Abstract:
An axial flow fan having impeller blade section fixed in a rotor of a motor where shaft supporting the rotation of the rotor is fitted to intermediate fastening section, and boss, which holds the synthetic resin fan with fan blades, surrounds and firmly connects the intermediate fastening section. The shaft is made from metal, and this allows a secure press fit with the metal intermediate fastening section. The neck joining the intermediate fastening section and the boss has a through hole for the shaft to pass and supporting arms project between boss and intermediate fastening section. In addition, the connecting sections between the shaft and the intermediate fastening section, and the boss and the intermediate fastening section may be knurled.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an axial flow fan with a strengthened coupling between the impeller blades and boss. 
     In the axial flow fan, the entire fan motor is flat in shape in order to mount the motor structure in the center of the fan. Because of this, the volume required for installation is small and the fan can be mounted simply on the side wall of an equipment, and so fans of this type are widely used for cooling in office automation equipment. 
     In normal axial flow fans, the stator of the motor passes through and is held in place by supporting arms in the center of a shallow round or square shaped cylindrical frame. The rotor rotates freely around the outside of this stator, and the impeller blades extend from this rotor in the direction of emission. The rotor causes the blades to revolve and causes air to flow in the axial direction of the frame. Normally, when the impeller blades are made from plastic resin, the shaft in the center of the stator is coupled to the boss in the center of the impeller shaft section by molding. 
     Conventionally, it has been usual to apply knurling to the molded resin shaft with the aim of reducing vibration during rotation, firmly fixing the shaft and increasing the strength of the bond between blade section boss and shaft. However, in cases where the ambient temperature is high and operation is carried out for a long time, heat generated by the rotor and stator causes the shaft to grow hot and expand by a very small amount. After operation is stopped, the shaft cools and shrinks back to its original size. When this process is repeated, the heat of the shaft during rotation cause the resin to soften and worsens the perpendicularity of the shaft in relation to the blades. The socalled shaft inclination and the rotational balance of the blades deteriorates, causing vibration during rotation. 
     The present invention is directed to overcoming the above disadvantages. This objective is accomplished by providing an axial flow fan consisting of impeller blades mounted in a rotor of the motor, by which the shaft supporting the rotor and the boss holding the blades are more firmly coupled, thus ensuring a longer service life for this coupling. 
     SUMMARY OF THE INVENTION 
     In order to achieve the above-mentioned object, the present invention provides an axial flow fan consisting of impeller blades mounted in a rotor of a motor, by which an intermediate fastening section is provided for the shaft which supports the rotation of the rotor, and the boss holding the synthetic resin impeller blades which form the sides of the blades surrounds the said intermediate fastening section to establish a close coupling. 
     The next present invention provides an axial flow fan further having a metal shaft into which the metal intermediate fastening section is fitted and fastened. 
     The other present invention provides an axial flow fan further having an intermediate fastening section possessing a hole through which pass the shaft and the neck coupled to the boss. 
     The another present invention provides an axial flow fan further having an intermediate fastening section possessing a hole through which pass the shaft and the neck coupled to the boss, and mounting arms extending from the intermediate fastening section to the boss. 
     The another present invention provides an axial flow fan further having a knurled section on the coupling between the shaft and the intermediate fastening section. 
     The another present invention provides an axial flow fan further having a knurled section on the coupling between the intermediate fastening section and the boss. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing an axial flow fan constructed according to a preferred embodiment of the present invention. 
     FIG. 2 is a front view of the rotor. 
     FIG. 3 is a sectional view of the rotor. 
     FIG. 4 is a front and a sectional view of the intermediate fastening section. 
     FIG. 5 is a sectional view showing of the rotor according to the second embodiment. 
     FIG. 6 is a front and a sectional view of the intermediate fastening section according to the 3rd embodiment. 
     FIG. 7 is a front and a sectional view of the intermediate fastening section according to the 4th embodiment. 
