Abstract:
A clutch is disclosed for a power tool. The clutch includes a disc, a drum, at least one spring and at least one pin. The disc defines at least one arched groove comprising a floor and an inclined wall. The drum defines at least one eccentric hole. The spring is put in the eccentric hole. An end of the pin is put in the eccentric hole and pushed by means of the spring. An opposite end of the pin is exposed from the eccentric hole for pushing the inclined wall before a predetermined value of torque is reached and for sliding on the inclined wall after the predetermined value of torque is reached.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates to a power tool and, more particularly, to a clutch for a power tool.  
         [0003]     2. Related Prior Art  
         [0004]     As disclosed in Taiwanese Patent Publication No. 257124, a clutch  4  is provided for a power tool  1 . The clutch  4  includes a frame  41 , a first hammer  42 , a second hammer  42 ′, an axle  43 , a first pin  44  and a second pin  44 . The frame  41  defines a space  411  for receiving the first hammer  42  and the second hammer  42 ′, apertures  412  for receiving the first pin  44  and the second pin  44  and an opening (not numbered) for receiving the axle  43 . The first hammer  42  is hollow in order to receive the axle  43 . The first hammer  42  includes a concave face  421  on the internal side and a recess  422  and groove  423  on the external side. The concave face  421  can contact and slide on a first anvil  433  formed on the axle  43 . The recess  422  receives a first portion of the first pin  44 . The first hammer  42  is hollow in order to receive the axle  43 . The groove  423  receives a first portion of the second pin  44 . The second hammer  42 ′ is hollow in order to receive the axle  43 . The second hammer  42 ′ includes a concave face  421 ′ on the internal side and a recess  422 ′ and groove  423 ′ on the external side. The concave face  421 ′ can contact and slide on a second anvil  434  formed on the axle  43 . The recess  422 ′ receives a second portion of the first pin  44 . The groove  423 ′ receives a second portion of the second pin  44 . In operation, the power tool  1  drives the frame  41 . The frame  41  drives the hammers  42  and  42 ′ through the pins  44 . Periodically, the hammers  42  and  42 ′ drive the axle  43  through the periodical engagement of the concave face  421  with the first anvil  433  and the periodical engagement of the concave face  421 ′ with the second anvil  434 .  
         [0005]     Several problems have however been encountered in the use of the clutch  4 . Firstly, its cost is high because it includes many parts that are assembled in a time-demanding process. Secondly, its life of service is short because it is weak. Thirdly, before the clutch  4  is finished, it is difficult to precisely determine the maximum torque that it transmits. Fourthly, it fails to provide an adequate torque. In practice, a manual wrench has to be used in addition in order to provide an adequate torque.  
         [0006]     An advantage of the clutch of the present invention is its low cost because it includes only a few parts and it takes only a little time to assemble the parts.  
         [0007]     Another advantage of the clutch of the present invention is its long life of service because it is strong.  
         [0008]     Another advantage of the clutch of the present invention is that precise determination of the maximum torque that it transmits is possible.  
         [0009]     Another advantage of the clutch of the present invention is the provision of an adequate torque.  
         [0010]     The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.  
       SUMMARY OF INVENTION  
       [0011]     According to the present invention, a clutch is disclosed for a power tool. The clutch includes a disc, a drum, at least one spring and at least one pin. The disc defines at least one arched groove comprising a floor and an inclined wall. The drum defines at least one eccentric hole. The spring is put in the eccentric hole. An end of the pin is put in the eccentric hole and pushed by means of the spring. An opposite end of the pin is exposed from the eccentric hole for pushing the inclined wall before a predetermined value of torque is reached and for sliding on the inclined wall after the predetermined value of torque is reached.  
         [0012]     Other advantages and novel features of the invention will become more apparent from the following detailed description in conjunction with the attached drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]     The present invention will be described via detailed illustration of embodiments referring to the drawings.  
         [0014]      FIG. 1  is a perspective view of a power tool equipped with a clutch according to a first embodiment of the present invention.  
         [0015]      FIG. 2  is an exploded view of the clutch shown in  FIG. 1 .  
         [0016]      FIG. 3  is a cross-sectional view taken along a line  3 - 3  in  FIG. 4 .  
         [0017]      FIG. 4  is a cross-sectional view taken along a line  4 - 4  in  FIG. 3 .  
         [0018]      FIG. 5  is similar to  FIG. 3  but shows the clutch in another position.  
         [0019]      FIG. 6  is a cross-sectional view taken along a line  6 - 6  in  FIG. 5 .  
