Patent Publication Number: US-8122971-B2

Title: Impact rotary tool with drill mode

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/654,111 filed Jan. 17, 2007, which is a divisional of U.S. application Ser. No. 11/225,784 filed Sep. 13, 2005, now U.S. Pat. No. 7,410,007, the entire contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to power tools, and in particular to an impact rotary tool capable of switching between different modes of operation. 
     A conventional combination drill may provide more than one mode of operation. For example, a first mode, referred to as a drill mode, provides continuous rotation of the output spindle without torque limitation during drilling operations. A second mode, referred to as an impact mode, provides the output spindle with impacting blows to rotate the output shaft in an impacting fashion. 
     Despite the convenience of a dual mode tool, it would still be desirable to provide a tool where the output torque can be adjusted to limit the potential for stripping the heads or threads of fasteners due to excess torque from the tool. 
     BRIEF SUMMARY 
     The present invention provides an impact rotary tool that can be selectively switched between an impact mode and a drill mode. The impact rotary tool includes an impact mechanism with a hammer block connected to a drive shaft and an anvil that is disposed concentrically with the drive shaft and configured to be selectively engaged by the hammer block. When the impact rotary tool is in the impact mode, the hammer block is movable along a longitudinal axis of the drive shaft against the biasing force of a spring and the hammer block reciprocatingly engages the anvil causing it to rotate. When the impact rotary tool is in the drill mode, the hammer block substantially constantly engages the anvil causing the anvil to rotate. 
     The impact rotary tool includes a mode selector to selectively transfer operation between an impact mode and a drill mode. When the mode selector is in the impact position, the stopper does not engage the hammer block. When the mode selector is in drill mode, the stopper engages the hammer block to maintain substantially constant contact between the hammer block and the anvil. 
     The present invention also provides an impact rotary tool that can selectively transfer operation between an impact mode, a drill mode, and a driving mode. 
     Advantages of the present invention will become more apparent to those skilled in the art from the following description of the preferred embodiments of the invention that have been shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modification in various respects. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial exploded view of the internal components forming the clutch and impact mechanisms of an first representative embodiment of an impact rotary tool according to the present invention; 
         FIG. 2  is a perspective view with a portion of the housing removed to show the impact rotary tool in an impact mode; 
         FIG. 3  is the view of  FIG. 2  in a driver mode; 
         FIG. 4  is the view of  FIG. 2  in a drill mode; 
         FIG. 5  is an exploded view of the components forming the motor and planetary gear train; 
         FIG. 6  is a front view of the mode selector and the components associated with the front gearbox housing in an impact mode; 
         FIG. 7  is the view of  FIG. 6  shown in a driver mode; 
         FIG. 8  is the view of  FIG. 6  shown in a drill mode; 
         FIG. 9  is a view of one half of the housing supporting the components of the rear gearbox housing; 
         FIG. 10  is a cross-sectional view of the internal components of a second embodiment of an impact rotary tool, showing the impact rotary tool in a drill or driver mode; 
         FIG. 11  is a cross-sectional view of the impact rotary tool of  FIG. 10 , showing the tool in an impact mode; 
         FIG. 12  is a cross-sectional view of the internal components of a third representative embodiment of an impact rotary tool, showing the impact rotary tool in an impact mode; and 
         FIG. 13  is a cross-sectional view of the impact rotary tool of  FIG. 12 , showing the tool in a drill or a driver mode. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1-4 , an impact rotary tool  10  according to the present invention is shown. The impact rotary tool  10  is selectively switchable between an impact mode, a drill mode, and a driver mode. Details of the structure used to establish the driver mode and select the desired maximum output torque of the impact rotary tool  10  are described in commonly assigned U.S. Ser. No. 11/090,947, which is fully incorporated herein by reference. 
     The impact rotary tool  10  includes a housing  12 , ( FIG. 9 ) (a second complementary piece is not shown), a motor  11  for generating torque, and a speed reduction gearbox  14 . The speed reduction gearbox  14  includes a rear gearbox housing  26  ( FIG. 5 ) and a front gearbox housing  28 . The speed reduction gearbox  14  is mounted within the housing pieces  12  and rotatably connects the output shaft (not shown) of the motor  11  to the drive shaft  18  via a clutch mechanism  16 . The clutch mechanism  16  is capable of switching the impact rotary tool  10  between a drill mode and a driver mode of operation as further described below and in U.S. Ser. No. 11/090,947. The drive shaft  18  is connected to an impact mechanism  17  that is connected to an output spindle  76  (that is shown as formed with an anvil) and chuck  100  adapted to securely grasp a tool bit for engaging a workpiece. 
