Patent Publication Number: US-2005140233-A1

Title: Air blower apparatus

Description:
TECHNICAL FIELD  
      The present invention relates to an air blower apparatus in which an electronic motor and an air blowing fan are integrated and, more particularly, to connecting means for connecting an electronic motor to an air blowing fan.  
     BACKGROUND ART  
      For the purposes of a smaller number of parts, more efficient assembling work, and the like, there has been used an air blower apparatus in which an electronic motor and an air blowing fan are assembled integrally in advance. This air blower apparatus is built in a system body such as an air conditioner as air blowing means, by which the whole of the system can be made smaller in size and lighter in weight and also the cost can be reduced.  
      As one example of an air blower apparatus of this type, for example, Patent Document 1 (Japanese Patent Application Publication No. H10-117462) has disclosed an air blower apparatus in which a rotating shaft provided in an end portion of a line flow fan (Cross-flow fan) extends into a stator of an inner rotor electronic motor, and a rotor of the electronic motor is installed integrally to the extending portion.  
      Also, Patent Document 2 (Japanese Patent Application Publication No. H9-247899) has disclosed an air blower apparatus using what is called an axial gap electronic motor in which a rotor and stator of an electronic motor are opposedly arranged in the axial direction of an output shaft. In this example, the axial gap electronic motor is of an air core inductor type.  
      Also, as another mode, Patent Document 3 (Japanese Patent Application Publication No. 2001-295788) has disclosed a method in which a rotor of an outer rotor electronic motor is used as a hub, and a turbofan or an axial flow fan is installed integrally to the hub.  
      According to this method, the electronic motor and the fan are connected to each other commonly by one rotating shaft system, so that each of the electronic motor and fan need not have a respective rotating shaft. Therefore, special-purpose connecting means is not needed, and further the length in the axial direction can be shortened, so that a small-size and lightweight air blower apparatus can be provided.  
      However, the above-described related art still has unsolved problems as described below. In the case where the line flow fan as described in Patent Document 1 is used, since the inner rotor electronic motor is used, the stator and rotor must be extended in the axial direction when a high output is obtained. However, if the axial lengths of the stator and rotor are increased, the length of the fan is shortened relatively, which reduces the air blowing capability.  
      Also, in the case where the electronic motor is a DC electronic motor, a high output can be obtained by making the magnetic flux density of a rotor magnet high. However, if the magnetic flux density is made high, dust is liable to be attracted to the rotor magnet, which causes poor contact. Also, when the stator is inserted for assembling, the stator collides with a fan casing or the rotor due to a magnetic attraction force, which may decrease the rotation accuracy or may cause initial failure.  
      Further, in the case of the air blower apparatus described in Patent Document 2, since the axial gap electronic motor of an air core inductor type is used, there arises a problem in that a high magnetic flux density is not obtained, and therefore a high output and high efficiency cannot be achieved. Also, since a winding is arranged on a circuit board, and the circuit board is installed to the casing of equipment, the air blower apparatus is disadvantageous in terms of vibration and strength.  
      In the case where the outer rotor electronic motor described in Patent Document 3 is used, likewise, when a high output is obtained, the axial dimension increases, so that a fan boss portion becomes large. Accordingly, the vent resistance increases, and resultantly the air blow performance decreases.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve the above-described problems, and accordingly an object thereof is to provide, at a low cost, an air blower apparatus capable of increasing the air blowing capability without an increase in size of an electronic motor, and having a high assembling ability.  
      To achieve the above object, the present invention has some features as described below. The invention of a first aspect is characterized in that in an air blower apparatus in which an electronic motor and an air blowing fan are assembled integrally via predetermined connecting means, the electronic motor is an axial gap electronic motor in which a rotor and a stator are arranged opposedly with a predetermined gap along the rotation axis direction of the rotor; the rotor is provided in a pair at the right and left with respect to the stator; and to at least one of the rotors, the air blowing fan is coaxially attached via the connecting mean.  
