Patent Publication Number: US-2023158623-A1

Title: Impact tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2021-191424, filed on Nov. 25, 2021, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
       1 . Technical Field 
     The present invention relates to an impact tool such as an impact driver. 
       2 . Description of the Background 
     An impact tool such as an impact driver includes a motor in its rear portion and a striker including an anvil for rotary striking as driven by the motor in its front portion. Such an impact tool is described in, for example, Japanese Unexamined Patent Application Publication No. 2020-188631. The striker further includes a spindle rotatable in response to rotation of the motor and a hammer connected to the spindle with a cam with balls in between. A coil spring externally mounted on the spindle urges the hammer to a forward position, allowing a tab on a front surface of the hammer to be engageable with an arm of the anvil in a rotation direction. 
     The striker is accommodated in a hammer case. The hammer case is filled with grease. The spindle has a through-hole and a connection hole that orthogonally connects with the through-hole. The grease in the hammer case is supplied to sliding surfaces of the spindle and the hammer from the through-hole through the connection hole. The impact tool may include a striker unit with another structure. 
     BRIEF SUMMARY 
     When an insufficient amount of grease is supplied to the sliding surfaces of the spindle and the hammer, the impact tool may have seizure and fail to strike. Such supply of an insufficient amount of grease may also occur to the striker unit with the other structure. 
     One or more aspects of the present disclosure are directed to an impact tool that supplies a sufficient amount of grease to sliding surfaces of a spindle and a hammer. 
     One or more aspects of the present disclosure are directed to an impact tool that supplies a sufficient amount of grease to a striker unit. 
     A first aspect of the present disclosure provides an impact tool, including:
     a motor;   a spindle rotatable by the motor;   a hammer externally and coaxially mounted on the spindle, the hammer being configured to receive rotation of the spindle and movable relative to the spindle in an axial direction;   an anvil located in front of the hammer and coaxial with the spindle, the anvil being configured to be struck by the hammer in a rotation direction; and   
 a hammer case accommodating the spindle, the hammer, and the anvil, the hammer case allowing a front end of the anvil to protrude frontward from the hammer case, the hammer case being filled with grease, 
   wherein the spindle includes 
   a grease supply path located in the spindle, the grease supply path being open in a sliding surface of the spindle on which the hammer slides, the grease supply path allowing grease to be supplied to the sliding surface, and   an accelerator disposed in the spindle, the accelerator being configured to accelerate a flow of the grease onto the sliding surface along the grease supply path in response to rotation of the motor.   
   

     A second aspect of the present disclosure provides an impact tool, including:
     a motor;   a striker unit drivable by the motor;   an anvil configured to be struck by the striker unit in a rotation direction; and   an accelerator configured to accelerate a flow of grease supplied to the striker unit.   

