Patent Publication Number: US-2010117468-A1

Title: Fan motor

Description:
FIELD OF THE INVENTION  
     The present invention relates to a fan motor which is used as an air cooling device in an information apparatus such as a personal computer and specifically relates to a fan motor which is capable of improving heat radiation characteristics. 
     BACKGROUND ART  
     Recently, with a tendency of advanced performance and function of an information apparatus, heat generation of electronic components (for example, CPU and the like) provided in the inside of the information apparatus has increased and thus importance of an efficient air-cooling has been increasing. For example, in a server as a host computer, a plurality of CPUs and memories are disposed for attaining a high density mounting and a high speed operation and thus a plurality of fan motors are disposed to enhance an air-cooling efficiency. 
     For example, in an axial fan motor disclosed in Patent Reference  1 , drive circuit components such as power transistors are disposed within a case which is protruded from a housing. An opening is formed in the case and a part of air which is generated by rotor blades and flown from the inside of the apparatus toward the outside is flown into through the opening. In this manner, when the rotor blades are rotated, the drive circuit components are self-cooled i.e., forcibly cooled by the air having flown into the case and, as a result, a heat generating source such as a power transistor which is disposed in the drive circuit is cooled.
     [Patent Reference 1] Japanese Patent Laid-Open No. 2002-112499 (paragraph [0018], FIG. 1)   

     DISCLOSURE OF THE INVENTION  
     Problems to be Solved by the Invention  
     However, as described above, with a recent advanced performance and function of an information apparatus, a further improvement for heat radiation characteristic is required. For example, in the axial fan motor which is described in Patent Reference  1 , self-cooling is performed by utilizing air entering from the opening as described above but an inflow amount of air entering from the opening has a limit and thus an effect of air-cooling is limited. Further, there is a requirement to reduce the number of fan motors as much as possible, for example, which are used in a server. However, when the number of the fan motors is really reduced, the rotation number of the fan motor is required to increase and, when the rotation number is increased, heat generated from the fan motor can not be radiated sufficiently. 
     In view of the problems described above, the present invention may provide a fan motor which is capable of providing a higher heat radiation characteristic. 
     Means to Solve the Problems  
     In order to solve the problems described above, at least an embodiment of the present invention provides as follows. 
     According to an embodiment of the present invention, there may be provided a fan motor including a frame provided with an inlet port and an outlet port and formed in a hollow tubular shape, a stator provided with a drive coil, a stator support part which supports the stator, a rotor which is rotatably supported by the stator support part, a magnet which is disposed on the rotor so as to face to the drive coil, a fan which is provided on an outer peripheral side of the rotor for generating airflow from the inlet port to the outlet port, a control circuit board having a drive control IC for controlling switching of polarity of the drive coil, and a mounting member which mounts the stator support part within the hollow tubular shape of the frame. The control circuit board is disposed in a substantially parallel to a rotation center axis of the rotor within the frame. 
     According to this embodiment, in the fan motor including a rotor which is rotatably supported by (rotation center shaft which is provided in) a stator support part, a fan, a control circuit board having a drive control IC, and a mounting member for mounting the stator support part, the control circuit board is disposed in the frame so as to be substantially parallel to the rotation center shaft of the rotor and thus a high degree of heat radiation characteristic is obtained. 
     In other words, in the axial fan motor which is disclosed in the conventional Patent Reference 1, the case which accommodates a drive circuit component (drive circuit board) on which power transistors and the like are mounted is disposed to be perpendicular to the rotation center shaft and is cooled by utilizing air which is flown into from an opening arranged in the case. Therefore, the drive circuit component cannot be directly cooled by the air. (Accordingly, an opening is formed in the case in Patent Reference 1). However, according to this embodiment, since the control circuit board is disposed to be substantially parallel to the rotation center shaft, the control circuit board is disposed within airflow by the rotor blade from the inlet port to the outlet port of the frame and thus airflow is directly passed through the entire or a part of the control circuit board. Therefore, a high degree of heat radiation characteristic is obtained. In accordance with an embodiment, the control circuit board may be covered by a certain member and, in this case, an opening may be formed in the certain member. 
