Abstract:
An impact tool includes: a spindle which makes a rotation motion; a hammer which makes a reciprocating motion in a longitudinal direction; a spring whose front end is supported on the hammer side and rear end is supported on the spindle side; and a stopper fixed to the spindle so that it abuts on the hammer when the hammer is moved rearward, and the rear end of the spring and the stopper are mutually overlapped with each other in the longitudinal direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to impact tools such as an impact driver and an impact wrench. 
       BACKGROUND ART 
       [0002]    Impact tools using an electric motor or a pneumatic motor as a driving source have been known. Impact tools apply an impact force and a rotational force to an object such as a screw, bolt, nut or the like. Patent Literature 1 discloses a structure of an impact driver that is one of the impact tools.  FIG. 1  is a cross-sectional view showing a structure of a portable electric impact driver.  FIG. 1  shows a cross section of an impact driver  200  taken along the rotation axis of an anvil  22 . This impact driver  200  has a handle  10  that is held by a worker during use. On an upper side of the handle  10 , a housing  20  in which a motor  21  serving as a driving source and the like are installed is provided. On a lower side of the handle  10 , a battery attachment unit  30  to which a battery  300  serving as a power source is attached is provided. The battery  300  includes a plurality of lithium ion cells. At a right end of the housing  20 , the anvil  22  to which a socket and the like (not shown) are attached is provided, and this anvil  22  is rotatably supported by a metal bush  221 . When a switch  11  is turned on, the motor  21  is rotated, so that an impact force in a forward direction (right direction in the figure) is applied to the anvil  22  and a rotational force (rotation torque) around a rotation axis is also applied to the anvil  22 . Thus, the work of tightening and loosening a bolt and a nut can be done with a socket attached to the anvil  22 . 
         [0003]    Inside the housing  20 , a mechanism for converting the rotational driving force output from the motor  21  into the above-mentioned impact force and rotational force is provided. A rotation shaft  211  of the motor  21  extends in a longitudinal direction (lateral direction in the figure). The rotation shaft  211  is supported by a bearing  212  inside the housing  20  and is connected to a planetary gear deceleration mechanism  23 . In the planetary gear mechanism  23 , the rotation motion of an inner gear  231  attached to the rotation shaft  211  is transmitted to an outer gear  233  through a plurality of planetary gears  232  provided on the outside of the inner gear  231 . In this case, since the outer gear  233  is fixed, a planetary gear shaft  234  that is the rotation shaft of each of the planetary gears  232  revolves in conjunction with the rotation of the inner gear  231 . More specifically, the revolution of the planetary gear shaft  234  is taken out as an output. 
         [0004]    The plurality of planetary gear shafts  234  are fixed to a spindle  74 , and when the motor  21  (rotation shaft  211 ) rotates, the spindle  74  rotates at a predetermined deceleration ratio. The spindle  74  includes a spindle shaft portion  741  having a substantially cylindrical shape which protrudes forward and a carrier portion  742  having a flange shape which is provided on a rear side of the spindle shaft portion  741  and expands outward of the spindle shaft portion  741 . 
         [0005]    A hammer  25  is attached to the spindle shaft portion  741  from the front side (right side in the figure), and an outer peripheral surface of the spindle shaft portion  741  and an inner peripheral surface of the hammer  25  are in contact with each other. In this case, on the outer peripheral surface of the spindle shaft portion  741  having the substantially cylindrical shape, a spindle cam groove  743  having a V shape is formed. Moreover, on the inner peripheral surface of the hammer  25  that is in contact with the outer peripheral surface of the spindle shaft portion  741 , a hammer cam groove  251  having a V shape corresponding to the spindle cam groove  743  is formed. Between the spindle shaft portion  741  and the hammer  25 , a V shaped hole is formed by combining the spindle cam groove  743  and the hammer cam groove  251  with each other. The spindle shaft portion  741  and the hammer  25  are engaged with each other via a ball  26  put into the hole. In conjunction with the movement of the ball  26  in the hole, the hammer  25  makes reciprocating motions in the longitudinal direction (lateral direction in the figure) as well as rotation motions. The hammer  25  and the spindle  74  can rotate at different rotation speeds from each other. When the hammer  25  rotates at a rotation speed different from that of the spindle  74 , the hammer  25  moves in the longitudinal direction. By the movement of the hammer  25  in the longitudinal direction, the relative positional relationships between the hammer  25  and the spindle  74  and between the hammer  25  and the anvil  22  are changed. 
