Patent Publication Number: US-11654543-B2

Title: Brushless motor system for power tools

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is a continuation of U.S. patent application Ser. No. 16/580,424 filed Sep. 24, 2019, which is a continuation of U.S. patent application Ser. No. 15/292,568 filed Oct. 13, 2016, now U.S. Pat. No. 10,500,708, which claims the benefit of U.S. Provisional Application No. 62/241,385 filed Oct. 14, 2015, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates to cordless power tools. More particularly, the present invention relates to a high-power cordless power tool and a brushless motor for high-power cordless power tools. 
     BACKGROUND 
     Cordless power tools provide many advantages to traditional corded power tools. In particular, cordless tools provide unmatched convenience and portability. An operator can use a cordless power tool anywhere and anytime, regardless of the availability of a power supply. In addition, cordless power tools provide increased safety and reliability because there is no cumbersome cord to maneuver around while working on the job, and no risk of accidently cutting a cord in a hazardous work area. 
     However, conventional cordless power tools still have their disadvantages. Typically, cordless power tools provide far less power as compared to their corded counterparts. Today, operators desire power tools that provide the same benefits of convenience and portability, while also providing similar performance as corded power tools. 
     Brushless DC (BLDC) motors have been used in recent years in various cordless power tools. While BLDC motors provide many advantages over universal and permanent magnet DC motors, challenges exist in incorporating BLDC motors into many power tools depending on power requirements and specific applications of tool. The power components needed for driving the BLDC motors in high power applications have conventionally generated too much heat, making BLDC motors unfeasible for high-power power tools. This is particularly true for tools used in environments where dust and particulate from the workpiece is abundant, making it difficult to create a clean air flow within the tool to cool the motor and associated components. These challenges need be addressed. 
     Furthermore, high power applications typically require larger motors. As power tools have become more ergonomically compact, it has become more desireable to reduce the size of the motor while providing the required power output. 
     SUMMARY 
     According to an embodiment of the invention, a power tool is provided including a tool housing and a brushless DC (BLDC) motor disposed within the tool housing, the motor having a stator assembly and a rotor assembly. In an embodiment, the stator assembly includes a stator core having stator teeth extending radially inwardly towards a center bore, where the center bore is arranged to receive the rotor assembly therein; stator windings respectively wound around the stator teeth; and insulating inserts having substantially the same longitudinal length as the stator core, the insulating inserts longitudinally received between adjacent stator windings at or near inner tips of the adjacent stator teeth to substantially seal the center bore of the stator assembly from the stator windings. 
     In an embodiment, the insulating inserts force and displace the adjacent stator windings radially and laterally away from the inner tips of the adjacent stator teeth so as to provide at minimum a predetermined electrical clearance between the stator windings and the inner tips of the corresponding stator teeth, where the predetermined electrical clearance is greater than a distance between the stator windings and the inner tips. 
     In an embodiment, the stator assembly further includes insulating shields formed between the stator windings and the corresponding stator teeth, the insulating inserts radially and circumferentially displacing the corresponding insulating shields away from the inner tips of the corresponding stator teeth. 
     In an embodiment, each of the insulating inserts includes a generally-rectangular side profile. 
     In an embodiment, a lateral width of the insulating inserts is greater than a lateral width of an opening between adjacent inner tips of the stator teeth. 
     In an embodiment, each insulating insert includes: a wedge portion received between adjacent stator windings at or near the inner tips of the adjacent stator teeth, and a radially extending portion that extends from the wedge portion to engage an inner surface of the stator core. 
     In an embodiment, a length of the radially extending portion along the radial direction is greater than a lateral width of the wedge portion, but smaller than a length of the stator teeth along the radial direction. 
     In an embodiment, each insulating insert includes a substantially U-shaped or rectangular-shaped middle portion arranged to be received between the inner tips of the adjacent stator teeth. 
     In an embodiment, each insulating insert further includes two laterally-extending wedge portions located between the inner tips of the stator teeth and the corresponding stator windings. 
     In an embodiment, an end insulator is disposed at an and of the stator core, the end insulator including a substantially ring-shaped outer body, insulating teeth extending radially inwardly from the outer body towards a center of the end insulator, tooth tips projecting from inner ends of each of the insulating teeth, and at least one guide located on each tooth tip, each guide being arranged to engage a side of a corresponding insulating insert. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings which form part of the specification: 
         FIG.  1    is a front perspective view of a power tool, in accordance with an embodiment; 
         FIG.  2    is a side view of the power tool partially showing internal components of the power tool, in accordance with an embodiment; 
         FIGS.  3  and  4    depict front and rear perspective exploded view of the power tool, in accordance with an embodiment; 
         FIG.  5    is another side view of the power tool, in accordance with an embodiment; 
         FIG.  6    is a rear perspective view of the power tool with filters detached, in accordance with an embodiment; 
         FIGS.  7 A and  7 B  depict a cut-off perspective view of the tool  10  and an enlarged view of an intake conduit  52  of the air intake  36 , with the filter  38  in a detached position, respectively. 
         FIGS.  7 C and  7 D  depict a cut-off perspective view of the tool  10  and an enlarged view of the intake conduit  52 , with the filter  38  attached, respectively. 
