Patent Publication Number: US-2021194321-A1

Title: Canned outer-rotor brushless motor for a power tool

Description:
RELATED APPLICATION 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 62/950,562 filed Dec. 19, 2019, content of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This disclosure relates to a brushless motor assembly for a rotary tool, and particularly to an outer-rotor motor assembly having a modular design. 
     BACKGROUND 
     A brushless direct-current (BLDC) motor typically includes a stator that is electronically commuted through various phases and a permanent magnet rotor that is rotatably driven relative to the stator as the phases of the stator are sequentially energized. The stator is commonly provided as a cylindrical core with a hollow center that receives the rotor therein. The rotor is mounted on a rotor shaft. 
     In some power tool applications, an outer-rotor BLDC motor is provided. Outer-rotor BLDC motors are typically capable of building more inertia in the rotor shaft due to the greater mass of the rotor and are more suitable for certain power tool applications. US Publication No. 2019/0058373, which is incorporated herein by reference, provides an example of a nailer that is provided with an outer-rotor BLDC motor, where a flywheel is integrally mounted on the outer surface of the rotor. 
     What is needed is a compact outer rotor motor having a high power density suitable for portable power tool applications. 
     SUMMARY 
     According to another embodiment, a BLDC motor is provided including a rotor shaft on which a rear motor bearing and a front motor bearing are mounted, and a motor housing through which the rotor shaft extends and includes a substantially cylindrical body having an open end and a radial wall opposite the open end, where the radial wall forms a first bearing pocket arranged to receive the front motor bearing therein. The BLDC motor further includes a stator assembly including a stator core having an aperture extending therethrough, stator teeth radially extending outwardly from the stator core and defining slots therebetween, and stator windings wound around the stator teeth. The BLDC motor further includes a stator mount including a radial member coupled to the open end of the motor housing, an elongated cylindrical member projecting axially from the radial member into the aperture of the stator core, a hollow portion extending through a length of the elongated cylindrical member through which the rotor shaft extends, and a second bearing pocket formed in the radial member supporting the rear motor bearing. The BLDC motor further includes an outer rotor including a cylindrical rotor core supporting at least one permanent magnet around an outer surface of the stator core. The BLDC motor further includes a rotor mount including an outer rim arranged to couple to the outer rotor, a radial wall extending inwardly from the outer rim, and an inner body mounted on the rotor shaft. An intermediary bearing is received at least partially within the aperture of the stator core to radially support the stator core relative to the rotor shaft. 
     In an embodiment, the radial wall of the motor housing includes an opening coaxially aligned with first bearing pocket through which the rotor shaft extends out of the motor housing. 
     In an embodiment, the second bearing pocket includes a recess having an open end facing away from the hollow portion. 
     In an embodiment, the BLDC motor includes an enclosure projecting around the recess from the radial member. 
     In an embodiment, the inner body of the rotor mount includes a first side provided adjacent the front motor bearing and a second side adjacent a radial plane formed by front ends of the stator windings. 
     In an embodiment, the BLDC motor includes a positional sensor board mounted on the stator assembly adjacent the stator mount, the positional sensor board including at least one magnetic sensor positioned to magnetically sense the permanent magnet of the rotor. 
     In an embodiment, signal sires are coupled to the positional sensor board and received through an opening of the stator mount. 
     In an embodiment, a ratio of a diameter of the aperture of the stator core to a diameter of the rotor shaft is at less than or equal to 1.2. 
     In an embodiment, the elongated cylindrical member of the stator mount extends through more than approximately 80% of a length of the aperture of the stator core and the intermediary bearing is disposed on a front end of the aperture adjacent the elongated cylindrical member of the stator mount. 
     In an embodiment, a power tool is provided including a housing and a BLDC motor according to any of the embodiments described above disposed within the housing. 
     In an embodiment, the removable battery pack outputs a maximum rated voltage of approximately 20 volts and a rated capacity of 2 Ampere-hours, and wherein the motor produces a maximum power output of at least 450 watts and the power tool has a power-to-weight ratio of at least 280 watts per pounds. 
     In an embodiment, the removable battery pack outputs a maximum rated voltage of approximately 12 volts and a rated capacity of 2 Ampere-hours, and wherein the motor produces a maximum power output of at least 340 watts and the power tool has a power-to-weight ratio of at least 200 watts per pounds. 
