Patent Publication Number: US-7717191-B2

Title: Multi-mode hammer drill with shift lock

Description:
FIELD 
   The present disclosure relates to a multi-mode hammer drill, and more particularly to a shift mechanism for such a drill. 
   BACKGROUND 
   The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
   Hammer-drills generally include a floating rotary-reciprocatory output spindle journaled in the housing for driving a suitable tool bit coupled thereto. In operation, the spindle can be retracted axially within the housing and against the force of a suitable resilient means, upon engagement of the tool bit with a workpiece and a manual bias force exerted by the operator on the tool. A fixed hammer member can be secured in the housing, and a movable hammer member can be carried by the spindle. The movable hammer member can have a ratcheting engagement with the fixed hammer member to impart a series of vibratory impacts to the spindle in a “hammer-drilling” mode of operation. A shiftable member can act upon the spindle to change from a “drilling” mode to the “hammer-drilling” mode, and vice versa. 
   Multi-speed drills typically include a transmission for transferring torque between a driven input member and an output spindle. The transmission can include a shifting mechanism for changing between a low-speed mode and a high-speed mode. The vibratory impacts in the hammer-drilling mode can create axial force oscillations that can affect the shifting mechanism. 
   SUMMARY 
   A multi-mode hammer drill comprises a support member having a lock surface. A shift member is mounted on a support member for movement along the support member between a first mode position corresponding to a first mode of operation and a second mode position corresponding to a second mode of operation. The shift member has a cooperating lock surface. A biasing member is configured to exert a biasing force on the shift member in a direction toward a lock position where the lock surface can engage against the cooperating lock surface, when the shift member is in the first position. An actuation member is coupled to the shift member in a configuration that generates a force sufficient to overcome the biasing force and move the shift member to an unlock position where the lock surface cannot engage against the cooperating lock surface. The actuation member generates the force is as part of a shifting operation from the first mode of operation to the second mode of operation. 
   A multi-mode hammer drill comprises a support member having a lock surface and a shift surface. A shift member has a cooperating lock surface. The shift member is mounted on the support member in a configuration permitting movement of the shift member along the shift surface between a first mode position corresponding to a first mode of operation and a second mode position corresponding to a second mode of operation. When the shift member is in the first mode position, the configuration permits limited movement of the shift member between a lock position and an unlock position in a direction that is substantially perpendicular to the shift surface. A biasing member is configured to exert a biasing force on the shift member toward the lock position where the lock surface can engage against the cooperating lock surface, when the shift member is in the first position. An actuation member is coupled to the shift member in a configuration that, during shifting between the first mode of operation and the second mode of operation, exerts a force on the shift member that is sufficient to overcome the biasing force and cause movement of the shift member in a direction that is substantially perpendicular to the shift surface to an unlock position where the lock surface cannot engage against the cooperating lock surface. Thereafter, the actuation member moves the shift member from the first mode position to the second mode position. 
   A multi-mode hammer drill comprises a support member having a lock surface, and a shift surface substantially perpendicular to the lock surface. A shift member has a cooperating lock surface. The shift member is mounted on the support member in a configuration permitting movement of the shift member along the shift surface between a first mode position corresponding to a first mode of operation and a second mode position corresponding to a second mode of operation. When the shift member is in the first mode position, the configuration permitting limited rotational movement between a lock position and an unlock position. A biasing member is configured to exert a biasing force on the shift member to cause rotation of the shift member toward the lock position where the lock surface can engage against the cooperating lock surface, when the shift member is in the first mode position. An actuation member is coupled to the shift member in a configuration that, during shifting between the first mode of operation and the second mode of operation, exerts a force on the shift member in a direction that is substantially parallel to a direction of movement of the shift member and offset from the shift surface. The force exerting a moment on the shift member, thereby overcoming the biasing force and causing counter-rotation of the shift member into the unlock position where the lock surface cannot engage against the cooperating lock surface. Thereafter, the actuation member moves the shift member from the first mode position to the second mode position. 
   Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 

   
     DRAWINGS 
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       FIG. 1  is a perspective view of an exemplary multi-speed hammer-drill constructed in accordance with the teachings of the present disclosure; 
       FIG. 2  is partial perspective view of a distal end of the hammer-drill of  FIG. 1  including a mode collar constructed in accordance with the teachings of the present disclosure; 
       FIG. 3  is a rear perspective view of the mode collar illustrated in  FIG. 2  including an electronic speed shift pin and a mechanical speed shift pin; 
       FIG. 4  is a rear perspective view of the mode collar of  FIG. 3 ; 
       FIG. 5  is another rear perspective view of the mode collar of  FIG. 3 ; 
       FIG. 6  is a rear view of the mode collar shown in a first mode corresponding to an electronic low speed; 
       FIG. 7  is a rear view of the mode collar shown in a second mode corresponding to a mechanical low speed; 
       FIG. 8  is a rear view of the mode collar shown in a third mode corresponding to a mechanical high speed; 
       FIG. 9  is a rear view of the mode collar shown in a fourth mode corresponding to a mechanical high speed and hammer mode; 
       FIG. 10  is an exploded perspective view of a transmission of the multi-speed hammer-drill of  FIG. 1 ; 
       FIG. 11  is a front perspective view of the mode collar and transmission of the hammer-drill of  FIG. 1  illustrating a shift fork according to the present teachings; 
       FIG. 12  is a perspective view of the mode collar and transmission of the hammer-drill of  FIG. 1  illustrating reduction pinions according to the present teachings; 
       FIG. 13  is a partial sectional view of the hammer-drill taken along lines  13 - 13  of  FIG. 11 ; 
       FIG. 14  is a partial side view of the transmission of the hammer-drill shown with the mode collar in section and in the first mode (electronic low); 
       FIG. 15  is a partial side view of the transmission of the hammer-drill shown with the mode collar in section and in the second mode (mechanical low); 
       FIG. 16  is a partial side view of the transmission of the hammer-drill shown with the mode collar in section and in the third mode (mechanical high); 
       FIG. 17  is a partial side view of the transmission of the hammer-drill shown with the mode collar in section and in the fourth mode (mechanical high-speed and hammer mode); 
       FIG. 18  is a plan view of an electronic speed shift switch according to the present teachings and shown in an un-actuated position; 
       FIG. 19  is a plan view of the electronic speed shift switch of  FIG. 18  and shown in an actuated position; 
       FIG. 20  is an exploded view of a portion of a transmission of the hammer-drill; 
       FIG. 21  is a partial cross-section view of the ratchet teeth of the low output gear and clutch member of the transmission of  FIG. 20 ; 
       FIG. 22  is a perspective view of the transmission of the hammer-drill of  FIG. 20  according to the present teachings; 
       FIG. 23  is a perspective view of the forward case of the hammer-drill in accordance with teachings of the present disclosure; 
       FIG. 24  is a partial perspective view of various hammer mechanism components; 
       FIG. 25  is a partial cross-section view of various hammer mechanism and housing components; and 
       FIG. 26  is a partial cross-section view of various shift locking member components. 
