Patent Publication Number: US-11646626-B2

Title: Brushless motor for a power tool

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/907,664 filed June 22, which is a continuation of U.S. patent application Ser. No. 16/775,858 filed Jan. 29, 2020, now U.S. Pat. No. 10,727,715, which is a continuation of U.S. patent application Ser. No. 15/481,538 filed Apr. 7, 2017, now U.S. Pat. No. 10,587,163, which claims the benefit of U.S. Provisional Patent Application No. 62/320,063, filed Apr. 8, 2016, all of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates to power tools. More particularly, the present invention relates to a power tool and a brushless motor for 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 size and power output advantages over universal and permanent magnet DC motors, it is always desired to manufacture more compact motors while providing the same or higher power output. 
     BLDC motors are available as canned motors, where all the motor components are securely assembled inside a cylindrical motor can or motor housing. The motor housing includes piloting features for the rotor end bearings to retain the rotor assembly securely within the stator. The motor housing is encapsulated inside a power tool via two power tool housing halves. 
     Alternatively, BLDC motors may be without a motor housing or can, where the stator/rotor assemblies are mounted directly inside the power tool. Such motors are typically provided with two end bearing support mounts provided at the two ends of the stator assembly. The bearing support mounts are axially fastened together on the stator via screws located on the outer surface of the stator. The bearing support mounts constraint the axial movement of the rotor within the stator. The bearing support mounts also typically include radial retention features, for example radial constraints that partially wrap around the outer surface of the stator, to constraint the radial movement of the rotor within the stator. Radial retention features have to be manufactured with great precision to ensure that an air gap is provided between the rotor and the inner surface of the stator. 
     U.S. patent application Ser. No. 13/919,352 (Publication No. 2013/0270934), which is incorporated herein by reference in its entirety, describes an example of a BLDC motor without a motor housing. As shown in  FIGS.  2 A and  2 B  of this disclosure, the two bearing support members (i.e., a ring gear mount and a hall board mount assembly, also commonly referred to as motor caps) and the stator all include fastener receptacles that allow the three components to be securely fastened together. Additionally, the two bearing support members include piloting and retention semi-cylindrical walls that partially cover the outer diameter (OC) of the stator lamination stack. These features radially retain the two bearing support members, and consequently the rotor assembly, with respect to the stator. 
     While these fastening and piloting features are important in precise and secure assembly of the rotor with respect to the stator, they add to the overall outer diameter of the motor. In particular, the piloting and retention walls add to the diameter of the stator lamination stack. Also, the screws receptacles add to the outer diameter of the stator and the two bearing support members. In BLDC motors, particularly in handheld portable power tools where space is limited, it would be greatly desirable to construct these piloting and retention features in a way that does not affect the length and diameter of the motor. 
     SUMMARY 
     According to an embodiment of the invention, a brushless direct-current (DC) motor is provided comprising a stator assembly and a rotor assembly. In an embodiment, the stator assembly includes a generally-cylindrical stator body having a center bore, teeth extending from the stator body towards the center bore and defining slots in between, and windings wound around the teeth. In an embodiment, the rotor assembly is rotatably received within the center bore of the stator assembly, and includes a rotor shaft and a generally-cylindrical rotor body mounted on the rotor shaft. In an embodiment, the motor further includes at least one rotor bearing mounted on the rotor shaft, and at least one bearing support member supporting the rotor bearing. In an embodiment, the bearing support member includes a radial body forming a bearing pocket at central portion thereon for receiving the rotor bearing therein, and axial post inserts received within the slots of the stator assembly between adjacent sets of windings and engaging an inner surface of the stator body to support the rotor bearing with respect to the stator assembly along a center axis of the center bore of the stator assembly so as to maintain a circumferential gap between the rotor body and the stator teeth within the center bore of the stator assembly. 
     In an embodiment, a rear bearing and a front bearing are disposed at two sides of the rotor body. In an embodiment, a first bearing support member is provided supporting the rear bearing and a second bearing support member is provided supporting the front bearing. 
     In an embodiment, the radial body of the bearing support member includes a mating surface that mates with an end portion of the stator assembly to form a substantially uniform cylindrical body between the stator assembly and the bearing support member. 
     In an embodiment, the bearing support member supports a circuit board on which positional sensors are mounted. In an embodiment, the positional sensors are arranged to sense a magnetic position of the rotor assembly. 
     In an embodiment, the bearing support member includes a series of openings formed around the bearing pocket to allow passage of air through the bearing support member. In an embodiment, a fan is mounted on the rotor shaft facing the bearing support member. The fan generates airflow that passes through the stator assembly and the openings of the bearing support member. 
     In an embodiment, the axial post inserts generally radially extend from a peripheral portion that is arranged to engage the inner surface of the stator body, to an end portion that is arranged at an open end of a corresponding slot and engages the edges of two corresponding stator teeth. In an embodiment, the axial posts include a generally rectangular cross-sectional profile. 
     In an embodiment, the stator assembly includes an end insulator arranged at an end surface of the stator body to insulate the stator teeth from the windings. In an embodiment, the radial body of the bearing support member includes a mating surface that mates with a corresponding mating surface of the end insulator to form a substantially uniform cylindrical body between the stator assembly and the bearing support member. 
     In an embodiment, the mating surfaces of the end insulator and the bearing support member include corresponding indentations and detents arranged to mate to properly align the bearing support member with respect to the stator assembly. 
     In an embodiment, the rotor bearing is positioned along approximately a same radial plane as at least one of the end insulator or ends of the plurality of stator windings. 
     In an embodiment, the bearing support member is configured to be fully slidingly received within the stator assembly. 
     According to an embodiment of the invention, a power tool is provided that includes a housing, and a motor as described above disposed within the housing. 
     In an embodiment, an inner surface of the power tool housing includes a plurality of piloting and retaining features configured to axially support the stator assembly and the bearing support member with respect to one another. 
    
