Patent Publication Number: US-7222559-B2

Title: Screwdriver with torque setting mechanism

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to screwdrivers and more particularly to a screwdriver having a torque setting mechanism such that torque exerted on a handle will not transmit to a shank if the torque exceeds a set value so as to prevent a screw from being over-driven by the shank. 
   2. Related Art 
   Screwdrivers are well known. It is typical that tightness of a driven screw is determined based on experience of a person working on it. It is understood that in one case the screw may be damaged if force (i.e., torque) exerted thereon exceeds a set value thereof. Thus, it is highly desirable to provide a screwdriver with a torque setting mechanism. However, how to design a torque setting mechanism in a limited internal space of a screwdriver while operation convenience and other advantageous features are still provided is a task to be accomplished. Thus, continuing improvements in the exploitation of such screwdriver are constantly being sought. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a screwdriver comprising a rotatable handle including a sleeve including an internal lower elastic member, a support ring urged against an internal shoulder by the elastic member, the support ring including a plurality of male members equally spaced around its upper surface, and a scale window on a surface of the handle; and a torque setting mechanism including an actuation rod passed the support ring and the elastic member and including a lower threaded section, an upper threaded section, two opposing intermediate flats extended from the upper threaded section to the lower threaded section, and a top socket for securely receiving one end of a shank; a clutch ring put on the flats and having a plurality of equally spaced female members formed on its lower surface for receiving portions of the male members; a torque adjustment ring rotatably provided on tops of the clutch ring and the handle with the actuation rod passed, the torque adjustment ring urged against a shoulder between the upper threaded section and the socket; a lower torque adjustment nut threadedly secured to the lower threaded section and provided under the sleeve to urge against a bottom of the elastic member; and a color ring provided at a bottom of the actuation rod and disposed corresponding to the scale window, the color ring being adapted to turn as the actuation rod longitudinally moves in a torque setting operation by turning the torque adjustment ring; wherein in a screw fastening operation fit an open end of the shank into the head of a screw, turn the handle to cause both the support ring and the torque adjustment ring to turn, the clutch ring disengages with the male members to move the torque adjustment ring upward if a torque exerted on the screw by the shank exceeds a set maximum torque value, and the actuation rod moves longitudinally such that the torque will not transmit to the shank so as to prevent the screw from being over-driven; and in a maximum torque value setting operation of a screw turn the torque adjustment ring about the upper threaded section to longitudinally move the actuation rod whereby moving the torque adjustment nut closer to the support ring will further compress the elastic member, and bring the clutch ring to further engage the support ring. 
   In one aspect of the present invention, the elastic member is a compression spring. 
   In another aspect of the present invention, the elastic member includes a plurality of resilient rings stacked together. 
   In yet another aspect of the present invention, the male members are steel balls and the female members are a plurality of recesses. 
   In a further aspect of the present invention, the male members are formed as teeth and the female members are formed as mated teeth. 
   The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a first preferred embodiment of screwdriver according to the invention; 
       FIG. 2  is a perspective view of the assembled screwdriver in  FIG. 1  where a shank is mounted; 
       FIG. 3  is a sectional view of  FIG. 2  where the shank has been removed; 
       FIG. 4  is a view similar to  FIG. 3  where torque set value is being set by rotating a torque adjustment ring; 
       FIG. 5A  is a view of upper portion of  FIG. 3 ; 
       FIG. 5B  is a view similar to  FIG. 5A  where a clutch ring disengages with steel balls when torque exceeds a set value; 
       FIGS. 6 and 7  are views similar to  FIG. 3  where second and third preferred embodiments of some components of the invention are shown; 
       FIG. 8  is an exploded view of a fourth preferred embodiment of some components (e.g., turning direction change mechanism) of the invention; 
       FIG. 9  is a longitudinal sectional view of upper portion of the assembled screwdriver in  FIG. 8 ; 
       FIG. 10  is a transverse sectional view showing a relative position of steel ball of direction change member with respect to positioning aperture; and 
       FIGS. 11A ,  11 B, and  11 C are transverse sectional views showing relative positions of steel balls in cavities when the direction change member turns. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 to 4 , a screwdriver in accordance with a first preferred embodiment of the invention comprises a torque setting mechanism  20  and a rotatable handle  10  with most portion of the torque setting mechanism  20  mounted therein. The handle  10  comprises a scale window  12  on its surface. The torque setting mechanism  20  comprises a sleeve  11  including a support ring  111  urged against an upper shoulder by a lower spring (e.g., compression spring)  24  as detailed later, the support ring  111  including a plurality of steel balls  112  equally spaced around its upper surface. The support ring  111  thus is able to turn as the sleeve  11  turns. 
   An actuation rod  21  has its most portion disposed in the sleeve  11  by passing the support ring  111  and the spring  24 . The actuation rod  21  comprises a lower threaded section  211 , an upper threaded section  214 , two opposing intermediate flats  213  extended from the upper threaded section  214  to the lower threaded section  211 , and a top socket  215  for securely receiving one end of a shank  91 . A clutch ring  23  is snugly put on the flats  213  and has a lower surface formed with a plurality of equally spaced recesses  231  for receiving projected portions of the steel balls  112 . 
