Patent Publication Number: US-2015083451-A1

Title: Power tool

Description:
TECHNICAL FIELD 
     The present invention relates to a mechanism and a structure of mode switching of a power tool having a plurality of operation modes. 
     BACKGROUND ART 
     An impact driver is a tool for carrying out fastening operations of screws and bolts. The impact driver is provided with an impact mechanism part including a hammer and an anvil. The hammer continuously impacts the anvil while rotating. The hammer impacts the anvil, then is placed over the anvil, moves over the anvil, and impacts the anvil again. The impact driver can obtain high fastening torque; however, large sound is produced since a fastening material is impacted in the axial direction of the fastening material. 
     In recent years, an impact driver in which a hammer which impacts an anvil is not moved in the axial direction of rotation has been known. This impact driver of a new system is known as an “electronic pulse driver” which is a product of the applicants. As described in Japanese Patent Application Laid-Open Publication No. 2011-31313 (Patent Document 1), the electronic pulse driver is a tool for carrying out fastening operations similar to those of conventional power tools for carrying out impact operations while a hammer is being retracted in the axial direction. However, in the electronic pulse driver, the hammer is not placed over the anvil. In the electronic pulse driver, when the motor is rotated in normal direction and opposite direction, the hammer is rotated in normal direction and opposite direction, and impact force is applied to the anvil. Therefore, since a fastening material is not struck in the axial direction of the fastening material by the electronic pulse driver, the electronic pulse driver has a low noise level. However, it has been difficult to obtain high fastening torque for the electronic pulse driver as compared with a conventional power tool for carrying out impact operations while the hammer is being retracted in the axial direction. 
     In order to solve these problems, a fastening tool in which a mechanism part, which limits the operation that the hammer is placed over the anvil (backward movement of the hammer in the axial direction), is provided in a hammer case is proposed in Japanese Patent Application Laid-Open Publication No. 2012-11502 (Patent Document 2). This fastening tool is capable of switching between an operation mode (impact mode) in which an impact operation is carried out while the hammer is being retracted in the axial direction and an operation mode (electronic pulse mode) in which the impact operation is carried out without retracting the hammer in the axial direction. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Application Laid-Open Publication No. 2011-31313 
         PTL 2: Japanese Patent Application Laid-Open Publication No. 2012-11502 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the fastening tool proposed by Patent Document 2, a switching mechanism of the operation modes includes a stopper and a pusher disposed in the hammer case. When the pusher is rotated, the stopper is moved, and the operation mode is switched. Specifically, the stopper moves to the hammer side, which is in the front of the pusher, and prevents backward movement of the hammer. However, since an operation part for operating the pusher is operated by a hand of an operator, the operation part has to penetrate from the inside of the hammer case to outside. Therefore, there has been a problem that an opening is formed in part of the hammer case, and grease is easily leaked from the opening. 
     An object of the present invention is to provide a power tool having a switching mechanism of a mode that allows backward movement of a hammer and a mode that prevents the movement, wherein an opening formed in a hammer case is configured so as not to be exposed to outside, and leakage of grease from the opening to outside is suppressed. 
     Solution to Problem 
     The typical ones of the inventions disclosed in the present application will be briefly described as follows. 
     According to an aspect of the present invention, a power tool includes: a housing that houses a driving source; a case that houses a transmission mechanism part driven by the driving source and is partially covered with the housing; and a switching member that changes an operation mode of the transmission mechanism part from outside. The switching member is extending from outside of the housing and the case to the transmission mechanism part in the case through a part between the housing and the case. 
     Advantageous Effects of Invention 
     The switching member that changes the operation mode from outside is extending from outside of the case to the transmission mechanism part in the case through the part between the housing and the case. Therefore, the connecting part of the switching member and the transmission mechanism part is covered with the housing, and grease leakage from the inside of the case is effectively prevented. 
     The effects obtained by typical aspects of the present invention will be briefly described below. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a vertical cross-sectional view illustrating an overall configuration of a power tool  1  (impact driver) according to an embodiment of the present invention. 
         FIG. 2  is a perspective view illustrating an external shape of a housing  2  and a hammer case  32  in  FIG. 1 . 
         FIG. 3  is an exploded perspective view illustrating an assembled structure of the hammer case, an impact mechanism part, and a switching mechanism  35  in  FIG. 1 . 
         FIG. 4  is a perspective view (normal position) of a impact mechanism part and the switching mechanism  35  in  FIG. 1 . 
         FIG. 5  is a perspective view (locked position) of the impact mechanism part and the switching mechanism  35  in  FIG. 1 . 
         FIG. 6A  is a schematic diagram for explaining the shapes of a stopper  41  and a pusher  45  of the switching mechanism  35 . 
         FIG. 6B  is a schematic diagram for explaining the shapes of the stopper  41  and the pusher  45  of the switching mechanism  35 . 
         FIG. 7  is a cross-sectional view of a change lever  48   b  part of the switching mechanism  35  in  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted. In the present specification, explanations will be given on the assumption that front/rear and top/bottom directions are the directions shown in the drawings. 
       FIG. 1  is a diagram illustrating an internal structure of a power tool  1  according to the present invention. In the power tool  1 , a chargeable battery  9  serves as a power source, a rotary impact mechanism part  22  is driven while using a motor  3  as a driving source, and rotative force and impact force are applied to an anvil  30 , which is an output shaft. When the rotative force and the impact force are applied to the anvil  30 , rotation impact force is intermittently transmitted to a tip tool, which is not illustrated, such as a driver bit retained by an anvil angular-hole part  30   c  covered with an attachment member  31 , and a screw or a bolt is fastened by the tip tool. 