    
     
       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 an exemplary power tool having a brushless DC motor, according to an embodiment of the invention; 
         FIGS.  2 A and  2 B  respectively depict front and rear respective views of an exemplary brushless DC motor, according to an embodiment; 
         FIGS.  3 A and  3 B  respectively depict front and rear exploded views of the motor, including a stator assembly, a rotor assembly, a first bearing support member, and a second bearing support member, according to an embodiment; 
         FIG.  4    depicts a perspective view of the first bearing support member of the motor, according to an embodiment; 
         FIG.  5    depicts a perspective view of the second bearing support member of the motor, according to an embodiment; 
         FIG.  6    depicts a perspective view of a first sub-assembly including the rotor assembly and the first bearing support member, according to an embodiment; 
         FIG.  7    depicts a perspective view of a second sub-assembly including the stator assembly and the second bearing support member, according to an embodiment; 
         FIG.  8    depicts a perspective radially-cut-off view of the motor, including the first bearing support member assembled on one side of the stator assembly and the rotor assembly, according to an embodiment; 
         FIG.  9    depicts a perspective axially-cut-off view of the motor, according to an embodiment; 
         FIG.  10    depicts a perspective partially-exploded view of the power tool and the motor, according to an embodiment; 
         FIG.  11    depicts a cut-off top perspective view of the power tool and the motor, according to an embodiment; 
         FIG.  12    depicts a perspective view of a brushless DC motor, according to an alternative embodiment of the invention; 
         FIG.  13    depicts a partially exploded perspective view of the motor, including the stator assembly and the rotor assembly, according to an embodiment; 
         FIG.  14    depicts an exploded view of a sub-assembly including the rotor assembly, and first and second bearing support members, according to an embodiment; 
         FIGS.  15 A and  15 B  depict front and rear perspective views of the second bearing support member, according to an embodiment; 
         FIG.  16    depicts a perspective view of a brushless DC motor, according to yet another alternative embodiment of the invention; 
         FIG.  17    depicts a partially exploded perspective view of the motor, including the stator assembly and the rotor assembly, according to an embodiment; 
         FIG.  18    depicts a perspective view of a sub-assembly including the rotor assembly, and first and second bearing support members, according to an embodiment; 
         FIG.  19    depicts an exploded view of the rotor assembly and the first and second bearing support members, according to an embodiment; and 
         FIGS.  20 A and  20 B  depict front and back perspective views of a rotor end cap, according to an embodiment. 
     
    
    