   

   DETAILED DESCRIPTION 
   With initial reference to  FIG. 1 , an exemplary hammer-drill constructed in accordance with the present teachings is shown and generally identified at reference numeral  10 . The hammer-drill  10  can include a housing  12  having a handle  13 . The housing  12  generally comprising a rearward housing  14 , a forward housing  16  and a handle housing  18 . These housing portions  14 ,  16 , and  13  can be separate components or combined in various manners. For example, the handle housing  18  can be combed as part of a single integral component forming at least some portion of the rearward housing  14 . 
   In general, the rearward housing  14  covers a motor  20  ( FIG. 18 ) and the forward housing  16  covers a transmission  22  ( FIG. 11 ). A mode collar  26  is rotatably disposed around the forward housing  16  and an end cap  28  is arranged adjacent the mode collar  26 . As will be described in greater detail herein, the mode collar  26  is selectively rotatable between a plurality of positions about an axis  30  that substantially corresponds to the axis of a floating rotary-reciprocatory output spindle  40 . The mode collar  26  is disposed around the output spindle  40  and may be concentrically or eccentrically mounted around the output spindle  40 . Each rotary position of the mode collar  26  corresponds to a mode of operation. An indicator  32  is disposed on the forward housing  16  for aligning with a selected mode identified by indicia  34  provided on the mode collar  26 . A trigger  36  for activating the motor  20  can be disposed on the housing  12  for example on the handle  13 . The hammer-drill  10  according to this disclosure is an electric system having a battery (not shown) removably coupled to a base  38  of the handle housing  18 . It is appreciated, however, that the hammer-drill  10  can be powered with other energy sources, such as AC power, pneumatically based power supplies and/or combustion based power supplies, for example. 
   The output spindle  40  can be a floating rotary-reciprocatory output spindle journaled in the housing  12 . The output spindle  40  is driven by the motor  20  ( FIG. 20 ) through the transmission  22  ( FIG. 11 ). The output spindle  40  extends forwardly beyond the front of the forward housing  16 . A chuck (not shown) can be mounted on the output spindle  40  for retaining a drill bit (or other suitable implement) therein. 
   Turning now to  FIGS. 2-9 , the mode collar  26  will be described in greater detail. The mode collar  26  generally defines a cylindrical body  42  having an outboard surface  44  and an inboard surface  46 . The outboard surface  44  defines the indicia  34  thereon. The indicia  34  correspond to a plurality of modes of operation. In the example shown (see  FIG. 2 ), the indicia  34  includes the numerals “ 1 ”, “ 2 ”, “ 3 ”, and drill and “hammer” icons. Prior to discussing the specific operation of the hammer-drill  10 , a brief description of each of these exemplary modes is warranted. The mode “ 1 ” generally identified at reference  50  corresponds to an electronic low speed drilling mode. The mode “ 2 ” generally identified at reference  52  corresponds to a mechanical low speed mode. The mode “ 3 ” generally identified at reference  54  corresponds to a mechanical high speed mode. The “hammer-drill” mode generally identified at reference  56  corresponds to a hammer-drill mode. As will become appreciated these modes are exemplary and may additionally or alternatively comprise other modes of operation. The outboard surface  44  of the mode collar  26  can define ribs  60  for facilitating a gripping action. 
   The inboard surface  46  of the mode collar  26  can define a plurality of pockets therearound. In the example shown four pockets  62 ,  64 ,  66 , and  68 , respectively ( FIG. 4 ), are defined around the inboard surface  46  of the mode collar  26 . A locating spring  70  ( FIGS. 6-9 ) partially nests into one of the plurality of pockets  62 ,  64 ,  66 , and  68  at each of the respective modes. As a result, the mode collar  26  can positively locate at each of the respective modes and provide feedback to a user that a desired mode has been properly selected. A cam surface  72  extends generally circumferentially around the inboard surface  46  of the mode collar  26 . The cam surface  72  defines a mechanical shift pin valley  74 , a mechanical shift pin ramp  76 , a mechanical shift pin plateau  78 , an electronic shift pin valley  80 , an electronic shift pin ramp  82 , an electronic shift pin plateau  84 , and a hammer cam drive rib  86 . 