      According to this invention, since the axial dimension is short, the electronic motor is made an axial gap electronic motor, and the connecting means is provided on the rotor thereof to directly attach the air blowing fan thereto, by which the size of electronic motor can be reduced, and accordingly the air blowing fan can be increased in size. Also, the fan can be attached to both of the rotors, so that the air blowing capability can further be increased.  
      The invention of a second aspect is characterized in that the connecting means consists of an engagement convex portion formed on either one of the attaching surfaces of the rotor and the air blowing fan and an engagement concave portion formed in the other of them as an mating element of the engagement convex portion.  
      According to this invention, as the connecting means, the engagement convex portion is provided on either one of the attaching surfaces of the rotor and the air blowing fan, and the engagement concave portion mating with the engagement convex portion is provided in the other of them, so that the air blowing fan can be attached directly to the rotor. The arrangement positions of the engagement concave portion and the engagement convex portion are not subject to any special restriction if these portions are provided at positions at which these portions engage with each other.  
      The invention of a third aspect is characterized in that the connecting means is a magnet coupling. According to this invention, by using the magnet coupling as the connecting means between the air blowing fan and the rotor, the air blowing fan can be attached to the rotor by a simpler method.  
      The invention of a fourth aspect is characterized in that a bearing is provided in a central portion of the stator, and the rotor is supported by the bearing via a radial bearing. According to this invention, since the stator is pivotally supported directly on the stator via the radial bearing, unlike the conventional apparatus, an output shaft is not needed, so that accordingly the cost can further be reduced.  
      The invention of a fifth aspect is characterized in that the control of the electronic motor is wide-angle energization not smaller than 120° and smaller than 180°. According to this invention, by satisfying the above-described range, an optimum torque curve is obtained, and hence the maximum torque can be obtained.  
      The invention of a sixth aspect is characterized in that a fan casing for covering the air blowing fan is further provided, and the fan casing is also used as a bracket for fixing the stator. According to this invention, since the fan casing of the air blowing fan is also used as the bracket covering an internal mechanism of the electronic motor, a separate bracket is not needed, so that accordingly the cost can further be reduced.  
      The invention of a seventh aspect is characterized in that an elastic member is interposed between the air blowing fan and the fan casing. According to this invention, since the air blowing fan is fixed to the fan casing via the elastic member, the vibration proofing ability can further be increased.  
      The invention of an eighth aspect is characterized in that the rotor is also used as one end plate in the axial direction of the air blowing fan. According to this invention, since the rotor of electronic motor is also used as the end plate of air blowing fan, the cost can further be reduced, and also the manpower for assembly can also be decreased.  
      The invention of a ninth aspect is characterized in that the fan casing is subjected to drip-proofing treatment and/or dust-proofing treatment. According to this invention, since the fan casing is subjected to drip-proofing treatment and dust-proofing treatment, the electronic motor can be prevented from being damaged by foreign matters such as waterdrop and dust intruding into the interior thereof.  
      The invention of a tenth aspect is characterized in that the stator has a plurality of core members each having a stator iron core in the interior, and the core members are connected to each other in a ring shape along the direction of rotation of the rotor. According to this invention, since one stator is formed by combining the core members with each other, all of the assembling ability, productivity, and electronic motor properties are improved significantly as compared with those in the case of the integrated formation.  
