Small sized fan motor

A small sized fan motor is disclosed, wherein an armature is supported by a disk-shaped support in a cantilever fashion, a rotor has an outer periphery for fixedly mounting a fan having a plurality of blades thereon and an inner periphery for fixedly mounting a permanent magnet thereon in a manner that the permanent magnet surrounds the armature with a clearance being provided therebetween, and a rotational bearing having an inner race secured to the disk-shaped support and an outer race secured to the inner periphery of the rotor in a manner that the rotational bearing is arranged coaxial with the permanent magnet within the rotor.

BACKGROUND OF THE INVENTION 
The invention relates to a small sized fan motor and more particularly 
relates to a mechanism of the fan motor including a single rotational 
bearing supporting a rotor and a fan having a plurality of blades 
resulting in reduction of the axial dimension of the motor. 
So far the conventional small sized fan motors have been of a brushless 
outer rotor type using Hall generators or Hall IC. As described in the 
publication "DC Servo-Motors for Mechatronics" the third edition published 
by the publisher Sogo Denshi of Japan, such a conventional small sized fan 
motor has a center shaft rotated with a rotor, the center shaft being 
supported by a pair of rotational bearings and having a fan secured 
thereto. With such a structure being provided, it is inevitable that the 
motor is accordingly elongated in the axial direction. Therefore the 
conventional small sized fan motor has been unsuitable to be used in a 
small sized electronic apparatus, especially in a thinner apparatus. Even 
in the conventional brushless outer rotor type of motor without using a 
center shaft, a pair of rotational bearings are employed in the axial 
direction of the motor resulting in limitation of reducing the axial 
dimension of the motor. More precisely these conventional small sized fan 
motors as mentioned above have the axial dimension about 24 mm-25 mm at 
least. 
OBJECTS AND SUMMARY OF THE INVENTION 
The present invention has been provided to eliminate such a defect and 
disadvantage of the prior art. It is therefore an object of the invention 
to provide a more or less elongated rotor to accomodate therein a 
permanent magnet and a rotational bearing side by side in the axial 
direction so as to reduce the axial dimension of the motor to 
approximately 12.5 mm which is about a half of that of the conventional 
small sized fan motor. It is another object of the invention to provide a 
grooved ball bearing as the rotational bearing which is sufficient enough 
to bear the thrust load which may be caused due to the rotation of the 
fan. It is another object of the invention to provide a support on which 
the fan is rotated by way of the rotational bearing and the rotor, the 
support having a plurality of holes provided at predetermined locations 
thereof so as to automatically determine the positions of Hall generators 
employed in the motor as inserted in the holes. It is still another object 
of the invention to provide a small sized fan motor which may be easily 
and precisely assembled. 
In short, the present invention comprises an armature, a disk-shaped 
support supporting the armature in a cantilever fashion, a rotor having an 
inner periphery and an outer periphery and made of magnetizable material, 
a permanent magnet mounted with the rotor, the permanent magnet having an 
outer-periphery secured to the inner periphery of the rotor and an inner 
periphery arranged around the armature, a fan having a plurality of blades 
secured therearound and being secured to the outer periphery of the rotor, 
a rotational bearing having an inner race and an outer race, the inner 
race being secured to the support and the outer race secured to the inner 
race of the rotor in a manner that the rotational bearing is arranged 
coaxial with the permanent magnet in the axial direction with the rotor.

DETAILED DESCRIPTION OF THE INVENTION 
In reference to FIGS. 1 and 5, the small sized fan motor 1 of the invention 
substantially comprises an armature 2, a support 3 in the form of disk, a 
permanent magnet 4, a rotor 5, a fan 6 and a rotational bearing 8. 
The armature 2 is composed of a core 9 and a coil 10 wound around the core 
9 which is formed with the lamination 9a of magnetizable material such as 
a silicon steel plate. The core 9 has three poles 9b by way of example and 
the coil 10 is wound around each of these poles 9b. The core 9 has a 
center shaft 11 secured thereto, and the shaft has one end 11a fixedly 
inserted into a center hole 3a of the support 3. Thus the armature 2 is 
fixedly mounted on the support 3 which acts as a cantilever. 