     In an embodiment, the power tool comprises a main body housing an output spindle, a handle portion having a girth smaller than the main body disposed between the battery receptacle and the handle portion, wherein the BLDC motor is housed within the handle portion. 
     In an embodiment, the girth of the handle portion is less than or equal to 34 mm. 
     In an embodiment, the main body supports a tool holder opposite the handle portion, and wherein a length of the tool from a front portion of the tool holder to a rear portion of the battery receptacle is less than or equal to 250 mm and the power tool produces a maximum power output of at least approximately 450 watts and a maximum speed of at least approximately 25,000 rotations-per-minute. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of this disclosure in any way. 
         FIG. 1  depicts a perspective view of an electric power tool, according to an embodiment; 
         FIG. 2  depicts a side view of the electric power tool with a housing half removed to expose an outer-rotor brushless motor therein, according to an embodiment; 
         FIG. 3  depicts a side cross-sectional view of the electric power tool, according to an embodiment; 
         FIGS. 4 and 5  depict a perspective and cross-sectional assembled views of the outer-rotor brushless motor driving the output spindle, according to an embodiment; 
         FIGS. 6 and 7  depict perspective partially-exploded modular views of the outer-rotor brushless motor and the output spindle, according to an embodiment; 
         FIG. 8  depicts a perspective cross-sectional view of the outer-rotor brushless motor prior to assembly of the stator within the rotor, according to an embodiment; 
         FIG. 9  depicts a perspective cross-sectional view of the outer-rotor brushless motor after assembly of the stator within the rotor, according to an embodiment; 
         FIGS. 10 and 11  depict a perspective view and a partially-exploded perspective view of the stator assembly, according to an embodiment; 
         FIGS. 12 and 13  depict perspective partially-exploded views of the rotor assembly, according to an embodiment; 
         FIG. 14  depicts a perspective cross-sectional view of the rotor assembly together with the output spindle, according to an embodiment; 
         FIGS. 15 and 16  depict cross-sectional views of the motor assembly attached to two output spindles having different size diameters, according to an embodiment; 
         FIG. 17  depicts a cross-sectional view of a motor assembly, according to an alternative embodiment; and 
         FIG. 18  depicts a cross-sectional view of a motor assembly, according to yet another embodiment. 
     
    
    
     Throughout this specification and figures like reference numbers identify like elements. 
     DETAILED DESCRIPTION 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide an explanation of various embodiments of the present teachings. 
     Referring to  FIGS. 1-3 , an electric power tool  10  is described herein, according to an embodiment. In an embodiment, power tool  10 , which in this exemplary embodiment is a drywall cut-out tool, includes a housing  12  formed by two clam shells. The housing  12  includes a handle portion  14  (also referred to as the motor housing) within which an electric brushless motor  100  is supported, a battery receptacle  16  disposed at a foot of the handle portion  14 , and a main body  18  forward of the handle portion  14 . 
     The battery receptacle  16  is configured to receive and lock in a sliding battery pack, such as a 20V Max power tool battery pack. The motor  100  is orientated along a longitudinal axis of the power tool  10  within the handle portion  14 . A control and/or power module  20  is also disposed within the handle portion  14  between the motor  100  and the battery receptacle  16 . The module  20  includes control and switching components, for example an inverter switch circuit controlled by a programmable controller, that controls flow of electric current to the motor  100 . 
     The main body  18  includes a larger diameter than the handle portion  14  and houses an output spindle  22  rotatably driven by the motor  100  therein. The main body  18  further houses a fan  24  mounted on the output spindle  22 , a front spindle bearing  26  that rotationally supports the output spindle  22 , and a tool holder  28  that receives a tool accessory (not shown) therein to be driven by the output spindle  22 . In an embodiment, main body  18  further supports an ON/OFF switch  30  that sends a signal to the module  20  to activate the motor  100 , and a spindle lock  32 . 
     In an embodiment, spindle lock  32  is biased radially outwardly via a pair of springs  34  out of engagement with the output spindle  22 . The spindle lock  32  includes a semi-hexagonal inner surface facing the output spindle  22 . The output spindle  22 , though cylindrical along most its axial length, includes a hexagonal outer profile in the area in-line with the spindle lock  32 . When the spindle lock  32  is pressed by the user, its inner surface engages with the hexagonal outer profile of the output spindle  22  to lock the output spindle  22  in place, thus allowing the user to attach a tool accessory to the tool holder  28 . In an embodiment, a collet release  36  may be disposed around the tool holder  28  to allow the user to tighten or loosen the tool accessory within the tool holder  28 . 
