The Morrison rotor, named after itsinventor, is a hybrid rotor for use in abearingless switched-reluctance electricmotor. The motor is characterized asbearingless in the sense that it does notrely on conventional mechanical bear-ings: instead, it functions as both a mag-netic bearing and a motor. Bearinglessswitched-reluctance motors are attrac-tive for use in situations in which largevariations in temperatures and/or otherextreme conditions preclude the use ofconventional electric motors and me-chanical bearings.

In the Morrison motor, as in a priorbearingless switched-reluctance motor, amultipole rotor is simultaneously levi-tated and rotated. In the prior motor, si-multaneous levitation and rotation areachieved by means of two kinds of statorwindings: (1) main motor windings and

(2) windings that exert levitating forceson a multipole rotor. The multipolegeometry is suboptimum for levitation inthat it presents a discontinuous surface tothe stator pole faces, thereby degradingthe vibration-suppression capability ofthe magnetic bearing.

The Morrison rotor simplifies the sta-tor design in that the stator containsonly one type of winding. The rotor is ahybrid that includes both (1) a circularlamination stack for levitation and (2) amultipole lamination stack for rotation.A prototype includes six rotor polesand eight stator poles (see figure). Dur-ing normal operation, two of the fourpairs of opposing stator poles (eachpair at right angles to the other pair)levitate the rotor. The remaining twopairs of stator poles exert torque on thesix-pole rotor lamination stack to pro-

duce rotation.The relative lengths of the circular

and multipole lamination stacks on therotor can be chosen to tailor the per-formance of the motor for a specificapplication. For a given overall length,increasing the length of the multipolestack relative to the circular stack re-sults in an increase in torque relative tolevitation load capacity and stiffness,and vice versa.

This work was done by Carlos R. Morrison ofGlenn Research Center. Further informa-tion is contained in a TSP (see page 1).

Inquiries concerning rights for the com-mercial use of this invention should be ad-dressed to NASA Glenn Research Center, Commercial Technology Office, Attn: SteveFedor, Mail Stop 4-8, 21000 BrookparkRoad, Cleveland Ohio 44135. Refer toLEW-17316

ASSEMBLED MOTOR ENLARGED VIEW OF ROTOR

Circular Lamination Stack

Six-Pole Lamination Stack

Stator pole(One of Eight)

In This Switched-Reluctance Bearingless Motor, the rotor was simultaneously levitated and rotated at a speed of 6,000 rpm.

Improved Bearingless Switched-Reluctance MotorPerformance is better and design simpler, relative to a prior bearingless switched-reluctance motor.John H. Glenn Research Center, Cleveland, Ohio

28 NASA Tech Briefs, October 2003