     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. 
     With reference to the  FIG.  1   , a power tool  100  constructed in accordance with the teachings of the present disclosure is illustrated in a longitudinal cross-section view. The power tool  100  in the particular example provided may be an impact wrench, but it will be appreciated that the teachings of this disclosure is merely exemplary and the power tool of this invention could be a drill, impact driver, hammer, grinder, circular saw, reciprocating saw, or any similar portable power tool constructed in accordance with the teachings of this disclosure. Moreover, the output of the power tool driven (at least partly) by a transmission constructed in accordance with the teachings of this disclosure need not be in a rotary direction. 
     The power tool shown in  FIG.  1    may include a tool housing  102  that houses a motor assembly  200  and a control module  106 , an input unit (e.g., a variable speed trigger)  110 , and a transmission assembly  114  having a gear case (not shown). The motor assembly  200  may be coupled through the gear case to an output spindle (not shown), which is rotatably coupled to a square wrench  107 . The tool housing  102  additionally includes handle  112  that, in an embodiment, houses the control module  106 . 
     According to an embodiment, motor  200  is disposed in housing  102  above the handle  112 . Motor  200  may be powered by an appropriate power source (electricity, pneumatic power, hydraulic power). In embodiments of the invention, the motor is a brushless DC electric motor and is powered by a battery pack (not shown) through a battery receptacle  111 , though it must be understood that power tool  100  may alternatively include a power cord to receive AC power from, for example, a generator or the AC grid, and may include the appropriate circuitry (e.g., a full-wave or half-wave bridge rectifier) to provide positive current to the motor  200 . 
     In an embodiment, input unit  110  may be a variable speed trigger switch, although other input means such as a touch-sensor, a capacitive-sensor, a speed dial, etc. may also be utilized. In an embodiment, variable speed trigger switch may integrate the ON/OFF, Forward/Reverse, and variable-speed functionalities into a single unit coupled and partially mounted within control unit  106  and provide respective inputs of these functions to the control unit  106 . Control unit  106 , which receives variable-speed, on/off, and/or forward/reverse signal from the input unit  110 , supplies the drive signals to the motor  200 . In the exemplary embodiment of the invention, the control unit  106  is provided in the handle  112 . It must be understood that while input unit  100  is a variable-speed unit, embodiments of the invention disclosed herein similarly apply to fixed-speed power tools (i.e., tools without a speed dial or speed trigger, having constant speed at no load). 
     In an embodiment, brushless motor  200  depicted in  FIG.  1    is commutated electronically by control unit  106 . Control unit  106  may include, for example, a programmable micro-controller, micro-process, digital signal processor, or other programmable module configured to control supply of DC power to the motor  200  and accordingly commutate of the motor  200 . Alternatively, control unit  106  may include an application-specific integrated circuit (ASIC) configured to execute commutation of the motor  200 . Using the variable-speed input, forward/reverse input, on/off input, etc., from the input unit  110 , control unit  106  controls the amount of power supplied to the motor  200 . In an exemplary embodiment, control unit  106  controls the pulse width modulation (PWM) duty cycle of the DC power supplied to the motor  200 . For example, control unit  106  may include (or be coupled to) a series of power switches (e.g., FETs or IGBTs) disposed in a three-phase inverter circuit between the power source and the motor  200 . Control unit  106  may control a switching operation of the switches to regulate a supply of power to the motor  200 , via motor wires  109 . 
     Commutation details of the brushless motor  200  or the control unit  106  are beyond the scope of this disclosure, and can be found in co-pending International Patent Publication No. WO 3081/1596212 by the same assignee as this application, which is incorporated herein by reference in its entirety. An example of an integrated switch and control module embodying an input unit  110  and a control unit  106  described herein may be found in application Ser. No. 14/6210,617 filed Mar. 30, 3085 by the same assignee as this application, also incorporated herein by reference in its entirety. 
     A first embodiment of the invention is described herein with reference to  FIGS.  2 A- 11   . 
       FIGS.  2 A and  2 B  depict two perspective views of a brushless DC (BLDC) motor  200 , according to an embodiment of the invention.  FIGS.  3 A and  3 B  depicts perspective exploded views of the same motor  200 , according to an embodiment. As shown in these figures, the exemplary motor  200  is a three-phase BLDC motor having a rotor assembly  210  rotatably received within a stator assembly  230 . Various aspects of motor  200  are described herein. It must be noted that while motor  200  is illustratively shown in  FIG.  1    as a part of an impact driver, motor  200  may be alternatively used in any other device or power tool. Further, while motor  200  is a three-phase motor having six windings, any other number of phases or winding configurations may be alternatively utilized. 
     In an embodiment, rotor assembly  210  includes a rotor shaft  212 , a rotor lamination stack  214  mounted on and rotatably attached to the rotor shaft  212 , and rear and front bearings  220 ,  222  arranged to secure the rotor shaft  212 , as discussed below. In an embodiment, rear and front bearings  220  and  222  provides radial and/or axial support for the rotor shaft  212  to securely position the rotor assembly  210  within the stator assembly  230 . 
     In various implementations, the rotor lamination stack  214  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  214  or embedded therein. The permanent magnets may be, for example, a set of four PMs that magnetically engage with the stator assembly  210  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  210  is securely fixed inside the rotor lamination stack  214 . 
     In an embodiment, rotor assembly  210  also includes a sense magnet  216  attached to an end of the lamination stack  214 . Sense magnet  216  includes a similar magnetic arrangement as the rotor permanent magnets and may be made of, for example, four magnet segments arranged in an N-S-N-S polar arrangement that align with the rotor permanent magnets. The sense magnet  216  is disposed in close proximity to and is sensed via a series of positional sensors (such as Hall sensors), which provide positioning signals related to the rotational position of the rotor assembly  210  to control module  106 . In an embodiment, sense magnet  216  additionally axially limits the movement of the magnets on one end of the rotor lamination stack  214 . In an embodiment, on the other end of the rotor lamination stack  214 , a rotor end cap  226  is disposed, which also axially limits the movement of the magnets, described later in detail in this disclosure. 
     In an embodiment, a fan  218  is mounted on and rotatably attached to a distal end of the rotor shaft  212 . Fan  218  rotates with the rotor shaft  212  to cool the motor  200 , particularly the stator assembly  230 . In an embodiment, a pinion  205  may be disposed on the other distal end of the shaft  212  for driving engagement with the transmission assembly  114 . 
     According to an embodiment, stator assembly  230  includes a generally cylindrical lamination stack  232  having a center bore configured to receive the rotor assembly  210 . Stator lamination stack  232  includes a plurality of stator teeth extending inwardly from the cylindrical body of the lamination stack  232  towards the center bore. The stator teeth define a plurality of slots therebetween. A plurality of stator windings  234  are wound around the stator teeth. The stator windings  234  may be coupled and configured in a variety of configurations, e.g., series-delta, series-wye, parallel-delta, or parallel-wye. The stator windings  234  are electrically coupled to motor terminals  238 . Motor terminals  238  are in turn coupled to the power switch inverter circuit provided in (or driven by) control module  106 . Control module  106  energizes the coil windings  234  via the power switch inverter circuit using a desired commutation scheme. In an embodiment, three motor terminals  238  are provided to electrically power the three phases of the motor  200 . 
