,  194   c . In other words, the rotating member  166  and the disc  194  can be fastened together by the screw  195  only when the shank  166   a  and the shank hole  194   b  are placed in a predetermined relative position. Thus, in the state fastened by the screw  195 , the first eccentric pin  167  of the rotating member  166  and the positioning recess  194   a  of the disc  194  are held in a predetermined positional relationship.  
         [0089]     The rotation transmitting shaft  163  has a flange  163   b  formed between a shank  163   a  and the third gear  164  and having a diameter larger than the diameter of the third gear  164 . A generally rectangular recess  163   c  (see  FIG. 19 ) is formed in the periphery of the flange  163   b  and has a width corresponding to the outside diameter of a shank end portion  192   a  of the positioning pin  191 . The rotation transmitting shaft  163  is a feature that corresponds to the “driving shaft” according to this invention. A circular mounting hole  107   d  (see  FIG. 16 ) for mounting the rotation transmitting shaft  163  is formed through the gear housing  107  in the vertical direction (in the longitudinal direction of the crank shaft  122 ). The rotation transmitting shaft  163  is inserted into the vertical mounting hole  107   d  from above in order to be mounted in the gear housing  107 . In this insertion mounting, the flange  163   b  of the rotation transmitting shaft  163  is allowed to pass the shank end portion  192   a  without interference with the shank end portion  192   a  when the recess  163   c  of the flange  163   b  is aligned with the shank end portion  192   a  of the positioning pin  191 , or when the recess  163   c  is placed in a position (see  FIGS. 17 and 19 ) corresponding to the shank end portion  192   a  in the circumferential direction. On the other hand, when the recess  163   c  of the flange  163   b  is not in alignment with the shank end portion  192   a , the flange  163   b  interferes with the shank end portion  192   a  and is thus prevented from being further inserted into the mounting hole  107   d . In other words, the rotation transmitting shaft  163  having the third gear  164  is allowed to be mounted in the gear housing  107  only when inserted into the mounting hole  107   d  with proper positioning in a predetermined relative position in the circumferential direction with respect to the positioning pin  191 . Further, the rotation transmitting shaft  163  is inserted into the gear housing  107  until the flange  163   b  passes the shank end portion  192   a  of the positioning pin  191  and is rotatably supported in the position by the inner wall surface of the mounting hole  107   d.    
         [0090]     As mentioned above, the rotating member  166  and the rotation transmitting shaft  163  are mounted in the gear housing  107  such that the respective longitudinal directions cross each other. In the state in which the rotating member  166  and the rotation transmitting shaft  163  are mounted in the gear housing  107 , the fourth gear (bevel gear)  165  of the rotating member  166  and the third gear (bevel gear)  164  of the rotation transmitting shaft  163  are engaged with each other in a predetermined proper positional relationship.  
         [0091]     A positioning member for the second gear  162  of the rotation transmitting shaft  163  and the first gear  161  of he mode switching member  155  will now be explained. As shown in  FIG. 16 , the mode switching member  155 , the first gear  161  and a cover  196  are connected together by a screw  197  and form a mode switching assembly. The mode switching assembly is inserted from above into a mounting hole  107   e  formed in the upper surface of the gear housing  107  in order to be mounted in the gear housing  107 . Specifically, in this mounting, the mode switching assembly is inserted into the mounting hole  107   e  while sliding in the direction of the gear thickness (in the long direction) with the teeth of the first gear  161  and the teeth of the second gear  162  engaged with each other.  
         [0092]     As shown in  FIG. 17 , the positioning member for the second gear  162  and the first gear  161  comprises a positioning wall  199  formed in the first gear  161 . The positioning wall  199  is formed on the lower end surface of the first gear  161  in the axial direction in such a manner as to cover one end of a teeth section  161   a  in the direction of the tooth thickness. Specifically, the positioning wall  199  has about the same outside diameter as the gear diameter of the first gear  161  and has an opening  199   a  in a predetermined region in the circumferential direction of the positioning wall  199 . In mounting the mode switching assembly in the gear housing  107 , the positioning wall  199  is allowed to pass a teeth section  162   a  of the second gear  162  without interference with the teeth section  162   a  when the opening  199   a  is placed in a position (see  FIGS. 17 and 19 ) corresponding to (in alignment with) the teeth section  162   a  of the second gear  162 . On the other hand, when the opening  199   a  is not in alignment with the teeth section  162   a  of the second gear  162 , the positioning wall  199  interferes with the teeth section  162   a  of the second gear  162  and is thus prevented from being inserted into the mounting hole  107   e . In other words, the mode switching member  155  having the first gear  161  is allowed to be mounted in the gear housing  107  only when the first gear  161  is property positioned in a predetermined relative position in the circumferential direction with respect to the second gear  162 . As a result, the first gear  161  and the second gear  162  are engaged with each other in a predetermined proper positional relationship. Thus, according to this embodiment, the mode switching member  155  and the first eccentric pin  167  are inevitably assembled in a predetermined positional relationship.  
