Patent Publication Number: US-2022224173-A1

Title: Electric tool

Description:
This application is a Continuation of application Ser. No. 16/611,521, filed Nov. 7, 2019, which in turn claims the benefit of International Application No. PCT/JP2018/021409, filed on Jun. 4, 2018, Japanese Patent Application Number No. 2017-117093 filed on Jun. 14, 2017, Japanese Patent Application Number No. 2017-117094 filed on Jun. 14, 2017, Japanese Patent Application Number No. 2017-117095 filed on Jun. 14, 2017, and Japanese Patent Application Number No. 2017-117096 filed on Jun. 14, 2017, the entirety of which is incorporated by reference. 
    
    
     BACKGROUND OF INVENTION 
     Technical Field 
     The present invention relates to an electric tool, such as a hammer drill, using a brushless motor as a driving source. 
     Background Art 
     A brushless motor (see Japanese Laid Open Patent Publication No. 2017-35784) that is compact and excellent in durability is used as a driving source of an electric tool. Recently, with an advance of a performance of a battery cell serving as a power supply, electric power input to the brushless motor has been increasing while the brushless motor has been also required to have an increased output. 
     To increase the output, thinning of electromagnetic steel plates is considered against a high space factor of a winding wire, an increase in size of the winding wire, and an increase in iron loss (heat loss) in a stator core. However, as in Japanese Laid Open Patent Publication No. 2017-35784, in the case of an integrated stator core, a coil is forced to be formed in a narrow space inside the stator core, making the high space factor difficult. Additionally, a thin steel plate costs high and leads to a cost increase without improvement of the yield. 
     Therefore, manufacturing a stator core by dividing the stator core and coupling a plurality of components is considered. Such a divided structure allows a large-sized stator core, achieves a high space factor, and further a yield in punching of an electromagnetic steel plate decreases and therefore a cost reduction can be expected. 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, with an electric tool, there is a situation where a working environment is severe, such as vibrations, dust, and an impact due to falling. Therefore, configuring a stator core of a brushless motor used in such a situation to be a divided structure has possibly resulted in deterioration of durability and a dust-proof performance. 
     In order to achieve downsizing and a weight reduction of the motor, since a surface area of the motor decreases, a cooling performance possibly gets worse. Especially, although the use of the above-described divided cores allows downsizing of the motor while efficiency and an output remain equivalent, the cooling performance is difficult to be improved. 
     Furthermore, vibrations cause disconnection of a coil in the electric tool in some cases, and there may be case where an extra terminal process is required. 
     In addition, the electric tool is sometimes used in the severe situation, such as dust and falling, in addition to vibrations, a concern remains about durability and a dust-proof performance in the divided structure where the stator core is divided in a circumferential direction. 
     Therefore, an object of the present invention is to provide an electric tool that achieves a high space factor and a low cost by configuring a stator core of a brushless motor as a divided structure and also allows ensuring durability and a dust-proof performance. 
     Further, an object of the present invention is to provide the electric tool that achieves the high space factor and the low cost by configuring the stator core of the brushless motor as the divided structure and also allows improving a cooling performance. 
     Furthermore, an object of the present invention is to provide the electric tool that can preferably reduce disconnection of a coil. 
     In addition, an object of the present invention is to provide the electric tool excellent in the durability and the dust-proof performance even when the stator core is divided. 
     Solutions to the Problems 
     In order to achieve the above-described object, there is provided an electric tool according to the present invention. The electric tool includes a brushless motor including a stator, a rotor, and a plurality of coils. The stator includes a stator core formed by laminating electromagnetic steel plates. The rotor includes a rotation shaft. The plurality of coils are wound around the stator core via an insulating member. While the stator core is formed by joining a plurality of divided cores divided in a circumferential direction, a varnish or an adhesive is applied over the coils and joining portions between the divided cores. 
     In the present invention according to another aspect, the adhesive has a high thermal conductivity. 
     In the present invention according to another aspect, the coils are wound around the respective divided cores. 
     In the present invention according to another aspect, the stator includes a sensor circuit board including a rotation detecting element of the rotor. The sensor circuit board is fixed via a plurality of fixing pins directly fixed to the stator core. 
     In the present invention according to another aspect, the fixing pin are fixed across the two adjacent divided cores. 
     In the present invention according to another aspect, the fixing pins are press-fitted to a disk made of metal disposed on an end surface of the stator core. 
     In the present invention according to another aspect, each of the divided cores has a shape fixed with an integrally molded resin. 
     In the present invention according to another aspect, each of the divided cores has a shape fixed with a dust core coating an outer surface thereof. 
     In the present invention according to another aspect, the respective divided cores are fixed with a tubular fixing member made of metal manufactured by shrinkage fitting or cold fitting. 
     In the present invention according to another aspect, which is in the configuration of any one of claims  1  to  12 , the respective divided cores have joining portions inclined with respect to an axial direction of the stator core. 
     In the present invention according to another aspect, which is in the configuration of any one of claims  1  to  13 , the electromagnetic steel plates have a plate thickness of 0.25 mm or less. 
     Effects of the Invention 
     According to the present invention, the varnish or the adhesive is applied over the coils and the joining portions of the divided cores (claim  1 ), or the joining portions of the divided cores have two different kinds of the shapes so as to alternately mesh with one another (claim  3 ), or the abutting portions between the insulating members in the insulating members have convexo-concave shapes alternately meshing with one another (claim  5 ). These configurations achieve a high space factor and a low cost by configuring the stator core as the divided structure and also ensure durability and a dust-proof performance. 
