Abstract-Electric city commuters are vehicles used for commuting from suburbs to inner cities and for movement within cities. Because of the short distances that they cover and their small battery size, such vehicles are beginning to attract attention. Generally, a high-performance permanent magnet (PM) composed of rare earth elements, such as neodymium and dysprosium, is used in the inwheel PM synchronous motor (PMSM) of an electric city commuter. However, rising prices of rare earth elements and export restrictions on them are serious problems. Development of an in-wheel PMSM that does not utilize rare earth PMs is therefore highly desirable for electric city commuter vehicles. Accordingly, our research group has focused on a surface PM type axial gap structure that can achieve a high torque density and a short motor length in the axial direction. The designed motor structure with ferrite PMs replacing the rare earth PMs and the results of a three-dimensional finite element analysis are introduced in detail in this paper. Moreover, to examine the fundamental characteristics of the designed motor, a prototype is produced and tested.Index Terms-permanent magnet synchronous motor, electric city commuter, axial gap motor, surface permanent magnet rotor structure, ferrite permanent magnet

Powerful rare earth permanent magnets (PMs) are generally utilized in in-wheel PM synchronous motors for electric city commuters. However, the use of rare earth PMs has become undesirable due to high prices. An in-wheel PM synchronous motor that does not employ rare earth PMs therefore needs to be developed. We have previously proposed an in-wheel axial-gap motor that can generate high torque density and has features such as a coreless rotor structure with ferrite PMs and a reduction gearbox inside the stator. Through further research, we confirmed that suppression of eddy current loss arising in the rotor is important for attaining higher efficiency in high output motors. Accordingly, here we introduce an improved rotor with slits which can suppress eddy current loss. The results of experiments on a new prototype show that the improved rotor is effective in producing high efficiency and can satisfy the properties demanded of the in-wheel motors for electric city commuters.

Small electric vehicles called city commuters are used for commuting and traveling short distances within cities. These vehicles have been extensively researched and developed because of their high environmental performance and small battery size. The in-wheel permanent magnet synchronous motor (PMSM) for electric city commuters generally utilizes powerful rare earth permanent magnets (PMs). However, the employment of rare earth PMs should be reduced, owing to increasing prices and export restrictions on rare earth materials, making it necessary to develop an in-wheel PMSM that does not use rare earth PMs. We propose a ferrite PM-type axial gap motor that generates high torque density and has features such as a coreless rotor structure and a reduction gearbox on the inner side of the stator. Detailed operational characteristics of the proposed motor remain unverified by experiment, so this paper presents such operational characteristics as obtained from experimentation on a prototype.

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