Abstract:
A power tool with a multi-speed transmission and a switch mechanism for shifting the transmission between a plurality of different speed ratios. The switch mechanism includes a single switch member that is slidably mounted on the housing. The power tool further comprises a clutch having a clutch profile that is coupled to a ring gear of the transmission. In some examples, the power tool further comprises a clutch that is configured to interact with a first stage of the transmission.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. Ser. No. 12/966,678 filed Dec. 13, 2010, which is a continuation of U.S. application Ser. No. 12/362,825 filed Jan. 30, 2009 (now U.S. Pat. No. 7,900,714 issued Mar. 8, 2011), which is a continuation of U.S. application Ser. No. 11/237,112 filed Sep. 28, 2005 (now U.S. Pat. No. 7,537,064 issued May 26, 2009), which is a continuation of U.S. application Ser. No. 10/792,659 filed Mar. 3, 2004 (now U.S. Pat. No. 7,101,300 issued Sep. 5, 2006), which is a continuation-in-part of U.S. application Ser. No. 10/384,809 filed Mar. 10, 2003 (now U.S. Pat. No. 6,984,188 issued Jan. 10, 2006), which is a divisional of U.S. application Ser. No. 09/964,078 filed Sep. 26, 2001, entitled First Stage Clutch (now U.S. Pat. No. 6,676,557 issued Jan. 13, 2004), which claims the benefit of U.S. Provisional Application No. 60/263,379 filed Jan. 23, 2001. The entire disclosure of each of the above applications is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to power tools such as rotatable drills, power screwdrivers, and rotatable cutting devices. More particularly, the present disclosure relates to a clutch for a multi-speed transmission for a power tool. 
       BACKGROUND 
       [0003]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0004]    Modernly, manufacturers of power tools have introduced power tools that have variable speed motors in an attempt to permit the users of these tools with sufficient control over the output speed of the tool so as to permit them to perform diverse operations without resort to additional, specialized tools. Many of the tools that are commercially available include a three-stage, two-speed transmission that permits even greater control over speeds of these tools. 
         [0005]    Typically available transmission arrangements have lacked a transmission arrangement that could produce a wide range of output speeds and torques that would permit the tool to perform diverse operations such as drilling holes with a large diameter hole saw, installing drywall screws or large diameter lag screws, and performing high-speed drilling operations. The single or dual speed transmissions that were generally employed in these tools typically did not have sufficient speed reducing capacity to permit these transmissions to be diversely employed as configuring these tools for high torque operations tended to impair their high speed performance. Furthermore, the rechargeable batteries that were employed in many of the early cordless rotary power tools were not well suited for use in low-speed, high torque operations due to the amount of energy that is consumed and the rate with which the energy is consumed by the power tool during such operations. Consequently, consumers were often forced to purchase two different rotary power tools, a medium-duty tool for “standard” applications such as drilling and fastening, and a heavy-duty tool having a low-speed, high torque output for more demanding tasks. 
         [0006]    With the advent of the modern high capacity, high voltage battery, it is now possible to meet the energy demands of a power tool that is used in low-speed, high torque operations. There remains, however, a need in the art for a power tool transmission having a relatively large range in its speed reducing capacity. 
         [0007]    Typical clutch arrangements permit the user of the tool to limit the torque that is output by the last stage of the tool&#39;s transmission. These clutch arrangements commonly employ a spring that biases two portions of the clutch into engagement. When the torque that is output by the transmission exceeds the predetermined clutch setting, the biasing force exerted by the spring is not sufficient to maintain the portion of the clutch in an engaged condition and as such, one of the portions of the clutch is able to rotate relative to the other portion of the clutch. The relative movement of these two portions effectively inhibits the transmission of torque to the output shaft of the tool. 
         [0008]    The use of such clutch arrangements with a transmission having a relatively large speed reducing range is often times impractical for the simple reason that the biasing force that is exerted by the spring does not have sufficient range to permit the clutch portions to be properly engaged and disengaged over the entire speed reducing range. Accordingly, it is relatively common to supply several different sized springs with a clutch arrangement, necessitating that the user select and install an appropriately sized spring for a given task. While this approach has been effective, it is nonetheless time consuming and inconvenient. 
       SUMMARY 
       [0009]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0010]    In one form, the present disclosure provides a portable power tool that includes a motor, a transmission, an output member and a clutch assembly. The motor has an output shaft. The transmission has a plurality of planetary transmission stages that include a first planetary transmission stage and a second planetary transmission stage. Each of the plurality of planetary transmission stages includes a sun gear, a planet carrier, a plurality of planet carriers journally supported by the planet carrier and meshingly engaged to the sun gear, and a ring gear having internal teeth that are engaged by the plurality of planet gears. The sun gear of the first planetary transmission stage is directly driven by the output shaft of the motor. The ring gear of the first planetary transmission stage is not shared by another of the plurality of planetary transmission stages. The first planetary transmission stage receives an input torque from the motor and produces an intermediate output torque in response thereto that is transmitted to the second planetary transmission stage. The output member is drivingly coupled to the transmission on a side of the transmission opposite the motor. The clutch assembly has a clutch profile and an engagement assembly. The clutch profile is coupled to a side of the ring gear of the first planetary transmission stage that is opposite the motor. The engagement assembly is disposed between the ring gear of the first planetary transmission stage and the output member. The engagement assembly including a follower, a follower spring and an adjustment collar. The follower spring applies a biasing force that is transmitted to the follower member to bias the follower member into engagement with the clutch profile. The adjustment collar is movable to change a magnitude of the biasing force. The follower assembly cooperates with the clutch profile to inhibit rotation of the ring gear of the first planetary transmission stage only when the magnitude of the intermediate output torque is less than a selected maximum torque. 
         [0011]    In still another form, the present teachings provide a power tool that includes a housing, a motor, a transmission, an output member and a clutch assembly. The motor is received in the housing and has an output shaft. The transmission has a plurality of planetary transmission stages with a first planetary transmission stage and a second planetary transmission stage. Each of the plurality of planetary transmission stages has a sun gear, a plurality of planet gears meshingly engaged to the sun gear, and a ring gear with internal teeth that are engaged by the plurality of planet gears. The sun gear of the first planetary transmission stage is directly driven by the output shaft of the motor. The ring gear of the first planetary transmission stage is not shared by another of the plurality of planetary transmission stages. The first planetary transmission stage receives an input torque from the motor and produces an intermediate output torque in response thereto that is transmitted to the second planetary transmission stage. The output member is drivingly coupled to the transmission on a side of the transmission opposite the motor. The clutch assembly includes a clutch profile and an engagement assembly. The clutch profile is coupled to a side of the ring gear of the first planetary transmission stage that is opposite the motor. The engagement assembly is disposed axially between the ring gear of the first planetary transmission stage and a distal end of the output member. The engagement assembly includes a follower and an adjustment collar that is movable to change a magnitude of a biasing force exerted by the follower member onto the clutch profile. The follower assembly cooperates with the clutch profile to permit continuous rotation of the ring gear of the first planetary transmission stage relative to the housing when the magnitude of the intermediate output torque exceeds a selected maximum torque to thereby limit rotary power that is output through the output member to a selected maximum tool torque. The follower assembly also cooperates with the clutch profile to inhibit rotation of the first ring gear relative to the housing when the magnitude of the intermediate torque does not exceed the selected clutch torque. 
         [0012]    In a further form, the present teachings provide a power tool that includes a housing, a motor, a transmission, an output member and a clutch assembly. The motor is received in the housing and includes an output shaft. The transmission has a plurality of planetary transmission stages including a first planetary transmission stage and a second planetary transmission stage. The first planetary transmission stage is directly driven by the output shaft of the motor and includes a first ring gear that is not shared with any other of the plurality of transmission stages. The second planetary transmission stage has an axially movable member that is movable between a first position and a second position to permit the second planetary transmission to be selectively operated in two different speed reduction ratios for transmitting torque. The output member is driven by the transmission. The clutch assembly has a clutch profile, which is coupled to the first ring gear, and a follower assembly with a follower that is disposed axially between the first ring gear and an output component of the transmission. The follower is configured to engage and cooperate with the clutch profile to permit continuous rotation of the first ring gear relative to the housing when a magnitude of an intermediate torque output from the first planetary transmission stage exceeds a selected clutch torque and to inhibit rotation of the first ring gear relative to the housing when the magnitude of the intermediate torque does not exceed the selected clutch torque. 
         [0013]    In another form, the present teachings provide a power tool that includes a housing, a motor, a planetary transmission, a clutch assembly and a switch mechanism. The housing defines a motor cavity and a handle. The motor cavity defines a longitudinal axis of the power tool. The housing has first and second axial ends. The handle is disposed between the first and second ends such that the handle is axially offset from the first end and axially offset from the second end. The motor is received in the motor cavity and has an output shaft. The planetary transmission has a plurality of stages including a first stage, at least one intermediate stage and an output stage. The first planetary stage receives rotary power directly from the output shaft of the motor. The first planetary stage outputs rotary power to the at least one intermediate stage. The at least one intermediate stage outputs power to the output stage. The output stage has an output member that is coupled to output spindle. The transmission is operable in at least three different speed ratios. One of the plurality of stages has a ring gear. The clutch assembly includes a clutch profile and an engagement assembly. The clutch profile is coupled to the ring gear. The engagement assembly includes a follower and an adjustment collar. The adjustment collar is movable to change a magnitude of a biasing force exerted by the follower member onto the clutch profile. The switch mechanism is configured for shifting the transmission between the at least three different speed ratios. The switch mechanism includes a single switch member that is slidably mounted on the housing for movement between a first switch position, a second switch position and a third switch position. The transmission operates in a first speed ratio when the switch member is in the first position, a second speed ratio when the switch member is in the second position and a third speed ratio when the switch member is in the third position. 
         [0014]    In still another form, the present teachings provide a power tool that includes a housing, a motor, an output spindle, a transmission, a clutch assembly and a switch mechanism. The motor is received in the housing and has an output shaft. The transmission has a plurality of planetary transmission stages including a first planetary transmission stage and an output stage. The first planetary stage receives rotary power directly from the output shaft of the motor, while the output stage has an output member that is coupled to output spindle. The transmission is operable in a plurality of different speed ratios. The clutch assembly that includes a clutch profile and an engagement assembly. The clutch profile is coupled to the ring gear. The engagement assembly includes a follower and an adjustment collar. The adjustment collar is movable to change a magnitude of a biasing force exerted by the follower member onto the clutch profile. The follower assembly cooperates with the clutch profile to permit continuous rotation of the ring gear of the first planetary transmission stage relative to the housing when the magnitude of the intermediate output torque exceeds a selected maximum torque to thereby limit rotary power that is output through the output member to a selected maximum tool torque. The follower assembly also cooperates with the clutch profile to inhibit rotation of the first ring gear relative to the housing when the magnitude of the intermediate torque does not exceed the selected clutch torque. The switch mechanism is configured for shifting the transmission between the different speed ratios. The switch mechanism has a single switch member that is slidably mounted on the housing. 