     A chassis of the power tool  1  includes a housing  2 , which is formed of a synthetic resin material, and a metal case (hammer case  32 ), which is attached to the front side of the housing and having a part thereof covered with the housing  2 . The hammer case  32  forms a cup-shape having an opening in the rear side, and a through hole through which an output shaft is penetrating is formed in a bottom part (front-end part) of the case. The motor  3  of a brushless DC type is housed in a tubular body part  2   a  of the housing  2 , which forms an approximately T-shape in a lateral view. A rotary shaft  3   c  of the motor  3  is rotatably retained by a bearing  18   a , which is provided in a vicinity of a center part of the body part  2   a  of the housing  2 , and a bearing  18   b  in the rear side. A rotor fan  13 , which is attached coaxially with the rotary shaft  3   c  and is rotated in synchronization with the motor  3 , is provided in the front of the motor  3 . An inverter circuit board  4  for driving the motor  3  is disposed in the rear of the motor  3 . When the rotor fan  13  is rotated, outside air is taken into the interior of the body part  2   a  from an air intake hole  17   a  and slots  17   b  (see  FIG. 2 ), which are formed in a housing part around the inverter circuit board  4 . The outside air taken into the interior of the body part  2   a  flows so as to pass through mainly the part between the rotor  3   a  and a stator  3   b , sucked in from the rear of the rotor fan  13 , flows in a radial direction of the rotor fan  13 , and is discharged from slots  17   c  (see  FIG. 2 ), which are formed in the housing part around the rotor fan  13 , to outside of the housing  2 . The inverter circuit board  4  is an substantially-circular double-sided board having a substantially the same shape as the motor  3 , and a plurality of switching elements  5  such as FETs (Field Effect Transistors) and a rotation-position detecting element  14  such as a Hall IC are mounted on the board. 
     A trigger switch  6  is disposed at an inner upper part of a handle part  2   b  integrally extending at a substantially right angle from the body part  2   a  of the housing  2 , and a switch board  7  is provided below the trigger switch  6 . A control circuit board  8  provided with a function of controlling the speed of the motor  3  based on a pulling operation of the trigger switch  6  is housed in a lower part in the handle part  2   b , and the control circuit board  8  is electrically connected to the battery  9  and the switch board  7 . A circuit for drive control of the motor  3  is mounted on the control circuit board  8 . The battery  9  such as a nickel-cadmium battery or a lithium-ion battery is detachably attached below the handle part  2   b.    
     In the body part  2   a  of the housing  2  and the hammer case  32 , the motor  3  and a transmission mechanism part (a reduction mechanism  20  and the rotary impact mechanism part  22 ), which transmits power of the motor  3  to the tip tool, are arranged and disposed in the axial direction of the motor  3 . An end part of the anvil  30  is projecting from a tip part of the hammer case  32 , and a tip tool such as a driver bit (not shown) is detachably inserted and fixed to the anvil angular-hole part  30   c . The tip tool can be fixed to the anvil angular-hole part  30   c  by a single-step operation. As a different tip tool, a bolt-fastening bit can be also attached to the anvil angular-hole part  30   c.    
     The reduction mechanism  20 , which has planetary gears including a planetary gear and a ring gear, and the rotary impact mechanism part  22  are provided on the front side of the body part  2   a  and in the hammer case  32 . The rotary impact mechanism part  22  is provided with a spindle  27  and a hammer  24 . A rear end of a rotation mechanism using the reduction mechanism  20  and the rotary impact mechanism part  22  is supported by a bearing  19   b  and a front end of the rotation mechanism is retained by a metal  19   a . When the trigger switch  6  is pulled to start the motor  3 , the motor  3  starts rotation in a direction set by a normal/opposite switching lever  10 , the rotative force of the motor is reduced by the reduction mechanism  20  and transmitted to the spindle  27 , and the spindle  27  rotates at a predetermined speed. In this case, the spindle  27  and the hammer  24  are coupled by a publicly-known cam mechanism. This cam mechanism includes: a V-shaped spindle cam groove  25  formed on an outer peripheral surface of the spindle  27 , a hammer cam groove  28  formed on an inner peripheral surface of the hammer  24 , and balls  26  engaged with these cam mechanisms  25  and  28 . 
     The hammer  24  is always energized forward by a spring  23 . During rest, the hammer  24  is positioned with a gap away from an end face of the anvil  30  by an engagement between the balls  26  and the cam grooves  25  and  28 . Not-illustrated projecting parts are symmetrically formed at two locations on mutually-opposed rotation planar surfaces of the hammer  24  and the anvil  30 . 
     In a screwing operation of an impact mode, the rotative force of the motor  3  transmitted from the rotary shaft  3   c  is reduced by the planetary gear and the ring gear included in the reduction mechanism  20  and is transmitted to the spindle  27 . When the spindle  27  is subjected to rotary drive, the rotation is transmitted to the hammer  24  via the cam mechanism, and, before the hammer  24  makes a half rotation, the projecting parts of the hammer  24  are engaged with the projecting parts of the anvil  30  and rotate the anvil  30 . If relative rotation is generated between the spindle  27  and the hammer  24  by the engagement reaction force of the moment, the hammer  24  starts retraction toward the motor  3  side while compressing the spring  23  along the spindle cam groove  25  of the cam mechanism. 