     FIG. 8 is a front and a sectional view of the intermediate fastening section according to the 5th embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an axial flow fan constructed according to a preferred embodiment of the present invention. In FIG. 1, the casing  1  contains the cylindrical venturi  2 , with its inner surface formed at an angle, and supporting arms  3  extending from the venturi  2  inwards holding the bearing box  4  in a one-piece structure. On the inside of the mount  5  in the center of the bearing box  4  there are two bearings  6  and  7 . The inside of bearings  6  and  7  support the shaft  8  and allow it to rotate freely. The collar  9  keeps the shaft  8  in place. 
     FIG. 2 shows plan views of the rotor and impeller blades. FIG. 3 is a sectional view of the rotor along the line A-O-A′ of FIG.  2 . As illustrated by FIGS. 1,  2  &amp;  3 , shaft  8  is made to form a single piece with the boss  11  of the impeller blade section  10  by the intermediate fastening section  12  formed from a ring shaped metal sheet being pressed in an approximately vertical direction into the axis. The boss  11  is surrounded by the cap  13 , from which extend a plurality of blades  14  in the emission direction. The above ring shaped intermediate fastening section  12  fits into the knurled section  15  of shaft  8  thus firmly holding shaft  8  in place. A yoke  16  is fitted to the inside of cap  13 , and its cylindrical inside wall retains the radially magnetized magnet  17 . 
     A circular PC board  18  is fitted below and around the mount  5  of bearing box  4  and upon this board are mounted electronic components and the drive circuit which drives the axial flow fan. The lead wire  19  supplies electric power. Around the circumference of mount  5  are fitted a core  20  comprising fixed magnets and yokes. Coil  22  passes through insulator  21  and is wound around core  20 . Core  20  and stator coil  22  make up the stator  23 . 
     The axial flow fan configured as described above operates as follows. When an electric power supply voltage is applied via lead wire  19  to the electronic circuit on PC board  18 , the cores  20  of stator  23  are excited in a prescribed order. The relationship between the resulting magnetic field and the magnetic field emitted by the magnets  17  cause the impeller blades to rotate around the axis of the shaft  8 . This rotation causes the sides of the fan blades  14  to generate a current of air in a constant direction within the venturi  2  inside the casing  1 . As shown in FIG. 2, the objective is this one piece structure formed using resin to bind the boss  11  of fan blades  10  onto the shaft  8  with the ring shaped intermediate fastening section  12  pressed vertically onto its axis. 
     In FIG. 3, the portion of the shaft where the ring shaped intermediate fastening section presses into it has had its surface roughened by knurling, and this has a large effect in strengthening the coupling between the shaft and the fan. In the above embodiment, the intermediate fastening section  12  pressed onto the shaft  8  is shown as being ring shaped, but a square shape may also be used as long as it maintains the perpendicularity between the shaft and the fan. 
     FIG. 4 shows another embodiment, looking at the intermediate fastening section from the same viewpoint, in which (a) is a front view and (b) is a sectional side view. Intermediate fastening section  30  is composed of the cylindrical neck  31  pressing on the tip of shaft  8 , flange  32  which projects from the upper edge of neck  31  in a direction orthogonal to the axis of the cylinder, six mounting arms  33  which project from flange  32  in the emission direction, and the through hole  34  in neck  31 . 
     FIG. 5 is a sectional view showing the rotor using the intermediate fastening section  30  illustrated in FIG.  4 . As can be seen from FIG. 5, the knurled section  15  of shaft  8  is firmly pressed into through hole  34  of neck  31 . In this way, intermediate fastening section  30  forms a single piece with shaft  8  which is molded onto rotor boss  11  to form one unit. Shaft  8  and intermediate fastening section  30  comprise two metal parts press fitted together and so even if the temperature varies looseness and clattering will not easily occur. In addition to rotor boss  11  being tightly fixed to neck  31 , the six mounting arms  33  project on the inside of boss  11 , firmly securing boss  11  and intermediate fastening section  30  to each other. As a result, shaft  8  and boss  11  are tightly fixed, and even if thermal stress or vibrational shock are received, shaft  8  and boss  11  will not easily separate. 