   With specific reference now to FIGS.  3  and  6 - 9 , the mode collar  26  communicates with a mechanical speed shift pin  90  and an electronic speed shift pin  92 . More specifically, a distal tip  94  ( FIG. 3 ) of the mechanical speed shift pin  90  and a distal tip  96  of the electronic speed shift pin  92 , respectively, each ride across the cam surface  72  of the mode collar  26  upon rotation of the mode collar  26  about the axis  30  ( FIG. 1 ) by the user.  FIG. 6  illustrates the cam surface  72  of the mode collar  26  in mode “ 1 ”. In mode “ 1 ”, the distal tip  96  of the electronic speed shift pin  92  locates at the electronic shift pin plateau  84 . Concurrently, the distal tip  94  of the mechanical speed shift pin  90  locates at the mechanical shift pin plateau  78 . 
     FIG. 7  illustrates the cam surface  72  of the mode collar  26  in mode “ 2 ”. In mode “ 2 ”, the distal tip  96  of the electronic speed shift pin  92  locates on the electronic shift pin valley  80 , while the distal tip  94  of the mechanical speed shift pin  90  remains on the mechanical shift pin plateau  78 .  FIG. 7  illustrates the dial  72  of the mode collar  26  in mode “ 3 ”. In mode “ 3 ”, the distal tip  96  of the electronic speed shift pin  92  locates on the electronic shift pin valley  80 , while the distal tip  94  of the mechanical speed shift pin  90  locates on the mechanical shift pin valley  74 . In the “hammer-drill” mode, the distal tip  96  of the electronic speed shift pin  92  locates on the electronic shift pin valley  80 , while the distal tip  94  of the mechanical speed shift pin  90  locates on the mechanical shift pin valley  74 . Of note, the distal tips  96  and  94  of the electronic speed shift pin  92  and the mechanical speed shift pin  90 , respectively, remain on the same surfaces (i.e., without elevation change) between the mode “ 3 ” and the “hammer-drill” mode. 
   As can be appreciated, the respective ramps  76  and  82  facilitate transition between the respective valleys  74  and  80  and plateaus  78  and  84 . As will become more fully appreciated from the following discussion, movement of the distal tip  96  of the electronic speed shift pin  92  between the electronic shift pin valley  80  and plateau  84  influences axial translation of the electronic speed shift pin  92 . Likewise, movement of the distal tip  94  of the mechanical speed shift pin  90  between the mechanical shift pin valley  74  and plateau  78  influences axial translation of the mechanical speed shift pin  90 . 
   Turning now to  FIGS. 10 ,  13 - 17 , the hammer-drill  10  will be further described. The hammer-drill  10  includes a pair of cooperating hammer members  100  and  102 . The hammer members  100  and  102  can generally be located adjacent to and within the circumference of the mode collar  26 . By providing the cooperating hammer members  100 ,  102  in this location a particularly compact transmission and hammer mechanism can be provided. As described hereinafter, hammer member  100  is fixed to the housing so that it is non-rotatable or non-rotating. On the other hand, hammer member  102  is fixed to the output spindle  40 , e.g., splined or press fit together, so that hammer member  102  rotates together with the spindle  40 . In other words, the hammer member  102  is rotatable or rotating. The hammer members  100  and  102  have cooperating ratcheting teeth  104  and  106 , hammer members  100  and  102 , which are conventional, for delivering the desired vibratory impacts to the output spindle  40  when the tool is in the hammer-drill mode of operation. The hammer members  100 ,  102  can be made of hardened steel. Alternatively, the hammer members  100 ,  102  can be made of another suitable hard material. 
   A spring  108  is provided to forwardly bias the output spindle  40  as shown in  FIG. 14 , thereby tending to create a slight gap between opposed faces of the hammer members  100  and  102 . In operation in the hammer mode as seen in  FIG. 17 , a user contacts a drill bit against a workpiece exerting a biasing force on the output spindle  40  that overcomes the biasing force of spring  108 . Thus, the user causes cooperating ratcheting teeth  104  and  106  of the hammer members  100  and  102 , respectively, to contact each other, thereby providing the hammer function as the rotating hammer member  102  contacts the non-rotating hammer member  100 . 
   Referring to  FIGS. 24 and 25 , axially movable hammer member  100  includes three equally spaced projections  250  that extend radially. The radial projections  250  can ride in corresponding grooves  266  in the forward housing  16 . An axial groove  252  can be located along an exterior edge of each radial projection  250 . The axial groove  252  provides a support surface along its length. Positioned within each axial groove  252  is a support guide rod  254  that provides a cooperating support surface at its periphery. Thus, the axial groove  252  operates as a support aperture having a support surface associated therewith, and the guide rod  254  operates as a support member having a cooperating support surface associated therewith. 
   Located on each hammer support rod  254  is a return spring  256 . The return spring  256  is a biasing member acting upon the non-rotating hammer member to bias the non-rotating hammer toward the non-hammer mode position. The proximal end of each hammer support rod  254  can be press-fit into one of a plurality of first recesses  260  in the forward housing  16 . This forward housing  16  can be the gear case housing. This forward housing  16  can be wholly or partially made of aluminum. Alternatively, the forward housing  16  can be wholly or partially made of plastic or other relatively soft material. The plurality of first recesses can be located in the relatively soft material of the forward housing  16 . The distal end of each hammer support rod  254  can be clearance fit into one of a plurality of second recesses  262  in the end cap  28 . The end cap  28  can be wholly or partially made of a material which is similar to that of the forward housing  16 . Thus, the plurality of second recesses  262  of the end cap  28  can be located in the relatively soft material. The end cap  28  is attached to the forward housing member  16  with a plurality of fasteners  264  which can be screws. 