         [0006]    Moreover, the planetary gear shaft  234  serving as the rotation shaft of the planetary gear  232  in the planetary gear deceleration mechanism  23  is inserted and fixed in the hole formed in the carrier portion  742  of the spindle shaft portion  741 . A spring  27  is provided between the hammer  25  and the carrier portion  742 , and a front end of the spring  27  is supported by the hammer  25  side and a rear end thereof is supported by the spindle  74  (carrier portion  742 ) side. Moreover, on the front side of the hammer  25  (right side in the figure, that is, the anvil  22  side), a hammer claw  252  is provided. When the hammer  25  that moves in the longitudinal direction is located on the front side, an anvil blade  222  formed on the rear side of the anvil  22  and the hammer claw  252  are meshed with each other, so that the rotation of the hammer  25  is transmitted to the anvil  22 . On the other hand, when the hammer  25  is located on the rear side, the anvil blade  222  and the hammer claw  252  are not meshed with each other, so that the hammer  25  rotates idly. 
         [0007]    When the motor  21  rotates in the state where the spring  27  is extended (in the state where the hammer  25  is located forward), the spindle  74  and the hammer  25  are integrally rotated. Moreover, in this state, the hammer claw  252  and the anvil blade  222  are meshed with each other. Therefore, the spindle  74 , the hammer  25  and the anvil  22  are rotated integrally. At this time, when the socket attached to the anvil  22  abuts on a bolt or a nut to start its tightening, a reaction torque is exerted on the anvil  22 . Consequently, since the spindle  74  continues to rotate while the anvil  22  is decelerated, the difference in rotation speed is caused between the hammer  25  engaged with the anvil  22  and the spindle  74 . Due to the difference in rotation speed, the ball  26  moves inside the V shaped hole and the hammer  25  retreats toward the carrier portion  742  (toward the left side in the figure). At this time, the spring  27  is compressed. 
         [0008]    When the hammer  25  retreats, the meshing between the hammer claw  252  and the anvil blade  222  is released, so that the torque is no longer transmitted to the anvil  22 . However, the spindle  74  continues to rotate even thereafter. After the hammer  25  reaches the maximum retreat position and the compression amount of the spring  27  is maximized, the hammer  25  advances forward in conjunction with the movement of the ball  26  inside the V shaped hole. At this time, a restoring force (reaction force) of the spring  27  is applied to the hammer  25 . Consequently, the hammer claw  252  and the anvil blade  222  are abruptly meshed with each other again, so that the anvil  22  is driven again. At this time, by the collision of the hammer  25  (hammer claw  252 ), a large impact force is applied to the anvil  22 . Then, forward large impact force and large torque are applied to a bolt or a nut on which the socket attached to the anvil  22  abuts. 
         [0009]    The above-mentioned operation of the anvil  22  is realized by the rotation motion and reciprocating motion of the hammer  25  on an extension line of the rotation shaft  211 . Therefore, in order to apply an appropriate impact force to the anvil  22 , it is necessary to ensure a certain degree of the stroke amount of the reciprocating motion of the hammer  25 . Moreover, it is also necessary to sufficiently enhance the precision of the motion of the hammer  25  including the rotation motion. Furthermore, at the time when the hammer  25  reaches the maximum retreat position, the ball  26  collides with a cam rear end portion  744  corresponding to the rearmost portion of the V shaped hole or the hammer  25  collides with the carrier portion  742 . Therefore, it is necessary to alleviate the impact at this time. For this reason, a contrivance to satisfy the above-mentioned demands has been made for a portion where the hammer  25  and the spindle  74  come in contact with each other.  FIG. 2  is an enlarged view showing a structure in the vicinity of the hammer  25  and the spindle  74 . Although  FIG. 2  mainly shows the structure below the rotation shaft, the structure above the rotation shaft is symmetric to the structure below the rotation shaft. 
