Abstract:
A rotary electric machine includes a stator including a plurality of teeth, a coil wound around each tooth, and a stator yoke core that connects the respective teeth, the teeth and the stator yoke core integrally fixed by a molding resin. The rotary electric machine also includes a rotor with a plurality of magnets that face the teeth, the magnets and teeth separated from each other by a space therebetween. Each of the teeth comprises a head portion facing opposite the magnets, a coil wind-up portion around which the coil is wound up, and an insert portion that can be inserted into the stator yoke core, the insert portion including a groove formed in a portion of the insert portion that protrudes from the stator yoke core, where the groove is fillable with the molding resin to inhibit the teeth from disengaging from the stator yoke core.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Japanese Patent Application No. 2005-210498, which was filed on Jul. 20, 2005. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotary electric machine having an improved fixing structure for teeth of a stator of the rotary electric machine, and also relates to an electric wheelchair (or electrically powered wheelchair) mounted with such rotary electric machine. 
     2. Related Art 
     In a known art, as such a rotary electric machine, there has been provided an axial gap type rotary electric machine as shown, for example, in  FIGS. 16 to 19 . 
     Referring to  FIGS. 16 to 19 , the rotary electric machine is provided with a stator  3  formed with teeth  2  and a rotor provided with a plurality of magnets (permanent magnets), not shown, in which the stator and the rotor are arranged with a gap in a rotation axis direction. 
     More in detail, as shown in  FIG. 18 , the each tooth  2  is composed of a plurality of steel plate sheets  2   a  laminated in a radial direction thereof for a countermeasure to core loss, and a plurality of such teeth  2  are arranged and fixed side by side with a predetermined distance in the circumferential direction of a disc, i.e., substantially ring-shaped, stator yoke core  6 . Coils  5  are wound up around these teeth  2  through insulating material as bobbins  4 . Further, as shown in  FIG. 19 , the teeth  2 , the stator yoke core  6  and the coils  5  are integrally fixed by means of molding resin  7  such that surfaces  2   b  of the teeth  2  opposing to the rotor are exposed. 
     The steel plates  2   a  of the teeth  2  are assembled separately into a fitting hole of the stator yoke core  6  and then molded and fixed together by means of molding resin  7 . 
     However, in such arrangement, because the molding resin  7  does not reach a portion surrounded by the bobbins  4 , it was difficult to firmly fix the teeth  2 . 
     Incidentally, the teeth  2  are attracted by magnets disposed so as to oppose to the teeth, and the attracting force of the magnet acts in an arrowed direction A in  FIG. 19 , so that it is necessary to consider a countermeasure for preventing the teeth  2  from coming off. 
     Then, it has been provided, as a method for preventing such coming-off of the teeth, to firmly push and fix the teeth  2  into a stator yoke core  6  or to fix the teeth by welding means. 
     In another method such as disclosed in the Japanese Patent Application Laid-open Publication No. HEI 11-146617, a notch is formed by means of punch to be fixed. 
     However, in such conventional methods, when the tooth  2  is pushed into the fitting hole of the stator yoke core  6  and then fixed thereto or is welded to thereby increase contacting strength therebetween, there is a fear that an electric resistance at this fixed portion is reduced and a closed circuit is formed around the fitting hole in a plan view, resulting in energy loss due to large induction current flow. 
     In addition, in the method of using the punch, a fixing process using the punch will be additionally required, and moreover, the use of the punch will give an adverse impact, thus being troublesome and inconvenient for dimensional control. 
     SUMMARY OF THE INVENTION 
     The present invention was conceived in consideration of the above prior art, and an object of the present invention is to provide a rotary electric machine capable of fixing teeth at reduced working steps and ensuring dimensional accuracy without reducing electric resistance at the teeth fixing portion and also to provide an electric wheelchair mounted with such rotary electric machine. 
     This and other objects can be achieved according to the present invention by providing, in one aspect, a rotary electric machine comprising: 
     a stator including a plurality of teeth which are each wound up by a coil and a stator yoke core connecting the respective teeth, the teeth and the stator yoke core being integrally fixed by means of molding resin; and 
     a rotor provided with magnets disposed so as to oppose to the teeth, respectively, with a space therebetween, 
     wherein each of the teeth is composed of a head portion opposing to the magnet, a coil wind-up portion which is wound up by the coil and an insert portion to be inserted into the stator yoke core, and a coming-off prevention portion for preventing the teeth from coming off is formed in the insert portion, the coming-off prevention portion being filled up with the molding resin. 