         FIG.  8    is a perspective sectional view illustrating air flow through the air intakes, motor case and gear case assemblies, and exhaust vents, in accordance with an embodiment; 
         FIG.  9    is a perspective view of the power tool additionally provided with a flange holder, in accordance with an embodiment; 
         FIGS.  10 A and  10 B  depict views of the flange holder, in accordance with an embodiment; 
         FIG.  11 A  is a rear perspective view of the motor assembly, in accordance with an embodiment; 
         FIG.  11 B  is a front perspective view of the motor assembly, in accordance with an embodiment; 
         FIG.  12    is a perspective exploded view of a motor assembly, in accordance with an embodiment; 
         FIG.  13    is a perspective exploded view a stator assembly, in accordance with an embodiment; 
         FIG.  14    is an enlarged sectional view of the stator assembly being wound, in accordance with an embodiment; 
         FIG.  15 A  is a perspective view of an end insulator according to a first embodiment; 
         FIG.  15 B  is a profile sectional view of a portion of the insulator according to the first embodiment; 
         FIG.  16 A  is a perspective view of an end insulator according to a second embodiment; 
         FIG.  16 B  is a profile sectional view of a portion of the insulator according to the second embodiment; 
         FIG.  17 A  is a perspective view of an end insulator according to a third embodiment; 
         FIG.  17 B  is a profile sectional view of a portion of the insulator according to the third embodiment; 
         FIG.  18 A  is a perspective view of an end insulator according to a fourth embodiment; 
         FIG.  18 B  is a profile sectional view of a portion of the insulator according to the fourth embodiment; 
         FIG.  19 A  is a perspective view of an end insulator according to a fifth embodiment; 
         FIG.  19 B  is a profile sectional view of a portion of the insulator according to the fifth embodiment; 
         FIG.  20 A  is a perspective view of an end insulator according to a sixth embodiment; 
         FIG.  20 B  is a profile sectional view of a portion of the insulator according to the sixth embodiment; 
         FIG.  21 A  is a perspective view of an end insulator according to a seventh embodiment; 
         FIG.  21 B  is a profile sectional view of a portion of the insulator according to the seventh embodiment; 
         FIG.  22 A  is a perspective view of an end insulator according to an eighth embodiment; 
         FIG.  22 B  is a profile sectional view of a portion of the insulator according to the eighth embodiment; 
         FIGS.  23 A- 23 D  depict various perspective views of end insulators according to various additional or alternative embodiments; 
         FIG.  24    is an end view of the stator assembly including insulating inserts, in accordance with an embodiment; 
         FIG.  25 A  is a perspective view of the stator assembly with insulating inserts removed, in accordance with an embodiment; 
         FIG.  25 B  is a perspective view of the stator assembly with insulating inserts installed, in accordance with an embodiment; 
         FIG.  26 A  depicts a partial cross-sectional view of the stator assembly with an insulating insert, in accordance with an embodiment; 
         FIG.  26 B  depicts a partial perspective view of the stator assembly with insulating inserts, in accordance with an embodiment; 
         FIG.  27    depicts a partial perspective view of the stator assembly with insulating inserts in accordance with an alternative embodiment; 
         FIG.  28    depicts a partial perspective view of the stator assembly with insulating inserts in accordance with yet another embodiment; 
         FIG.  29    depicts an axial view of the stator assembly with insulating inserts in accordance with yet another alternative and/or additional embodiment; 
         FIG.  30 A  depicts a partial cut-off perspective view of the motor housing including the seal member integrated therein, according to an embodiment; 
         FIG.  30 B  depicts a perspective view of the inside of the motor housing including the seal member integrated therein, according to an embodiment; 
         FIGS.  31 A and  31 B  depict perspective views of the seal member alone, according to an embodiment; 
         FIG.  32    is a perspective view of the seal member mating with the stator assembly, in accordance with an embodiment; 
         FIGS.  33 A and  33 B  depict perspective exploded views of a power module adjacent a motor housing, in accordance with an embodiment; 
         FIG.  34    depicts a perspective view of the assembled power module adjacent the motor housing, in accordance with an embodiment; 
         FIG.  35    depicts a perspective view of an alternative assembled power module adjacent an alternative motor housing, in accordance with an embodiment; 
         FIG.  36    is a partially-exploded perspective view of the motor housing and the power module, with insulator pads disposed therebetween, in accordance with an embodiment; 
         FIG.  37 A  is an enlarged perspective view of the motor assembly showing insulator pads disposed around input terminals, in accordance with an embodiment; 
         FIG.  37 B  is an enlarged perspective view of the motor assembly showing insulator pads disposed between the motor housing and power module, in accordance with an embodiment; 
         FIG.  38    is a perspective view of the motor assembly including input terminals detached, in accordance with an embodiment; and 
         FIG.  39    is an enlarged perspective view of the motor assembly showing input terminals attached to the power module, in accordance with an embodiment; and 
         FIG.  40    depicts a partially-exploded perspective view of the motor assembly showing the relative positions of the power module and the rotor assembly, according to an embodiment; 
         FIG.  41    depicts a perspective view of the motor assembly showing the rotor assembly outside the motor housing, according to an embodiment; and 
         FIG.  42    depicts a perspective view of the motor assembly showing the rotor assembly fully assembled inside the motor housing, according to an embodiment. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. 
     DETAILED DESCRIPTION 
     The following description illustrates the claimed invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the disclosure, describes several embodiments, adaptations, variations, alternatives, and uses of the disclosure, including what is presently believed to be the best mode of carrying out the claimed invention. Additionally, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     As shown in  FIGS.  1 - 4   , according to an embodiment of the invention, a power tool  10  is provided including a housing  12  having a gear case  14 , a motor case  16 , a handle portion  18 , and a battery receiver  20 .  FIG.  1    provides a perspective view of the tool  10 .  FIG.  2    provides a side view of tool  10  including its internal components.  FIGS.  3  and  4    depict two exploded views of tool  10 . Power tool  10  as shown herein is an angle grinder with the gear case  14  housing a gearset (not shown) that drives a spindle  24  arranged to be coupled to a grinding or cutting disc (not shown) via a flange (or threaded nut)  25  and guarded by a disc guard  26 . It should be understood, however, that the teachings of this disclosure may apply to any other power tool including, but not limited to, a saw, drill, sander, and the like. 
     In an embodiment, the motor case  16  attaches to a rear end of the gear case  14  and houses a motor  28  operatively connected to the gear set  22 . The handle portion  18  attaches to a rear end  30  of the motor case  16  and includes a trigger assembly  32  operatively connected to a control module  11  disposed within the handle portion  18  for controlling the operation of the motor  28 . The battery receiver  20  extends from a rear end  31  of the handle portion  18  for detachable engagement with a battery pack (not shown) to provide power to the motor  28 . The control module  11  is electronically coupled to a power module  34  disposed substantially adjacent the motor  28 . The control module  11  controls a switching operation of the power module  34  to regulate a supply of power from the battery pack to the motor  28 . The control module  11  uses the input from the trigger assembly  32  to control the switching operation of the power module  34 . In an exemplary embodiment, the battery pack may be a 60 volt max lithium-ion type battery pack, although battery packs with other battery chemistries, shapes, voltage levels, etc. may be used in other embodiments. 
     In various embodiments, the battery receiver  20  and battery pack may be a sliding pack disclosed in U.S. Pat. No. 8,573,324, hereby incorporated by reference. However, any suitable battery receiver and battery back configuration, such as a tower pack or a convertible 20V/60V battery pack as disclosed in U.S. patent application Ser. No. 14/715,258 filed May 18, 2015, also incorporated by reference, can be used. The present embodiment is disclosed as a cordless, battery-powered tool. However, in alternate embodiments power tool can be corded, AC-powered tools. For instance, in place of the battery receiver and battery pack, the power tool  10  include an AC power cord coupled to a transformer block to condition and transform the AC power for use by the components of the power tools. Power tool  10  may for example include a rectifier circuit adapted to generate a positive current waveform from the AC power line. An example of such a tool and circuit may be found in US Patent Publication No. 2015/0111480, filed Oct. 18, 2013, which is incorporated herein by reference in its entirety. 
     Referring to  FIG.  2   , the trigger assembly  32  is a switch electrically connected to the control module  11  as discussed above. The trigger assembly  32  in this embodiment is an ON/OFF trigger switch pivotally attached to the handle  18 . The trigger  32  is biased away from the handle  18  to an OFF position. The operator presses the trigger  32  towards the handle to an ON position to initiate operation of the power tool  10 . In various alternate embodiments, the trigger assembly  32  can be a variable speed trigger switch allowing the operator to control the speed of the motor  28  at no-load, similar to variable-speed switch assembly disclosed in U.S. Pat. No. 8,573,324, hereby incorporated by reference. However, any suitable input means can be used including, but not limited to a touch sensor, a capacitive sensor, or a speed dial. 
