Patent Publication Number: US-2012031637-A1

Title: Device for power tool preventing axial vibration in reverse rotation

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a ratchet device for a power tool and in particular to a ratchet device which prevent axial vibration when an output shaft of the power tool rotates in reverse direction. 
     2. The Prior Arts 
     A conventional power tool, such as a power drill, generally outputs power from the motor to the output shaft by the gear unit. Besides, in order to tighten the bolts or to loosen the bolts, some of the power tools are equipped with an axial vibration function which can output an impact force to tighten the bolts or loosen the bolts. 
     The conventional impact power tool with the vibration function generally comprises an output shaft, a stationary ratchet gear and a movable ratchet gear mounted to the output shaft, at least one block located between the stationary ratchet gear and the movable ratchet gear, a case for accommodating the parts mentioned above, and an adjusting knob which is threadedly connected to the case. The stationary ratchet gear is cooperated with a bearing and located within the case and is rotatable relative to the case. The movable ratchet gear is fixed to the output shaft and is co-rotated with the output shaft. When the adjusting knob is rotated in the forward direction or the reverse direction, the block is controlled to move axially toward the front end or the rear end of the case so as to control the protrusions on the block to be engaged with or disengaged from the ribs on the stationary ratchet gear. When the protrusions are not engaged with the ribs and the output shaft is applied by an axial force to engage the movable ratchet gear with the stationary ratchet gear, because the stationary ratchet gear is freely rotatable, the output shaft driven by the power source device provides the output in the form of pure rotation. When the protrusions are engaged with the ribs and the output shaft is applied by the axial force to engage the movable ratchet gear with the stationary ratchet gear, because the stationary gear is fixed, so that the power source device drives the output shaft to rotate and the ratchet teeth on the movable ratchet gear are forced to move over the ratchet teeth on the stationary ratchet gear. By the interference, the output shaft outputs axial vibration. 
     The disadvantages of the conventional design is that when the protrusions of the block are engaged with the ribs of the stationary ratchet gear, the output shaft is applied by the axial force and rotates in the reverse direction (restricted direction of the ratchet teeth), the movable ratchet teeth and the stationary ratchet teeth will catch against the steeply sloped edges of the teeth. The mechanical stress is very high and therefore the movable ratchet teeth and the stationary ratchet teeth are very likely to break. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to provide a ratchet device for a power tool which overcomes the disadvantage of the conventional designs. When the output shaft is rotated in the forward direction (unrestricted direction of the ratchet teeth), the output modes of the power tool include pure rotation and rotation combined with vibration in the axial direction. When the output shaft is rotated in the reverse direction (restricted direction of the ratchet teeth), the axial vibration function is automatically released and the output mode includes pure rotation only so as to protect the inner parts of the device. 
     In order to achieve the objective, a device for a power tool which prevents axial vibration in the reverse rotation according to the present invention comprises a movable ratchet gear and a stationary ratchet gear which is engageable with the movable ratchet gear. The movable ratchet gear is connected to and co-rotated with the output shaft of the power tool. The stationary ratchet gear is separated from the output shaft. The present invention provides a clutch mechanism which is operated to let the output shaft output in the form of pure rotation only in both directions, or output in the form of rotation in the forward direction and axial vibration. However, there is no axial vibration when the output shaft is rotated in the reverse direction. 
     A characteristics of the present invention is that the stationary ratchet gear has ribs on the circumferential surface thereof and each rib has an inclined surface. A locking member has at least one pawl. The locking member is controlled to move to engage the pawl with the rib or disengage the pawl from the rib. When the pawl is not engaged with the rib, the stationary ratchet gear is free to rotate. The output shaft drives the stationary ratchet gear and can output power in a form of rotation in the forward direction and the reverse direction. When the pawl is engaged with the ribs, the stationary ratchet gear is fixed. The movable ratchet gear rotates in the forward direction and interference happens between the movable ratchet teeth and the stationary ratchet teeth to generate vibration. When the movable ratchet gear drives the stationary ratchet gear in the reverse direction, the inclined surfaces of the ribs push the pawls to generate relative slip. The rib of the stationary ratchet gear is disengaged from the pawl of the locking member. Because the stationary ratchet gear is not fixed so that the movable ratchet gear does not generate axial vibration. 
     The power tool having the device according to the present invention comprises an output unit, a stationary ratchet gear unit, at least one spring disposed between the output unit and the stationary ratchet gear unit, a locking member having a pawl, a case for accommodating the parts mentioned above and a control device threadedly connected to the case. The output unit includes an output shaft having a first bearing and a movable ratchet gear. The movable ratchet gear has movable ratchet teeth facing the stationary ratchet teeth of the stationary ratchet gear. The stationary ratchet gear includes ribs and each rib has an inclined surface. The inclination of the inclined surfaces is smaller than the inclinations of the forward rotation side and the reverse rotation side of the stationary ratchet teeth. The two ends of the spring are pressed against the output unit and the stationary ratchet gear unit. By operating the switch ring of the control unit, the locking member is movable along the axial direction of the case so as to control the engagement between the pawls and the ribs. The spring keeps biasing the locking member to maintain the pawls to contact with the ribs so as to smoothly engage the pawls with the ribs. 