     In an embodiment, in addition to front spindle bearing  26 , an additional (middle) bearing  40  is mounted on the output spindle  22  adjacent the motor  100 . The front and middle bearings  26  and  40  provide axial and radial support for the output spindle  22  and the motor  100  relative to the housing  12 . The housing  12  includes retention features for retaining the front and middle bearings  26  and  40 . In addition, in an embodiment, two slug rings  38  and  42  are mounted on the output spindle  22  adjacent the front and middle bearings  26  and  40 . The slug rings  38  and  42  are used for appropriate balancing the output spindle  22  and the motor  100 , where small holes are drilled into the slug rings  38  and  42  during balance testing until the desired balancing level is reached. This arrangement is helpful in reducing noise and vibration. 
       FIGS. 4 and 5  depict a perspective and cross-sectional assembled views of the outer-rotor brushless motor  100  driving the output spindle  24 , according to an embodiment.  FIGS. 6 and 7  depict perspective partially exploded modular views of the outer-rotor brushless motor  100  and the output spindle  24 , according to an embodiment. 
     Referring to these figures, in an embodiment, outer-rotor brushless (BLDC) motor  100 , which is also referred to as a modular outer-rotor motor  100 , includes an inner stator assembly  110  disposed within an outer rotor assembly  140 , according to an embodiment. In an embodiment, stator assembly  100  and rotor assembly  140  are modularly separable, as described here in detail. 
     In an embodiment, stator assembly  110  includes a stator lamination stack  112  formed by a series of laminations. The stator lamination stack  112  includes a stator core mounted on a stator mount  114  and a series of radially-outwardly projecting teeth on which stator windings  116  are wound. In an exemplary embodiment, the stator windings  116  are wound in three phases, which, when respectively energized by the control and/or power module  20 , cause rotation of the rotor assembly  140 . In an embodiment, a piloting pin  118  is received within an axial portion of the stator mount  114 . Though piloting pin  118  is shown as a separate component, it should be understood that the piloting pin  118  can be provided integrally as a part and extension of the stator mount  114 . In an embodiment, a positional sensor board  120  is mounted on an end of the stator  110  for sensing a rotary position of the rotor assembly  140 . These features are described later in more detail. 
     In an embodiment, rotor assembly  140  includes a cylindrical rotor core  142  formed around the stator assembly  110 , a series of magnets  144  surface-mounted on the inner surface of the rotor core  142  facing the stator assembly  110  with a small airgap therebetween, and a rotor mount  146  that supports the rotor assembly  110  relative to the stator assembly via motor bearing  148 . In an embodiment, motor bearing  148  includes an outer race coupled to the rotor mount  146  and an inner race that receives the piloting pin  118  of the stator assembly  100 . In an embodiment, rotor mount  146  includes radial walls  150  forming air inlets  152  therebetween that allow fluid communication between the fan  24  and the stator assembly  110 . 
       FIGS. 8 and 9  depict perspective cross-sectional views of the outer-rotor brushless motor  100  prior to and after assembly of the stator assembly  110  within the rotor assembly  140 , according to an embodiment. In an embodiment, as described below in more detail, rotor mount  146  is formed around the outer race of the motor bearing  148 . This may be done by, for example, press-fitting, insert-molding, heat-staking, or other similar process. The output spindle  22  is also press-fit or otherwise securely received within the rotor mount  146 . This arrangement allows the rotor assembly  140 , the fan  24 , and the output spindle  22  to be tested together as a unit for balancing and vibration, independently and separately from the stator assembly  110 . 
     In an embodiment, piloting pin  118  includes a rear portion  130  having a generally cylindrical body that is located within the stator core  112 , a front portion  132  also having a generally cylindrical body with a smaller diameter than the rear portion  132  that extends away from the stator core  112 , and an intermediary rim portion  133  projecting annularly between the rear portion  130  and the front portion  132 . The front portion  132  is sized to be slidingly and form-fittingly received within an inner race of the motor bearing  148 . 