     Additionally, according to the present invention, the plurality of protrusion portions are disposed on the outer surface on the divided core (claim  15 ) or the plurality of protrusion portions are disposed on the outer periphery of the fixing member to fix the divided cores (claim  18 ). These configurations achieve a high space factor and a low cost by configuring the stator core of the brushless motor as the divided structure and also allow improving a cooling performance. 
     Furthermore, according to the present invention, disconnection of the coil can be preferably reduced (claim  21  and the like). 
     In addition, according to the present invention, even when the stator core is divided, preferred durability and dust-proof performance can be maintained (claim  29  and the like). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a vertical cross-sectional view of a hammer drill. 
         FIG. 2  is a perspective view of a stator from a lower side. 
         FIG. 3  is a perspective view of a divided core. 
         FIG. 4A  is a perspective view of the divided core in which a resin molded portion is formed, and  FIG. 4B  is a perspective view of a divided body. 
         FIG. 5  is a perspective view of the stator from the lower side before coated with varnish. 
         FIG. 6  is a perspective view of the stator from the lower side to which a sensor circuit board is mounted. 
         FIG. 7  is a perspective view of the stator from the lower side to which a terminal unit is mounted. 
         FIGS. 8A to 8F  are explanatory views of connection patterns. 
         FIG. 9  is a vertical cross-sectional view of a stator illustrating a modification example of the terminal unit. 
         FIG. 10A  is a perspective view illustrating a modification example of the divided core, and  FIG. 10B  is a perspective view of a divided body. 
         FIGS. 11A and 11B  are explanatory views illustrating modification examples of upper and lower insulating portions. 
         FIG. 12A  is a perspective view illustrating a modification example of the divided core, and  FIG. 12B  is a perspective view illustrating a coupled state with a fixing pin. 
         FIG. 13  is a perspective view of the stator from a lower side in which the fixing pins double as mounting of the sensor circuit board and joining of the divided cores. 
         FIG. 14  is a perspective view of the stator from the lower side coated with a dust core. 
         FIG. 15  is a perspective view of the stator from the lower side using a fixing member having ridges. 
         FIG. 16  is a perspective view of the stator from a lower side using the fixing member with the ridges inclined. 
         FIG. 17  is a perspective view of the stator from the lower side using divided cores with end edges of arc portions inclined. 
         FIG. 18  is a perspective view of the stator from the lower side using divided cores including protrusion portions on outer peripheral surfaces of the arc portions. 
         FIG. 19  is a perspective view of an outer peripheral portion. 
         FIG. 20  is a perspective view of a tooth. 
         FIG. 21A  is a perspective view of the tooth in which the resin molded portion is formed, and  FIG. 21B  is a perspective view of a divided body. 
         FIG. 22  is a perspective view from a lower side in a state of arranging the divided bodies. 
         FIG. 23  is a perspective view from the lower side illustrating a state in which the divided bodies are joined to the outer peripheral portion. 
         FIG. 24  is a perspective view illustrating a modification example of coupling the teeth together with joints. 
         FIG. 25  is a perspective view from a lower side in a state where the divided bodies with the resin molded portions mutually connected are arranged, and 
         FIG. 26  is a perspective view illustrating an example in which an outer peripheral portion is longer than teeth. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following describes embodiments of the present invention with reference to the drawings. 
     [Description of Hammer Drill] 
       FIG. 1  is a vertical cross-sectional view of the hammer drill as one example of an electric tool. A hammer drill  1  includes an output housing  4 , which houses an output unit  5  and extends forward, on an upper side of a motor housing  2  in an up-down direction housing a brushless motor  3 . A battery mounting portion  6  that houses a controller  7  and has a lower side to which two battery packs  8 ,  8  are mountable is disposed on the lower side of the motor housing  2 . Reference numeral  9  denotes a handlebar disposed to extend in the up-down direction from the rear of the output housing  4  to the battery mounting portion  6 . 
     The brushless motor  3  is an inner rotor type including a stator  10  and a rotor  11  inside the stator  10  and is housed in the motor housing  2  with a posture in which a rotation shaft  12  of the rotor  11  facing above. The stator  10  includes a stator core  13 , an upper insulator  14  and a lower insulator  15 , which are disposed on the top and bottom of the stator core  13 , and a plurality of coils  16 ,  16 , and so on ( FIG. 2  and the like) wound around the inside of the stator core  13  via the upper and lower insulators  14 ,  15 . The stator core  13  has a divided structure constituted of a plurality of components, and details of this divided structure will be described later. 
     The rotor  11  includes the rotation shaft  12  positioned at its axial center, a tubular rotor core  17  arranged around the rotation shaft  12 , and a plurality of permanent magnets  18 ,  18 , and so on arranged inside the rotor core  17 . A sensor circuit board  19  and a terminal unit  20  to connect terminals of the coils  16  are fixed to the lower end of the lower insulator  15 . The sensor circuit board  19  includes a rotation detecting element (not illustrated) that detects positions of the permanent magnets  18  in the rotor core  17  and outputs a rotation detection signal. The rotation shaft  12  has a lower end supported to a bearing  21 , which is disposed on the bottom portion of the motor housing  2 , and an upper end supported to a bearing  22 , which is disposed in the output housing  4  and projects into the output housing  4 . A pinion  23 , which is formed on the upper end of the rotation shaft  12 , meshes with gear  26 ,  27 , which are disposed on respective intermediate shaft  24  and crankshaft  25  on the front and rear. A centrifugal fan  28  is disposed on the lower side of the bearing  22  and on the rotation shaft  12 , and a baffle plate  29  is disposed below the centrifugal fan  28  and inside the motor housing  2 . 
