Abstract:
A power hand tool includes a housing that houses a motor, a transmission gear set, a torque control mechanism and an impact mechanism. The torque control mechanism has an adjustment device that is movable between a first position and a second position inside the housing by a rotation action to set a predetermined output torque of the power hand tool. The output torque of the power hand tool is at the minimum condition and the adjustment device stops the impact mechanism from working to prevent destruction to the torque setting of the power hand tool when the adjustment device is in the second position.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to power hand tools and more particularly, to a power hand tool having a torque control mechanism and an impact mechanism. 
   2. Description of the Related Art 
   A conventional power impact wrench is known comprising a motor, a transmission gear set, and an impact mechanism. The transmission gear set reduces the revolving speed of the rotary driving force of the motor to a predetermined level for output. The impact mechanism is adapted to produce an impact against the output shaft of the power hand tool intermittently and rapidly in same direction of rotation when the output shaft of the power hand tool encountered a resisting force that surpasses the output torque, for enabling the output shaft to overcome the resisting force and to keep working. 
   There is known an electric screwdriver, which comprises a motor, a transmission gear set, and a torque control mechanism. The transmission gear set reduces the revolving speed of the rotary driving force of the motor to a predetermined level for output. The torque control mechanism is adapted to set the maximum output torque of the electric screwdriver, preventing damage to the workpiece. 
   The aforesaid impact mechanism and torque control mechanism are designed to fit two reversed requirements. Normally, these two mechanisms do not coexist in a power hand tool. However, these two mechanisms may be required in a certain condition. For example, when a user uses an electric wrench to dismount a tire from a vehicle, the electric wrench needs an impact function to overcome the dismounting obstacle, which may be produced due to rust on the screw bolts at the tire or other reasons; in order to prevent damage to the screw bolts at the tire due to an excessive high torque when mounting the tire, it is necessary to have a torque setting function in the power hand tool. However, when arranging these two mechanisms in a power hand tool, the functioning of the torque setting mechanism may be damaged when starting the impact mechanism, and the impact mechanism fail to function when started the torque setting mechanism. 
   Therefore, it is desirable to provide a power hand tool having a torque control mechanism and an impact mechanism, which eliminates the aforesaid problem. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished under the circumstances in view. It is therefore one object of the present invention to provide a power hand tool having a torque control mechanism and an impact mechanism, which allows switching of the impact mechanism between the working position and the non-working position. 
   To achieve this object of the present invention, the power hand tool comprises a housing that accommodates a motor, a transmission gear set, a torque control mechanism, and an impact mechanism therein. The torque control mechanism has an adjustment device that is movable between a first position and a second position inside the housing by a rotation action to set the output torque of the power hand tool. The output torque of the power hand tool is at the minimum condition and the adjustment device stops the impact mechanism from working to prevent destruction to the torque setting of the power hand tool when the adjustment device is in the second position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a power hand tool according to a preferred embodiment of the present invention. 
       FIG. 2  is another exploded view in an enlarge scale of a part of the power hand tool according to the preferred embodiment of the present invention. 
       FIG. 3  is a schematic sectional view of the present invention showing the adjustment device is at the second position. 
       FIG. 4  is another schematic sectional view of the present invention showing the adjustment device is at first position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1–3 , a power hand tool  1  in accordance with the present invention is shown comprised of a housing  10 , a motor  20 , a battery pack  30 , a transmission gear set  40 , a torque control mechanisms  50 , and an impact mechanism  60 . 
   The housing  10  is comprised of a left half shall  11 , a right half shell  12 , a front shell  13 , and a front cap  14 . The left half shell  11  and the right half shell  12  are abutted against each other. The front shell  13  is fastened to the front side of the abutted left half shell  11  and right half shell  12 . The front cap  14  has a rear coupling flange  141  pivotally coupled to the inside wall of the front shell  13  in front of the left half shell  11  and the right half shell  12  for allowing rotary motion of the front cap  14  relative to the front shell  13 , and a plurality of locating blocks  142  equiangularly spaced around the inside wall. 
   The motor  20  is fixedly mounted inside the housing  10 , having a motor shaft  21 . 
   The battery pack  30  is detachably mounted to the housing  10 , and adapted to provide the necessary working electricity to the motor  20 . 