     In another aspect, the coming-off prevention portion is formed to an end portion, which is a portion that penetrates the stator yoke core, of the insert portion of the tooth. 
     In another aspect, there is also provided a rotary electric machine comprising: 
     a stator including a plurality of teeth which are each wound up by a coil and a stator yoke core connecting the respective teeth, the teeth and the stator yoke core being integrally fixed by means of molding resin; and 
     a rotor provided with magnets disposed so as to oppose to the teeth, respectively, with a space therebetween, 
     wherein each of the teeth is composed of a head portion opposing to the magnet, a coil wind-up portion which is wound up by the coil and an insert portion to be inserted into the stator yoke core, and the head portion is formed with an opposing surface to the rotor and at least a portion of the opposing surface is covered with the molding resin so as to provide a coming-off prevention portion for preventing the teeth from coming off. 
     In another aspect, the teeth and the magnets may be arranged so as to oppose to each other with a space in a rotation axis direction. 
     It is desirable that each of the teeth is composed of a plurality of magnetic steel plates which are laminated one by one, and fitting portions are formed to the respective steel plates so as to have protruded portions and recessed portions such that the protruded portion of the fitting portion of one magnetic steel plate is fitted and fixed to the recessed portion of the fitting portion of an adjacent magnetic steel plate when the magnetic steel plates are laminated together. 
     It may be desired that each of the teeth is formed into T shape by laminating the plurality of magnetic steel plates and has a head portion and a leg portion, the head portion being a wider portion of the T shape which is opposed to the magnet, the leg portion including the coil wind-up portion around which the coil is wound up and which has a substantially constant width and the insert portion which is inserted into the stator yoke core. 
     Furthermore, in a further aspect of the present invention, there is provided an electric wheelchair which comprises: 
     a frame structure constituting a vehicle body frame; 
     a seat disposed on the frame structure; 
     a pair of driving wheel units including two wheels; 
     a rotary electric machine mounted to each of the paired driving wheel units; and 
     an operation member operatively connected to the rotary electric machine for operating the driving wheel units, 
     the rotary electric machine having the structures defined in the above aspects. 
     According to the rotary electric machine of the present invention mentioned above, when the teeth and the stator yoke core are integrally fixed by means of the molding resin, the molding resin is filled in the coming-off prevention portions of the insert portions of the teeth, so that the teeth can be firmly fixed, thus preventing the teeth from coming off toward the rotor side. 
     In addition, this coming-off prevention process can be completed together with the filling process of the molding resin, thus eliminating the increase in the number of working processes, and the coming-off prevention process can be easily performed. 
     Moreover, as is different from the conventional technology, since the teeth are not fixed by press-fitting or welding process, the lowering in the electric resistance at this fixing portion can be effectively suppressed, and any large induction current does not pass, thus preventing the energy loss from occurring. No use of punch can eliminate damage from impact, thus ensuring the dimensional accuracy. 
     Furthermore, the coming-off prevention portions are made at the end portions, which is a portion that penetrates the stator yoke core, of the respective teeth. Therefore, the magnetic flux flow is not disturbed, and hence, the performance of the rotary electric machine is not deteriorated. The coming-off prevention function in the direction opposing to the insert direction can be more effectively performed. 
     Still furthermore, when the teeth are integrally fixed together with the coils and the stator yoke core by using the molding resin, at least a portion of the opposing surface of the head portion of each tooth is covered with the molding resin, so that the teeth can be firmly fixed, thus preventing the teeth from coming off toward the rotor (magnet) side. 
     Still furthermore, since the rotary electric machine is formed as an axial gap type machine, the rotary electric machine of the present invention can be made smaller, flatter, light-weighted and compact. 
     Still furthermore, each of the fitting portions formed to the magnetic steel plates has protruded and recessed portions, and the protruded portion of one steel plate is fitted into the recessed portion of the other adjacent steel plate to thereby easily laminate and fix the respective steel plates together. 
     Still furthermore, the electric wheelchair mounted with the improved rotary electric machine having compact structure and high output performance can be provided. 
