Abstract:
A tool holder for use with a power tool includes an input shaft with a rear portion couplable to a power tool, and an output shaft with a front portion couplable to a tool bit. A clutch assembly releasably non-rotationally couples a front portion of the input shaft to a rear portion of the output shaft, and includes a recess in the front portion of the input shaft or the rear portion of the output shaft, an aperture in the other of the front portion of the input shaft or the rear portion of the output shaft, a roller received in the aperture, and a spring that biases the roller radially inwardly toward the recess. The spring enables release of the roller radially outwardly from the recess when a predetermined torque threshold is exceeded, such that torque is not transmitted from the input shaft to the output shaft.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/846,912, filed Jul. 30, 2010, titled “Tool Bit or Tool Holder for Power Tool,” which claims priority, under 35 U.S.C. §119, to U.S. Provisional Patent Application No. 61/274,042, filed Aug. 12, 2009, titled “Tool holder for Impact Driver.” Each of the aforementioned applications is incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This application relates to a tool bit or a tool holder for use with a power tool, such as an impact driver, a screwgun, a drill, a hammer drill, or a screwdriver. 
     BACKGROUND 
     When a power tool (e.g., an impact driver, a screwgun, a drill, a hammer drill, or a screwdriver) is utilized to drive fasteners, such as screws or nuts, into a workpiece, a large driving torque (e.g., approximately 500 inch-lbs) may be generated. In certain situations, such as with use with an impact driver or hammer drill, that torque may be generated in rapid cycles (e.g., approximately every 2 milliseconds). Due to the large driving torque and the rapid cycling, current tool bits (e.g., screwdriving bits) and/or tool holders often fail when used with these types of power tools, especially with impact drivers. This may be due to the fact that the tool bits and tool holders often have a lower torque rating (e.g., approximately 200 inch-lbs) than the torque rating of the power tool. It would be desirable to have a tool bit and/or a tool holder that can withstand the torque loading of such power tools in these situations. 
     SUMMARY 
     This application relates to a tool, such as a tool bit (e.g., a screwdriving bit or drill bit) or tool holder (e.g., for a screwdriving bit, a drill bit, or a screw or nut), for use with a power tool (e.g., an impact driver, a screwgun, a drill, a hammer drill, or a screwdriver). The tool bit or tool holder includes a clutch that that releases the force transmitted from the power tool to the tool when the torque exceeds a pre-determined amount. In one embodiment, the clutch makes use of a radial band-spring to prevent a series of rollers from slipping over an incline. By tuning the incline&#39;s geometry and the spring geometry it is possible to achieve the necessary torque for seating a screw prior to slipping. The spring-band geometry can be tuned to deliver the required radial force while minimizing the internal stresses to have adequate durability. 
     In one aspect, a tool for use with a power tool includes an input shaft, an output shaft, and a clutch assembly. The input shaft has a rear portion with a shank configured to be removably coupled to a power tool, and a front portion. The output shaft has a front portion configured to be coupled to a tool bit, and a rear portion, the rear portion of the output shaft rotatably coupled to the front portion of the input shaft. The clutch assembly releasably couples the input shaft to the output shaft, and includes: (i) at least one recess defined in one of the front portion of the input shaft and the rear portion of the output shaft; (ii) at least one aperture defined in the other of the front portion of the input shaft and the portion of the output shaft; (iii) at least one roller received in the at least one aperture; and (iv) a spring that biases the at least one roller radially inwardly into the at least one recess such that torque is transmitted from the input shaft to the output shaft when a predetermined torque threshold is not exceeded, and that enables release of the at least one roller radially outwardly from the at least one recess such that torque is not transmitted from the input shaft to the output shaft when the predetermined torque threshold is exceeded. 