         [0093]     As mentioned above, according to this embodiment, the rotation transmitting shaft  163  having the third gear  164  and the rotating member  166  having the fourth gear  165  can be mounted in the gear housing  107  only when inserted in a predetermined relative position defined by the positioning pin  191 . Further, the mode switching member  155  having the first gear  161  can be mounted in the gear housing  107  only when positioned in a predetermined relative position defined by the positioning wall  199 . As a result, the third and fourth gears  164  and  165  and the first and second gears  161  and  162  can be reliably engaged with each other in respective predetermined paper positional relationships or can be reliably prevented from being engaged with each other in improper positional relationship.  
         [0094]     Further, according to this embodiment, the third gear  164  and the fourth gear  165  can be positioned by using the axial end portion of the shank  192  and the peripheral edge portion of the flange  193  of the positioning pin  191 , so that the third gear  164  and the fourth gear  165  arranged crisscross with respect to each other can be efficiently engaged in a predetermined relative position by using the single positioning pin  191 .  
         [0095]     Further, in this embodiment for the purpose of positioning the positioning pin  191  and the fourth gear  165 , the positioning recess  194   a  is formed in the disc  194  of the rotating member  166 . However, such a positioning recess may be formed in the positioning pin  191 . Further, in this embodiment, for the purpose of positioning the third gear  164  with respect to the positioning pin  191 , the positioning recess  163   c  is formed in the flange  163   b  of the rotation transmitting shaft  163 . Such a positioning recess may be formed in the positioning pin  191 .  
         [0096]     Further, the driving-side rotating member or the driven-side rotating member may be constructed as follows according to the invention:  
         [0097]     “One or both of the driving-side rotating member and the driven-side rotating member include a plurality of elements that can be engaged with each other, and the plurality of elements are allowed to be engaged with each other only when placed in a predetermined relative position and are prevented from being engaged with each other when placed in a position other than the predetermined relative position.” 
         [0098]     “The driven-side rotating member includes a plurality of elements that are fitted together in the direction of the driven shaft and in this state fastened together, and the plurality of elements are allowed to be fitted together only when placed in a predetermined relative position in the circumferential direction around the direction of the driven shaft, while being prevented from being fitted together when placed in a position other than the predetermined relative position.” 
         [0099]     In his construction, the “plurality of elements” may typically comprise the rotating member  166  and the disc  194 . According to this embodiment, the plurality of elements can be properly fastened in a predetermined relative position.  
       Fourth Representative Embodiment  
       [0100]     A fourth representative embodiment of the present invention is explained with reference to FIGS.  21  to  27 . This embodiment relates to a technique to reduce vibration caused during an operation work by adding a dynamic vibration reducer to the power tool. Therefore, components which are substantially identical to those in the first embodiment are given like numerals as in the first, second and/or third embodiment and will not be described.  
         [0101]     The motion converting mechanism  113  and the power transmitting mechanism  117  are housed within a hermetically closed driving section housing chamber  151  defined by the gear housing  107 . Sliding parts are lubricated by lubricant (grease) filled in the driving section housing chamber  151 . The driving section housing chamber  151  is partitioned into an upper chamber  151   a  and a lower chamber  151   b  by a bearing  128  (ball bearing)  128  that rotatably supports the crank shaft  122 . The upper chamber  151   a  and the lower chamber  151   b  are features that correspond to the “crank chamber” and the “clutch chamber”, respectively, according to this invention. The upper chamber  151   a  houses the crank mechanism  114  of the motion converting mechanism  113 , and the lower chamber  151   b  houses the driving gear  121 , the driven gear  123  and the clutch member  124 , and most of the power transmitting mechanism  117 . One end of the upper chamber  151   a  in a longitudinal direction of the cylinder  141  is open.  
