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In recent years, electric motors having flat shape are desired in order to minimize system size as well as enhancing the efficiency. Therefore, axial gap motors (AGMs) have attracted significant attention because they can achieve higher torque density in flat shape than that of conventional radial gap motors (RGMs). In general, AGMs employ the soft magnetic composite (SMC) for the stator core since they have three dimensional magnetic paths unlike RGMs. If AGMs employ the SMC which has low iron loss characteristic, the efficiency can be improved. On the other hand, the average torque is decreased because the SMC basically has tradeoff-relationship between the iron loss characteristic and the permeability. Hence, in this research, an AGM having coreless rotor structure that torque performance is not easily affected by the permeability of the SMC is proposed. In this paper, many virtual SMC materials which have different iron loss and permeability are considered for the proposed AGM employing the coreless rotor structure. Finally, suitable SMC characteristic to enhance the efficiency over a wide operating range is revealed by three-dimensional finite element analysis (3D-FEA).

An axial gap motor using neodymium bonded magnet, which our research group has proposed, achieved high torque density and high efficiency at high torque region in the previous paper. However, further improvement in efficiency is required in a wide operation range including not only high torque region but also low torque region. Hence, this paper discusses soft magnetic composite (SMC) suitable for high efficiency of the proposed axial gap motor. In the SMC, there is a trade-off relationship between low iron loss characteristic and high magnetic permeability. Therefore, at low torque region, the efficiency of the axial gap motor using the SMC was lower than that of the radial gap motor using the electromagnetic steel sheet. The proposed axial gap motor adopts a coreless rotor structure. Thus, it is possible to suppress the torque reduction, because the magnetic circuit of the proposed axial gap motor is hardly affected by the magnetic permeability of the stator core due to the large magnetic reluctance of the coreless rotor. For the proposed axial gap motor, HX3 of the newly material having lower iron loss characteristic than the electromagnetic steel sheet is developed, even though the magnetic permeability decreases. Consequently, improvement of efficiency and high torque are compatible by HX3. In this paper, we show the material properties of HX3 and the experimental results of a prototype machine of the proposed motor using HX3 of the newly material. From the experimental results, we report that the proposed motor can achieve improvement of efficiency around low torque region.

We developed Fe/FeSiAl soft magnetic powder cores (SMCs) for realizing the miniaturization and high efficiency of an electromagnetic conversion coil in the high-frequency range (∼20 kHz). We found that Fe/FeSiAl SMCs can be formed with a higher density under higher compaction pressure than pure-iron SMCs. These SMCs delivered a saturation magnetic flux density of 1.7 T and iron loss (W1/20k) of 158 kW/m3. The proposed SMCs exhibited similar excellent characteristics even in block shapes, which are closer to the product shapes.