1. Field of the Invention
The present invention relates to an improvement of an axial flow fan motor for use of OA (office automation) appliance.
2. Conventional Art
Since most OA appliances comprise various electronic circuits within their housings. And, every electronic part consisting of those circuits generates heat. And, due to this heat generation, electronic parts of those circuits are threatened to be broken or deteriorated, so that, in this kind of OA appliances an axial flow fan motor is used for cooling. In particular, in the recent tendency of miniaturization of OA appliances, since the influence by the above heat generation becomes great, a countermeasure against the heat has become an important technical problem. And, on the other hand, the products of OA appliances such as being mass-produced have the demand for low cost from the viewpoint of easy assembly workability.
Next, a conventional axial flow fan motor is explained based on FIG. 7, a central projection 2 is provided in a unit with a resin casing 1. Around the outer circumference of this central projection 2, iron cores 3 are fixed, around which stator windings 5 are wound through bobbins 4 made of insulating material. By this iron core 3, the bobbin 4 and the stator winding 5 the stator of the flow fan motor is formed. On the other hand, on an inner circumference of the central projection 2 bearings 6 are coupled with, and on these bearings a shaft 7 is supported. These bearings 6 are fixed by stepped portions 8 and 9 provided on the inner circumference of the central projection 2, a snap ring 10 and a spring 11. On one end of the shaft 7, a yoke 13 is fixed through a zinc casting 12 and on the inner circumference of the yoke 13, a magnet 14 is fixed. With this yoke 13 and the magnet 14, a rotor of the axial flow fan motor is formed. And on the outer circumference of the yoke 13, a resin made impeller 15 is pressed in and fixed, on which wings 16 are mounted.
FIG. 8 shows another conventional axial flow fan motor. What is different from the conventional art shown in FIG. 7 resides in that a bearing box 17 is provided separately from the central projection 2 and adhered to the inner circumference of the central projection 2. And, by a concavo-convex engagement portion 18, the bearing box 17 is prevented from being removed. Further, this bearing box 17 is made of metal in consideration of heat resistance. The other portions of that bearing box 17 are similar with what are shown in FIG. 7, so that, by attaching the similar signs to the similar portions, explanation thereof are omitted.
In the above conventional art, since what is shown in FIG. 7, the central projection 2 is provided in a unitary manner in the resin made casing 1 and adapted to couple the bearings 6 with the projection 2 to support the shaft 7, the number of parts is reduced which is advantageous in assembling and invites a low cost, however, there is another problem such as mentioned below. That is, the stator consisting of the iron core 3 and the stator winding 5 may generate heat due to the copper wearing and the iron wearing. And, the iron core 3 is mounted on the outer circumference of the central projection 2 directly, so that due to the heat generated the central portion is threatened to be deformed and accelerated in its deterioration.
Further, by the heat too generated from the electronic parts accommodated in OA appliances the central projection is threatened to be deformed and accelerated to be deteriorated. Thus, when the central projection is deformed, the shaft center of the rotor formed with the yoke 13 and the magnet 14 is made to be displaced to cause the function of the axial flow fan motor to be deteriorated, and that, due to the deterioration of the central projection, a use life of the axial flow fan motor becomes short, by which the use life of OA appliance as a whole is threatened to become short.
Next, in the conventional art shown in FIG. 8, since the bearing box 17 is made of a metal, there are following defects to be improved. That is, although, since the bearing box itself is made of a metal, there is no trouble against heat, due to the great thermal conductivity, the central projection 2 is heated indirectly. Accordingly, as well as in FIG. 7 which shows the conventional art, the central projection is deformed by the heat and accelerated in being deteriorated, and as a result the function of the axial flow fan motor and the use life thereof too are threatened to become short. In addition, in order to solve the problem it is recommended to make the casing 1, which is formed in a unitary manner with the central projection 2, with a resin having a heat resistance, however, at that time, a high priced resin has to be used in a great amount for that, so that the axial flow fan motor has to become high-priced.
Further, when the metal made bearing box 17 is inserted in the central projection 2 made of a resin, since the coefficient of thermal expansion is different between a resin and a metal with each other, there happens a case where the coupling is loosened due to the heat to be generated between different materials to be coupled. In the case, where a loosening is thus generated, since the shaft center of the rotor to the stator is resulted in being displaced, the function of the axial flow fan motor is deteriorated and a vibration is generated, which is not preferable for the OA appliance.
Still further, since the bearing box 17 and the central projection 2 are fixed by gluing, there need a application process of a glue and a drying process thereof, which invites a difficulty of an automatic assembly to cause a decrease of productivity. In addition, since the assembly of the stator and the rotor can not be carried-out before the bearing box 17 is fixed on the central projection 2 by solidification of the glue, which causes to waste time and is not preferable from the viewpoint of assembling workability and productivity. Accordingly, one object of the present invention is to provide an axial flow fan motor, in which, in order to solve the above problems, the thermal deformation and deterioration of the bearing box are reduced to maintain the function of the axial flow fan motor, prolong the use life, reduce the use amount of a high priced resin to decrease the cost and increase the assembling workability avoiding the use of glue to increase the productivity.