   The support rods  254  can be made of hardened steel. Alternatively, the support rods  254  can be made of another suitable hard material, so that the support rods are able to resist inappropriate wear which might otherwise be caused by the axially movable hammer member  100 , during hammer operation. The hammer members  100 ,  102  can be made of the same material as the support rods  254 . To resist wear between the support rods  254  (which can be of a relatively hard material) and the recesses  260 ,  262  (which can be of a relatively soft material), the recesses  260 ,  262  can have a combined depth so they can together accommodate at least about 25% of the total axial length of the support rod  254 ; or alternatively, at least about 30% the length. In addition, press-fit recesses  260  can have a depth so it accommodates at least about 18% of the total axial length of the support rod  254 ; or alternatively, at least about 25% of the length. Further, each of the recesses  260 ,  262  can have a depth of at least about 12% of the axial length of the support rod  254 . 
   Thus, the hammer member  100  is permitted limited axial movement, but not permitted to rotate with the axial spindle  40 . The support rods  254  can provide the rotational resistance necessary to support the hammer member  100  during hammer operation. As a result, the projections  250  of the typically harder hammer member  100  can avoid impacting upon and damaging the groove  266  walls of the forward housing  16 . This can permit the use of an aluminum, plastic, or other material to form the forward housing  16 . 
   On the side of hammer member  100  opposite ratcheting teeth  104 , a cam  112  having a cam arm  114  and a series of ramps  116  is rotatably disposed axially adjacent to the axially movable hammer member  100 . During rotation of the mode collar  26  into the “hammer-drill” mode, the cam arm  114  is engaged and thereby rotated by the hammer cam drive rib  86  ( FIG. 4 ). Upon rotation of the cam  112 , the series of ramps  116  defined on the cam  112  ride against complementary ramps  118  defined on an outboard face of the axially movable hammer member  100  to urge the movable hammer member  100  into a position permitting cooperative engagement with the rotating hammer member  102 . Spring  184  is coupled to cam arm  144 , so that upon rotation of the mode collar  26  backwards, out of the hammer mode, the spring  184  anchored by bolt  266  rotates cam  112  backwards. 
   With continued reference to  FIGS. 10-17 , the transmission  22  will now be described in greater detail. The transmission  22  generally includes a low output gear  120 , a high output gear  122 , and a shift sub-assembly  124 . The shift sub-assembly  124  includes a shift fork  128 , a shift ring  130 , and a shift bracket  132 . The shift fork  128  defines an annular tooth  136  ( FIG. 12 ) that is captured within a radial channel  138  defined on the shift ring  130 . The shift ring  130  is keyed for concurrent rotation with the output spindle  40 . The axial position of the shift ring  130  is controlled by corresponding movement of the shift fork  128 . The shift ring  130  carries one or more pins  140 . The pins  140  are radially spaced from the output spindle  40  and protrude from both sides of the shift ring  130 . One or more corresponding pockets or detents (not specifically shown) are formed in the inner face of the low output gear  120  and the high output gear  122 , respectively. The pins  140  are received within their respective detent when the shift ring  130  is shifted axially along the output spindle  40  to be juxtaposed with either the low output gear  120  or the high output gear  122 . 
   The shift fork  128  slidably translates along a static shift rod  144  upon axial translation of the mechanical speed shift pin  90 . A first compliance spring  146  is disposed around the static shift rod  144  between the shift bracket  132  and the shift fork  128 . A second compliance spring  148  is disposed around the static shift rod  144  between the shift bracket  132  and a cover plate  150 . The first and second compliance springs  146  and  148  urge the shift fork  128  to locate the shift ring  130  at the desired location against the respective low or high output gear  120  or  122 , respectively. In this way, in the event that during shifting the respective pins  140  are not aligned with the respective detents, rotation of the low and high output gears  120  and  122  and urging of the shift fork  128  by the respective compliance springs  146  and  148  will allow the pins  140  to will be urged into the next available detents upon operation of the tool and rotation of the gears  120 ,  122 . In sum, the shift sub-assembly  124  can allow for initial misalignment between the shift ring  130  and the output gears  120  and  122 . 
   An output member  152  of the motor  20  ( FIG. 18 ) is rotatably coupled to a first reduction gear  154  ( FIG. 12 ) and a first and second reduction pinions  156  and  158 . The first and second reduction pinions  156 ,  158  are coupled to a common spindle. The first reduction pinion  156  defines teeth  160  that are meshed for engagement with teeth  162  defined on the low output gear  120 . The second reduction pinion  158  defines teeth  166  that are meshed for engagement with teeth  168  defined on the high output gear  122 . As can be appreciated, the low and high output gears  120  and  122  are always rotating with the output member  152  of the motor  20  by way of the first and second reduction pinions  156  and  158 . In other words, the low and high output gears  120  and  122  remain in meshing engagement with the first and second reduction pinions  156  and  158 , respectively, regardless of the mode of operation of the drill  10 . The shift sub-assembly  124  identifies which output gear (i.e., the high output gear  122  or the low output gear  120 ) is ultimately coupled for drivingly rotating the output spindle  40  and which spins freely around the output spindle  40 . 
   With specific reference now to  FIGS. 14-17 , shifting between the respective modes of operation will be described.  FIG. 14  illustrates the hammer-drill  10  in the mode “ 1 ”. Again, mode “ 1 ” corresponds to the electronic low speed setting. In mode “ 1 ”, the distal tip  96  of the electronic speed shift pin  92  is located on the electronic shift pin plateau  84  of the mode collar  26  (see also  FIG. 6 ). As a result, the electronic speed shift pin  92  is translated to the right as viewed in  FIG. 14 . As will be described in greater detail later, translation of the electronic speed shift pin  92  causes a proximal end  172  of the electronic speed shift pin  92  to slidably translate along a ramp  174  defined on an electronic speed shift switch  178 . Concurrently, the mechanical speed shift pin  90  is located on the mechanical shift pin plateau  78  of the mode collar  26  (see also  FIG. 6 ). As a result, the mechanical speed shift pin  90  is translated to the right as viewed in  FIG. 14 . As shown, the mechanical speed shift pin  90  urges the shift fork  128  to the right, thereby ultimately coupling the low output gear  120  with the output spindle  40 . Of note, the movable and fixed hammer members  100  and  102  are not engaged in mode “ 1 ”. 