     As shown in  FIGS.  2 - 5   , by housing the motor  28  and the power module  34  substantially within the motor case  16  and beyond a gripping area of the handle portion  18 , the handle portion  18  can be ergonomically designed without regards to the physical constraints of the motor  28  and the power module  34  to provide the operator with a more comfortable and effective operation and balance of the power tool during operation. For instance, the handle portion  18  can be provided with reduced girth and contoured for easier and more comfortable gripping by the operator to reduce the user&#39;s hand fatigue. 
     As shown in  FIG.  5   , in various embodiments, the handle portion  18  can have a circumference of approximately 110 to 140 mm (more preferably 120 to 130 mm, e.g. approximately 125 mm) measured at line A proximate the rear end  31  of the handle portion  18 , a circumference of approximately 120 to 150 mm (more preferably 130 to 140 mm, e.g. approximately 135 mm) measured at line B at about a mid-point  33  between the end  31  of the handle portion  18  and the trigger assembly  32 , and a circumference of approximately 140 to 190 mm (more preferably 150 to 180 mm, e.g., approximately 165 mm) measured at line C at the position of the trigger assembly  32 . By contrast, the circumference of the motor case  16  that houses the motor  28  may be over approximately 200 mm, e.g., 245 mm, as measured at line D. This arrangement represents a motor case  16  to handle portion  18  girth ratio of approximately 1.5× to 2×, according to an embodiment. 
     As mentioned above and discussed later in detail, according to an embodiment, power tool  10  described herein is high-power power tool configured to receive a 60V max battery pack or a 60V/20V convertible battery pack configured in its 60V high-voltage-rated state. The motor  28  is accordingly configured for a high-power application with a stator stack length of approximately 30 mm. Additionally, as later described in detail, the power module  34 , including its associated heat sink, is located within the motor case  16  in the vicinity of the motor  28 . As shown in  FIG.  5   , the relative positions and weight of the gear case  14  and the motor case  16  including the motor  28  and power module  34  allows the center of gravity of the tool  10  with the battery pack attached to the battery receiver  20  to be within the tool handle  18  substantially close to the trigger  32 , despite the heavy weight of the 60V battery pack. Specifically, while using a 60V pack with conventional grinders would place the center of gravity of the tool at the foot of the handle portion  18  near the battery receiver  20  due to the heavy weight of the battery pack, according to an embodiment the center of gravity is around in close proximity to the trigger  32 , i.e., at point E substantially in line with the operator&#39;s wrist as the operator grabs the handle portion  32 , which reduces hand fatigue and balances the tool  10  within the operator&#39;s hand. In an exemplary embodiment, handle portion  18  has a length of about 130-170 mm (e.g., 150 mm), and the motor case  16  with motor  28  has a length of about 70-100 (e.g., 84 mm), which represents a handle portion  18  to motor case  16  length ratio of approximately 1.3× to 2.5×, preferably 1.6× to 2×, more preferably 1.7× to 1.8×, according to an embodiment. 
     The embodiments described herein provide a high-power portable cordless power tool  10 , such as a grinder, that operates with a high voltage battery pack, for example, a battery pack having a maximum voltage of approximately 60V or nominal voltage of approximately 54V, and produces maximum power output of over 1600 Watts, a maximum torque of over 30 inch-pounds (In*Lbs) and maximum speed of over 8000 rotations-per-minute (RPM). No cordless grinder currently in the marketplace provides such performance parameters, particularly from a small grinder having geometric ergonomics described above. 
     Another aspect of the invention is discussed herein with reference to  FIGS.  6 - 8    and continued reference to  FIGS.  1 - 5   . As discussed briefly above and later in detail, power module  34  is provided within the motor case  16  near the motor  28 , or at the end of the handle portion  18  near the motor case  16 . As it is well known in the art, power module  34  switching arrangement generates a considerable amount of heat that should be carried away from the motor case in an effective manner. 
     According to an embodiment, referring to  FIGS.  2  and  6 - 8   , the motor case  16  defines a pair of generally oblong air intakes  36  around a periphery of the power module  34 . The air intakes  36  are arranged to direct air flow into the motor case  16  in a manner that air is circulated around the power module  34  as well as the motor  28 . In an embodiment, air intakes  36  are sized and shaped to receive a corresponding pair of air filters  38  and extend the majority of the circumference of the motor case  16 . The intakes  36  are positioned radially about the rear end  30  of the motor case  16  adjacent to the handle  18 , and generally corresponding with the position of the power module  34 . Positioning the intakes  36  forward of the handle portion  18  locates them generally away from the normal trajectory of the grinding particulate caused by grinding operation on a work piece, thus lessening the ingestion of grinding particulate and increasing service and reliability of the tool. 
     In addition, in an embodiment, each air intake  36  includes a plurality of intake conduits  52  arranged to receive and direct air from outside the tool  10  into the motor case  16 . Intake conduit  52  are defined by (and separated via) axial walls  53  provided axially within the air intake  36 , and an acruate baffle  54  described below. The angular orientation of the baffles  54  within the intake conduits  52  results in a path of air flow outside the air intakes  36  that is considerably different from the path of the particulate stream caused by the grinding operation on the work piece, and thus prevents a direct path by for the particulate stream to enter into the intakes  36 . 
     Referring to  FIG.  6   , each filter  38  can include two generally oblong bands  42  with a plurality of ribs  44  extending therebetween. The plurality of ribs  44  generally correspond to the axial walls  53  of the air intakes  36 . Each filter  38  further includes filter material  46  extending between the bands  42 . The filter  38  is arcuate along its length to correspond with intakes  36 . In an embodiment, each filter  38  includes a pair of retaining tabs  48  extend inwardly from each end of the filter  38  that securely mate with (e.g., snap-fit into) the edges of intakes  36 . Each filter  38  may further include a pin  50  extending inwardly from a midpoint of the filter  38  that fits into a corresponding hole  51  provided within the intakes  36 . The filters  38  provide further limit entry of contamination, debris, and grinding particulate from entering through the intakes  36 . 
       FIGS.  7 A and  7 B  depict a cut-off perspective view of the tool  10  and an enlarged view of the intake conduit  52  of the air intake  36 , with the filter  38  in a detached position, respectively.  FIGS.  7 C and  7 D  depict a cut-off perspective view of the tool  10  and an enlarged view of the intake conduit  52 , with the filter  38  attached, respectively. 
     As shown in these figures, acruate baffle  54  of the air intake  36  extends from a rear edge  59  of the air intake  36  at an angle with respect to an axis of the tool  10 , inwardly towards the motor  28 . Formed between a distal end  57  of the acruate baffle  54  and a front edge  56  of the air intake  36  are inlets  55  radially arranged and separated via axial walls  53 . During operation, the arcuate shape and the angular orientation of the baffle  54  effectively directs incoming air in the direction of the motor  28 , thus created an air flow path outside the tool  10  that is considerably different from the path of the particulate stream caused by the grinding operation. 