         [0010]    As shown in  FIG. 2 , on the front side (right side in the figure) of the carrier portion  742 , a stopper  51  and a washer  81  are attached to the periphery of the spindle shaft portion  741 . The stopper  51  is formed of an elastic material into a disk-like shape, and the spindle shaft portion  741  penetrates in the center of the stopper  51 . The stopper  51  alleviates an impact of the collision between the hammer  25  that has reached the maximum retreat position and the carrier portion  742 , by which the impact of the collision between the cam rear end portion  744  and the ball  26  is alleviated. The washer  81  has a stepped shape. Concretely, the washer  81  includes a washer front end portion  811 , a washer rear end portion  812  that is formed on the outer side than the washer front end portion  811 , and a washer raised portion  813  that connects these portions with each other. As shown in the figure, the stopper  51  is covered with the washer front end portion  811  and the washer raised portion  813  from the front side, and fixed on the outside of the spindle shaft portion  741 . Moreover, the washer raised portion  813  is surrounded by the rear end side of the spring  27 , and the rearmost end of the spring  27  is supported by the front surface of the washer rear end portion  812 . More specifically, the washer  81  functions also as a spring supporting member. Furthermore, the planetary gear shaft  234  penetrates through the hole formed in the carrier portion  742 , and is supported and fixed by the back surface of the washer rear end portion  812 . 
         [0011]    As described above, the stopper  51 , the spring  27  and the planetary gear shaft  234  are fixed by using the washer  81 . Therefore, the position of the washer  81  in the radial direction of the spindle  74  is important. In other words, the distance of the washer  81  from the center axis of the spindle  74  is important. For this reason, a step portion that protrudes toward the front side is formed on the front surface of the carrier portion  742 , and the stopper  51  is attached to this step portion. The step portion to which the stopper  51  is attached is covered with the washer  81  from the front side. In  FIG. 2 , a cavity is formed between the stopper  51  and the planetary gear shaft  231 . However, at a position not shown in  FIG. 2  (position where no planetary gear shaft  231  is present), the portion corresponding to this cavity is formed as a part of the carrier portion  742 . More specifically, in order to precisely fix the washer  81  to the spindle  74 , a step difference corresponding to the washer raised portion  813  is formed in the carrier portion  742 , and the height of the step portion in the longitudinal direction (lateral direction in the figure) is denoted by La. Thus, the inner surface of the washer raised portion  813  is in contact with the outer peripheral surface of the step portion, so that both of the stopper  51  and the washer  81  are fixed to the spindle  74 . 
         [0012]    When the step difference La is small, the contact area between the inner surface of the washer raised portion  813  and the outer peripheral surface of the step portion becomes small, with the result that the fixing precision of the washer  81  is deteriorated. Therefore, the step difference La is preferably set to, for example, 1 mm or more. As can be seen from  FIG. 2 , the length of the washer raised portion  813  in the longitudinal direction needs to be a length corresponding to the step difference La and the thickness of the stopper  51 . In order to sufficiently absorb the impact, the stopper  51  needs to have a thickness of, for example, about 1 mm, and in this case, the length of the washer raised portion  813  in the longitudinal direction is set to, for example, 2 mm or more. 
         [0013]    By fixing the washer  81  to the spindle  24  with high precision, it becomes possible to fix the stopper  51 , the rear end portion of the spring  27 , the planetary gear shaft  234  and the like with high precision. Consequently, the hammer  25  can be operated with high precision. 