     FIG. 15  illustrates the hammer-drill  10  in the mode “ 2 ”. Again, mode “ 2 ” corresponds to the mechanical low speed setting. In mode “ 2 ”, the distal tip  96  of the electronic speed shift pin  92  is located on the electronic shift pin valley  80  of the mode collar  26  (see also  FIG. 7 ). As a result, the electronic speed shift pin  92  is translated to the left as viewed in  FIG. 15 . Translation of the electronic speed shift pin  92  causes the proximal end  172  of the electronic speed shift pin  92  to slidably retract from engagement with the ramp  174  of the electronic speed shift switch  178 . Retraction of the electronic speed shift pin  92  to the left is facilitated by a return spring  180  captured around the electronic speed shift pin  92  and bound between a collar  182  and the cover plate  150 . 
   Concurrently, the mechanical speed shift pin  90  is located on the mechanical shift pin plateau  78  of the mode collar  26  (see also  FIG. 7 ). As a result, the mechanical speed shift pin  90  remains translated to the right as viewed in  FIG. 15 . Again, the mechanical speed shift pin  90  locating the shift fork  128  to the position shown in  FIG. 15  ultimately couples the low output gear  120  with the output spindle  40 . Of note, as in mode  1 , the movable and fixed hammer members  100  and  102  are not engaged in mode “ 2 ”. Furthermore, shifting between mode  1  and mode  2  results in no change in the axial position of one of the shift pins (shift pin  90 ), but results in an axial change in the position of the other shift pin (shift pin  92 ) as a result of the cam surface  72  of the mode collar  26 . 
     FIG. 16  illustrates the hammer-drill  10  in the mode “ 3 ”. Again, mode “ 3 ” corresponds to the mechanical high speed setting. In mode “ 3 ”, the distal tip  96  of the electronic speed shift pin  92  is located on the electronic shift pin valley  80  of the mode collar  26  (see also  FIG. 8 ). As a result, the electronic speed shift pin  92  remains translated to the left as viewed in  FIG. 16 . Again, in this position, the proximal end  172  of the electronic speed shift pin  92  is retracted from engagement with the ramp  174  of the electronic speed shift switch  178 . Concurrently, the mechanical speed shift pin  90  is located on the mechanical shift pin valley  74  of the mode collar  26  (see also  FIG. 8 ). As a result, the mechanical speed shift pin  90  is translated to the left as viewed in  FIG. 16 . Again, the mechanical speed shift pin  90  locating the shift fork  128  to the position shown in  FIG. 16  ultimately couples the high output gear  120  with the output spindle  40 . Of note, the movable and fixed hammer members  100  and  102  are not engaged in mode “ 3 ”. Again, shifting between mode  2  and mode  3  results in no change in the axial position of one of the shift pins (shift pin  92 ), but results in an axial change in the position of the other shift pin (shift pin  90 ) as a result of the cam surface  72  of the mode collar  26 . 
     FIG. 17  illustrates the hammer-drill  10  in the “hammer-drill” mode. Again, the “hammer-drill” mode corresponds to the mechanical high speed setting with the respective movable and fixed hammer members  100  and  102  engaged. In the “hammer-drill” mode, the distal tip  96  of the electronic speed shift pin  92  is located on the electronic shift pin valley  80  of the mode collar  26  (see also  FIG. 9 ). As a result, the electronic speed shift pin  92  remains translated to the left as viewed in  FIG. 17 . Again, in this position the proximal end  172  of the electronic speed shift pin  92  is retracted from engagement with the ramp  174  of the electronic speed shift switch  178 . Concurrently, the mechanical speed shift pin  90  is located on the mechanical shift pin valley  74  of the mode collar  26  (see also  FIG. 9 ). As a result, the mechanical speed shift pin  90  remains translated to the left as viewed in  FIG. 17 . Thus, in shifting between mode  3  and mode  4 , both the electronic speed shift pin  92  and the mechanical shift pin  90  remain in the same axial position. As discussed below, however, another (non-speed) mode selection mechanism changes position. Specifically, cam  112  is caused to rotate (into an engaged position) by cooperation between the cam drive rib  86  of the mode collar  26  and the cam arm  114  of the cam  112 . A return spring  184  ( FIG. 10 ) urges the cam  112  to rotate into an unengaged position upon rotation of the mode collar  26  away from the “hammer-drill” mode. 
   In the “hammer-drill” mode, however, the respective axially movable and hammer member  100  is axially moved into a position where it can be engaged with rotating hammer member  102 . Specifically, the manual application of pressure against a workpiece (not seen), the output spindle moves axially back against biasing spring  108 . This axial movement of the output spindle  40  carries the rotating hammer member  102  is sufficient that, since the axially movable hammer member  100  has been moved axially forward, the ratchets  104 ,  106  of the hammer members  100  and  102 , respectively, are engagable with each other. Moreover, selection of the “hammer-drill” mode automatically defaults the shift sub-assembly  124  to a position corresponding to the mechanical high speed setting simply by rotation of the mode collar  26  to the “hammer-drill” setting  56  and without any other required actuation or settings initiated by the user. In other words, the mode collar  26  is configured such that the hammer mode can only be implemented when the tool is in a high speed setting. 