      The invention of an eleventh aspect is characterized in that each of the core members is formed with a bobbin-shaped insulator including a flange for winding a coil, and the insulator is provided with core connecting means for connecting the adjacent core members to each other. According to this invention, by providing the insulator, the winding properties of coil are improved, and also the assembling ability between the individual core members is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view schematically showing an internal construction of an air blower apparatus in accordance with a first embodiment of the present invention;  
       FIG. 2  is a sectional view schematically showing an internal construction of an electronic motor in accordance with the first embodiment;  
       FIG. 3  is a side view of an electronic motor in accordance with the first embodiment;  
       FIG. 4  is a sectional view showing a modification of an air blower apparatus in accordance with the first embodiment;  
       FIG. 5  is a sectional view of an electronic motor for the modification shown in  FIG. 2 ;  
       FIG. 6  is a sectional view showing a state in which an electronic motor and an air blowing fan are connected to each other by using a magnet coupling;  
       FIG. 7  is an exploded sectional view for explaining the construction of coupling;  
       FIG. 8  is a side view of an air blowing fan having a magnet coupling;  
       FIG. 9  is a sectional view schematically showing an internal construction of an air blower apparatus in accordance with a second embodiment of the present invention;  
       FIG. 10  is a sectional view showing a modification of the second embodiment;  
       FIG. 11  is a schematic sectional view showing an internal construction of an axial gap electronic motor used for an air blower apparatus of the present invention;  
       FIG. 12  is a side view showing a stator core that an axial gap electronic motor has;  
       FIG. 13  is a plan view of a stator core of an axial gap electronic motor;  
       FIG. 14A  is a front view of a core member contained in a stator core of an axial gap electronic motor;  
       FIG. 14B  is a plan view of a core member;  
       FIG. 14C  is a right side view of a core member;  
       FIG. 14D  is a bottom view of a core member; and  
       FIG. 15  is a sectional view taken along the line z-z of a core member. 
    
    
     DETAILED DESCRIPTION  
      Embodiments of the present invention will now be described with reference to the accompanying drawings. An air blower apparatus  1   a  includes an air blowing fan  2  including a cross flow fan (line flow fan) and an electronic motor  3  serving as a driving source for the air blowing fan  2 . The air blowing fan  2  and the electronic motor  3  are housed coaxially along the rotation axis L in a fan casing  4 .  
      The air blowing fan  2  is a cross flow fan that can be rotated with the rotation axis L being used as a center axis, and a large number of fan blades  21  are arranged therein in a ring form along the axial direction. At both ends of the air blowing fan  2 , end plates  22  and  23  for fixing both ends of the fan blades  21  are provided.  
      On one end plate  22  (left-hand side in  FIG. 1 ), a rotating shaft  24  is provided coaxially along the axis L. The rotating shaft  24  is pivotally supported by a bearing  41  provided on the fan casing  4 . By rotating the air blowing fan  2  with the rotating shaft  24  being used as the center axis, an air flow is produced in the radial direction of the air blowing fan  2 .  
      In the other end plate  23  (right-hand side in  FIG. 1 ) of the air blowing fan  2 , there is provided an engagement concave portion  25 , which is one connecting means for attaching the air blowing fan  2  to the electronic motor  3 . The engagement concave portion  25  includes engagement holes formed in the end plate  23  at predetermined intervals on a concentric circle around the center axis L. By engaging an engagement convex portion  36  provided on the electronic motor  3  with the engagement concave portion  25 , the electronic motor  3  and the air blowing fan  2  are connected to each other.  
      Next, referring to  FIGS. 2 and 3 , the electronic motor  3  is explained. The electronic motor  3  is what is called an axial gap electronic motor provided with a stator  31  formed in a disc shape and a pair of rotors  32  and  33  arranged opposedly on both side surfaces of the stator  31  with a predetermined gap being provided therebetween.  
      The rotors  32  and  33  are connected to each other coaxially by a connection shaft  34 , and the connection shaft  34  is pivotally supported by a bearing  312  of the stator  2 . In this embodiment, the electronic motor  3  is a permanent magnet electronic motor in which the rotors  32  and  33  each are provided with a rotor magnet  35 .  
      The stator  31  has a stator core  311  formed in a ring shape at a position opposed to the rotor magnet  35  and the bearing  312  for pivotally supporting the connection shaft  34 , which is provided in the center of the stator core  311 . The stator core  311  and the bearing  312  are formed of a synthetic resin  313 .  
      The stator core  311  has an iron core consisting of a laminated body of magnetic steel sheets, and a coil is wound on a bobbin in a multiple form with the iron core being the center. In the present invention, specific constructions of the stator core  311  and the bearing  312  are described later.  
      A necessary construction requirement of the present invention is the use of the two rotors  32  and  33  with respect to the stator  31 . Specifically, usually, in the axial gap electronic motor, there is formed a magnetic circuit generating a loop such that a magnetic flux coming out of, for example, one magnet enters the iron core of the stator  31  via an air gap, and after being drawn by the opposite-side magnet pole via the air gap again, the magnetic flux returns to the opposite-side pole through a magnetic path or a yoke in the magnet.  