     Implementations of this aspect may include one or more of the following features. The shank may have at least a portion having a hex shaped cross-section. The shank may also include a portion having a round cross-section disposed between the portion having the hex-shaped cross-section and the front portion of the input shaft to enable attachment of the shank to a screwgun. The front portion of the output shaft may define a socket configured to removably receive and a retain a tool bit. A tool bit may be integral with the front portion of the output shaft. The at least one recess may include a plurality of longitudinal grooves. The at least one aperture may include a plurality of longitudinal slots. The at least one roller may include a plurality of pins, each pin received in one of the plurality of longitudinal slots. The spring may include at least one spring band received around the longitudinal slots and pins to bias the pins into the longitudinal grooves when the predetermined torque threshold is not exceeded, and that expands to release the pins from the longitudinal grooves when the predetermined torque threshold is exceeded. The at least one spring band may include an inner spring band and an outer spring band at least partially overlapping the inner spring band. A clutch lock-out member may be moveable between a first position and a second position, wherein in the second position the clutch lock-out member prevents interruption of torque transmission from the input shaft to the output shaft 
     In another aspect, a tool for use with a power tool, includes an input shaft, an output shaft, a spring-biased clutch, and a clutch lock-out assembly. The input shaft has a rear portion with a shank configured to be removably coupled to an output of a power tool. The output shaft has a front portion configured to be coupled to a tool bit. The spring-biased clutch couples a front portion of the input shaft to a rear portion of the output shaft so that torque is transmitted from the input shaft to the output shaft when a predetermined torque threshold is not exceeded, and torque transmission from the input shaft to the output shaft is interrupted when the predetermined torque threshold is exceeded. The clutch lock-out assembly is moveable between a first position and a second position, wherein in the second position the clutch lock-out member prevents interruption of torque transmission from the input shaft to the output shaft. 
     Implementations of this aspect may include one or more of the following features. The spring biased clutch may include: (i) a generally cylindrical shaft formed on one of a front portion of the input shaft and a rear portion of the output shaft, the cylindrical shaft defining at least one recess; (ii) a generally cylindrical sleeve formed on the other of the front portion of the input shaft and the rear portion of the output shaft, the sleeve received over the cylindrical shaft, and defining at least one aperture; (iii) at least one roller received in the at least one aperture; and (iv) at least one spring band received over the generally cylindrical sleeve, wherein the spring band biases the at least one roller into the at least one recess such that torque is transmitted from the input shaft to the output shaft when a predetermined torque threshold is not exceeded, and that expands to enable release of the at least one roller from the at least one recess such that torque is not transmitted from the input shaft to the output shaft when the predetermined torque threshold is exceeded. 
     The clutch lock-out assembly may include a longitudinally moveable bushing received over the spring band, the busing having an internal shoulder, such that when the bushing is in the first position, the bushing enables expansion of the spring band, and when the bushing is in the second position, the shoulder abuts the spring band to prevent expansion of the spring band. The at least one recess may include a plurality of longitudinal grooves, the at least one aperture may include a plurality of longitudinal slots, and the at least one roller may include a plurality of pins, each pin received in one of the plurality of longitudinal slots. The at least one spring band may include an inner spring band and an outer spring band at least partially overlapping the inner spring band. The shank may include a fitting having a hex shaped cross-section. The front portion of the output shaft may define a socket configured to removably receive and a retain a tool bit. A tool bit may be integral with the front portion of the output shaft. 