     In an embodiment, airflow through the air intake  36  is generated via motor fan  37 , which is rotatably attached to the motor  28 . In conventional designs, where power components are disposed within the handle portion  18 , it is important for the air flow generated by the motor fan to circulate through the handle portion  18  as well as the motor case  16  in order to cool the power components and the motor. In the above-described embodiment, by contrast air intakes  36  are positioned near a rear end  30  of the motor case  16  and in much closer proximity to the fan  37  and exhaust vents  58 . The reduced distance between the intakes  36 , fan  37 , and exhaust vents  58  provide better air flow efficiency around the power module  34  and the motor  28 , which generate the most heat, bypassing the control unit  11  and other components within the handle portion  18  that do not generate a considerable amount of heat. In the present exemplary embodiment, while there is still some air leakage through the battery receiver  20  and the handle portion  18 , the airflow through the handle portion  18  is reduced to about 0-2 Cubic Feet per Minute (CFM), which is less than 10% of the total air flow that enters the motor case  16 , while over 90% of the total airflow (e.g., 15-17 CFM) is entered through the air intakes  36 . 
       FIG.  8    depicts a partial perspective view of tool  10 , including a cut-off view of the motor  28 , and air flow paths entering the motor case  16  through the air vents  36 . As shown in this figure, the incoming air entering through the air intakes  36  circulates the power module  34 , particularly around the heat sink, before entering the motor  28 . The air then circulates around the motor shaft, the rotor and the stator (as will be described later in detail) before exiting through the exhaust vents  58 . Some of the outgoing air also exits through the gear case and around the spindle (not shown). 
     Another aspect of the disclosure is described herein with reference to  FIGS.  9 ,  10 A and  10 B . 
     In conventional power tools, such as grinders, that use rotary accessories, it is common practice to fixedly attach the accessory to the spindle via a backing plate and a threaded nut (referred to as a flange set) provided with the power tool. Alternatively the accessory itself integrally includes a threaded insert that eliminates the need for a flange set. In use, tool operators may variously switch between different grinding and cutting accessories, some of which may require a flange set and some may include integral threads. In practice, the separation of the tool from the flange set may lead to the flange set being lost or misplaced. 
     According to an embodiment, to overcome this problem, a flange attachment mechanism is provided on power tool  10  to provide the operator the ability to attach the flange set  25  to the tool  10  at an auxiliary location when the flange set  25  is not needed, i.e., when an accessory with integral threaded insert is being used on the tool  10 , without inhibiting the operator&#39;s ability to use the power tool  10 . As shown in  FIG.  9   , in an embodiment, a flange holder  400  is provided at the foot of the power tool  10 , e.g., on a side of the battery receiver  20 . The flange holder  400  may alternatively be provided at the end of the handle portion  18 , under the motor case  16 , or any other suitable location where it does not interfere with the operator&#39;s handling of the tool  10 . Alternatively, if tool  10  is a corded tool, the flange holder  400  may be provided on the cord. 
       FIGS.  10 A and  10 B  depict front and back perspective views of the flange holder  400 . As shown herein, flange holder  400  includes a threaded portion  402  extending from a base portion  404 . A back side of the base portion  404  includes pin-shape inserts  406  and a flexible projection  408  arranged to be received or snapped into corresponding openings or retaining features on the tool  10  battery receiver  20 . When tool operator is not using the flange set  25 , he or she may tighten the flange set  25  onto the flange holder  400 . 
     Various aspects of the disclosure relating to the motor  28  are discussed herein. 
       FIGS.  11 A and  11 B  depict two perspective views of motor  28 , according to an embodiment.  FIG.  12    depicts an exploded view of the motor  28 , according to an embodiment. As shown in these figures, the motor  28  is a three-phase brushless DC (BLDC) motor having a can or motor housing  29  sized to receive a stator assembly  70  and a rotor assembly  72 . Various aspects and features of the motor  28  are described herein in detail. It is noted that while motor  28  is illustratively shown in  FIGS.  1 - 9    as a part of an angle grinder, motor  28  may be alternatively used in any power tool or any other device or apparatus. 
     In an embodiment, rotor assembly  72  includes a rotor shaft  74 , a rotor lamination stack  76  mounted on and rotatably attached to the rotor shaft  74 , a rear bearing  78  arranged to axially secure the rotor shaft  74  to the motor housing  29 , a sense magnet ring  324  attached to a distal end of the rotor shaft  74 , and fan  37  also mounted on and rotatably attached to the rotor shaft  74 . In various implementations, the rotor lamination stack  76  can include a series of flat laminations attached together via, for example, an interlock mechanical, an adhesive, an overmold, etc., that house or hold two or more permanent magnets (PMs) therein. The permanent magnets may be surface mounted on the outer surface of the lamination stack  76  or housed therein. The permanent magnets may be, for example, a set of four PMs that magnetically engage with the stator assembly  70  during operation. Adjacent PMs have opposite polarities such that the four PMs have, for example, an N-S-N-S polar arrangement. The rotor shaft  74  is securely fixed inside the rotor lamination stack  76 . Rear bearing  78  provide longitudinal support for the rotor  74  in a bearing pocket (described later) of the motor housing  29 . 
     In an embodiment, fan  37  of the rotor assembly  72  includes a back plate  60  having a first side  62  facing the motor case  16  and a second side  64  facing the gear case  14 . A plurality of blades  66  extend axially outwardly from first side  62  of the back plate  60 . Blades  64  rotate with the rotor shaft  44  to generate an air flow as previously discussed. When motor  28  is fully assembled, fan  37  is located at or outside an open end of the motor housing  28  with a baffle  330  arranged between the stator assembly  70  and the fan  37 . The baffle  330  guides the flow of air from the blades  64  towards the exhaust vents  58 . 
     In an embodiment, power module  34  is secured to another end of the motor housing  29 , as will be described later in detail. 
     Referring now to the exploded view of  FIG.  13    and with continued reference to  FIG.  12   , in an embodiment, stator assembly  70  includes a generally cylindrical lamination stack  80  having center bore  88  configured to receive the rotor assembly  72 . Lamination stack  80  further includes a plurality of stator teeth  82  extending inwardly from a stator ring  83  towards the center bore  88 . The stator teeth  82  define a plurality of slots  84  therebetween configured. A plurality of coil windings  86  are wound around the stator teeth  82  into the slots  84 . The stator teeth  82  are generally rectangular-shaped with two tips  85  extending from an end portion  87  thereof. Each slot  84  is generally trapezoidal shaped with a gap  91  extending between opposing tips  85  of end portions  87  of each pair of teeth  82 . An insulating shield  90  is received within each stator slot  84  and generally surrounds each winding  86  to electrically insulate the winding  86  from the lamination stack  80 . In various instances, the insulating shield  90  can be made from flexible insulating material such as paper material. 