     In an embodiment, front and end insulators  236  and  237  may be provided on the end surfaces of the stator lamination stack  232  to insulate the lamination stack  232  from the stator windings  234 . The end insulators  236  and  237  may be shaped to be received at the two ends of the stator lamination stack  232 . In an embodiment, each insulator  236  and  237  includes a radial plane that mates with the end surfaces of the stator lamination stack  232 . The radial plane includes teeth and slots corresponding to the stator teeth and stator slots. The radial plane further includes axial walls that penetrate inside the stator slots. The end insulators  236  and  237  thus cover and insulates the ends of the stator teeth from the stator windings  234 . 
     According to an embodiment, motor  200  is additionally provided with two bearing support members  250  and  270  formed as motor caps disposed at and secured to the two ends of the stator assembly  230 , as described herein. In an embodiment, both bearing support members  250  and  270  are made of insulating (e.g., plastic) material molded in the structural form described herein. 
     As shown in the perspective view of  FIG.  4    and with continued reference to  FIGS.  2 A- 3 B , first bearing support member  250  (also referred to as rear bearing mount or the hall board mount) provides structural support for rear rotor bearings  220 , as well as printed circuit board  260  for mounting the positional sensors (herein referred to as hall board  260 ). In an embodiment, first bearing support member  250  includes a substantially planar radial body  254  forming a first bearing pocket  252 , which in this example is a through-hole in the center of the planar radial body  254 . The rear rotor bearing  220  is positioned and secured inside the first bearing pocket  252  via, for example, heat-staking, insert-molding, clamping via a small fastener, or other known method. In an embodiment, the rotor shaft  212  is press-fitted inside the rear bearing  220  during the assembly process after the rear bearing  220  is secured inside the first bearing pocket  252 . 
     In an embodiment, the fan  218  is disposed on the rotor shaft  212  adjacent the first bearing support member  250  opposite the rotor assembly  210 . First bearing support member  250  includes several openings  256  formed between respective teeth  258  around the first bearing pocket  252  that allow passage of airflow generated by fan  218  through the motor  200 . 
     In an embodiment, the rear surface of the first bearing support member  250  facing the fan  218  acts as a baffle for the fan  218  and directs the air coming from the motor  200  into the fan  218  radially away from the rotor shaft  212 , thus significantly preventing the airflow from flowing back into the stator assembly  230  from the fan side. In an embodiment, the rear surface of the first bearing support member  250  includes semi-circular walls  251  around the circumference of the fan  218  to control the flow of the outgoing air, for example, through an exhaust vent in the power tool housing  102 . 
     In an embodiment, hall board  260  is mounted on an inner surface of the first bearing support member  250  facing the rotor assembly  210 . In an embodiment, hall board  260  includes three hall sensors (or other positional sensors)  262  arranged around the first bearing pocket  252 , and a hall terminal  264  accessible at or outside the periphery of the hall board mount  250 . In an embodiment, first bearing support member  250  includes retaining features  266  (e.g., snap features) for securely retaining the hall board  260 . 
     As shown in the perspective view of  FIG.  5    and with continued reference to  FIGS.  2 A- 3 B , second bearing support member (also referred to as front bearing mount)  270  provides structural support for front rotor bearings  222 , in an embodiment. In an embodiment, second bearing support member  270  includes a substantially planar radial body  274  defining a second bearing pocket  272 . Second bearing pocket  272  in this example includes a pocket in which front bearing  222  of the rotor assembly  210  is securely received, and a through-hole  273  having a smaller diameter than the pocket through which the rotor shaft  212  extends out. In an embodiment, the front bearing  222  is first mounted (e.g., via press-fitting) on the rotor shaft  212  during the rotor assembly process. The front bearing  222  is then received inside the second bearing pocket  272  during the full motor assembly process. 
     In an embodiment, second bearing support member  272  includes several slots  276  formed between respective teeth  278  that allow passage of airflow generated by fan  218  into the stator assembly  230  from a frontal side of the motor  200 . 
     It is noted that the terms “rear” and “front” as they relate to the bearings or other motor components are relative to the positioning of the components with respect to motor output connected to the transmission assembly  114 . 
     As previously discussed, in conventional BLDC motors without a motor housing, the two bearing support structures that support the rotor bearings with respect to the stator include piloting and retention semi-cylindrical walls that partially cover the outer surface of the stator lamination stack. These features provide radial alignment for the rotor with respect to the stator. The bearing support members also include peripheral through-holes and fastening receptacles for fastening the bearing support members, either to the stator, or one another, over the outer diameter of the stator lamination. The fasteners provide axial alignment for the rotor with respect to the stator. Presence of these features in the bearing support members results in increased overall outer diameter of the motor assembly. 
     In order to reduce the overall diameter of the motor, according to an embodiment of the invention, bearing support member piloting and retention features are provided on the inner-diameter (ID) of the stator lamination stack as described herein. 
     In an embodiment, as shown in  FIGS.  4  and  5   , first and second bearing support members  250  and  270  are provided with axial post inserts  280  and  290  shaped to be received within the slots of the stator lamination stack  232  between respective adjacent stator windings  234 . In an embodiment, first bearing support member  250  includes six axial post inserts  280  projecting from the planar radial body  254  around the first bearing pocket  252 . Similarly, second bearing support member  270  includes six axial post inserts  290  projecting from the planar radial body  274  around the second bearing pocket  272 . In an embodiment, axial post inserts  290  include a generally rectangular cross-sectional profile extending from a peripheral portion  292 , which is arranged to engage an inner surface of a corresponding lamination stack slot, to an end portion  294 , which may be slightly thicker than the peripheral portion  292  and is arranged to be disposed at an open end of the lamination stack slot, between an in engagement with two adjacent stator tooth edges. In an embodiment, axial post inserts  280  have a similar construction with a generally rectangular cross-sectional profile extending from a peripheral portion  282 , which is arranged to engage an inner surface of a corresponding lamination stack slot, to an end portion  284 , which may be slightly thicker that the peripheral portion  282  and is arranged to be disposed at an open end of the lamination stack slot, between and in engagement with two adjacent stator tooth edges. In an embodiment, two of the post inserts  281  adjacent the hall board  260  may include a shortened end portion to accommodate the hall board  260 . 
     It is noted that while in the illustrated embodiment, the axial posts inserts  280  and  290  are generally-rectangular shaped engaging an inner surface and two tooth edges of the stator lamination slots, it is envisioned that axial members with various other shapes and engaging other surfaces of the stator lamination slots are within the scope of this disclosure. 
     During the assembly process, as shown in the perspective view of  FIG.  6   , rotor assembly  210  is first assembled with the first bearing support member  250  to provide a first sub-assembly. In this step the rotor shaft  212  is press-fitted into the rear rotor bearing  220 . The axial post inserts  280  are in this manner located at a circumferential distant around the rotor lamination stack  214 . 
