Current Situation of Motors for Industrial and Home Appliances
As with other equipment, high reliability, high efficiency, small size and light weight, low vibration, low noise, and low cost are required for motors for industrial and home appliances. In order to meet these requirements, while improving the design, it is also necessary to improve the magnet material and production technology to achieve high efficiency, miniaturization and light weight of the motor according to the application. However, these methods have limitations, so it is very important to apply new materials and improve motor structures in motor technology development. As soft magnetic materials for electromagnetic equipment, dust cores and amorphous metals have been developed. Compared with electrical steel sheets, the dust core is a fine iron powder coated with an insulating film, which reduces eddy current losses. Motors using this material have been used in some fields, and are currently being studied for application in a wider range of fields. In addition, amorphous metals used in practical applications such as transformers have higher magnetic permeability than electrical steel sheets, and iron loss is very small, so it is expected to greatly improve the efficiency of motors. The following will introduce the high efficiency, small size and light weight of the motor when two soft magnetic materials, powder magnetic core and amorphous metal, are used in the motor.
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Motor structure and existing problems
Motor losses are roughly divided into copper losses (induction motors are divided into primary copper losses and secondary copper losses), iron losses, mechanical losses and stray load losses. Among these losses, most of the losses are copper losses and iron losses, and reducing these two losses can achieve high motor efficiency. Regarding copper loss, for a motor in which electrical steel sheets are used as iron core materials, the iron core is a two-dimensional structure composed of laminated electrical steel sheets. When windings are wound, the windings at both ends of the iron core have no effect on the torque, resulting in copper loss. Copper losses can be reduced by densification of the windings and removal of axial ends. This shows that the motor structure should be further studied. For iron loss, the use of powder magnetic core can reduce the eddy current loss, and the use of amorphous metal can reduce the iron loss by an order of magnitude.
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Motors with Dust Cores
The structure of the powder magnetic core is to compress the iron powder covered by the insulating film, so it is characterized by ensuring the insulation between the iron powders, which can reduce the eddy current loss, and can adopt a three-dimensional design. The disadvantage is that if the forming density is not high, only the characteristics of low magnetic permeability and saturation magnetic flux density can be obtained, so there are problems such as high pressure must be applied during compression forming, low mechanical strength of the formed body, and difficult operation. In the study of the motor structure, a claw-shaped magnetic pole structure motor (claw-tooth type motor: pattern design patent registered by Hitachi, Ltd.) is proposed that fully utilizes the three-dimensional isotropic magnetic properties of the powder magnetic core. This structure can achieve the above-mentioned high-density winding and remove the axial ends, and is expected to achieve miniaturization and high efficiency compared with the traditional slot structure motor. The structure and materials of this motor are all new motor structures that are completely different from the traditional concept. The single-phase stator core is a claw-toothed iron core with a three-dimensional claw-shaped structure. In addition, the rotor has a multi-pole magnet structure having NS poles in the circumferential direction. The stator iron cores of each phase are independently arranged in the axial direction, so they are stacked at the same distance from the magnetic poles of the rotor to form a three-phase claw-toothed iron core. The magnetic properties of the powder magnetic core depend on the density change of the formed body. The higher the density, the greater the magnetic permeability, which is more beneficial to the motor. In order to achieve high efficiency, small size and light weight of the motor, the density is required to be greater than 75mg/m3. The developed claw-tooth type structure has a plurality of parts with small cross-sections in the pressing direction such as the tip of the claw. Since the pressing area of the stamping die punch is small, when the required pressure is applied, a die may be generated. damage, etc. This problem is solved by adopting the shape of the claw teeth and balancing the motor characteristics to reduce the stress on the metal mold during molding. The above is the result of the trial production of the 200W claw motor. Compared with the traditional slot-type motor, the shaft length of the motor is reduced by about 1/2, and the efficiency is more than equal to that of the traditional motor.
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Motors with Amorphous Metals
The saturation magnetic flux density of amorphous metal is low, but its magnetic permeability is high, and the iron loss is more than an order of magnitude lower than that of electrical steel sheet. The iron core is made of amorphous metal, which can greatly reduce the iron loss and is expected to achieve high efficiency. Copper losses can be reduced by the high lamination factor of the winding. However, the thickness of amorphous metal is thinner than that of electrical steel sheet used in ordinary motors, which is less than 1/10 of that of electrical steel sheet, and its hardness is several times that of electrical steel sheet. Therefore, it is difficult to process iron cores for motors with complex shapes, and its application range is not wide. In order to use such amorphous metals for motor cores, the disadvantages of amorphous metals must be overcome. Therefore, a motor structure in which a wound iron core is used as a motor iron core without processing such as punching of an amorphous metal has been studied. The traditional slot structure motor is composed of rotors with radial magnetic flux on the stator core. To use a wound iron core, the connection between the magnetic pole part and the yoke part and the front end of the magnetic pole are arc-shaped, and the wound iron core is difficult to achieve. In order to use a wound iron core, as a structure without a yoke, a structure equipped with permanent magnet rotors on both sides is adopted, as shown in Figure 1. The permanent magnets used are not rare earth magnets, but sintered ferrite magnets. The production of the wound iron core has a great influence on the performance of the motor. As a wound iron core suitable for an axial type motor, the shape of the wound iron core is determined in consideration of factors such as the space at which the winding starts, the winding radius, and the winding space. In this way the windings can become aligned coils. The amorphous metal used is a foil with a thickness of 25 μm, which is cut and processed to a predetermined size. Amorphous metal has a low lamination factor and poor magnetic properties, so the gap between the foils should be as small as possible during coiling. The stator is formed by arranging the wound iron core into which the winding group is inserted and arranged in the circumferential direction, and using a resin mold. The rotor is a permanent magnet structure in which magnetism is fixed parallel to the axial direction of an iron yoke. The application effect of the trial production of 200W amorphous wound iron core, compared with the traditional motor, the efficiency can reach the same level or above.
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Epilogue
In the future, motors for industrial and home appliances will usher in a new era of soft magnetic materials. To cope with this era, cooperation between materials and motor manufacturers will be very important.
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