1. Abstract

It is very important to improve the motor efficiency because their total power consumption occupies over 1/2 of domestic power consumption. And noise reduction is strongly required because many motors are used in daily life. To solve these motor common problems, we developed a new technologies that assemble the motor with measuring the amount of eccentricity and realize a motor with almost zero eccentricity. We make the clearance between the stator and rotor short and we also devise the manufacturing method of the motor. As a result, the noise level of the newly developed motor is very low, and the efficiency of the motor is improved by 3% compared with the conventional motor.

2.Contents of the technology

The developed technology is what we devise with a novel idea. They are briefly explained below.

(1) Measurement and manufacturing technology to reduce motor eccentricity to almost zero

In order to reduce the motor noise, it is important to reduce the eccentricity of the rotor and stator. However, there is a limit in the improvement in machining accuracy and assembly accuracy of each part. Through this development, we found out we can detect the eccentricity using the winding which is a component of the motor (Fig.1). We use the detecting eccentricity value to the manufacturing process, so that we developed a motor of eccentricity was almost zero. As a result, the electromagnetic noise was greatly reduced (Fig. 2). And, since eccentricity of the motor was made to be almost zero, the gap length between stator and rotor was shortened to 1/2 of the conventional one, and high efficiency was realized.

(2) Manufacturing technology to improve the winding density of the stator

In order to improve the winding density for the space for winding space, we have developed a method in which the stator is divided, the structure of the insulating member is devised, and the stator is press-fitted after winding. As a result, the total length of the windings was reduced to 1/2 of the conventional one, and the amount of copper and loss of the stator were drastically reduced (Fig. 3).

(3) Twisting process technology to reduce the rotor loss

We found out that the short circuit between rotor core and aluminum is a main factor for the loss of the rotor. Therefore, we devised an original method to insulate the rotor core and aluminum by twisting process for the rotor (Fig. 4). The loss in the rotor was drastically reduced by this manufacturing process.

3. Summary

As a result of applying these technologies to an induction motor for an exhaust fan, almost no noise was generated, and motor efficiency was improved by 3%, and a volume reduction of 62% was realized in a motor of equivalent efficiency. This technology is a common technology that can be applied to other motors, and since it is product development that enables social contribution such as environmental improvement, I felt the importance of mechanical engineering again.

(a) Method for applying voltage      (b) Relation between voltage and eccentricity

Fig.1 Development method for the motor eccentricity sensing

(a) Newly developed motor　　　　　　 (b) Conventional motor

Fig.2 Effect of the noise reduction

(a) Newly developed motor　 (b) Conventional motor

Fig.3 Photograph of the stator portion

Fig.4 Insulation method by the rotor twisting process

Yoshio Yoshikuwa*1

Haruyuki Kometani*2

Yoshinori Miyamoto*2

Masaki Kameyama*2

Toshihiko Mizutani*2

*1 Member, Mitsubishi Electric Corporation（2-7-3, Marunouchi, Chiyoda-ku,Tokyo, 100-8310, Japan）

^*2 Mitsubishi Electric Corporation（2-7-3, Marunouchi, Chiyoda-ku,Tokyo, 100-8310, Japan）