     The stator assembly  110  is assembled into the rotor assembly  140  by simply inserting the rear portion  132  of the piloting pin  118  into the inner race of the motor bearing  148 . In this manner, one end of the stator assembly  110  is secured radially and axially with respect to the rotor assembly  140 . In an embodiment, power tool housing  12  includes retention features that radially and axially secure the stator mount  114 . Once the motor assembly  100  is mounted into the power tool housing  12 , the retention features of the housing  12  ensure that the other end of the stator assembly  110  is radially and axially secured with respect to the rotor assembly  140 , maintaining an airgap therebetween. 
     Utilizing the outer-rotor motor assembly  100  as described above into rotary power tool  10  offers power density benefits not previously seen in comparable conventional power tools. In an embodiment, motor assembly  100  includes an outer diameter (i.e., diameter of the rotor core  142 , WM in  FIG. 3 ) of approximately 22 mm to 38 mm, preferably approximately 24 mm to 36 mm, preferably approximately 26 mm to 34 mm, and more preferably approximately 28 mm to 32 mm. The stator length is approximately 20 mm to 30 mm, preferably approximately 25 mm. This motor configuration is configured to provide maximum power output of approximately 400 W to 550 W, preferably 450 W to 500 W, and more specifically approximately 470 W, with a maximum speed of approximately 25,000 to 30,000 rpm. The motor assembly  100  may be suitable for compact and light-weight power tool applications that require a low power output to weight ratio. 
     In the exemplary embodiment, power tool  10  has a handle (motor housing) diameter (WH,  FIG. 3 ) of approximately 32 mm to 48 mm, preferably approximately 34 mm to 46 mm, preferably approximately 36 mm to 44 mm, and more preferably approximately 38 mm to 42 mm. The ratio of power output to motor housing diameter (i.e., handle girth) is approximately in the range of 10 to 12 W per mm. At a length (L,  FIG. 3 ) of approximately 220 mm to 250 mm, power tool  10  has a weight of approximately 1.5 lbs to 1.7 lbs, preferably approximately 1.6 lbs. When using a power tool battery pack having a maximum rated voltage of 20V and rated capacity of 2 Amp-hours, power tool  10  is capable of outputting a maximum power output of at least approximately 450 to 500 watts, preferably at least 470 watts, offering a power-to-weight ratio of approximately 270 to 320 W per pound, more preferably approximately 280 to 310 W per pound, and more preferably approximately 290 to 300 W per pounds. Similarly, when using a power tool battery pack having a maximum rated voltage of 12V and rated capacity of 2 Amp-hours, power tool  10  is capable of outputting a maximum power output of at least approximately 330 to 360 watts, preferably at least 340 watts, offering a power-to-weight ratio of approximately 190 to 240 W per pound, more preferably approximately 200 to 230 W per pound, and more preferably approximately 210 to 220 W per pounds. The power output and power to weight ratio may be increased when using a higher capacity battery pack. 
     These ratios of power to motor housing and power to weight have not been seen in comparable power tools with comparable power outputs. Power tool  10  as described in this disclosure is unique in its portability and ease of use without sacrificing power output and speed needed to handle required cutting applications. 
       FIGS. 10 and 11  depict a perspective view and a partially-exploded perspective view of the stator assembly  110 , according to an embodiment. As shown here, and with continued reference to  FIGS. 8 and 9 , stator mount  114  includes an elongated cylindrical portion  122  sized to be received securely within a central aperture  126  of the stator lamination stack  112 . In an embodiment, the stator lamination stack  112  may be press-fitted over the cylindrical portion  122  of the stator mount  114 . Cylindrical portion  122  includes a tubular front portion  124  in which a hollow portion  128  is sized to receive the rear portion  130  of the piloting pin  118  by, for example, press-fitting. The front portion  132  of the piloting pin  118  is received within the inner race of the motor bearing  148 , as described above. In an embodiment, the hollow portion  128  may extend through the entire length or a portion of the cylindrical portion  122 . In an embodiment, as shown in  FIGS. 8 and 9 , cylindrical portion  122  includes a hollow opening that meets the hollow portion  128 , but has a smaller diameter than the hollow portion  128 . 
     In an embodiment, stator mount  114  further includes a radial portion  134  at an end of the cylindrical portion  122  disposed adjacent to the positional sensor board  120 . Radial portion  134  includes radial projections  136  that mate with corresponding retention features of the tool housing  12  to axially and rotationally retain the stator mount  114 . 