       CITATION LIST 
     Patent Literature 
       [0014]    [PTL 1] 
         [0015]    Japanese Patent Application Laid-Open Publication No. 2013-208678 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0016]    In the structure shown in  FIG. 2 , the maximum retreat position of the hammer  25  is determined by the position of the stopper  51 . On the other hand, the position of the rear end portion of the spring  27  is located on further rear side than the stopper  51 . Therefore, the shape of the spindle  74  (carrier portion  742 ) needs to be formed into a shape corresponding to the position of the rear end portion of the spring  27 . More specifically, in the above-mentioned structure, when the step difference La is increased so as to fix the washer  81  to the spindle  74  with high precision, the total length of the spindle  74  needs to be increased. 
         [0017]    However, the increase of the total length of the spindle  74  hinders the size reduction and the weight reduction of the entire device. Alternatively, when a predetermined length of La is ensured, with the total length of the spindle  74  being determined, there is fear that the amount of stroke of the hammer  25  is reduced and a desired impact force cannot be obtained. 
         [0018]    That is, it has been difficult to achieve the size reduction of an impact tool, while ensuring the precise motion of a hammer. 
         [0019]    The present invention has been made in view of these problems, and an object of the present invention is to solve the above-mentioned problems. 
       Solution to Problem 
       [0020]    In an aspect of the present invention, an impact tool includes: a spindle which makes a rotation motion; a hammer which makes a reciprocating motion in a longitudinal direction; a spring whose front end is supported on the hammer side and rear end is supported on the spindle side; and a stopper fixed to the spindle so that it abuts on the hammer when the hammer is moved rearward, and the rear end of the spring and the stopper are mutually overlapped with each other in the longitudinal direction. 
       Advantageous Effects of Invention 
       [0021]    According to the present invention, it is possible to achieve the size reduction of an impact tool, while ensuring the precise motion of a hammer. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a cross-sectional view showing a conventional impact driver. 
           [0023]      FIG. 2  is a cross-sectional view showing a peripheral structure of a hammer and a spindle in the conventional impact driver. 
           [0024]      FIG. 3  is a cross-sectional view showing an impact driver to which the present invention is applied. 
           [0025]      FIG. 4  is a cross-sectional view showing a peripheral structure of a hammer and a spindle in the impact driver to which the present invention is applied. 
           [0026]      FIG. 5A  is a cross-sectional view showing a relationship between a spindle and a washer in the impact driver to which the present invention is applied. 
           [0027]      FIG. 5B  is a front view showing a relationship between the spindle and the washer in the impact driver to which the present invention is applied. 
           [0028]      FIG. 6A  is a cross-sectional view showing a modified example of the impact driver to which the present invention is applied. 
           [0029]      FIG. 6B  is a cross-sectional view showing a peripheral structure of a hammer and a spindle in the impact driver shown in  FIG. 6A . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    One example of an impact driver (impact tool) to which the present invention is applied will be described.  FIG. 3  is a cross-sectional view of the impact driver  1  and corresponds to  FIG. 1 . Like the impact driver  200  mentioned above, the impact driver  1  includes the handle  10 , the housing  20  and the battery attachment unit  30 , and the battery  300  is attached to the battery attachment unit  30 . The motor  21 , the anvil  22 , the planetary gear mechanism  23 , the hammer  25  and the like housed in the housing  20  are also the same as those provided in the impact driver  200 . The structure in which the anvil  22  is driven via the spindle  24  and the hammer  25  is also the same as the structure mentioned above. Concretely, the spindle  24  includes a spindle shaft portion  241  and a carrier portion  242 . A spindle cam groove  243  is formed on the spindle shaft portion  241 , and the spindle cam groove  243  and a hammer cam groove  251  are combined with each other. The motions of the spindle  24 , the hammer  25  and the anvil  22  in the impact driver  1  are the same as the motions of those in the impact driver  200  mentioned above. The spring  27  and the stopper  51  are used for the same purpose as that in the impact driver  200  mentioned above. 