     Then, when the projecting parts of the hammer  24  move over the projecting parts of the anvil  30  to cancel the engagement between them because of the backward movement of the hammer  24 , the hammer  24  is rapidly accelerated in a rotation direction and to the front side by the elastic energy accumulated in the spring  23  and working of the cam mechanism in addition to the rotative force of the spindle  27 . Then, the projecting parts of the accelerated hammer  24  are engaged again with the projecting parts of the anvil  30 , and the hammer  24  and the anvil  30  start to rotate integrally. At this point, strong rotation impact force is applied to the anvil  30 ; therefore, the rotation impact force is transmitted to a screw, a bolt, or the like via the not-illustrated tip tool attached to the anvil angular-hole part  30   c  of the anvil  30 . Thereafter, similar operations are repeated to repeatedly transmit the rotation impact force intermittently to the screw or bolt from the tip tool, and the screw or bolt is screwed to a not-illustrated member to be fastened such as a timber. 
     The battery  9  of a pack-type serving as a driving power source of the motor  3  is detachably attached to a lower end part of the handle part  2   b . A plurality of battery cells composed of, for example, not-illustrated lithium-ion secondary batteries or nickel-cadmium secondary batteries are housed in the battery  9 . The battery  9  is electrically connected to the inverter circuit board  4  via the trigger switch  6  provided at a part of the handle part  2   b . The inverter circuit board  4  is electrically connected to a coil (for example, a star-connected three-phase coil) included in the stator  3   b  of the motor  3 , and the rotor  3   a  is rotated in a predetermined direction when sequentially energized to predetermined phases. An inverter circuit including a known bridge circuit for distributing a drive current to the three-phase coil of the motor  3  is mounted on the inverter circuit board  4 , and a control circuit consisting of a CPU, etc. which controls the inverter circuit is mounted on the control circuit board  8 . 
     A switching mechanism used for switching of operation modes, i.e., the impact mode and an electronic pulse mode is provided in the rear of the hammer  24 . Specifically, a slipping member  36 , a stopper  41 , and a pusher  45  are provided in the hammer case  32  and in the rear of the hammer  24 , and the slipping member  36  is energized to the rear side (motor  3  side) by a switching spring  39  interposed between the slipping member  36  and a step part of the hammer case  32 . A change lever  48   b  for operating the switching mechanism is provided outside of the hammer case  32 . 
     By using the power tool  1  structured in the above described manner, when the “impact mode” is set by operating the change lever  48   b  and an operator pulls the trigger switch  6  while holding the handle part  2   b , the trigger switch  6  is put in an on-state, and operation of the impact driver can be started. When a predetermined load torque or the torque higher than that is applied to the anvil  30  (tip tool) during screw fastening, the hammer  24  converts rotative force to impact force while being placed over the anvil  30  by working of the spring  23 . As a result, rotation impact force is applied to the tip tool attached to the anvil  30 , and a screw is fastened. 
     On the other hand, when the change lever  48   b  is operated to set the “electronic pulse mode” and the operator pulls the trigger switch  6  while holding the handle part  2   b , the trigger switch  6  becomes an on-state, and operation of an electronic pulse driver can be started. In a screw fastening operation of the electronic pulse mode, the rotative force of the normal rotation and the opposite rotation of the motor  3  transmitted from the rotary shaft  3   c  is reduced by the reduction mechanism  20  having the planetary gear and the ring gear, and the hammer  24  applies rotation impact force to the anvil  30  (tip tool). During screw fastening, when predetermined load torque or the torque higher than that is applied to the hammer  24 , the hammer  24  is promoted to move to the rear. However, backward movement of the hammer  24  is regulated by the stopper  41  via the slipping member  36 ; therefore, the hammer  24  is not placed over the anvil  30 . Therefore, the motor  3  is controlled so as to alternately repeat normal rotation and opposite rotation by a control unit for carrying out rotation control of the motor  3 . As a result, the hammer  24  applies rotation impact force to the tip tool attached to the anvil  30 . 
     Next, the external shapes of the housing  2  and the hammer case  32  will be explained with reference to  FIG. 2 . In  FIG. 2 , the hammer case  32  is connected to the front side of the housing  2 , thereby constituting the housing of the power tool  1 . The change lever  48   b  for carrying out switching of the “impact mode” and the “electronic pulse mode” is provided at an upper part of the housing  2 . The change lever  48   b  is movable in a circumferential direction along an outer peripheral surface of the hammer case  32 . A recessed part (part recessed from the front to the rear of the housing  2 ) which defines a movable range of the change lever  48   b  is formed on the body part  2   a  of the housing  2 . In a state in which the change lever  48   b  is abutting circumferential-direction end part  49   a  or  49   b  of the recessed part, the switching mechanism operates as the “impact mode” or the “electronic pulse mode”. In this case, the change lever  48   b  is positioned on the outer side (outer peripheral side) of the hammer case  32  housing a power transmitting part; therefore, opening of the hammer case  32  is not present in the movable range of the change lever  48   b , and leakage of grease from the opening can be suppressed. A change member  48  in which the change lever  48   b  is formed is disposed so as to be inserted to the inner side of the housing  2  in vicinities of the peripheral end parts  49   a  and  49   b . More specifically, in a vicinity of an arrow A in the vicinity of the circumferential-direction end part  49   b , the housing  2  (non-movable member), the change member  48  (movable member), the hammer case  32  (non-movable member) are disposed so as to be overlapped in this order from the outer side of the radial direction; therefore, by virtue of the Labyrinth effect caused by the overlapping thereof, leakage of grease in the hammer case  32  to outside can be effectively suppressed. 
