Patent Abstract:
An impact tool includes a motor, a hammer casing with an opened rear end and a disk-shaped member coupled to the hammer casing to close the opened rear end and to rotatably support a spindle. A first engagement member is formed on an outer face of the disk-shaped member. A second engagement member is formed on an inner face of the recess and engaging with the first engagement member to restrict a movement of the hammer casing in a second direction parallel to a rotation axis of the spindle. A third engagement member is formed on an outer face of the hammer casing. A fourth engagement member is formed on an inner face of the housing body and engaging with the third engagement member so as to restrict a movement of the hammer casing in the first direction.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an impact tool in which a hammer casing installed with an impact mechanism is mounted on a front section of a housing body housing a motor. 
     For example, Japanese Patent Publication No. 2003-145439A discloses an impact driver in which an internal gear casing and a hammer casing are mounted on a front section of a housing body which houses a motor. In the hammer casing, an impact mechanism is installed. This impact mechanism comprises: a spindle operable to rotate to transmit a power from an output axis of the motor by way of a planetary reduction gear mechanism; a hammer coupled to an outer periphery of the spindle so as to be movable in an axial direction of the spindle and so as to rotate together with the spindle; and an anvil disposed in a front side of the hammer so as to project toward a front side of the hammer casing. The hammer is urged toward the anvil by a coiled spring so that an engaging claw provided on a front face of the hammer is engaged with an arm provided on a rear end of the anvil. 
     With this configuration, when the motor is driven to rotate the spindle, the anvil is accordingly rotated by way of the hammer, so that a screwing operation can be performed by a bit attached on the anvil. If an excessive load is imparted on the anvil at a final stage of the screwing operation, the hammer is retracted against the urging force of the coiled spring and disengaged from the anvil. The disengaged hammer is then rotated together with the spindle and proceeded toward the anvil with the aid of the urging force of the coiled spring to again engage with the anvil. The disengagement and re-engagement are repeated to provide intermittent impacts on the anvil, thereby additional screwing forces are applied to finalize the screwing operation. 
     On the other hand, the internal gear casing is fixed on the housing body by screwing. Male screw portions provided on an outer periphery of a front end of the internal gear casing is screwed into female screw portions provided on an inner periphery of a rear end of the hammer casing, so that the internal gear casing and the hammer casing are coupled to each other. The undesired movement of the hammer casing relative to the internal gear casing in a circumferential direction thereof is prevented by fixing a lack on a lower face of the hammer casing in the housing body with screws in order to cause the lack to mesh with dimples provided on the outer periphery of the hammer casing. 
     In the above impact driver, since the fixation of the internal gear casing with respect to the housing body, and the fixation of the hammer casing with respect to the housing body are separately performed, and since the undesired rotation of the hammer casing relative to the housing body is prevented with different parts. Therefore, the number of parts will be naturally increased, and the assembling work well be troublesome. Further, there is a probability that the parts are fallen out when the impact driver is disassembled for the maintenance purpose. 
     Since the internal gear casing is covered with the hammer casing after the internal gear casing is fixed on the housing body with screws, it is difficult to downsize the hammer casing. Accordingly, the operability and the workability are not so good at a narrow space, for example. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a downsized impact tool in which an assembling structure of a hammer casing is simplified; and inner parts are prevented from being fallen out. 
     In order to achieve the above object, according to the invention, there is provided an impact tool, comprising: 
     a housing body, having a recess; 
     a motor, housed in the housing body at a rear side of the recess; 
     a hammer casing, housing a rotatable spindle and an impact mechanism operable to convert the rotation of the spindle into intermittent impact actions in a first direction which is a circumferential direction of the spindle, and having an opened rear end, the hammer casing mounted in the recess; 
     a disk-shaped member, coupled to the hammer casing so as to close the opened rear end and to rotatably support the spindle, the disk-shaped member having a through hole receiving an output axis of the motor, thereby causing the output axis of the motor to couple with the spindle to transmit a rotation of the motor to rotate the spindle; 
     a first engagement member, formed on an outer face of the disk-shaped member; 
     a second engagement member, formed on an inner face of the recess and engaging with the first engagement member so as to restrict a movement of the hammer casing in a second direction parallel to a rotation axis of the spindle; 
     a third engagement member, formed on an outer face of the hammer casing; and 
     a fourth engagement member, formed on an inner face of the housing body and engaging with the third engagement member so as to restrict a movement of the hammer casing in the first direction. 