   The transmission gear set  40  is mounted inside the housing  10 , comprising a first sun gear  41  fixedly mounted on the motor shaft  21  of the motor  20 , a first planet carrier  42 , a second sun gear  421  provided at the center of the first planet carrier  42 , a first planet gear set  43  rotatably supported on the first planet carrier  42  and meshed with the first sun gear  41 , a second planet carrier  44 , a third sun gear  441  provided at the center of the second planet carrier  44 , a second planet gear set  45  rotatably supported on the second planet carrier  44  and meshed with the second sun gear  421 , a third planet carrier  46 , an output shaft  461  fixedly provided at the center of the third planet carrier  46 , a third planet gear set  47  rotatably supported on the third planet carrier  46  and meshed with the third sun gear  441 , a first internally toothed ring  48  meshed with the first planet gear set  43 , a second internally toothed ring  49  selectively meshed with the second planet gear set  45  or the first planet carrier  42 , and a barrel  491  affixed to the inside of the housing  10  to house the aforesaid parts of the transmission gear set  40 . The transmission gear set  40  reduces the speed of the rotary driving force from the motor  20  for output through the output shaft  461 . Further, shifting the position of the second internally toothed ring  49  changes the revolving speed of the output shaft  461 . Because this transmission gear set  40  is a known design commonly used in conventional power hand tools, no further detailed description in this regard is necessary. 
   The torque control mechanism  50  comprises an internal gear  51 , a holder shell  52 , an adjustment device  53 , a plurality of springs  54 , a plurality of steel balls  55 , and a plurality of pins  56 . 
   The internal gear  51  is meshed with the third planet gear set  47  inside the housing  10 , having an actuating end face  511  and a plurality of protruding portions  512  respectively extending from the actuating end face  511  and spaced from one another at an equal angle. 
   The holder shell  52  comprises a shell body  521  and a round shank  524 . The shell body  521  has a first end face  522  and a second end face  523 . The round shank  524  extends perpendicularly from the second end face  523  of the shell body  521 , having an outer thread  525  around the periphery and two longitudinal sliding grooves  526  at two sides. The shell body  521  has a plurality of through holes  527  cut through the first end face  522  and the second end face  523 . The holder shell  52  defines an axial hole  528  extending through the center of the shell body  521  and the center of the round shank  524 . The holder shell  52  is fixedly mounted inside the housing  10  adjacent to one side relative to the internal gear  51  with the first end face  522  facing the actuating end face  511  of the internal gear  51 . 
   The adjustment device  53  is comprised of an adjustment ring  531 , a needle bearing  532 , and a ring member  533 . The adjustment ring  531  has a first end face  5311 , a second end face  5312  opposite to the first end face  5311 , an inside wall  5313 , an outside wall  5314 , an inner thread  5315  extending around the inside wall  5313  and corresponding to the outer thread  525  of the round shank  524  of the holder shell  52 , and a plurality of locating grooves  5316  spaced around the outside wall  5314  and adapted to receive the locating blocks  142  of the front cap  14 . The inner thread  5315  of the adjustment ring  531  is meshed with the outer thread  525  of the round shank  524  of the holder shell  52 , keeping the locating grooves  5316  respectively coupled to the locating blocks  142 . Therefore, rotating the front cap  14  causes the adjustment ring  531  to move along the round shank  524  of the holder shell  52  between a first position and a second position. The ring member  533  has two protruded positioning portions  5331  at the inner wall thereof. The ring member  533  is sleeved onto the round shank  524  of the holder shell  52  such that the two protruded positioning portions  5331  are respectively coupled to the longitudinal sliding grooves  526  of the holder shell  52  and the ring member  533  is located between the second end face  523  of the holder shell  52  and the first end face  5311  of the adjustment ring  531 . The needle bearing  532  is attached to the second end face  5312  of the adjustment ring  531 . 
   The springs  54  are respectively mounted in the through holes  527  of the holder shell  52 . 
   The steel balls  55  are respectively stopped between the springs  54  and the actuating end face  511  of the internal gear  51 . 
   The pins  56  are respectively inserted into the through holes  527  of the holder shell  52  and stopped between the springs  54  and the ring member  533  against the first end face  5311  of the adjustment ring  531 . 
   When the adjustment ring  531  is in the first position as shown in  FIG. 4 , the steel balls  55  receive a first pressure from the springs  54 . When the adjustment ring  531  is in the second position as shown in  FIG. 3 , the steel balls  55  receive a second pressure from the springs  54 . The second pressure is greater than the first pressure. 