     The technique according to the above aspects of the present disclosure allows supply of a sufficient amount of grease to the sliding surfaces of the spindle and the hammer or to the striker unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a longitudinal central sectional view of an impact driver according to a first embodiment. 
         FIG.  2    is an enlarged view of a body in  FIG.  1   . 
         FIG.  3    is an exploded perspective view of a spindle and a pump member as viewed from the rear. 
         FIG.  4    is an enlarged perspective view of the pump member as viewed from the front. 
         FIG.  5    is a longitudinal central sectional view of a striker in an impact driver according to a second embodiment. 
         FIG.  6    is a longitudinal central sectional view of a striker in an impact driver according to a third embodiment. 
         FIG.  7    is a longitudinal central sectional view of a striker in an impact driver according to a fourth embodiment. 
         FIG.  8    is a longitudinal central sectional view of a striker in an impact driver according to a fifth embodiment. 
         FIG.  9    is a longitudinal central sectional view of a striker in an impact driver according to a sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     Embodiments of the present disclosure will now be described with reference to the drawings. 
       FIG.  1    is a longitudinal central sectional view of a rechargeable impact driver as an example of an impact tool.  FIG.  2    is an enlarged view of a body in  FIG.  1   . 
     An impact driver  1  includes a body  2  and a grip  3 . The body  2  includes a central axis extending in a front-rear direction. The grip  3  extends downward from the body  2 . 
     The impact driver  1  includes a housing including a body housing  4 , a rear cover  5 , and a hammer case  6 . The body housing  4  includes a motor housing  7 , a grip housing  8 , and a battery mount  9 . A battery pack  10 , which serves as a power supply, is attached to the battery mount  9 . The motor housing  7  is cylindrical and defines a rear portion of the body  2 . The grip housing  8  defines the grip  3 . 
     The body housing  4  includes a pair of right and left housing halves fastened with screws. The rear cover  5  is a cap. The rear cover  5  is joined to the motor housing  7  from the rear with screws. 
     The body  2  includes a brushless motor  11  and a striker  12  in this order from the rear. The motor housing  7  and the rear cover  5  accommodate the brushless motor  11 . 
     The brushless motor  11  is an inner-rotor motor and includes a stator  13  and a rotor  14 . The stator  13  is held in the motor housing  7 . The rotor  14  includes a rotational shaft  15  at its center. The rotational shaft  15  extends through the stator  13  in the front-rear direction. A fan  16  is fixed to a rear end of the rotational shaft  15 . 
     The striker  12  includes an outer shell including the hammer case  6  and a bearing box  18 . The hammer case  6  is formed from a metal and is cylindrical and tapered frontward. The bearing box  18  is formed from a metal and is disk-shaped. The bearing box  18  is screwed in an opening at the rear end of the hammer case  6 . The striker  12  is held by the motor housing  7  and causes a front portion of the hammer case  6  to protrude frontward. The rotational shaft  15  extends through the bearing box  18  and protrudes in the striker  12 . The rotational shaft  15  is supported by a bearing  19  held in the bearing box  18 . A pinion  20  is fixed to a distal end of the rotational shaft  15 . 
     The striker  12  includes a reducer  21 , a spindle  22 , a hammer  23 , a coil spring  24 , and an anvil  25 . 
     The reducer  21  includes an internal gear  26  and three planetary gears  27 . The internal gear  26  is held in a rear portion of the striker  12 . Each planetary gears  27  is supported by a carrier  29  on the spindle  22  in the internal gear  26  with a pin  28 . The planetary gears  27  mesh with the pinion  20  on the rotational shaft  15 . 
     The spindle  22  includes the carrier  29  in its rear portion. The carrier  29  is hollow and disk-shaped. The spindle  22  has its rear end supported by the bearing box  18  with a bearing  30  in between. 
     The spindle  22  has a through-hole  35  at its axial center. The through-hole  35  includes a rear larger-diameter hole  36  and a front smaller-diameter hole  37 . The larger-diameter hole  36  is open in a rear end face of the spindle  22 . The smaller-diameter hole  37  is open in a front end face of the spindle  22 . A medium-diameter hole  38  shorter in the front-rear direction is located between the larger-diameter hole  36  and the smaller-diameter hole  37 . The pinion  20  on the rotational shaft  15  protrudes from the rear of the spindle  22  in the larger-diameter hole  36  and meshes with the planetary gears  27 . 
     The hammer  23  is externally mounted on the spindle  22 . The hammer  23  includes a set of tabs (not shown) on its front surface. The hammer  23  includes a pair of outer cam grooves  40  on its inner peripheral surface. The pair of outer cam grooves  40  are point-symmetric to each other about an axis of the hammer  23 . The outer cam grooves  40  extend rearward from the front end. The spindle  22  includes a pair of inner cam grooves  41  on its outer peripheral surface. The inner cam grooves  41  are V-shaped and have their tips facing frontward. Balls  42  are fitted in the corresponding outer cam grooves  40  and in the corresponding inner cam grooves  41 . Each ball  42  is received across the corresponding grooves. The balls  42  allow the hammer  23  and the spindle  22  to rotate and translate. The hammer  23  has an annular groove  43  on its rear surface. 