     In an embodiment, positional sensor board  120  is disc-shaped with an outer diameter that approximately matches the outer diameter of the rotor assembly  140  and an inner diameter that is slightly smaller than the diameter of the stator lamination stack  112  but is slightly greater than a diameter formed by the stator windings  116 . In this manner, in an embodiment, the positional sensor board  120  can be mounted at the end of the stator lamination stack  112  (or on an end insulator  133  mounted at the end of the stator lamination stack  112 ) around the ends of the stator windings  116 . Positional sensors  121 , which are magnetic sensors such as Hall Effect sensors, are mounted on the positional sensor board  120  outside the diameter of the stator lamination stack  112  facing axial ends of the rotor magnets  144  to sense a magnetic leakage flux of the rotor magnets  144 . A connector  138  is mounted on the rear surface of the positional sensor board  120  positioned between two projections  136  of the stator mount  114 . Positional signals from the positional sensors  121  are sent to the control and/or power module  20  via the connector  138 . 
     In an embodiment, a series of legs  130  project axially into corresponding through-holes  131  of the positional sensor board  120  to support the positional sensor board  120  with respect to the stator assembly  110 . In an embodiment, legs  130  are provided integrally as a part of the end insulator  133 . Alternatively, three or all six of the legs  130  are motor terminals that facilitate electrical connection between the windings and the positional sensor board  120 . In the latter embodiment, positional sensor board  120  includes metal routings that couple the motor terminals  130  to the connector  138 . In a further embodiment, positional sensor board  120  also includes metal routings that facility connections between the respective motor terminals  130  in, for example, a series or a parallel, and a wye or a delta, configuration. 
       FIGS. 12 and 13  depict perspective partially-exploded views of the rotor assembly, according to an embodiment.  FIG. 14  depicts a perspective cross-sectional view of the rotor assembly together with the output spindle, according to an embodiment. As shown in these figures, and with continued reference to  FIGS. 8-11 , in an embodiment, rotor mount  146  of the rotor assembly  140  includes the inner body  154  of the rotor mount  146  that is substantially cylindrical and forms a bearing pocket at its rear end that receives the outer race of the motor bearing  148  therein, by e.g., press-fitting, heat-staking, or other means, through one end. In an embodiment, a front end of the inner body  154  may be open-ended and receive a spacer  156 . An end of the output spindle  22  is securely received via the spacer  156  within the front end of the inner body  154 . This arrangement allows ends of the output spindle  22  and the piloting pin  118  to be received within the inner body  154  of the rotor mount  146  adjacent one another without blocking the air inlets  152  of the rotor assembly  140 . 
     In an embodiment, radial walls  156  project outwardly at an angle from the inner body  154  to an outer rim  158 . A cylindrical lip  160  projects axially from the outer rim  158  fittingly into the rotor core  142  to secure the rotor core  142  to the rotor mount  146 . In an embodiment, the lip  160  mates with ends of the rotor magnets  144  and a series of projections  162  project from the lip  160  between the rotor magnets  144  for improved alignment and positioning. 
     In an embodiment, the radial wall  156  is coupled at an angle to front end of the inner body  154 , and the rear end of the inner body  154  extends axially rearwardly from the front end at an acute angle relative to the radial wall  156 . This arrangement allows the motor bearing  148  to be radially substantially aligned with the contact surface of the outer rim  158  and the rotor core  142 . 
       FIGS. 15 and 16  depict cross-sectional views of the motor assembly  100  attached to two output spindles  22  having different size diameters, according to an embodiment. As shown in these figures, different diameter output spindles  22  may be coupled to the motor assembly  100  of this disclosure. As shown in  FIG. 15 , output spindle  22  may have a greater diameter than motor bearing  148  such that a rear cavity of the output spindle  22  receives the outer race of the motor bearing  148  directly. In an embodiment, rotor mount  146  is mounted on the outer surface of the output spindle  22 . In another embodiment, as shown in  FIG. 16 , the output spindle  22  may include a diameter that is substantially equal to or greater than the diameter of the rotor core  142 . In this embodiment, output spindle  22  may be integrally incorporated with the rotor mount  146  in one piece and coupled to the rotor core  142   
       FIG. 17  depicts a cross-sectional view of a motor assembly  200 , according to an alternative embodiment. Motor assembly  200  is similar in many respects to motor assembly  100  described above, and to the extent that the same or similar elements are provided, the same reference numerals are used. The difference between motor assembly  200  and the above-described motor assembly  100  is that the output spindle  222  is provided with an extension pole  224  received into the central opening  126  of the stator assembly  110  and is supported with respect the stator via rear bearing  248 . In an embodiment, outer race of the rear bearing  248  is supported within the stator central opening  126  and its inner race received the extension  224  of the output spindle  222 . The output spindle  222  is supported to the tool housing via front bearing  246 . 