     Additionally, as shown in the perspective view of  FIG.  7   , stator assembly  230  is assembled with the second bearing support member  270  to provide a second sub-assembly. In this step, the axial post inserts  290  are tightly pressed into the stator slots, against the frictional force of the inner surface of the lamination stack  232 , between the stator windings  234 , until mating surfaces of the front end insulator  236  and the second bearing support member  270  come into contact. 
     Once these steps are completed, the first sub-assembly is assembled into the second sub-assembly to form the motor  200 . In this step, the axial post inserts  280  of the first bearing support member  250  are tightly pressed into the stator slots, against the frictional force of the inner surface of the lamination stack  232 , between the stator windings  234  and opposite the axial post inserts  290  of the second bearing support member  270 , until mating surfaces of the rear end insulator  237  and the first bearing support member  250  come into contact. The front rotor bearing  222  is also form-fittingly received inside the bearing pocket  272  of the second bearing support member  270 , with the rotor shaft  212  and the pinion  205  extending through the through-hole  273 . 
     Referring to  FIGS.  3 A,  3 B,  5  and  7   , in an embodiment, each end insulator  236  and  237  includes various peripheral indentations  231  and detents  239 . In an embodiment, a mating surface of the first and second bearing support member  270  includes corresponding detents  250 / 297  and indentations  293 / 298 . During assembly, these indentations and detents are lined up for proper alignment and piloting of the stator assembly  230  and the two bearing support members  250  and  270 , and engage one another to form a substantially uniform cylindrical body. 
     In an embodiment, the first bearing support member  250  includes one or more flexible posts  285 , made of resiliently elastic material such as rubber, axially extending its mating surface  291 . When the rotor assembly  210  is received inside the stator assembly  230 , flexible posts  285  of the first bearing support member  250  come in contact with and press against the rear end insulator  237 . Flexible posts  285  account for and absorb any tolerances associated with the stator assembly  230 , the rotor assembly  210 , or the first bearing support member  250 , relative to one another. 
     In an embodiment, the second bearing support member  270  also includes one or more flexible posts  275 , made of resiliently elastic material such as rubber, axially extending from its end surface opposite the stator assembly  230 . As discussed below in detail, when the motor  200  is assembled inside the power tool housing  102 , flexible posts  275  absorb any tolerances associated with the stator assembly  210 , the second bearing support member  270 , or the power tool housing  102 , relative to one another. 
       FIG.  8    depicts a perspective radially-cut-off view of the motor  200 , including the first bearing support member  250  assembled on one side of the stator lamination stack  232  and rotor lamination stack  214 . As shown herein, in an embodiment, stator teeth  240  of the stator lamination stack  230  extending inwardly from the cylindrical portion  242  of the lamination stack  232  towards the center bore and define slots  244  therebetween. Stator windings  234  are wound around the stator teeth  240  within adjacent slots  244 . Peripheral portions  282  of axial post inserts  280  nest against an inner surface of the cylindrical portion  242  of the lamination stack  232  within the slots  244 . End portions  284  of axial post inserts  280  engage adjacent tooth edges  246  of adjacent stator teeth  240  for added support. In this manner, the peripheral portions  282  are firmly held against the inner surface of the cylindrical portion  242  of the lamination stack  232 , constraining the lateral and/or radial movement of the first bearing support member  250  with respect to the stator assembly  230 . 
       FIG.  9    depicts a perspective axially-cut-off view of the motor  200 , according to an embodiment. This cut-off view is provided along a plane intersecting the center of the motor shaft  212  and opposing axial post inserts  280  and  290 . As shown herein, the axial post inserts  280  and  290  project partially within the stator lamination stack  232  slots. In an embodiment, the axial post inserts  280  and  290  may each project to approximately a quarter-way to a half-way point within the stator lamination stack  232 . Axial post inserts  280  and  290  are firmly supported by the stator lamination stack  232 , and thus restrain the lateral and/or radial movement of the bearing support members  250  and  270  with respect to the stator lamination stack  232 . 
     As shown in  FIGS.  8  and  9   , this arrangement ensures that the rotor lamination stack  214  is radially secured inside the stator lamination stack  232  and a substantially-uniform air gap is maintained between the outer circumference of the rotor lamination stack  214  and the stator assembly teeth  240  with a high degree of precision. 
     In an embodiment, the rear and front bearings  220 ,  222  axially restrain and secure the bearing support members  250  and  270  on the two sides of the rotor assembly  210  and the stator assembly  230 . In addition, as described herein, the power tool housing  102  and the motor  200  may be provided with retaining and piloting features to help locate and secure the motor  200  within the power tool  100 . These retaining and piloting features provide additional axial support to the motor  200  components. 
       FIG.  10    depicts a partially-exploded perspective view of the power tool  100  with motor  200  shown at a distance from housing half  102 .  FIG.  11    depicts a cut-off top perspective view of the power tool  100 . The retaining and piloting features of the tool housing  102 , and corresponding tabs, projections, or recesses of the motor  200  components that engage the retaining and piloting features of the tool housing  102 , are described herein with reference to these figures, and with continued reference to  FIGS.  2 - 7   . 
     In an embodiment, first bearing support member  250  includes two opposing generally-rectangular peripheral tabs  304  (one of which is shown in  FIG.  10   . Tool housing  102  includes corresponding channels or recesses  320  (only one of which is shown in  FIG.  10   ) arranged to receive the peripheral tabs  304  on both sides of the motor  200  when fully assembled. 
     In addition, in an embodiment, end insulator  237  of the stator assembly  230  facing the first bearing support member  250  includes two pairs of opposing U-shaped walls  308  (one pair being shown in  FIG.  10   ) in close proximity or in contact with the peripheral tab  304 . U-shaped walls  308  form recess portions  310  therein. Tool housing  102  includes corresponding posts  324  on both sides of the motor  200  that, when assembled, are received inside recessed portions  310  and engage the U-shaped tabs  308 . In an embodiment, posts  324  and U-shaped tabs  320  may be provided with elastic pads  330  and  332  to account for small tolerances associated with the motor  200  components. 
     In addition, in an embodiment, the tool housing  102  is further provided with inner ribs walls  326  that, when fully assembled, engage two edges  271  of the second bearing support member  270  on both sides of the motor  200 . 
     These piloting and retaining features  320 ,  324 , and  326  of the power tool housing  102  not only help proper placement and alignment of the motor within the power tool  100 , they provide axial constraints against the first bearing support member  250 , the stator assembly  230 , and the second bearing support member  270 . These axial restraints reinforce the axial restraints provided by the front and rear bearings  222  and  220 . 
     The above-described embodiments of the invention reduce the overall outside diameter (OD) of the motor. Alternatively, given the same space laminations inside the power tool housing, a motor according to embodiments of the invention can be provided with a larger OD stator lamination stack, providing more torque and power. 
     Table A below provides a comparison between two exemplary conventional BLDC motors (without a motor can or motor housing) having piloting and retention features and fasteners on the outer surface of the stator assembly (1st with a 48 mm stator lamination stack OD, and the 2 nd  with a 51 mm stator lamination stack OD), and an improved BLDC motor with a 51 mm stator lamination stack OD having inner diameter (ID) piloting and retention features and no fasteners according to embodiments of this disclosure. 
     