   With reference now to  FIGS. 18 and 19 , the electronic speed shift switch  178  will be described in greater detail. The electronic speed shift switch  178  generally includes an electronic speed shift housing  186 , an intermediate or slide member  188 , return springs  190 , an actuation spring  192 , and a push button  194 . Translation of the electronic speed shift pin  92  to the position shown in  FIG. 14  (i.e., the electronic low speed setting) corresponding to mode  1  causes the proximal end  172  of the electronic shift pin  92  to slidably translate along the ramp  174  and, as a result, urge the slide member  188  leftward as viewed in  FIG. 19 . 
   In the position shown in  FIG. 18 , the compliance spring applies a biasing force to the push button  194  that is weaker than the biasing force of the push button spring (not shown) inside the switch. As the slide member  188  is moved to the position shown in  FIG. 19 , The biasing force from the actuation spring  192  pressing on the push button  194 , overcomes the resistance provided by the pushbutton  194 . Thus, the large movement of the slide member  188  is converted to the small movement used to actuate the push button  194  via the actuation spring  192 . The return springs  190  operate to resist inadvertent movement of the slide member  188 , and to return the slide member  188  to its position in  FIG. 18 . 
   Of note, the slide member  188  is arranged to actuate in a transverse direction relative to the axis of the output spindle  40 . As a result, inadvertent translation of the slide member  188  is reduced. Explained further, reciprocal movement of the hammer-drill  10  along the axis  30  may result during normal use of the hammer-drill  10  (i.e., such as by engagement of the hammer members  100  and  102  while in the “hammer-drill” mode, or other movement during normal drilling operations). By mounting the electronic speed shift switch  178  transverse to the output spindle  40 , inadvertent translation of the slide member  188  can be minimized. 
   As shown from  FIG. 18  to  FIG. 19 , the push button  194  is depressed with enough force to activate the electronic speed shift switch  178 . In this position ( FIG. 19 ), the electronic speed shift switch  178  communicates a signal to a controller  200 . The controller  200  limits current to the motor  20 , thereby reducing the output speed of the output spindle  40  electronically based on the signal. Since the actuation is made as a result of rotation of the mode collar  26 , the electronic actuation is seamless to the user. The electronic low speed mode can be useful when low output speeds are needed such as, but not limited to, drilling steel or other hard materials. Moreover, by incorporating the electronic speed shift switch  178 , the requirement of an additional gear or gears within the transmission  22  can be avoided, hence reducing size, weight and ultimately cost. Retraction of the electronic speed shift pin  92  caused by a mode collar selection of either mode “ 2 ”, “ 3 ”, or “hammer-drill”, will return the slide member  188  to the position shown in  FIG. 18 . The movement of the slide member  188  back to the position shown in  FIG. 18  is facilitated by the return springs  190 . While the electronic speed shift switch  178  has been described as having a slide member  188 , other configurations are contemplated. For example, the electronic speed shift switch  178  may additionally or alternatively comprise a plunger, a rocker switch or other switch configurations. 
   Referring now to  FIGS. 1 ,  11 , and  23 , another aspect of the hammer-drill  10  is illustrated. As mentioned above, the hammer-drill  10  includes the rearward housing  14  (i.e., the motor housing) for enclosing the motor  20  and the forward housing  16  (i.e., the transmission housing) for enclosing the transmission  22 . The forward housing  16  includes a gear case housing  149  ( FIGS. 1 and 23 ) and a cover plate  150  ( FIGS. 11 and 23 ). 
   The gear case housing  149  defines an outer surface  179 . It is understood that the outer surface  179  of the gear case housing  149  partially defines the overall outer surface of the hammer-drill  10 . In other words, the outer surface  179  is exposed to allow a user to hold and grip the outer surface  179  during use of the hammer-drill  10 . 
   The cover plate  150  is coupled to the gear case housing  149  via a plurality of first fasteners  151 . As shown in  FIG. 23 , the first fasteners  151  are arranged in a first pattern  153  (represented by a bolt circle in  FIG. 23 ). The first fasteners  151  can be located within the periphery of the gear case housing  149  and can hold the cover plate  150  against a lip  290  within the gear case housing  149 . In one embodiment, the forward housing  16  includes a seal (not shown) between the gear case housing  149  and the cover plate  150 , which reduces leakage of lubricant (not shown) out of the forward housing  16 . 
   The forward housing  16  and the rearward housing  14  are coupled via a plurality of second fasteners  159  ( FIG. 1 ). In the embodiment represented in  FIG. 23 , the second fasteners  159  are arranged in a second pattern  161  (represented by a bolt circle in  FIG. 23 ). As shown, the second pattern  161  of the second fasteners  159  has a larger periphery than the first pattern  153  of the first fasteners  151 . In other words, the second fasteners  159  are further outboard than the first fasteners  151 . Thus, when the forward housing  16  and the rearward housing  14  are coupled, the forward housing  16  and the rearward housing  14  cooperate to enclose the first fasteners  151 . 
   Also, in the embodiment shown, the cover plate  150  can include a plurality of pockets  155 . The pockets  155  can be provided such that the heads of the first fasteners  151  are disposed beneath an outer surface  157  of the cover plate  150 . As such, the first fasteners  151  are unlikely to interfere with the coupling of the rearward and forward housings  14 ,  16 . 
   The cover plate  150  also includes a plurality of projections  163  that extend from the outer surface  157 . The projections  163  extend into the rearward housing  14  to ensure proper orientation of the forward housing  16 . The cover plate  150  further includes a first aperture  165 . The output member  152  of the motor  20  extends through the aperture  165  to thereby rotatably couple to the first reduction gear  154  ( FIG. 12 ). 