      However, in the case where one rotor is used, a portion opposed to the opposite-side magnet is a mere space. Therefore, only a mere magnetic resistance is present in this portion, and a magnetic field produced accordingly is small, so that a high torque is difficult to provide. Therefore, the present invention is based on the use of two rotors.  
      On the outer peripheral surface of the stator  31 , there is formed a fixing portion  314  for fixing the stator  31  along the inner peripheral surface of the fan casing  4 . In this embodiment, the fixing portion  314  is provided at four locations at intervals of 90 degrees so as to be in contact with the internal wall of the fan casing  4  of a square tubular shape.  
      The outer peripheral portion of the stator  31  is further provided with a connector portion  315  connected to a driver device, not shown, in order to energize a coil wound around the stator core  311 .  
      The rotors  32  and  33  each have a disc-shaped rotor body  321 ,  331  fixed to the connection shaft  34  and the rotor magnet  35  supported by the rotor body  321 ,  331 . The rotor magnet  35  includes a plurality of magnet chips, not shown, formed in a fan shape for each magnetic pole, and is assembled integrally to each of the rotor bodies  321 ,  331 .  
      On the fan attaching surface of the rotor  32  on the side to which the air blowing fan  2  is attached (left-hand side in  FIG. 2 ), the engagement convex portion  36 , which is the other connecting means, is formed integrally. As shown in  FIG. 3 , the engagement convex portion  36  includes a plurality of cylindrical ribs projectingly provided on the attaching surface of the rotor  32 , the cylindrical ribs being arranged at predetermined intervals (in this embodiment, eight ribs are provided at intervals of 45 degrees) on a concentric circle around the center axis.  
      According to this configuration, the air blowing fan  2  is engaged well with the rotor  32 , so that the rotation torque produced by the rotor  32  can be transmitted surely to the air blowing fan  2 . Also, since screwing etc. is not needed, the air blower apparatus can be manufactured at a low cost. Further, the positioning work is also unnecessary.  
      In this embodiment, the engagement convex portion  36  and the engagement concave portion  25 , serving as connecting means, include round holes and cylindrical ribs. However, the rib may be formed in, for example, a ring shape. The shape is arbitrary if it can surely transmit the driving force of the electronic motor  3  to the air blowing fan  2 . Also, these connecting means need not be arranged on a concentric circle if they are provided at positions at which they can be fitted to each other.  
      Between the air blowing fan  2  and the rotor  32 , there is interposed a vibration-proof member  5  for preventing vibrations of the electronic motor  3  from propagating to the air blowing fan  2 . The vibration-proof member  5  is made of a material having vibration damping properties, such as rubber. In this embodiment, the vibration-proof member  5  is formed in a disc sheet shape, and is attached integrally to the end plate  23  of the air blowing fan  2 .  
      The vibration-proof member  5  absorbs a slight parallelism distortion produced between the end plate  23  of the air blowing fan  2  and the flat surface of the rotor  3 , and also has a function as coming-off preventive means for surely holding the engagement convex portion  36  projectingly provided on the rotor  32  in the engagement concave portion  25  in the end plate  23 .  
      Referring again to  FIG. 1 , the fan casing  4  is made of a molded product such as a synthetic resin, and is formed into a hollow tubular body extending in the axial direction. At the bottom (far side of paper in  FIG. 1 ) of the fan casing  4 , a blowoff hole (not shown) is provided to deliver an air flow generated by the air blowing fan  2  to the outside of the fan casing  4 .  
      It is possible to connect the air blowing fan  2  to the rotor  32  without the use of the vibration-proof member  5 . However, when the vibration-proof member  5  is not interposed, the noise-reducing properties decrease. Therefore, in such a case, by carrying out operation control such that a torque ripple at the time of rotation of the electronic motor  3  decreases, i.e., the operation control by sinusoidal wave drive for 120 to 180° wide-angle energization, the occurrence of vibrations can be restrained, and resultantly the noise-reducing properties can be increased. Further, by the sinusoidal wave drive, the effect in restraining vibrations can be increased. It is a matter of course that the interposing of the vibration-proof member  5  brings about a greater vibration-proof effect.  