       FIG. 18  depicts a cross-sectional view of a motor assembly  300 , according to an alternative embodiment. 
     In an embodiment, outer-rotor brushless (BLDC) motor  300 , which is also referred to herein as a canned outer-rotor motor  300 , is similar in some respects to BLDC motor  100  described above. In an embodiment, BLDC motor  300  includes an inner stator assembly  310  disposed within an outer rotor assembly  340 , according to an embodiment. 
     In an embodiment, stator assembly  310  includes a stator lamination stack  312  formed by a series of laminations. The stator lamination stack  312  includes a stator core mounted on a stator mount  314  and a series of radially-outwardly projecting teeth on which stator windings  316  are wound. In an embodiment, stator mount  314  includes an elongated cylindrical portion  322  sized to be received securely within a central aperture of the stator lamination stack  312 , and a radial portion  134  at an end of the cylindrical portion  322  disposed adjacent to the positional sensor board  320 . In an embodiment, the stator lamination stack  312  may be press-fitted over the cylindrical portion  322  of the stator mount  314 . In an embodiment, a positional sensor board  320  is mounted on an end of the stator assembly  310  for sensing a rotary position of the rotor assembly  340 . 
     In an embodiment, rotor assembly  340  includes a cylindrical rotor core  342  formed around the stator assembly  110 , a series of magnets  344  surface-mounted on the inner surface of the rotor core  342  facing the stator assembly  310  with a small airgap therebetween. In an embodiment, a rotor mount  346  supports the rotor assembly  340 . In an embodiment, rotor mount  346  includes an inner body  354  that is substantially cylindrical, radial wall  350  projecting angularly outwardly from the inner body  354  and forming air inlets therebetween, and an outer rim  358 . A cylindrical lip  360  projects axially from the outer rim  358  fittingly into the rotor core  342  to secure the rotor core  342  to the rotor mount  346 . 
     Unless otherwise described below, stator assembly  310 , stator mount  314 , rotor assembly  340 , and rotor mount  346  include similar features to stator assembly  110 , stator mount  114 , rotor assembly  140 , and rotor mount  146  described above. Additionally, the motor size, power output, and power to weight ratios described above are also applicable to the present embodiment. Unlike BLDC motor  100 , BLDC motor  300  of this embodiment does not include a modular and separable design. Rather, the stator assembly  310  and the rotor assembly  340  are provided within a motor housing  302  that structurally support the stator assembly  310  and the rotor assembly  340  via rear motor bearing  272  and front motor bearing  374 , and a rotor shaft  370  that extends axially through the motor housing  302 . Further, in an embodiment, an intermediate ball bearing  376  is provided within the stator assembly  310  mounted on the rotor shaft  370 . These features are described here in detail. 
     In an embodiment, inner body  354  of the rotor mount  346  is initially securely mounted on the rotor shaft  370 , by for example press-fitting or other known method, during the assembly process. Inner body  354  may be a metal hub. This allows the rotor mount  346  to securely and fixedly support the rotor assembly  340  relative to the rotor shaft  370   
     In an embodiment, motor housing  302  includes a generally cylindrical body extending from a radial wall  304  to an open end  306 . Radial wall  304  includes a recessed portion  308  forming a bearing pocket for placement of the front bearing  374 . During the assembly process, the front bearing  372  is securely disposed within the recessed portion  308  of the radial wall  304 . The rotor assembly  340  and rotor mount  346  are then together placed within the motor housing  302  as the rotor shaft  370  received through the inner race of the front bearing  372 . The rotor shaft  370  is extended out of an opening  309  provided within the recessed portion  308  of the radial wall  304  until the front bearing  372  is located adjacent the inner body  354  of the rotor mount  346 . 