     In accordance with an embodiment of the present invention, a sensor circuit board is provided which includes a magnetic pole detection sensor for detecting a magnetic pole of the magnet to generate a magnetic pole detection signal, and the sensor circuit board is disposed so that the magnetic pole detection sensor is located in a vicinity of the magnet, and the sensor circuit board is provided separately from the control circuit board. 
     According to this embodiment, the sensor circuit board having the magnetic pole detection sensor is disposed so that the magnetic pole detection sensor is located in a vicinity of the magnet and the sensor circuit board is provided separately from the control circuit board and thus degree of freedom for arranging the control circuit board and the sensor circuit board is improved. Therefore, the control circuit board and the sensor circuit board can be accommodated within a limited space of the frame without largely disturbing airflow, for example, without stagnating airflow from the inlet port to the outlet port of the frame which is generated by the rotor blades. Further, distances of components such as the drive IC on the control circuit board, the sensor on the sensor circuit board and the like can be widened. 
     In accordance with an embodiment of the present invention, an electric current supply means is provided for supplying an electric current to the drive coil on the basis of a control signal from the drive control IC, and at least a part of the electric current supply means is disposed on an extending part of the control circuit board which is extended toward an inner wall of the frame. 
     According to this embodiment, an electric current supply means for supplying an electric current to the drive coil on the basis of a control signal from the drive control IC is provided in the fan motor, and at least a part of the electric current supply means is disposed on an extending part of the control circuit board which is extended toward an inner wall of the frame. Therefore, the electric current supply means (for example, FET, power transistor or the like) which commonly generates large amount of heat can be disposed within airflow from the inlet port to the outlet port of the frame that is generated by the rotor blades. As a result, the electric current supply means is effectively air-cooled and thus heat radiation characteristic of the entire fan motor can be improved. 
     In accordance with an embodiment of the present invention, a connecting part for power supply or for a control line is provided on the extending part near the inner wall of the frame. 
     According to this embodiment, a connecting part for power supply or for a control line is provided on the extending part near the inner wall of the frame. Therefore, in order that electric power or a control signal is supplied to the fan motor from the outside, electrical connection may be simply arranged without being largely incurred by an effect due to airflow from the inlet port to the outlet port of the frame which is generated by the rotor blades. 
     In accordance with an embodiment of the present invention, a cover member is provided which is fixed to the stator support part for covering the sensor circuit board, and the cover member is formed with a slot which is cut in a direction parallel to the control circuit board. 
     According to this embodiment, the cover member which is fixed to the stator support part for covering the sensor circuit board is provided and the cover member is formed with a slot which is cut in a direction parallel to the control circuit board. Therefore, the control circuit board is firmly fixed to the fan motor by means of that the control circuit board is pinched by utilizing (inserted or fitted to) the slot. Further, wobbling of the control circuit board is prevented by being fixed to the slot. 
     In accordance with an embodiment of the present invention, the cover member is formed with a circuit board support part which is extended toward an inner wall of the frame from an end part of the slot in a direction perpendicular to the rotation center axis for supporting the control circuit board. 
     According to this embodiment, the cover member is formed with a circuit board support part which is extended toward an inner wall of the frame from an end part of the slot in a direction perpendicular to the rotation center axis for supporting the control circuit board. Therefore, the control circuit board which is disposed to be parallel to the rotation center shaft is securely fixed and wobbling of the control circuit board can be prevented securely. 
     In accordance with an embodiment of the present invention, the circuit board support part is formed with a groove part for supporting the extending part of the control circuit board. 
     According to this embodiment, the circuit board support part is formed with a groove part for supporting the extending part of the control circuit board. Therefore, the control circuit board is firmly fixed by means of that a part of the control circuit board is fitted into the groove part. 
     In accordance with an embodiment of the present invention, a face of the circuit board support part which is opposite to a face formed with the groove part is formed in a stream-line shape whose thickness becomes thinner toward windward of the airflow. 
     According to this embodiment, a face of the circuit board support part which is opposite to a face formed with the groove part is formed in a stream-line shape whose thickness becomes thinner toward windward of the airflow. Therefore, a wind pressure resistance is reduced and thus air amount supplied by the fan motor can be increased. In this embodiment, the “stream-line shape” is a shape whose tip end may be a sharp shape such as a so-called triangular shape or an arrowhead shape, or may be formed in any shape where a wind pressure resistance can be reduced. 