         [0020]      FIG. 7  is similar to  FIG. 5  but shows the clutch in another position.  
         [0021]      FIG. 8  is a cross-sectional view taken along a line  8 - 8  in  FIG. 7 .  
         [0022]      FIG. 9  is similar to  FIG. 7  but shows the clutch in another position.  
         [0023]      FIG. 10  is similar to  FIG. 9  but shows the clutch in another position.  
         [0024]      FIG. 11  is similar to  FIG. 10  but shows the clutch in another position.  
         [0025]      FIG. 12  is a cross-sectional view taken along a line  12 - 12  in  FIG. 11 .  
         [0026]      FIG. 13  is an exploded view of a clutch according to a second embodiment of the present invention.  
         [0027]      FIG. 14  is an exploded view of a clutch according to a third embodiment of the present invention.  
         [0028]      FIG. 15  is an exploded view of a clutch according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0029]     Referring to  FIG. 1 , a power tool  10  is equipped with a clutch according to a first embodiment of the present invention. The power tool  10  includes a front shell  11  for receiving the clutch.  
         [0030]     Referring to  FIGS. 2 through 4 , the clutch includes a first stage  20  to be constantly driven by means of the power tool  10  and a second stage  30  to be periodically driven by means of the first stage  20 .  
         [0031]     The first stage  20  includes a first pin  24 , a second pin  24 ′, a first spring  27 , a second spring  27 ′ and a drum  28 . The drum  28  defines a central hole  21  in a first end, a first eccentric hole  22  in the first end, a second eccentric hole  22 ′ in the first end, a first vent  23  in a second end and in communication with the first eccentric hole  22  and a second vent  23 ′ in the second end and in communication with the second eccentric hole  22 ′.  
         [0032]     The vents  23  and  23 ′ allow the passage of air. The first eccentric hole  22  is located further from the central hole  21  than the second eccentric hole  22 ′ is. The first eccentric hole  22  receives the first spring  27  and the first pin  24 . The second eccentric hole  22 ′ receives the second spring  27 ′ and the second pin  24 ′.  
         [0033]     The first pin  24  includes an end  25  and a chamfered portion  26  near the end  25 . The end  25  and the chamfered portion  26  may be replaced with a dome. The second pin  24 ′ includes an end  25 ′ and a chamfered portion  26 ′ near the end  25 ′. The end  25 ′ and the chamfered portion  26 ′ may be replaced with a dome.  
         [0034]     The second stage  30  includes a disc  39 , a first shaft  31  formed on a first side  33  of the disc  39  and a second shaft  32  formed on a second side (not numbered) of the disc  39 . The first shaft  31  is inserted in the central hole  21 . The second shaft  32  is exposed from the front shell  11 .  
         [0035]     The disc  39  defines, in the first side  33 , a first arched groove  34  and a second arched groove  34 ′.  
         [0036]     The first arched groove  34  is located corresponding to the first eccentric hole  22  in order to receive the end  25  and the chambered portion  26  periodically. The first arched groove  34  includes a floor  35 , a first wall  36  and a second wall (not numbered). The floor  35  is inclined, i.e., the first arched groove  34  includes a deep end and a shallow end. The first wall  36  of the first arched groove  34  is inclined. The floor  35  contacts the end  25  periodically. The first wall  36  of the first arched groove  34  contacts the chamfered portion  26  periodically. The chamfered portion  26  contacts the first wall  36  of the first arched groove  34  once in every round of rotation.  
         [0037]     The second arched groove  34 ′ is located corresponding to the second eccentric hole  22 ′ in order to receive the end  25 ′ and the chambered portion  26 ′. The second arched groove  34 ′ includes a floor  35 ′, a first wall  36 ′ and a second wall (not numbered). The floor  35 ′ is inclined, i.e., the second arched groove  34 ′ includes a deep end and shallow end. The first wall  36 ′ of the second arched groove  34 ′ is inclined. The floor  35 ′ contacts the end  25 ′ periodically. The first wall  36 ′ of the second arched groove  34 ′ contacts the chamfered portion  26 ′ periodically. The chamfered portion  26 ′ contacts the first wall  36 ′ of the second arched groove  34 ′ once in every round of rotation.  
         [0038]     The maximum torque that the first stage  20  transmits to the second stage  30  is determined based on the strength of the springs  27  and  27 ′, the lengths and depths of the arched grooves  34  and  34 ′, and the slope of the walls  36  and  34 .  
