Embodiments disclosed herein describe methods for improved permanent magnet motor rotor systems for submersible electric motors. The improved rotor system includes a single piece of material shaft with surface mounted permanent magnets. The single piece of material shaft minimizes the number of shaft bearings and locates the bearings outside of the stator windings.

The rotor includes ribs and permanent magnets mounted as spokes in pole pairs. A second wall of each rotor air gap of a plurality of rotor air gaps is parallel to an edge of a permanent magnet of the permanent magnets. A length of the second wall is less than 80% of a length of the edge. A fifth wall of each rotor air gap of the rotor air gaps is formed by a first side of a rib. Each pair of permanent magnets has an associated pair of rotor air gaps of the rotor air gaps. A first rotor air gap of each pair of rotor air gaps of the rotor air gaps is a mirror image of a second rotor air gap of each pair of rotor air gaps. Each pair of rotor air gaps is separated by an associated rib of the plurality of ribs.

A magnet unit includes a plurality of arc-shaped magnets arranged in a circumferential direction and a magnet holder to which the magnets are secured. Each of the magnets has arc-shaped easy axes of magnetization which extend more parallel to the d-axis in a region close to the d-axis than those in a region close to the q-axis. The easy axes of magnetization define arc-shaped magnetic paths extending therealong. The magnets are arranged to be separate from each other across the d-axis or the q-axis. Each of the magnets has a q-axis end surface facing in the circumferential direction and placed in surface-to-surface contact with that of the circumferentially adjacent magnet. Each of the magnets has an armature-remote peripheral surface which faces away from the armature. Each of the armature-remote peripheral surfaces facing an attachment surface of the magnet holder through a clearance which is filled with a resin adhesive.

A magnet unit includes a plurality of arc-shaped magnets arranged in a circumferential direction and a magnet holder to which the magnets are secured. Each of the magnets has arc-shaped easy axes of magnetization which extend more parallel to the d-axis in a region close to the d-axis than those in a region close to the q-axis. The easy axes of magnetization define arc-shaped magnetic paths extending therealong. The magnets are arranged to be separate from each other across the d-axis or the q-axis. Each of the magnets has a q-axis end surface facing in the circumferential direction and placed in surface-to-surface contact with that of the circumferentially adjacent magnet. Each of the magnets has an armature-remote peripheral surface which faces away from the armature. Each of the armature-remote peripheral surfaces facing an attachment surface of the magnet holder through a clearance which is filled with a resin adhesive.

A magnet orientation device includes an upper plate disposed on a magnet raw material, a lower plate disposed below the magnet raw material, and dies disposed on sides of the magnet raw material. The upper plate has a convex upward arc shape. The upper plate includes a first magnetic region and a first non-magnetic region that surround the first magnetic region and the lower plate includes a second magnetic region and a second non-magnetic region that surround the second magnetic region. A lower surface of the first magnetic region provides a plurality of grooves and an upper surface of the second magnetic region provides a plurality of protrusions. A horizontal length of the first magnetic region is greater than a horizontal length of the magnet raw material and a horizontal length of the second magnetic region is equal to or less than the horizontal length of the magnet raw material.