     Effects of the Invention  
     As described above, in the fan motor in accordance with at least an embodiment of the present invention, the control circuit board having a drive control IC is disposed in the frame so as to be substantially parallel to the rotation center shaft of the rotor. Therefore, airflow generated by the rotor blades is directly passed through the entire or a part of the control circuit board and thus a high degree of heat radiation characteristic can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
         FIGS. 1(   a ) and  1 ( b ) are views showing a mechanical structure of a fan motor in accordance with an embodiment of the present invention. 
         FIGS. 2(   a ) and  2 ( b ) are enlarged views showing a control circuit board. 
         FIG. 3  is a circuit diagram showing an electrical structure of a fan motor in accordance with an embodiment of the present invention. 
         FIGS. 4(   a ) and  4 ( b ) are enlarged views showing a control circuit board which is mounted on a fan motor in accordance with another embodiment of the present invention. 
         FIG. 5  is a sectional view showing a fan motor in accordance with another embodiment of the present invention. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS  
     
         
           1  fan motor 
           11  blade part (fan) 
           12  magnet 
           13  yoke 
           14  rotation shaft 
           15  hub 
           16  ball bearing 
           17  laminated core 
           18  core support member 
           19  guide blade 
           20  spring 
           21  drive coil 
           22  sensor circuit board 
           23  control circuit board 
           24  connecting part (connecting plate, connector) 
           25  cover part 
           26  stator support part 
           27  magnetic pole detection sensor 
           28  support part 
           30  fan case 
           100  rotor 
           200  stator 
       
    
     An embodiment of the present invention will be described below with reference to the accompanying drawings. 
     [Mechanical Structure] 
       FIGS. 1(   a ) and  1 ( b ) are views showing a mechanical structure of a fan motor  1  in accordance with an embodiment of the present invention. Specifically,  FIG. 1(   a ) is a longitudinal sectional view showing the fan motor  1  and  FIG. 1(   b ) is a view showing the fan motor  1  shown in  FIG. 1(   a ) which is viewed from an under side in the drawing (frame is omitted). 
     The fan motor  1  shown in  FIG. 1(   a ) includes a fan case  30  as a hollow pipe-shaped frame which is provided with an inlet port  400  and an outlet port  500 , a stator  200  provided with a drive coil  21 , a stator support part  26  which supports the stator  200 , a rotor  100  which is rotatably supported by the stator support part  26 , a magnet  12  which is disposed on the rotor  100  so as to face the drive coil  21 , a blade part (fan)  11  which is provided on an outer peripheral side of the rotor  100  for generating airflow from the inlet port  400  to the outlet port  500 , a control circuit board  23  having a drive control IC  23   a  for controlling switching of the polarity of the drive coil  21 , and guide blades  19  as a mounting member for mounting the stator support part  26  within a hollow portion of the fan case  30 . The control circuit board  23  is disposed within the fan case  30  in a substantially parallel manner with respect to a rotation center axis of the rotor  100 . In this embodiment, a three-phase brushless motor is used as a motor  10 . However, the present invention is not limited to this embodiment. For example, a motor in a single-phase full-wave drive system or a motor in a two-phase drive system may be used. 
     As shown in  FIG. 1(   a ), the motor  10  of the fan motor  1  includes the rotor  100 , the stator  200 , ball bearings  16  as a bearing, a circuit board assembly comprising the control circuit board  23 , a sensor circuit board  22  and a connecting part (connecting plate)  24 . The rotor  100  includes the magnet  12 , a yoke  13 , a rotation shaft  14  and a hub  15 , and the stator  200  includes a laminated core  17 , a core support member  18 , the drive coil  21  and the stator support part  26 . 
     The blade part  11  is provided with a plurality of blades  11   a  and the blades  11   a  are formed in a shape so that wind is sent from the inlet port  400  to the outlet port  500  (from the upper to the lower in  FIG. 1(   a )) by rotation of the blade part (fan)  11 . The blade part  11  is mounted on the rotation shaft  14  through the hub  15  and is rotated together with the rotation shaft  14 . 