      The inner peripheral surface of the fan casing  4  is formed in an arcuate shape along the outer peripheral surface of the air blowing fan  2 , and the electronic motor  3  is supported along the inner peripheral surface of the fan casing  4  via the fixing portions  314 . In this embodiment, the fan casing  4  is also used as a bracket for concealing the stator  31  and the rotors  32  and  33  of the electronic motor  3 . According to this configuration, the cost can be kept low because a bracket for the electronic motor  3  is not needed.  
      The fixing portion  314  is preferably formed of an elastic material such as rubber. By doing this, the fixing portion  314  can effectively absorb vibrations produced by the electronic motor  3 , and also functions to prevent the rotation of the electronic motor  3  with respect to the fan casing  4 . The elastic material may be a plurality of materials or a single material, or may be plastics.  
      In order to use the fan casing  4  also as the bracket, it is preferable to prevent dust or water from entering the interior as far as possible. Therefore, the fan casing  4  is preferably subjected to protection treatment such as waterproofing treatment and dust-proofing treatment.  
      According to this configuration, by assembling the air blowing fan  2  and the electronic motor  3  integrally via the fan casing  4  and by using an axial gap electronic motor as the electronic motor  3 , the length in the axial direction of the electronic motor  3  can be decreased, and accordingly the length in the axial direction of the air blowing fan  2  can be increased, so that the air blowing quantity can be increased.  
      Because the fan casing  4  functions as the bracket for the electronic motor  3 , a bracket need not be provided specially, and accordingly, the assembling manpower and the production cost can be reduced.  
      Although the air blowing fan  2  is installed to only one rotor  32  of the electronic motor  3  in the above-described first embodiment, the air blowing fan  2  may be installed to each of the rotors  32  and  33 . Specifically, as shown in  FIGS. 4 and 5 , in an air blowing apparatus  1   b , the electronic motor  3  is arranged in the center of the fan casing  4 , and the air blowing fans  2 ,  2  are installed to the end surfaces of the rotors  32  and  33 .  
      According to this configuration, two air blowing fans  2 ,  2  can be mounted to one electronic motor  3 , so that not only the air blowing capacity can be increased, but also the rotation balance of the air blowing fans  2 ,  2  is good because the electronic motor  3  is arranged in the center. Such a mode is also embraced in the present invention.  
      Also, in the above-described embodiment, the air blowing fan  2  and the electronic motor  3  are connected to each other via the engagement means consisting of an irregular portion. However, in the case where each of the rotors  32 ,  33  are a back yoke formed of a magnetic material, the air blowing fan  2  and the electronic motor  3  may be connected to each other by a method, for example, shown in FIGS.  6  to  8 .  
      Specifically, in an air blowing apparatus Ic, the air blowing fan  2  and the electronic motor  3  are connected to each other via connecting means consisting of a magnet coupling. As shown in  FIG. 8 , on the end plate  23  of the air blowing fan  2 , a fan-shaped magnet chip  6  is provided at four locations at angular intervals of 90 degrees in this embodiment.  
      The magnet chip  6  is generally formed by a ferrite-base or neodymium-base magnet or the like. However, the magnetic chip  6  may have any configuration if it can provide a magnetic force capable of transmitting the rotational drive force of the electronic motor  3  surely to the air blowing fan  2 . Also, a yoke etc. can be mounted on the air blowing fan  2  side to increase the magnetic force. Also, the magnetic chip  6  may be affixed on the end plate  23  or may be embedded therein.  
      Between the air blowing fan  2  and the rotor  32  of the electronic motor  3 , the vibration-proof member  5  is interposed to restrain vibrations. In this embodiment, the vibration-proof member  5  includes a flat disc-shaped ring body, and the central portion thereof is recessed along the end plate  23  of the air blowing fan  2 .  
