EV駆動モータ用大型Nd-Fe-Bリング磁石について

概要

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A radially oriented Nd-Fe-B ring magnet to be installed in a EV driving motor was made by backward extrusion of a preform which was made from melt-spun ribbons. The magnet has an outer diameter of 139mm, an inner diameter of 127mm, and a height of 100mm. The magnetic properties and the multi-pole magnetizability of the huge ring magnet were investigated. And, a suitable material as an inner yoke for the magnet is also reported.The ring magnet shows the maximum energy product of about 33MGOe and the intrinsic coercivity of about 16kOe except in the initially extruded portion which was not subjected to sufficient deformation.The ring magnet was magnetized from the outer diameter side to 10 poles with various conditions. The magnetization at higher electric capacitance was more effective in obtaining a high flux density than magnetization at higher voltage.Thermal stress which is caused by the thermal expansion difference between a Nd-Fe-B ring magnet and an inner yoke (S45C or Invar alloy) was estimated. Invar alloy as an inner yoke shows much smaller thermal stress in comparison with the critical stress of a magnet.
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