     The hub  15  is mounted with the magnet  12  through the yoke  13 . The magnet  12  is formed in a cylindrical shape and is alternately magnetized with an “N”-pole and an “S”-pole in a circumferential direction. In addition, an inner peripheral face of the magnet  12  is disposed so as to face an outer peripheral face of the laminated core  17 . The rotation shaft  14  and the blade part  11  are rotated through the yoke  13  and the hub  15  by an electromagnetic force based on a magnetic field generated in the vicinity of the laminated core  17 . In this embodiment, the rotation shaft  14  is supported by the core support part  18  through the ball bearings  16 . Further, a lateral pressure is applied to the ball bearing  16  in a rotation shaft direction by the spring  20  to stabilize rotation of the rotation shaft  14  and the blade part (fan)  11 . 
     The laminated core  17  is fixed to the core support member  18  and the drive coil  21  is wound around the laminated core  17  (see  FIG. 1(   a )). When a switching-controlled electric current is supplied to the drive coil  21  from the control circuit board  23 , a drive magnetic field is generated in the vicinity of the laminated core  17 . As described above, the magnet  12  structuring the rotor  100  is rotated by the electromagnetic force of the drive magnetic field. 
     The core support member  18  is fixed to the stator support part  26  to structure a part of the stator support part  26 . The guide blade  19  is provided on an outer side in a radial direction of the stator support part  26  for guiding air which is sent by the blade part  11 . The guide blade  19  is a mounting member for mounting the stator support part  26  on the fan case  30  (frame) and is provided with a function for converting turbulent flow, which is generated by rotation of the blade part  11 , into a direct flow. In this embodiment, one end of the guide blade  19  is mounted on the stator support part  26  and the other end is mounted on the inner side of the fan case  30 , and a plurality of the guide blade  19  is formed radially from the outer peripheral face of the stator support part  26 . The wind converted into the direct flow blows on the control circuit board  23  more efficiently. In this manner, the control circuit board  23  (especially, a drive control IC  23   a  and FET units  23   e  described below) is cooled down effectively. In this embodiment, the fan case  30  as a frame in a hollow tubular shape is formed in a rectangular tube whose cross section is quadrangular. 
     In the present invention, an axial center of the rotation shaft  14  is a rotation center axis of the rotor  100 . The stator  200  includes the coil (drive coil)  21  and the laminated core  17 , and the stator support member  250  includes the core support member  18  and the stator support part  26 . Further, the rotation shaft  14 , the magnet  12 , the yoke  13  and the hub  15  structures the rotor  100 . Further, the stator support part  26  is integrally molded with the guide blade  19  as a mounting member and the core support member  18  is fixed to a bottom part on an inner peripheral side of the cup-shaped stator support part  26  with a screw or the like. In addition, a sensor circuit board  22  is mounted on an opposite side of the stator support part  26  with respect to the core support member  18 . 
     As described above, the stator support part  26  supports the stator  200  and the rotor  100  is rotatably supported through the rotation shaft  14  which is provided in the hub  15 . Further, the magnet  12  is disposed on the inner peripheral face of the rotor  100  so as to face the drive coil  21  and the blade part  11  as a fan is provided on the outer peripheral side of the rotor  100 . The rotor  100  and the stator  200  are disposed within the fan case  30  (frame in a hollow tubular shape). In addition, the stator support part  26  is mounted within the fan case  30  by the guide blade  19 . 
     On the other hand, in  FIG. 1(   a ), a circuit board assembly comprised of the sensor circuit board  22 , the control circuit board  23  and the connecting part  24  is provided on the outlet port  500  side of airflow in the inside of the fan case  30  of the fan motor  1 . 
     The sensor circuit board  22  is formed in a disk-like shape having a size substantially the same as the inner peripheral bottom part of the stator support part  26 . The sensor circuit board  22  is provided with a magnetic pole detection sensor  27  for detecting magnetic poles of the magnet  12  to generate a magnetic pole detection signal. In other words, when the magnet  12  is rotated together with the blade part  11 , the magnetic field in the vicinity of the magnetic pole detection sensor  27  such as a Hall IC is varied. When the magnetic pole detection sensor  27  detects variation of the magnetic field, it is transmitted to the control circuit board  23  as a magnetic pole detection signal. In this embodiment, the magnetic pole sensors  27  on the sensor circuit board  22  are disposed in the vicinity of the magnet  12  at positions facing the inner peripheral face of the magnet  12  with an equal interval in the circumferential direction. In addition, as shown in  FIGS. 1(   a ) and  1 ( b ), the sensor circuit board  22  is formed with the connecting part  24  for holding the control circuit board  23 . The connecting part  24  is formed with a plurality of metallic pins and is electrically connected to the sensor circuit board  22  through the metallic pins. Further, the sensor circuit board  22  and the control circuit board  23  are separately structured. 