     In another aspect, a tool for use with a power tool includes an input shaft having a rear portion with a shank of hex-shaped cross-section configured to be removably coupled to an output of a power tool, an output shaft having a front portion defining a socket and a retaining member configured to receive a tool bit; and a clutch assembly coupling the input shaft to the output shaft. The clutch assembly includes: (i) a generally cylindrical shaft formed on one of a front portion of the input shaft and a rear portion of the output shaft, the cylindrical shaft defining a plurality of longitudinal grooves; (ii) a generally cylindrical sleeve formed on the other of the front portion of the input shaft and the rear portion of the output shaft, the sleeve received over the cylindrical shaft, and defining a plurality of longitudinal slots; (iii) a plurality of roller pins, each roller pin received in one of the plurality of longitudinal slots; and (iv) at least one spring band received over the generally cylindrical sleeve, the spring band biasing the roller pins into the longitudinal grooves such that torque is transmitted from the input shaft to the output shaft when a predetermined torque threshold is not exceeded, and spring band expanding to enable release of the roller pins from the longitudinal grooves such that torque is not transmitted from the input shaft to the output shaft when the predetermined torque threshold is exceeded. A clutch lock-out assembly that includes a bushing with an internal shoulder is received over the spring band and moveable between a first position and a second position, wherein when the bushing is in the first position, the bushing enables expansion of the spring band and interruption of torque transmission from the input shaft to the output shaft when the predetermined torque threshold is exceeded, and when the bushing is in the second position, the shoulder abuts the spring band to prevent expansion of the spring band and prevent interruption of torque transmission from the input shaft to the output shaft even when the predetermined torque threshold is exceeded. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of a tool. 
         FIG. 2  is an exploded view of the tool of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the clutch of the tool of  FIG. 1  in the engaged condition. 
         FIG. 4  is a cross-sectional view of the clutch of the tool of  FIG. 1  in the disengaged condition. 
         FIG. 5  is a perspective view of the band spring of the clutch of the tool of  FIG. 1 . 
         FIGS. 6 and 7  are perspective views of a second embodiment of a tool. 
         FIG. 8  is an exploded view of the tool of  FIG. 6 . 
         FIG. 9  is a cross-sectional view of the tool of  FIG. 6 . 
         FIGS. 10 and 11  are a perspective views, partially in cross-section, of the tool of  FIG. 6 . 
         FIG. 12  is a cross-sectional view of the clutch of the tool of  FIG. 6  in the engaged condition and with the clutch lock-out assembly removed. 
         FIG. 13  is a cross-sectional view of the clutch of the tool of  FIG. 6  in the disengaged condition and with the clutch lock-out assembly removed. 
         FIG. 14  is a side view, partially in cross-section, of the tool of  FIG. 6 , with the clutch lock-out assembly in the locked-out position. 
         FIG. 15  is a side view, partially in cross-section, of the tool of  FIG. 6 , with the clutch lock-out assembly in the unlocked-out position. 
         FIG. 16  is a perspective view of a third embodiment of a tool. 
         FIG. 17  is a perspective view of a fourth embodiment of a tool. 
         FIG. 18  is a perspective view showing the second embodiment of the tool in use with an impact driver. 
         FIG. 19  is a perspective view showing the second embodiment of the tool in use with a screwgun. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , in one embodiment, a tool  10  for use with a power tool, such as an impact driver, a screwgun, a drill, a hammer drill, or a screwdriver, has a generally cylindrical input shaft  12 , a generally cylindrical output shaft  20 , and a clutch assembly  30  releasably coupling the input shaft  12  to the output shaft  20 . The input shaft  12  has a rear portion  14 , a middle portion  13 , and a front portion  18 . The rear portion  14  comprises a shank  16  with a hex-shaped cross-section and an annular groove  17 , for coupling the rear portion  14  to a tool holder, such as a chuck, of the power tool. In other embodiments, the shank could have a different cross-sectional shape, such as round or square. The middle portion  13  is has a round cross-section and receives a large sleeve bearing  15 . The front portion  18  has a round gross-section and plurality of recesses in the form of longitudinal grooves  38 , the purpose of which will be described below. The front portion  18  also has a smaller diameter nose  19  of round cross-section, over which a small sleeve bearing  21  is received. 
     The output shaft  20  has a rear portion  23  and a front portion  33 . The rear portion  23  defines a longitudinal bore  22  in which the front portion  18  of the input shaft  12 , the small bearing  21 , the middle portion  13  of the input shaft, and the large bearing  15  are rotatably received. The large sleeve bearing  15  and the small sleeve bearing  21  function as bearings between the input shaft  12  and the output shaft  20  to enable the shafts to rotate relative to one another. Received over the middle portion  13  of the input shaft  12  is an end cap  25  that axially retains the input shaft  12  relative to the output shaft  20 . 