     Next, a disassembled configuration of the hammer case  32 , an impact mechanism part, and the switching mechanism  35  of the present embodiment will be explained with reference to  FIG. 3 . In the present embodiment, the switching mechanism  35  according to the present embodiment is incorporated between the reduction mechanism  20  and the hammer  24  of the mechanical impact mechanism part, which has been conventionally used. The switching mechanism  35  mainly includes four members. The stopper  41  is a member which moves to the front and the rear in the axial direction so as to cause the slipping member  36  disposed on the front side to abut the hammer  24  and limits movement of the hammer  24  to the rear in the axial direction. The pusher  45  is a member which changes the position thereof relative to the stopper  41  by rotating at 45 degrees or more, for example, at about 67 degrees in the rotation direction. The change member  48  has engagement holes  48   c , which are provided at both end parts of an annular part  48   a  (a member having a shape formed by as if cutting a ring-like member into half), and the change lever (operation lever)  48   b , which is provided in a vicinity of the center of the two engagement holes  48   c . As illustrated by dotted lines in the drawing, the engagement holes  48   c  are engaged with projections  46   c  (only one of them is visible in the drawing), which are provided at two locations at diagonal positions in the circumferential direction of the pusher  45 . The engagement structure of the change member  48  and the pusher  45  is not limited to the example illustrated in the drawing, the sides to which the recessed parts and the projecting parts are attached may be reversed, or another joint form may be adopted. The positions for providing the two engagement holes  48   c  are most preferable to be diagonally provided with respect to the rotation center (in other words, the positions at which the two engagement holes  48   c  are away from each other by 180 degrees); however, the angle may be equal to or less than 180 degrees, and they are only required to be provided to be away from the change lever  48   b  to some extent in the circumferential direction. The change member  48  serving as a switching member to change the operation mode of the transmission mechanism part ( 20 ,  22 ) from outside is disposed so as to extend to the transmission mechanism part ( 20 ,  22 ) in the hammer case  32  through a part between the housing  2  and the hammer case  32  (in a vicinity of the arrow A in  FIG. 2 ). 
     The hammer case  32  is fixed in a vicinity of the front end of the housing  2 . A flange part (outer peripheral part)  32   b  is formed at the periphery of the rear-side opening of the hammer case  32  (on the side where the opening of the cup-shaped hammer case  32  is present), and the step part  32   e  is formed in the front side of the flange  32   b . A latching part having a substantially L-shaped cross-sectional shape and bent toward the inner side or a latching part having a recessed groove continued in the circumferential direction is provided at a part of the housing  2  for retaining the hammer case  32 , and the latching part is retained so as to latch the step part  32   e , thereby retaining the hammer case  32  so that the case is not removed from the housing  2  to the front side. In this manner, the flange part  32   b  is projecting from the hammer case  32  to the outer side, and the flange part  32   b  is fixed so as to be fitted in the latching part formed in an inner peripheral side of the housing  2 . Upon impact by the impact mechanism part, the hammer case  32  is promoted to move to the front side with respect to the housing  2 ; however, this movement is prevented by the flange part  32   b  and the step or the recessed part of the latching part. Therefore, large tensile stress is generated in the hammer case  32  in the front of the step part  32   e ; however, stress is small in the rear of the step part  32   e . A method of fixing the hammer case  32  to the housing  2  is not limited only to the method of the present embodiment, and another fixing method may be used. 
     The hammer  24  has a shape similar to that of a hammer of an impact driver which has been widely used, and the hammer  24  is attached to the spindle  27  via the cam mechanism. The spring  23  is provided in the rear side of the hammer  24 , the spring  23  is positioned inside of the members of the switching mechanism  35 , and the members of the switching mechanism  35  are disposed so as not to be in contact with the spring  23 . The hammer case  32  is integrally formed of a metal such as an aluminum alloy. The hammer case  32  is provided with the through hole  32   a  which has a front-tapered shape and is for allowing the anvil  30  to penetrate therethrough. In the hammer case  32  in the present embodiment, recessed parts  32   c  cut-away toward the front side are formed partly at the periphery of the rear-side opening of the hammer case  32 . The recessed parts  32   c  are formed in order to ensure space for allowing movement of the projections  46   c  of the pusher  45  and are diagonally formed at two locations of the hammer case  32 . When the recessed parts  32   c  are formed in the flange part  32   b , which is in the rear of the step part  32   e , stress is not easily concentrated at the recessed parts  32   c , and the hammer case  32  can be prevented from being broken. The change member  48  is disposed along the outer side of the vicinity of the outer peripheral surface  32   d  of the hammer case  32 , and an annular part  46  of the pusher  45  is disposed in the inner peripheral side of the vicinity of the rear end part of the hammer case  32 . The change member  48  and the pusher  45  are switching members which carry out switching by the switching mechanism  35 , and the stopper  41  is a switched member which is to be switched. 
     The slipping member  36  includes a plurality of rollers  38  and a ring member  37 , which is made of a synthetic resin and rotatably retains the rollers  38 . The stopper  41  does not rotate with respect to the hammer  24 , which rotates about the output-shaft rotary shaft; therefore, the slipping member  36  is inserted in order not to disturb rotation of the hammer  24  by the stopper  41  in a state in which the stopper  41  is moved forward and prevents backward movement of the hammer  24 . Therefore, the shape of the slipping member  36  is not limited to the shape shown in the drawing; and the slipping member may be a bearing mechanism or a slipping mechanism having another shape as long as it is a bearing member that receives the force (thrust) that works in the axial direction of the hammer  24 , which is a rotating body. 