     In various embodiments, stator assembly  70  further includes a first end insulator  92  and second end insulator  94  attached to respective ends of the lamination stack  80  using any suitable method, such as, snap fit, friction fit, adhesive, or welding to provide electrical insulation between the windings  86  and the lamination stack  80 . Each end insulator  92  and  94  generally corresponds to the shape of end laminations on the lamination stack  80  so that it generally covers the end of the lamination stack  80 . In an embodiment, each insulator includes a generally cylindrical outer ring  96  corresponding to the stator ring  83 , with a plurality of tooth portions  98  extending inwardly from the outer ring  96  towards the center of the end insulator  92  and  94 . Each tooth portion  98  is generally shaped to cover a corresponding tooth  82  of the stator  70  with side walls  100  extending axially inwardly into stator lamination slots  84  for proper alignment and retention of the end insulators  92  and  94  at the ends of the lamination stack  80 , as well as providing further electrical insulation within the slots  84 . A tab  102  extends outwardly away from the lamination stack  80  from an end  101  of each tooth portion  98  corresponding to end portion  87  of respective stator teeth  82 . The first end insulator  92  includes a plurality of retention members  108  that defines receiving slots  106  for receiving the input terminals  104 , as described later in detail. 
     Referring now to  FIG.  14   , a partial radial view of the stator lamination stack  80  during a winding of stator windings  86  is depicted, according to an embodiment. Generally, during the winding process of the stator windings  86 , two routers T of a winding machine (not shown) moved longitudinally back and forth within the slots  84  to wind the stator windings  86  around stator teeth  82 . Generally, as the windings  86  are wound, they stack on top of each other around a center portion of the corresponding tooth  82  within the slots  84 , leaving gaps between the windings  86  and the stator ring  83 . This limits the amount of coil that can be wound within each slot  84 , which adversely impacts motor power output. 
     Referring now to  FIGS.  15 A to  23 D , with continued reference to  FIG.  13   , in order to maximize the amount of coil wound in stator slots  84 , according to an embodiment of the invention, the tooth portions  98  of the end insulators  92 ,  94  are contoured to include a sloped profile configured to bias the windings  86  away from a center bore  88  of the stator lamination stack  80  and towards the outer circumference of the stator lamination stack  80  (i.e., stator ring  83 ) while the windings  86  are being wound around the stator teeth  82 . Specifically, as the winding wire is wound around the teeth portions  98  of the end insulators  92 ,  92  at longitudinal ends of the stator teeth  82 , the sloped profile of the teeth portions  98  slidingly bias the winding wire in the direction of the slope and towards the outer ring  96 . Various profiles of the teeth portions  98  are discussed herein, according to various embodiments. 
     In a first embodiment shown in  FIG.  15 A  and the partial side view of  FIG.  15 B , each tooth portion  98  includes a sloped portion  112  extending at an angle from the tab  102  downwardly towards the outer ring  96 , and generally flat portion  110  extending around the sloped portion  98  from the tab  102  to the outer ring  96 . In an embodiment, the sloped portion  112  may occupy approximately a third of the total width of the tooth portion  98 . In an embodiment, the sloped portion  112  may extend at an angle of, e.g., 2 to 10 degrees. 
     In the second embodiment shown in  FIG.  16 A  and the partial side view of  FIG.  16 B , each tooth portion  98  includes a sloped portion  122  extending at an angle from the tab  102  downwardly towards the outer ring  96 . The sloped portion  122  may occupy approximately the entire total width of the tooth portion  98 . An end portion  124  of the sloped portion  112  near the outer ring  96  may slightly recessed by, e.g., 0.2 to 2 mm, from a plane of the outer ring  96 . Furthermore, in an embodiment, a flat portion  126  may additionally be arranged between the tab  102  and the sloped portion  122 . A radial length of the flat portion  126  may be less than the radial length of the sloped portion  122 , for example, 10% to 40%, preferably 15% to 25%, of the radial length of the sloped portion  122 . The sloped portion  112  may extend from the flat portion  126  at an angle of, e.g., 5 to 15 degrees. In an embodiment, sloped portion  112  may be laterally flat or may include a laterally arcuate surface. 
     In the third embodiment shown in  FIG.  17 A  and the partial side view of  FIG.  17 B , each tooth portion  98  includes a sloped portion  132 , a recessed end portion  134 , and a flat portion  136 , similarly to the second embodiment described above, but a radial length of the flat portion  136  is approximately close to or greater than the radial length of the sloped portion  132 . For example, the radial length of the flat portion  136  may be over 40%, preferably 50% to 60%, the radial length of the sloped portion  132 . The sloped portion  112  may extend at an angle of, e.g., 5 to 20 degrees. 
     The fourth embodiment shown in  FIG.  18 A  and the partial side view of  FIG.  18 B  is a combination of the first and the second embodiments. Specifically, in this embodiment, each tooth portion  98  includes a first sloped portion  142 , a recessed end portion  144 , and a flat portion  146 , similarly to the second embodiment described above. In addition, each tooth portion  98  includes a second sloped portion  148  similar to sloped portion  112  of the first embodiment. The second sloped portion  148  extends from the tab  102  over a middle portion of the flat portion  146  and the first sloped portion  142 , at an angle that is greater than the angle of extension of the first sloped portion  142 . In an embodiment, the second sloped surface  148  may have an angle of 1 to 10 degrees with respect to the first sloped surface  142 . 
     The fifth embodiment shown in  FIG.  19 A  and the partial side view of  FIG.  19 B  is similar to the fourth embodiment above, but the second sloped surface  158  has a greater extension angle. In an embodiment, the second sloped surface  158  may have an angle of 10 to 20 degrees with respect to the first sloped surface  152 . 
     The sixth embodiment shown in  FIG.  20 A  and the partial side view of  FIG.  20 B  is a combination of the first and the third embodiments. Specifically, in this embodiment, each tooth portion  98  includes a sloped portion  162 , a recessed end portion  164 , and an extended flat portion  166 , similarly to the third embodiment described above. In addition, each tooth portion  98  includes a second sloped portion  168  similar to sloped portion  112  of the first embodiment. The second sloped portion  168  extends from the tab  102  over a middle portion of the flat portion  166  and the first sloped portion  162 , at an angle that is greater than the angle of extension of the first sloped portion  142 . In an embodiment, the second sloped surface  148  may have an angle of 10 to 20 degrees with respect to the first sloped surface  142 . 
     The seventh embodiment shown in  FIG.  21 A  and the partial side view of  FIG.  21 B  is similar to the sixth embodiment above, but the second sloped surface  178  has a smaller extension angle. In an embodiment, the second sloped surface  178  may have an angle of 0 to 10 degrees with respect to the first sloped surface  152 . The eighth embodiment of shown in  FIG.  22 A  and the partial side view of  FIG.  22 B , is similar to the first embodiment described above, except that sloped portion  182  extends angularly from the outer ring  96  to a flat portion  184  disposed between the sloped portion  182  and the tab  102 . In an embodiment, the sloped portion  182  may have an angle of 20 to 30 degrees with respect to a plane of the outer ring  96 . 
       FIGS.  23 A- 23 D  depict several other alternative embodiments of the end insulator  92  having various combinations of sloped surfaces discussed above. 
     Another aspect of the invention is described herein with reference to  FIGS.  24  to  29   . 