         [0102]     The upper chamber  151   a  and the lower chamber  151   b  defined by the bearing  128  are allowed to communicate with each other only through a clearance formed in the bearing  128 . Therefore, when the crank mechanism  114  is driven and the cylinder  129  reciprocates within the cylinder bore, the capacity of the upper chamber  151   a  is increased or reduced, so that the pressure within the upper chamber  151   a  fluctuates. At this time, the lower chamber  151   b  is held unaffected or hardly affected by the pressure fluctuations of the upper chamber  151   a.    
         [0103]     A dynamic vibration reducer  211  will now be explained with reference to FIGS.  24  to  27 . A pair of dynamic vibration reducers  211  are provided in the body  103  in order to reduce vibration generated in the axial direction of the hammer bit during operation of the power tool. The dynamic vibration reducers  211  are arranged on the right and left sides of the outside surface of the gear housing  107  on the both sides of the axis of the hammer bit  119  (see  FIG. 24 ). The dynamic vibration reducer  211  is shown by broken lines in FIGS.  21  to  23 . The construction of the dynamic vibration reducer  211  is shown in detail in  FIG. 25 .  FIGS. 26 and 27  are sectional views taken along line A-A and line B-B in  FIG. 24 . The right and left dynamic vibration reducers have the same construction. As shown in  FIG. 25 , each of the dynamic vibration reducers  211  mainly includes a cylindrical body  213  that is disposed adjacent to the body  103 , a weight  215  that is disposed for vibration reduction within the cylindrical body  213 , and biasing springs  217  that are disposed on the both sides of the weight  215  in the axial direction. The biasing springs  217  exert a spring force on the weight  215  in a direction toward each other when the weight  215  moves in the longitudinal direction of the cylindrical body  213  (in the axial direction of the hammer bit). The dynamic vibration reducer  211  having the above-described construction serves to reduce impulsive and cyclic vibration caused when the hammer bit  119  is driven. Specifically, the weight  215  and the biasing springs  217  serve as vibration reducing elements in the dynamic vibration reducer  211  and cooperate to passively reduce vibration of the body  103  of the hammer drill  101  on which a predetermined outside force (vibration) is exert. Thus, the vibration of the hammer drill  101  of this embodiment can be effectively alleviated or reduced.  
         [0104]     Further, in the dynamic vibration reducer  211 , a first actuation chamber  219  and a second actuation chamber  221  are defined on the both sides of the weight  215  in the axial direction within the cylindrical body  213 . The first actuation chamber  219  normally communicates with the upper chamber  151   a  via a first communicating portion  219   a  (see  FIGS. 24 and 26 ). As shown in  FIG. 26 , the first communicating portion  219   a  has a tubular member  219   b  that protrudes upward to a predetermined height in the upper chamber  151   a  and has a protruding end open to the upper chamber  151   a . With this arrangement, lubricant within the upper chamber  151   a  is prevented from entering the first actuation chamber  219 . The second actuation chamber  221  normally communicates with a cylinder accommodating space  223  of the gear housing  107  via a second communicating portion  221   a  (see  FIGS. 24 and 27 ). The cylinder accommodating space  223  is not in communication with the upper chamber  151   a . As mentioned above, the pressure within the upper chamber  151   a  fluctuates when the motion converting mechanism  113  is driven. Such pressure fluctuations are caused when the piston  129  forming the motion converting mechanism  113  linearly moves within the cylinder  141 . The fluctuating pressure caused within the upper chamber  151   a  is introduced to the first actuation chamber  219  through the first communicating portion  219   a , and the weight  215  of the dynamic vibration reducer  211  is actively driven. In this manner, the dynamic vibration reducer  211  performs a vibration reducing function. Specifically, the dynamic vibration reducer  211  serves as an active vibration reducing mechanism for reducing vibration by forced vibration in which the weight  215  is actively driven. Thus, the vibration which is caused in the body  103  during hammering operation can be further effectively reduced or alleviated.  