     The impact mechanism  17  includes a hammer block  70 . The hammer block  70  is cup shaped with a front face from which at least one projection  72  extends toward the front of the tool. Desirably, the hammer block  70  has two projections  72 . The hammer block  70  has a central aperture through which the shaft extends. A cavity is defined between an inner peripheral wall adjacent the shaft and an outer peripheral wall spaced from the inner peripheral wall. The cavity has a size suitable to receive a spring  78 , as described in more detail below. 
     The hammer block  70  is rotated by the drive shaft  18  based on torque ultimately received from the motor  11  and transferred through the gearbox  14 . The hammer block  70  rotates along with the drive shaft  18  but can move in a direction parallel to the longitudinal axis of the drive shaft  18 , when the impact rotary tool  10  is placed in impact mode. The hammer block  70  is held stationary with respect to the drive shaft  18  when the impact rotary tool  10  is in either a drill or a driver mode. 
     The portion of the inner wall of the hammer block  70  includes a groove  73 . A bearing (not shown) is located radially between drive shaft  18  and the groove  73  in the portion of the inner peripheral wall to form a cam mechanism. When the impact rotary tool  10  is in the impact mode, the drive shaft  18  rotates the hammer block  70  and the cam mechanism provides a relatively frictionless surface for the hammer block  70  to selectively translate longitudinally along the longitudinal axis of the drive shaft  18 . 
     In the impact mode, the hammer block  70  selectively engages an anvil  76  to transfer torque to the anvil  76 . The anvil  76  includes radially extending arms  77  that can be engaged by the projection  72  on the hammer block  70 . The hammer block  70  is biased in a direction toward the anvil  76  by a spring  78  that fits within the cavity and is retained in position by a spring plate  79 . When the drive shaft  18  rotates, at least one projection  72  rotatingly engages the arms  77  on the anvil  76  to transfer torque to spin the anvil  76 . Eventually, the counter-torque felt on the anvil  76  due to the operation of the output tool on a workpiece (not shown) increases in magnitude relative to the torque provided to the hammer block  70 . In this situation, the hammer block  70  feels less resistance by translating laterally along the cam with respect to the drive shaft  18  in a direction away from the anvil  76  until the hammer block  70  no longer engages the anvil  76 . As the hammer block  70  translates longitudinally away from the anvil  76 , the spring  78  compresses and gains potential energy. 
     After the spring  78  is sufficiently compressed, the amount of potential energy within the spring  78  becomes large enough to decompress the spring  78  and accelerate the hammer block  70  along the longitudinal axis of the drive shaft  18 , as aided by the cam, toward the anvil  76 . The front face of the hammer block  70  strikes the arm  77  of the anvil  76  and, because the hammer block  70  is rotating, the projections contact the arms  77  to rotate the anvil  76 . After the initial impact, the counter-torque again may again be relatively high compared to the torque in the hammer block  70  such that the hammer block  70  translates away from the anvil  76  along the cam and the impacting cycle continues and the anvil  76  (and output tool) rotates in an impacting or pulsating manner. 
     As best seen in  FIGS. 3 and 4 , (driver and drill mode, respectively) the hammer block  70  is prevented from translating in the longitudinal direction along the drive shaft  18 . As a result, the projections  72  continuously contact the arms  77  of the anvil  76  and are not permitted to slip from contact (as in the impact mode). In other words, all the torque transferred to the hammer block  70  is transferred to the anvil  76  and the anvil  76  rotates smoothly. 
     A stopper  80 , best seen in  FIG. 1 , is provided and, depending on the selected mode, the stopper can prevent the hammer block  70  from translating with respect to the drive shaft  18  (driver and drill mode) or allow it to translate (impact mode). The stopper  80  is annular with a central bore that surrounds the drive shaft yet allows the stopper to move along the drive shaft  18 . To prevent the stopper  80  from rotating with respect to the drive shaft  18 , the central bore has a flat portion  80   a  along a chord that engages a corresponding flat region  18   a  of the drive shaft. The flat portion  80   a  of the stopper  80  and the flat region  18   a  of the drive shaft  18  interact to prevent the stopper  80  from rotating with respect to the drive shaft  18 . 
     The stopper  80  includes two arms  81  that extend axially from a forward surface of the stopper  80 . The stopper  80  also includes an aperture  80   b  that extends through a diameter of the stopper  80  along an axis parallel to the front surface of the stopper  80  and perpendicular to the flat portion  80   a  of the center hole. 