     The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a side view of an electric wheelchair mounted with an electric motor according to a first embodiment of the present invention; 
         FIG. 2  is a sectional view of the electric motor for the electric wheelchair of the first embodiment; 
         FIG. 3  is a perspective view of a rotor of the electric motor of  FIG. 2 ; 
         FIG. 4  is a front view of the rotor of the electric motor of  FIG. 2 ; 
         FIG. 5  is a perspective view of a stator of the electric motor of the electric wheelchair of the first embodiment; 
         FIG. 6  is a back-side view of the stator of  FIG. 5 ; 
         FIG. 7  is a perspective view of the stator, before molding, of the electric motor according to the first embodiment; 
         FIG. 8  is a developed perspective view showing a portion of the stator of the electric motor of the electric wheelchair of the first embodiment; 
         FIG. 9  is a front view of the tooth of the stator of the electric motor according to the first embodiment; 
         FIG. 10  is a sectional view taken along the line X-X in  FIG. 9 ; 
         FIG. 11  is a sectional view, in an enlarged scale, showing a state in which the stator yoke core, the tooth (teeth) and the coil, which are fixed to a mold, according to the first embodiment; 
         FIG. 12  is a sectional view, corresponding to  FIG. 11 , according to the second embodiment of the present invention; 
         FIG. 13  is a perspective view of a stator of an electric motor according to the third embodiment of the present invention; 
         FIG. 14  is a sectional view, in an enlarged scale, showing a state in which the stator yoke core, the tooth and the coil, which are fixed to a mold, according to the third embodiment; 
         FIG. 15  is a sectional view showing a state that the stator yoke core, the tooth and the coil are clamped by upper and lower mold halves and fixed thereto according to the third embodiment; 
         FIG. 16  is a perspective view of a stator of a conventional structure; 
         FIG. 17  is a perspective view showing a stator yoke core and tooth of the stator of  FIG. 16 ; 
         FIG. 18  is a perspective view of the tooth (each of the teeth) of the conventional structure; and 
         FIG. 19  is a sectional view showing the conventional structure corresponding to  FIG. 11 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the present invention will be described hereunder with reference to the accompanying drawings. 
     First Embodiment 
     The first embodiment of the present invention is represented by  FIGS. 1 to 11 . 
     With reference to  FIGS. 1 and 2 , reference numeral  11  denotes an electric wheelchair or electrically powered wheelchair mounted with an electric motor  12  as a rotary electric machine according to the present invention, and the electric wheelchair is driven and traveled by the driving force of the electric motor  12 . 
     The electric wheelchair  11  is provided with a frame  13  as a framework of a vehicle (electric wheelchair body), a seat  14  on which a user sits and a pair of driving wheel units  15  in which the electric motors  12  (see  FIG. 2 ) are mounted. When an operation unit  17  of the electric wheelchair  11  is operated, the paired driving wheel units  15  are driven so as to drive driven wheels  16  by predetermined amount (distance). The driven wheels  16  are operated independently, and by operation of the operation unit  17 , the driven wheels  16  are changed in their rotating directions and driven speed, respectively, optionally. 
     The driving wheel unit  15  is composed, as a unit, of the electric motor  12 , the driving unit, the driven wheels  16  and so on, and as shown in  FIG. 2 , the driving wheel unit  15  is fixed to the frame  13  by means of a bolt  19  and a nut  19   a.    
     The electric motor  12  is of an axial gap type composed of a stator  21  and a rotor  22 , which are accommodated in a space defined by a case  23  and a cover  24 . The bolt  19  is planted to the cover  24 . 
     The stator  21  is fastened to the case  23  by means of a bolt  51 , and on the other hand, the rotor  22  is fitted to a rotor shaft  30 , through serration fitting, provided for the case  23  to be rotatable through bearings  27 ,  27  and fixed thereto by nut  31 . 
     The rotor  22  has, as shown in  FIGS. 3 and 4 , a disc shaped rotor yoke  33 , which has a central portion fitted to the rotor shaft  30  through the serration fitting. A plurality of magnets  34 , each having a rectangular shape, are arranged and fixed to the peripheral edge portion of the rotor yoke  33  at a predetermined constant interval in the circumferential direction thereof. These magnets  34  are disposed so as to oppose to the stator  21  with a gap C ( FIG. 2 ) in the rotation axis direction. 
     These magnets  34  are arranged so that N and S poles are adjacently alternated and bonded and fixed to the rotor yoke  33  in the shape of circle. 