         [0031]    However, in this impact driver  1 , the rear end portion of the spring  27  or the front surface of the spring supporting member which supports the rear end portion of the spring  27  is not located on further rear side than the stopper  51 . In the impact driver  1 , the rear end portion of the spring  27  or the front surface of the spring supporting member which supports the rear end portion of the spring  27  is located at a position that is overlapped with the stopper  51  in the longitudinal direction. For this reason, the total length of the spindle  24  can be shortened. 
         [0032]      FIG. 4  is an enlarged view showing a peripheral structure of the hammer  25  and the spindle  24  in the impact driver  1  and corresponds to  FIG. 2 . The stopper  51  and the washer (spring supporting portion)  52  shown in  FIG. 4  are used for the same purpose as that in the impact driver  200  mentioned above. The stopper  51  is fixed to the spindle  24  by the washer  52 . Moreover, the planetary gear shaft  234  is fixed by the washer  52  from the front side. Therefore, the fact that the precision of the fixing of the washer  52  to the spindle  24  is important is also the same as the case of the impact driver  200  mentioned above. 
         [0033]    The washer  52  has a stepped shape. Concretely, the washer  52  includes a washer front end portion  521 , a washer rear end portion  522  that is formed on the outer side than the washer front end portion  521 , and a washer raised portion  523  that connects these portions with each other. The configuration and function of the washer  52  are the same as those of the washer  81 . However, the fixing method of the washer  52  to the carrier portion  24  is different from the fixing method mentioned above. Therefore, the length of the washer raised portion  523  in the longitudinal direction is greatly different from that of the washer raised portion  813  mentioned above. 
         [0034]    In the impact driver  1 , the positioning (fixing) of the washer  52  to the carrier portion  242  is made by a washer locking portion  245  provided on the outer periphery of the carrier portion  242 . The washer locking portion  245  protrudes toward the front side (right side in the figure) on the outer periphery of the carrier portion  242 , and supports the washer rear end portion  522  from the outside. More specifically, the washer  52  is fitted to the spindle  24  and the inner surface of the washer locking portion  245  formed on the spindle  24  (carrier portion  242 ) is in contact with the outer peripheral surface of the washer rear end portion  522  of the washer  52 . For this reason, a step difference for fixing the washer  52  needs not to be provided on the carrier portion  242 . Moreover, the length of the washer raised portion  523  in the longitudinal direction can be shortened to a minimum length required for fixing the stopper  51 . In other words, the length La shown in  FIG. 2  can be reduced to 0 (zero). On the other hand, although the washer locking portion  245  needs to be formed on the carrier portion  242 , it is easy to avoid the interference between the washer locking portion  245  and the hammer  25  when the hammer  25  has reached the maximum retreat position. Therefore, the washer locking portion  245  does not give any adverse effects to the operations of the spindle  24  and the hammer  25 . 
         [0035]    Accordingly, it is not necessary to lengthen the spindle  24  in the longitudinal direction. Thus, it is possible to achieve the size reduction of the impact driver  1 . Alternatively, it is possible to increase the amount of stroke of the hammer  25  without increasing the total length of the spindle  24 . Therefore, a strong impact force can be applied to the anvil  22 . Moreover, since the washer  52  can be attached to the spindle  24  with high precision, the precision of the motion of the hammer  25  can be improved. 
         [0036]    Note that it is not necessary to form the washer locking portion  245  shown in  FIG. 4  over the entire periphery of the washer  52 . The length and the number of washer locking portions  245  can be desirably determined, as long as the position of the washer  52  can be fixed. For example, the washer locking portions  245  may be formed at 4 positions locally in the circumferential direction of the washer  52 . 