     When the stopper  80  is moved to the forward position within the tool, (the structure to move the stopper  80  is discussed below) the stopper arms  81  engage a rear member  71  ( FIGS. 2 and 3 ) formed on the inner peripheral wall of the hammer block  70  to prevent longitudinal movement of the hammer block  70  away from the anvil  76 . Because the hammer block  70  cannot move along the longitudinal axis of the drive shaft  18 , the projections  72  from the hammer block  70  continually contact with the arms  77  of the anvil  76 , and the torque felt by the hammer block  70  is smoothly transferred to the anvil. 
     The drive shaft  18  includes a longitudinal slot  83  that extends along a plane perpendicular to the flattened region on the engagement portion  18   a  of the drive shaft  18 . A first pin  84  is respectively inserted through the aperture in the stopper  80  and through the longitudinal slot  83  in the drive shaft  18 . Therefore, the stopper  80  can translate linearly with respect to the drive shaft  18  along the length bounded by the longitudinal slot  83 . 
     The drive shaft  18  additionally contains a hollow cavity that runs through the length and along the longitudinal axis of the drive shaft  18 . A blind section  18   d  of the cavity extending from the forward end toward the rear end has a diameter greater than the section of the cavity behind the blind section  18   d  that extends to the rear end of the drive shaft  18  to define a flange  18   e . In some embodiments, the blind section  18   d  of the cavity may be hexagonal shaped. 
     A biasing mechanism  19  that includes a first leg  87 , a flange  87   a , and a spring  85  are disposed within the blind section  18   d  of the cavity. The biasing mechanism  19  is retained within the cavity by a cap  86 . The flange  87   a  has a diameter such that it abuts flange  18   e  to prevent rearward travel of the biasing mechanism  19 . The rear end of the first leg  87  is positioned within the drive shaft  18  forward of the first pin  84  and the first leg  87  is movable within the drive shaft  18  along the range of potential motion of the first pin  84  within the longitudinal slot  83 . 
     In addition, the spring  85  has not end that rests against the flange  87   a  while the other end contacts the cap  86 , to bias the biasing mechanism  19  in a rearward direction. Although this biasing force is not sufficient to prevent the forward motion of the first pin  84  and the first leg  87  within the drive shaft  18 , when the force that moves the first pin  84  forward is removed, the biasing force of the spring  85  moves the first leg  87  and the first pin  84  rearwardly away from the anvil  76 .  FIG. 2  shows the flange  87   a  and the first leg  87  biased to the rear position of the slot  83  by the spring  85 .  FIGS. 3 and 4  show the flange  87   a  and the first leg  87  in the forward position within the drive shaft  18  and further compressing the spring  85 . 
     The first leg  87  and the first pin  84  are moved in the forward direction within the drive shaft  18  when the first pin  84  is pressed forward by the second leg  92 . The second leg  92  is provided with a forward end inserted into the drive shaft  18  cavity so that it contacts the first pin  84  and extends out of the rear end of the drive shaft  18 .  FIGS. 2-4  show the engagement between the forward end of the second leg  92  and the first pin  84  within the drive shaft  18 . 
     As seen in the figures, the rear end of the drive shaft  18  is inserted into the hollow planet carrier  36 , which extends through the length of the body portion  28   a  and into the shoulder portion  28   b  of the front gearbox housing  28 . As seen in  FIG. 1 , the forward end of the planet carrier  36  includes a slot  88 . The slot  88  accepts a pin  89  that can be moved within the slot  88  based on corresponding forward motion of a link  90  through mutual engagement of the link  90  and the pin  89  with a spacer  91 . The pin  89  also contacts the rear end of the second leg  92  such that forward motion of the pin  89  within the slot  88  causes the second leg  92  to move forward within the drive shaft  18 , causing forward motion of the first pin  84 , first leg  87  and flange  87   a , which compresses the spring  85 . When the link  90  no longer forces the components forward, the biasing force of the spring  85  causes the first leg  87 , the first pin  84 , the second leg  92 , and the second pin  89  to move rearwardly away from the anvil  76 . 
     Each end of the second pin  89  extends out of the slot  88  in the planet carrier  36  and is accepted into holes  91   a  formed along a diameter of a spacer  91 . The spacer  91  also has an indented portion  91   b  that is adapted to retain an arcuate portion  90   c  of the link  90 , as discussed below. 