     The rotor yoke  33  is press-worked as shown in  FIGS. 2 and 3  so as to provide a central recessed shape  33   a , and in this recessed portion  33   a , an electromagnetic brake  36  fixed to the cover  24  is accommodated. An annular rotary body  36   a  and the rotor  22 , of which rotations are stopped by the electromagnetic brake  36 , are made stationary in the rotating direction through a pin  37 . Moreover, on the other hand, a sensor magnet  38  is bonded and fixed to the side opposing to the recessed portion  33   a , and a pole position sensor (hole IC)  40  opposing to the sensor magnet  38  is fixed to the case  23 . The pole position sensor  40  is electrically connected to a controller  39 , and the pole position of the rotor  22  is detected by the pole position sensor  40 . 
     Further, a sun-gear  30   a  is mounted to the rotor shaft  30  so as to be meshed with a two-staged planetary gear  42   a  of a planetary reduction gear  42 . The planetary reduction gear  42  reduces the rotation of the rotor  22 , which is then transmitted to a hub  44 , and the rotation of the hub  44  rotates the driving wheel  16 . 
     On the other hand, the stator  21  is provided with a substantially disc (ring) shaped stator yoke core  47 , a plurality of teeth  48  arranged in the circumferential direction of the stator yoke core  47  with a predetermined interval and a coil  50  wound up around each of the teeth (i.e., tooth)  48  by means of bobbins  49 . The stator yoke core  47 , the teeth  48  and the coils  50  are integrally molded and fastened together by the molding resin  52 . At this time, a plurality of collars  53  are inserted around the stator  21  to thereby simultaneously form mount flanges  52   a.    
     These mount flanges  52   a  are fixed to the case  23  by means of bolts  51 . 
     The coil  50  is coupled with each of U, V and W-phases, and one end of each coupling coil is electrically connected (neutral point) and the other one end thereof is led outside of the mold so as to be connected to a driver. 
     More in detail, the stator yoke core  47  is formed from a plurality of disc-shaped (substantially ring shape) magnetic steel plates  54 , which are laminated as shown in  FIG. 8 , and formed with fitting holes  47   a  into which teeth  48  are inserted. 
     The tooth  48  is formed by laminating a plurality of magnetic steel plates  57  so as to provide a T-shape, and is composed of a head portion  48   a , which is a wider portion of the T-shaped tooth  48 , and a leg portion  48   b  thereof. The leg portion  48   b  includes a coil wind-up portion  48   c  having a constant width which is wound up by the coil  50  and an insert portion  48   d  to be inserted into the fitting hole  47   a  of the stator yoke core  47 . 
     The wind-up portion  48   c  is formed with a plurality of half pierce portions  57   a , two portions in the illustration, as fitting portions for fixing a plurality of laminated magnetic steel plates  57 . Further, as shown in  FIG. 10 , the half pierce portion  57   a  is in the form of half blind hole shape (having protruded half portion and recessed half portion), so that this portion is called as “half pierce portion”  57   a  herein, and the substantially rectangular, in section, protruded half portion  57   b  of one magnetic steel plate  57  is fitted to the recessed half portion  57   c  of adjacent one magnetic steel plate  57 . 
     Furthermore, as shown in  FIG. 11 , the tooth  48  is formed with a resin filling groove  48   f , as a tooth coming-off prevention portion for preventing the tooth  48  from coming off, by filling the molding resin  52  into the insert portion  48   d  of the tooth  48 . 
     The resin filling groove  48   f  is formed on the end surface side of the end portion, which is a portion that penetrates the stator yoke core  47 , of the insert portion  48   d  of the tooth  48 . The resin filling groove  48   f  has a narrow entrance, large inner space and approximately circular shape. 
     The head portion  48   a  of the tooth  48  is formed with a surface  48   g  opposing to the magnet  34  of the rotor  22 , and this opposing surface  48   g  is formed with a protruded portion  48   h  extending in a radial direction at the central portion in the circumferential direction of the stator. This protruded portion  48   h  has uniform height and width along the entire length direction. The opposing surfaces  48   g  other than the protruded portion  48   h  are embedded with the molding resin  52  as shown in  FIG. 11 . 
     The opposing surfaces  48   g  of the teeth  48  and the magnets  34  of the rotor  22  are arranged so as to oppose to each other through a gap C in the axial direction of the rotation shaft. 
     Further, in  FIG. 2 , reference numeral  59  denotes a spoke of the wheel and  60  denotes a hand rim. 
     The first embodiment will be operated in the manner mentioned hereunder. 
     When current passes the coil  50  to be energized, the electric motor  12  is driven and the magnetic force of the coil  50  and that of the magnet  34  are combined to thereby generate magnetic force between the stator  21  and the rotor  22 , thus rotating the rotor  22  and then driving the driven wheel  16  through the rotor shaft  30 , the hub  44  and so on. 