       
         
           
               
               
               
               
             
               
                 TABLE A 
               
               
                   
               
               
                   
                 1st Conv.  
                 2nd Conv.  
                 Improved  
               
               
                   
                 BLDC 
                 BLDC 
                 BLDC 
               
               
                   
               
             
            
               
                 Stator Lamination OD 
                   48 mm 
                   51 mm 
                    51 mm 
               
               
                 First (Fan-Side) Motor Cap 
                 54.4 mm 
                   58 mm 
                 54.4 mm 
               
               
                 (Bearing Support Member) 
                   
                   
                   
               
               
                 Second Motor Cap 
                 53.5 mm 
                 57.4 mm 
                   51 mm 
               
               
                 (Bearing Support Member) 
                   
                   
                   
               
               
                 Screws (threads) 
                 50.2 mm 
                 54.9 mm 
                 n/a 
               
               
                   
               
            
           
         
       
     
     As shown in this table, in the first exemplary conventional BLDC motor with 48 mm stack lamination stack OD, the diameters of the two motor caps (i.e., bearing support members), as measured between opposing fastening receptacles, are 54.4 mm and 53.5 mm respectively. Thus, the motor caps increase the diameter of the motor by approximately 10-15%. The diameter of the stator, as measured between opposing screws on the outside surface of the lamination stack, is also increased by approximately 2 mm to 50.2 mm. 
     In the second exemplary conventional BLDC motor with 51 mm stack lamination OD, the diameters of the two motor caps (i.e., bearing support members), as measured between opposing fastening receptacles, are 58 mm and 57.4 mm respectively. Thus, the motor caps once again increase the overall diameter of the motor by approximately 10-15%. The diameter of the stator, as measured between opposing screws on the outside surface of the lamination stack, is also increased by approximately 4 mm to 54.9 mm. 
     It was found by inventors of this application that removing the screws and the associated fastening receptacles from the motor caps of the second exemplary conventional BLDC motor, in accordance with the above-described embodiments of the invention, reduces the diameter of the motor caps by approximately 3 mm. It was further found that using the inner diameter (ID) piloting and retention features, in accordance with the above-described embodiments of the invention, further reduces the diameter of the motor caps (not including the rectangular peripheral tabs  304 ) to approximately 51 mm—approximately the same diameter as the OD of the stator lamination stack. It is noted that the distance between the rectangular peripheral tabs  304  in the first bearing support member  250 , as noted in Table A, is approximately 54.4 mm, which is only an approximately 5% increase. However, the rectangular peripheral tabs  304  are received in channels  322  of the housing and therefore do not contribute to a considerable increase to the motor diameter. 
     Accordingly, in accordance with embodiments of the invention, given the same space constraints in the power tool housing, a BLDC motor may be provided with a larger stator lamination stack OD without increasing the overall diameter of the motor. In the example above, the lamination stack OD was increased from 48 mm to 51 mm while maintaining the overall diameter of the motor at no more than 54.4 mm. It was further found by the inventors that such an increase to the OD of the stator lamination stack substantially increases power output, torque output, and efficiency. Specifically, it was found that given the same stator slot area, stator slot fill, and stator lamination stack length, magnet grade, lamination grade, and magnet length, and while maintaining the maximum no-load speed, increasing the stator lamination stack diameter in this matter results in an increase in the power output by 10% to 20%, particularly by approximately 15%; an increase in the torque output by 40% to 55%, particularly by 30 to 40%, more particularly by approximately 35%; and an increase in efficiency by approximately 5%. 
     Table B below sets forth the size and performance parameters of an improved BLDC according to embodiments of the invention. In an embodiment, given the space limitations set forth below and parameters provided below, the motor of this invention outputs more than 900 W Max Out power and over 0.80 Nm of torque at Max Watts out. 
     
       
         
           
               
               
               
             
               
                 TABLE B 
               
               
                   
               
               
                   
                 1st Conv. BLDC 
                 Improved BLDC 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Stator Lamination OD 
                   48  
                 mm 
                   51  
                 mm 
               
               
                 First (Fan-Side) Motor Cap 
                 54.4  
                 mm 
                 54.4  
                 mm 
               
               
                 Stator Stack length 
                   25  
                 mm 
                   25  
                 mm 
               
               
                 Rotor Stack Length 
                 25.6  
                 mm 
                 25.6  
                 mm 
               
               
                 Rotor Magnet Length 
                   26  
                 mm 
                   26  
                 mm 
               
            
           
           
               
               
               
            
               
                 Slot Fill 
                 36% 
                 36% 
               
               
                 Magnet Grade 
                 48H 
                 48H 
               
               
                 Lamination Grade 
                 35H360 Nippon  
                 35H360  
               
               
                   
                 Steel 
                 Nippon Steel 
               
               
                 No-Load Speed 
                 20,500 rpm 
                 20,500 rpm 
               
            
           
           
               
               
               
               
               
            
               
                 Max Power (Max Watts  
                 806  
                 W 
                 929  
                 W 
               
               
                 Out) 
                   
                   
                   
                   
               
            
           
           
               
               
               
            
               
                 Max Efficiency 
                 85% 
                 89% 
               
            
           
           
               
               
               
               
               
            
               
                 Torque at Max Watts Out 
                 0.67  
                 Nm 
                 0.90  
                 Nm 
               
               
                   
               
            
           
         
       
     
