Because same magnetic flux is used to control rotor as to drive it, size, weight, and power required are minimized. Constant total current keeps motor torque invarient, and absence of mechanical bearings eliminates wear and reduces frictional power loss

Studer, P. A.

English

NASA Technical Reports Server

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August 1973	 -	 B73-10304 
NASA TECH BRIEF S	 Goddard Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
An Electric Motor with Magnetic Bearings: A Concept 
.
The problem: 
The rotors of electric motors and generators are sup-
ported by mechanical bearings and bushings. These 
bearings have a limited life, can operate only at limited 
speeds, and require frequent lubrication. 
The solution: 
A new concept in electric motors that uses the 
magnetic fluxes that drive the rotor as a rotor bearing. 
How it's done: 
A sectional view of a dc motor with magnetic 
bearings is shown in Figure 1. The motor has four 
parallel magnetic pole pieces centered on two mutually
perpendicular axes. Two of these are shown in the 
illustration. The armature is a circular iron core with 
teeth and is attached to the pole piece by a non-
magnetic insulating material. The rotor consists of two 
toothed iron rings that are connected by a nonmagnetic 
binder, but are otherwise separated by an air gap. Figure 
2 is a view of the rotor, armature, and pole piece. 
The legs of the pole pieces and the armatures are 
each wound with copper wire. The flux flow is de-
termined by the width of the air gaps in the motor. As 
shown in Figure 2, the flux out of the first rotor segment 
and into the second rotor segment interacts with the 
current in the armature to produce a torque that drives 
the rotor. 
Potting	 Pole 
Compound	 Piece	 .	 Armature
.
Figure 1. Cross Sectional View of Motor Showing 
Two of Four Pole Pieces.
(cdntinued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.	 .
https://ntrs.nasa.gov/search.jsp?R=19730000304 2020-03-17T06:59:51+00:00Z
The brushless photoelectric commutator is triggered 
by slots in a flange attached to the end ring (which is 
attached to the rotor binders). As the slots rotate 
between the fixed light source and photo detector, 
switching voltages are fed to an electronic network that 
controls the current direction in the armature coils. 
The rotor is kept properly aligned by the driving 
magnetic forces, rather than by mechanical bearings. 
Axial motion of the rotor is automatically prevented by 
the magnetic reluctance. The flux tends to follow the 
path of least magnetic reluctance, and the motor is 
designed so that any axial motion of the rotor would 
lengthen this path. Thus the magnetic force opposes 
the motion. The transverse motion of the rotor (lateral 
motion in the drawings) is maintained by varying the 
ce 
Figure 2. Detailed View of Rotor Armature and a Pole Piece 
Showing Magnetic Flux Lines.
current in the windings around the pole pieces. De- 
tectors that determine the position of the rotor are 
connected to a control network that adjusts the current 
to center the rotor. Torsional stability, or resistance to 
tilt, requires either a motor with a large diameter or two 
units axially spaced on the same shaft. 
Because the same magnetic flux is used to control the 
rotor as to drive it, the size, weight, and power 
required are minimized. The constant total current 
keeps the motor torque invarient, and the absence of 
mechanical bearings eliminates wear and reduces fric-
tional power loss. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP73-1 0304 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,694,041). Inquiries concerning nonex-
clusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Goddard Space Flight Center 
Code 204 
Greenbelt, Maryland 20771 
Source: Philip A. Studer
Goddard Space Flight Center
(XGS-07805)
. 
. 
B73-10304	 Category 01


An electric motor with magnetic bearings: A concept

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