     As best seen in  FIG. 1 , the shoulder portion  28   b  of the front gearbox housing  28  has a recessed section  28   c  with an outer diameter that is movably engaged by a sleeve  94 . The recessed section  28   c  additionally includes two longitudinal slots  96  (only one shown in the figures, which is representative) arranged along a single plane. The slots  96  are the same width as the recessed section  28   c . A link  90  is provided with two arms  90   a ,  90   b  that extend away from each other along the same line and an arcuate section  90   c  connecting the arms  90   a ,  90   b . The arcuate section  90   c  is enclosed within the hollow center of the shoulder portion  28   b  of the front gearbox housing  28  and within a curved indented portion  91   b  of the spacer  91  that surrounds the planet carrier  36 , through which the second pin  89  extends (along with the planet carrier  36 ). Each arm  90   a ,  90   b  of the link  90  extends through one of the slots  96  in the recessed section  28   c . Because both the second pin  89  and the link  90  engage the spacer  91 , longitudinal motion of either the link  90  or the second pin  89  causes the same longitudinal motion of the other of these components. 
     The sleeve  94  is formed in the shape of a “C” and is positioned over the recessed section  28   c  of the front gearbox housing  28 . The sleeve  94  includes two tracks  95  on opposite sides of the sleeve  94 . An arm  90   a ,  90   b  of the link  90  is inserted through a respective slot  96  in the first gearbox housing  28  and a track  95  of the sleeve  94 . Each track  95  is formed such that rotation of the sleeve  94  with respect to the front gearbox housing  28  causes the link  90  to translate linearly along the longitudinal axis of the slots  96  formed in the front gearbox housing  28 . 
     Each of the two tracks  95  have a first portion  95   a  and a second portion  95   b . The first portion  95   a  causes longitudinal motion of the respective arm along the slot in the recessed section  28   c  when the sleeve  94  is rotated with respect to the front gearbox housing  28 . The second portion  95   b  maintains the arms in the forward end of the slot when the sleeve  94  is rotated further with respect to the front gearbox housing  82 , i.e. the second portion  95   b  of the track  95  is perpendicular to the second slot  88  when the sleeve  94  is on the front gearbox housing  28 . 
     As will be discussed below, when the arms  90   a ,  90   b  are each at the rear end of the first portion  95   a  of each track  95  (shown in  FIG. 2 ), the tool is in impact mode. When the arms are at the vertex between the two portions  95   a ,  95   b  of the tracks  95  (shown in  FIG. 3 ), the impact rotary tool is in driver mode. When the arms are at the end of the second portion  95   b  of the track  95  (shown in  FIG. 4 ), the impact rotary tool is in drill mode. 
     As discussed above, the pin  89  engages the rear end of the second leg  92 . Therefore, when the sleeve  94  is rotated to cause the link  90  to move forward within the track  95 , the second leg  92  also moves forward within the drive shaft  18  because of the forward movement of the second pin  89 . As discussed above, this forward motion of the second leg  92  causes forward motion of the first pin  84 , the stopper  80 , and the first leg  87 , which further compresses the spring  85 . When the stopper  80  moves forward, it engages the hammer block  70  and prevents any rearward motion of the hammer block  70 . Therefore, the hammer block  70  makes constant contact with the anvil  76  to rotate it in a smooth fashion. When the sleeve  94  is rotated in the opposite direction, the link  90  and the second pin  89  translate rearwardly within the tool; releasing the force that compresses the spring  85  within the blind cavity  18   d . The spring  85  then expands, biasing the first leg  87  and first pin  84  rearwardly. The stopper  80  also moves rearwardly and no longer contacts the hammer block  70  allowing the hammer block  70  to reciprocate along the drive shaft  18 . 
     The sleeve  94  additionally includes a plurality of tabs  94   b  that extend radially from its outer circumference. The tabs  94   b  are oriented to fit within a plurality of keyways  41  formed within the mode selector  40 . The mode selector  40  surrounds the sleeve  94  and the recessed section  28   c  of the front gearbox housing  28 . The mode selector  40  includes a handle  43  that extends out of the tool housing  12  to allow the user to rotate the mode selector  40  to change the mode of operation of the impact rotary tool. Because the tabs  94   b  of the sleeve  94  are engaged within the keyways  41  on the mode selector, rotation of the mode selector  40  causes simultaneous rotation of the sleeve  94 , which allows the impact rotary tool  10  to switch between impact mode and drill or driver modes, as discussed above. The movement of the mode selector  40  between the drill mode position and the driver mode position switches the tool between these modes by engaging and disengaging the clutch mechanism  16 , in the manner that is discussed below. 
     As mentioned above, the impact rotary tool includes a motor  11  to rotate the drive shaft  18  through a gearbox  14 . The impact rotary tool also includes a clutch mechanism  16  that allows the user to control the maximum amount of output torque applied to the output spindle when the tool is in driver mode (shown in  FIGS. 3 and 7 ). The clutch mechanism  16  is discussed in detail below. 