      An advantage of the use of the magnet coupling is the improvement in assembling ability. Specifically, the air blowing fan  2  can be fixed to the electronic motor  3  merely by installing the end plate  23  of the air blowing fan  2  along the rotor  32  of the electronic motor  3 . Inversely, at the time of repair etc. as well, the disassembling ability is high. In employing the magnet coupling, positioning means may be provided separately to surely perform positioning at the time of installation.  
       FIG. 9  shows an air blower apparatus in accordance with a second embodiment of the present invention. The feature of an air blower apparatus  1   d  is the bearing construction of the electronic motor  3 . In this embodiment, the same reference numerals are applied to elements that are the same or regarded as the same as those in the above-described embodiment, and the explanation thereof is omitted.  
      The air blower apparatus  1   d  is an axial gap electronic motor in which the electronic motor  3  is provided projectingly with a boss  311   a  in the center on both sides of the stator  31 , and the rotors  32  and  33  are supported via first and second bearings  311 A,  311 A each including a radial bearing, the connection shaft  34  rotating shaft) being not provided.  
      In this embodiment, the bearings  311 A,  311 A are configured so that the inner race of the radial bearing is fixed to the boss  311   a  of the stator  31 , and the outer race thereof is fixed to the rotor side. However, the support positions of the inner race and outer race may be reversed.  
      According to this configuration, since the rotors  32  and  33  are held directly by the stator  31  via the radial bearing, the rotors  32  and  33  can be supported with a larger diameter as compared with the case where the connection shaft  34  is used for connection. Accordingly, the stability (bearing accuracy) of the rotors  32  and  33  is improved, so that the vibrations due to the rotation can be restrained effectively. Such a mode is also embraced in the present invention.  
      In the second embodiment, a radial bearing is used as bearing means, and the inner race thereof is fixed to the stator  31  and the outer race thereof is fixed to the rotors  32  and  33 . However, the configuration may be such that, inversely, the inner race is fixed to the rotors and the outer race is supported by the stator.  
       FIG. 10  shows a modification of the second embodiment. In an air blower apparatus  1   e , the rotor  32 ,  33  of the electronic motor  3  is also used as the end plate  23 ,  23  of the air blowing fan  2 . Specifically, on the end plate  23  of the air blowing fan  2 , the rotor magnet  35  for driving and a bearing  311 B with respect to the stator  31  are formed integrally.  
      For the bearing  311 B, the outer race of radial bearing is fixed, and the inner race of radial bearing is fitted on a boss projected from the stator  31 . Thereby, the end plates  23 ,  23  of the air blowing fan  2  can be used as the rotors  32 ,  33 , so that the length in the axial direction can further be decreased, and also the cost can be reduced.  
      In the above-described embodiments, the air blowing fans  2  are provided on the rotors  32  and  33  of the electronic motor  3  so as to be symmetric in the right-and-left direction. However, the configuration may be such that, for example, the air blowing fan  2  is provided on one rotor side, and another driving mechanism is provided on the other rotor side.  
      Next, referring to FIGS.  11  to  15 , a stator construction of the electronic motor  3  used for the air blower apparatus of the above-described embodiments is explained. In this embodiment, the stator  50  has a construction having the output shaft  34 , which connects the rotors  32  and  33  to each other, in the center (refer to  FIG. 11 ).  
      The axial gap electronic motor  3  includes the stator  50  of a substantially disc shape and the paired rotors  32  and  33  which are arranged opposedly on both sides of the stator  50  with a predetermined gap being provided therebetween. The rotors  32  and  33  commonly have the same rotor output shaft  34 , and the stator  2  is provided with a bearing  51  for supporting the rotor output shaft  34  on the inner periphery side of the stator  2 . The axial gap electronic motor  3  is housed in the fan casing  4 .  
      The stator  50  includes a stator core  52  formed in a ring shape (doughnut shape) and a bearing housing  53  coaxially inserted to the inner periphery side of the stator core  52 , and these elements are integrally molded by a synthetic resin  54 .  
      As shown in  FIG. 12 , the stator core  52  is formed by connecting a plurality of (nine slots in this example) core members  5   m  to  5   u  to each other in a ring shape. All of the core members  5   m  to  5   u  have the same shape, and therefore  FIG. 14  shows one core member  5   m  as an example.  FIGS. 14A, 14B ,  14 C and  15  are a front view of the core member  5   m , a plan view thereof, a bottom view thereof, a left side view thereof, and a sectional view of a principal portion, respectively.  