         [0039]     The second stage  30  further includes a shock absorber  37 . The shock absorber  37  defines an aperture  38  through which the second shaft  32  is inserted. Thus, the shock absorber  37  can be provided against the second side of the disc  39 . The shock absorber  37  absorbs shocks that occur when the chamfered portions  26  and  26 ′ strike the walls  36  and  36 ′, respectively.  
         [0040]     Referring to  FIGS. 3 and 4 , when the drum  28  is still, the end  25  of the first pin  24  and the end  25 ′ of the second pin  24 ′ both contact the first side  33  of the disc  39 .  
         [0041]     Referring to  FIGS. 5 and 6 , the first stage  20  is rotated clockwise. The first pin  24  is moved into the deep end of the first arched groove  34 , and the second pin  24 ′ is moved into the deep end of the second arched groove  34 ′. The end  25  of the first pin  24  strikes the floor  35 . The end  25 ′ of the second pin  24 ′ strikes the floor  35 ′. At that instant, the disc  30  moves and compresses the shock absorber  37 . The shock absorber  37  absorbs the shocks, thus reducing vibration and noise during the operation of the clutch.  
         [0042]     As the rotation of the drum  28  continues, the end  25  of the first pin  24  slides on the floor  35 , and the end  25 ′ of the second pin  24 ′ slides on the floor  35 ′. Then, the chamfered portion  26  of the first pin  24  contacts the first wall  36  of the first arched groove  34 , and the chamfered portion  26 ′ of the second pin  24 ′ contacts the first wall  36 ′ of the second arched groove  34 ′.  
         [0043]     Referring to  FIGS. 7 through 9 , as the rotation of the drum  28  continues, the chamfered portion  26  of the first pin  24  and pushes the first wall  36  of the first arched groove  34 , and the chamfered portion  26 ′ of the second pin  24 ′ pushes the first wall  36 ′ of the second arched groove  34 ′. Hence, the first stage  20  drives the second stage  30 .  
         [0044]     As the rotation of the drum  28  continues, the torque that the first stage  20  transmits to the second stage  30  accumulates. As the maximum torque is reached, the springs  27  and  27 ′ are compressed  11 . Thus, the chamfered portion  26  of the first pin  24  slides on the first wall  36  of the first arched groove  34 , and the chamfered portion  26 ′ of the second pin  24 ′ slides on the first wall  36 ′ of the second arched groove  34 ′.  
         [0045]     Referring to  FIGS. 10 through 12 , as the rotation of the drum  28  continues, the first pin  24  is moved from the first arched groove  34 , and the second pin  24 ′ is moved from the second arched groove  34 ′. The end  25  of the first pin  24  and the end  25 ′ of the second pin  24 ′ both slide on the first side  33  of the disc  39 .  
         [0046]     The above-mentioned process will be repeated for a plurality of times before the power tool  10  fastens a nut on a bolt for example. To release such a nut from such a bolt, the power tool  10  is switched to reversed mode in order to drive the first stage  20  counterclockwise.  
         [0047]      FIG. 13  shows a clutch according to a second embodiment of the present invention. The second embodiment is similar to the first embodiment except for saving the second eccentric hole  22 ′, the second spring  27 ′, the second pin  24 ′ and the second arched groove  34 ′. The cost of the second embodiment is lower than the first embodiment because the second embodiment includes fewer parts and requires less time to assemble the parts than the first embodiment does.  
         [0048]      FIG. 14  shows a clutch according to a third embodiment of the present invention. The third embodiment is similar to the first embodiment except that the second eccentric hole  22 ′ is identical to the first eccentric hole  22  and that the second arched groove  34 ′ is identical to the first arched groove  34 . Thus, the first stage  20  drives the second stage  30  twice in every round of rotation.  
         [0049]      FIG. 15  shows a clutch according to a fourth embodiment of the present invention. The fourth embodiment is similar to the first embodiment except for including a second stage  40  instead of the second stage  30 . The second stage  40  includes a disc  49  with a first side  43  and a second side (not numbered). The disc  49  is similar to the disc  39  except for including a V-shaped cutout  44  instead of the arched grooves  34  and  34 ′. The V-shaped cutout  44  includes an inclined floor  45  and an inclined wall  46 . The first stage  20  drives the second stage  40  twice in every round of rotation.  
         [0050]     The clutch of the present invention includes several advantageous features. Firstly, its cost is low because it includes only a few parts and it takes only a little time to assemble the parts. Secondly, its life of service is long because it is strong. Thirdly, it is possible to precisely determine the maximum torque that it transmits. Fourthly, it provides an adequate torque.  
         [0051]     The present invention has been described via the foregoing detailed description of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.