     The coil spring  24  is externally mounted on the spindle  22  between the carrier  29  and the hammer  23 . The coil spring  24  is positioned with its rear end in contact with the front surface of the carrier  29  and its front end placed in the annular groove  43 . 
     The anvil  25  is located in front of the spindle  22  and the hammer  23  and coaxial with the spindle  22 . Two bearings  45  arranged in the front-rear direction are at the front end of the hammer case  6 . The bearings  45  support the anvil  25 . The anvil  25  includes a set of arms  46  behind the bearings  45 . The coil spring  24  urges the hammer  23  to the forward position in  FIG.  1   . At the forward position, the tabs on the hammer  23  are engageable with the arms  46  in the rotation direction. The anvil  25  has its front end protruding frontward from the hammer case  6 . The anvil  25  has a bit insertion hole  47  along its axis. An operation sleeve  48  for attaching or detaching a bit is located at the front end of the anvil  25 . 
     The anvil  25  has a fitting recess  49  at the center of its rear surface. The spindle  22  includes a fitting protrusion  50  fitted in the fitting recess  49  at the center of its front end. The smaller-diameter hole  37  of the through-hole  35  extends through the fitting protrusion  50  and is connected to the fitting recess  49 . 
     The spindle  22  has a front connection hole  51  and a rear connection hole  52 . The front connection hole  51  is connected to the smaller-diameter hole  37  between the pair of inner cam grooves  41  and is open in the outer peripheral surface of the spindle  22 . The rear connection hole  52  is connected to the medium-diameter hole  38  and is open in the outer peripheral surface of the spindle  22 . The front connection hole  51  and the rear connection hole  52  are orthogonal to each other as viewed from the front and face the inner peripheral surface of the hammer  23  at the forward position. 
     The larger-diameter hole  36  accommodates a pump member  55 . The pump member  55  is a circular shaft as viewed from the front as shown in  FIGS.  3  and  4   . The pump member  55  is formed from a resin or a metal. The pump member  55  has, on its outer peripheral surface, a groove  56  that spirals in a counterclockwise direction toward the front. The groove  56  has a semicircular cross section. The pump member  55  has, in its rear portion, a blind hole  57  open in the rear surface. The blind hole  57  has an inner peripheral surface defining a gear-shaped engagement portion  58 . The pinion  20  on the rotational shaft  15  has its outer shape to be fitted in the engagement portion  58 . 
     The larger-diameter hole  36  accommodates the pump member  55  with the front end of the pinion  20  engaged with the engagement portion  58  to be integral with each other in the rotation direction. In this case, the front end of the pump member  55  is near a front inner surface of the larger-diameter hole  36 . The groove  56  extends to the front surface of the pump member  55  and is connected to the medium-diameter hole  38 . 
     The striker  12  is filled with grease. The grease flows into the larger-diameter hole  36  in the spindle  22  through a gap in the carrier  29 . 
     The grip  3  accommodates a switch  60  in its upper portion. A trigger  61  protrudes in front of the switch  60 . 
     A forward-reverse switch lever  62  for the brushless motor  11  is located between the striker  12  and the switch  60 . A mode switch  63  is located in front of the forward-reverse switch lever  62 . The mode switch  63  faces frontward and has a button exposed on the front surface. The button in the mode switch  63  is repeatedly pressed to switch impact forces or registered striking modes. 
     The battery mount  9  accommodates a terminal base  65  and a controller  66 . The terminal base  65  is electrically connected to the battery pack  10 . The controller  66  is located above the terminal base  65 . The controller  66  includes a control circuit board  67  receiving, for example, a microcomputer and switching elements. A display panel  68  is located on the upper surface of the battery mount  9 . The display panel  68  displays the rotational speed of the brushless motor  11  and the remaining battery level of the battery pack  10 . 
     In the impact driver  1 , the trigger  61  is pressed to turn on the switch  60  after a bit (not shown) is attached to the anvil  25 . The brushless motor  11  is then powered to rotate (rotate forward) the rotational shaft  15  with the rotor  14 . Thus, the planetary gears  27  engaged with the pinion  20  revolve in the internal gear  26 . This causes the spindle  22  to rotate at a lower speed with the carrier  29 . The hammer  23  then rotates together with the spindle  22  with the balls  42  in between, thus rotating the anvil  25  with the arms  46  engaged with the tabs. This allows tightening a screw with the bit. 
     As a screw is tightened and increases the torque of the anvil  25 , the hammer  23  retracts against the urging force from the coil spring  24  while rolling the balls  42  along the inner cam grooves  41  on the spindle  22 . After the tabs are disengaged from the arms  46 , the hammer  23  rotates forward along the inner cam grooves  41  under the urging force from the coil spring  24 . This then causes the tabs to be reengaged with the arms  46 . Thus, the anvil  25  generates a rotational striking force (impact). This process is repeated to further tighten the screw. 