      As shown in  FIG. 14A , the core member  5   m  has teeth (iron core)  51   a  formed by laminating a plurality of magnetic steel sheets in the radial direction, and around the teeth  51   a , an insulator  50   a  formed of a synthetic resin is integrally formed excluding both sides thereof (surface of iron core facing to the rotor). The provision of iron core increases the magnetic flux density, and can form a strong magnetic field near the rotors  32  and  33 , so that the torque of electronic motor can be made high.  
      The insulator  50   a  can be formed by insert molding method in which the teeth  51   a  is put in a cavity in a mold, not shown, and molten resin is injected into the cavity. In this embodiment, as the molten resin, SPS (syndiotactic polystyrene) with relatively high flowability is used.  
      In this embodiment, the insulator  50   a  is formed by insert molding method using the teeth  51   a . However, it may be formed by a method in which, for example, the insulator  50   a  is formed by two pieces in advance, and these two pieces are installed from both sides with the teeth  51   a  being held therebetween.  
      On the teeth  51   a , there is formed a skew  511   a  inclined at a predetermined angle in the direction of rotation of the rotors  32  and  33 , in this embodiment, in the clockwise direction. In this embodiment of 9 slots and 8 poles, the skew angle is set at 5 degrees. Thereby, the occurrence of cogging torque can be restrained, and hence the energy conversion efficiency is improved.  
      The skew  511   a  is formed in a straight line shape with respect to a gap surface between the adjacent core members. Besides, the skew  511   a  may have an arcuate shape. The shape thereof is not subject to any special restriction as long as it achieves an effect of effectively restraining cogging torque.  
      The insulator  50   a  is formed so that the whole thereof including substantially fan-shaped flanges  52   a  and  53   a  arranged in a pair in the right-and-left direction along both side surfaces of the teeth  51   a  has a bobbin form having an H-shaped cross section. By the presence of the insulator  50   a , a coil  7  can be wound on the teeth  50   a  in a regular manner.  
      Each of the flanges  52   a ,  53   a  is provided with connecting means for connecting the adjacent core members to each other. In this example, the connecting means is provided on the inner periphery side of each of the flanges  52   a ,  53   a.    
      The connecting means includes a boss  541   c  formed on the inner periphery side of one edge  501  of each of the flanges  52   a ,  53   a  and an engagement groove  542   c  formed on the inner periphery side of the other edge  502 . By engaging these elements with each other, a ring-shaped stator core  50  as shown in  FIG. 12  is formed.  
      In this embodiment, the boss  541   c  and the engagement groove  542   c  include a prismatic body and a rectangular groove corresponding to the prismatic body, respectively. By engaging the prismatic body with the rectangular groove, the connecting means can also be used as positioning means for the skew  511   a.    
      In the side surfaces of the flanges  52   a  and  53   a , a connecting wire storage groove  55   a ,  55   b ,  55   c  for treating a connecting wire  71  of the coil  7  is provided at three locations. In this embodiment, each of the connecting wire storage grooves  55   a  to  55   c  is formed in an arcuate shape along the outer periphery in the side surface of each of the flanges  52   a ,  53   a . Two connecting wire storage grooves  55   a  and  55   b  are formed on one flange  52   a  side, and the remaining connecting wire storage groove  55   c  is formed on the other flange  53   a  side.  
      As shown in  FIG. 15 , each of the connecting wire storage grooves  55   a  to  55   c  consists of a U-shaped groove. More preferably, the storage groove should be designed so that the groove width of the opening portion is equal to or smaller than the groove width of the interior. This configuration achieves an effect of preventing the connecting wire  71  from coming off.  
      Each of the connecting wire storage grooves  55   a  to  55   c  is preferably configured so that the tip end portion (opening end side) thereof has a smaller thickness than other portions. In this configuration, when the core members  5   m  to  5   u  are integrated by a synthetic resin  54  after being connected to each other, the heat of molten resin propagates to the tip end portion, by which the tip end portion is softened to wrap the connecting wire  71  stored in the interior. Therefore, the effect of preventing the connecting wire  71  from coming off is further increased.  