     The control circuit board  23  is fixed to the sensor circuit board  22  through the connecting part  24  and is electrically connected to the sensor circuit board  22  by using a plurality of the metallic pins formed in the connecting part  24 . In accordance with an embodiment of the present invention, any connecting technique of the sensor circuit board  22  with the control circuit board  23  may be utilized. For example, a slot may be formed for connection or a socket may be used for connection. 
     As shown in  FIGS. 2(   a ) and  2 ( b ) described below, the control circuit board  23  is provided with the drive control IC  23   a  where switching of a magnetism of the drive coil  21  is controlled. Further, as shown in  FIG. 1(   a ), the control circuit board  23  is formed in a “T”-shape and is provided with extending parts  23   b  extending toward an inner wall of the frame. 
     The cover member  25  is formed in a truncated-cone shape and is fixed to the stator support part  26  with a screw to cover the sensor circuit board  22 . Further, the cover member  25  is formed with a slot  25   a  so as to be parallel to the control circuit board  23  and the circuit board support part  28  is formed from an end part of the slot  25   a  to the fan case  30  in a direction perpendicular to the rotation shaft  14 . 
     The circuit board support part  28  is fixed to the stator support part  26 . Further, the circuit board support part  28  is formed with a groove part  28   a  which supports the extending part  23   b  of the control circuit board  23  so as to be roughly perpendicular to the slot  25   a . Further, an opposite face (convex face  28   b ) of the circuit board support part  28  to a face formed with the groove part  28   a  is formed in a stream-line shape whose thickness becomes thinner toward the windward of airflow (see  FIG. 1(   b )). In the embodiment described above, the connecting part  24  is a connector and, as shown by the dotted line frame in  FIG. 1(   b ), the connecting part  24  is fixed to the sensor circuit board  22  and inserting connection part  23   c  of control circuit board  23  is inserted into metal pins formed in the connector to electrically connect (fix) the sensor circuit board  22  with the control circuit board  23 . 
       FIGS. 2(   a ) and  2 ( b ) are enlarged views showing the control circuit board  23 . Specifically,  FIG. 2(   a ) shows a front face of the control circuit board  23  and  FIG. 2(   b ) shows a rear face of the control circuit board  23 . 
     In  FIGS. 2(   a ) and  2 ( b ), the control circuit board  23  is disposed with the drive control IC  23   a  as described above and is provided with the extending parts  23   b  which are formed so as to extend toward the inner wall of the fan case  30 . Specifically, the front face of the control circuit board  23  shown in  FIG. 2(   a ) is disposed with the inserting connection part  23   c , which is inserted into the connecting part  24 , and the connecting part  23   d  for power supply or control lines. The inserting connection part  23   c  is, for example, in a contact structure which is formed on the control circuit board  23 . The connecting part  23   d  is disposed on the extending part  23   b  at a position on an inner wall side of the fan case (frame)  30 . Therefore, the connecting part  23   d  is structured so that an effect due to airflow from the inlet port  400  to the outlet port  500  is not largely incurred and so that connecting wires are easily drawn out from the slit  30   a  of the fan case (frame)  30 . In addition, the rear face of the control circuit board  23  shown in  FIG. 2(   b ) is provided with three FET units  23   e  (example of the electric current supply means) for switching and supplying an electric current to the drive coil  21  on the basis of a control signal from the drive control IC  23   a . Each of the FET units  23   e  is respectively structured of two FETs (see  FIG. 3  described below). Further, in  FIG. 2(   b ), the most left side FET unit  23   e  is disposed on the extending part  23   b  of the control circuit board  23 . In this embodiment, only one FET unit  23   e  is disposed on the extending part  23   b  but, for example, two or three FET units  23   e  may be disposed on the extending part  23   b . Alternatively, all of six (two by three pairs) FETs (for example, MOSFET) which structure the individual FET unit  23   e  may be disposed on the extending part  23   b.    