     As the rotational shaft  15  and the pinion  20  rotate, the pump member  55  engaged with the pinion  20  rotates (rotates forward) integrally. This generates a difference in a rotational speed between the pump member  55  rotating integrally with the pinion  20  and the spindle  22  that rotates at a lower speed reduced by the reducer  21 . This difference in the rotational speed causes, in the larger-diameter hole  36 , grease between the outer peripheral surface of the pump member  55  and the inner peripheral surface of the larger-diameter hole  36  to be fed forward along the groove  56  that rotates. The grease fed forward flows into the medium-diameter hole  38  from the front end of the groove  56 . A portion of the grease is supplied to the sliding surfaces of the spindle  22  and the hammer  23  through the rear connection hole  52  under a centrifugal force. Another portion of the grease flowing into the medium-diameter hole  38  flows inside the smaller-diameter hole  37  and is supplied to the sliding surfaces of the spindle  22  and the hammer  23  through the front connection hole  51  under a centrifugal force. Thus, the sliding surfaces are lubricated during an operation of the impact driver  1 . 
     A portion of the grease flowing through the front connection hole  51  into the smaller-diameter hole  37  flows into the fitting recess  49  on the anvil  25  to lubricate the spindle  22  and the anvil  25 . 
     As the rotational shaft  15  and the pinion  20  rotate reversely, the pump member  55  also rotates reversely. The difference in the speed between the spindle  22  and the pump member  55  causes grease between the outer peripheral surface of the pump member  55  and the inner peripheral surface of the larger-diameter hole  36  to be fed backward along the groove  56 . The grease thus lubricates portions of the pinion  20  and the planetary gears  27  engaged with each other. 
     The impact driver  1  according to the first embodiment includes the brushless motor (an example of a motor)  11  and the spindle  22  rotatable by the brushless motor  11 . The impact driver  1  includes the hammer  23  that is externally and coaxially mounted on the spindle  22  to receive rotation of the spindle  22  and movable relative to the spindle  22  in the axial direction. The impact driver  1  includes the anvil  25  that is located in front of the hammer  23  and coaxial with the spindle  22  and is struck by the hammer  23  in the rotation direction. The impact driver  1  includes the hammer case  6  accommodating the spindle  22 , the hammer  23 , and the anvil  25  and allowing the front end of the anvil  25  to protrude frontward from the hammer case  6 . The hammer case  6  is filled with grease. The spindle  22  has the through-hole  35 , the front connection hole  51 , and the rear connection hole  52  (examples of a grease supply path) that are open in the sliding surface of the spindle  22  on which the hammer  23  slides to allow grease to be supplied to the sliding surface. The spindle  22  also includes the pump member  55  (an example of an accelerator) that accelerates the flow of the grease onto the sliding surface in the through-hole  35  in response to rotation of the brushless motor  11 . 
     This structure uses the pump member  55  to supply a sufficient amount of grease to the sliding surfaces of the spindle  22  and the hammer  23 . 
     The accelerator is the pump member  55  (an example of a rotation member) that rotates in the through-hole  35  in response to rotation of the brushless motor  11 . 
     The pump member  55  rotates to accelerate the flow of the grease. 
     The rotational shaft  15  in the brushless motor  11  protrudes into the through-hole  35 . The pump member  55  rotates integrally with the rotational shaft  15 . 
     Thus, the rotational shaft  15  can be used to effectively rotate the pump member  55 . 
     The rotational shaft  15  includes, on its distal end, the pinion  20  that reduces the speed of the spindle  22 . The pump member  55  is engaged with the pinion  20  and rotates integrally with the pinion  20 . 
     Thus, the pinion  20  can be used to easily rotate the pump member  55  integrally with the rotational shaft  15 . The difference in the rotational speed between the pinion  20  and the spindle  22  causes the grease to be fed. 
     The pump member  55  includes the spiral groove  56  on its outer peripheral surface. 
     This allows the grease to be efficiently fed to the sliding surfaces. 
     The grease supply path has the through-hole  35  located at the axial center of the spindle  22 , and the front connection hole  51  and the rear connection hole  52  (examples of a connection hole) that are connected to the through-hole  35 , extend in the radial direction of the spindle  22 , and are open in the outer peripheral surface of the spindle  22 . 
     This structure easily defines the grease supply path and allows efficient supply of grease to the sliding surfaces under a centrifugal force in response to rotation of the spindle  22 . 
     The front end of the spindle  22  and the rear end of the anvil  25  are coaxially fitted to each other. The through-hole  35  extends beyond the front connection hole  51  to the fitting portion between the front end of the spindle  22  and the rear end of the anvil  25 . 
     This structure allows effective lubrication of the fitting portion between the spindle  22  and the anvil  25 . 
     The rotation member  55  is received in the through-hole  35 . 
     Thus, the through-hole  35  allows easy installation of the pump member  55 . 
     In the first embodiment, the pump member may have the groove with the width, depth, and other features changed as appropriate. The cross section of the groove is not limited to the semicircular cross section, and may be V-shaped. 
     The pump member may include multiple grooves. In this case, the width, depth, and cross-sectional shape of each groove may be changed. 
     The pump member may include multiple components. 
     Second Embodiment 