         [0015]    In yet another form, the present teachings provide a power tool that includes a housing, a motor, an output spindle, a transmission, a clutch assembly and a switch mechanism. The motor is received in the housing and has an output shaft. The transmission has a plurality of planetary transmission stages including a first planetary transmission stage, at least one intermediate stage and an output stage. The first planetary stage receives rotary power directly from the output shaft of the motor. The first planetary stage has a ring gear and outputs rotary power to the at least one intermediate stage. The at least one intermediate stage outputs power to the output stage. The output stage has an output member that is coupled to output spindle. The transmission is operable in at least three different speed ratios. The clutch assembly includes a clutch profile and an engagement assembly. The clutch profile is coupled to the ring gear. The engagement assembly includes a follower and an adjustment collar. The adjustment collar is movable to change a magnitude of a biasing force exerted by the follower member onto the clutch profile. The follower assembly cooperates with the clutch profile to permit continuous rotation of the ring gear of the first planetary transmission stage relative to the housing when the magnitude of the intermediate output torque exceeds a selected maximum torque to thereby limit rotary power that is output through the output member to a selected maximum tool torque. The follower assembly also cooperates with the clutch profile to inhibit rotation of the first ring gear relative to the housing when the magnitude of the intermediate torque does not exceed the selected clutch torque. The switch mechanism is configured for shifting the transmission between the at least three different speed ratios and includes a single switch member that is slidably mounted on the housing for movement between a first switch position, a second switch position and a third switch position. The transmission operates in a first speed ratio when the switch member is in the first position, a second speed ratio when the switch member is in the second position, and a third speed ratio when the switch member is in the third position. 
         [0016]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0017]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0018]    Additional advantages and features of the present disclosure will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a side view of a power tool constructed in accordance with the teaching of the present disclosure; 
           [0020]      FIG. 2  is an exploded perspective view of a portion of the power tool of  FIG. 1 ; 
           [0021]      FIG. 3  is a perspective view of a portion of the housing of the power tool of  FIG. 1  illustrating the rear of the end cap assembly; 
           [0022]      FIG. 4  is a front view of the end cap assembly; 
           [0023]      FIG. 5  is a section view taken along the line  5 - 5  of  FIG. 4 ; 
           [0024]      FIG. 6  is a rear view of a portion of the power tool of  FIG. 1  with the end cap assembly removed; 
           [0025]      FIG. 7  is a side view of a portion of the power tool of  FIG. 1  with the end cap assembly removed; 
           [0026]      FIG. 8  is a view similar to that of  FIG. 4 , but illustrating the end cap shell prior to the overmolding operation; 
           [0027]      FIG. 9  is a view similar to that of  FIG. 5 , but illustrating the end cap shell prior to the overmolding operation; 
           [0028]      FIG. 10  is a view similar to that of  FIG. 4 , but illustrating an alternate construction of the overmold member; 
           [0029]      FIG. 11  is a partial sectional view of a portion of a power tool that employs an end cap assembly having an overmold member constructed in the manner illustrated in  FIG. 10 ; 
           [0030]      FIG. 12  is an exploded perspective view of a portion of the power tool of  FIG. 1 , illustrating the transmission assembly in greater detail; 
           [0031]      FIG. 13  is an exploded perspective view of a portion of the power tool of  FIG. 1 , illustrating the reduction gearset assembly, the transmission sleeve, a portion of the housing and a portion of the clutch mechanism in greater detail; 
           [0032]      FIG. 13   a  is a sectional view taken along a longitudinal axis of the second ring gear; 
           [0033]      FIG. 13   b  is a sectional view taken along a longitudinal axis of the third ring gear; 
           [0034]      FIG. 14  is a side view of the transmission sleeve; 
           [0035]      FIG. 15  is a rear view of the transmission sleeve; 
           [0036]      FIG. 16  is a sectional view taken along the line  16 - 16  of  FIG. 15 ; 
           [0037]      FIG. 17  is a sectional view taken along the line  17 - 17  of  FIG. 15 ; 
           [0038]      FIG. 18  is an exploded view of the reduction gearset assembly; 
           [0039]      FIG. 19  is a sectional view taken along a longitudinal axis of the power tool of  FIG. 1  illustrating a portion of the reduction gearset assembly in greater detail; 
           [0040]      FIG. 20  is a front view of a portion of the first reduction carrier; 
           [0041]      FIG. 21  is a sectional view taken along a longitudinal axis of the power tool of  FIG. 1  illustrating a portion of the reduction gearset assembly in greater detail; 
           [0042]      FIG. 22  is a rear view of a portion of the third reduction carrier; 
           [0043]      FIG. 23  is an sectional view taken along the longitudinal axis of the power tool of  FIG. 1  and illustrating the transmission assembly as positioned in the first speed ratio; 
           [0044]      FIG. 24  is a sectional view similar to that of  FIG. 23  but illustrating the transmission assembly as positioned in the second speed ratio; 
           [0045]      FIG. 25  is a sectional view similar to that of  FIG. 23  but illustrating the transmission assembly as positioned in the third speed ratio; 
           [0046]      FIG. 26  is a top view of a portion of the power tool of  FIG. 1  illustrating the speed selector mechanism in greater detail; 
           [0047]      FIG. 27   a  is a side view of the rotary selector cam; 
           [0048]      FIG. 27   b  is a top view of the rotary selector cam; 
           [0049]      FIG. 27   c  is a sectional view taken through along the central axis of the speed selector mechanism; 
           [0050]      FIG. 28  is a rear view of the output spindle assembly; 
           [0051]      FIG. 29  is an exploded perspective view of the clutch mechanism; 
           [0052]      FIG. 29   a  is a perspective view of a portion of the clutch mechanism illustrating another configuration of the clutch member; 
           [0053]      FIG. 29   b  is an exploded perspective view illustrating a multi-piece construction for the first ring gear and clutch member; 
           [0054]      FIG. 30  is a schematic illustration of the adjustment structure in an “unwrapped” state; 
           [0055]      FIG. 31  is a schematic illustration similar to that of  FIG. 30  but showing an alternate construction of the adjustment profile; and 
           [0056]      FIG. 32  is a schematic illustration similar to that of  FIG. 30  but showing a portion of another alternate construction of the adjustment profile; 
           [0057]      FIGS. 33 through 35  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a second transmission constructed in accordance with the teachings of the present disclosure; 
           [0058]      FIGS. 36 through 38  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a third transmission constructed in accordance with the teachings of the present disclosure; 
           [0059]      FIGS. 39 through 41  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a fourth transmission constructed in accordance with the teachings of the present disclosure; 
           [0060]      FIGS. 42 through 44  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a fifth transmission constructed in accordance with the teachings of the present disclosure; 
           [0061]      FIGS. 45 through 47  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a sixth transmission constructed in accordance with the teachings of the present disclosure; 
           [0062]      FIGS. 48 through 50  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a seventh transmission constructed in accordance with the teachings of the present disclosure; 
           [0063]      FIGS. 51 through 53  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of an eighth transmission constructed in accordance with the teachings of the present disclosure; and 
           [0064]      FIGS. 54 through 56  are sectional views similar to  FIGS. 23 through 25 , respectively, taken along the longitudinal axis of a ninth transmission constructed in accordance with the teachings of the present disclosure. 
       
    
    
       [0065]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0066]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0067]    With reference to  FIGS. 1 and 2  of the drawings, a power tool constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral  10 . As those skilled in the art will appreciate, the preferred embodiment of the present disclosure may be either a cord or cordless (battery operated) device, such as a portable screwdriver or drill (e.g., drill, hammer drill). In the particular embodiment illustrated, power tool  10  may be a cordless drill having a housing  12 , a motor assembly  14 , a multi-speed transmission assembly  16 , a clutch mechanism  18 , an output spindle assembly  20 , a chuck  22 , a trigger assembly  24  and a battery pack  26 . Those skilled in the art will understand that several of the components of power tool  10 , such as the chuck  22 , the trigger assembly  24  and the battery pack  26 , can be conventional in nature and need not be described in significant detail in this application. Reference may be made to a variety of publications for a more complete understanding of the operation of the conventional features of power tool  10 . One example of such publications is commonly assigned U.S. Pat. No. 5,897,454 issued Apr. 27, 1999, the disclosure of which is hereby incorporated by reference as if fully set forth herein. 
         [0068]    Housing  12  can include an end cap assembly  30  and a handle shell assembly  32  that can include a pair of mating handle shells  34 . Handle shell assembly  32  can include a handle portion  36  and a drive train or body portion  38 . Trigger assembly  24  and battery pack  26  can be mechanically coupled to handle portion  36  and can be electrically coupled to motor assembly  14 . Body portion  38  can include a motor cavity  40  and a transmission cavity  42 . Motor assembly  14  may be housed in motor cavity  40  and can include a rotatable output shaft  44 , which can extend into transmission cavity  42 . A motor pinion  46  having a plurality of gear teeth  46   a  may be coupled for rotation with output shaft  44 . Trigger assembly  24  and battery pack  26  cooperate to selectively provide electric power to motor assembly  14  in a manner that is generally well known in the art so as to control the speed and direction with which output shaft  44  rotates. 
         [0069]    Transmission assembly  16  may be housed in transmission cavity  42  and can include a speed selector mechanism  60 . Motor pinion  46  can couple transmission assembly  16  to output shaft  44 , transmitting a relatively high speed, low torque drive input to transmission assembly  16 . Transmission assembly  16  can include a plurality of reduction elements that can be selectively engaged by speed selector mechanism  60  to provide a plurality of speed ratios. Each of the speed ratios can multiply the speed and torque of the drive input in a predetermined manner, permitting the output speed and torque of the transmission assembly  16  to be varied in a desired manner between a relatively low speed, high torque output and a relatively high speed, low torque output. The transmission output may be transmitted to the output spindle assembly  20 , to which the chuck  22  may be coupled for rotation, to permit torque to be transmitted to a tool bit (not shown). The clutch mechanism  18  may be coupled to transmission assembly  16  and may be operable for limiting the magnitude of the torque associated with the drive input to a predetermined, selectable torque limit. 
       Functional Overmold 
       [0070]    With specific reference to  FIGS. 2 through 9 , end cap assembly  30  may include an end cap shell  100  and an overmold member  102 . In the example provided, the end cap shell  100  may be injection molded from a plastic material, such as ABS. The end cap shell  100  defines an end cap cavity  104  that may be sized to receive the portion of the motor assembly  14  that extends rearwardly of the handle shell assembly  32 . A plurality of first and second radial tab apertures  108  and  110  and an abutting face  127  can be formed into the forward face  114  of the end cap shell  100  and a plurality of screw bosses  116  can be formed into the perimeter of the end cap shell  100 . Each of the first and second radial tab apertures  108  and  110  may be sized to receive one of the first radial tabs  120  and second radial tabs  122 , respectively, that can be formed into the rearward face  124  of the handle shells  34 . The first and second radial tab apertures  108  and  110  can cooperate with the first and second radial tabs  122  to align the end cap shell  100  to the handle shell assembly  32 , as well as to inhibit relative rotation therebetween. An arcuate portion  128  of the forward face  114  of the end cap shell  100  may be angled to match the abutting face  132  of the rearward face  124  of the handle shells  34 . The screw bosses  116  can be employed to fixedly couple the end cap shell  100  to the motor cover  136  via a plurality of screws  138 . The geometry of the motor cover  136  may be such that it is constrained to the handle shells  34 . As such, fastening of the end cap shell  100  to the motor cover  136  can fixedly retain the end cap shell  100  against the rearward face  124  of the handle shell assembly  32 , as well as to close off the rear handle aperture  139  in the handle shell assembly  32 . 