     The output unit  5  includes a rotatable, tubular tool holder  30  extending in a front-rear direction. A bevel gear  31 , which is externally mounted to a rear end of the tool holder  30 , meshes with a bevel gear  32  disposed on an upper end of the intermediate shaft  24 . A cylinder  33  is inserted into and mounted to the inside of the tool holder  30 , and a piston  34  disposed inside the cylinder  33  is coupled to a crank pin  36 , which is disposed at an eccentric position on the upper end of the crankshaft  25 , via a connecting rod  35 . 
     A striker  38  is housed inside the cylinder  33  and ahead of the piston  34  in an air chamber  37  to be movable back and forth, and an impact bolt  39  is housed inside the tool holder  30  ahead of the striker  38  to be movable back and forth. Here, when a tool bit, such as a drill bit, is inserted from a distal end of the tool holder  30 , a rear end of the tool bit retreats the impact bolt  39  up to a position where the impact bolt  39  abuts on a receiving ring  40  ahead of the cylinder  33  to cause the rear end to project into the cylinder  33 . Reference numeral  41  denotes an operation sleeve externally mounted to a front end of the tool holder  30  for performing attachment and removal operations of the tool bit. 
     Meanwhile, inside the battery mounting portion  6 , two terminal blocks  42 ,  42  on which the battery packs  8 ,  8  are slidably mounted from a right-left direction are arranged back and forth, and the controller  7  is housed on the upper side. The controller  7  includes a control circuit board (not illustrated) including a microcomputer and a switching element and is supported by U-shaped ribs  43 ,  43 , which are disposed upright on an inner surface of the battery mounting portion  6 , in the front-rear direction. A light  44  that irradiates the front side of the tool holder  30  with an LED is disposed in front of the controller  7 . Guard plates  45 ,  45  to cover the front and rear of the mounted battery packs  8 ,  8  are formed to project downward on the front and rear of the battery mounting portion  6 . 
     A switch  46  and a capacitor  47  electrically coupled to the controller  7  are disposed in the handlebar  9 , and a switch lever  48  is disposed on a plunger projecting forward from the switch  46 . 
     Accordingly, with this hammer drill  1 , pushing the switch lever  48  by a hand gripping the handlebar  9  and performing an ON operation on the switch  46  feeds the power from the battery pack  8  to the brushless motor  3  to rotate the rotation shaft  12 . That is, the microcomputer in the controller  7  obtains the rotation detection signal indicative of the position of the permanent magnet  18  of the rotor  11  output from the rotation detecting element in the sensor circuit board  19  to obtain the rotating state of the rotor  11 . According to the obtained rotating state, the microcomputer controls ON/OFF of the respective switching elements and flows a current in sequence to the respective coils  16  in the stator  10  in order to rotate the rotor  11 . 
     Thus rotating the rotation shaft  12  decelerates and rotates the intermediate shaft  24  via the gear  26  and rotates the tool holder  30  together with the tool bit via the bevel gears  32 ,  31 . Simultaneously, the crankshaft  25  decelerates and rotates via the gear  27 , the piston  34  reciprocates inside the cylinder  33  via the connecting rod  35  to move the striker  38  back and forth via the air chamber  37 . Accordingly, the striker  38  hits the tool bit via the impact bolt  39 . 
     Air inlets (not illustrated) are formed on right and left side surfaces of the battery mounting portion  6 , which serve as both right and left sides of the controller  7 . Exhaust outlets (not illustrated) are formed on right and left side surfaces of the motor housing  2 , which serve as both right and left sides of the centrifugal fan  28 , and the controller  7  is arranged between the air inlets and the brushless motor  3 . Accordingly, by the rotation of the centrifugal fan  28  in association with the rotation of the rotation shaft  12 , air suctioned from the air inlets first contacts the controller  7  to cool the controller  7 , and after that, the air pass through the inside of the motor housing  2  to cool the brushless motor  3 . The air is then discharged from the exhaust outlets via the baffle plate  29 . 
     [Description of Structure of Stator] 
     Next, the following describes the structure of the stator  10  in detail.  FIG. 2  is a perspective view of the stator  10  before the sensor circuit board  19  and the terminal unit  20  are mounted,  FIG. 2  is upside down of  FIG. 1 . The stator core  13  has a tubular body including a plurality (here, 12 pieces) of teeth  52 ,  52 , and so on having a T shape in plan view and projecting toward the center on an inner periphery of the stator core  13 . Here, as illustrated in  FIG. 3 , the stator core  13  is divided by 12 pieces of divided cores  50 ,  50 , and so on formed of arc portions  51  as a part of the tubular body and the teeth  52  projecting inward from inner surfaces of arc portions  51 , thus forming the stator core  13  by joining the divided cores  50 ,  50  adjacent in the circumferential direction. On both ends of the arc portions  51  serving as joining portions of the divided cores  50 ,  50 , protruding portions  53  projecting into a triangular shape in plan view and depressed portions  54  depressed into a V shape in plan view are each formed on one ends and the other ends across the whole length in the up-down direction. The protruding portion  53  and the depressed portion  54  have shapes fittable to one another. A through-hole  55  penetrating up and down is formed at the center in the circumferential direction of the arc portion  51 . 
     Electromagnetic steel plates (for example, a plate thickness t=0.25 mm or less) punched into an identical shape are laminated and integrally molded with resin, thus manufacturing the divided cores  50 . The use of the electromagnetic steel plates having the thin plate thickness leads to a reduction in loss due to eddy current. 
     As illustrated in  FIG. 4A , an integrally molded resin molded portion R having a predetermined thickness coats an outer periphery of the divided core  50  excluding parts of the protruding portion  53  and the depressed portion  54  on both ends of the arc portion  51 , the projecting end of the tooth  52 , and the through-hole  55 . However, insulation papers (not illustrated) are interposed inside the resin molded portion R on both right and left surfaces of the tooth  52  in the circumferential direction, thus double insulations are provided. 