     As best seen in  FIG. 5 , the gearbox  14  includes at least one, and as shown in the figure, a pair of planetary gear sets  20  and  22  having a conventional structure for transmitting rotation or torque of the motor  12  and reducing the speed of the motor  11 . The shaft (not shown) of the motor  11  forms a sun gear (not shown) that rotatably engages the first planetary gear set  20 , which drives the second planetary gear set  22 . As can be appreciated by one of ordinary skill in the art, the first and second planetary gear sets  20  and  22  are arranged inside a rear gearbox housing  26  to provide a two-speed gear reduction between the output shaft of the motor  11  and the pinion gear  34  of the second planetary gear set  22 . A speed selector switch (not shown) may be provided on the rear gearbox housing  26  for selecting a high speed range for fast drilling or driving applications or a low speed range for high power and torque applications. When using the rotary tool  10  in the high speed range, the speed will increase and the drill will have less torque. When using the rotary tool  10  in the low speed range, the speed will decrease and the drill will have more torque. When the rotary tool  10  is operated in impact mode in the high speed range, the tool provides a maximum tightening torque for high torque applications. When the rotary tool  10  is operated in impact mode in low speed range, the tool provides less tightening torque to avoid over tightening that could lead to damage to soft surfaces or a fastener. 
     The gearbox  14  may further include a third planetary gear set  24  that is arranged inside the front gearbox housing  28  for cooperating with the clutch mechanism  16  to rotate the drive shaft  18 . The third planetary gear set  24  includes a ring gear  30  and a set of planetary gears  32 . The ring gear  30  is selectively rotatably disposed inside a body portion  28   a  of the front gearbox housing  28 . The body portion  28   a  of the front gearbox housing  28  is secured to the rear gearbox housing  26  ( FIG. 5 ), for example, using fasteners (not shown) that are received in threaded holes formed on the outer surface of the body portion  28   a  and corresponding through holes formed on a flange of the rear gearbox housing  26 . The planetary gears  32  mesh with the ring gear  30  and the pinion gear  34  of the second planetary gear set  22 . The planetary gears  32  are rotatably supported on axial projections  36   a  of a planet carrier  36  that is coupled to the rear end of the drive shaft  18  for rotation therewith. The drive shaft  18  is rotatably received inside a shoulder portion  28   b  of the front gearbox housing  28 . As best seen in  FIG. 1 , both the rear end of the drive shaft  18  and the forward internal circumference of the planet carrier  36  may be formed and connected together with spline connections to prohibit any relative rotation between the two and transfer the torque felt on the planet carrier  36  to the drive shaft  18 . 
     The pinion gear  34  of the second planetary gear set  22  operates as a sun gear to drive the planetary gears  32  of the third planetary gear set  24 . If the ring gear  30  is rotatably fixed inside the body portion  28   a  of the front gearbox housing  28 , the planetary gears  32  will orbit the pinion gear  34  to drive the planet carrier  36  and the drive shaft  18  to rotate about the axis of the pinion gear  34 . This arrangement positively transmits torque from the pinion gear  34  to the drive shaft  18 . In contrast, if the ring gear  30  is allowed to rotate or idle inside the front gearbox housing  28 , the pinion gear  34  may not transmit torque to the drive shaft  18  and may instead drive the planetary gears  32  to spin about their own axis on the axial projections  36   a  of the carrier  36 . 
     A plurality of protrusions  30   a  are formed circumferentially on the outer shoulder of ring gear  30  for cooperating with the clutch mechanism  16  to selectively inhibit the ring gear  30  from rotating relative to the front gearbox housing  28 , as described in further detail below. The protrusions  30   a  are arranged to cooperate with a set of pass through openings  38  that are formed circumferentially in the body portion  28   a  of the front gearbox housing  28  and that extend through the body portion  28   a.    
     The clutch mechanism  16  includes a set of link members  46 , a mode selector  40 , and a set of bypass members  44 . Each opening  38  in the body portion,  28   a  movably receives at least one link member  46 , for example, a cylindrical or spherical member, therein. The mode selector  40 , for example, in the form of a ring, is rotatably mounted on the shoulder portion  28   b  of the front gearbox housing  28  and is axially fixed on the recessed section  28   c  immediately adjacent the body portion  28   a . The mode selector  40  is provided with a notch spring (not shown) that cooperates with one or more notches (not shown) formed on the body portion  28   a  to secure the mode selector  40  when it is rotated between the different positions, as described in further detail above and below. 