         [0071]    A plurality of side apertures  140  can be formed into the sides of the end cap shell  100  to permit air to flow through the handle shell assembly  32  and cool the motor assembly  14  in a manner that is well known in the art. A plurality of rear apertures  144  can be formed into the rear of the end cap shell  100 , with each of the rear apertures  144  including a recessed portion  146 , which can extend partially into the outer surface  148  of the end cap shell  100 , and a through-portion  150  that can extend completely through the end cap shell  100 . A pair of retaining tabs  152  can be formed to extend from the interior surface  154  of the end cap shell  100  inwardly into the end cap cavity  104 . A channel  156  may be formed into the interior surface  154  of the end cap shell  100  and can intersect each of the rear apertures  144  and the retaining tabs  152 . 
         [0072]    The overmold member  102  may be formed from a resilient material, such as thermoplastic elastomer (e.g., HYTREL® manufactured by E.I. du Pont de Nemours and Company) and may be simultaneously formed and coupled to the end cap shell  100  in an injection molding operation. In the particular example provided, the overmold member  102  can include a plurality of bumper members  170 , a pair of isolators  172  and a linking member  174 . Each of the bumper members  170  can extend from a point roughly coincident with the interior surface  154  of the end cap shell  100  to a point rearwardly of the outer surface  148  of the end cap shell  100  by about 0.5 mm to about 1.5 mm and preferably about 0.75 mm. Construction in this manner permits the bumper members  170  to provide a degree of shock absorption which reduces the likelihood of damaging the end cap shell  100  in the event that the tool  10  is dropped. Furthermore, it is sometimes necessary for an operator to apply a relatively high force to the tool  10 , as when employing a hole saw to drill large diameter holes. In such situations, the operator is inclined to press onto the rear of the tool  10  to apply a force that is in-line with the axis of the chuck  22 . In such situations, the bumper members  170  provide the operator with a relatively soft and comfortable surface which tends to resist slipping as well as attenuate the vibrations that can be transmitted to the operator. 
         [0073]    The isolators  172  can be formed about the retaining tabs  152  on the interior surface  154  of the end cap shell  100 . In the example provided, each of the isolators  172  can include an annular member  180  that extends forwardly of the interior surface  154  of the end cap shell  100 . Construction in this manner permits the end cap shell  100  to engage the isolators  172  to the outer cylindrical surface  14   a  and the rear surface  14   b  of the motor housing  14   c  to fixedly retain the motor  14   d  within the motor cover  136 . This can prevent the components of the motor assembly  14  from moving along the longitudinal axis of the tool  10 , as well as dampen vibrations that can be created during the operation of the motor assembly  14 . The linking member  174  may be fixedly coupled to each of the bumper members  170  and the isolators  172 . The linking member  174  can provide a flow path through which the resilient material flows during the formation of the bumper members  170  and the isolators  172 . The linking member  174  can also interconnect the bumper members  170  and the isolators  172 , thereby rendering their removal from the end cap shell  100  more difficult. 
         [0074]    Those skilled in the art will appreciate that this aspect of the present disclosure may be incorporated into various other positions within the handle assembly  32  for sealing between two or more components, dampening vibrations or positioning one component relative to another. One such example is illustrated in  FIGS. 10 and 11  where the isolators  172  can be modified to extend around the perimeter of a portion of the end cap cavity  104  and sealingly contact the rear surface  14   b  of the motor  14   d . The isolators  172  seal the interface between the end cap shell  100  and the motor assembly  14 , while the bumper members  170  seal the rear apertures  144  in the end cap shell  100 . The space  188  defined by the isolators  172  can be filled with grease or another suitable lubricant, which lubricates a motor armature bearing  190 . 
       Transmission Assembly 
       [0075]    With reference to  FIG. 12 , the transmission assembly  16  may be a three-stage, three-speed transmission that may include a transmission sleeve  200 , a reduction gearset assembly  202  and the speed selector mechanism  60 . With additional reference to  FIGS. 13 through 17 , the transmission sleeve  200  may include a wall member  210  that can define a transmission bore or hollow cavity  212  into which the reduction gearset assembly  202  may be disposed. The transmission sleeve  200  can include a body  214  and a base  216 . The body  214  of the transmission sleeve  200  may be fairly uniform in diameter and can be generally smaller in diameter than the base  216 . The inside diameter of the base  216  may be sized to receive the cylindrical nose portion  220  of the motor cover  136 . 
         [0076]    A plurality of raised lands  226  can be formed into the base  216 . The raised lands  226  can define a plurality of first grooves  228  in the outer surface  230  of the base  216  and a plurality of second grooves  232  in the inner surface  234  of the base  216 . The first grooves  228  can be configured to receive the alignment ribs  238  that can be formed into the inner surface  242  of the handle shells  34  to align the transmission sleeve  200  to the handle shells  34  and inhibit relative rotation between the transmission sleeve  200  and the housing  12 . The first grooves  228  and alignment ribs  238  can be configured in a manner that the transmission sleeve  200  can only be assembled to the handle shells  34  in one orientation (i.e., the configuration of the first grooves  228  and alignment ribs  238  prevents the transmission sleeve  200  from being rotated 180° out of position relative to the handle shells  34 ). The second grooves  232  will be discussed in greater detail, below. 
         [0077]    The body  214  of the transmission sleeve  200  may include a cylindrical body portion  246  and a pin housing portion  248 . In the particular embodiment illustrated, the cylindrical body portion  246  can include a selector cam guide  250 , a plurality of lubricant grooves  252  and first and second sets of ring engagement teeth  254  and  256 , respectively. The selector cam guide  250  may be generally rectangular in cross section, extending outwardly from the top of the outer surface  258  of the body portion  246 . The lubricant grooves  252  can be formed concentrically around the upper half of the perimeter of the body portion  246 . The lubricant grooves  252  have a depth of about 0.01 inch to about 0.030 inch to hold a lubricant, such as grease, on the upper half of the perimeter of the body portion  246 . The operation of the selector cam guide  250  and the lubricant grooves  252  will be discussed in detail, below. 
         [0078]    A raised bead  264  can segregate the interior of the body portion  246  into first and second housing portions  260  and  262 , respectively. The first set of ring engagement teeth  254  can be formed onto the inner surface  266  of the body portion  246  and can extend rearwardly from the raised bead  264  toward the base  216 . The second set of ring engagement teeth  256  can be also formed into the inner surface of the body portion  246  and can extend forwardly from the raised bead  264 . The teeth  268  of the first and second sets of ring engagement teeth  254  and  256  can be uniformly spaced around the inner surface  266  of the body portion  246 . The configuration of each tooth  268  in the first and second sets of ring engagement teeth  254  and  256  can be similar in that each tooth can extend from the raised bead  264 , can have a pair of parallel engagement surfaces  270  and can terminate at a tip portion  272 . The tip portion  272  of each tooth  268  may be both rounded and tapered to enhance the ability with which it will mesh with a portion of the reduction gearset assembly  202  as will be described in detail, below. 
         [0079]    The pin housing portion  248  can extend downwardly from the body portion  246  over a portion of the length of the body portion  246 . An actuator aperture  274  may be formed into the pin housing portion  248  and can extend rearwardly through the base  216  of the transmission sleeve  200 . In the particular embodiment illustrated, the actuator aperture  274  may be stepped, having a first portion  276  with a first diameter at the rear of the transmission sleeve  200  and a second portion  278  with a smaller second diameter at the front of the transmission sleeve  200 . In the example shown, the first portion  276  of the actuator aperture  274  breaks through the wall of the first housing portion  260  and forms a groove  280  into the inner surface  234  of the base  216 . The pin housing portion  248  will be discussed in further detail, below. 
         [0080]    A pair of first clip slots  284  and a pair of second clip slots  286  can be formed into the transmission sleeve  200 , extending along the sides of the transmission sleeve  200  in a manner that may be parallel the longitudinal axis of the transmission sleeve  200 . The first pair of clip slots  284  may be formed through the sides of the body portion  246  rearwardly of the raised bead  264  and extends rearwardly toward the base  216 . The depth of the first pair of clip slots  284  may be such that they do not extend through the portion of the wall member  210  that defines the base  216 . The second pair of clip slots  286  can be also formed through the sides of the body portion  246  beginning forwardly of the raised bead  264  and extending through the front face  288  of the transmission sleeve  200 . 
         [0081]    With reference to  FIGS. 12 ,  13 ,  18  and  23 , the reduction gearset assembly  202  may include a first reduction gear set  302 , a second reduction gear set  304  and a third reduction gear set  306 . The first, second and third reduction gear sets  302 ,  304  and  306  can be operable in an active mode and in the particular example provided, the second and third reduction gear sets  304  and  306  may also be operable in an inactive mode. Operation in the active mode causes the reduction gear set to perform a speed reduction and torque multiplication operation, while operation of the reduction gear set in an inactive mode for causes the reduction gear set to provide an output having a speed and torque that may be about equal to the speed and torque of the rotary input provided to that reduction gear set. In the particular embodiment illustrated, each of the first, second and third reduction gear sets  302 ,  304  and  306  can be planetary gear sets. Those skilled in the art will understand, however, that various other types of reduction gear sets that can be well known in the art may be substituted for one or more of the reduction gear sets forming the reduction gearset assembly  202 . 
         [0082]    As shown, the first reduction gear set  302  may include a first reduction element or ring gear  310 , a first set of planet gears  312  and a first planet or reduction carrier  314 . The first ring gear  310  may be an annular structure, having a plurality of gear teeth  310   a  formed along its interior diameter. A clutch face  316  may be formed into the outer perimeter of the front face  318  of the first ring gear  310  and will be discussed in greater detail, below. The first ring gear  310  may be disposed within the portion of the hollow cavity  212  defined by the base  216 ; the front face  318  of the first ring gear  310  contacts a step  320  formed into the transmission sleeve  200 , thereby limiting the ability of the first ring gear  310  to move forwardly into the hollow cavity  212 . 
         [0083]    The first reduction carrier  314  may be formed in the shape of a flat cylinder, having plurality of pins  322  that extend from its rearward face  324 . A plurality of gear teeth  314   a  can be formed into almost the entire outer perimeter of the first reduction carrier  314 , with a valley  314   b  being formed between each pair of adjacent gear teeth  314   a . Due to the spacing of the gear teeth  314   a , one of the valleys (i.e., valley  314   b ′) is relatively larger than the remaining valleys  314   b  due to the omission of a tooth  314   a  in the outer perimeter of the first reduction carrier  314 . In the particular embodiment illustrated, the gear teeth  314   a  of the first reduction carrier  314  can be configured so as not to be meshingly engagable with the gear teeth  310   a  of the first ring gear  310 . 
         [0084]    With specific reference to  FIGS. 19 and 20 , the profile of the gear teeth  314   a  is illustrated in greater detail. As shown, each gear tooth  314   a  terminates at a gradual radius  326  at the forward face  328  of the first reduction carrier  314  but terminates abruptly at the rearward face  324  of the first reduction carrier  314 . A radius  330  is also formed on the valleys  314   b  between the gear teeth  314   a.    