     The rear portion  23  of the output shaft  20  also defines a plurality apertures in the form of longitudinal slots  34  that receive a plurality of rollers in the form of pins  36 , the purpose of which will be described below. The front portion  33  has a socket  26  for receiving a tool bit, such as a screwdriving bit or a drill bit. In the embodiment shown, the socket  26  has a hex shape for receiving a bit having a hex shaped shank. However, it should be understood that the socket  26  can have alternative shapes and/or configurations, such as a round shape. Inside the socket  26  is a magnet  28  that helps retain the tool bit inside the socket  26 . It should be understood that additional or other bit retaining features may be included such as a retaining ring or a biased ball. In the alternative, the bit may be made integral with the output shaft (not shown). 
     The clutch assembly  30  releasably couples the input shaft  12  to the output shaft  20 . The clutch assembly  30  includes the longitudinal grooves  38  in the input shaft  18 , the longitudinal slots  34  and the pins  36  in the output shaft  36  and a spring band  42  that substantially surrounds the rear portion  23  of the output shaft  20 , the pins  36 , and the front portion  18  of the input shaft  12 . The large bearing  15  and the cap  25  are received over the input shaft  12  to keep the input shaft  12 , output shaft  20 , and spring band  30  attached together in an axial direction. 
     Referring also to  FIG. 3 , when the clutch  30  is engaged, the spring  42  biases the rollers  36  into the grooves  38  of the input shaft  12  so that rotation of the input shaft  12  by the power tool is transmitted to the output shaft  20 , and thus to the bit being held in the socket  26 . Referring also to  FIG. 4 , when the torque input to the input shaft  12  exceeds a predetermined amount (e.g., when the toque output from the power tool exceeds the torque rating on the clutch assembly), the spring  42  expands, and the rollers  36  escape from the grooves  38  on the input shaft  12  so that no torque is transmitted from the input shaft  12  to the output shaft  20 . In this way, the clutch assembly  30  protects the tool  10  and the bit from instances of excessively high torque. 
     Referring also to  FIG. 5 , the spring is a split band spring with overlapping halves. This design enables the spring to be tuned to the amount of force required to have the clutch release upon a predetermined amount of torque being applied to the shank. 
     Referring to  FIGS. 6-9 , in a second embodiment, a tool  10  for use with a power tool has a generally cylindrical input shaft  112 , a generally cylindrical output shaft  120 , and a clutch assembly  130  releasably coupling the input shaft  112  to the output shaft  120 . The input shaft  112  has a rear portion  114 , a middle portion  113 , and a front portion  118 . The rear portion  114  comprises a shank  116  with a hex-shaped cross-section and an annular groove  117 , for coupling the rear portion  114  to a tool holder, such as a chuck, of the power tool. In other embodiments, the shank could have a different cross-sectional shape, such as round or square. The middle portion  113  is has a round cross-section and receives a large sleeve bearing  115  and a large hog ring  127 . that axially retains the sleeve bearing  115  on the middle portion  113  of the input shaft  112 . In addition, a spacer sleeve  125  is received on the middle portion  113  of the input shaft  112  behind the large hog ring  127 , and a small hog ring  129  axially retains the spacer sleeve  125  on the middle portion  113 . The front portion  118  of the input shaft  112  has a round cross-section and plurality of recesses in the form of longitudinal grooves  138 , the purpose of which will be described below. The front portion  118  also has a smaller diameter nose  119  of round cross-section, over which a washer  131  and a small sleeve bearing  121  are received. 
     The output shaft  120  has a rear portion  123  and a front portion  133 . The rear portion  123  defines a longitudinal bore  122  in which the front portion  118  of the input shaft  112 , the small bearing  121 , the a part of the middle portion  113  of the input shaft  112 , and the large bearing  115  are rotatably received. As shown in  FIG. 9 , the large sleeve bearing  115  and the small sleeve bearing  121  together function as bearings between the input shaft  112  and the output shaft  120  so that the shafts can rotate relative to one another. The rear portion  123  also defines a plurality apertures in the form of longitudinal slots  134  that receive a plurality of rollers in the form of pins  136 , the purpose of which will be described below. A spacer ring  160 , the purpose of which is described below, is held onto rear portion  123  by a C-clip  162 . 
