Patent ID: 8598763

Claim:
A field element, comprising: a plurality of field magnets; and a field element core having: a perimeter exposed around a predetermined axis; and a plurality of field magnet insertion holes disposed circularly around said predetermined axis, at least one of said plurality of field magnets being inserted into each of said at least one of said plurality of field magnet insertion holes, wherein: said at least one of said plurality of field magnets inserted into each of said plurality of field magnet insertion holes is disposed with a magnetic pole surface of a single polarity facing said perimeter; one of said plurality of field magnet insertion holes and another of said plurality of field magnet insertion holes are adjacent to each other in a circumferential direction with said predetermined axis being a center, said magnetic pole surface of said single polarity of said at least one of said plurality of field magnets inserted into said one of said plurality of field magnet insertion holes and said magnetic pole surface of said at least one of said plurality of field magnets inserted into said another of said plurality of said field magnet insertion holes being different from each other in polarity; between a first position positioned in said circumferential direction at a center of said one of said plurality of field magnet insertion holes in said circumferential direction and a second position positioned in said circumferential direction at which a center between said one of said plurality of field magnet insertion holes and said another of said plurality of field magnet insertion holes in said circumferential direction, a distance between said predetermined axis and said perimeter decreases in a monotonically non-increasing manner from said first position toward said second position along said circumferential direction and then increases in a monotonically non-decreasing manner; each of said plurality of field magnet insertion holes has, at both ends in said circumferential direction, first cavity portions on a side closer to said perimeter than said at least one of said plurality of field magnets inserted thereinto; said field element core further has second cavity portions each disposed along said perimeter on said first position side with respect to said first cavity portions, apart from said first cavity portions in said circumferential direction; at a point on said perimeter, said distance turns from decreasing to increasing between said first position and said second position is positioned on a side closer to said second position in said circumferential direction than an end of said second cavity portion on said first position side in said circumferential direction; and said first cavity portion and said second cavity portion are substantially positioned between said point and said second position in said circumferential direction.