     A second embodiment of the present disclosure will now be described. The structure according to the present embodiment is the same as in the first embodiment except an accelerator included in a striker, and will be described focusing on the accelerator. 
     A pump member  55 A in a striker  12  shown in  FIG.  5    has, at its axial center, a bypass hole  70  that extends through the pump member  55 A in the front-rear direction. 
     The pump member  55 A in the striker  12  in the present embodiment rotates (rotates frontward) integrally with a rotational shaft  15  and a pinion  20  in response to rotation of the rotational shaft  15  and the pinion  20 . This causes grease between the outer peripheral surface of the pump member  55 A and the inner peripheral surface of a larger-diameter hole  36  to be fed forward along a groove  56  that rotates, as described in the first embodiment. At the same time, grease in a blind hole  57  in the pump member  55 A flows through the bypass hole  70  and reaches a medium-diameter hole  38 . A grease portion fed from the groove  56  and a grease portion fed from the bypass hole  70  meet at the medium-diameter hole  38 . A portion of the grease is then supplied to the sliding surfaces of a spindle  22  and a hammer  23  through a rear connection hole  52  under a centrifugal force. The other effects are the same as in the first embodiment. 
     In the impact driver  1  according to the second embodiment as well, the spindle  22  has a through-hole  35 , a front connection hole  51 , and the rear connection hole  52  that are open in the sliding surface of the spindle  22  on which the hammer  23  slides to allow grease to be supplied to the sliding surface. The spindle  22  also includes the pump member  55 A that accelerates the flow of the grease onto the sliding surface in the through-hole  35  in response to rotation of a brushless motor  11 . 
     The pump member  55 A allows supply of a sufficient amount of grease to the sliding surfaces of the spindle  22  and the hammer  23 . In particular, the pump member  55 A has the bypass hole  70  that extends through the pump member  55 A in the axial direction, thus allowing a large amount of grease to be supplied to the sliding surfaces. 
     In the second embodiment as well, the width, depth, and other features of the groove on the pump member may be changed as appropriate. The cross section of the groove is not limited to the semicircular cross section, and may be V-shaped. 
     The pump member may include multiple grooves. In this case, the width, depth, and cross-sectional shape of each groove may be changed. 
     The bypass hole may not be located at the axial center of the pump member. The pump member may have multiple bypass holes. 
     The pump member may include multiple components. 
     Third Embodiment 
     A striker  12  in a third embodiment shown in  FIG.  6    includes a pump member that also functions as a pinion  20 . The pinion  20  extending frontward in a gear shape has its front surface near the front inner surface of a larger-diameter hole  36 . More specifically, the pinion  20  includes, as a pump  55 B, a portion extending frontward from its portion engaged with planetary gears  27 . 
     In response to rotation (frontward rotation) of a rotational shaft  15  and the pinion  20  in the striker  12  in the present embodiment, grease in the larger-diameter hole  36  is fed forward through the pump  55 B in the pinion  20 . The grease reaches a medium-diameter hole  38 . A portion of the grease is then supplied to the sliding surfaces of a spindle  22  and a hammer  23  through a rear connection hole  52  under a centrifugal force. The other effects are the same as in the first embodiment. 
     In the impact driver  1  according to the third embodiment as well, the spindle  22  has a through-hole  35 , a front connection hole  51 , and the rear connection hole  52  that are open in the sliding surface of the spindle  22  on which the hammer  23  slides to allow grease to be supplied to the sliding surface. The impact driver  1  includes the pump  55 B that accelerates the flow of the grease onto the sliding surface in the through-hole  35  in response to rotation of a brushless motor  11 . 
     The pump  55 B allows supply of a sufficient amount of grease to the sliding surfaces of the spindle  22  and the hammer  23 . 
     In particular, the pinion  20  is located on the distal end of the rotational shaft  15 . The pump member as the pump  55 B is integral with the pinion  20 . Thus, the pinion  20  allows easy installation of the pump member. 
     In the third embodiment, the pump on the pinion may not be a gear with straight teeth. For example, the gear may be a helical gear. The pump may be a shaft having a circular cross section and having a spiral groove on its outer peripheral surface, as in the first embodiment. 
     The length of the pump in the front-rear direction may be changed as appropriate. 
     Fourth Embodiment 
     In a striker  12  in a fourth embodiment shown in  FIG.  7   , a pinion  20  also functions as a pump member, as in the third embodiment. The pinion  20  includes, as a pump  55 B, a portion extending frontward to have its front surface near the front inner surface of a larger-diameter hole  36  and extending frontward from its portion engaged with planetary gears  27 . 
     A spiral groove  56   a  with a semicircular cross section is located frontward from the portion of the pinion  20  that is engaged with the planetary gears  27  on the inner peripheral surface of the larger-diameter hole  36 . 
