Patent ID: 8294319

Claim:
A motor rotor comprising: (a) a hollow cylindrical motor shaft; (b) a hollow cylindrical permanent magnet surrounding the motor shaft around an axis; (c) a pair of end rings surrounding the motor shaft around the axis and pinching the permanent magnet from both sides in an axial direction; and (d) a hollow cylindrical outer sleeve surrounding the permanent magnet and the pair of end rings in a fastening state around the axis, wherein the hollow cylindrical outer sleeve surrounding the permanent magnet and the pair of end rings in the fastening state around the axis is fitted to the permanent magnet and the pair of end rings by a shrink fit so the hollow cylindrical outer sleeve applies a compression load to the permanent magnet and to the pair of end rings that is sufficient to prevent idle running of the permanent magnet and the pair of end rings when the motor rotor is rotating at a maximum rotating speed, and wherein the hollow cylindrical outer sleeve comprises two end portions, wherein one end portion or both of the two end portions have been pruned sufficiently to correct a rotating balance of the motor rotor, wherein one end portion or both of the two end portions of the outer sleeve protrudes further in the axial direction than an end surface of one or both of the end rings.