   A torque adjustment ring  25  is rotatably provided on tops of both the clutch ring  23  and the handle  10  with the actuation rod  21  passed. The torque adjustment ring  25  comprises a lower knurled circular member  251  for facilitating gripping prior to turning. A shoulder between the upper threaded section  214  and the socket  215  is rested upon top of the torque adjustment ring  25 . 
   A lower torque adjustment nut  212  is threadedly secured to the lower threaded section  211  and is provided under the sleeve  11  to urge against a bottom of the spring  24 . Thus, as stated above the support ring  111  is urged upward by the spring  214 . A color ring  216  is provided at a bottom of the actuation rod  21  and is disposed corresponding to the scale window  12 . The color ring  216  is adapted to turn as the actuation rod  21  longitudinally moves in a torque setting operation by turning the torque adjustment ring  25 . As such, a user may be visually aware whether a desired torque set value has been set or not by viewing the color ring  216  through the scale window  12 . 
   Referring to  FIGS. 5A and 5B , in operation a user may first mount a shank  91  at the socket  215 . Next, fit an open end of the shank  91  into the head of a screw prior to turning the handle  10 . The turning of the handle  10  will turn both the support ring  111  and the torque adjustment ring  25 . The clutch ring  23  will disengage with the steel balls  112  (i.e., the torque adjustment ring  25  disengages with the handle  10  as the clutch ring  23  pushes the torque adjustment ring  25  upward) if the exerted force (i.e., torque) exceeds a set value (i.e., the exerted force larger than expansion force of the spring  24  when the screw has been fastened). Thus, turning of the steel balls  112  has no effect to the clutch ring  23 . Also, the upward movement of the torque adjustment ring  25  will longitudinally move the actuation rod  21 . As a result, torque exerted on the handle  10  will not transmit to the shank  91  so as to prevent the screw from being over-driven by the shank  91 . 
   Referring to  FIG. 4  again, for setting maximum torque values of different screws simply turn the torque adjustment ring  25  about the upper threaded section  214  to longitudinally move the actuation rod  21 . Substantially, movement of the torque adjustment nut  212  closer to the support ring  111  will further compress the spring  24 , and bring the clutch ring  23  to further engage the support ring  111 . In short, turning the torque adjustment ring  25  can set a maximum torque value of a screw to be driven. 
   Referring to  FIG. 6 , the engagement of the support ring  111  and the clutch ring  23  by means of steel balls  112  and recesses  231  can be replaced by teeth and mated teeth. Referring to  FIG. 7 , the spring  24  can be replaced by a plurality of resilient rings  24 A stacked together. 
   Referring to  FIGS. 8 ,  9 , and  10 , a turning direction change mechanism as a fourth preferred embodiment of the invention is provided and comprises a hollow cylindrical seat  30  including a longitudinal hole  31  and a pin  32  snugly projected from a transverse through hole; a ring-shaped direction change member  40  fitted on the seat  30  and including a longitudinal hole  41  including first, second, and third positioning apertures  411 ,  412 , and  413  on its inner surface  42 , and two opposite arcuate cavities  43  with the longitudinal hole  41  disposed therebetween; a cylindrical auxiliary seat  50  including a top socket  51  for securely receiving one end of a shank, and a downward peg  52  extended into the longitudinal hole  31  through the longitudinal hole  41  and including a transverse aperture  53 , a spring  531  fitted in the aperture  53 , a steel ball  532  biased between the spring  531  and one of the first, second, and third positioning apertures  411 ,  412 , and  413 , two opposite flats  54  formed on a peripheral surface such that either steel ball  56  is adapted to snugly fit in a space defined by the flat  54 , the seat  30 , and the cavity  43 , and an annular groove  55  proximate a bottom end of the peg  52 . The pin  32  is projected into the groove  55  for permitting the auxiliary seat  50  to turn about the seat  30  without disengagement. 
   As shown in  FIGS. 9 and 10 , the direction change member  40  is adapted to turn clockwise or counterclockwise to cause the steel ball  532  to move from the first positioning aperture  411  into the third positioning aperture  413  or the second positioning aperture  412  for locking. Relative positions of other associated components about this turning are shown in  FIGS. 11A ,  11 B, and  11 C. 
   As shown in  FIG. 11A , the steel balls  56  are located at centers of the cavities  43 . In  FIG. 11B , turning the auxiliary seat  50  counterclockwise will move one steel ball  56  to a first position P 1  at one end of the cavity  43 . The seat  30  also turns counterclockwise to form a gap between the steel ball  56  and the seat  30 . As a result, force is exerted on the peg  52 . In  FIG. 11C , turning the auxiliary seat  50  clockwise will move one steel ball  56  to a second position P 1  at the other end of the cavity  43 . The seat  30  also turns clockwise. As a result, no force is exerted on the peg  52 . 
   While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.