     In response to rotation (frontward rotation) of a rotational shaft  15  and the pinion  20  in the striker  12  in the present embodiment, grease in the larger-diameter hole  36  is fed forward through the pump  55 B in the pinion  20 . At the same time, the grease between the inner peripheral surface of the larger-diameter hole  36  and the pump  55 B is fed frontward along the groove  56   a  that rotates. The grease reaches a medium-diameter hole  38 . A portion of the grease is then supplied to the sliding surfaces of a spindle  22  and a hammer  23  through a rear connection hole  52  under a centrifugal force. The other effects are the same as in the first embodiment. 
     In the impact driver  1  according to the fourth embodiment as well, the spindle  22  has a through-hole  35 , a front connection hole  51 , and the rear connection hole  52  that are open in the sliding surface of the spindle  22  on which the hammer  23  slides to allow grease to be supplied to the sliding surface. The impact driver  1  includes the pump  55 B that accelerates the flow of the grease onto the sliding surface in the through-hole  35  in response to rotation of a brushless motor  11 . 
     The pump  55 B allows supply of a sufficient amount of grease to the sliding surfaces of the spindle  22  and the hammer  23 . 
     In particular, the pinion  20  is located on the distal end of the rotational shaft  15 . The pump member as the pump  55 B is integral with the pinion  20 . Thus, the pinion  20  allows easy installation of the pump member. The groove  56   a  on the inner peripheral surface of the larger-diameter hole  36  allows grease to be efficiently fed to the sliding surface along the groove  56   a . 
     In the fourth embodiment as well, the pump on the pinion may not be a gear with straight teeth. For example, the pump may be a helical gear. The pump may be a shaft having a circular cross section and having a spiral groove on its outer peripheral surface, as in the first embodiment. 
     The length of the pump in the front-rear direction may be changed as appropriate. 
     The width, depth, and other features of the groove located on the inner peripheral surface of the larger-diameter hole may be changed as appropriate. The cross section of the groove is not limited to the semicircular cross section, and may be V-shaped. 
     Multiple grooves may be located on the inner peripheral surface of the larger-diameter hole  36 . In this case, the width, depth, and cross-sectional shape of each groove may be changed. 
     Fifth Embodiment 
     In a striker  12  in a fifth embodiment shown in  FIG.  8   , a pump member  55 C extends not only into a larger-diameter hole  36  but also to a position adjacent to the front end of a through-hole  35 . The pump member  55 C further includes a medium-diameter portion  71  and a smaller-diameter portion  72 . The medium-diameter portion  71  is placed in a medium-diameter hole  38 . The smaller-diameter portion  72  is placed in a smaller-diameter hole  37 . A groove  56  extends continuously from the outer peripheral surface of the medium-diameter portion  71  to the outer peripheral surface of the smaller-diameter portion  72 . 
     The pump member  55 C in the striker  12  in the present embodiment rotates (rotates frontward) integrally with a rotational shaft  15  and a pinion  20  in response to rotation of the rotational shaft  15  and the pinion  20 . This causes grease between the outer peripheral surface of the pump member  55 C and the inner peripheral surface of a larger-diameter hole  36  to be fed forward along a groove  56  that rotates, as described in the first embodiment. The grease reaches the outer peripheral surface of the medium-diameter hole  38 . A portion of the grease is then supplied to the sliding surfaces of a spindle  22  and a hammer  23  through a rear connection hole  52  under a centrifugal force. Another portion of the grease is fed frontward in the smaller-diameter hole  37  along the groove  56  in the smaller-diameter portion  72 . A portion of the other portion of the grease is then supplied halfway to the sliding surfaces of the spindle  22  and the hammer  23  through the front connection hole  51  under a centrifugal force. The remaining portion of the other portion of the grease is fed to a fitting recess  49  from the smaller-diameter hole  37 . 
     In the impact driver  1  according to the fifth embodiment as well, the spindle  22  has a through-hole  35 , a front connection hole  51 , and the rear connection hole  52  that are open in the sliding surface of the spindle  22  on which the hammer  23  slides to allow grease to be supplied to the sliding surface. The spindle  22  also includes the pump member  55 C that accelerates the flow of the grease onto the sliding surface in the through-hole  35  in response to rotation of a brushless motor  11 . 
     The pump member  55 C allows supply of a sufficient amount of grease to the sliding surfaces of the spindle  22  and the hammer  23 . In particular, the pump member  55 C extends beyond the front connection hole  51  to the front end of the spindle  22 . This structure allows effective supply of grease to the fitting portion between the spindle  22  and an anvil  25 , thus allowing the fitting portion to remain lubricated. 
     In the fifth embodiment, the groove on the pump member may not be continuous to the smaller-diameter portion, and may be separate in the medium-diameter portion and in the smaller-diameter portion. The medium-diameter portion and the smaller-diameter portion may have grooves with different structures, or may have features other than grooves. 
     The pump member may include multiple components. 
     Sixth Embodiment 
     In a striker  12  in a sixth embodiment shown in  FIG.  9   , a spindle  22  does not include a pump member. In the present embodiment, the spindle  22  has a larger-diameter hole  36  with a slope portion  73 . The larger-diameter hole  36  thus has an internal diameter gradually increasing frontward. 
