Abstract:
A screwdriver having a ratchet mechanism includes a handle and a switch assembly. A ratchet base is provided in the handle. The ratchet base is provided with a locating device. The switch assembly is pivotally connected to the handle. A locating plate extends from the edge of the switch assembly and corresponds in position to the locating device of the ratchet base. The locating plate has recesses for the locating device to be secured thereat. The screwdriver can be operated accurately to change the turning direction of a tool sleeve and to replace and secure a tool head in position.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a screwdriver having a ratchet mechanism, in particular to a ratchet mechanism provided in a rear portion of a handle to change the turning direction of a tool sleeve and to replace a tool head accurately. 
   2. Description of the Prior Art 
   There are various ratchet hand tools on the market. Each has its special function, such as U.S. Pat. No. 5,875,693 which uses a gear to secure and to change the turning direction. The gear may get damaged easily, causing meshing inappropriately. 
   A ratchet mechanism for a screwdriver, such as U.S. Pat. Nos. 6,070,503, 6,253,654 and 6,854,363, is provided at a front portion or at a front end of a handle, which may accidentally touch an adjusting switch when operating the screwdriver. 
   In addition, a conventional screwdriver has the parts assembled in an axial direction, and is provided with a knob to change the direction. This design has a locating device to do the adjustment. The locating direction of the locating device is parallel to the assembled direction of the screwdriver. It is difficult to adjust the locating device. 
   SUMMARY OF THE INVENTION 
   It is the primary objective of the present invention to provide a screwdriver having a ratchet mechanism, which can be operated accurately to change the turning direction of a tool sleeve. 
   It is another objective of the present invention to provide a screwdriver having a ratchet mechanism, which is not easy to be worn out and can last longer. 
   It is a further objective of the present invention to provide a screwdriver having a ratchet mechanism, which provides an accurate position. 
   According to the present invention, there is provided a screwdriver having a ratchet mechanism comprising a tool sleeve provided with a ratchet head, said ratchet head having ratchet teeth; a handle comprising a hollow chamber to accommodate said tool sleeve and a ratchet base, said ratchet base comprising a compartment, first and second recesses and a locating device, said first and second recesses interconnecting with said compartment, said compartment accommodating said ratchet head and said ratchet teeth, said locating device being disposed at an outer side of said ratchet base; a first detent accommodated in said first recess of said ratchet base of said handle, said first detent comprising a stud to be connected to said ratchet base; a first elastic element disposed in said first recess and engaging with said first detent and said ratchet base, urging said first detent to engage with said ratchet teeth of said ratchet head; a second detent accommodated in said second recess of said ratchet base of said handle, said second detent comprising a stud to be connected to said ratchet base; a second elastic element disposed in said second recess and engaging with said second detent and said ratchet base, urging said second detent to engage with said ratchet teeth of said ratchet head; and a switch assembly comprising a through hole, a fastener, a first stud, a second stud and a locating plate, said ratchet head being inserted through said through hole and pivotally connected to said handle by means of said fastener, said first stud engaging with said first detent, said second stud engaging with said second detent, said locating plate extending from the edge of said switch assembly and corresponding in position to said locating device of said ratchet base, said locating plate having recesses for securing said locating device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a preferred embodiment of the present invention; 
       FIG. 2  is a perspective view of the preferred embodiment of the present invention; 
       FIG. 3  is a cross-sectional view of the preferred embodiment of the present invention in a two-way engagement status. 
       FIG. 4  is a cross-sectional view of the preferred embodiment the present invention in a clockwise engagement status; and 
       FIG. 5  is a cross-sectional view of the preferred embodiment the present invention in a counterclockwise engagement status. 
       FIG. 6  is a cross-sectional view of the preferred embodiment of the present invention showing that an opening of a disc is turned to align with a cavity; and 
       FIG. 7  is a cross-sectional view of the preferred embodiment of the present invention showing that the disc is turned to close the cavity. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As shown in  FIGS. 1 and 2 , a preferred embodiment of the present invention comprises a tool sleeve  1 , a handle  2 , a first detent  3 , a first elastic element  4 , a second detent  5 , a second elastic element  6 , and a switch assembly  7 . 
   The tool sleeve  1  comprises a groove  11  at a front portion and a ratchet head  12  at a rear end thereof. The tool sleeve  1  has a front end to receive a tool head  14  therein. The ratchet head  12  is formed with ratchet teeth  13  on its outer surface. The tool sleeve  1  may be coupled with other tool heads  14 A stored in the handle  2 , and a C-shaped fastener  15  is provided on the tool sleeve  1 . 