     The front portion  133  of the output shaft  120  has a socket  126  for receiving a tool bit, such as a screwdriving bit or a drill bit. In the embodiment shown, the socket  126  has a hex shape for receiving a bit having a hex shaped shank. However, it should be understood that the socket  126  can have alternative shapes and/or configurations, such as a round shape. Inside the socket  126  is a magnet  128  and a retaining ring  135  that help retain the tool bit inside the socket  126 . It should be understood that additional or other bit retaining features may be included such as a biased ball. In the alternative, the bit may be made integral with the output shaft (not shown). 
     The clutch assembly  130  releasably couples the input shaft  112  to the output shaft  120 . The clutch assembly  130  includes the longitudinal grooves  138  in the input shaft  118 , the longitudinal slots  134  and the pins  136  in the output shaft  136  and a pair of nested spring bands in the form of an inner spring band  142  and an outer spring band  143  that substantially surround the rear portion  123  of the output shaft  120 , the pins  136 , and the front portion  118  of the input shaft  112 . 
     Referring also to  FIG. 12 , when the clutch  130  is engaged, the spring bands  142  and  143  bias the rollers  136  into the grooves  138  of the input shaft  112  so that rotation of the input shaft  112  by the power tool is transmitted to the output shaft  120 , and thus to the bit being held in the socket  126 . Referring also to  FIG. 13 , when the torque input to the input shaft  112  exceeds a predetermined amount (e.g., when the torque output from the power tool exceeds the torque rating on the clutch assembly), the spring  142  expands, and the rollers  36  escape from the grooves  38  on the input shaft  12  so that no torque is transmitted from the input shaft  12  to the output shaft  20 . In this way, the clutch assembly  30  protects the tool  10  and the bit from instances of excessively high torque. 
     Referring also to  FIGS. 14 and 15 , the tool  100  further includes a clutch lock-out assembly  150  for selectively locking out operation of the clutch  130 . The clutch lock-out assembly  130  includes a bushing  152  with a front portion  153  and a rear portion  155 . The bushing  152  is received over the outer spring band  143  and axially moveable between a forward or locked-out position ( FIG. 14 ) and a rearward or unlocked-out position ( FIG. 15 ). The front portion  153  of the busing  152  includes an internal annular groove  154  in which is received an O-ring  156 , which supports the front portion  153  of the bushing  152  on the output shaft  120 . When the bushing is in the forward position ( FIG. 14 ), the O-ring  156  surrounds a portion of the front portion  133  of the output shaft  120 , and when bushing is in the rearward position ( FIG. 15 ), the O-ring  156  is seated in an annular groove  158  in the front portion  133  of the output shaft  120  to help retain the bushing  152  in the latter position. The rear portion  155  of the bushing  152  is supported on the spacer ring  160  and includes a retaining ring  158  that abuts the spacer ring  160  when in the forward position to prevent the bushing  152  from being removed in a forward axial direction. 
     The internal surface of the bushing  152  defines a shoulder  164 . When the bushing  152  is in the forward position ( FIG. 14 ), the shoulder  164  abuts against the outer spring band  143 , preventing expansion of the inner spring band  142  and the outer spring band  143 , which prevents disengagement of the pins  136  from the longitudinal grooves  138  of the input shaft  112 . Thus, in the forward position, the input shaft  112  and output shaft  120  rotate together regardless of the amount of torque applied to the input shaft  112 . When the bushing is in the rearward position ( FIG. 15 ), the shoulder  164  is clear of the spring bands  142 ,  143 , and they are allowed to expand and release the pins  136  from the longitudinal grooves  138  in the input shaft  112  when the predetermined torque threshold is exceeded. Thus, in the rearward position, the clutch  130  is permitted to act to prevent torque transmission from the input shaft  112  to the output shaft  120  when the predetermined torque threshold is exceeded. 