     The stopper  41  is a metal member integrally includes, at three locations in the circumferential direction of an annular part  42  formed like a ring, cam members  43  at the three locations which are provided so as to project from the annular part  42  to the rear. In the present embodiment, the stopper  41  is movable to the front and rear (movable in the axial direction) by working of the pusher  45 , and spline projections  44  are provided at three locations in the circumferential direction so as not to rotate in the rotation direction upon the movement. The spline projections  44  are engaged with spline grooves (not illustrated), which are formed on an inner wall part of the hammer case  32  and parallel to the axial direction, thereby stopping movement in the rotation direction but allowing movement in the axial direction of the stopper  41 . 
     The pusher  45  is a member for moving the stopper  41  by pushing the stopper  41  from the rear to the front in the axial direction and is a metal member integrally includes cam members  47  at three locations, which are provided so as to project to the front from the annular part  46 . The pusher  45  is rotatable in the circumferential direction about the rotation axis of the spindle  27 , but does not move in the axial direction. This rotation in the circumferential direction is carried out when the operator operates the change lever  48   b  of the change member  48  connected to the pusher  45 . In this case, each of the cam members  47  and the cam members  43  has a substantially trapezoidal shape when exploded in the circumferential direction, and the detailed shape thereof will be described later. Step parts  47   e  corresponding to step parts  42   a  (when viewed in the radial direction thereof, the parts in which the diameters of partial regions thereof are reduced) formed on the annular part  42  of the stopper  41  are formed at tips of the cam members  47 . When the step parts  42   a  and the step parts  47   e  abut each other in this manner, a good contact state without rattling can be realized. 
       FIG. 4  is a perspective view of the impact mechanism part and the switching mechanism and is illustrating a position (normal position) upon an operation in the impact mode. As is understood from the drawing, an interval B between a front face of the slipping member  36  and a rear end face of the hammer  24  is sufficiently larger than the axial-direction thickness of projection parts  30   a  and  30   b  on which impacting faces of the anvil  30  are formed. By virtue of this positional relation, the hammer  24  can be retracted to the rear in the axial direction, the projecting parts  24   a  and  24   b  of the hammer  24  can move over the projecting parts  30   a  and  30   b  of the anvil  30 , and normal mechanical impact operation can be carried out. In this process, the cam members  47  and the cam members  43  have a positional relation in which the members are alternately arranged in a row in the circumferential direction, and a distance between the annular part  42  of the stopper  41  and the annular part  46  of the pusher  45  is the shortest. In this manner, in the impact mode, the slipping member  36  and the stopper  41  are positioned in the rear, and the hammer  24  can be moved to the rear upon driving; therefore, normal impact striking can be carried out. During rotation of the motor  3 , the slipping member  36 , the stopper  41 , and the pusher  45  are not moved both in the axial direction and the circumferential direction from the state of  FIG. 4 ; therefore, the rotation operation of the hammer  24  is not adversely affected. Furthermore, since the slipping member  36  is always biased to the rear side by the switching spring  39  (see  FIG. 1 ), resonance of the slipping member  36  caused by vibrations in fastening operation can be prevented. 
       FIG. 5  is a perspective view of the impact mechanism part and the switching mechanism and is illustrating a position (lock position) of a case in which operation is carried out in the electronic pulse mode. As is understood from the drawing, an interval C between the front face of the slipping member  36  and the rear end face of the hammer  24  is almost zero. In this state, the hammer  24  cannot move backward; therefore, the normal impact operation which is carried out while the projecting parts  24   a  and  24   b  of the hammers  24  move over the projecting parts  30   a  and  30   b  of the anvil  30  cannot be carried out. Therefore, in this state, the anvil  30  is impacted by moving the hammer  24  with respect to the anvil  30  by a predetermined angle (however, less than 180 degrees) while alternately repeating the rotation of the motor  3  in the forward-rotation direction and the reverse-rotation direction. In other words, the impact operation in the so-called “electronic pulse mode” is carried out. In the state of  FIG. 5 , the rear end faces of the cam members  43  and the front end faces of the cam members  47  are in a mutually abutting state; therefore, the stopper  41  and the pusher  45  are disposed in series in the axial direction without being overlapped in the circumferential direction. In  FIG. 5 , the change lever  48   b  is not moved to the circumferential-direction end part  49   a  of the housing  2  (in other words, a state during movement), and the contact area of the rear end faces of the cam members  43  and the front end faces of the cam members  47  is somewhat small. 
     When changing the impact mode to the electronic pulse mode, the change lever  48   b  is rotated in the circumferential direction, and the state of  FIG. 4  is switched to the state of  FIG. 5 . The rotating of the change lever  48   b  is transmitted to the pusher  45  via the projections  46   c ; and, as the pusher  45  rotates in the circumferential direction, inclined surfaces  47   c  of the cam members  47  and inclined surfaces  43   c  of the cam members  43  move while sliding to move the stopper  41  to the front. Along with the forward movement of the stopper  41 , the sliding member  36  is also moved to the front and is fixed. A publicly-known retention mechanism (or a latch mechanism) which imparts a clicking sensation at a still position when the change lever  48   b  is moved may be provided. In this manner, in the electronic pulse mode, the slipping member  36 , and the stopper  41  are positioned in the front side, and, upon driving of the motor  3 , movement of the hammer  24  to the rear is regulated; therefore, the hammer  24  cannot be placed over the anvil  30 , and pulse impact in accordance with the forward rotation and the reverse rotation which are electronic pulse operations can be carried out. 