     With the above configuration, at the same time as the hammer casing is mounted in the recess, the restrictions for the rotation in the first direction and the movement in the second direction can be effected. Accordingly, not only the number of parts can be decreased but also the assembling workability can be enhanced. Especially, since the disk-shaped member is integrated with the hammer casing housing the impact mechanism as a unit, not only the parts of the impact mechanism can be prevented from falling out even when the impact tool is disassembled for the maintenance purpose, but also the downsizing of the hammer casing can be attained, thereby enhancing the operability and workability at a narrow space. 
     The first engagement member may be a flange and the second engagement member may be a groove receiving the flange. 
     With this configuration, the structure for restricting the movement of the hammer casing in the second direction can be easily provided with a less space. 
     Here, the flange may have a polygonal cross section in a third direction perpendicular to the second direction. 
     With this configuration, the disk-shaped member can be rotated for attaching to or detaching from the hammer casing through the use of the polygonal flange. 
     The third engagement member may be a first rib projected from the outer face of the hammer casing, and the fourth engagement member may be a second rib coming into contact with the first rib in the first direction. 
     With this configuration, the structure for restricting the rotation of the hammer casing in the first direction can be provided by efficiently utilizing a given space (e.g., a space for housing another unit). 
     The outer face of the hammer casing may include a first curved face and a first flat face which serves as the third engagement member. The inner face of the housing body may include a second curved face and a second flat face which comes in contact with the first flat face to serve as the fourth engagement member. 
     With this configuration, the undesired rotation of the hammer casing can be reliably avoided. 
     Here, a projection may be formed on one of the first flat face and the second flat face. A recess receiving the projection may be formed on the other one of the first flat face and the second flat face. 
     With this configuration, the contact state between the first flat face and the second flat face can be secured and stabilized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is a vertical section view of an impact driver according to one embodiment of the invention; 
         FIG. 2  is a perspective view of a hammer casing and a bearing box in the impact driver, showing a disassembled state; 
         FIG. 3  is a rear side view of the bearing box; and 
         FIG. 4  is a lateral section view of the impact driver. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     As shown in  FIG. 1 , an impact driver  1  according to one embodiment of the invention is roughly constituted by right and left half housings  4 ,  5  (see also  FIG. 4 ) and a housing body  2  provided with a handle section  3  extending downward. A motor  6  is housed in a rear section (left side in  FIG. 1 ) of the housing body  2 . A hammer casing  8  in which an impact mechanism  30  is disposed is mounted on a mount section  2   a  of the housing body  2  which is shaped into a bottomed cylinder at a front side of the motor  6 . Reference numerals  9 ,  10  and  11  denotes a switch, a trigger and a battery, respectively. 
     The hammer casing  8  is a bell-shaped member cylindrical member. A cylinder  12  having a relatively small diameter is formed at a front end of the hammer casing  8 . A bearing box  13  shaped into a circular cap is integrally coupled to the hammer casing  8  so as to close a rear opening of the hammer casing  8 . Specifically, a female thread  14  is formed on an inner periphery of the opened rear end of the hammer casing  8  and a male thread  15  is formed on an outer periphery of a front end of the bearing box. The coupling of the bearing box  13  and the hammer casing  8  is performed by screwing the male thread  15  into the female thread  14 , so that the rear section of the hammer casing  8  is closed except a through hole  16  formed at a center portion of the bearing box  13 . 