     In this resin molded portion R, a part positioned on the top side of the arc portion  51  becomes an upper insulating portion  56  constituting the upper insulator  14  and a part positioned on the bottom side of the arc portion  51  becomes a lower insulating portion  57  constituting the lower insulator  15 . That is, the upper and lower insulators  14 ,  15  are divided into twelve pieces, similarly to the stator core  13 . 
     An upper outer rib  58  and a lower outer rib  59  to receive the outer side of the coil  16  are disposed upright on inner edges on the tooth  52  side of the upper and lower insulating portions  56 ,  57 , respectively, and a pair of terminal plates  60 ,  60  are disposed outside the lower outer rib  59 . This terminal plates  60  have a U-shape with both ends facing downward, and end portions  60   a  on both ends sides of the arc portions  51  are formed longer so as to extend downward with respect to end portions  60   b  inside the end portions  60   a . Furthermore, a slit  61  opening downward is formed at the center of the lower outer rib  59 , and an expansion portion  62  having a widening width is formed on the lower side of the slit  61 . An upper inner rib  63  and a lower inner rib  64  to receive the inside of the coil  16  are each disposed upright on the top and bottom of the projecting end of the tooth  52  in the resin molded portion R. 
     In the divided core  50  thus integrally molded with resin, a magnet wire is wound around to each tooth  52  to form the coil  16 . After both terminals  16   a ,  16   a  of the coil  16  are pulled out from both sides of the lower insulating portions  57  and pressure shaping is performed on the coil  16 , both terminals  16   a ,  16   a  are coupled to the right and left terminal plates  60 ,  60  by fusing, soldering, or the like. Then, as illustrated in  FIG. 4B , the coil  16  is wound around the divided core  50  via the upper and lower insulating portions  56 ,  57 , and the divided body  65  in which the terminals  16   a ,  16   a  are fixed to the terminal plates  60 ,  60  are obtained. 
     Thus, the shape of each divided core  50  is fixed with the resin molded portion R coating the outer surface of the divided core  50 . Therefore, the divided core  50  is insulated at the same time together with the integration of the electromagnetic steel plates. Since the coil  16  is formed on each divided core  50 , the magnet wire can be easily wound at identical timing. 
     Twelve pieces of the divided bodies  65  are circumferentially arranged such that the arc portions  51  of the respective divided cores  50  are circumferentially coupled, and the adjacent protruding portions  53  and depressed portions  54  are fitted to one another and joined by welding or the like. Then, as illustrated in  FIG. 5 , the respective divided bodies  65 ,  65 , and so on are circumferentially coupled. In this state, applying varnishes  66 ,  67  over the outer peripheral surfaces of the respective coils  16  and the joining parts of the divided cores  50 ,  50  (both upper and lower ends of the fitting parts between the protruding portions  53  and the depressed portions  54 ) allows obtaining the stator  10  illustrated in  FIG. 2 . The varnishes  66 ,  67  are to insulate and protect the coils  16  and may be adhesives, and especially, applying the adhesives over the joining parts of the divided cores  50 ,  50  allows expecting improvement in strength. The use of an adhesive having a high thermal conductivity (for example, a resin adhesive mainly containing epoxy resin) facilitates releasing heat generated in the coils  16  and improves heat resistance performance. 
     As illustrated in  FIG. 6 , the sensor circuit board  19  is mounted on the lower insulator  15  of the stator  10 . The sensor circuit board  19  has an outer diameter such that the sensor circuit board  19  can be housed in an inner space surrounded by the respective lower outer ribs  59  on the lower insulator  15 , has a ring shape having a through-hole for the rotor  11  at the center, and has an outer periphery on which three installation pieces  70 ,  70 , and so on radially protrude at regular intervals in the circumferential direction. This installation piece  70  engages the expansion portions  62  of the slits  61  and projects outward with respect to the lower outer rib  59  at the corresponding position, and a fixing pin  72  is press-fitted between a through hole  71  disposed at the distal end and the through-hole  55  in the divided core  50  positioned immediately below the through hole  71 . Thus, the sensor circuit board  19  is supported to the divided cores  50  via the fixing pins  72 ,  72 , and so on. 
     [Effects Brought by Fixing Structure of Sensor Circuit Board with Fixing Pins] 
     Thus, the sensor circuit board  19  is fixed via the plurality of fixing pins  72 ,  72 , and so on directly fixed to the stator core  13 . Accordingly, the sensor circuit board  19  can be positioned with respect to the stator core  13  without via the lower insulator  15  made of resin having low accuracy. Accordingly, the rotation position of the rotor  11  can be accurately detected, controllability is improved, and a permanent magnet for detection of the rotation becomes unnecessary. 
     As illustrated in  FIG. 7 , by insert-molding a plurality of terminal metal fittings with resin, the terminal unit  20  has a structure in which bifurcated end portions  76 ,  76 , and so on of terminal metal fittings  75 ,  75 , and so on project so as to match positions of the terminal plates  60 ,  60  of the respective divided bodies  65  on an outer periphery of an insulating ring  74 , which has a diameter approximately identical to that of the sensor circuit board  19  and has a through-hole for the rotor  11  at the center. The longer end portions  60   a  of the corresponding terminal plates  60  are inserted into the respective bifurcated end portions  76  and coupled by soldering or the like, thus mounting to the stator  10  is performed. Changing the shapes of the terminal metal fittings  75  and the disposed configuration in the insulating ring  74  makes the connection pattern of the coils  16  selectable. Coupling that the adjacent divided bodies  65 ,  65  are reversely wound also becomes possible. 