     The locking member preferably includes two pawls disposed diametrically opposite to each other and each pawl has an extension extending inward therefrom. The extension may engage with the rib, or slip from the rib via the inclined surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which: 
         FIG. 1  is an exploded view showing a device for a power tool which prevents axial vibration in the reverse rotation according to the present invention; 
         FIG. 2  is an exploded view showing a power tool having the device in accordance with the present invention; 
         FIG. 3  is a cross-sectional view showing the device according to the present invention, wherein the device is switched to be the mode of pure rotation; 
         FIG. 4  is a cross-sectional view showing the device according to the present invention, wherein the device is switched to be the mode of rotation combined with vibration; and 
         FIG. 5  is a cross-sectional view showing the device according to the present invention, wherein the extensions of the locking member move along the inclined surface of the stationary ratchet gear. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings and in particular to  FIG. 1 , a ratchet device for a power tool which prevents axial vibration in the reverse rotation in accordance with the present invention comprises a movable ratchet gear  13 , a stationary ratchet gear  21  and a locking member  3 . The stationary ratchet gear  21  has a plurality of ribs  212  disposed on a circumferential surface thereof and each rib  212  has an inclined surface  213 . The locking member  3  has at least one pawl  31  which has an extension  311  extending inward from a distal end thereof. The locking member  3  is moveable to control the engagement or disengagement between the extension  311  of the pawl  31  and the ribs  212  of the stationary ratchet gear  21 . A clutch mechanism K comprises the ribs  212  having the inclined surface  213  and the locking member  3 . 
     With reference to the  FIG. 2 , a power tool having the ratchet device according to the present invention comprises an output unit  1 , a stationary ratchet gear unit  2 , the locking member  3 , a spring washer  4 , a positioning washer  5 , a case  6  and a control unit  7 . The output unit  1  comprises an output shaft  11 , a first bearing  12  and the movable ratchet gear  13 . The output shaft  11  includes multiple sections with different diameters and the sections include a first section with a larger diameter and a second section with a smaller diameter. The first bearing  12  is connected to the first section of the output shaft  11  and the movable ratchet gear  13  is connected to the second section of the output shaft  11 . The movable ratchet gear  13  has a plurality of movable ratchet teeth  131  disposed on a side surface thereof. 
     The stationary ratchet gear unit  2  comprises the stationary ratchet gear  21  and a second bearing  22 . The stationary ratchet gear  21  includes a plurality of stationary ratchet teeth  211  disposed at a side surface thereof facing the movable ratchet teeth  131  and the ribs  212  disposed on the circumferential surface thereof. Each rib  212  has the inclined surface  213  which is located on the same side of each rib  212  and has the same inclination. The inclination of each of the inclined surfaces  213  is smaller than the inclinations of forward rotation (unrestricted direction) side and reverse rotation (restricted direction) side of the stationary ratchet teeth  211 . The stationary ratchet gear  21  has a central hole  210  through which the output shaft  11  extends. The second bearing  22  is a needle roller bearing and has an axial hole. 
     The integrally formed locking member  3  is pressed to form and then is bended to form the L-shaped pawls  31 . The two pawls  31  are located diametrically opposite to each other on the locking member  3 . The extension  311  is extended inward from the distal end of the pawl  31 . The locking member  3  has a plurality of notches  32  defined in a circumferential surface thereof. 
     The case  6  has a tubular body  61  which has a space  610  to accommodate the parts mentioned above. A plurality of axial positioning holes  62  and recesses  63  are defined in the case  6 . The output shaft  11  extends through a first spring  191 , a first washer  181 , a second spring  192 , a second washer  182 , the locking member  3 , the stationary ratchet gear  21 , the second bearing  22 , washers  17 ,  14 , and a third bearing  16 . All of the parts mentioned above are assembled in the space  610  and the third bearing  16  is secured in an inner periphery of the space  610  and fixed to the output shaft  11  by a clip  15 , such that the output shaft  11  is not disengaged from the case  6 . After all of the parts are assembled, two ends of the first spring  191  are pressed against the first bearing  12  and the extension  311  of the pawl  31 , respective. Two ends of the second spring  192  are pressed against the first bearing  12  and the side surface of the stationary ratchet gear  21 , respectively. 