     In the above-described first embodiment, the two bearing support members  250  and  270  are provided as end caps arranged at the two ends of the stator assembly  230 . A second alternative embodiment of the invention is described herein with reference to  FIGS.  12 - 15 B . 
       FIG.  12    depicts a perspective view of a BLDC motor  400 , according to an embodiment.  FIG.  13    depicts a partially exploded view of the same motor  400 , according to an embodiment. 
     Similarly to the first embodiment, motor  400  is a three-phase motor including a rotor assembly  410  rotatably received within a stator assembly  430 . 
     In an embodiment, stator assembly  430  is similar to and includes many of the same features as stator assembly  230  of the first embodiment. To provide an overview, stator assembly  430  includes a generally cylindrical lamination stack  434  having a center bore and a plurality of teeth extending inwardly from the cylindrical portion of the lamination stack  434  defining a plurality of slots. Stator windings  434  are wound around the stator teeth within the adjacent slots. Front and rear end insulators  436  and  437  are provided on the end surfaces of the stator lamination stack  432  to insulate the lamination stack  432  from the stator windings  434 . Front and rear end insulators  436  and  437  may be shaped to be received at the two ends of the stator lamination stack  432 . In an embodiment, each end insulator  437  and  436  includes a radial plane that mates with the end surfaces of the stator lamination stack  432 , and teeth and slots corresponding to the stator teeth and stator slots. Unlike the embodiment of  FIGS.  3 A and  3 B , in the illustrative embodiment, terminals  438  are disposed at an axial end of the stator assembly  230 , with the rear end insulator  436  including retention features disposed circumferentially around the end of the stator assembly  430  for holding the terminals  438 . 
       FIG.  14    depicts an exploded perspective view of a sub-assembly including the rotor assembly  410  and bearing support members  450  and  470 . Rotor assembly  410  is similar to and includes many of the same features as rotor assembly  210  of the first embodiment. To provide an overview, as shown in  FIG.  14   , and with continued reference to  FIGS.  12  and  13   , rotor assembly includes a rotor shaft  412 , a rotor lamination stack  414  having a series of flat laminations, and permanent magnets  415  disposed within axial slots of the lamination stack  414 . In an embodiment, a fan  418  is mounted on one distal end of the rotor shaft  412 , and a pinion  415  is disposed one the other distal end of the rotor shaft  412  for engagement with the transmission assembly  114 . In an embodiment, two rotor caps  411  are disposed on the two ends of the rotor lamination stack  414  to axially restrain the magnets  415  within the lamination stack  414 . In an embodiment, rotor end caps  411  may be similar to end caps  226  shown in  FIG.  3 B  and described later in this disclosure in great detail. In an embodiment, sense magnet  416  is disposed on the rotor  412  via a bushing  417  between the second bearing support member  470  (described below) and the pinion  415 . 
     In an embodiment, the first bearing support member  450  is disposed on a rear side of the rotor assembly  410  between the rotor assembly  410  and the fan  418 . In an embodiment, first bearing support member  450  includes many of the same features as the first bearing support member  250  previously described, including axial post inserts  280  projecting from a planar radial body and slots  456  formed between respective teeth that allow passage of airflow generated by the fan  418  through the stator assembly  430 . A center portion of the first bearing support member  450  defines a bearing pocket that receives the rear rotor bearing  420  therein. In this example, the first bearing support member  450  is not provided with a hall board. It must be understood, however, that the sense magnet  416  may be disposed between the rotor lamination stack  414  and the first bearing support member  450  (e.g., in place of the corresponding rotor end cap  411 ), and the first bearing support member  450  may be provided with a hall board, as previously described with reference to  FIGS.  3 B and  4   . 
     The second bearing support member  470  is described herein with reference to  FIGS.  15 A and  15 B , and with continued reference to  FIGS.  12 - 14   . In an embodiment, second bearing support member  470  is shaped and configured to be received axially through the stator assembly  430 . The second bearing support member  470 , in an embodiment, includes a substantially disc-shaped planar portion  476  having a through-hole  474  in its center portion therein forming a bearing pocket for receiving the front rotor bearing  422  therein. The second bearing support member  470  further includes a series of axial post inserts  472  disposed axially around and attached to the circumference of the planar portion  476  via a series of radial connection members  473 . In an embodiment, the axial post inserts  472  are sized such that a peripheral portion  471  of the axial post inserts  472  engage an inner surface of stator lamination stack  432  slots to hold and radially restrain the second bearing support member  470  within the stator lamination stack  432 . 
     Unlike the previous embodiment, the second bearing support member  470  does not include a mating surface that mates with an outer surface of the stator assembly. This allows the second bearing support member  470  to traverse through the length of the stator lamination stack  432 , with the axial post inserts  472  engaging and forcefully sliding against the inner surface of stator lamination stack  432  slots. 
     During the assembly process, in an embodiment, the rear and front bearings  420  and  422  are received with the bearing pockets of the first and second bearing support members  450  and  470 . The first and second bearing support members  450  and  470  are then mounted (e.g., via press-fitting) onto the rotor shaft  412  on two sides of the rotor assembly  410 , sandwiching the rotor assembly  410  on its two ends, to form the sub-assembly shown in  FIG.  14   . The fan  418 , sense magnet  516 , and pinion  405  may also be mounted on the rotor shaft  412  as shown in  FIG.  14   . 
     In an embodiment, the entire sub-assembly including the rotor assembly  410  and the first and second bearing support members  450  and  470  may then be axially received within the stator assembly  430 , from the rear side of stator assembly where the rear end insulator  437  is located, until the rear end insulator  437  comes into contact with a mating surface of the first bearing support member  450 . As the assembly is being inserted into the stator assembly  430 , the axial post inserts  472  are forced against the inner surface of the stator lamination stack  432  slots, within the gaps between adjacent stator windings. 
     In an embodiment, similarly to the embodiment described above, the rear end insulator  437  and the first bearing support member  450  may include corresponding indentations and detents that mate together to help pilot and locate the two sub-assemblies. The rear end insulator  437  and the first bearing support member  450  also include peripheral tabs and other engagement features (e.g., U-shaped walls  408 ) for piloting and placement of the motor  400  within a power tool housing. 
     In an embodiment, the front end insulator (see  FIG.  12   ) includes axial channels or recesses  452  that receive the end portions of the axial post inserts  472  of the second support member  470  therein as the second support member  470  is being axially pressed through the lamination stack  438 . 