     In response to rotation (frontward rotation) of a rotational shaft  15  and a pinion  20  in the striker  12  in the present embodiment, grease in the larger-diameter hole  36  is fed forward along the inner surface of the slope portion  73  under a centrifugal force. The grease accumulates on the front end of the larger-diameter hole  36  and then overflows into a medium-diameter hole  38 . A portion of the grease is then supplied to the sliding surfaces of the spindle  22  and a hammer  23  through a rear connection hole  52  under a centrifugal force. The other effects are the same as in the first embodiment. 
     In the impact driver  1  according to the sixth embodiment as well, the spindle  22  has a through-hole  35 , a front connection hole  51 , and the rear connection hole  52  that are open in the sliding surface of the spindle  22  on which the hammer  23  slides to allow grease to be supplied to the sliding surface. The spindle  22  also includes the slope portion  73  (an example of an accelerator) that accelerates the flow of the grease onto the sliding surface in the through-hole  35  in response to rotation of the brushless motor  11 . 
     The slope portion  73  allows supply of a sufficient amount of grease to the sliding surfaces of the spindle  22  and the hammer  23 . In particular, the accelerator is the slope portion  73  defined by the internal diameter of the larger-diameter hole  36  in the spindle gradually increasing frontward. This allows grease to be fed under a centrifugal force. The accelerator has a simple structure. This structure eliminates the pump member and may reduce the cost as compared with the structures according to other embodiments. 
     In the sixth embodiment, the slope portion may extend frontward and connect directly to the rear connection hole, with the medium-diameter hole being eliminated. 
     The slope portion may have a spiral groove on the inner peripheral surface. 
     Other modifications will now be described. 
     Each of the above embodiments may not be implemented alone but may be combined with one another. 
     For example, the structure according to the second embodiment shown in  FIG.  5    may be combined with the structure according to the sixth embodiment shown in  FIG.  9    to form a slope defined by the internal diameter of the larger-diameter hole gradually increasing frontward. The gap between the larger-diameter hole and the pump member defines the slope. This produces an additional effect of allowing grease to be fed under a centrifugal force, in addition to the grease being fed along the groove. The same applies to the structure according to the third embodiment shown in  FIG.  6    and to the structure according to the fifth embodiment shown in  FIG.  8   . More specifically, the structure according to embodiment shown in  FIG.  9    can be combined with the structure according to any embodiment. 
     The structure according to the fifth embodiment shown in  FIG.  8    may have the bypass hole described in the second embodiment in  FIG.  5   . In this case, the bypass hole may extend to the front end of the smaller-diameter portion, or may extend halfway to the medium-diameter portion or to the smaller-diameter portion and be open in the outer peripheral surface of the pump member through the through-hole orthogonal to the axial center. 
     The structures according to the first embodiment in  FIG.  2   , the second embodiment in  FIG.  5   , and the fifth embodiment in  FIG.  8    may each include the groove on the inner peripheral surface of the larger-diameter hole in the fourth embodiment in  FIG.  7   . This produces an additional effect of allowing grease to be fed under a centrifugal force, in addition to the grease being fed along the groove on the outer peripheral surface of the pump member. 
     When the grease supply path includes the accelerator as in the sixth embodiment, the shape of the accelerator is not limited to the slope portion described in the above embodiment. For example, the larger-diameter hole may not be tapered, and may include a spiral groove alone on its inner peripheral surface. In this case, the larger-diameter hole may function as the accelerator. The groove is not limited to the spiral groove. The groove may be, for example, a rectangular groove extending in the axial direction of the spindle to feed grease. 
     The reducer may include any other number of planetary gears. The reducer may include, in the axial direction, internal gears and planetary gears in multiple stages. The reducer is not limited to the structure using the planetary gears. 
     The fitting structure between the spindle and the anvil may be reversed from the fitting structure described in the above embodiments. More specifically, the fitting recess may be located on the front end of the spindle, and the fitting protrusion may be located on the rear end of the anvil. 
     The striker unit is not limited to the striker in each of the above embodiments. For example, the striker unit may include the hammer that does not move in the front-rear direction. For example, the striker unit may include the anvil located behind the hammer. For example, the striker unit may have any other structure including no hammer or may have the structure that is changed as appropriate. In any such example, any other structure including the motor, the striker unit drivable by the motor, the anvil that is struck in the rotation direction by the striker unit, and the accelerator that accelerates the flow of grease supplied to the striker unit can supply a sufficient amount of grease to the striker unit. 
     The motor is not limited to the brushless motor. The power source is not limited to a battery pack, but may be utility power. 
     The present disclosure is also applicable to impact tools other than an impact drive, such as an angle impact driver. 
     