   Also, as shown in  FIG. 13 , the cover plate  150  includes a support  167  extending toward the interior of the forward housing  16 . The support  167  is generally hollow and encompasses the output spindle  40  such that the output spindle  40  journals within the support  167 . 
   As shown in  FIGS. 18 ,  19 , and  23  and as described above, the proximal end  172  electronic speed shift pin  92  extends out of the forward housing  16  through the cover plate  150  so as to operably engage the electronic speed shaft switch  178  ( FIG. 19 ). Also, as described above, the return spring  180  is disposed around the electronic speed shift pin  92  and is bound between the collar  182  and the cover plate  150 . Thus, the return spring  180  biases the electronic speed shift pin  92  against the cover plate  150  toward the interior of the forward housing  16 . 
   Furthermore, as described above and seen in  FIGS. 11 and 13 , static shift rod  144  is supported at one end by the gear case cover plate  150 . In addition, the second compliance spring  148  that is disposed about the static shift rod  144  and extends between the shift bracket  132  and the cover plate  150 . As such, the second compliance spring  148  can be biased against the shift bracket  132  and the cover plate  150 . 
   The configuration of the cover plate  150  and the outer shell  149  of the forward housing  16  allows the transmission  22  to be contained independent of the other components of the hammer-drill  10 . As such, manufacture of the hammer-drill  10  can be facilitated because the transmission  22  can be assembled substantially separate from the other components, and the forward housing  16  can then be subsequently coupled to the rearward housing  14  for added manufacturing flexibility and reduced manufacturing time. 
   Furthermore, the cover plate  150  can support several components including, for instance, the output spindle  40  the static shift rod  144  and the electronic shift rod  92 . In addition, several springs can be biased against the cover plate, for instance, compliance spring  148  and spring  180 . Thus, proper orientation of these components are ensured before the rearward housing  14  and the forward housing  16  are coupled. In addition, the cover plate  150  holds the transmission and shift components and various springs in place against the biasing forces of the springs. As such, the cover plate  150  facilitates assembly of the hammer-drill  10 . 
   Referring now to  FIGS. 20 through 22 , clutch details of an embodiment of the transmission  22  of the hammer drill  10  is illustrated. The transmission  22  can include a low output gear  220 , a clutch member  221 , a high output gear  222 , and a shift sub-assembly  224 . The shift sub-assembly  224  can include a shift fork  228 , a shift ring  230 , and a shift bracket  232 . 
   As shown in  FIG. 20 , the clutch member  221  generally includes a base  223  and a head  225 . The base  223  is hollow and tubular, and the head  225  extends radially outward from one end of the base  223 . The base  223  encompasses the spindle  40  and is fixedly coupled (e.g., splined) thereto such that the clutch member  221  rotates with the spindle  40 . The head  225  defines a first axial surface  227 , and the head  225  also defines a second axial surface  229  on a side opposite to the first axial surface  227 . 
   The base  223  of the clutch member  221  extends axially through the bore of the low output gear  220  such that the low output gear  220  is supported by the clutch member  221  on the spindle  40 . The low output gear  220  can be supported for sliding axial movement along the base  223  of the clutch member  221 . Also, the low output gear  220  can be supported for rotation on the base  223  of the clutch member  221 . As such, the low output gear  220  can be supported for axial movement and for rotation relative to the spindle  40 ′. 
   The transmission  22  also includes a retaining member  231 . In the embodiment shown, the retaining member  231  is generally ring-shaped and disposed within a groove  233  provided on an end of the base  223 . As such, the retaining member  231  is fixed in an axial position relative to the first axial surface  227  of the base  223 . 
   The transmission  22  further includes a biasing member  235 . The biasing member  235  can be a disc spring or a conical (i.e., Belleville) spring. The biasing member  235  is supported on the base  223  between the retaining member  231  and the low output gear  220 . As such, the biasing member  235  biases a face  236  of the low output clutch  220  against the face  227  of the base  223  by pressing against the retaining member  231  and low output gear  220 . 
   The clutch member  221  also includes at least one aperture  241  ( FIG. 20 ) on the second axial surface  229 . In the embodiment shown, the clutch member  221  includes a plurality of apertures  241  arranged in a pattern corresponding to that of the pins  240  of the shift ring  230  ( FIG. 21 ). As will be described below, axial movement of the shift ring  230  causes the pins  240  to selectively move in and out of corresponding ones of the apertures  241  of the clutch member  221  such that the shift ring  230  selectively couples to the clutch member  221 . 
   Furthermore, the head  225  of the clutch member  221  includes a plurality of ratchet teeth  237  on the first axial surface  227  thereof, and the low output gear  220  includes a plurality of corresponding ratchet teeth  239  that selectively mesh with the ratchet teeth  237  of the clutch member  221 . More specifically, as shown in  FIG. 22 , the ratchet teeth  237  of the clutch member  221  are cooperate with the ratchet teeth  239  of the low output gear  220 . Each tooth of the ratchet teeth  237  and  239  can include at least one cam surface  245  and  249 , respectively. As will be described, as the clutch member  221  is coupled to the low output gear  220 , the ratchet teeth  237  mesh with corresponding ones of the ratchet teeth  239  such that the cam surfaces  245 ,  249  abut against each other. 
   As shown in  FIG. 22 , the cam surfaces  245 ,  249  of the low output gear  220  and the clutch member  221  are provided at an acute angle α relative to the axis  30  of the spindle  40 . As will be described below, when the clutch member  221  and the low output gear  220  are coupled, an amount of torque is able to transfer therebetween up to a predetermined threshold. This threshold is determined according to the angle α of the cam surfaces  245 ,  249  and the amount of force provided by the biasing member  235  biasing the low output gear  220  toward the clutch member  221 . 