The disk shaped support 3 is composed of a flange portion 3e and a cylinder 
portion 3f having a periphery 3g and the center hole 3a for supporting the 
core shaft 11. As particularly shown in FIG. 5, the flange portion 3e has 
a pair of holes 3c formed therein for securing a pair of Hall generators 
12 thereon, each having leads 12a, and another hole 3d through which the 
leads of the coil 10 is drawn out. Each of the holes 3c for securing the 
Hall generators 12 is rectangular and 2.1 mm long and 1.6 mm wide for 
example in case each of Hall generators 12 is 2 mm long and 1.5 mm wide, 
such that a gap of approximately 0.1 mm remains when each Hall generator 
12 is secured to each hole 3c. On the other hand, the hole 3d is circular. 
Further the support 3 is made of a non-magnetizable material such as a 
synthetic resin. 
The permanent magnet 4 is in the form of a ring arranged as surrounding the 
armature 2 and is rotatable with respect to the latter with an air gap C 
of a predetermined width being provided therebetween. This ring shaped 
magnet 4 may be of the type partly magnetized or may be divided into so 
many parts. 
The rotor 5 is made of a magnetizable material such as an iron in the form 
of a hollow cylinder more or less elongated in the axial direction and 
having an outer periphery 5c and an inner periphery 5a to which the 
permanent magnet 4 is secured. If the magnet 4 is made of a synthetic 
resin, this may be pressed into the rotor. If the magnet is made of 
ferrite, this may be secured to the rotor 5 by other proper means such as 
the fastening screws. 
Further the rotational bearing 8 is pressed into the rotor 5 as being 
coaxial with the permanent magnet 4. The rotational bearing 8 is 
substantially composed of an outer race 8a and an inner race 8b. The outer 
race 8a of the rotational bearing 8 is secured to the inner periphery 5a 
of the rotor 5, and the inner race 8b of the rotational bearing 8 is 
secured to the periphery 3g of the cylinder portion 3f of the support 3. 
Between the permanent magnet 4 and the rotational bearing 8 there is 
provided a thrust washer 14 which may be made of a magnetizable or 
non-magnetizable material. 
The fan 6 is in the form of a cylinder 6b having a number of blades 6a 
secured therearound. The fan 6 has a wall 6c secured to one end of the 
cylinder 6b. The wall 6c has a plurality of projections formed thereon to 
be pressed against the permanent magnet 4. The fan 6 is secured to the 
outer periphery 5c of the rotor 5 by means of any proper means and the 
like. 
The rotational bearing 8 enables the rotor 5 to rotate on the support 3 and 
is a grooved ball bearing made of a steel. The rotational bearing 8, 
however, may be preferable to be made of ceramics and the like of 
non-magnetizable material in view of the magnetic circuit to be employed. 
Thus the small sized fan motor 1 of the invention has the single rotational 
bearing 8 carries the rotor 5 and the fan 6 to enable the latter to rotate 
on the support 3. 
A disk 15 is secured to the flange portion 3e of the support 3 by means of 
fastening screws, rivets or welding. The disk 15 has three sets of 
terminals 15a, 15b, 15c arranged thereon spaced about 120.degree. C. from 
each other, which correspond to the holes 3c, 3c, 3d respectively of the 
flange portion 3e of the support 3. In combination with the small sized 
fan motor 1 of this invention, a specific control circuit is employed, 
which is disclosed in the copending U.S. patent application Ser. No. 
751,281. Due to the employment of the specific control circuit, the 
generally four leads of each Hall generator 12 may be reduced to three 
leads l2a, and accordingly each set of terminals 15a, 15b, 15c consists of 
three terminals. The leads 16 (in FIG. 3) for each Hall generator 12, 
which are soldered to the sets of terminals 15a, 15b. may be comparatively 
fine because the electric current flowing through the leads 16 is weak. On 
the other hand, the leads 18 to be soldered to the set of terminals 15c 
for the coil 10 are comparatively thick because the current flowing 
through the leads 18 is of comparatively high value. 