       FIG. 8  illustrates examples of the connection patterns of 12 pieces of the coils  16 ,  16  . . . , and so on distinguished by numbers (1) to (12) in  FIG. 5 ,  FIG. 8A  illustrates a Star (Y) connection of four series,  FIG. 8B  illustrates a Star (Y) connection of four parallel,  FIG. 8C  illustrates a Star (Y)-connection of two series and two parallel,  FIG. 8D  illustrates a Delta (Δ) connection of four series,  FIG. 8E  illustrates a Delta (Δ)-connection of two series and two parallel, and  FIG. 8F  illustrates a Delta (Δ) connection of four parallel. 
     As illustrated in  FIG. 9 , the terminal unit  20  may integrally include a bearing holder  77  that holds the bearing  21  of the rotation shaft  12 . Disposing the holding portion for the bearing  21  in the motor housing  2  likely causes a cumulative tolerance, and the use of the divided cores  50  likely causes a difficulty of ensuring the coaxiality between the stator  10  and the rotor  11 . However, supporting the rotation shaft  12  with the bearing holder  77  via the bearing  21  using the terminal unit  20  facilitates providing the coaxiality between the stator  10  and the rotor  11 . 
     [Effects Brought by Varnish or Adhesive] 
     With the stator  10 , while the stator core  13  is formed by joining the plurality of divided cores  50 ,  50 , and so on, which are divided in the circumferential direction, applying the varnish or the adhesive over the respective coils  16  and the joining portions between the divided cores  50 ,  50  increases integrity and adhesiveness. Accordingly, while the stator core  13  is configured as the divided structure to achieve a high space factor and a low cost, durability and a dust-proof performance can be ensured. 
     Moreover, in the application of the adhesive, the use of an adhesive having a high thermal conductivity facilitates releasing the heat in the coils  16  to the stator  10 , thus improving heat resistance. 
     Meanwhile, the use of the divided cores  50  possibly generates a chattering sound caused by an electromagnetic force generated between the divided cores  50 ,  50  during switching of excitation. However, applying the varnish or the adhesive over the respective coils  16  and the joining portions between the divided cores  50 ,  50  increases integrity and adhesiveness. Therefore, a reduction effect of the chattering sound can be expected. 
     [Effects Brought by Two Terminals Disposed on Each Coil] 
     With the stator  10 , since the two terminal plates  60 ,  60  coupled to the magnet wire forming the coil  16  are disposed on each coil  16 , the magnet wire can be coupled to the terminal plates  60 ,  60  with tension applied to the coil  16 . Accordingly, there is no possibility of causing a looseness and a deflection in the coil  16 , and a disconnection and a layer short are reduced. 
     Therefore, the present invention is also usable for a stator in which a stator core is not divided. 
     [Effects Brought by Terminal Unit] 
     Here, the stator  10  includes the terminal unit  20  including the plurality of terminal metal fittings  75 ,  75 , and so on to couple the predetermined terminal plates  60 ,  60  to one another, and the coupling between the terminal metal fittings  75  on the terminal unit  20  and the terminal plates  60  connects the respective coils  16 . That is, after a plurality of the terminal units  20  having the terminal metal fittings  75  different in the shapes and the disposed configuration are prepared, the respective coils  16  are wound around the stator cores  13 , and the respective magnet wires are coupled to the terminal plates  60 , any of the terminal units  20  is selected and fixed to the stator  10 . Then, the terminal metal fittings  75  on the terminal unit  20  and the terminal plates  60  are coupled, and the respective coils  16  can be connected via the terminal unit  20 . Accordingly, the use of the terminal unit  20  according to the purpose allows easily selecting the series, parallel, Y-connection, and the A connection as illustrated in  FIG. 8 . Thus, since only the change of the terminal unit  20  can change the connection method, optimal winding wire specifications of a manufacturing period (number of turnings) and manufacturability (wire diameter) are selectable according to the respective manufacturing specifications using the identical winding wire facility. 
     Accordingly, the present invention according to the terminal unit is also usable for a stator in which a stator core is not divided. 
     With the terminal unit  20 , coupling a starting end of a magnet wire of one coil  16  and a terminating end of a magnet wire of another coil  16  adjacent to one another in the identical phase allows producing the divided bodies  65  using the identical winding wire facility even when a fractional slot is used. 
     [Modification Example of Divided Cores (Shapes of Joining Portions Alternately Different)] 
     Like a divided core  50 A illustrated in  FIG. 10A , the divided core may include the arc portion  51  having the protruding portions  53  and the depressed portions  54  on both ends in the circumferential direction. The protruding portions  53  and the depressed portions  54  may have convexo-concave shapes of two different kinds of shapes appearing in alternation such that the adjacent divided cores  50 A,  50 A alternately mesh with one another. 
     The convexo-concave shapes can be formed by stacking electromagnetic steel plates having different both end shapes in which one end portion of the arc portion  51  is configured to be a protruding shape and the other end portion is configured to be a depressed shape while changing orientations by every predetermined number of plates. 
     On this divided core  50 A, the resin molded portion R including the upper insulating portion  56  and the lower insulating portion  57 , the upper and lower outer ribs  58 ,  59 , and the like is formed with resin similarly, the coil  16  is wound around, and both terminals  16   a ,  16   a  are electrically coupled to the terminal plates  60 ,  60 . Then, as illustrated in  FIG. 10B , a divided body  65 A including the arc portion  51  of the divided core  50 A having both ends in the circumferential direction exposed as the convexo-concave shapes is obtained. 