         [0037]    In the example shown in  FIG. 5A  and  FIG. 5B , the plurality of washer locking portions  245  are formed in the region of the carrier portion  242  corresponding to the outer periphery of the washer  52  (washer rear end portion  522 ). Concretely, each of the washer locking portions  245  is formed on the upper and lower sides and right and left sides of the region mentioned above. The washer locking portions  245  are formed at four positions on the carrier portion  242 , but the washer locking portions  245  may be formed at five positions or more or at three positions on the carrier portion  242 . Moreover, the intervals between the plurality of washer locking portions  245  are not necessarily equal to each other. 
         [0038]    In the above-mentioned embodiment, the outer peripheral portion of the washer  52  (washer rear end portion  522 ) is supported by the spindle  24  (carrier portion  242 ). For this reason, although the washer locking portion  245  is formed on the carrier portion  242 , the basic structure of the washer  52  is the same as the conventional washer  81 . 
         [0039]    However, it is also possible to make the spindle support the outer periphery of the washer by changing the shape of the washer in place of forming the washer locking portion on the spindle. Also in this case, the total length of the spindle is shortened. 
         [0040]    A spindle  94  shown in  FIG. 6A  and  FIG. 6B  also includes a spindle shaft portion  941 , a carrier portion  942  and a spindle cam groove  943 . However, the shape of the carrier portion  942  is different from that of the carrier portion  243  mentioned above. Concretely, no washer supporting portion is formed on the carrier portion  942 . In short, in the spindle  94 , no special structure for supporting the washer including the step difference in the conventional spindle  74  is formed. 
         [0041]    On the other hand, the shape of the washer  53  shown in  FIG. 6A  and  FIG. 6B  is different from those of the washers  52  and  81  mentioned above. The washer  53  also has a stepped shape like the washer  52  mentioned above. Concretely, the washer  53  includes a washer front end portion  531 , a washer rear end portion  532  that is formed on the outer side than the washer front end portion  531 , and a washer raised portion  533  that connects these portions with each other. In the washer  53 , however, a spindle supporting portion  534  that protrudes rearward (left side in the figure) is provided on the outside of the washer rear end portion  532 . The spindle supporting portion  534  abuts on the outer peripheral surface of the carrier portion  942 . Therefore, the washer  53  can be fitted to the spindle  94  so that the outer peripheral surface of the carrier portion  942  is in contact with the inner surface of the spindle supporting portion  534  in the washer  53 , thereby fixing the washer  53  to the spindle  94 . 
         [0042]    As can be seen from  FIG. 6B , the spindle supporting portion  534  that protrudes rearward from the washer  53  does not disturb the operations of the spindle  94  and the hammer  25 . Moreover, the washer  53  can be attached to the spindle  94  with high precision and the total length of the spindle  94  is not increased. 
         [0043]    It is not necessary to form the spindle supporting portion  534  over the entire periphery of the washer  53  (washer rear end portion  532 ). It is also possible to separately form a plurality of spindle supporting portions  534  along the circumferential direction of the washer  53 . 
         [0044]    In the embodiments mentioned above, the washers  52  and  53  function as spring supporting portions. Concretely, a part of each of the washers  52  and  53  (front surfaces of washer rear end portions  522  and  532 ) supports the rear end portion of the spring  27 . Moreover, another part of each of the washers  52  and  53  supports the planetary gear shaft  234  and fixes the stopper  51 . However, another member fixed to the spindle may support the planetary gear shaft  234  and fix the stopper  51 . 
         [0045]    In the present specification, the present invention has been described by taking an impact driver as an example. However, the present invention contributes to the size reduction and weight reduction of a device provided with a spindle and a hammer which are operated in the same manner as the spindle and the hammer mentioned above. More specifically, the present invention is effectively applied to overall impact tools provided with a spindle and a hammer. For example, the present invention is effectively applied also to an impact tool having a pneumatic motor (high pressure air) as a driving source.