       FIGS. 6A and 6B  are schematic diagrams for explaining the shapes of the stopper  41  and the pusher  45  of the switching mechanism  35 .  FIG. 6A  illustrates a relative positional relation of the stopper  41  and the pusher  45  in the state of  FIG. 4 .  FIG. 6A  illustrates a state, in which one third of the switching mechanism in the length of the circumferential direction is planarly exploded, for the convenience of explanation. To facilitate explanation, the interval between the stopper  41  and the pusher  45  is extremely widely illustrated, and the shapes, sizes, etc. of the cam members  43  and  47  are also roughly illustrated. In the stopper  41 , the cam members  43  at the three locations are provided in the circumferential direction. The cam member  43  is a trapezoidal member having a lower base  43   a , which is in contact with the annular part  42 , and an upper base  43   b , which is opposed thereto. Among the two sides connecting the upper base  43   b  and the lower base  43   a  of the trapezoidal part, the side  43   d  is provided at a right angle to the annular part  42 , and the other side is formed as the inclined side (inclined surface)  43   c . On the other hand, the pusher  45  side also has a similar trapezoidal shape, and the cam members  47  are provided at the three locations in the circumferential direction. The cam member  47  is a trapezoidal member having a lower base  47   a , which is in contact with the annular part  46 , and an upper base  47   b , which is opposed thereto. Among the two sides connecting the upper base  47   b  and the lower base  47   a  of the trapezoidal part, the side  47   d  is provided at a right angle to the annular part  46 , and the other side is formed as the inclined side (inclined surface)  47   c . In this case, the angle 
     θ
 
formed by the side  43   c  and the annular part  42  and the angle
 
θ
 
formed by the side  47   c  and the annular part  46  are made equal to each other, and the lengths of the sides  43   c  and  47   c , which are inclined parts, are mutually the same. In the normal position illustrated in  FIG. 4 , the flat surface part (the step part  42   a  shown in  FIG. 3 ) of the annular part  4  and the upper base  47   b  abut each other, and a flat surface part  46   a  of the annular part  46  and the upper base  43   b  abut each other (In  FIG. 6 , they are separately illustrated to explain correspondence with reference symbols). When such a positional relation is used, the relative positions of the stopper  41  and the pusher  45 , particularly, the relative interval between the annular parts  42  and  46  can be minimized.
 
       FIG. 6B  illustrates the relative positional relation of the stopper  41  and the pusher  45  in the state of  FIG. 5  and illustrates a state in which the pusher  45  is rotated by a rotation angle of about 67 degrees from the state of  FIG. 6A . When the pusher  45  is rotated from the state of  FIG. 6A  (in the exploded view of the drawing, the pusher  45  is moved downward), the pusher  45  rotates while the inclined sides  43   c  and  47   c  are in contact with each other; therefore, the stopper  41  is moved in the direction to be away from the pusher  45 . Then, when the contact state of the inclined sides  43   c  and  47   c  is released, the upper bases  43   b  and  46   a  is put into a state in which the upper bases abut each other. In this state, the interval between the annular part  42  of the stopper  41  and the annular part  46  of the pusher  45  is twice as large as compared with that in the state of  FIG. 6A . 
     In the working of the present invention, the shapes and the sizes of the cam members  43  and  47  can be arbitrarily set depending on the size of the impact mechanism part including the hammer  24 . The degree of a rotation angle a2 degrees of the inclined sides  43   c  and  47   c  can be optionally set. In that case, if the rotation angle a2 degrees is ensured to be large to some extent, the force that is required for moving the change lever  48   b  can be reduced. If a rotation angle a1 degrees is ensured to be large to some extent, rigidity of the switching mechanism  35  upon retraction suppression of the hammer  24  can be increased. The shapes of the cam members  43  and  47  are not limited to trapezoidal shapes like the present embodiment. The shapes of the cam members to be achieved are comparatively optional as long as the cam members are provided with: surfaces which abut each other when the stopper  41  and the pusher  45  approach each other (for example, the upper base  43   b  and the flat surface part  46   a , the step part  42   a  and the upper base  47   b ); surfaces which abut each other when the stopper  41  and the pusher  45  gets away from each other (for example, the upper base  43   b  and the upper base  46   a ); and working surfaces which convert the rotary motion of the pusher  45  to axial-direction locomotion of the stopper  41  (for example, the inclined surfaces  43   c  and  47   c ). 
       FIG. 7  is a cross-sectional view perpendicular to the axial direction that passes through the change member  48  of the switching mechanism  35 . The change member  48  extends from outside of the housing  2  and the hammer case  32  to the transmission mechanism part (the reduction mechanism  20 , the rotary impact mechanism part  22 ) in the hammer case  32  through the part between the housing  2  and the hammer case  32 . The annular part  46  of the pusher  45  is provided inside of the outer peripheral surface  32   d  of the hammer case  32 . The change member  48  is provided in the outer side of the outer peripheral surface  32   d  of the hammer case  32 , and the change lever  48   b  is exposed to outside from the part between the circumferential-direction end parts  49   a  and  49   b  of the housing. In this case, the movable range of the change lever  48   b  is b1 when viewed in the rotation direction about the rotation axis. The engagement holes  48   c  of the change member  48  are engaged with the projections  46   c  of the annular part  46  in the body part  2   a  of the housing  2 . In this case, the movable range of the projections  46   c  and the engagement holes  48   c  is b2 when viewed in the rotation direction about the rotation axis. Herein, the movable range b1 of the change lever  48   b  and the movable range b2 of the projections  46   c  and the engagement holes  48   c  are configured so as not to be mutually overlapped when viewed in the circumferential direction. In such an arrangement, the movable range of the change lever  48   b  is positioned in the outer peripheral side of the hammer case  32 , the movable range of the contact location of the change member  48  and the pusher  45  is positioned on the inner peripheral side of the hammer case  32 , and the ranges are set so as not to be mutually overlapped; therefore, an opening which is directly exposed to outside from the hammer case  32  can be eliminated, and the risk that grease therein leaks out to the outside from a gap in the vicinity of the change lever  48   b  can be significantly suppressed. 
