Hiroyuki Mitani

Examination of an Interior Permanent Magnet Type Axial Gap Motor for the Hybrid Electric Vehicle

Hybrid electric vehicles (HEVs) that emit less carbon dioxide have attracted much attention and rapidly become widespread, but further popularization of HEVs requires further technical advancement of mounted traction motors. Accordingly, our research group focuses on axial gap motors that can realize high torque density. In this paper, an axial gap motor with a novel interior permanent magnet (IPM) rotor structure is proposed and an examination of the proposed motor at the actual motor size of an HEV is presented. For comparison, we selected the newest radial gap-type 60 kW IPM synchronous motor equipped in the third-generation Toyota Prius. Under the condition that the size of the proposed motor be the same as the comparison motor, we confirmed through three-dimensional finite-element analysis that the proposed motor could output twice the maximum torque of the comparison motor. In addition, a comparison was made with a previously reported conventional IPM-type axial gap motor, and the proposed motor was found to be more effective in generating reluctance torque. Moreover, the proposed motor exhibited sufficient durability to irreversible demagnetization of the permanent magnets, to stress caused by rotating the rotor, and to unbalanced electromagnetic forces caused by axial rotor eccentricity.

Fatigue-damage evaluation in aluminum heat-transfer tubes by measuring dislocation cell-wall thickness

Evolution of dislocation structure during low cycle fatigue in 3003 aluminum alloy was investigated for the purpose of finding a possible parameter to indicate fatigue damage prior to crack initiation. In low cycle fatigue, it is observed that by increasing the number of cycles, the dislocation structure develops to random cells, then changes to clear cells and finally to sub-grains. In other words, the cell-wall thickness decreases with increasing number of cycles. It is also found that measuring the cell-wall thickness is a valuable method to evaluate fatigue damage when the cell structure is formed. The fatigue damage index (the number of cycles/cycles up to fracture) is found to be inversely proportional to the average cell-wall thickness, regardless of the applied stress level. This phenomenon can be explained by dynamic recovery of dislocation during fatigue, i.e. mutual annihilation of dislocations, which takes place during each half cycle.