     The bearing box  13  has a two-stage structure in which a diameter is reduced stepwise toward the rear side thereof. Specifically, the bearing box  13  has a large diameter section  17  holding a ball bearing  19  therein and a small diameter section  18  holding a ball bearing  20  therein. As shown in  FIGS. 2 and 3 , at an outer periphery of a rear end of the large diameter section  17 , a hexagonal flange  21  is coaxially provided. On the other hand, in a central part of the bottom of the mount section  2   a , a recess  22  having a two-stage structure adapted to receive the bearing box  13 . At a portion in the recess  22  to be oppose the flange  21  is formed with a groove  23 , so that the flange  21  engages with the groove  23  when the bearing box  13  is fitted into the recess  22 . With this structure, the hammer casing  8  coupled with the bearing box  13  is prevented from falling off forward. Since the flange  21  shaped into hexagonal, it is easily rotate the large diameter section  17  to detach the bearing box  13  from the hammer casing  8  in order to perform the maintenance work for the impact mechanism  30 . 
     A spindle  24  having a hollowed portion  25  at a rear end thereof is axially housed in the hammer casing  8 . The ball bearing  19  held by the large diameter section  17  supports an outer periphery of the rear end of the spindle  24 . In a front side of the ball bearing  19 , a pair of planetary gears  26  are supported by the spindle  24  in a point symmetrical relationship relative to an axis of the spindle  24 . The planetary gears  26  are exposed to the hollowed space  25  and adapted to mesh with a pinion  51  of an output axis of the motor  6  which is placed in the hollowed space  25  in the assembled condition. 
     The planetary gears  26  mesh with an internal gear  27  held in the hammer casing  8 . Grooves  28  are formed on the inner periphery of the rear end portion of the hammer casing  8  so as to extend in the axial direction of the hammer casing  8 . Ribs  29  are formed on an outer periphery of the internal gear  27  so as to extend in an axial direction of the internal gear  27 . Fitting the ribs  29  into the grooves  28 , the internal gear  27  is held in the hammer casing  8  while being prevented from rotating. 
     The impact mechanism  30  comprises: the spindle  24 ; a hammer  31  fitted on an outer periphery of the spindle  24 ; an anvil  32  coaxially held by the cylinder  12  in the front side of the hammer  31 ; and a coiled spring  33  urging the hammer  31  forward. Guide grooves  34  are formed on an inner periphery of a front end portion of the hammer  31  so as to extend in an axial direction of the hammer  31 . Steel balls  35  are fitted onto the outer periphery of the spindle  24 . Fitting the steel balls  35  into the guide grooves  34 , the hammer  31  is coupled with the spindle  24  so as to be rotatable together and movable in the axial direction. 
     Engagement claws  36  are projected from a front face of the hammer  31 . A pair of arms  37  are formed on a rear end of the anvil  32  so as to extend in a radial direction of the anvil  32 . The hammer  31  is urged by the coiled spring  33  to such a position that the claws  36  can engage with the arms  37  as a result of the movement in a circumferential direction of the anvil  32 . A front end of the spindle  24  is loosely and coaxially inserted into a hole formed in the rear section of the anvil  32 . 
     Reference numeral  38  denotes a bearing provided in the cylinder  12 . Reference numeral  39  denotes a washer interposed between the cylinder  12  and the arms  37  to regulate a front position of the anvil  32 . Reference numeral  40  denotes a chuck sleeve provided for detachably fit a bit into a mount hole formed on a front end of the anvil  32 . 
     In the body housing  2  opposing a lower face of the hammer casing  8 , an extended portion  41  is provided so as to extend forward to cover a part of the lower face. A light unit  42  is provided in a front side of the extended portion  41  and is connected to a drive circuit of the motor  6  so that it is turned on when the motor  6  is driven to illuminate a front side of the anvil  32 . As shown in  FIG. 4 , in the extended portion  41 , a pair of vertical ribs  43  are projected downward and extended in a front-rear direction. Front ends of the vertical ribs  43  are made continuous. Ribs  44  are formed on an inner face of each of the half housings  4 ,  5  forming the extended portion  41  so as to extend laterally. The horizontal ribs  44  are abutted against an outer face of each of the vertical ribs  43 . According to this interference between the vertical ribs  43  and  44  in the circumferential direction, unnecessary rotation of the hammer casing  8  can be prevented. 