     In the fan motor  1  in accordance with this embodiment, as shown in  FIG. 1(   a ), the sensor circuit board  22  is disposed within the frame in a perpendicular manner to the rotation shaft  14 . Further, the control circuit board  23  is disposed within the fan case (frame)  30  in a parallel manner to the rotation shaft  14 . Therefore, air which is sent from the inlet port  400  toward the inside of the fan case (frame)  30  by the blade part  11  and passed through the guide blade  19  is directly (forcibly) blown on the front-rear face of the control circuit board  23  and on the front-rear face of the extending part  23   b . In this manner, the FET unit  23   e  which is disposed on the extending part  23   b  is effectively air-cooled and thus heat radiation characteristic is improved. 
     [Electrical Structure] 
       FIG. 3  is a circuit diagram showing an electrical structure of the fan motor  1  in accordance with an embodiment of the present invention. Respective electric elements shown in  FIG. 3  are disposed on the sensor circuit board  22  or the control circuit board  23 . 
     In  FIG. 3 , the electrical structure of the fan motor  1  mainly includes the drive control IC  23   a  which controls switching of polarity of the drive coil  21 , a magnetic pole detection sensor  27  for generating a magnetic pole detection signal, and three FET units  23   e  for supplying an electric current to the drive coil  21  (“U”-phase, “V”-phase and “W”-phase). 
     The magnetic pole detection sensor  27  is structured of three Hall elements (“U”-phase, “V”-phase and “W”-phase) for detecting the position of the magnet  12 . The drive control IC  23   a  is capable of recognizing a rotational state of the blade part  11  by receiving electric signals from the Hall elements. A type using InSb or a type using GaAs may be used as the Hall element but any type may be used. Further, in this embodiment, the Hall IC is used to detect the magnetic pole. 
     A “Vsp” terminal is a terminal for receiving a control signal which is sent from a high-order device and an “FG” terminal is a terminal for outputting an “FG” signal which is periodically varied depending on the rotation number of the blade part  11 . The control signal which is sent from the high-order device is a PWM signal in a PWM control system. The PWM control system is a system in which a width ratio (so-called duty ratio) of a voltage pulse is varied to control a power supply. On the other hand, the FG signal is generated on the basis of an electric signal which is received by the Hall IC (Hall element). In this embodiment, a “Vcc” terminal is a terminal to which a power supply of DC voltage 12V is connected and a “G” terminal is a ground terminal (GND terminal). 
     [Effects of Embodiment] 
     According to the fan motor  1  in accordance with the embodiment described above, the FET unit  23   e  which is a main heat generating source is disposed on the extending part  23   b  of the control circuit board  23 . Therefore, air which is flown from the inlet port  400  toward the outlet port  500  through the guide blade  19  is directly blown on the FET unit  23   e  and thus heat radiation characteristic can be improved. Especially, for example, in an IU server, the number of fans for cooling is limited (for example, one for each server). Therefore, in this case, a rotation number of one fan motor is required to increase to attain a high air-quantity. However, when a rotation number is increased, a problem of heat generation may occur. According to the fan motor  1  in accordance with the embodiment described above, since the above-mentioned countermeasure for heat radiation is adopted, the problem of heat generation can be eliminated (as a high air-quantity is required, strength of wind blowing on the control circuit board  23  is increased and, as a result, heat radiation characteristic can be improved). 
     Therefore, according to the fan motor  1 , the number of fan motors used in one server can be reduced. Further, according to the fan motor  1  whose heat radiation characteristic is improved, another heat radiation countermeasure such as a heat sink can be omitted. Further, the control circuit board may be covered by another additional member and, in this case, an opening may be formed in the additional member. 
     Further, the sensor circuit board  22  is separately provided from the control circuit board  23  and is disposed to be perpendicular to the rotation shaft  14 . Therefore, the circuit board (control circuit board and sensor circuit board) are accommodated within the fan case (frame)  30  having a limited space and thus the size of the fan motor can be reduced. Further, a degree of freedom of arrangement of the control circuit board having a large heat generating amount and the sensor circuit board having a relatively little heat generating amount is improved or a degree of freedom of arrangement of components having different heat generating amounts is improved. 
     Further, as shown in  FIGS. 2(   a ) and  2 ( b ), the connecting part  23   d  for power supply or for control lines is arranged near the inner wall side on the extending part  23   b  of the control circuit board  23 . Therefore, the connecting wires can be easily connected. 