     In an embodiment, the above-described arrangement provides a motor assembly  400  in which one of the rotor bearings (i.e., front bearing  422 ) that radially supports the rotor assembly  410  within the stator assembly  430  is structurally supported fully within the stator assembly  430 , i.e., on the inner diameter of the stator lamination stack  432  and the front end insulator  436 . This arrangement significantly eases the manufacturing process, allowing both bearings  420 ,  422  to be mounted on the rotor shaft  412  prior to assembly of the rotor  410  into the stator assembly  430 . 
     In addition, with this arrangement the motor  400  is provided without a front motor end cap for supporting the front bearing  422 , thus reducing the length of the motor  400  by several millimeters. In an embodiment, as shown in  FIG.  12   , the front bearing  422  (hidden behind the sense magnet  416 ) may be positioned along approximately the same radial plane as the front end insulator  436  and/or the ends of the stator windings  434 . Thus, the supporting structure for the front bearing  422  does not add to the overall length of the motor  400 . 
     The third embodiment of the invention is described herein with reference to  FIGS.  16 - 19   . In this embodiment, both front and rear bearing support structures are fully supported within the stator assembly  430 . 
       FIG.  16    depicts a perspective view of a BLDC motor  500  having internally supported bearing support structures, according to an embodiment.  FIG.  17    depicts a partially exploded view of the same motor  500 , according to an embodiment. 
       FIG.  18    depicts a perspective view of a sub-assembly including the rotor assembly  410 , the second bearing support member  470  as described above with reference to  FIGS.  12 - 15 B , and an alternative and/or improved first bearing support member  550 , according to an embodiment.  FIG.  19    depicts an exploded view of the sub-assembly shown in  FIG.  18   . 
     In an embodiment, most components of the motor  500  of this embodiment are similar to motor  400  of the second embodiment described above, with the exception of the first bearing support member  550 , described here. 
     In an embodiment, first bearing support member  550 , similarly to the second bearing support member  470 , is shaped and configured to be axially received and pressed through the stator assembly  430 . The first bearing support member  550 , in an embodiment, includes a substantially disc-shaped planar portion  556  having a through-hole  554  in its center portion therein forming a bearing pocket for receiving the rear rotor bearing  520  therein. The first bearing support member  550  further includes a series of axial post inserts  552  disposed axially around and attached to the circumference of the planar portion  556  via a series of radial connection members. In an embodiment, the axial post inserts  552  are sized such that their peripheral portions engage an inner surface of stator lamination stack  432  slots to hold and radially restrain the first bearing support member  550  within the stator lamination stack  432 . 
     In an embodiment, the first bearing support member  550  does not include a mating surface that mates with an outer surface of the stator assembly  430  (i.e., at end insulator  437 ). This allows the first bearing support member  550  to be received into the stator lamination stack  432 , with the axial post inserts  552  engaging and forcefully sliding against the inner surface of stator lamination stack  432  slots. 
     In an embodiment, axial post inserts  552  may have a generally rectangular cross-sectional profile extending from a peripheral portion  562  (see  FIG.  18   ), which is arranged to engage an inner surface of a corresponding lamination stack slot, to an end portion  564 , which may be slightly thicker that the peripheral portion  562  and is arranged to be disposed at an open end of the lamination stack slot, between and in engagement with two adjacent stator tooth edges. In an embodiment, the peripheral portions  562  of the axial post inserts  552  align with peripheral portions of axial post inserts  472  of the second bearing support member  470 . 
     In an embodiment, first bearing support member  550  may include a series of notches  566  (see  FIG.  18   ) around bases of the axial post inserts  552 . Rear end insulator  437  may also include corresponding detents  570  (see  FIG.  17   ) that receive the notches  566  therein, and thus axially restrain the first bearing support member  550 , when rotor assembly  410  and the two bearing support members  470  and  550  are fully inserted into the stator assembly  430 . 
     In an embodiment, the above-described arrangement provides a motor assembly  400  in which both the rotor bearings  422  and  520  that radially supports the rotor assembly  410  within the stator assembly  430  are structurally supported fully within the stator assembly  430 , i.e., on the inner diameter of the stator lamination stack  432  and the front end insulator  436 ,  437 . With this arrangement the motor  400  is provided without front and rear motor end caps for supporting the front bearing  422 , thus reducing the length of the motor  400  significantly. In an embodiment, when fully assembled, the front bearing  422  may be positioned along approximately the same radial plane as the front end insulator  436  and/or the front ends of the stator windings  434 . Similarly, the rear bearing  520  may be positioned along approximately the same radial plane as the rear end insulator  437  and/or the rear ends of the stator windings  434 . Thus, the supporting structures for the rear and front bearings  420  and  422  do not add to the overall length of the motor  400 . 
     Another aspect/embodiment of the invention is described herein with reference to  FIGS.  20 A and  20 B . 
     As previously described, the rotor permanent magnets are axially contained within the rotor lamination stack via two rotor end cap on both sides, or via a rotor end cap on one side and a sense magnet disc on the other. The rotor end cap may be a disc-shaped plate, as shown in the exemplary embodiments of  FIGS.  14  and  19    (see end cap  411 ). Alternatively, as shown in  FIGS.  3 B and  6   , an improved rotor end cap  226  may be provided to improve thermal transfer and cooling of the rotor lamination stack  210 , according to an embodiment. 
       FIGS.  20 A and  20 B  depict front and back perspective views of rotor end cap  226 , according to an embodiment. As shown in these figures, rotor end cap  226  may include a peripheral planar portion  606  that mounted on axial end(s) of the rotor lamination stack, a center bore  604  through which the rotor shaft is received, and a series of ribs  608  disposed at an angle with respect to the plane of the planer portion  606  that extend from the planar portion  606  to a frontal end  605  of the center bore  604 . A series of axial openings  602  are formed between the ribs  608 , which allow air to come into contact with the end of the rotor lamination stack, including the permanent magnets. Further, the angular disposition of the ribs  608  allows the air to circulate tangentially between adjacent openings  602  under the ribs  608  and in contact with the end of the lamination stack. 
     In an embodiment, one or more inner walls  603  extend from the planar portion  606  to a rear end  607  of the central bore. The planar portion  606 , together with the inner walls  603 , engage at least a portion of the end of each of the permanent magnets, ensuring that the permanent magnets are fully axially retained within the rotor lamination stack. 
     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.