     Twelve pieces of the divided bodies  65 A,  65 A, and so on are arranged in the circumferential direction such that the arc portions  51  of the respective divided cores  50 A are coupled in the circumferential direction, and the protruding portions  53  and the depressed portions  54  are alternately fitted and are joined by welding or the like. Then, similarly to  FIG. 5 , the respective divided bodies  65 A,  65 A, and so on are in the state of being coupled in the circumferential direction. In this state, applying the varnishes  66 ,  67  over the outer peripheral surfaces of the respective coils  16  and the joining parts between the divided cores  50 A,  50 A obtains the stator  10  similar to  FIG. 2 . It is only necessary to similarly fix the sensor circuit board  19  and the terminal unit  20 . 
     [Effects Brought by Shapes of Joining Portions Alternately Different] 
     Thus, the end portions of the joining portions between the divided cores  50 A,  50 A in the respective divided cores  50 A are configured such that the protruding portions  53  and the depressed portions  54  having the two different shapes appear in alternation. Accordingly, the end portions mesh with one another with the divided cores  50 A,  50 A in the joined state, thereby allowing ensuring strength and adhesiveness in a thrust direction. Accordingly, while the stator core  13  is configured as the divided structure to achieve the high space factor and the low cost, durability and a dust-proof performance can be ensured. 
     It should be noted that, not limited to the triangular-shaped protruding portion  53  and the V-shaped depressed portion  54 , as long as meshing is possible with two different shapes, the shapes of the end portions are appropriately changeable, such as fitting of semicircular-shaped convex portion and concave portion and a protruding portion and a depressed portion literally. The same applies to the divided core  50  illustrated in  FIG. 3 , and the shapes are appropriately changeable not limited to the protruding portion  53  and the depressed portion  54 . 
     [Modification Example of Divided Cores (Shapes of Insulating Portions Alternately Different)] 
     Such structures that are alternately different are applicable to the upper and lower insulating portions  56 ,  57 . For example, as illustrated in  FIG. 11A , the upper insulating portion  56  in one divided core  50  ( 50 A) is configured as an uneven portion  78   a  having a lower side extending to the adjacent divided cores  50  ( 50 A) side and an upper side retreating to a side of itself, and the upper insulating portion  56  in another divided core  50  ( 50 A) is configured as a reversed uneven portion  78   b  having an upper side extending to the adjacent divided core side and a lower side retreating to the side of itself. In this case as well, the uneven portions  78   a ,  78   b  alternately mesh with one another in the joined state. The same applies to the lower insulating portion  57 . 
     [Effects Brought by Shapes of Insulating Portions Alternately Different] 
     Thus, when the respective upper and lower insulating portions  56 ,  57  are divided similarly to the divided cores  50  ( 50 A) and arranged on the respective divided cores  50  ( 50 A), and abutting portions between the upper insulating portions  56 ,  56  and between the lower insulating portions  57 ,  57  are configured to have convexo-concave shapes alternately meshing with one another, an insulation distance can be ensured long. While the stator core  13  is configured as the divided structure to achieve the high space factor and the low cost, the integrated upper and lower insulating portions  56 ,  57  allows enhancing the strength in the thrust direction and ensuring durability and a dust-proof performance. 
     It should be noted that the convexo-concave shapes are not limited to these shapes, the numbers of depressed portions and protruding portions may be increased, and not limited to the convexo-concave shapes, as illustrated in  FIG. 11B , inclined surfaces  79 ,  79  can abut on one another. 
     [Modification Example of Divided Cores (Fixing Pin is Doubled)] 
     Like a divided core  50 B illustrated in  FIG. 12A , tubular hinge portions  80  and concave surface portions  81  to which the hinge portions  80  are fitted are formed in alternation on both ends of the arc portion  51  such that the hinge portions  80 ,  80  coaxially overlap in alternation between end portions of the arc portions  51  on the adjacent divided cores  50 B,  50 B. 
     Similarly to the divided cores  50 A, the hinge portions  80  and the concave surface portions  81  can be formed by stacking electromagnetic steel plates having different both end shapes in which one end portions are configured to be ring shapes as a part of the hinge portions  80  and the other end portions are configured to be concave shapes as a part of the concave surface portions  81  while changing orientations by every predetermined number of plates. 
     As illustrated in  FIG. 12B , penetrating the fixing pin  72  for the sensor circuit board  19  across the hinge portions  80 ,  80  coaxially positioned between the adjacent divided cores  50 B,  50 B allows joining between the divided cores  50 B,  50 B. 
     In this case, it is sufficient that the fixing pins  72 ,  72  are extended long downward, as illustrated in  FIG. 13 , the respective installation pieces  70  on the sensor circuit board  19  are positioned between the divided cores  50 B,  50 B not the expansion portions  62  of the slits  61  on the lower outer ribs  59 , the respective fixing pins  72  are inserted into the through holes  71  in the respective installation pieces  70 , and the sensor circuit board  19  is mounted. 
     It should be noted that, in  FIG. 13 , in a divided body  65 B configured by fixing each divided core  50 B with the resin molded portion R, one terminal plate  60  disposed on the lower insulating portion  57  has an L shape not having the longer end portion  60   a , and the bifurcated end portion  76  of the terminal metal fitting  75  of the terminal unit  20  is electrically coupled to only the longer end portion  60   a  of the other terminal plate  60 . In a state of being coupled with a crossover wire  16   b , which meanders the outer side of the fixing pin  72 , the coils  16 ,  16  on the adjacent divided bodies  65 B,  65 B are electrically coupled and connected to the respective U-shaped terminal plate  60  and L-shaped terminal plate  60 , which are adjacent to one another and between which the fixing pin  72  is sandwiched. 