     A single opening or, as shown, a plurality of openings  42  are formed circumferentially on the mode selector  40  to cooperate with the pass through openings  38  in the body portion  28   a . Each opening  42  in the mode selector  40  movably receives a bypass member  44  therein, for example, in the form of a spherical member, a pin having a hexagonal, square, or circular cross section, or other shapes. In this way, the link members  46  abut against the shoulder of ring gear  30  at one end of the body portion  28   a  and the bypass members  44  at the opposite end of the body portion. 
     A retaining washer  48  and a spring  50  are loosely supported on the shoulder portion  28   b  of the front gearbox housing  28  in front of the mode selector  40 . The spring  50  presses against the retaining washer  48  to urge the bypass members  44  into engagement with the link members  46  so as to bias the link members  46  against the shoulder of the ring gear  30 . 
     The spring  50  is disposed between the retaining washer  48  and an annular spring seat  52 . The spring seat  52  is non-rotatably fitted over the shoulder portion  28   b  of the front gearbox housing  28 . The inner surface of the spring seat  52  and the outer surface of the shoulder portion  28   b  have cooperating surfaces such that the spring seat  52  is moveable only in an axial direction relative to the shoulder portion  28   b . For example, 13 radial projections formed on the inner surface of the spring seat  52  are received in corresponding axial slots or grooves formed on the shoulder portion  28   b.    
     The spring seat  52  has a threaded outer portion to engage a threaded inner portion of a torque adjustment shroud  54  to vary the force acting on the retaining washer  48 . The torque adjustment shroud  54  is axially fixed to the front gearbox housing  28  with the use of a cap  58  that surrounds the periphery of the torque adjustment shroud  54 . The cap  58  is connected to the front gearbox housing  28  with a plurality of fasteners (not shown) to retain the torque adjustment shroud  54  in position. 
     This arrangement allows the torque adjustment shroud  54  to rotate relative to the housing  28 . Rotation of the torque adjustment shroud  54  causes the threaded inner portion to engage and move the spring seat  52  in an axial direction. The direction of rotation of the torque adjustment shroud  54  determines whether the spring seat  52  is moved against or away from the spring  50  for increasing or decreasing the force acting on the retaining washer  48 . 
     As best seen in  FIGS. 6 and 8 , in each of the impact and drill modes, the mode selector  40  is rotated to a first position such that the openings  42  in the mode selector  40 , and the bypass members  44  received therein, are oriented away from the openings  38  in the body portion  28   a . In this way, the link members  46  inside the openings  38  are axially blocked between the shoulder of ring gear  30  and the mode selector  40 . This arrangement causes the protrusions  30   a  on the shoulder of the ring gear  30  to firmly engage the link members  46  so as to prevent the ring gear  30  from rotating inside the front gearbox housing  28 . Accordingly, the motor  11  will drive the drive shaft  18  for sustained rotation without any torque limitation of the ring gear  30 . 
     As best seen in  FIG. 7 , in the driver mode the mode selector  40  is rotated to a position such that the openings  42  are aligned with the openings  38  in the body portion  28   a . As a result, the link members  46  and the bypass members  44  can be displaced forward in an axial direction against the force of the retaining washer  48  and the spring  50 . If the load on the output shaft is sufficient to overcome the torque on the ring  30 , the ring gear  30  will lift the link members  46  over the protrusions  30   a  so as to rotate inside the front gearbox housing  28 . In particular, the protrusions  30   a  have a ramped surface for biasing the link members  46  axially when the ring gear  30  rotates. When the ring gear  30  is made rotatable in this way, the motor  11  will not transmit torque to the drive shaft  18 . In the driver mode, the torque limitation of the ring gear  30  is adjusted by rotating the torque adjustment shroud  54  to vary the spring force acting on the retaining washer  48 , as described above. 
     Therefore, this arrangement for the clutch mechanism  16  using the mode selector  40  to block the link members  46 , as described above, allows a user to switch between the drill and driver modes of operation without affecting the torque limitation setting of the drive mode. 
     A second embodiment of the impact rotary tool is shown in  FIGS. 10 and 11 . The second embodiment includes many of the standard features of an impact rotary tool  200  including a motor (not shown) and a gear train (not shown) that provides an output to rotate the spindle  210 . The structure disclosed in this second embodiment also allows the impact rotary tool  200  to operate in either impact mode, as shown in  FIG. 11 , or in drill or driver mode, as shown in  FIG. 10 . The gear train includes a clutch mechanism (not shown) that is similar in structure and operation to that described in the first embodiment above, and fully disclosed in commonly owned U.S. patent application Ser. No. 11/090,947, which is fully incorporated by reference herein. 