In reference to FIGS. 2 to 4, a case 19 for the small sized fan motor 1 is 
composed of a fan shroud 19a which is sectionally circular and a mount 19b 
of a square shape by which the case 19 is secured to an electronic 
apparatus (not shown). The mount 19b has attaching holes 19c formed at the 
four corners thereof. The fan shroud 19b is so formed as to surround the 
fan 6 with a proper clearance 20 being provided therebetween. The mount 
19b of the fan shroud 19 has a center wall 19d which is formed with a 
plurality of arcuated slots 19e as particularly shown in FIGS. 3 and 5. 
The center wall 19d has a guide wall 19f extending toward one side 19h of 
the mount 19b, and has an inner face formed with a guid groove 19g as 
particularly shown in FIG. 2. The leads 16, 18, which are soldered to the 
respective terminals 15a, 15b, 15c of the disk 15, are extended along the 
guide groove 19g of walls 19d, 19f and drawn out of the guide groove 19g 
at the side 19h of the mount 19b, and then are soldered to external leads 
21. The exposed ends of the leads 16, 18 are protected by a cover 22 at 
the side 19h of the mount 19b, the cover 21 being secured to the side 19h 
by way of the supersonic waves or the like. 
The two Hall generators 12 are partly inserted into the respective holes 
13c of the support as shown in FIG. 1 in a manner as to receive the 
magnetic flux from the inner periphery 4c of the permanent magnet 4. 
Further the Hall generators 12 are respectively located at the positions 
corresponding to the spaces between the core poles 9b of the armature 2. 
With the structure of the invention as mentioned above, when the external 
leads 21 are connected to a power source (not shown), the current is 
supplied to the armature 2 and is energized, and then the permanent magnet 
4 starts to rotate with the attracting and repulsing actions between the 
magnet 4 and the armature 2, and accordingly the rotor 5 and the fan 6 
secured to the rotor are rotated. As the result, the air flows in the 
direction as indicated by an arrow mark A in FIG. 1 to cool down the 
electronic apparatus in which the fan device of the invention is 
incorporated. If the rotational bearing 8 is made of a magnetizable 
material such as a steel iron, the rotational bearing will be attracted to 
the permanent magnet 4 during rotation thereof, and the thrust load is 
applied to the thrust washer 14. However the thrust load will give no 
adverse effect because the rotational bearing is a ball bearing of deep 
grooved type which is sufficient enough to bear the thrust load. Further 
the radial load will give no adverse effect because the outer race 8a of 
the rotational bearing 8 is made sufficiently wide and is considerably 
spaced from the inner race 8b. The rotational bearing 8 is therefore free 
from the undesired eccentric deformation during rotation thereof and will 
be smoothly rotated. 
According to the invention, since the rotor 5 is supported by a single 
rotational bearing 8, the small sized fan motor of the invention may have 
a thickness remarkably reduced to a minimum, for example, to 12.5 mm which 
has so far never been obtained. 
Further the two holes 3c of the support 3 for securing the two Hall 
generators 12 are arranged as angularly spaced from each other and each 
dimensioned more than the Hall generators such that approximately 0.1 mm 
will remain when the Hall generators are inserted into the respective to 
the support 3 with the required angular space being maintained 
therebetween. Moreover with the center shaft 11 of the armature 2 being 
pressed into the center hole 3a of the support 3, the relative positions 
will be determined between the Hall generators 12 and the poles 9b of the 
core 9. Thus the small sized fan motor of the invention is very easily 
assembled with a required accuracy. 
Although the present invention has been fully described by way of a 
preferred embodiment in reference to the attached drawings, it is to be 
noted that various changes and modifications will be apparent to those who 
are skilled in the art. Such changes and modifications will not be 
regarded as being inventive but will be regarded as being included in the 
spirit and scope of the appended claims.