     In an embodiment, stator mount  314  includes recessed portion  324  formed radially in-line with the radial wall  304 . The recessed portion  324  is disposed rearwardly of and coaxially with the elongated cylindrical portion  322 . Recessed portion  324  includes an open end  326  facing away from the elongated cylindrical portion  322 . In an embodiment, an enclosure  327  projects from the radial wall  304  around the recessed portion  324 . Recessed portion  324  forms a bearing pocket within which the rear bearing  372  is received through the open end  326  and secured. In an embodiment, intermediary bearing  376  is placed at least partially within a front opening of the stator core  320  adjacent the front end of the elongated cylindrical portion  322 . In an embodiment, a series of electric motor wires  380  for driving the stator windings  316  and control wires  382  coupled to the sensors of the positional sensor board  320  are received through the stator mount  314 . 
     In an embodiment, during the assembly process, after completion of the steps above, the rear end of the rotor shaft  370  is received through the elongated cylindrical portion  322  and securely received into an inner race of the rear bearing  372 . The radial wall  304  is also mated with and fastened to open end  306  of the motor housing  302 . In this manner, the stator mount  314  radially supports the stator assembly  310 , rotor shaft  370 , and motor housing  30  relative to one another. In an embodiment, a cap (not shown) is mounted on the enclosure  327  to fully enclose the rear bearing  372  within the recessed portion  324 . 
     In an embodiment, radial wall  350  of the rotor mount  346  is provided as a series of walls (or blades) defining openings in between (see  150  in  FIG. 13  as an example). This allows the radial wall  350  to generate an airflow through the motor assembly  300 , particularly in contact with the stator windings  316 , without need for an additional fan disposed within the motor housing  302 . 
     In an embodiment, the inner body  354  of the rotor mount includes a first side  355  provided adjacent to or in contact with the front motor bearing  374  and a second side  357  provided adjacent or intersecting a radial plane formed by front ends of the stator windings  316 . In an embodiment, second side  357  has a smaller diameter than the first side  355 , which allows the inner body  354  to project into the body of the stator assembly  310  between the front end portions of the stator windings  316 , forming a labyrinth for protection against ingress of debris and contamination into the area of the intermediary bearing  376 . 
     In an embodiment, the rotor shaft  370  has an outer diameter of approximately 4 mm to 6 mm, preferably approximately 5 mm. The inner diameter of the stator lamination stack  312 , i.e., the diameter of the central aperture and/or the outer diameter of the elongated cylindrical portion  322 , is approximately 8 mm to 12 mm, preferably approximately 10 mm. Thus, the ratio of the inner diameter of the stator lamination stack  312  to the outer diameter of the rotor shaft  370  is approximately 1.5 to 3, preferably less than 2.5, more preferably less than 2.2, in an example approximately 2. In an embodiment, the intermediary bearing  375  provides additional support for the stator assembly  310  relative to the rotor shaft  370  to account for the small ratio of the inner diameter of the stator lamination stack  312  to the outer diameter of the rotor shaft  370 . In addition, in the event the stator mount  314  becomes disengaged from the motor housing  302 , the intermediary bearing  375  can still support the stator assembly  310 . 
     In an embodiment, the motor assembly  300  to be utilized for high torque applications exceeding 220 N.m., preferably exceeding 240 N.m., even more preferably exceeding 255 N.m. 
     In an embodiment, cylindrical portion  322  is sized to extend more than half the length of the stator core  312 , preferably more than 75% of the length of the stator core  312 , and even more preferably approximately 80% to 90% of the length of the stator core  312 . This allows the intermediary  376  to be disposed at the front end of the stator assembly  310  close to, or in contact with, the front end of the cylindrical portion  322  of the stator mount  314 . 
     Example embodiments have been provided so that this disclosure will be thorough, and to fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Terms of degree such as “generally,” “substantially,” “approximately,” and “about” may be used herein when describing the relative positions, sizes, dimensions, or values of various elements, components, regions, layers and/or sections. These terms mean that such relative positions, sizes, dimensions, or values are within the defined range or comparison (e.g., equal or close to equal) with sufficient precision as would be understood by one of ordinary skill in the art in the context of the various elements, components, regions, layers and/or sections being described. 
     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.