         [0085]    Returning to  FIGS. 12 ,  13 ,  15 ,  18  and  23 , a first thrust washer  332  having a first annular portion  334 , a second annular portion  336  and a plurality of retaining tabs  338  may be positioned rearwardly of the first reduction gear set  302 . The retaining tabs  338  engage the second grooves  232  in the base  216  of the transmission sleeve  200  and as such, relative rotation between the first thrust washer  332  and the transmission sleeve  200  may be inhibited. The inside diameter of the base  216  may be sized to receive the motor cover  136  and as such, the front face  340  of the motor cover  136  inhibits the axial movement of the first thrust washer  332 . The first annular portion  334  contacts the rear face  342  of the first ring gear  310 , providing a wear surface and controlling the amount by which the first ring gear  310  is able to move in an axial direction. The second annular portion  336  may be spaced axially apart from the first annular portion  334 , extending forwardly of the first annular portion  334  to provide a wear surface for the first set of planet gears  312  that also controls the amount by which they can move in an axial direction. 
         [0086]    The first set of planet gears  312  may include a plurality of planet gears  344 , each of which being generally cylindrical in shape, having a plurality of gear teeth  344   a  formed into its outer perimeter and a pin aperture  346  formed its their center. Each planet gear  344  may be rotatably supported on an associated one of the pins  322  and the first reduction carrier  314  and may be positioned such that its teeth  344   a  meshingly engage the teeth  314   a  of the first ring gear  310 . A raised portion  348  may be formed into the front and rear face  350  and  352  of each planet gear  344  that inhibits the teeth  344   a  from rubbing on the first reduction carrier  314  and the first thrust washer  332  and creating dust or chips that would impair the performance of the transmission assembly  16  and reduce its operating life. As the teeth  46   a  of the motor pinion  46  on the output shaft  44  can be also meshingly engaged with the teeth  344   a  of the planet gears  344 , the motor pinion  46  serves as a sun gear for the first reduction gear set  302 . 
         [0087]    The second reduction gear set  304  may be disposed within the portion of the hollow cavity  212  defined by the first housing portion  260  and may include a second sun gear  358 , a second reduction element or ring gear  360 , a second set of planet gears  362  and a second planet or reduction carrier  364 . The second sun gear  358  may be fixed for rotation with the first reduction carrier  314 . The second sun gear  358  can include a plurality of gear teeth  358   a  that extend forwardly of the forward face  328  of the first reduction carrier  314 . 
         [0088]    The second ring gear  360  may be an annular structure, having a plurality of gear teeth  360   a  formed along its interior diameter. The gear teeth  360   a  may be heavily chamfered at the rear face  366  of the second ring gear  360  but terminate abruptly at the front face  368 . More preferably, a heavy radius  369  may be formed onto the rear face  366  and the sides of each of the gear teeth  360   a , with the heavy radius  369  being employed rather than the heavy chamfer as the heavy radius  369  on the gear teeth  360   a  provides for better engagement between the second ring gear  360  and the first reduction carrier  314 . 
         [0089]    A plurality of sleeve engagement teeth  370  can be formed into the outer perimeter of the second ring gear  360 ; the sleeve engagement teeth  370  extend forwardly toward the front face  368  of the second ring gear  360  and terminate at a tip portion  372  that may be rounded and tapers forwardly and inwardly. An annular clip groove  374  may also formed into the outer perimeter of the second ring gear  360 . In the example illustrated, the clip groove  374  may be a rectangular slot having a pair of sidewalls  376 . The clip groove  374  will be discussed in greater detail, below. 
         [0090]    The second reduction carrier  364  may be formed in the shape of a flat cylinder, having plurality of pins  378  that extend from its rearward face  380 . The second set of planet gears  362  may include a plurality of planet gears  382 . Each planet gear  382  may be generally cylindrical in shape, having a plurality of gear teeth  382   a  formed into its outer perimeter and a pin aperture  384  formed its center. Each planet gear  382  may be rotatably supported on an associated one of the pins  378  and the second reduction carrier  364  may be positioned such that the gear teeth  382   a  of the planet gears  382  meshingly engage the gear teeth  360   a  of the second ring gear  360 . The gear teeth  358   a  of the second sun gear  358  can be also meshingly engaged with the gear teeth  382   a  of the planet gears  382 . 
         [0091]    The third reduction gear set  306  may be disposed within the portion of the hollow cavity  212  defined by the second housing portion  262  and may include a third sun gear  398 , a third reduction element or ring gear  400 , a third set of planet gears  402  and a third planet or reduction carrier  404 . The third sun gear  398  may be fixed for rotation with the second reduction carrier  364 . The third sun gear  398  can include a plurality of gear teeth  398   a  that extend forwardly of the front face  406  of the second reduction carrier  364 . 
         [0092]    The third ring gear  400  may be an annular structure, having a plurality of gear teeth  400   a  formed along its interior diameter. The gear teeth  400   a  may be heavily chamfered at the front face  412  of the third ring gear  400 , but terminate abruptly at the rear face  414 . More preferably, a heavy radius  407  may be formed onto the front face  412  and the sides of each of the gear teeth  400   a , with the heavy radius  407  being employed rather than the heavy chamfer as the heavy radius  407  on the gear teeth  400   a  provides for better engagement between the third ring gear  400  and the third reduction carrier  404 . A plurality of sleeve engagement teeth  418  can be formed into the outer perimeter of the third ring gear  400 ; the sleeve engagement teeth  418  extend rearward toward the rear face  414  of the third ring gear  400  and terminate at a tip portion  420  that may be rounded and taper both rearwardly and inwardly. An annular clip groove  422  may also be formed into the outer perimeter of the third ring gear  400 . In the example illustrated, the clip groove  422  may be a rectangular slot having a pair of sidewalls  424 . The clip groove  422  will be discussed in greater detail, below. 
         [0093]    The third reduction carrier  404  may be formed in the shape of a flat cylinder, having plurality of pins  428  that extend from its rearward face  430 . A plurality of gear teeth  404   a  can be formed into almost the entire outer perimeter of the third reduction carrier  404 , with a valley  404   b  being formed between each pair of adjacent teeth  404   a . Due to the spacing of the teeth  404   a , one of the valleys  404   b  (i.e., valley  404   b ′) is relatively larger than the remaining valleys  404   b  due to the omission of a tooth  404   a  in the outer perimeter of the third reduction carrier  404 . In the particular embodiment illustrated, the gear teeth  404   a  of the third reduction carrier  404  can be configured so as not to be meshingly engagable with the gear teeth  382   a  of the second planet gears  382 . 
         [0094]    With brief additional reference to  FIGS. 21 and 22 , the profile of the gear teeth  404   a  is illustrated in greater detail. As shown, the rear face  430  of the third reduction carrier  404  may be chamfered and a heavy radius  434  may be formed into each of sides of the teeth  404   a  and valleys  404   b . Each gear tooth  404   a  terminates abruptly at the forward face  436  of the third reduction carrier  404 . 
         [0095]    Returning back to  FIGS. 12 ,  13 ,  15 ,  18  and  23 , the third set of planet gears  402  may include a plurality of planet gears  438 . Each planet gear  438  may be generally cylindrical in shape, having a plurality of gear teeth  438   a  formed into its outer perimeter and a pin aperture  440  formed through its center. Each planet gear  438  may be rotatably supported on an associated one of the pins  428  and the third reduction carrier  404  may be positioned such that the gear teeth  438   a  of the planet gears  438  meshingly engage the gear teeth  400   a  of the third ring gear  400 . A raised portion  442  may be formed into each of the front and rear faces of the planet gears  438  which inhibits the gear teeth  438   a  from rubbing on the third reduction carrier  404  and creating dust or chips that would impair the performance of the transmission assembly  12  and reduce its operating life. A second thrust washer  450  may be disposed around the third sun gear  398  and the teeth  398   a  of the third sun gear  398  can be meshingly engaged with the gear teeth  438   a  of the planet gears  438 . The second thrust washer  450  may include a plurality of retaining tabs  452  that can be configured to engage corresponding tab grooves  454  ( FIG. 13 ) that can be formed in the inner surface  266  of body portion  246  of the transmission sleeve  200 . The retaining tabs  452  and the tab grooves  454  cooperate to inhibit relative rotation between the second thrust washer  450  and the transmission sleeve  200 . 
         [0096]    The output spindle assembly  20  may include a transmitting means  458  for coupling a spindle  460  for rotation with the third reduction carrier  404  so as to transmit drive torque from the reduction gearset assembly  202  to the chuck  22 . Such transmitting means  458  are well known in the art and easily adapted to the transmission assembly of the present disclosure. Accordingly, a detailed discussion of the transmitting means  458  need not be included herein. 
         [0097]    With reference to  FIGS. 13 ,  13   a,    13   b,    16 ,  17 ,  18  and  23  through  28 , the speed selector mechanism  60  may be movable between a first position  500 , a second position  502  and a third position  504  and can include a switch portion  510  for receiving a speed change input and an actuator portion  512  for manipulating the reduction gearset assembly  202  in accordance with the speed change input. The actuator portion  512  may be operatively coupled to the reduction gearset assembly  202  and moves the second and third reduction gear sets  304  and  306  between the active and inactive modes in response to movement of the switch portion  510  between the first, second and third positions  500 ,  502  and  504 . In the particular embodiment illustrated, the actuator portion  512  can include a rotary selector cam  520 , a plurality of wire clips  522  and a spring member  523 . Each of the wire clips  522  may be formed from a round wire which may be bent in the shape of a semi-circle  524  with a pair of tabs  526  extending outwardly from the semi-circle  524  and positioned on about the centerline of the semi-circle  524 . The semi-circle  524  may be sized to fit within the clip grooves  374  and  422  in the second and third ring gears  360  and  400 , respectively. In this regard, the semi-circle  524  neither extends radially outwardly of an associated one of the ring gears ( 360 ,  400 ), nor binds against the sidewalls ( 376 ,  424 ) of the clip grooves ( 374 ,  422 ). In the example provided, the sidewalls ( 376 ,  424 ) of the clip grooves ( 374 ,  422 ) are spaced apart about 0.05 inch and the diameter of the wire forming the wire clips  522  may be about 0.04 inch. 
         [0098]    The tabs  526  of the wire clips  522  extend outwardly of the hollow cavity  212  into an associated one of the clip slots ( 284 ,  286 ) that may be formed into the transmission sleeve  200 . The tabs  526  can be long enough so that they extend outwardly of the outer surface  258  of the body  214  of the transmission sleeve  200 , but not so far as to extend radially outwardly of the portion of the first clip slots  284  in the base  216  of the transmission sleeve  200 . Configuration of the wire clips  522  in this manner facilitates the assembly of the transmission assembly  16 , permitting the wire clips  522  to be installed to the second and third ring gears  360  and  400 , after which these assemblies can be inserted into the hollow cavity  212  along the longitudinal axis of the transmission sleeve  200 . 
         [0099]    With specific reference to  FIGS. 13 and 27   a  through  27   c , the rotary selector cam  520  may include an arcuate selector body  530 , a switch tab  532  and a plurality of spacing members  534 . A pair of first cam slots  540   a  and  540   b , a pair of second cam slots  544   a  and  544   b , a spring aperture  546  and a guide aperture  548  can be formed through the selector body  530 . The selector body  530  may be sized to engage the outside diameter of the body portion  246  of the transmission sleeve  200  in a slip-fit manner. The guide aperture  548  may be generally rectangular in shape and sized to engage the front and rear surfaces of the selector cam guide  250 . The guide aperture  548  may be considerably wider than the width of the selector cam guide  250 , being sized in this manner to permit the rotary selector cam  520  to be rotated on the transmission sleeve  200  between a first rotational position, a second rotational position and a third rotational position. The selector cam guide  250  and cooperates with the guide aperture  548  to limit the amount by which the rotary selector cam  520  can be rotated on the transmission sleeve  200 , with a first lateral side of the selector cam guide  250  contacting a first lateral side of the guide aperture  548  when the rotary selector cam  520  is positioned in the first rotational position, and a second lateral side of the selector cam guide  250  contacting a second lateral side of the guide aperture  548  when the rotary selector cam  520  is positioned in the third rotational position. 