     FIG. 6 shows a 3rd embodiment of the intermediate fastening section, in which (a) is the front view of the part and (b) is a sectional view cut along the length of through hole  41 . In order to strengthen the coupling to the boss, the side surface of intermediate fastening section  40  can be knurled. In this way, intermediate fastening section  40  forms a single piece with shaft  8  which is molded onto rotor boss  11  to form one unit. Shaft  8  and intermediate fastening section  40  comprise two metal parts press fitted together and so even if the temperature varies looseness and clattering will not easily occur. In addition to rotor boss  11  being tightly fixed to intermediate fastening section  40 , boss  11  and intermediate fastening section  40  are rigidly mounted. As a result, shaft  8  and boss  11  are tightly fixed, and even if thermal stress or vibrational shock are received, shaft  8  and boss  11  will not easily separate. 
     FIG. 7 shows a 4th embodiment of the intermediate fastening section, in which (a) is the front view of the part and (b) is a sectional view. It can be seen from FIG. 7 that intermediate fastening section  50  is formed in a cap shape, in the lower part of which the neck  51  is shaped so as to achieve a coupling with shaft  8 , and in the center of which is through hole  52 , through which passes shaft  8 . In order to strengthen the coupling to the boss, the side surface  53  of intermediate fastening section  50  can be knurled. In this way, intermediate fastening section  50  forms a single piece with shaft  8  which is molded onto rotor boss  11  to form one unit. Shaft  8  and intermediate fastening section  50  comprise two metal parts press fitted together and so even if the temperature varies looseness and clattering will not easily occur. In addition to rotor boss  11  being tightly fixed to intermediate fastening section  50 , boss  11  and intermediate fastening section  50  are rigidly mounted. As a result, shaft  8  and boss  11  are tightly fixed, and even if thermal stress or vibrational shock are received, shaft  8  and boss  11  will not easily separate. 
     FIG. 8 shows a 5th embodiment of the intermediate fastening section, in which (a) is the front view of the part and (b) is a sectional view. Intermediate fastening section  60  is composed of the cylindrical neck  61  pressing on the tip of shaft  8 , flange  62  which projects from the upper edge of neck  61  in a direction orthogonal to the axis of the cylinder, six mounting arms  63  which project from flange  62  in the emission direction, and the through hole  64  in the center of neck  61  through which passes shaft  8 . 
     In the same way as the above embodiments, the knurled section  15  of shaft  8  is press fitted into the neck  61  of through hole  64 . In this way, intermediate fastening section  60  forms a single piece with shaft  8  which is molded onto rotor boss  11  to form one unit. Shaft  8  and intermediate fastening section  60  comprise two metal parts press fitted together and so even if the temperature varies looseness and clattering will not easily occur. In addition to rotor boss  11  being tightly fixed to neck  61 , the six mounting arms  63  project on the inside of boss  11 , firmly securing boss  11  and intermediate fastening section  60  to each other. As a result, shaft  8  and boss  11  are tightly fixed, and even if thermal stress or vibrational shock are received, shaft  8  and boss  11  will not easily separate. 
     Although the present invention has been described above by means of embodiments, various modifications and applications, for example to the shape of the single unit comprising intermediate fastening section and shaft, are not excluded from the scope of the present invention. 
     As described above in detail, the present invention uses an intermediate fastening section on the shaft to strengthen the coupling between shaft and fan blades, increase the anti-force of a shaft falls out, and at the same time ensure that the perpendicularity of the shaft with the fan blades is maintained even under excessive operating conditions, with the result that vibration does not increase during rotation. 
     In the present invention, when a shaft and an intermediate fastening section both were made of metal and engaged fixedly together, the effect of strengthening the coupling between them are increased further. 
     The other present invention uses a through hole formed in the neck of the intermediate fastening section, into which the shaft is strongly pressed, thus increasing the area of the connecting surface with the boss on the neck, and which allows the strengthening of the coupling between shaft, intermediate fastening section and boss. 
     In the invention, when the fixing arms was extended on the boss, the strengthening of the coupling between shaft, intermediate fastening section and boss is increased further. 
     The another present invention, the knurling to the section coupling the shaft and the intermediate fastening section, and to the section coupling the boss and the intermediate fastening section is added, thus making it possible to greatly strengthen the coupling between shaft, intermediate fastening section and boss.