     Tapered sections  45  are formed on lateral outer faces of the hammer casing  8  so as to extend parallel to each other. In the mount section  2   a  to be covered with the hammer casing  8 , flat portions  46  are formed so as to oppose the tapered sections  45 . In a central portion of each of the tapered sections  45 , a projection  47  is formed so as to extend in the front-rear direction. On the other hand, in each of the flat portions  46 , a groove  48  into which the projection  47  is fitted is formed. Thus, the undesired rotation of the hammer casing  8  is prevented also by the abutment between the tapered sections  45  and the flat portions  46  and by the engagement between the projections  47  and the grooves  48 . 
     As shown in  FIG. 1 , a cover  49  made of synthetic resin is detachably mounted on the hammer casing  8  to prevent the user from contacting the hammer casing  8  which becomes high temperature at working, thereby maintaining good operability. An annular damper  50  made of rubber is attached on a proximal end of the cylinder  12  of the hammer casing  8  in the front side of the cover  49 . Covering the front end portion of the hammer casing  8  with the damper  50 , damage on a worked object due to the collision of the hammer casing  8  at working can be avoided. 
     When the impact driver  1  as configured the above is assembled, the bearing box  13  holding the ball bearing  19  is coupled with the hammer casing  8  installed with the impact mechanism  30 , the planetary gears  26  and the internal gear  27  in a screwing manner. As a result, an assembled unit containing parts disposed in the front side of the ball bearing  19  is obtained. Here, since the rear end of the hammer casing  8  is closed except the through hole  16  formed in the central portion of the bearing box  13 , internal parts can be prevented from falling out therefrom. 
     Next, the motor  6  is coupled to the rear section of the hammer casing  8  such that the output axis  7  attached with the ball bearing  20  and the pinion  51  is inserted into the through hole  16 . Here, the pinion  51  enters the hollowed portion  25  in the spindle  24  and meshes with the planetary gears  26 , and the ball bearing  20  is held by the small diameter section  18  of the bearing box  13 . Thus, the motor  6  and the above assembled unit are integrated. In this state, the integrated unit is mounted on a prescribed position in one of the half housings  4 ,  5  such that the flange  21  on the bearing box  13  is fitted into the groove  23 . One of the vertical ribs  43  is placed on the horizontal ribs  44  formed in the extended portion  41 , thereby the tapered section  45  and the flat portion  46  are opposed to each other. 
     After the switch  9  and so on are assembled, the other one of the half housings  4 ,  5  is mounted so as to cover the above integrated unit and fixed with screws  52 . Since screws  52   a ,  52   b  are arranged between the motor  6  and the hammer casing  8  and in an outer side of the large diameter section  17  of the bearing box  13 , dead spaces formed by the bearing box  13  can be efficiently utilized and it is possible to avoid upsizing of the housing body  2  in the front-rear direction for obtaining screwing positions. 
     With the above assembling work, the vertical ribs  43  are held between the horizontal ribs  44 , and the projections  47  are fitted into the grooves  48 . Thus, restrictions for rotation in the circumferential direction and movement in the front-rear direction of the hammer casing  8  can be effected at the same time. 
     When the trigger  10  is actuated, the motor  6  is driven and the spindle  24  is rotated. The anvil  32  is accordingly rotated by way of the hammer  31  so that screwing work with the bit attached on the anvil can be performed. When a load imparting on the anvil  32  exceeds a threshold level at the final stage of the screwing work, the hammer  31  is retracted rearward against the urging force of the coiled spring  33  and disengaged from the anvil  32 . But immediately thereafter, the hammer  31  again proceeds forward in accordance with the urging force of the coiled spring  33  while being rotated with the spindle  24 , and then the claws  36  again engage with the arms  37  on the anvil  32 . The above disengagement and engagement are repeated so that intermittent impacts are provided in the circumferential direction of the anvil  32  and additional screwing forces are applied to finalize the screwing operation. 