         [0100]    Each of the first cam slots  540   a  and  540   b  may be sized to receive one of the tabs  526  of the wire clip  522  that is engaged to the second ring gear  360 . In the particular embodiment illustrated, first cam slot  540   a  can include a first segment  550 , a second segment  552  and an intermediate segment  554 . The first segment  550  may be located a first predetermined distance away from a reference plane  558  that may be perpendicular to the longitudinal axis of the rotary selector cam  520  and the second segment  552  may be located a second distance away from the reference plane  558 . The intermediate segment  554  couples the first and second segments  550  and  552  to one another. The configuration of first cam slot  540   b  is identical to that of first cam slot  540   a , except that it is rotated relative to the rotary selector cam  520  such that each of the first, second and intermediate segments  550 ,  552  and  554  in the first cam slot  540   b  can be located 180° apart from the first, second and intermediate segments  550 ,  552  and  554  in the first cam slot  540   a.    
         [0101]    Each of the second cam slots  544   a  and  544   b  may be sized to receive one of the tabs  526  of a corresponding one of the wire clips  522 . In the particular embodiment illustrated, second cam slot  544   a  can include a first segment  560 , a second segment  562 , a third segment  564  and a pair of intermediate segments  566  and  568 . The first and third segments  560  and  564  can be located a third predetermined distance away from the reference plane and the second segment  562  may be located a fourth distance away from the reference plane  558 . The intermediate segment  566   a  couples the first and second segments  560  and  562  to one another and the intermediate segment  568  couples the second and third segments  562  and  566  together. The configuration of second cam slot  544   b  is identical to that of second cam slot  544   a , except that it is rotated relative to the rotary selector cam  520  such that each of the first, second, third and intermediate segments  560 ,  562 ,  564  and  566  and  568  in the second cam slot  544   b  can be located 180° apart from the first, second, third and intermediate segments  560 ,  562 ,  564  and  566  and  568  in the second cam slot  544   a.    
         [0102]    With the tabs  526  of the wire clips  522  engaged to the first cam slots  540   a  and  540   b  and the second cam slots  544   a  and  544   b , the rotary selector cam  520  may be rotated on the transmission sleeve  200  between the first, second and third positions  500 ,  502  and  504  to selectively engage and disengage the second and third ring gears  360  and  400  from the first and third reduction carriers  314  and  404 , respectively. During the rotation of the rotary selector cam  520 , the first cam slots  540   a  and  540   b  and the second cam slots  544   a  and  544   b  confine the wire tabs  526  of their associated wire clip  522  and cause the wire tabs  526  to travel along the longitudinal axis of the transmission sleeve  200  in an associated one of the first and second clip slots  284  and  286 . Accordingly, the rotary selector cam  520  may be operative for converting a rotational input to an axial output that causes the wire clips  522  to move axially in a predetermined manner. A lubricant (not specifically shown) may be applied to the lubricant grooves  252  formed into body portion  246  of the transmission sleeve  200  may be employed to lubricate the interface between the transmission sleeve  200  and the rotary selector cam  520 . 
         [0103]    Positioning the rotary selector cam  520  in the first rotational position  500  causes the tabs  526  of the wire clip  522  that is engaged to the second ring gear  360  to be positioned in the first segment  550  of the first cam slots  540   a  and  540   b  and the tabs  526  of the wire clip  522  that is engaged to the third ring gear  400  to be positioned in the first segment  560  of the second cam slots  544   a  and  544   b . Accordingly, positioning of the rotary selector cam  520  in the first rotational position causes the second and third ring gears  360  and  400  to be positioned in meshing engagement with the second and third planet gears  362  and  402 , respectively. Simultaneously with the meshing engagement of the second and third ring gears  360  and  400  with the second and third planet gears  362  and  402 , the sleeve engagement teeth  370  and  418  of the second and third ring gears  360  and  400 , respectively, can be positioned in meshing engagement with the first and second sets of ring engagement teeth  254  and  256 , respectively, to inhibit relative rotation between the second and third ring gears  360  and  400  and the transmission sleeve  200  to thereby providing the transmission assembly  16  with a first overall gear reduction or speed ratio  570  as shown in  FIG. 23 . Those skilled in the art will understand that the tip portion  272  of the teeth  268  of the first and second sets of ring engagement teeth  254  and  256  and the tip portions  372  and  420  of the sleeve engagement teeth  370  and  418 , respectively, can be rounded and tapered so as to improve their capability for meshing engagement in response to axial repositioning along a longitudinal axis of the transmission assembly  16 . 
         [0104]    Positioning the rotary selector cam  520  in the second rotational position  502  causes the tabs  526  of the wire clip  522  that is engaged to the second ring gear  360  to be positioned in the first segment  550  of the first cam slots  540   a  and  540   b  and the tabs  526  of the wire clip  522  that is engaged to the third ring gear  400  to be positioned in the second segment  562  of the second cam slots  544   a  and  544   b . Accordingly, positioning of the rotary selector cam  520  in second rotational position causes the second ring gear  360  to be in meshing engagement with the second planet gears  362  and the third ring gear  400  in meshing engagement with both the third planet gears  402  and the third reduction carrier  404 . Positioning of the rotary selector cam  520  in the second rotational position  502  also positions the sleeve engagement teeth  370  of the second ring gear  360  in meshing engagement with the first set of ring engagement teeth  254  while the sleeve engagement teeth  418  of the third ring gear  400  can be not meshingly engaged with the second set of ring engagement teeth  256 . As such, relative rotation between the second ring gear  360  and the transmission sleeve  200  is inhibited, while relative rotation between the third ring gear  400  and the transmission sleeve  200  is permitted to thereby provide the transmission assembly  16  with a second overall gear reduction or speed ratio  572  as illustrated in  FIG. 24 . 
         [0105]    Positioning the rotary selector cam  520  in the third rotational position  504  causes the tabs  526  of the wire clip  522  that is engaged to the second ring gear  360  to be positioned in the second segment  552  of the first cam slots  540   a  and  540   b  and the tabs  526  of the wire clip  522  that is engaged to the third ring gear  400  to be positioned in the third segment  564  of the second cam slots  544   a  and  544   b . Accordingly, positioning of the rotary selector cam  520  in the third rotational position causes the second ring gear  360  to be in meshing engagement with both the second planet gears  362  and the first reduction carrier  314  while the third ring gear  400  in meshing engagement with only the third planet gears  402 . Positioning the rotary selector cam  520  in the third rotation position  504  also positions the sleeve engagement teeth  370  on the second ring gear  360  out of meshing engagement with the first set of ring engagement teeth  254  and the sleeve engagement teeth  418  on the third ring gear  400  in meshing engagement with the second sets of ring engagement teeth  256  to inhibit relative rotation between the second ring gear  360  and the transmission sleeve  200  and permit relative rotation between the third ring gear  400  and the transmission sleeve  200  to provide the transmission assembly  16  with a third overall gear reduction or speed ratio  574 . 
         [0106]    In the example shown in  FIGS. 13 ,  27   b  and  28 , the spring member  523  may be formed from a flat rectangular piece of spring steel and can include a flattened Z-shaped portion  580  and a raised portion  584 . The flattened Z-shaped portion  580  may be configured to wrap around two reinforcement bars  586  that extend into the spring aperture  546 , thereby permitting the raised portion  584  to be maintained at a predetermined position and also to transmit a spring force between the rotary selector cam  520  and the spring member  523 . With additional reference to  FIG. 28 , the raised portion  584  of the spring member  523  may be sized to engage internal notches  590  formed in the housing  592  of the output spindle assembly  20 . Lands  594  that can be circumferentially spaced from the rotary selector cam  520  can be formed between the notches  590 . When the output spindle assembly  20  is positioned over the transmission assembly  16  and the speed selector mechanism  60  is positioned in one of the first, second and third rotational positions  500 ,  502  and  504 , the raised portion  584  of the spring member  523  engages an associated one of the notches  590 . The force that is generated by the spring member  523  when the raised portion  584  is moved downwardly toward the rotary selector cam  520  in response to contact between the raised portion  584  and the land  594  acts to inhibit unintended rotation of the speed selector mechanism  60 . Furthermore, placement of the raised portion  584  in a notch  590  provides the user with a tactile indication of the positioning of the rotary selector cam  520 . 
         [0107]    In the particular embodiment illustrated in  FIGS. 13 and 27   c , switch portion  510  may include an arcuate band  600  having a raised hollow and rectangular selector button  602  formed therein. The arcuate band  600  may be formed from a plastic material and may be configured to conform to the outer diameter of the rotary selector cam  520 . The open end of the selector button  602  may be configured to receive the switch tab  532 , thereby permitting the switch portion  510  and the rotary selector cam  520  to be coupled to one another in a fastenerless manner. The plurality of spacing members  534  can be raised portions formed into the rotary selector cam  520  that can be concentric to and extend radially outwardly from the selector body  530 . The spacing members  534  elevate the arcuate band  600  to prevent the arcuate band from contacting the wire tabs  526  in the first cam slots  540   a  and  540   b . The spacing members  534  may also be employed to selectively strengthen areas of the rotary selector cam  520 , such as in the areas adjacent the first cam slots  540   a  and  540   b.    
         [0108]    Those skilled in the art will understand that the rotary selector cam  520  (i.e., the first cam slots  540   a  and  540   b  and the second cam slots  544   a  and  544   b ) could be configured somewhat differently so as to cause the second ring gear  360  to meshingly engage both the second planet gears  362  and the first reduction carrier  314  while the third ring gear  400  meshingly engages both the third planet gears  402  and the third reduction carrier  404 . Configuration in this manner provides the transmission assembly  16  with a fourth overall gear reduction or speed ratio. 
         [0109]    Those skilled in the art will also understand that selector mechanisms of other configurations may be substituted for the selector mechanism  60  illustrated herein. These selector mechanisms may include actuators that can be actuated via rotary or sliding motion and may include linkages, cams or other devices that are well known in the art to slide the second and third ring gears  360  and  400  relative to the transmission sleeve  200 . Those skilled in the art will also understand that as the second and third ring gears  360  and  400  can be independently movable between the active and inactive modes (i.e., the placement of one of the second and third ring gears  360  and  400  does not dictate the positioning of the other one of the second and third ring gears  360  and  400 ), the switch mechanism  60  could also be configured to position the second and third ring gears  360  and  400  independently of one another. 