         [0105]     Further, according to this embodiment, the rotation transmitting shaft  163 , the third and fourth gears  164 ,  165  and the rotating member  166  which form the switching operation transmitting mechanism  169  for transmitting the switching operation of the mode switching member  155  to the rotating member  166  are disposed outside the driving section housing chamber  151 . Therefore, the capacity of the driving section housing chamber  151  can be reduced by the capacity for housing these components of the switching operation transmitting mechanism  169 . Further, with the construction in which the switching operation transmitting mechanism  169  is disposed outside the driving section housing chamber  151 , the driving section housing chamber  151  can be partitioned into the upper chamber  151   a  and the lower chamber  151   b  such that the lower chamber  151   b  is held unaffected by the pressure fluctuations of the upper chamber  151   a , or such that communication between the upper chamber  151   a  and the lower chamber  151   b  is substantially interrupted. As a result, the capacity of the upper chamber  151   a  is reduced. Thus, a wider range of pressure fluctuations (a higher rate of volumetric change of the upper chamber  151   a  which is caused by reciprocating movement of the piston  129 ) can be caused in the upper chamber  151   a  when the crank mechanism  114  is driven. As a result, in the construction in which the weight  215  of the dynamic vibration reducer  211  is actively driven by utilizing the pressure fluctuations in the upper chamber  151   a , the effectiveness of reducing vibration of the body  103  by the dynamic vibration reducer  211  can be enhanced.  
         [0106]     Further, with the construction in which switching of the clutch member  124  is effected by utilizing rotation of the rotating member  166 , the opening  168  connecting the lower chamber  151   b  and the housing space  152  can be closed all the time by the rotating member  166 . Thus, even in the construction in which the switching operation transmitting mechanism  169  is disposed outside the lower chamber  151   b , switching of the clutch member  124  can be efficiently effected while avoiding the lubricant from leaking out of the lower chamber  151   b.    
         [0107]     Based on the above-described, following features can be made to define one of the aspects of the invention.  
         [0108]     As to the power tool of claim  8 , the driven-side rotating member may actuate a switching member for switching operation modes of the power tool by rotating around the driven shaft and the driven-side rotating member may have an eccentric pin extending along the direction of the driven shaft in a position displaced from the driven shaft. When the driven-side rotating member is cause to rotate by the driving-side rotating member, the eccentric pin may eccentrically revolve on the driven shaft and the driven-side rotating member actuates the operation mode switching member via components of the eccentric revolving movement in the direction crossing the driven shaft.  
         [0109]     Further, as to the power tool of claim  9 , the positioning member my have a positioning pin. And the relative positions of the positioning member with respect to the driving-side rotating member and the driven-side rotating member may be defined by using an axial end portion and an peripheral edge portion of the positioning pin, respectively.  
       DESCRIPTION OF NUMERALS  
       [0000]    
       
           101  hammer drill (power tool)  
           103  body (power tool body)  
           105  motor housing  
           107  gear housing  
           107   a  pin  
           107   b  guide pin  
           109  handgrip  
           109   a  trigger  
           111  driving motor  
           113  motion changing mechanism  
           114  crank mechanism  
           115  striking mechanism  
           117  power transmitting mechanism  
           119  hammer bit (tool bit)  
           121  driving gear  
           123  driven gear  
           123   a  clutch teeth  
           124  clutch member  
           124   a  clutch teeth  
           124   b  flange  
           125  crank plate  
           126  biasing spring  
           127  crank arm  
           128  bearing  
           129  piston  
           132  intermediate gear  
           133  intermediate shaft  
           134  small bevel gear  
           135  large bevel gear  
           135   a  clutch teeth  
           141  cylinder  
           141   a  air chamber  
           143  striker  
           145  impact bolt  
           147  slide sleeve  
           147   a  clutch teeth  
           147   b  rotating locking teeth  
           147   c  stepped portion  
           148  biasing spring  
           149  lock ring  
           149   a  teeth  
           151  crank chamber  
           152  housing space  
           153  mode switching mechanism  
           155  mode switching member (switching member)  
           155   a  disc  
           155   b  operating grip  
           155   c  eccentric portion  
           157  first switching mechanism  
           159  second switching mechanism  
           161  first gear  
           162  second gear  
           163  rotation transmitting shaft (switching operation transmitting mechanism)  
           164  third gear  
           165  fourth gear  
           166  rotating member  
           167  first eccentric pin (actuating member)  
           168  opening  
           169  switching operation transmitting mechanism  
           173  frame member  
           173   a  base  
           173   b  leg  
           173   c  connecting pin  
           173   d  oblong hole  
           173   e  engagement end  
           175  second eccentric pin  
           181  first switching mechanism  
           183  swinging member (switching operation transmitting mechanism)  
           183   a  horizontal plate portion  
           183   b  vertical plate portion  
           183   c  slot  
           183   d  gear  
           183   e  guide groove  
           185  rotating member  
           185   a  circular gear  
           187  first eccentric pin