       
         
           
               
               
             
               
                 Reference Signs List 
               
             
            
               
                 
                   1 
                 
                 impact driver 
               
               
                 
                   2 
                 
                 body 
               
               
                 
                   3 
                 
                 grip 
               
               
                 
                   4 
                 
                 body housing 
               
               
                 
                   6 
                 
                 hammer case 
               
               
                 
                   11 
                 
                 brushless motor 
               
               
                 
                   12 
                 
                 striker 
               
               
                 
                   15 
                 
                 rotational shaft 
               
               
                 
                   18 
                 
                 bearing box 
               
               
                 
                   20 
                 
                 pinion 
               
               
                 
                   21 
                 
                 reducer 
               
               
                 
                   22 
                 
                 spindle 
               
               
                 
                   23 
                 
                 hammer 
               
               
                 
                   24 
                 
                 coil spring 
               
               
                 
                   25 
                 
                 anvil 
               
               
                 
                   29 
                 
                 carrier 
               
               
                 
                   35 
                 
                 through-hole 
               
               
                 
                   36 
                 
                 larger-diameter hole 
               
               
                 
                   37 
                 
                 smaller-diameter hole 
               
               
                 
                   38 
                 
                 medium-diameter hole 
               
               
                 
                   51 
                 
                 front connection hole 
               
               
                 
                   52 
                 
                 rear connection hole 
               
               
                   55 ,  55 A,  55 C 
                 pump member 
               
               
                   55 B 
                 pump 
               
               
                   56 ,  56   a   
                 groove 
               
               
                 
                   57 
                 
                 blind hole 
               
               
                 
                   58 
                 
                 engagement portion 
               
               
                 
                   60 
                 
                 switch 
               
               
                 
                   66 
                 
                 controller 
               
               
                 
                   70 
                 
                 bypass hole 
               
               
                 
                   71 
                 
                 medium-diameter portion 
               
               
                 
                   72 
                 
                 smaller-diameter portion 
               
               
                 
                   73 
                 
                 slope portion