     [Effects Brought by Doubled Fixing Pin] 
     Thus fixing the fixing pin  72  across the adjacent two divided cores  50 B,  50 B allows the fixing pin  72  to double as the coupling between the divided cores  50 B,  50 B and the mounting of the sensor circuit board  19 . 
     Especially, as in  FIG. 12B , in a case where an interval between the divided cores  50 B,  50 B is expanded in a state of being coupled with the fixing pin  72  and an interval between the teeth  52 ,  52  is expanded, the coils  16 ,  16  are easily wound around after the resin molded portions R are formed and can be wound around without cutting the magnet wires, thereby ensuring reducing the number of terminal plates. In a connection structure in  FIG. 13 , the fixing pins  72  are usable for positioning the crossover wires  16   b  between the coils  16 ,  16 . 
     A disk-shaped coupling ring  82  made of metal is disposed outside the upper outer ribs  58  on the end surface of the upper insulator  14 , and upper ends of the respective fixing pins  72  are coupled to the coupling ring  82  by press-fitting or the like. In this case, since the fixing pins  72  are integrated with the coupling ring  82 , the integrity of the divided cores  50 B,  50 B, and so on is enhanced. 
     As in  FIG. 12 , with the use of the fixing pin  72  for coupling of the divided cores  50 B,  50 B, in order to avoid the arc portions  51 ,  51  to mutually turn excessively from positions where the arc portions  51 ,  51  are continuous in the circumferential direction, stopper surfaces  80   a ,  81   a  that abut on one another to restrict the excessive turning are preferably disposed inside the hinge portions  80  and the concave surface portion  81 . 
     [Modification Example of Divided Cores (Fixation and Heat Release Structure)] 
     The fixation of the divided cores  50  ( 50 A,  50 B) are not limited to the integral molding with resin, and as illustrated in  FIG. 14 , outer peripheries can be coated with a dust core (a mixed material of a magnetic material, such as iron, and resin)  83 , and as illustrated in  FIG. 15 , the outer peripheries can be fixed with a tubular fixing member  84  made of metal manufactured by shrinkage fitting or cold fitting. The use of such dust core  83  and fixing member  84  facilitates fixing the divided cores  50  ( 50 A,  50 B). 
     Especially, by disposing a plurality of ridges  85 ,  85 , and so on as protrusion portions extending up and down at regular intervals in the circumferential direction on the outer periphery of the fixing member  84 , the heat generated in the coils  16  can be effectively released via the fixing member  84 . Additionally, the varnish or the adhesive may be interposed between the outer peripheries of the respective divided cores  50  ( 50 A,  50 B) and the fixing member  84  to improve integrity. The fixing member is not limited to have the cylindrical shape but may have a cornered tubular shape, or a part of the outer peripheral surface may be depressed. 
     As illustrated in  FIG. 16 , the ridges  85  can be inclined with respect to an axial direction of the stator core. This configuration increases a surface area (cooling area) of the fixing member  84  including the ridges  85 , leading to improvement in a heat release effect. It should be noted that, instead of the ridges, a plurality of protrusions may be formed. 
     In a case that the ridges  85  and the protrusions are arranged such that the cooling air from the centrifugal fan  28  is straightened, a noise caused by the cooling air can be reduced. 
     It should be noted that the bearing holder  77  to hold the bearing  21  on the lower side can be disposed on the fixing member  84 , not the terminal unit  20 . 
     Further, as illustrated in  FIG. 17 , both ends of the arc portions  51  of the divided cores  50  ( 50 A,  50 B) need not have a structure being formed into a straight line along the axial direction of the stator  10  but may have a structure of being inclined with respect to the axial direction and inclined end edges  51   a ,  51   a  are mutually joined by mating fitting. By thus inclining the joining portions, the integrity in the thrust direction is enhanced. 
     [Modification Example of Divided Cores (Heat Release Structure)] 
     As illustrated in  FIG. 18 , a plurality of protrusion portions  86 ,  86 , and so on can be disposed in the outer peripheral surface of the arc portion  51  of each divided core  50  ( 50 A,  50 B). The protrusion portions  86  are disposed such that rows arranged at regular intervals in the up-down direction (the stacking direction of the electromagnetic steel plates) are disposed plurally at regular intervals in the circumferential direction. Between the rows adjacent in the circumferential direction, the protrusion portions  86 ,  86  are arranged such that the phases are displaced in the up-down direction in alternation. It should be noted that, on both ends of the arc portions  51 , protrusion portions  86   a ,  86   a , and so on are formed so as to be continuously arranged in the up-down direction, and rows of the protrusion portions  86   a ,  86   a  are adjacent between the end portions of the respective arc portions  51 . The adjacent rows of the protrusion portions  86   a ,  86   a  are joined together by welding, with a separate sandwiching member, or the like to ensure the joining between the divided cores  50  ( 50 A,  50 B). 
     The respective protrusion portions  86  may be formed into a laminated state by forming a part of the protrusion portions  86 ,  86   a  on the respective electromagnetic steel plates forming the divided cores  50  ( 50 A,  50 B), or the separate protrusion portions  86 ,  86   a  may be joined to the arc portions  51 . 
     [Effects Brought by Heat Release Structure of Protrusion Portions] 
     By thus disposing the plurality of protrusion portions  86 ,  86   a  on the outer peripheral surfaces of the respective divided cores  50  ( 50 A,  50 B), the heat generated in the coils  16  can be effectively released. 
     Especially, here, since the protrusion portions  86 ,  86   a  are arranged at the regular intervals along the stacking direction of the electromagnetic steel plates, the heat release effect can be equally obtained. 