     In this manner, the change member  48  has the annular part  48   a , which is a ring-shaped part corresponding to a half cycle, and the change member  48  and the pusher  45  are engaged with each other by the projections  46   c  and the engagement holes  48   c  substantially diagonally in the body part  2   a  of the housing  2 ; therefore, the rotation operation of the change lever  48   b  can be stably transmitted to the rotation operation of the pusher  45 . The pusher  45 , which is rotated, has the annular part  46  and is engaged with the change member  48  by two points on of the annular part  46  in the substantially diagonal line; therefore, the pusher  45  can be stably operated by the two locations, and rotating of the pusher  45  can be smoothly carried out. 
     In the foregoing, the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention. 
     According to an aspect of the present invention, in a power tool provided with a housing that houses a driving source and a case that houses a transmission mechanism part driven by the driving source and is partially covered with the housing, a switching member that changes an operation mode of the transmission mechanism part from outside extends from outside of the housing and the case to the transmission mechanism part in the case through a part between the housing and the case. The transmission mechanism part includes: a spindle that is rotated by the driving source; a hammer that is moved in an axial direction of the spindle while the hammer is being rotated by working of a cam mechanism provided on the spindle; an anvil to which rotative force and impact force are applied by the hammer; a spring that energizes the hammer to the anvil side; and a regulating unit that limits movement of the hammer in a direction opposite to the energizing direction of the spring. The regulating means switches the operation mode by the switching member. The regulating unit is a stopper disposed in the rear of the hammer, and the switching member includes a pusher that abuts the stopper and a change lever that rotates the pusher coaxially with a spindle. On a side, on which the pusher and the stopper are mutually abutting, of each of the pusher and the stopper, a working member that causes a relative interval between the stopper and the pusher to be adjustable by rotating the pusher is formed. The change lever is engaged with the pusher in an opening formed in the case, and an operation part of the change lever is projected to outside at a location other than an opening of the case. When viewed in a circumferential direction of the hammer case, a circumferential-direction movable range of the operation part is arranged so as not to be overlapped with a circumferential-direction movable range of an engagement part of the change lever and the pusher. 
     According to another aspect of the present invention, a recessed part that serves as a circumferential-direction movable region of the engagement part is formed in a rear end part of the hammer case. The change lever is an arc-shaped member being disposed along an outer wall of the hammer case and not being continued in a circumferential direction and has engagement parts formed to be engaged with pusher parts in vicinities of both ends of the arc-shaped member at, for example, two points of the arc-shaped member being substantially diagonal on a ring part. The operation part is provided substantially at the center of the two engagement parts of the change lever. An operation position of the operation part has a normal position that allows backward movement of the hammer and allows the anvil to carry out impacting and a lock position that prevents backward movement of the hammer with respect to the anvil. The pusher has a plurality of cam members projecting toward the front in the axial direction and along an annular member. The stopper has a plurality of cam members projecting toward the rear in the axial direction and along an annular member. The backward movement of the hammer is limited when the cam members are arranged in series in the axial direction, and the backward movement of the hammer is allowed when the cam members are alternately aligned in a circumferential direction. 
     According to another aspect of the present invention, when exploded, each of the cam members is a trapezoidal member, an inclined surface is formed on one of sides connecting an upper base and a lower base, and switching between the normal position and the lock position is carried out by relatively rotating the stopper with respect to the pusher while the inclined surfaces are brought into contact with each other. The cam members of the pusher and the stopper are disposed at three locations in the circumferential direction, and inclination angles of the inclined surfaces are mutually equal. Each of the circumferential-direction lengths of abutting surfaces when the cam members are arranged in series in the axial direction is preferable to be 45 degrees or larger in a circumferential angle. The driving source is a brushless motor and is provided with a control part that controls a rotation direction and a rotation speed of the brushless motor, and, at the lock position, the control part controls so as to carry out an impacting operation while the hammer is driven in normal-rotation and opposite-rotation directions. The hammer has a first impact mode in which the hammer carries out impact fastening in which the hammer is placed over the anvil upon impacting and a second impact mode in which the hammer carries out impact fastening in which the hammer is not placed over the anvil upon impacting. The case has a flange part formed in a cup shape continued in the circumferential direction at the opening of the case, a latch part formed to latch a step of the flange part at a front edge part of the housing, and the case is fixed to the housing by latching the flange part and the latch part, and a recessed part is formed to be closer to the opening than to the step of the flange part. 
     According to one of the other aspects of the present invention, the regulating unit that limits the backward movement of the hammer is provided, and the operation mode is switched by moving the regulating unit by the switching member; therefore, the power tool (electric power tool) having the plurality of operation modes is achieved. 
     According to one of the other aspects of the present invention, the switching mechanism part includes the stopper and the pusher disposed in the rear of the hammer, and, when the pusher is rotated, the stopper is moved to carry out switching. The change lever that rotates the pusher in the coaxial direction with the spindle is provided, the change lever being engaged with the pusher by the opening of the hammer case, and the operation part is projecting to the outside at a portion other than the opening of the hammer case. Therefore, when viewed from outside, the opening of the hammer case can be eliminated, and leakage of grease from the opening is thus suppressed. 