     Referring to  FIG.  24   , in the present embodiment, an axial view of the stator assembly  70  including lamination stack  80 , radial ends  101  of stator teeth  82 , and stator windings  86  wound around stator teeth  82 , according to an embodiment. 
     Each winding  86  is distributed around the lamination stack  80  to form an even number of poles. For instance, in a three-phase stator, each winding  86  includes a pair of windings arranged at opposite ends of the lamination stack  80  to face each other. The windings  86  may be connected in a variety of configurations, such as, a series delta configuration, a parallel delta configuration, a series wye configuration, or a parallel wye configuration. Although the present embodiment depicts a respective set of three windings, three retention members, and three input terminals, any suitable number can be used. 
     In high power applications, e.g., power tools powered by 120V battery packs or 120V AC power, there are regulatory requirements imposed by safety organizations, i.e., Underwriters Laboratories (“UL”), on insulating distance required between one conductive surface to another. In the stator assembly  70 , the stator windings  86  are insulated from the stator lamination stack  80  via insulating shield  90  previously discussed, but UL standards require  2   mm  of insulation clearance between the windings  86  and the exposed area of the stator lamination stack  80 , i.e., at the tips  85  of stator teeth  82 . 
     In order to provide sufficient insulation between the tips  85  of stator teeth  82  and the stator windings  86 , according to an embodiment of the invention as shown in perspective views of  FIGS.  25 A and  25 B , and zoomed-in views of  FIGS.  26 A and  26 B , a plurality of generally rectangular insulating inserts  260  (also referred to as slot wedges) are inserted at respective gaps  91  between the teeth  82 .  FIG.  26 A  depicts a cross-sectional view of the stator assembly  70  without the end insulators  92 ,  94 , whereas  FIG.  26 B  depicts a perspective view of the stator assembly  70  including the end insulator  92 . The insulating inserts  260  laterally push and bias the windings  86  generally outwardly away from the tips  85  of the stator teeth  82 . 
     While slot wedges are conventionally used in universal motor armatures, insulating inserts  260  are inserted directly above the gaps  91  within each slot  84  of the stator  70  such that each end of the insulating insert  260  is fitted between a tip  85  of the stator tooth  82  and the stator windings  86 . The insulating inserts  260  bias and displace the windings both radially and circumferentially such that, when inserted, the insulating inserts  260  provide a predetermined clearance between the windings  86  and the tips  85  of the teeth  82 , as required for compliance with UL standards. 
     In addition, in an embodiment, the insulating inserts  260  may be inserted under the insulating shield  90 , i.e., between the ends of the shield  90  and the teeth tips  85 , to displace the insulating shield  90  laterally as well. In various embodiments, the predetermined clearance is at least equal to the minimum clearance specified under UL standards for high voltage tools (e.g.,  2   mm ). As arrow  261  of  FIG.  26 A , this clearance is measured from the tip  85  of the tooth  82 , around the insulating insert  260  and the tip of the insulating shield  90 , to the windings  86 . It is noted that the distance is not measured as a straight line between the tooth  82  and the windings  86 . 
     In an embodiment, in addition to providing electrical insulation between the stator lamination stack  80  and the stator windings  86 , the insulating inserts  260  effectively form a mechanical seal between the stator assembly  70  and the rotor assembly  72  to prevent airflow therebetween. During operation, the insulating inserts  260  substantially prevent air, including particles and contamination, from flowing through the gaps  91  between the end portions  87  of stator teeth  82  (see  FIG.  13   ), effectively isolating the paths of air flow through the rotor assembly  72  and the stator assembly  70 . This arrangement reduces the chances of air particulate and contamination from bouncing off the rotor assembly  72  at high speed and hitting the stator windings  86 , which would cause substantial damage to the stator windings  86 . In an embodiment, insulating inserts  260  may be made of paper or plastic material. 
     In an embodiment, as shown in  FIGS.  26 B and  26 C , for end insulator  92 ,  94  (only end insulator  92  shown herein), tips  103  of end portions  101  of the end insulator tooth  98  include guides  105  that engage the sides of the insulating inserts  260  and facilitate the insertion of the insulation inserts  260  between the tips  85  of the stator teeth  82  and the insulating shield  90 . The guides  105  make it easier for the insulating inserts  260  to be inserted during the assembly process. 
       FIG.  27    shows an alternative embodiment of the invention, where insulating inserts  264  are provided as beaker shaped wedges that can be inserted, such as with a form-fit and/or friction-fit, into respective stator slots  84 . The inserts  264 , includes a wedge portion  263  that, similarly to the above-described embodiment, bias the windings  86  laterally and outwardly to provide a predetermined clearance between the windings  86  and the stator teeth  82 . The inserts  264  in this embodiment additionally include a radially extending portion  265  that extend from the wedge portion  263  toward the stator ring  83  of the stator lamination stack  80  and engage an inner surface of the stator ring  83  within the slot  84 . In this manner, the radially extending portion  265  securely holds the wedge portion  263  in place. 
       FIG.  28    depicts yet another embodiment, where insulating inserts  364  are provided with a substantially U-shaped or rectangular-shaped middle portion  366  arranged to be received between respective tips  85  of adjacent stator teeth  82 . The middle portion  366  may be inserted form-fittingly and/or friction-fittingly inside the gap  91  extending between opposing tips  85  of end portions  87  of each pair of teeth  82  in a way to securely retain the wedge portions  368  in place between the stator windings  86  and the tips  85  of stator teeth  82 , as described above. 
       FIG.  29    depicts yet another embodiment, where insulating inserts  374  have a rectangular-shaped or U-shaped middle portion  376  and wedge portions  378 , as described above, but additionally includes a projection  379  opposite the middle portion  376  to further straighten insulation inserts  374 . 
     Another aspect of the invention is described herein with reference to  FIGS.  30 A to  32   . 
     As described to above, insulating inserts  260 ,  263 ,  364 ,  374  mechanically seal the gaps  91  between the stator teeth  82 , thus substantially preventing flow of air between the stator windings  86  and the rotor assembly  72  over the length of the stator lamination stack  80 . However, at ends of the stator assembly  70 , particularly at the one of end of the stator housing  70  close to the air intakes  36  where the air first enters the motor  28 , due to the arcuate shape of the ends of the stator windings  86  and the tabs  102  of the end insulator  92 , air can still leak from the stator assembly  70  to the rotor assembly  72  and vice versa. In order to overcome this deficiency, according to an embodiment of the invention, a cylindrical seal member  268  is provided at the end of the stator assembly  70 , described herein. 