     Further, the control circuit board  23  is fixed to the slot  25   a  and the extending part  23   b  is fixed by the circuit board support part  28 . Especially, the extending part  23   b  is inserted into the groove part  28   a  of the circuit board support part  28  to be fixed further securely. Therefore, wobbling of the control circuit board  23  is prevented. 
     Further, as shown in  FIG. 1(   b ), the face (convex face  28   b ) of the circuit board support part  28  opposite to the face formed with the groove part  28   a  is formed in a stream-line shape. Therefore, disturbance of airflow which is blown through the guide blade  19  is restrained. 
     Further, as shown in  FIG. 1(   a ), since the ball bearing  16  is used for supporting a part of the rotation shaft  14 , the blade part  11  is prevented from being rotated while moving up and down and, as a result, occurrence of unusual noise due to impact and deterioration of rotation efficiency can be prevented. 
     Modified Example  
       FIGS. 4(   a ) and  4 ( b ) are enlarged views showing a control circuit board  23 A which is mounted on a fan motor  1 A in accordance with another embodiment of the present invention. Especially, as shown in  FIG. 4(   a ), a front face of the control circuit board  23 A is disposed with a drive control IC  23   a  and, as shown in  FIG. 4(   b ), a rear face of the control circuit board  23 A is disposed with three FET units  23   e.    
     The control circuit board  23 A shown in  FIGS. 4(   a ) and  4 ( b ) is not provided with the extending part  23   b , which is different from the control circuit board  23  shown in  FIGS. 2(   a ) and  2 ( b ). However, even in this shape, when the cover member  25  is removed or when air holes are formed in a part of the cover member  25 , air which is passed through the guide blade  19  from the inlet port  400  can be blown on the drive control IC  23   a  and the FET unit  23   e  and, as a result, heat radiation characteristic can be enhanced. 
       FIG. 5  is a sectional view showing a fan motor  1 B in accordance with another embodiment of the present invention. A view of the fan motor  1 B shown in  FIG. 5  which is viewed from a lower side in the drawing is the same as that in  FIG. 1(   b ) and thus the view is not shown. 
     The fan motor  1 B shown in  FIG. 5 , which is different from the fan motor  1  shown in  FIG. 1 , is a shaft fixing type in which a shaft as a rotation center is not rotated. Further, a dynamic pressure bearing is adopted as a bearing instead of using the ball bearing  16 . In other words, in  FIG. 1 , the elements structuring the rotor  100  includes the magnet  12 , the yoke  13  and the hub  15 , and the elements structuring the stator  200  includes the laminated core  17  and the drive coil  21 , and the elements structuring the stator support member  250  includes the support member  18  and the stator support part  26 . On the other hand, in  FIG. 5 , the elements structuring the rotor  100  includes a magnet  12 , a yoke  13  and a hub  15 , and the elements structuring the stator  200  includes a fixed shaft  14 A and a drive coil  21 . In this embodiment, the fixed shaft  14 A is fixed to and stood on a bottom part of the stator support part  26  by caulking or the like. Other structure of the stator support part  26  is similar to the embodiment shown in  FIG. 1(   a ). 
     Regarding a radial bearing  32 , one side of the radial bearing  32  facing through a radial dynamic pressure face  32 A is fixed to the hub  15  (rotation side) and the other side of the radial bearing  32  is fixed to a fixed shaft  14 A side. An inner peripheral side dynamic pressure face  32 A formed on a radial bearing face is circumferentially recessed with radial dynamic pressure generating grooves (not shown) having a herringbone shape so as to be divided into two blocks (within rectangular frames shown by the dotted line in  FIG. 5 ) in an axial direction. Lubrication fluid is pressurized by pumping operations of both the radial dynamic pressure generating grooves to generate a dynamic pressure, and the radial bearing  32  is supported while being floated in a radial direction by the dynamic pressure of the lubrication fluid. Further, in this embodiment, the radial bearing  32  is mounted with magnets  160  and  161  for determining a position in an axial direction of the rotor  100  with respect to the stator  200 . A position of the rotor  100  can be determined with respect to the stator  200  by means of that the magnets  160  and  161  are attracted to each other. In this manner, the present invention may be applied to the fan motor  1 B in which the rotation shaft  14  is fixed. 
     INDUSTRIAL APPLICABILITY  
     The fan motor in accordance with the present invention is effective for improving heat radiation characteristics. 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
     The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.