     The protrusion portions  86   a  are disposed side by side into the straight line on both ends where the divided cores  50  ( 50 A,  50 B) are mutually joined and the rows of the protrusion portions  86   a  between the adjacent divided cores  50  ( 50 A,  50 B) are mutually welded or the like to join the divided cores  50  ( 50 A,  50 B). Therefore, a rational structure in which the divided cores  50  ( 50 A,  50 B) can be joined by using the protrusion portions  86   a  for heat release can be constructed. 
     It should be noted that when the protrusion portions  86  are arranged such that the cooling air from the centrifugal fan  28  is straightened, the noise caused by the cooling air can be reduced. 
     [Modification Example of Divided Configuration] 
     While the divided cores  50  ( 50 A,  50 B) according to the embodiments described above and modification examples have the structure formed of the arc portions  51  and the teeth  52  dividing the stator core  13  in the circumferential direction, the divided configuration is not limited to this configuration. For example, the stator core  13  can be divided into a cylindrical shaped outer peripheral portion  90  illustrated in  FIG. 19  and a plurality of teeth  91 ,  91 , and so on illustrated in  FIG. 20 . Here, dovetail grooves  92 ,  92 , and so on penetrating up and down are formed at a positions where the teeth  91  are arranged in an inner surface of the outer peripheral portion  90 , a dovetail tenon  93  fitted to the dovetail groove  92  is formed on an outer end of each tooth  91 , and the through-hole  55  for the fixing pin  72  is formed in the dovetail tenon  93 . 
     Meanwhile, as illustrated in  FIG. 21A , the resin molded portion R is integrally molded into a tubular shape as follows. The resin molded portion R including the upper and lower insulating portions  56 ,  57  has an opening R 1  into which the tooth  91  is inserted from the dovetail tenon  93  side to cover the tooth  91 , and only the lower insulating portion  57  projects outside from the upper and lower outer ribs  58 ,  59 . The coil  16  is wound around the resin molded portion R, and both terminals  16   a ,  16   a  are formed in a state being coupled to the terminal plates  60 ,  60 . 
     Accordingly, as illustrated in  FIG. 21B , when the tooth  91  is joined to the resin molded portion R from the inside such that the dovetail tenon  93  is inserted first, divided bodies  94 ,  94 , and so on where the dovetail tenons  93  project outside are obtained as illustrated in  FIG. 22 . When the dovetail tenons  93  of the respective divided bodies  94  are fitted to the respective dovetail grooves  92  in the outer peripheral portion  90  from the lower side, the respective divided bodies  94  are joined to the outer peripheral portion  90  as illustrated in  FIG. 23 , thus obtaining the stator  10  becoming the stator core  13 . 
     [Effects Brought by Divided Configurations of Outer Peripheral Portion and Teeth] 
     Thus, the stator core  13  is divided into the cylindrical shaped outer peripheral portion  90  and the plurality of teeth  91 , which project from the inside of the outer peripheral portion  90  and around which the respective coils  16  are wound, and the stator core  13  is formed by joining the outer peripheral portion  90  and the teeth  91 , thus ensuring maintaining the strength by the use of the continuous outer peripheral portion  90 . 
     Especially, here, the teeth  91  are inserted into the resin molded portions R around which the coils  16  are preliminarily wound and are joined to the outer peripheral portion  90 . Therefore, the assembly can be easily performed. 
     It should be noted that a relationship between the dovetail groove and the dovetail tenon may be set reverse to the configuration described above such that the dovetail tenons is formed in the outer peripheral portion and the dovetail grooves is formed in the teeth. 
     While the divided configuration forms each of the teeth  91  independently, between projecting ends  95 ,  95  of the adjacent teeth  91 ,  91 , joints  96 ,  96 , and so on joining both projecting ends may be disposed, and all teeth  91 ,  91 , and so on may be mutually fixed with the projecting ends  95 ,  95  to be integrated as illustrated in  FIG. 24 . In this case, it is sufficient to form the electromagnetic steel plates so as to have a shape including the joints  96 . 
     Further, as illustrated in  FIG. 25 , coupling portions  97 ,  97  to couple between the upper and lower inner ribs  63 ,  64  may be integrally disposed between the projecting ends  95 ,  95  of the adjacent teeth  91 ,  91  in the respective resin molded portions R to ensure integrating all resin molded portions R via the coupling portions  97  as integrally molded resin. 
     Thus integrating the teeth  91  or the resin molded portions R facilitates the assembly to the outer peripheral portion  90  and also facilitates management. 
     Meanwhile, with such a divided configuration, separately forming the outer peripheral portion  90  and the teeth  91  can differentiate their axial lengths.  FIG. 26  illustrates an example of forming the outer peripheral portion  90  longer than the teeth  91  to the one end side. Thus forming the outer peripheral portion  90  axially longer than the teeth  91  allows forming a three-dimensional magnetic circuit and increasing a freedom of design, leading to downsizing and a weight reduction. 
     The outer peripheral portions of these are not limited to have the cylindrical shape, and the outer peripheral surface and the inner peripheral surface may be a non-circular shape (a polygon and a shape having a partial unevenness). 
     Besides, in each of the present inventions, to achieve heat release, the switching element disposed in the controller may be thermally bonded to the protrusion portion on the stator core and the ridges on the fixing member via a thermal bonding member, and the switching element may be disposed in the sensor circuit board and similarly may be thermally bonded to the protrusion portion on the stator core and the ridges on the fixing member via the thermal bonding member. 
     As the magnet wire forming the coil, a flat wire may be used. 
     Furthermore, the number of coils (slots) is not limited to 12 and may be any number other than 12. Obviously, not limited to a hammer drill, as long as the brushless motor is used as a driving source, each of the present inventions is applicable to another electric tool, such as an impact driver and a circular saw.