       FIG.  30 A  depicts a partial cut-off perspective view of the motor housing  29  including the seal member  268  integrated therein, according to an embodiment.  FIG.  30 B  depicts a perspective view of the inside of the motor housing  29  including the seal member  268  integrated therein, according to an embodiment.  FIGS.  31 A and  31 B  depict perspective views of the seal member  268  alone, according to an embodiment. In these figures, the rear end  267  of the motor housing  29  defines a generally cylindrical rear bearing pocket  266  disposed to receive rear bearing  78  of the rotor assembly  72 , previously described. The motor housing  29  further includes, round a periphery of the bearing pocket  266  and in an axial direction of the motor housing  29  towards the motor 28 , a cylindrical sealing member  268 . In an embodiment, the sealing member  268  includes a crown-shaped cylindrical portion  270  terminating with an annular mating surface  272  defining generally arcuate or semi-circular indents  274  that correspond to the shape of windings  86  and separated by crown teeth  276 . In an embodiment, the inner surface  278  of crown teeth  276  tapers outwardly, thereby reducing the thickness of crown teeth  276  as they approach the end mating surface  272 , effectively forming a wedge or chamfer that enhance the mechanical seal between the windings  86 . Those skilled in the art will recognize that other configurations of the crown teeth  276  can be used, including, but not limited to, rectangular, curved, triangular, and the like. Also, other configurations of the indents  274  can also be used, including to, but not limited to, square, rectangular, curvilinear, and the like. Furthermore, those skilled in the art will recognize that while sealing member  268  is shown as an integral part of the motor housing  29 , sealing member  268  may be provided, integrally or as a separate piece, within any part of the tool, e.g., the tool housing. 
     As shown in  FIG.  32   , when the motor  28  is assembled into the motor housing  29 , the arcuate or generally semi-circular indents  274  mate with the ends of the stator windings  86 , tabs  102  of the end insulator  92 , or the area in between the stator windings  86  and the tabs  102 . Meanwhile the crown teeth  276  fit into gaps between adjacent stator windings  86 , adjacent tabs  102  of the end insulator  92 , or somewhere in between. In an embodiment, crown teeth  276  rest against or over ends of insulating inserts  260 . In this manner, the sealing member  268  forms a mechanical seal that substantially blocks flow of air between the stator assembly  70  and the rotor assembly  72 , thus reduces entry of debris and contamination from entering the rotor assembly  72 . 
     Another aspect of the invention is described herein with reference to  FIGS.  33 A- 35   . 
       FIGS.  33 A and  33 B  depict exploded views of the power module  34  adjacent the motor  28 , according to an embodiment. As shown herein, in an embodiment, power module  34  includes a power board  280 , a thermal interface  282 , and a heat sink  284  which attach to the rear end of the motor housing  29  via fasteners  291 . Power module  34  may be further provided with a clamp ring  290  that acts to clamp and cover the power board  280  and act as a secondary heat sink. Power module  34  may be disc-shaped to match the cylindrical profile of the motor  28 . Additionally, power module  34  may define a center through-hole  292  that extends through the power board  280  to accommodate the rotor shaft  44  in some embodiments. In an embodiment, through-holes  285 ,  287 , and  289  similarly extend through the clamp ring  290 , thermal interface  282 , and heat sink  284 , as further described later. 
     In an embodiment, power board  280  is a generally disc-shaped printed circuit board (PCB) with six power transistors  294  that power the stator windings  86  of the motor  28 , such as MOSFETs and/or IGTBs, on a first surface  295  thereof. Power board  280  may additionally include other circuitry such as the gate drivers, bootstrap circuit, and all other components needed to drive the MOSFETs and/or IGTBs. In addition, power board  280  includes a series of positional sensors (e.g., Hall sensors)  322  on a second surface  297  thereof, as explained later in detail. 
     In an embodiment, power board  280  is electrically coupled to a power source (e.g., a battery pack) via power lines  299  for supplying electric power to the transistors  294 . Power board  280  is also electrically coupled to a controller (e.g., inside control unit  11  in  FIG.  2   ) via control terminal  293  to receive control signals for controlling the switching operation of the transistors  294 , as well as provide positional signals from the positional sensors  322  to the controller. The transistors  294  may be configured, for example, as a three-phase bridge driver circuit including three high-side and three low-side transistors connected to drive the three phases of the motor  28 , with the gates of the transistors  294  being driven by the control signals from the control terminal  293 . Examples of such a circuit may be found in US Patent Publication No. 2013/0342144, which is incorporated herein by reference in its entirety. In an embodiment, power board  280  includes slots  298  for receiving and electrically connecting to the input terminals  104 . In an embodiment, slots  298  may be defined and spread around an outer periphery of the power board  280 . The outputs of the transistors bridge driver circuit is coupled to the motor  28  phases via these input terminals  104 . 
     As those skilled in the art will appreciate, power transistors  294  generate a substantial amount of heat that need to be transferred away from the power module  34  in an effective manner. In an embodiment, heat sink  284  is provided on the second surface  297  of the power board  270  for that purpose. In an embodiment, heat sink  284  is generally disc-shaped, square-shaped, or rectangular shaped, with a generally-planer body having a substantially flat first surface  340  facing the power board  282  and extending parallel thereto. The second surface  341  of the heat sink  284  may also be flat, as depicted herein, though this surface may be provided with fins to increase the overall surface area of the heat sink  284 . The size and width of the heat sink  284  may vary depending on the power requirements of the tool and thus the type and size of transistors  294  being used. It is noted, however, that for most 60V power tool applications, the width of the heat sink  284  is approximately 1-3 mm. 
     In an embodiment, thermal interface  282  may be a thin layer made of Sil-Pad® or similar thermally-conductive electrically-insulating material. Thermal interface  282  may be disposed between the heat sink  284  and the power board  280 . 
     In an embodiment, heat sink  284  and thermal interface  282  include slots  342  and  343  on their outer periphery to allow a passage for input terminals  104  to be received within slots  298  of the power board  280 . Slots  342  are generally larger than slots  298  to avoid electrical contact between the heat sink  284  and the terminals  104 . 
     In an embodiment, positional sensors  322  are disposed at a distant on the second surface  297  of the power board  280 , around a periphery of the through-hole  292 . Where a through-hold  292  does not exist, the positional sensors  322  are still provided at a distant near a middle potion of the second surface  297  of the power board  280  to detect a magnetic position of the rotor assembly  72 , as will be discussed later in detail. In order to allow the positional sensors  322  to have exposure to the motor  28 , irrespective of whether power board  280  includes a through-hole  292 , heat sink  284  and thermal interface  282  are provided with through-holes  287  and  289  large enough to accommodate the positional sensors  322 . In an embodiment, the through-holes may be circular (e.g., through-hole  287 ) semi-circular (e.g., through-hole  289 ), or any other shape needed to allow the positional sensors  322  to be axially accessible from the motor  22 . In an embodiment, through-hole  287  on the heat sink  284  has a radius that is approximately 1.5 to 3 times the radius of through-hole  292  on the power board  280 . 
       FIGS.  34  and  35    depict two alternative exemplary embodiments of the mounting mechanism and associated components of the power module  34  and motor housing  29 . 