     The spindle  210  includes a forward engaging end  216  that can selectively engage either a rear end of an inner shaft  220  through a spline connection  216 ,  224  to transfer the torque ultimately from the motor to the inner shaft, or can engage a bracket  226  that is coupled with an outer shaft  230  to transfer torque to the outer shaft  230 . The outer shaft  230  is coaxial with and surrounds the inner shaft  220 , although the two shafts are assembled to allow either shaft to rotate without the other shaft rotating. 
     Each of the inner shaft  220  and the outer shaft  230  can be selectively engaged with the output shaft  240  to provide torque to rotate a tool that is connected to the output shaft  240  by a chuck  250 , depending on the mode of tool operation selected by the user. 
     As shown in  FIG. 10 , the impact rotary tool  200  is oriented in a drill or a driver mode. The inner shaft  220  is engaged with the spindle  210  and the forward end  222  of the inner shaft  220  engages a rear end of the output shaft  240  through a spline connection to transfer torque to the output shaft  240 . In this orientation, the output shaft  240  freely rotates with respect to the anvil  244 , which remains stationary. Because the anvil  244  and the outer shaft  230  do not rotate in this orientation, the hammer block  260  also remains stationary. A spring  236  is positioned between the forward end  222  of the inner shaft  220  and the rear end  242  of the output shaft  240 . The spring  236  operates to bias the inner shaft  220  rearwardly such that when the inner shaft  220  is not being driven by the spindle  210 , the inner shaft  220  does not engage the output shaft  240  through the spline connection. 
     As shown in  FIG. 11 , the impact rotary tool  200  is oriented in an impact mode. The rear end  232  of the outer shaft  230  is connected to the bracket  226 , which can engage the forward end of the spindle  210  through a spline connection. In this orientation, the inner shaft  220  does not engage the spindle  210  and therefore does not rotate with the spindle. As shown in  FIG. 11 , the outer shaft  230  rotates with the spindle  210 , which causes the hammer block  260  to also rotate. The hammer block  260  is rotatably connected to the outer shaft through a cam  270  that operates with a bearing (not shown) riding within a recess  238  formed in the outer shaft  230 . The hammer block  260  includes projections  262  that selectively engage arms  246  that extend from anvil  244  to transfer torque to spin the anvil  244 . The hammer block  260  translates parallel to the longitudinal axis of the outer shaft  230  with the motion of the cam  270  against the biasing force of a spring  266  to make repeated reciprocating contact with the anvil  244 . 
     The anvil  244  engages the output shaft  240  of the driver when the tool  200  is in impact mode to transfer the reciprocating impact torque felt on the anvil  244  to the output shaft  240 . Because the hammer block  260 , anvil  244 , and the outer shaft  230  are stationary during operation of the impact rotary tool  200  in drill or driver modes, the impact rotary tool  200  is operated more efficiently because power is not needed to overcome the inertia to rotate these components and keep the hammer block  260  reciprocating. 
     A third embodiment of an impact rotary tool is shown in  FIGS. 12-13 . This embodiment includes many of the standard features of an impact rotary tool  300  including a motor (not shown) and a gear train (not shown) that provides an output to rotate the spindle  320 . The structure disclosed in this third embodiment also allows the tool to operate in either an impact mode, as shown in  FIG. 12 , or in a drill or a driver mode, as shown in  FIG. 13 . The gear train includes a clutch mechanism (not shown) that is similar in structure and operation to that described in the first embodiment above, and fully disclosed in commonly owned U.S. patent application Ser. No. 11/090,947, which is fully incorporated by reference herein. 
       FIG. 12  shows the impact rotary tool  300  in an impact mode. The impact rotary tool  300  includes a drive shaft  320  that is rotatably engaged by an input spindle (not shown), which receives torque ultimately from the motor through a gear train. The drive shaft  320  includes a center bore  324  that extends from the rear end of the drive shaft  320  through a majority of the length of the drive shaft  320  but does not extend through the front end of the shaft  320 . A rod  350  is inserted into the bore  324  to extend out of the rear end of the drive shaft  320 . The drive shaft  320  additionally includes a cavity  327  that extends from the outer circumference of the drive shaft and intersects with the center bore  324 . A bracket  354  shaped as a ‘T” is positioned within the cavity  327  and is rotatably mounted to the drive shaft  320  with a pin  358 . The lower tip  355  of the bracket  354  extends within the volume that includes part of the center bore  324  and the cavity  327  and the forward end of the rod  350  that engages the rear of the lower tip  355  of the bracket  354 . 