   When the hammer-drill  10  is in the low speed setting (electrical or mechanical) and torque transferred between the low output gear  220  and the clutch member  221  is below the predetermined threshold amount, the corresponding cam surfaces  245 ,  249  remain in abutting contact to allow the torque transfer. However, when the torque exceeds the predetermined threshold amount (e.g., when the drill bit becomes stuck in the workpiece), the cam surfaces  245  of the clutch member  221  cam against the cam surfaces  249  of the low output gear  220  to thereby move (i.e., cam) the low output gear  220  axially away from the clutch member  221  against the biasing force of the biasing member  235 . As such, torque transfer between the clutch member  221  to the low output gear  220  is interrupted and reduced. 
   It will be appreciated that the clutch member  221  limits the torque transfer between the output member  152  of the motor  20  and the spindle  40  to a predetermined threshold. It will also be appreciated that when the hammer-drill  10  is in the mechanical high speed setting, torque transfers between the second reduction pinion  258  and the spindle  40  via the high output gear  222 , and the clutch member  221  is bypassed. However, the gear ratio in the mechanical high speed setting can be such that the maximum torque transferred via the high output gear  222  is less than the predetermined threshold. In other words, the transmission  22  can be inherently torque-limited (below the predetermined threshold level) when the high output gear  222  provides torque transfer. 
   Thus, the clutch member  221  protects the transmission  22  from damage due to excessive torque transfer. Also, the hammer-drill  10  is easier to use because the hammer-drill  10  is unlikely to violently jerk in the hands of the user due to excessive torque transfer. Furthermore, the transmission  22  is relatively compact and easy to assemble since the clutch member  221  occupies a relatively small amount of space and because only one clutch member  221  is necessary. Additionally, the transmission  22  is relatively simple in operation since only the low output gear  220  is clutched by the clutch member  221 . Moreover, in one embodiment, the hammer-drill  10  includes a pusher chuck for attachment of a drill bit (not shown), and because of the torque limiting provided by the clutch member  221 , the pusher chuck is unlikely to over-tighten on the drill bit, making the drill bit easier to remove from the pusher chuck. 
   Additional locking details of the shifting mechanism are illustrated in  FIG. 26 . For clarity, these additional locking details have been omitted from the remaining drawings. Thus, as described hereinafter, the transmission shifting mechanism described herein can include a locking mechanism to maintain the transmission in the high speed gear mode. This high speed gear mode can be the only mode in which the hammer mode can also be active. This locking mechanism, therefore, can resist any tendency of the pins  140  of the shift ring  138  to walk out of the corresponding holes  270  in the high speed gear  122 , during hammer mode operation. 
   The static shift rod  144  operates as a support member for supporting the shift bracket  132 . The shift bracket  132  or shift member is mounted on the static shift rod  144  in a configuration permitting movement of the shift member along the outer surface of the shift rod between a first mode position corresponding to a first mode of operation and a second mode position corresponding to a second mode of operation. The shift bracket  132  can also mounted on the static shift rod  144  in a configuration permitting limited rotational or perpendicular (to the shift surface) movement between a lock position and an unlock position in a direction that is substantially perpendicular to the shift surface. As illustrated, the shift bracket includes two apertures  282 ,  284  through which the static shift rod  144  extends. At least one of the apertures  282  can be slightly larger than the diameter of the static shift rod to allow the limited rotational or perpendicular movement of the shift bracket  144 . 
   A groove  268  can be located in the static shift rod  144 . The groove  268  has a sloped front surface  272  and a back surface  274  that is substantially perpendicular to the axis of the static shift rod  144 . Located on the static shift rod  144  and coupled to the shift bracket  132  is a lock spring member  276 . The lock spring  276  fits into an opening  278  in the shift bracket  132 , so that the lock spring  276  moves along the axis of the static shift rod  144  together with the shift bracket  132 . Thus, when return spring  148  moves the shift bracket  132  into the high speed gear position, the shift bracket  132  aligns with the groove  268 . The lock spring  276  exerts a force in a direction of arrow X, which pushes the shift bracket  132  into the groove  268 . 
   The biasing force in the direction of arrow X provided by the lock spring  276  retains the shift bracket  132  in the groove  268 . In combination with the perpendicular back surface  274  of the groove  268 , which operates with the shift bracket  132  to provide cooperating lock surfaces, the lock spring  276  prevents shift bracket  132  from moving backwards along the static shift rod  144  during hammer mode operation. In this way, the axial forces that are repeatedly exerted on the transmission during hammer mode operation can be resisted by the shifting mechanism. 
   When shifting out of the high speed gear mode, shift pin  90  operates as an actuation member and exerts a force in the direction of arrow Y. Since this force is offset from the surface of the static shift rod  144 , upon which the shift bracket  132  is mounted, this force exerts a moment on the shift bracket  132 ; thereby providing a force in the direction of arrow Z. This force along arrow Z exceeds the biasing spring force along arrow X, which causes the shift bracket  132  to move out of the groove  268 ; thereby allowing movement into the low speed gear mode. The locking spring member  276  includes a protrusion  280  which extends into a cooperating opening  282  of the shift bracket  132  to prevent the opposite side of the shift bracket  132  from entering the groove  268  in response to the force in the direction of arrow Z. The protrusion  280  can be in the form of a lip. 
   For clarity, the direction of the force along arrow X is perpendicular to the axis of the static shift rod  144  and toward the force along arrow Y. The direction of the force along arrow Z is opposite to that of arrow X. The direction of the force along arrow Y is parallel to the axis of the static shift rod  144  and toward the force along arrow X. In addition, the force along arrow Y is spaced away from the axis of the static shift rod  144 , so that its exertion on shift bracket  132  generates a moment that results in the force along arrow Z, which opposes the force along arrow X. 
   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.