     In  FIG.  34   , where the heat sink  284  is disc-shaped of substantially the same size as the power board  280 , a series of fastener receptacles  359  are provided on rear end of the motor housing  29  approximately half-way between the shaft  44  and the outer periphery of the motor housing  29 . A series of corresponding through-holes  361  are provided on the power module  34 , allowing fasteners  290  to securely fasten the power module  34  to the fastener receptacle  359  of the motor housing  29 . In an embodiment, individual components of the power module  34  may be held together via fasteners  355  prior to assembly of the power module  34  onto the motor housing  29 . Alternatively, the components of the power module  34  may be assembled onto motor housing  29  and held together via fasteners  291  in a single step. 
     In  FIG.  35   , where the heat sink  284  is rectangular-shaped with a larger surface area than the power board  280 , fastener receptacles  358  are provided near the outer periphery of the motor housing  29 . A series of corresponding through-holes  360  are provided on the four corners of the heat sink  284 . In this embodiment, the components of the power module  34  are held together via fasteners  355  prior to the assembly of the power module  34  onto the motor housing  29 . Then, fasteners  291  are received through the through-holes  260  to securely fasten the power module  34  onto the fastener receptacle  358  of the motor housing  29 . 
     In an embodiment, as shown in both  FIGS.  34  and  35   , the rear end of the motor housing  29  is provided with alignment posts  350  projecting form its outer periphery towards the power module  34  for proper alignment of the power module  34 . The power module is similarly provided with corresponding slots, or through-holes  352  to receive the posts  350  therein during the assembly process. Also, the rear end of the motor housing  29  is provided with a series of openings  309  through which the input terminals  101  of the stator assembly project outside the rear end of the motor housing  29 . 
     According to a further embodiment, as shown in  FIGS.  36 ,  37 A and  37 B , insulator pads  300  are disposed in between the motor housing  29  and the power module  34  around the input terminals  104 . The pads  300  provide insulation between the input terminals  104  and the heat sink  284  to reduce the risk of electrical short between the two due to contamination of the components. In an embodiment, each pad  300  includes a slot  302  arranged to receive the terminal  101  therethrough. Each pad  300  sits on a substantially planar platform  301  provided on the rear portion of the motor housing  29  with the terminal penetrating therein. In order to prevent the pads  300  to add to the total length of the tool, in an embodiment, the heat sink  284  is provided with cutout regions  302  corresponding to the shape of the pads  300 , typically provided on the outer periphery of the heat sink  284 . The insulator pads  300  are shaped to be contained within the cutout regions  302 , thereby providing electrical insulation between the input terminals  104  and the heat sink  284  in both the axial and radial directions. Each pad  300  is configured to fit into the cutout regions  303  of the heat sink  284 . 
     Referring now to  FIG.  38   , a perspective view of the stator assembly  70  (not including the stator windings) is depicted with the input terminals  104  disassembled.  FIG.  39    depicts a zoomed-in view of the stator assembly  70  showing the interface between the terminals  104  and the power module  34 . According to an embodiment, each input terminal  104  has a generally planar retention portion  306  including two legs  305  configured for coupling with the receiving slot  106  of the retention member  108 , such as with a snap-fit. The retention portion  306  includes a generally J-shaped wire-receiving member  308 . During the assembly process, after an input terminal  104  is inserted into a corresponding receiving slot  106 , an end of a corresponding stator winding (not shown herein) is routed around the end insulator  92  towards the input terminal  104  and wrapped around the wire-receiving member  308  to electrically connect the input terminal  104  with the corresponding winding  86 . A generally rectangular tab portion  310  extends from the retention portion  306  at about a 90° offset for connection to the power module  34 . When the stator assembly  70  is assembled into the motor housing  29 , the tab portions  310  extend through openings  309  (see  FIGS.  34  and  35   ) of the motor housing  29 . When the power module  34  is assembled at the rear end of the motor housing  29 , the tab portions  310  are tightly received inside slots  298  in the power board  280 , as described above, to operatively connect to the power module  34  for communication of power from the power module  34  to the windings  86 . The power module includes metal routings (not shown) that connect the respective terminal  104  to the appropriate transistors  294 . In this way, the input terminals  104  provide direct power connectivity between the stator assembly  70  and the power module  34  without use of any additional wires, which tend to be difficult to rout and install during the assembly process. In addition, the terminals  101  provide improved alignment for easier and quicker assembly by insuring that the power module  34  is properly orientated with the motor housing  29 . 
     Another aspect of the invention is described herein in reference to  FIGS.  40 - 42   . 
     As previously discussed, and shown in  FIG.  40   , power module  34  is designed to allow positional sensors  322  disposed on the second surface  297  of the power board  280  to be exposed to the motor  28 . Specifically, heat sink  284  and thermal interface  282  include through-holes  287  and  289  shaped and sized to allow the positional sensors  322  to be axially exposed towards the motor  28 . 
     Conventionally BLDC motors are provided with sense magnets positioned adjacent the rotor and mounted on the rotor shaft. The sense magnets may include, for example, four magnets disposed on a ring with adjacent magnets having opposite polarities, such that rotation of the magnet ring along with the motor rotor allows positional sensors to sense the change in magnetic polarity their vicinity. The problem with the conventional BLDC motor designs, however, is that positional sensors have to be arranged within the motor in close proximity to the sense magnet ring. 
     According to an embodiment, as shown in  FIGS.  41  and  42   , in order to provide positional sensors  322  with means to detect the rotational position of the rotor shaft  44 , sense magnet  324  (configured as a sense magnet ring including two or four magnets) is disposed near the end of the rotor shaft  44  such that, when the rotor assembly  72  is assembled into the motor housing  28 , the sense magnet  324  sits within (or projects out of) a corresponding through-hole  320  in the rear end of the motor housing  28 . This arrangement allows the sense magnet  324  to be disposed substantially close to the positional sensors  322 . In an embodiment, the sense magnet  324  may be at least partially received within the through-hole  287  of the heat sink  284 . In an embodiment, the motor housing  28  is provided with a ring-shaped labyrinth  326  around the through-hole  320  to substantially block debris and contamination from entering into the rotor assembly  72  from the area around the sense magnet  324 . 
     In an embodiment, in order to facilitate the assembly of the rotor assembly  72  into the motor housing  28  as described above, the rear bearing  78  is disposed between the rotor lamination stack  76  and the sense magnet  324 . The bearing pocket  266  is formed inside the motor housing  28  around the through-hole  320 . As the rear bearing  78  is received and secured inside the bearing pocket  266 , the sense magnet  324  is received inside the through-hole  320 , projecting at least partially out of the rear end of the motor housing  28 . 
     Some of the techniques described herein may be implemented by one or more computer programs executed by one or more processors residing, for example on a power tool. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage. 
     Some portions of the above description present the techniques described herein in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. These operations, while described functionally or logically, are understood to be implemented by computer programs. Furthermore, it has also proven convenient at times to refer to these arrangements of operations as modules or by functional names, without loss of generality. 
     Certain aspects of the described techniques include process steps and instructions described herein in the form of an algorithm. It should be noted that the described process steps and instructions could be embodied in software, firmware or hardware, and when embodied in software, could be downloaded to reside on and be operated from different platforms used by real time network operating systems. 
     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. 
     Example embodiments are provided so that this disclosure will be thorough, and will 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.