     According to one of the other aspects of the present invention, the circumferential-direction movable range of the operation part is not overlapped with the circumferential-direction movable range of the engagement part of the pusher. Therefore, since the operation part can be disposed at a position away from the opening for allowing penetration of the engagement part of the hammer case, leakage of grease from the opening part to the outside is suppressed. 
     According to one of the other aspects of the present invention, the change lever is the arc-shaped member that is disposed along the outer wall of the hammer case and is not continued in the circumferential direction, and has the engagement parts formed to be engaged with the pusher part in vicinities of the both ends of the arc-shaped member. The operation part is provided substantially at the center of the two engagement parts of the change lever. Therefore, the pusher can be stably operated at the two locations, and rotating of the pusher can be smoothly carried out. 
     According to one of the other aspects of the present invention, the operation position of the operation part has the normal position that allows backward movement of the hammer and allows the anvil to carry out impacting and the lock position that prevents the backward movement of the hammer with respect to the anvil. Therefore, the backward movement of the hammer can be easily limited by operating the operation part. 
     According to one of the other aspects of the present invention, the backward movement of the hammer is limited when the hammer is at the rotation position at which the cam members are arranged in series in the axial direction, and, when the cam members are alternately aligned in the circumferential direction, the backward movement of the hammer is allowed. Therefore, the interval of the stopper and the pusher can be easily adjusted only by relatively rotating the stopper and the pusher. Moreover, stable retention can be performed at the position after the adjustment. 
     According to one of the other aspects of the present invention, when the stopper is relatively rotated with respect to the pusher in the state in which the inclined surfaces of the cam members are in contact with each other, the switching between the normal position and the lock position is carried out. Therefore, the stopper can be easily moved in the axial direction with small force, and thus the switching mechanism with good operability is achieved. 
     According to one of the other aspects of the present invention, the cam members are respectively disposed at the three locations in the circumferential direction, and the stopper is not easily rattled and thus the stopper can be stably retained. The inclination angles of the inclined surfaces are mutually equal; therefore, the stopper can be smoothly moved in the axial direction. 
     According to one of the other aspects of the present invention, each of the circumferential-direction lengths of the abutting surfaces when the cam members are arranged in series in the axial direction is 45 degrees or larger in the circumferential angle; therefore, sufficient contact surfaces are ensured. 
     According to one of the other aspects of the present invention, at the lock position, the control part carries out the impact operation while driving the hammer in the forward-rotation and reverse-rotation directions. Therefore, an impact mechanism of an electronic pulse type is achieved by using an already used impact mechanism. 
     According to one of the other aspects of the present invention, since two impact modes are prepared, various fastening operations can be carried out with one power tool. 
     According to one of the other aspects of the present invention, the flange part continued in the circumferential direction is formed at the opening of the case, the latch part that latches the step of the flange part is formed at the front edge part of the housing, the case is fixed to the housing by latching them, and the recessed part is formed in the side close to the opening than to the step of the flange part. Therefore, stress is not easily concentrated on the recessed part, and the hammer case can be prevented from being broken. 
     In the above-described embodiment, the electric power tool which can use both of the functions of the impact driver and the electronic pulse driver has been proposed. However, the tool may be a tool that has the functions of an impact driver and a drill driver. In the above-described embodiment, the example of the electric power tool using a brushless motor as a driving source has been described as an example of the power tool. However, the tool may be an electric power tool using a motor equipped with a brush or may be a power tool using an air motor. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Power tool 
               2  Housing 
               2   a  Body part 
               2   b  Handle part 
               3  Motor 
               3   a  Rotor 
               3   b  Stator 
               3   c  Rotary shaft 
               4  Inverter circuit board 
               5  Switching element 
               6  Trigger switch 
               7  Switch board 
               8  Control circuit board 
               9  Battery 
               10  Forward/reverse switching lever 
               13  Rotor fan 
               14  Rotation-position detecting element 
               17   a  Air intake hole 
               17   b ,  17   c  Slot 
               18   a ,  18   b  Bearing 
               19   a  Metal 
               19   b  Bearing 
               20  Reduction mechanism 
               22  Rotary impact mechanism part 
               23  Spring 
               24  Hammer 
               24   a ,  24   b  Projecting part 
               25  Spindle cam groove 
               26  Ball 
               27  Spindle 
               28  Hammer cam groove 
               30  Anvil 
               30   a ,  30   b  Projecting part 
               30   c  Anvil angular-hole part 
               31  Attachment member 
               32  Hammer case 
               32   a  Through hole 
               32   b  Flange part 
               32   c  Recessed part 
               32   d  Outer peripheral surface 
               32   e  Step part 
               35  Switching mechanism 
               36  Member 
               37  Ring member 
               38  Roller 
               39  Switching spring 
               41  Stopper 
               42  Annular part 
               42   a  Step part 
               43 ,  47  Cam members 
               43   a ,  47   a  Lower base (of cam member) 
               43   b ,  47   b  Upper base (of cam member) 
               43   c ,  47   c  Inclined surface (of cam member) 
               43   d ,  47   d  Side (of cam member) 
               44  Spline projection 
               45  Pusher 
               46  Annular part 
               46   a  Flat surface part 
               46   c  Projection 
               47   e  Step part 
               48  Change member 
               48   a  Annular part 
               48   b  Change lever (operation part) 
               48   c  Engagement hole 
               49   a ,  49   b  Circumferential-direction end part