   When the internal gear  51  is locked and prohibited from rotary motion, the transmission gear set  40  reduces the revolving speed of the rotary driving force from the motor  20  for output through the output shaft  461 . When the internal gear  51  is unlocked and allowed to rotate and when the output shaft  461  receives a resisting force, the internal gear  51  will be rotated, causing the transmission gear set  40  to run idle. When wishing to cause rotation of the internal gear  51 , it is necessary to have the protruding portions  512  at the actuating end face  511  of the internal gear  51  overcome the pressure from the steel balls  55 . Therefore, when the pressure from the steel balls  55  at the actuating end face  511  of the internal gear  51  is relatively increased, the internal gear  51  must receive a relatively greater rotary driving force to overcome the pressure from the steel balls  511 , i.e., the output shaft  461  must receive a relatively greater resisting force to have the internal gear  51  be rotated, and this resisting force is the relatively maximum torque outputted from the output shaft  461  at that condition. Therefore, when the adjustment ring  531  is in the second position, the pressure from the steel balls  55  against the actuating end face  511  of the internal gear  51  reaches the maximum, and this pressure is the maximum torque that the output shaft  461  can output. When the adjustment ring  531  is in the first position, the pressure from the steel balls  55  at the actuating end face  511  becomes the least, and this pressure is the smallest output torque of the output shaft  461 . 
   The impact mechanism  60  comprises a final output shaft  61 , a transmission shaft  62 , an impact element  63 , and a spring member  64 . The output shat  61  of the impact mechanism  60  is rotatably mounted in the front cap  14  and partially extended out of the front cap  14 , having a coupling portion  611  at one end. The transmission shaft  62  is coupled to the output shaft  461  of the second planet carrier  46  of the transmission gear set  40  for synchronous rotation with the output shaft  461 . The impact element  63  is sleeved onto the transmission shaft  62  and axially movable along the transmission shaft  62  between two positions, namely, the third position and the fourth position. The impact element has a coupling portion  631 . When the impact element  63  is in the third position, the coupling portion  631  of the impact element  63  is kept coupled to the coupling portion  611  of the final output shaft  61  of the impact mechanism  60 , allowing rotation of the final output shaft  61  with the transmission shaft  62  and the output shaft  461  of the second planet carrier  46  of the transmission gear set  40 . When the impact element  63  is in the fourth position, the coupling portion  631  of the impact element  63  is disengaged from the coupling portion  611  of the final output shaft  61  of the impact mechanism  60 . The spring member  64  is supported between the transmission shaft  62  and the impact element  63  to hold the impact element  63  in the third position. 
   Further, when the adjustment ring  531  is in the aforesaid first position, the second end face  5312  is pressed on the needle bearing  532  against the impact element  63  to hold the impact element  63  in the aforesaid third position, prohibiting movement of the impact element  63  to the aforesaid fourth position. 
   Referring to  FIG. 4  and  FIG. 3  again, when the user rotated the front cap  14  to move the adjustment ring  531  to the aforesaid second position as shown in  FIG. 3 , the output torque of the output shaft  461  of the transmission gear set  40  reaches the maximum. When the final output shaft  61  receives a resisting force at this time, the impact element  63  is forced to move from the aforesaid third position to the aforesaid fourth position and then disengaged from the final output shaft  61 . At the time the impact element  63  disengages from the final output shaft  61 , the spring member  64  immediately pushes the impact element  63  back to the third position to force the coupling portion  631  of the impact element  63  into engagement with the coupling portion  611  of the final output shaft  61 , thereby achieving the designed impact effect. This impact effect won&#39;t stop till the resisting force received by the final output shaft  61  is reduced. 
   When the user rotated the front cap  14  to move the adjustment ring  531  to the aforesaid first position, the output torque of the output shaft  461  of the transmission gear set  40  reaches the minimum, and the adjustment ring  531  is stopped at the needle bearing  532  against the impact element  63  to hold the impact element  63  in the aforesaid third position. When the final output shaft  61  receives a resisting force at this time, the adjustment ring  53  prohibits the impact element  63  from moving to the fourth position, and therefore the impact mechanism  60  cannot produce an impact effect at this time. If the resisting force received by the final output shaft  61  surpasses the torque outputted from the output shaft  461  of the transmission gear set  40  at this time, the internal gear  51  will be rotated to interrupt transmission of force from the motor  20  to the output shaft  461  of the transmission gear set  40 . Therefore, the power hand tool  1  can only output the set torque, preventing the production of a transient high torque due to the effect of the impact mechanism  60 , thereby preventing damage to the workpiece. 
   Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.