     The control unit  7  comprises a knob  71 , a switch ring  72  and a nut  73 . The nut  73  has outer threads  731  and the knob  71  has inner threads  711  which are threadedly connected to the outer threads  731 . The positioning washer  5  has a plurality of protrusions  51  extending axially therefrom and the protrusions  51  are inserted into the positioning holes  62  of the case  6 , and a plurality of springs  52  are disposed between the positioning washer  5  and the case  6 . The switch ring  72  and the knob  71  are then connected to the case  6  to let the positioning washer  5  be mechanically connected with the switch ring  72 . The knob  71  of the control unit  7  is cooperated with the nut  73 , the spring washer  4  and a plurality of torsion springs  42  to adjust the output torque of the output shaft  11 . The switch ring  72  is connected to the positioning washer  5  and cooperated with the springs  52  and the locking member  3  to switch the modes of the output power from the output shaft  11 . The spring washer  4  includes a plurality of axial rods  41  and each rod  41  is mounted with a torsion spring  42 . The spring washer  4  is then mounted to the tubular body  61  of the case  6 . The torsion springs  42  are inserted into the recesses  63  of the case  6  to contact with the gears of a power source (not shown). 
     The distal end of the output shaft  11  is connected to the power source (not shown) located at the rear end of the case  6  and the power source includes a motor and a gear units. When the motor is in operation, the power is transferred to the output shaft  11  through the gear unit. When rotating the knob  71  to adjust the torque output from the output shaft  11 , the nut  73  is moved axially in the knob  71  and the spring washer  4  is pushed by the nut  73 . When rotating the knob  71  to move the nut  73  to axially push the spring washer  4  to compress the torsion springs  42 , the torsion springs  42  apply a force to the gears of the transmission mechanism to slow down the speed of the gears so as to increase the torque. Similarly, if the speed of the gears increases, the output torque reduces. In other words, the output torque is adjusted by adjusting how far the spring washer  4  compresses the torsion spring  42 . 
     The output shaft  11  is adjusted between modes of rotation in the forward direction (unrestricted direction of the ratchet teeth), rotation in the forward direction combined with axial vibration and rotation in the reverse direction (restricted direction of the ratchet teeth) by rotating the switch ring  72 . As shown in  FIG. 3 , the positioning washer  5  and the locking member  3  are mechanically connected to the inside of the switch ring  72 . Thus, the switch ring  72  can drive the positioning washer  5  and the locking member  3  to move axially along the tubular body  61  of the case  6 . When the switch ring  72  is rotated to a first position, the extensions  311  of the pawls  31  of the locking member  3  are held by the switch ring  72 . The extensions  311  of the locking member  3  are not engaged with the ribs  212  of the stationary ratchet gear  21  and therefore the stationary ratchet gear  21  is not fixed. The user applies an axial force to the output shaft  11  and the axial force is toward the case  6 . The output shaft  11  is driven to rotate in the forward direction or the reverse direction by the power source, and the movable ratchet teeth  131  on the side surface of the movable ratchet gear  13  are engaged with the stationary ratchet teeth  211  on the side surface of the stationary ratchet gear  21 . Thus, by the operation of the movable ratchet gear  13 , the stationary ratchet gear  21  is co-rotated with the output shaft  11 . The output shaft  11  outputs in the form of pure rotation in both forward and reverse directions. 
     Referring to  FIG. 4 , when the switch ring  72  is rotated to a second position, the locking member  3  is driven so that the extensions  311  are engaged with the ribs  212 . Therefore the stationary ratchet gear  21  is fixed and unable to rotate. The user applies a force to the output shaft  11  and the force is toward the case  6  in the axial direction of the case  6 . Although the movable ratchet teeth  131  are engaged with the stationary ratchet teeth  211 , the stationary ratchet gear  21  is fixed. Therefore, if the output shaft  11  is driven by the power source to rotate in the forward direction, the movable ratchet teeth  131  are forced to move over the stationary ratchet teeth  211 . Due to the interference between the movable ratchet teeth  131  and the stationary ratchet teeth  211 , the output shaft  11  rotates in the forward direction and provides an axial vibration. 
     Referring to  FIG. 5 , when the extensions  311  of the locking member  3  are engaged with the ribs  212  of the stationary ratchet gear  21 , gaps are defined between the extensions  311  and the ribs  212 . At the state that the extensions  311  of the locking member  3  are engaged with the ribs  212  of the stationary ratchet gear  21 , when the switch ring  72  is switched to a third position to rotate the output shaft  11  in the reverse direction, due to the gap and the inclined surface  213 , the extensions  311  move along the inclined surface  213  and the locking member  3  moves along the axial direction. Then, the extensions  311  are disengaged from the ribs  212  and the stationary ratchet gear  21  is released from being fixed. Because the stationary ratchet gear  21  is no longer fixed, the stationary ratchet gear  21  is rotated in the reverse direction with the movable ratchet gear  13 . The movable ratchet teeth  131  do not move over the stationary ratchet teeth  211  and therefore there is no axial vibration. The stationary ratchet teeth  211  and the movable ratchet teeth  131  are protected from being damaged by the stress. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.