     The bracket  354  is rotatably connected with the pinned connection to the drive shaft  320  so that it rotates with the movement of the rod  350  within the center bore  324  of the drive shaft  320 . For example, when the rod  350  is moved forward within the drive shaft  320 , the bracket rotates clockwise as shown in  FIG. 12 . The bracket  354  is biased to rotate in the counter-clockwise direction by a spring  353  positioned within the center bore  324  within the drive shaft, between the forward end of the center bore  324  and the forward end of the lower tip  355  of the bracket  354 . When the rod  350  is urged forward within the drive shaft  320 , the bracket  354  rotates so that the forward tip  356  rises above the outer circumference of the drive shaft  320  while also compressing the spring  353 . When the rod  350  is no longer urged forward within the drive shaft  320 , the spring  353  expands to rotate the bracket  354  in the counter-clockwise direction, which lowers the forward tip  356  of the bracket  354  and improves the rod  350  rearwardly through the center bore  324  of the drive shaft  320 . 
     The impact rotary tool  300  additionally includes a hammer block  330  that is connected to the drive shaft  320 . The hammer block  330  rotates based on the torque felt in the drive shaft  320  and also reciprocates parallel to the longitudinal axis of the drive shaft  320  against the biasing force of a spring  333 , similar to the operation of the hammer blocks discussed above. A cam formed with a steel ball  326  rides within a recess  325  within the drive shaft  320 . The operation of the cam is similar to the operation of the cams described above. 
     As with conventional impact rotary tools, and the embodiments discussed above, the hammer block  330  has projections  332  that make reciprocating contact with an anvil  340  to transfer the torque in the drive shaft  320  to the anvil  340  in an impacting fashion. The anvil  340  is connected to or integral with an output chuck  346  that holds an output tool (not shown), as is conventional in impact rotary tools. 
       FIG. 12  shows the impact rotary tool  300  in the impact mode. The bracket  354  is aligned (based on the position of the rod  350  within the center bore  324 ) such that the front end  356  is in line with the outer circumference of the drive shaft  320  and the hammer block  330  is free to reciprocate with respect to the drive shaft  320  and impart impacting blows on the anvil  340 . 
       FIG. 13  shows the impact rotary tool  300  in a drill or a driver mode. The bracket  354  is aligned (based on the position of the rod  324  within the center bore  324 ) such that the front end  356  of the bracket  354  extends above the circumference of the drive shaft  320  and prevents the hammer block  330  from moving rearwardly within the impact rotary tool  300 . Because the hammer block  330  is prevented from moving rearwardly, it makes substantially constant contact with the anvil  340  and therefore smoothly transfers the torque on the drive shaft to the anvil  340 . When the impact rotary tool  300  is transferred back to impact mode, the rod  350  is moved rearwardly and the spring  353  expands to rotate the bracket  354  in the counter-clockwise direction. This lowers the forward end  356  of the bracket  354  and again allows the hammer block  330  to reciprocate and impart impact blows to rotate the anvil  340 . 
     The rod  350  is moved within the center bore  324  of the drive shaft  320  based on the rotation of the switch  370 . In a preferred embodiment, the forward surface  372  of the switch has a ramped surface (not shown) which acts as a cam to move the rod  350  within the center bore  324  of the drive shaft  320 . Therefore, when the impact rotary tool  300  is in the impact mode, the switch  370  is oriented such that the ramp surface allows the bracket  354  (and rod  350 ) to be biased by the spring  353  into a position where the forward end  356  is in-line with the circumference of the drive shaft  320  to allow the hammer block  330  to reciprocate with respect to the drive shaft  320 . When the impact rotary tool  300  is switched to the drill or driver modes, the switch is rotated so that rod  350  engages a portion of the ramp surface that extends further forward and moves the rod  350  forward within the center bore  324  to rotate the bracket  354  clockwise against the biasing force of the spring  353  until the forward end  356  extends above the circumference of the drive shaft  320  to stop the hammer block  330  from reciprocating. 
     As discussed above, when the switch  370  is rotated to the impact mode, the spring  353  forces the lower tip  355  of the bracket  354  and the rod  350  rearward until the bracket  354  rotates counter-clockwise to allow the hammer block  330  to again reciprocate within the tool and impart impacting forces on the anvil  340 . The structure discussed in the embodiments above can be adapted to selectively move the rod  350  to change the mode of operation of the impact rotary tool  300 . Additionally, other methods of moving the rod  350  linearly within the drive shaft that are known to those of ordinary skill in the art can be used as well. 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.