       Clutch Mechanism 
       [0110]    In  FIGS. 23 ,  26  and  28  through  30 , the clutch mechanism  18  may include a clutch member  700 , an engagement assembly  702  and an adjustment mechanism  704 . The clutch member  700  may be an annular structure that may be fixed to the outer diameter of the first ring gear  310  and which extends radially outwardly therefrom. The clutch member  700  may include the clutch face  316  that may be formed into the front face  318  of the first ring gear  310 . The outer diameter of the clutch member  700  may be sized to rotate within the portion of the hollow cavity  212  that is defined by the base  216  of the transmission sleeve  200 . With specific brief reference to  FIG. 29 , the clutch face  316  of the example illustrated is shown to be defined by a plurality of peaks  710  and valleys  712  that can be arranged relative to one another to form a series of ramps that can be defined by an angle of about 18°. Those skilled in the art will understand, however, that other clutch face configurations may also be employed, such as a sinusoidally shaped clutch face  316 ′ ( FIG. 29   a ). 
         [0111]    While the first ring gear  310  and the clutch member  700  have been illustrated as a one piece (i.e., unitarily formed) construction, those skilled in the art will understand that they may be constructed otherwise. One such embodiment is illustrated in  FIG. 29   b  wherein the first ring gear  310 ′ may include an annular collar  1000  and a plurality of tab apertures  1002 . The annular collar  1000  may include a plurality of ramps  1004  that have dual sloping sides, but is otherwise flat. The first ring gear  310 ′ is otherwise identical to the first ring gear  310 . An annular damper  1008  abuts the annular collar  1000  and can include a plurality of tab members  1010  that engage the tab apertures  1002  in the first ring gear  310 ′ to prevent the damper  1008  from rotating relative to the first ring gear  310 ′. The damper  1008  can include a body portion  1012  that may be configured to match the contour of the annular collar  1000  and as such, can include a plurality of mating ramped portions  1014  that can be configured to engage each of the ramps  1004 . The damper  1008  may be formed from a suitable impact dampening material, such as acetyl. The clutch member  700 ′, which may be an annular member that may be formed from a wear resistant material, such as hardened  8620  steel, may be disposed over the damper  1008 . Like the damper  1008 , the clutch member  700 ′ can include a plurality of tab members  1020 , which lock into the tab apertures  1002  to prevent rotation relative to the first ring gear  310 ′, and a plurality of mating ramped portions  1022 . The mating ramped portions  1022  of the clutch member  700 ′, however, matingly engage the mating ramped portions  1014  of the damper  1008 . While the construction in this manner is more expensive relative to the previously described embodiment, it is more tolerant of high impact forces that can be associated with the operation of the clutch mechanism  18 . 
         [0112]    In the particular embodiment illustrated, the engagement assembly  702  can include a pin member  720 , a follower spring  722  and a follower  724 . The pin member  720  can include a cylindrical body portion  730  having an outer diameter that may be sized to slip-fit within the second portion  278  of the actuator aperture  274  that is formed into the pin housing portion  248  of the transmission sleeve  200 . The pin member  720  also can include a tip portion  732  and a head portion  734 . The tip portion  732  may be configured to engage the adjustment mechanism  704  and in the example shown, is formed into the end of the body portion  730  of the pin member  720  and defined by a spherical radius. The head portion  734  may be coupled to the end of the body portion  730  opposite the tip portion  732  and may be shaped in the form of a flat cylinder or barrel that is sized to slip fit within the first portion  276  of the actuator aperture  274 . Accordingly, the head portion  734  prevents the pin member  720  from being urged forwardly out of the actuator aperture  274 . 
         [0113]    The follower spring  722  may be a compression spring whose outside diameter may be sized to slip fit within the first portion  276  of the actuator aperture  274 . The forward end of the follower spring  722  contacts the head portion  734  of the pin member  720 , while the opposite end of the follower spring  722  contacts the follower  724 . The end portion  740  of the follower  724  may be cylindrical in shape and sized to slip fit within the inside diameter of the follower spring  722 . In this regard, the end portion  740  of the follower acts as a spring follower to prevent the follower spring  722  from bending over when it is compressed. The follower  724  also can include a follower portion  744  having a cylindrically shaped body portion  746 , a tip portion  748  and a flange portion  750 . The body portion  746  may be sized to slip fit within the first portion  276  of the actuator aperture  274 . The tip portion  748  may be configured to engage the clutch face  316  and in the example shown, is formed into the end of the body portion  746  of the follower  724  and defined by a spherical radius. The flange portion  750  may be formed at the intersection between the body portion  746  and the end portion  740 . The flange portion  750  may be generally flat and configured to receive a biasing force that may be exerted by the follower spring  722 . 
         [0114]    The adjustment mechanism  704  may also include an adjustment structure  760  and a setting collar  762 . The adjustment structure  760  may be shaped in the form of a generally hollow cylinder that may be sized to fit a housing portion  766  of the output spindle assembly  20 . The adjustment structure  760  can include an annular face  768  into which an adjustment profile  770  may be formed. The adjustment profile  770  can include a first adjustment segment  772 , a last adjustment segment  774 , a plurality of intermediate adjustment segments  776  and a ramp section  778  between the first and last adjustment segments  772  and  774 . In the embodiment illustrated, a second ramp section  779  is included between the last intermediate adjustment segment  776   z  and the last adjustment segment  774 . Also in the particular embodiment illustrated, the portion of the adjustment profile  770  from the first adjustment segment  772  through the last one of the intermediate adjustment segments  776   z  is formed as a ramp having a constant slope. Accordingly, a follower  780  that is coupled to the housing portion  766  of the output spindle assembly  20  may be biased radially outwardly toward the inside diameter of the adjustment structure  760  where it acts against the plurality of detents  782  that can be formed into the adjustment mechanism  704  (e.g., in the setting collar  762 ). The follower  724  and plurality of detents  782  cooperate to provide the user of tool  10  with a tactile indication of the position of the adjustment profile  770  as well as inhibit the free rotation of the adjustment structure  760  so as to maintain the position of the adjustment profile  770  at a desired one of the adjustment segments  772 ,  774  and  776 . 
         [0115]    The setting collar  762  may be coupled to the exterior of the adjustment structure  760  and may include a plurality of raised gripping surfaces  790  that permit the user of the tool  10  to comfortably rotate both the setting collar  762  and the adjustment structure  760  to set the adjustment profile  770  at a desired one of the adjustment segments  772 ,  774  and  776 . A setting indicator  792  may be employed to indicate the position of the adjustment profile  770  relative to the housing portion  766  of the output spindle assembly  20 . In the example provided, the setting indicator  792  can include an arrow  794  formed into the housing portion  766  of the output spindle assembly  20  and a scale  796  that is marked into the circumference of the setting collar  762 . 
         [0116]    During the operation of the tool  10 , an initial drive torque is transmitted by the motor pinion  46  from the motor assembly  14  to the first set of planet gears  312  causing the first set of planet gears  312  to rotate. In response to the rotation of the first set of planet gears  312 , a first intermediate torque is applied against the first ring gear  310 . Resisting this torque is a clutch torque that is applied by the clutch mechanism  18 . The clutch torque inhibits the free rotation of the first ring gear  310 , causing the first intermediate torque to be applied to the first reduction carrier  314  and the remainder of the reduction gearset assembly  202  so as to multiply the first intermediate torque in a predetermined manner according to the setting of the switch mechanism  60 . In this regard, the clutch mechanism  18  biases the first reduction gear set  302  in the active mode. 
         [0117]    The magnitude of the clutch torque is dictated by the adjustment mechanism  704 , and more specifically, the relative height of the adjustment segment  772 ,  774  or  776  that is in contact with the tip portion  732  of the pin member  720 . Positioning of the adjustment mechanism  704  at a predetermined one of the adjustment segments  772 ,  774  or  776  pushes the pin member  720  rearwardly in the actuator aperture  274 , thereby compressing the follower spring  722  and producing the a clutch force. The clutch force is transmitted to the flange portion  750  of the follower  724 , causing the tip portion  748  of the follower  724  to engage the clutch face  316  and generating the clutch torque. Positioning of the tip portion  748  of the follower  724  in one of the valleys  712  in the clutch face  316  operates to inhibit rotation of the first ring gear  310  relative to the transmission sleeve  200  when the magnitude of the clutch torque exceeds the first intermediate torque. When the first intermediate torque exceeds the clutch torque, however, the first ring gear  310  is permitted to rotate relative to the transmission sleeve  200 . Depending upon the configuration of the clutch face  316 , rotation of the first ring gear  310  may cause the clutch force to increase a sufficient amount to resist further rotation. In such situations, the first ring gear  310  will rotate in an opposite direction when the magnitude of the first intermediate torque diminishes, permitting the tip portion  748  of the follower  724  to align in one of the valleys  712  in the clutch face  316 . If rotation of the first ring gear  310  does not cause the clutch force to increase sufficiently so as to fully resist rotation of the first ring gear  310 , the first reduction gearset  302  will rotate so as to limit the transmission of torque to the first reduction carrier  314 . 
         [0118]    Configuration of the clutch mechanism  18  in this manner is highly advantageous in that the clutch torque is sized to resist the first intermediate torque, as opposed to the output torque of the tool  10  that is generated by the multi-reduction transmission assembly  16  and transmitted through the chuck  22 . In this regard, the clutch mechanism  18  may be sized in a relatively small manner, thereby improving the ability with which it may be incorporated or packaged into the tool  10 . Furthermore, as the speed or gear ratios can be changed after or down stream of the first ring gear  310 , the clutch mechanism  18  is operable over a relatively large span of output torques. In comparison with conventional clutch mechanisms that operate to limit the output torque of a transmission, these devices can be typically operable over a relatively narrow torque band, necessitating a change in their clutch spring if a considerable shift in the magnitude of the output torque is desired. In contrast, the clutch mechanism  18  of the present disclosure can accommodate a considerable shift in the magnitude of the output torque of the tool  10  by simply operating the transmission assembly  16  in a different (i.e., lower or higher) gear ratio. 
         [0119]    In the operation of rotary power tools such as tool  10 , it is frequently desirable to change between two clutch settings, as when the tool  10  is used to both drill a hole and thereafter install a screw in that hole. Accordingly, the adjustment mechanism  704  may be rotated relative to the output spindle assembly  20  to position the adjustment mechanism  704  at a desired one of the adjustment segments  772 ,  774  and  776  to perform the first operation and thereafter rotated to a second one of the adjustment segments  772 ,  774  and  776  to perform the second operation. In contrast to the known clutch arrangements, the adjustment mechanism  704  of the present disclosure is configured such that the adjustment structure  760  and the setting collar  762  can be rotatable through an angle of 360°. Assuming the adjustment structure  760  to be positioned at an intermediate adjustment segment  776   x , rotation of the adjustment mechanism  704  through an angle of 360° would rotate the adjustment structure  760  past the other intermediate adjustment segments  776 , as well as the first and last adjustment segments  772  and  774  and the ramp section  778  such that the adjustment structure  760  would again be positioned at the intermediate adjustment segment  776   x . The feature is especially convenient when it is necessary to change the clutch setting between a relatively high clutch setting and a relatively low clutch setting. In this regard, the ramp section  778  permits the setting collar  762  (and adjustment structure  760 ) to be rotated from highest clutch setting, corresponding to the last adjustment segment, to the lowest clutch setting, corresponding to the first clutch setting, without positioning the clutch mechanism  18  in one of the intermediate clutch settings. Accordingly, the user of the tool  10  is able to vary the clutch setting from its maximum setting to its minimum setting (and vice versa) by rotating the setting collar  762  a relatively small amount. 