     Referring to  FIG. 18 , in one use, the hex-shaped shank  116  of the input shaft  112  is received inside and coupled to a hex-shaped cavity of a tool holder  502  of an impact driver  500 . A bit, e.g., a screwdriving bit  504  is received in and coupled to the recess  126  of the output shaft  120  to drive a fastener, e.g., a screw  506  into a workpiece W. The clutch  150  is engaged and the impact driver  502  is actuated by the user to drive the screw  506  into the workpiece. If the torque input to the input shaft  112  exceeds a predetermined amount (e.g., when the torque output from the power tool exceeds the torque rating on the clutch assembly), the spring  142  expands, and the rollers  136  escape from the grooves  138  on the input shaft  112  so that no torque transmission from the input shaft  112  to the output shaft  120  is interrupted. In this way, the clutch assembly  130  protects the screwdriving bit  504  from excessively high torque. 
     Referring to  FIG. 19 , in an alternative use, the entire rear portion  114  of the input shaft  112 , and at least a portion of the spacer sleeve  125  is received inside and coupled to a cavity of a nosepiece  602  of a drywall screwgun  600 . The spacer sleeve  125  provides clearance for the nosepiece  602  to move axially relative to the input shaft  112  without releasing the input shaft  112  to actuate the clutch (not shown) that is inside the nosepiece  602 . The structure and operation of the clutch inside of the nosepiece  602  is well understood to those of ordinary skill in the art. A bit, e.g., a screwdriving bit  604  is received in and coupled to the recess  126  of the output shaft  120  to drive a fastener, e.g., a screw  606  into a workpiece W. The clutch  150  is engaged and the screwgun  600  is actuated by the user to drive the screw  606  into the workpiece. If the torque input to the input shaft  112  exceeds a predetermined amount (e.g., when the torque output from the power tool exceeds the torque rating on the clutch assembly), the spring  142  expands, and the rollers  136  escape from the grooves  138  on the input shaft  112  so that no torque transmission from the input shaft  112  to the output shaft  120  is interrupted. In this way, the clutch assembly  130  protects the screwdriving bit  604  from excessively high torque. 
     Referring to  FIG. 16 , in a third embodiment, a tool  210  for use with a power tool has a generally cylindrical input shaft  212 , a generally cylindrical output shaft  220 , and a clutch assembly  230  that are substantially the same as the input shaft  112 , the output shaft  112  and the clutch assembly  130  of the second embodiment of the tool  110 . The third embodiment of the tool  230  differs from the second embodiment of the tool  110  only in that the output shaft  220  is integrally coupled to a tool bit  222  (e.g., a screwdriving bit or a drill bit) so that the tool  210  functions as a tool bit, as opposed to a tool bit holder. 
     Referring to  FIG. 17 , in a fourth embodiment, a tool  310  for use with a power tool has a generally cylindrical input shaft  312 , a generally cylindrical output shaft  320 , and a clutch assembly  330  that are substantially the same as the input shaft  112 , the output shaft  112  and the clutch assembly  130  of the second embodiment of the tool  110 . The fourth embodiment of the tool  330  differs from the second embodiment of the tool  110  only in that the output shaft  320  includes a front portion  333  having a hex-shaped recess  326  that is configured to receive a head of a screw or a nut, so that the tool  320  functions as a nutdriver. There may be a magnet (not shown) disposed in the recess  326  to facilitate holding a screw or nut in the recess. 
     Numerous modifications may be made to the exemplary implementations described above. For example, a different design for the clutch can be used, such as by using round recesses and openings in the input and output shafts, and balls instead of pins. In addition, other types of springs may be used in the clutch. Further, the tension on the springs may be user adjustable to adjust the threshold torque setting of the clutch. Also, the tool holder can include other mechanisms for holding a bit instead of a magnet, such as spring clips and/or spring loaded balls. These and other implementations are within the scope of the invention.