     At this time, the magnetic flux flows through the rotor yoke  33 , the magnets  34 , the teeth  48  and the stator yoke core  47 , and as shown in  FIG. 11 , magnet attracting force acts to the teeth  48  in the arrowed direction A. 
     In the described embodiment, when the teeth  48  are molded and fixed integrally with the molding resin  52  together with the coils  50  and the stator yoke core  47 , the molding resin  52  fills in the resin filling groove  48   f  of the insert portion  48   d  of the tooth  48  and the portion other than the protruded portion  48   h  of the opposing surface  48   g  is covered with the molding resin  52 , and accordingly, the tooth can be firmly fixed and prevented from coming off. 
     Furthermore, different from the conventional structure, since the teeth  48  are not fixed by press-fitting or welding process, the lowering in the electric resistance at this fixed portion can be suppressed, any large induction current does not pass and a large energy loss can be prevented from causing. 
     In addition, since there is no impact by the use of a punch, dimensional accuracy can be maintained. Moreover, a usual molding process using the molding resin  52  can perform simultaneously the coming-off prevention function. Accordingly, different from the conventional technology, no additional working process is needed. 
     Still furthermore, the resin filling groove  48   f  is formed to the end portion, which is a portion that penetrates the stator yoke core  47 , of the tooth  48 , the flow of the magnetic flux is not disturbed, and hence, the performance is not deteriorated, and moreover, the tooth  48  can be effectively prevented from coming off in a direction reverse to the inserting direction into the stator yoke core  47 . 
     Each of the teeth (i.e., tooth)  48  is formed by laminating one kind of plural magnetic steel plates  57 , so that the processing cost and mold cost can be significantly reduced. These magnetic steel plates  57  can be fitted and fixed together easily through the half pierce portions formed to the respective plates. 
     Further, according to the electric motor  12  of the embodiment of the present invention, the energy loss can be suppressed effectivily, so that an electric wheelchair  11  provided with the electric motor  12  having compact structure and high output performance can be also preferably provided. 
     Second Embodiment 
       FIG. 12  represents the second embodiment of the present invention. 
     In this second embodiment, the structure of the “coming-off preventing portion” differs from that of the first embodiment. 
     That is, in the first embodiment, the resin filling groove  48   f  as the “coming-off preventing portion” is formed on the end surface side of the end portion, which is a portion that penetrates the stator yoke core  47 , of the insert portion  48   d  of the tooth  48 , but in this second embodiment, a cut-out groove  48   i  as “coming-off preventing portion” is formed on the side surface side of the end portion, which is a portion that penetrates the stator yoke core  47 , of the insert portion  48   d  of the tooth  48 . 
     Even in this second embodiment having the above structure, the cut-out groove  48   i  is filled up with the molding resin  52 , thus preventing the tooth  48  from coming off. 
     The structures and functions other than the above are substantially the same as those mentioned with reference to the first embodiment, and accordingly, the descriptions thereof will be omitted herein. 
     Third Embodiment 
       FIGS. 13 to 15  represent the third embodiment of the present invention. 
     In the first embodiment, a portion other than the protruded portion  48   h  of the tooth opposing surface  48   a  are covered entirely with the molding resin  52 . However, in this third embodiment, the portion other than the protruded portion  48   h  is partially covered with the molding resin  52 . 
     In this embodiment, at a time when the stator  21  is molded, the protruded portion  48   h  of the tooth opposing surface  48   a  is pressed by a pressing portion  63   a  of an upper half mold  63 , as shown in  FIG. 15 , and the portion other than the protruded portion  48   h  is partially pressed by the other pressing portion  63   b  of the upper half mold  63 . 
     Further, the stator yoke core  47  is positioned by abutting a positioning pin  64   a  formed to a lower half mold  64  against this stator yoke core  47 . 
     As mentioned above, the tooth (teeth)  48  can be prevented from coming off by partially covering the portion other than the protruded portion  48   h  of the tooth opposing surface  48   a  with the molding resin  52 . 
     The structures and functions other than the above are substantially the same as those mentioned with reference to the first embodiment, and accordingly, the descriptions thereof will be omitted herein. 
     It is to be noted that the present invention is not limited to the described embodiment and many other changes and modifications may be made without departing from the scopes of the appended claims. 
     For example, the rotary electric motor of the present invention is not limited to the axial-gap type and other types may be adopted as far as the teeth are fixed by the molding resin.