   The handle  2  comprises a hollow chamber  21  therein. The tool sleeve  1  is accommodated in a front portion of the chamber  21 . A ratchet base  22  is provided in a rear portion of the chamber  21 . The ratchet base  22  comprises a compartment  221 , a first recess  222 , a second recess  222 ′, an aperture  223 , a first hole  224  and a second hole  224 ′. The compartment  221  interconnects with the first recess  222  and the second recess  222 ′. The aperture  223 , the first hole  224  and the second hole  224 ′ are disposed at the bottom of the ratchet base  22 . The ratchet head  12  with the ratchet teeth  13  is accommodated in the compartment  221 . The tool sleeve  1  is inserted through the aperture  223 . The handle  2  further comprises a disc  23  which is pivotally connected to the tool sleeve  1  and secured by the fastener  15  to confine its movement. The disc  23  comprises a through hole  231  and an opening  232 . The through hole  231  is for the tool sleeve  1  to extend through. The handle  2  further comprises a plurality of cavities  24  to accommodate tool heads  14 A. The opening  232  is to replace the tool heads  14 A. A locating device  225  is provided at an outer side of the ratchet base  22 . The locating device  225  comprises a bearing  2251  and an elastic element  2252  which urges the bearing  2251  inwardly. The handle  2  further comprises protuberances  25 . The disc  23  is formed with arc troughs  233  and holes  234  for insertion of the protuberances  25 . There are at least two cavities  24  equally spaced from each other in the handle  2 . The center of each arc trough  233  and the center of each hole  234  are also equally spaced from each other so as to correspond in position to the cavities  24  of the handle  2 . 
   The first detent  3  is a plate and accommodated in the first recess  222  of the ratchet base  22  of the handle  2 . The first detent  3  comprises a stud  31  to be inserted into the hole  224  of the ratchet base  22 . 
   The first elastic element  4  is located in the recess  222  between the first detent  3  and the ratchet base  22 , urging the first detent  3  to engage with the ratchet teeth  13  of the ratchet head  12 . 
   The second detent  5  is a plate and accommodated in the recess  222 ′ of the ratchet base  22  of the handle  2 . The detent  5  comprises a stud  51  to be inserted into the hole  224 ′ of the ratchet base  22 . 
   The second elastic element  6  is located in the recess  222 ′ between the second detent  5  and the ratchet base  22 , urging the second detent  5  to engage with the ratchet teeth  13  of the ratchet head  12 . 
   The switch assembly  7  is secured to the tool sleeve  1  and pivotally connected to the handle  2 . The switch assembly  7  comprises a first stud  71 , a second stud  72 , a through hole  73 , a fastener  74  and a locating plate  75 . The locating plate  75  extends from the edge of the switch assembly  7  and corresponds in position to the locating device  225  of the ratchet base  22 . The locating plate  75  has recesses  751  for the locating device  225  to be secured thereat. The through hole  71  is for the tool sleeve  1  to be inserted therethrough, and the fastener  74  is secured to the tool sleeve  1 . The first stud  71  engages with the first detent  3 , and the second stud  72  engages with the second detent  5 . 
   The tool sleeve  1 , the ratchet base  22 , the ratchet head  12  and the switch assembly  7  are accommodated in the handle  2  in sequence. The first detent  3 , the first elastic element  4 , the second detent  5 , and the second elastic element  6  are accommodated in the ratchet base  22 . The first detent  3  and the second detent  5  engage with the ratchet teeth  13  of the ratchet head  12 , respectively. By adjusting the first stud  71  and the second stud  72  of the switch assembly  7  to engage with and to link the first detent  3  and the second detent  5 , respectively, the turning direction of the tool sleeve  1  is able to change. 
     FIG. 3  shows two-way engagement of the present invention. When the switch assembly  7  is located at the center, both the first detent  3  and the second detent  5  are engaged with the ratchet teeth  13  of the ratchet head  12 . The first stud  71  and the second stud  72  are disengaged from the first detent  3  and the second detent  5 , thus the tool head  14 A is direct linked with the handle  2 . 
   As shown in  FIGS. 4 and 5 , the turning direction of the operation of the present invention is changed.  FIG. 4  shows a clockwise turning direction.  FIG. 5  shows a counterclockwise turning direction. When the switch assembly  7  is pushed towards one side, either of the first stud  71  and the second stud  72  will link the first detent  3  or the second detent  5  to be retreated from the ratchet teeth  13  of the ratchet head  12 , thus the turning direction of the tool sleeve  1  is able to change towards the direction as desired. 
   As shown in  FIG. 6 , when the disc  23  is turned to align the opening  232  with one of the cavities  24 , the protuberances  25  will be engaged with respective ends of the arc trough  233  provided with the opening  232 , thus a desired tool head  14 A may be picked up from the cavity  24 , and the other tool heads  14 A may be placed back into the cavities  24  through the opening  232 . 
   As shown in  FIG. 7 , when the disc  23  is turned to close the cavities  24 , the opening  23  and the cavities  24  are in a staggered status. One of the protuberances  25  is located in one of the holes  234 , while the other of the protuberance  25  is located in the center of the arc trough  233  to secure the disc  23  in place and to block the tool heads  14 A within the cavities  24 .