         [0120]    While the adjustment profile  770  has been described thus far as having a constant slope, those skilled in the art will appreciate that the disclosure, in its broader aspects, may be constructed somewhat differently. For example, the adjustment profile  770 ′ may be formed such that each of the first, last and intermediate adjustment segments  772 ′,  774 ′ and  776 ′ is detented as illustrated in  FIG. 31 . In this arrangement, the detents  782  in the adjustment structure  760  and the follower  780  in the housing portion  766  of the output spindle assembly  20  can be unnecessary as the adjustment segments  772 ′,  774 ′ and  776 ′ will cooperate with the engagement  702  to provide the user of the tool  10  with a tactile indication of the position of the adjustment profile  770 ′, as well as inhibit the free rotation of the adjustment structure  760 . 
         [0121]    Another example is illustrated in  FIG. 32  wherein the adjustment profile  770 ″ is generally similar to the adjustment profile  770  except that the ramp section  779  has been omitted so that the last intermediate adjustment segment  776   z  is immediately adjacent the last adjustment segment  774 . 
         [0122]    While the transmission assembly  16  has been described thus far as including a three-stage, three speed transmission, those of ordinary skill in the art will appreciate from this disclosure that the disclosure, in its broader aspects, may be constructed somewhat differently. For example, another (i.e., fourth) or different speed ratio may be provided by operating two of the reduction gear sets (e.g., both the second and third reduction gear sets  304  and  306 ) in the inactive mode. Those of ordinary skill in the art will also appreciate from this disclosure that the second reduction gear set  304  may be placed in the inactive mode by coupling the second ring gear  360  to the second planet carrier  364  (rather than to the first planet carrier  314 ) and/or that the third reduction gear set  306  may be placed in the inactive mode by coupling the third ring gear  400  to the second planet carrier  364  (rather than to the third planet carrier  404 ). 
         [0123]    Other transmission assemblies constructed in accordance with the teachings of the present disclosure are illustrated in  FIGS. 33 through 56 . Generally speaking, these configurations are similar to that which is described above and illustrated in detail in  FIGS. 23 through 25 . Accordingly, similar or corresponding elements of the alternately constructed transmission assemblies are identified by similar reference numerals as were used to describe the transmission assembly  16 . 
         [0124]    In the example of  FIGS. 33 through 35 , the transmission assembly  16 - 1  may include one or more movable elements which may be employed to selectively couple the ring gears  360 - 1  and  400 - 1  of the second and third reduction gear sets  304 - 1  and  306 - 1 , respectively, to the transmission sleeve  200 - 1 . The movable elements, which may be pins  2000  and  2002 , may be housed in the transmission sleeve  200 - 1  and extend through corresponding apertures  2004  and  2006 , respectively, in the transmission sleeve  200 - 1  and may be translated into and out of engagement with a respective one of the ring gears (i.e., ring rears  360 - 1  and  400 - 1 ). In the example provided, each of the ring gears  360 - 1  and  400 - 1  can include teeth  370 - 1  and  418 - 1 , respectively, (similar to teeth  370  and  418 , respectively, that are shown in  FIG. 23 ) that are spaced apart by a sufficient distance to receive the pins  2000  and  2002 , respectively, therebetween. With the ring gears  360 - 1  and  400 - 1  locked to the transmission sleeve  200 - 1  as shown in  FIG. 33 , the transmission assembly  16 - 1  operates in a manner that is similar to that which is described in conjunction with  FIG. 23 , above. 
         [0125]    In  FIG. 34 , the transmission assembly  16 - 1  is shown in a second overall speed or gear reduction ratio, wherein the first and second reduction gear sets  302 - 1  and  304 - 1  are in an active mode and the third reduction gear set  306 - 1  is in an inactive mode. The third reduction gear set  306 - 1  may be inactivated by moving (e.g., translating) the pin  2002  out of engagement with the teeth  418 - 1  of the ring gear  400 - 1  and engaging the third planet carrier  404 - 1  to the third ring gear  400 - 1 . This latter task may be accomplished, for example, by sliding the third planet carrier  404 - 1  toward and into engagement with the third ring gear  400 - 1 . Any appropriate means may be employed to engage the third planet carrier  404 - 1  and the third ring gear  400 - 1  to one another, including friction (i.e., frictional engagement), or features, such as pins or teeth, that may be formed on one or both of the third planet carrier  404 - 1  and the third ring gear  400 - 1 . In the example provided, teeth  2010 , which are formed on the third ring gear  400 - 1 , engage mating teeth  2012  that are formed on the planet carrier  404 - 1 . 
         [0126]    In  FIG. 35 , the transmission assembly  16 - 1  is shown in a third overall speed or gear reduction ratio, wherein the first and third reduction gear sets  302 - 1  and  306 - 1  are in an active mode and the second reduction gear set  304 - 1  is in an inactive mode. The second reduction gear set  304 - 1  may be inactivated by moving (e.g., translating) the pin  2000  out of engagement with the teeth  370 - 1  of the ring gear  360 - 1  and engaging the first planet carrier  314 - 1  to the second ring gear  360 - 1 . 
         [0127]    This latter task may be accomplished, for example, by sliding the first planet carrier  314 - 1  toward and into engagement with the second ring gear  360 - 1 . Any appropriate means may be employed to engage the first planet carrier  314 - 1  and the second ring gear  360 - 1  to one another, including friction (i.e., frictional engagement), or features, such as pins or teeth, that may be formed on one or both of the first planet carrier  314 - 1  and the second ring gear  360 - 1 . In the example provided, teeth  2014 , which are formed on the second ring gear  360 - 1 , engage mating teeth  2016  that are formed on the first planet carrier  314 - 1 . 
         [0128]    Those skilled in the art will appreciate that although the movable elements (e.g., pins  2000  and  2002 ) have been illustrated as translating in a direction that is generally perpendicular to the longitudinal axis of the transmission assembly  16 - 1 , the disclosure in its broadest aspects, however, may be configured somewhat differently. For example, each of the movable elements may be translated in a direction that is generally parallel to the longitudinal axis of the transmission  16 - 1  between a first position, which permits the movable element to engage a feature on a respective one of the ring gears, and a second position, which aligns the movable element to an annular groove or a smooth, featureless portion on the respective ring gear so that the movable element does not inhibit the rotation of the respective ring gear. 
         [0129]    The transmission assembly  16 - 2  of  FIGS. 36 through 38  is generally similar to the embodiment of  FIGS. 33 through 35 , except that the first set of planet gears  344  of the first reduction gear set  302 - 2  and the third set of planet gears  402  of the third reduction gear set  306 - 2  remain in a fixed position relative to the first and third ring gears  310  and  400 - 1 , respectively, regardless of the position of the first and third planet carriers  314 - 2  and  404 - 2 , respectively. The first planet carrier  314 - 2  can be in a rearward position (shown in  FIG. 36 ) when the second reduction gear set  304 - 2  is in an active mode and a forward position when the second reduction gear set  304 - 2  is in an inactive mode. The third planet carrier  404 - 2  can be in a forward position (shown in  FIG. 36 ) when the third reduction gear set  306 - 2  is in an active mode and a rearward position (shown in  FIG. 37 ) when the third reduction gear set  306 - 2  is in an inactive mode. In contrast, the first set of planet gears  344  and the third set of planet gears  402  slide with the first and third planet carriers  314 - 1  and  404 - 1 , respectively, in the embodiment of  FIGS. 33 through 35 . 
         [0130]    With reference to  FIGS. 39 through 41 , the transmission assembly  16 - 3  may include one or more locking elements that may be selectively employed to lock the second and third ring gears  360 - 3  and  400 - 3  to the first and third planet carriers  314 - 3  and  404 - 3 , respectively. The locking elements may include, for example first and second idler gears  2050  and  2052 , for example, that may have teeth  2050   a  and  2052   a , respectively, that may be meshingly engaged to teeth  314   a  and  404   a , respectively, that are formed on the first and third planet carriers  314 - 3  and  404 - 3 , respectively. The locking elements  2050  and  2052  may be rotatably supported on pins  2054  and  2056 , respectively, that may be mounted to another portion of the power tool, such as the transmission sleeve  200 - 3 . In a first speed reduction ratio, which is illustrated in  FIG. 39 , the second and third ring gears  360 - 3  and  400 - 3  are fixed to the transmission sleeve  200 - 3 , for example by teeth  370 - 3  and  418 - 3 , respectively, on the outer diameter of the ring gears  360 - 3  and  400 - 3 , respectively, and mating teeth  254 - 3  and  256 - 3 , respectively, that are formed on the interior of the transmission sleeve  200 - 3 . 
         [0131]    In  FIG. 40 , the transmission assembly  16 - 3  is shown in a second overall speed or gear reduction ratio, wherein the first and second reduction gear sets  302 - 3  and  304 - 3  are in an active mode and the third reduction gear set  306 - 3  is in an inactive mode. The third reduction gear set  306 - 3  may be inactivated by translating the third ring gear  400 - 3  such that the teeth  418 - 3  are not engaged with the mating teeth  256 - 3  on the transmission sleeve  200 - 3  but rather with the teeth  2052   a  of the second idler gear  2052 . Translation of the third ring gear  400 - 3  may also cause the third planet carrier  404 - 3  to slide on the second idler gear  2052  and/or the third set of planet gears  402  to slide relative to the transmission sleeve  200 - 3 . 
         [0132]    In  FIG. 41 , the transmission assembly  16 - 3  is shown in a third overall speed or gear reduction ratio, wherein the first and third reduction gear sets  302 - 3  and  306 - 3  are in an active mode and the second reduction gear set  304 - 3  is in an inactive mode. The second reduction gear set  304 - 3  may be inactivated by translating the second ring gear  360 - 3  such that the teeth  370 - 3  are not engaged with the mating teeth  254 - 3  on the transmission sleeve  200 - 3  but rather with the teeth  2050   a  of the first idler gear  2050 . Translation of the second ring gear  360 - 3  may also cause the first planet carrier  314 - 3  to slide on the first idler gear  2050  and/or the first set of planet gears  344  to slide relative to the transmission sleeve  200 - 3 . 
         [0133]    With reference to  FIGS. 42 through 44 , the transmission assembly  16 - 4  may be configured such that portions of the second reduction gear set  304 - 4  and the third reduction gear set  306 - 4  may slide into and out of locking engagement with another element of the transmission assembly  16 - 4 . In the example provided, the second and third sets of planet gears  382 - 4  and  402 - 4 , respectively, may be translated between a first position, in which they meshingly engage an associated ring gear, and a second position, in which they non-rotatably engage an associated planet carrier as well as meshingly engage the associated ring gear. In a first speed reduction ratio, which is illustrated in  FIG. 42 , the second and third ring gears  360 - 4  and  400 - 4  are fixed to the transmission sleeve  200 - 4 , in a manner that is similar to that which was described above in conjunction with  FIG. 33 . 
         [0134]    In  FIG. 43 , the transmission assembly  16 - 4  is shown in a second overall speed or gear reduction ratio, wherein the first and second reduction gear sets  302 - 4  and  304 - 4  are in an active mode and the third reduction gear set  306 - 4  is in an inactive mode. The third reduction gear set  306 - 4  may be inactivated by translating the pin  2002  out of engagement with the teeth  418 - 1  on the third ring gear  400 - 4  and translating the third set of planet gears  402 - 4  into engagement with the third planet carrier  404 - 4  such that the third set of planet gears  402 - 4  are maintained in a stationary condition relative to the third planet carrier  404 - 4 . Engagement of the third set of planet gears  402 - 4  to the third planet carrier  404 - 4  may be made in any desired manner, such as frictional engagement or through mating features. In the example provided, teeth  2076  are formed into an axial end face of the third set of planet gears  402 - 4  and mating teeth  2078  are formed on the third planet carrier  404 - 4  which meshingly engage the teeth  2076  on the third set of planet gears  402 - 4 . The third ring gear  400 - 4  may optionally translate with the third set of planet gears  402 - 4 . 
