The present invention relates to a method of manufacturing an electric motor for use with a household electrical appliance such as an air conditioner, industrial equipment and the like, and more particularly to a rotor of the electric motor causing little vibration during rotation.
The electric motor has been used for various electrical products, and as regards the air conditioner, in most cases, for its fan motor, there has been used an inner rotor type fan motor, in which a rotor is arranged inside a stator for generating a revolving magnetic field.
As the air conditioner is installed indoors, silence is required of the electric motor. In order to comply with this request, the inner rotor type has been improved in various ways, and its one example has been disclosed in Japanese Patent Application published under Publication No. 7-32841.
As shown in a cross-sectional view of FIG. 4 and a side view of FIG. 5, the rotor of this electric motor has a rotating shaft 1 and a permanent magnet 3 formed in a ring shape to be arranged coaxially to the rotating shaft 1. A rotational support (core) 2 having smaller outside diameter than an inside diameter of the permanent magnet 3 is fixed to the rotating shaft 1.
On coupling the rotating shaft 1 to the permanent magnet 3, a pair of left and right cushioning members 4 and 5 made of rubber is fitted in from the opposite sides respectively along the axial direction of the rotating shaft 1 in such a manner that they sandwich the rotational support 2 from both sides and that they enter between the rotational support 2 and the permanent magnet 3.
Thus, after end plates 6 and 7 are applied to the outside of each cushioning member 4, 5 while predetermined pressure is being applied, several (two pieces in this example) pins 8 are inserted through from one end plate 6 side to the other end plate 7, and their pin ends are fastened by belleville spring-shaped stoppers 9.
Thereby, the cushioning members 4 and 5 expand by pressure to be given by the end plates 6 and 7 to be brought into tight contact with the rotational support 2 and the permanent magnet 3 so that the rotational shaft 1 and the permanent magnet 3 are integrally assembled.
According to this structure, even if vibration is caused in the permanent magnet 3 during rotation, the vibration is absorbed by the cushioning members 4 and 5, and is not conveyed to the rotating shaft 1, and therefore, a vibration isolation effect is exhibited. Also, the structure of the cushioning member 4 or 5 is made bilaterally symmetrical, whereby both inclination and eccentricity of the permanent magnet 3 can be prevented. However, there was the following problem in the manufacture.
More specifically, in order to make a contact area between the rotating shaft 1 and the cushioning members 4, 5 larger, and to strongly couple them, it is necessary to fix the rotational support 2 to the rotating shaft 1. Also, in order to prevent the permanent magnet 3 from inclining and decentering, two cushioning members 4 and 5 having the left-right symmetrical shape are required, and in addition, the end plates 6 and 7 for fixing those, pins 8 and stoppers 9 are required, and the total number of parts becomes large to increase the manufacturing cost.
Next, as a result of a trial operation by actually mounting, for example, a fan to the rotating shaft 1 as a load after an electric motor is assembled using this rotor, when natural frequency of the load coincides with torsional natural frequency of the rotating shaft 1 to cause resonance, the design is forced to be substantially changed. Because the number of parts is large, it may come to design the electric motor again at the worst.