      Also, in the case where the connecting wire storage groove  55   a ,  55   b ,  55   c  is provided at two or more locations, i.e., in the case where the groove is provided like the connecting wire storage grooves  55   a  and  55   b  shown in  FIG. 15 , the connecting wire storage grooves  55   a  and  55   b  are arranged so as to have a different height position via a step portion. The height position in this embodiment means a height in the axial direction.  
      In this embodiment, the connecting wire storage groove  55   a  on the outer periphery side is formed one step lower than the connecting wire storage groove  55   b  on the inner periphery side. According to this configuration, the molten resin flows in the mold cavity smoothly, so that the molten resin is allowed to flow uniformly without the formation of a void etc. between the stator core  52  and the synthetic resin  54 .  
      An external wall surface  57   a  on the inner periphery side of the connecting wire storage groove on the inside diameter side (in this embodiment, the connecting wire storage grooves  55   b  and  55   c ) of the connecting wire storage grooves  55   a  to  55   c  preferably includes a tapered surface inclined in the radial direction. According to this configuration, the molten resin flowing from the center to the outer periphery side is allowed to flow to the outer periphery side more smoothly.  
      Further, as means for smoothening the flow of molten resin, resin introduction paths  521   a  and  531   a  are provided at a part of the flanges  52   a  and  53   a  to smoothen the flow of resin when the core members  5   m  to  5   u  are connected to and integrated with each other. The resin introduction path  521   a ,  531   a  includes a U-shaped groove formed on the inside diameter side of each of the flanges  52   a ,  53   a  along the radial direction, so that the molten resin flows from this groove to the outer peripheral portion after passing through the side surface of each of the flanges  52   a ,  53   a.    
      In this embodiment, a resin introduction path  58   a  is provided at only one location along the radial direction on the inner periphery side of each of the flanges  52   a ,  53   a . However, the resin introduction path  58   a  may be provided, for example, at a plurality of locations, and the number and shape thereof are not subject to any special restriction.  
      The connecting wire storage grooves  55   a  to  55   c  are provided with engagement grooves  56   a  to  56   d  cut along the radial direction. The engagement grooves  56   a  to  56   d  are provided at two locations of the connecting wire storage grooves  55   a  to  55   c . By hooking a part of the connecting wire  71  to each of the engagement grooves  56   a  to  56   d , the connecting wire  71  is prevented from being unfastened, for example, at the time of transportation.  
      In the procedure for assembly and wiring of the stator cores  5   m  to  5   u , in order to generate a rotating magnetic field, in the case of the nine slot type, it is necessary to arrange the U, V and W phases in the order of (+)→(−)→(+), and it is necessary to make the winding direction of the center stator core reverse, or to connect the wire reversely. For example, when  5   m ,  5   n  and  5   o  are in a U phase,  5   p ,  5   q  and  5   r  are in a V phase, and  5   s ,  5   t  and  5   u  are in a W phase, winding is performed so that  5   m  is (+),  5   n  is (−), and  5   o  is (+).  
      After the stator cores  5   m  to  5   u  are assembled, the stator  2  is formed by insert molding method using the synthetic resin  21 . Usually, the resin is caused to flow from the center of the stator  2  into the cavity in a molten state, and to flow toward the outer periphery side. In this embodiment, contrivance is made to smoothen the flow of molten resin; for example, the connecting wire storage grooves  55   a  to  55   c  are provided in the side surface of the flanges  32   a  and  33   a , or the tapered surface is provided, so that the stator  2  having more homogeneous properties can be obtained.  
      Thus, when the core members are fixed permanently by the synthetic resin  54  finally, a second connecting means provided on the inner periphery side of the core member is not necessarily needed. Also, although the paired rotors  32  and  33  are provided in the above-described example, a one-side rotor may be provided. Thus, the present invention embraces various changes and modifications without departing from the spirit of the invention and within the scope of being equivalent technically.