         [0135]    In  FIG. 44 , the transmission assembly  16 - 4  is shown in a third overall speed or gear reduction ratio, wherein the first and third reduction gear sets  302 - 4  and  306 - 4  are in an active mode and the second reduction gear set  304 - 4  is in an inactive mode. The second gear set  304 - 4  may be inactivated by translating the pin  2000  out of engagement with the teeth  370 - 1  of the second ring gear  360 - 4  and translating the second set of planet gears  382 - 4  into engagement with the first planet carrier  314 - 4  such that the second set of planet gears  382 - 4  are maintained in a stationary condition relative to the first planet carrier  314 - 4 . Engagement of the second set of planet gears  382 - 4  to the first planet carrier  314 - 4  may be made in any desired manner, such as frictional engagement or through mating features. In the example provided, teeth  2072  are formed into an axial end face of the second set of planet gears  382 - 4  and mating teeth  2074  are formed on the first planet carrier  314 - 4  which meshingly engage the teeth  2072  on the second set of planet gears  382 - 4 . The second ring gear  360 - 4  may optionally translate with the second set of planet gears  382 - 4 . 
         [0136]    In  FIGS. 45 through 47  yet another transmission assembly  16 - 5  constructed in accordance with the teachings of the present disclosure is illustrated. The transmission assembly  16 - 5  may include movable elements, such as pins  2000  and  2002 , which may be employed to lock the second and third ring gears  360 - 5  and  400 - 5 , respectively, in a stationary position, and locking elements, such as first and second idler gears  2050 - 5  and  2052 - 5 , respectively, that may be employed to lock each of the second and third ring gears  360 - 5  and  400 - 5 , respectively, to the first and third planet carriers  314 - 5  and  404 - 5 , respectively. With specific reference to  FIG. 45 , the transmission  16 - 5  is illustrated in a first overall speed reduction or gear ratio wherein the pins  2050 - 5  and  2052 - 5  may be positioned in engagement with teeth  370 - 1  and  418 - 1 , respectively, on the second and third ring gears  360 - 5  and  400 - 5 , respectively, to maintain the second and third ring gears  360 - 5  and  400 - 5  in a stationary position. In this condition, the first and second idler gears  2050 - 5  and  2052 - 5  may be disengaged from the teeth  370 - 1  and  418 - 1  of the second and third ring gears  360 - 5  and  400 - 5 , respectively, as well as from the teeth  314   a  and  404   a  of the first and third planet carriers  314 - 5  and  404 - 5 . 
         [0137]    In  FIG. 46 , the transmission assembly  16 - 5  is illustrated in a second overall speed reduction or gear ratio wherein the first and second reduction gear sets  302 - 5  and  304 - 5 , respectively, are in an active mode and the third reduction gear set  306 - 5  is in an inactive mode. The third reduction gear set  306 - 5  may be inactivated by translating the pin  2002  out of engagement with the teeth  418 - 1  of the third ring gear  400 - 5  and moving the idler gear  2052 - 5 , e.g., by translation and/or rotation, into a position where the teeth  2052   a  of the idler gear  2052 - 5  meshingly engage both the teeth  418 - 1  of the third ring gear  400 - 5  and the teeth  404   a  of the third planet carrier  404 - 5 . 
         [0138]    In  FIG. 47 , the transmission assembly  16 - 5  is illustrated in a third overall speed reduction or gear ratio wherein the first and third reduction gear sets  302 - 5  and  306 - 5  are in an active mode and the second reduction gear set  304 - 5  is in an inactive mode. The second reduction gear set  304 - 5  may be inactivated by translating the pin  2000  out of engagement with the teeth  370 - 1  of the second ring gear  360 - 5  and moving the idler gear  2050 - 5 , e.g., by translation and/or rotation, into a position where the teeth  2050   a  of the idler gear  2050 - 5  meshingly engage both the teeth  370 - 1  of the second ring gear  360 - 5  and the teeth  314   a  of the first planet carrier  314 - 5 . 
         [0139]    In  FIGS. 48 through 50  yet another transmission assembly  16 - 6  constructed in accordance with the teachings of the present disclosure is illustrated. The transmission assembly  16 - 6  may include movable elements, such as idler gears  2050 - 6  and  2052 - 6  which may be employed to lock the ring gears  360 - 6  and  400 - 6 , respectively, into a stationary position relative to the transmission sleeve  200 - 6  or to lock the second and third ring gears  360 - 6  and  400 - 6  for rotation with the first and third planet carriers  314 - 6  and  404 - 6 , respectively. With specific reference to  FIG. 48 , the transmission assembly  16 - 6  is illustrated in a first overall speed reduction or gear ratio wherein the idler gears  2050 - 6  and  2052 - 6  are positioned to maintain the second and third ring gears  360 - 6  and  400 - 6  in a stationary position. The idler gears  2050 - 6  and  2052 - 6  may engage a feature, such as teeth  2090  and  2092 , respectively, that is formed on another part of the power tool, such as the housing  12 - 6  or the transmission sleeve  200 - 6 , which inhibits their rotation and thereby locks a respective one of the ring gears in a stationary position. 
         [0140]    In  FIG. 49 , the transmission assembly  16 - 6  is illustrated in a second overall speed reduction or gear ratio wherein the first and second reduction gear sets  302 - 6  and  304 - 6  are in an active mode and the third reduction gear set  306 - 6  is in an inactive mode. The third reduction gear set  306 - 6  may be inactivated by translating the idler gear  2052 - 6 , e.g., along the journal pin  2096 , into a position where the teeth  2052   a  of the idler gear  2052 - 6  do not engage the tooth or teeth  2092  but engage both the teeth  418 - 1  of the third ring gear  400 - 6  and the teeth  404   a  of the third planet carrier  404 - 6 . 
         [0141]    In  FIG. 50 , the transmission assembly  16 - 6  is illustrated in a third overall speed reduction or gear ratio, wherein the first and third reduction gear sets  302 - 6  and  306 - 6  are in an active mode, and the second reduction gear set  304 - 6  is in an inactive mode. The second reduction gear set  304 - 6  may be inactivated by translating the idler gear  2050 , e.g., along the journal pin  2096 , into a position where the teeth  2050   a  of the idler gear  2050 - 6  do not engage the tooth or teeth  2090  but engage both the teeth  370 - 1  of the second ring gear  360 - 6  and the teeth  314   a  of the first planet carrier  314 - 6 . 
         [0142]    In  FIGS. 51 through 53  a further transmission assembly  16 - 7  constructed in accordance with the teachings of the present disclosure is illustrated. The transmission assembly  16 - 7  may include movable, intermediate locking elements, such as collars  3000  and  3002 , which may be employed to lock the second and third ring gears  360 - 7  and  400 - 7  in a stationary position or for rotation with the first and third planet carriers  314 - 7  and  404 - 7 , respectively. With specific reference to  FIG. 51 , the transmission  16 - 7  is illustrated in a first overall speed reduction or gear ratio wherein the collars  3000  and  3002  are positioned to maintain the second and third ring gears  360 - 7  and  400 - 7  in a stationary position. The collars  3000  and  3002  may engage the teeth  370 - 1  and  418 - 1  of the second and third ring gears  360 - 7  and  400 - 7  and may include features, such as teeth or pins  3004  and  3006 , respectively, that may engage a mating feature, such as teeth or apertures  3008 , that may be formed into another portion of the power tool, such as the transmission sleeve  200 - 7 , to thereby lock a respective one of the ring gears in a stationary position. Alternatively, the pins  3004  and  3006  of the collars  3000  and  3002 , respectively, may extend through apertures (not shown) that can be formed in the second and third ring gears  360 - 7  and  400 - 7 , respectively. 
         [0143]    In  FIG. 52 , the transmission assembly  16 - 7  is illustrated in a second overall speed reduction or gear ratio wherein the first and second reduction gear sets  302 - 7  and  304 - 7  are in an active mode and the third reduction gear set  306 - 7  is in an inactive mode. The third reduction gear set  306 - 7  may be inactivated by translating the collar  3002  into a position where the pins  3006  disengage the apertures  3008  in the transmission sleeve  200 - 7  and the collar  3002  engages both the teeth  418 - 1  of the third ring gear  400 - 7  and the third planet carrier  404 - 7 . Any appropriate means may be employed to engage the collar  3002  and the third planet carrier  404 - 7  to one another, including friction (i.e., frictional engagement), or features, such as pins or teeth, that may be formed on one or both of the third planet carrier  404 - 7  and the collar  3002 . In the example provided, the collar  3002  frictionally engages the planet carrier  404 - 7 . 
         [0144]    In  FIG. 53 , the transmission assembly  16 - 7  is illustrated in a third overall speed reduction or gear ratio wherein the first and third reduction gear sets  302 - 7  and  306 - 7  are in an active mode and the second reduction gear set  304 - 7  is in an inactive mode. The second reduction gear set  304 - 7  may be inactivated by translating the collar  3000  into a position where the pins  3004  disengage the apertures  3008  in the transmission sleeve  200 - 7  and the collar  3000  engages both the teeth  370 - 1  of the second ring gear  360 - 7  and the first planet carrier  314 - 7 . Any appropriate means may be employed to engage the collar  3000  and the first planet carrier  314 - 7  to one another, including friction (i.e., frictional engagement), or features, such as pins or teeth, that may be formed on one or both of the first planet carrier  314 - 7  and the collar  3000 . In the example provided, the collar  3000  frictionally engages the first planet carrier  314 - 7 . 
         [0145]    The embodiment of  FIGS. 54 through 56  is generally similar to that of  FIGS. 51 through 53 , except that each of the collars  3000 - 8  and  3002 - 8  can include teeth  3050  and  3052 , respectively, that meshingly engage the teeth  370 - 8  and  418 - 8 , respectively, that can be formed on the second and third ring gears  360 - 8  and  400 - 8 , respectively. As shown in  FIG. 56 , the collar  3000 - 8  may be translated into a position where the teeth  3050  meshingly engage both the teeth  370 - 8  of the second ring gear  360 - 8  and the teeth  314   a  of the first planet carrier  314 - 8  to thereby place the second reduction gear set  304 - 8  into the inactive mode. Similarly, the collar  3002 - 8  may be translated into a position where the teeth  3052  engage both the teeth  418 - 8  of the third ring gear  400 - 8  and the teeth  404   a  of the third planet carrier  404 - 8  to thereby place the third reduction gear set  306 - 8  into the inactive mode as is shown in  FIG. 55 . The first reduction gear set  302 - 8  is in the active mode in each of  FIGS. 54 through 56 . 
         [0146]    While the disclosure has been described in the specification and illustrated in the drawings with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various embodiments is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one embodiment may be incorporated into another embodiment as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this disclosure, but that the disclosure will include any embodiments falling within the foregoing description and the appended claims. 
         [0147]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.