     As has been described the above, in the impact driver  1  according to this embodiment, the bearing box  13  supporting the spindle  24  and formed with the through hole  16  adapted to receive the output axis  7  of the motor  6  is integrally coupled with the rear end section of the hammer casing  8 . In addition, the flange  21  is formed on the rear face of the bearing box  13  and the groove  21  is formed on the recess  22  in the mount section  2   a . The hammer casing  8  is prevented from moving forward by the engagement between the flange  21  and the groove  23 . Moreover, the members for preventing the hammer casing  8  from moving in the circumferential direction thereof are provided on the housing body  2  and the hammer casing  8 . Thus, at the same time as the hammer casing  8  is mounted on the housing body  2 , the restrictions for the rotation in the circumferential direction and the movement in the forward-rear direction can be effected. Accordingly, not only the number of parts can be decreased but also the assembling workability can be enhanced. Especially, since the bearing box  13  is integrated with the hammer casing  8  housing the impact mechanism  30  as a unit, not only the parts of the impact mechanism  30  can be prevented from falling out even when the impact driver  1  is disassembled for the maintenance purpose, but also the downsizing of the hammer casing  8  can be attained, thereby enhancing the operability and workability at a narrow space. 
     Since the structure for restricting the movement of the hammer casing  8  in the front-rear direction is embodied by the flange  21  formed on the large diameter section  17  of the bearing box  13  and the groove  23  formed on the mount section  2   a  and adapted to receive the flange  21 , such a structure can be easily provided with a less space. Especially, since the flange  21  is shaped into hexagonal, the bearing box  13  can be rotated for attaching to or detaching from the hammer casing  8  through the use of the flange  21 . 
     Since the structure for restricting the rotation of the hammer casing  8  in the circumferential direction is embodied by the vertical ribs  43  projected from the outer face of the hammer casing  8  and disposed in the extended portion  41 , and the horizontal ribs  44  formed on the inner face of the extended portion  41  and adapted to come in contact with the vertical ribs  43 , such a structure can be provided by efficiently utilizing a given space. 
     In addition, the tapered sections  45  formed on the outer face of the hammer casing  8  and the flat portions  46  formed on the inner face of the mount section  2   a  covering the hammer casing  8  and adapted to come in contact with the tapered sections  45  also constitutes the structure for restricting the rotation of the hammer casing  8 . The undesired rotation of the hammer casing  8  can be reliably avoided. Especially, since the projection  47  is formed on each of the tapered sections  45  and the groove  48  adapted to receive the projection  47  is formed on each of the flat portions  46 , the contact state between the tapered sections  45  and the flat portions  46  can be secured and stabilized. 
     A plurality of flanges and grooves for restricting the front-rear movement of the hammer casing  8  may be arranged in the front-rear direction. The flange  21  may be a projection which is partly provided on the outer face of the bearing box  13 . The groove  23  may be formed so as to adapt to receive such a projection. To the contrary to the above embodiment, the flange  21  may be formed on the mount section  2   a  and the groove  23  may be formed on the bearing box  13 . 
     The flange  21  may not be hexagonal only if the rotating work of the bearing box  13  is still facilitated, that is, it may be shaped into other polygon such as rectangle and pentagon. Alternatively, the flange  21  may be circular but holes may be formed in the rear face of the flange  21  so that a jig can be inserted into the holes to rotate the bearing box  13 . 
     As to the structure for restricting the rotation of the hammer casing  8 , the number and the extending direction of the vertical ribs  43  and the horizontal ribs  44  may be arbitrary only if the interference between such members in the circumferential direction can be effected. Similarly, the number and the positions of the tapered sections  45  and the flat portions  46  may be arbitrary. To the contrary to the above embodiment, the projections  47  may be formed on the flat portions  46  and the grooves  48  may be formed on the tapered sections  45 . The number and the positions of the projections  47  and the grooves  48  may be arbitrary and may be omitted. 
     One of the combination of the vertical ribs  43  and the horizontal ribs  44  and the combination of the tapered sections  45  and the flat portions  46  for restricting the rotation of the hammer casing  8  may be omitted only if the undesired rotation of the hammer casing  8  can be reliably prevented. 
     The shape of the hammer casing  8 , the structure of the planetary gears  26  and the impact mechanism  30  installed therein are not limited to the configuration as described the above. The bearing of the spindle  24  may be a needle bearing. A plurality of planetary reduction gear mechanisms may be arranged in the front-rear direction of the housing body  2 . The internal gear  27  may be held by the bearing box  13 . The impact tool may be driven by alternating current. 
     Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.

Technology Classification (CPC): 1