Flux damper for permanent magnet electric motors

Details Flux damper for permanent magnet electric motors Flux damper for permanent magnet electric motors

1995-12-22

2001-07-03

Nguyen, Tran (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S051000

Reexamination Certificate

active

06255754

ABSTRACT:

The invention concerns damping of changes in magnetic flux which occur in electric motors, thereby damping noise and vibration which the flux changes induce.
BACKGROUND OF THE INVENTION
FIGS. 1-5
provide simplified illustration of some events which occur in electric motors, and give some possible explanations of vibration and noise.
FIG. 1A
illustrates permanent magnets
3
, having poles north N and south S, as contained within a permanent magnet electric motor (motor is not shown).
FIG. 1B
illustrates an armature
6
, which includes a single-turn coil
9
and a commutator
12
. In operation, brushes
15
contact the commutator
12
.
FIG. 1C
illustrates the components of
FIGS. 1A and 1B
when assembled.
FIG. 2A
illustrates magnetic field lines
18
produced by the magnets
3
of FIG.
1
A.
FIG. 2B
illustrates current
21
induced by voltage V+ applied to the brushes
15
, and also the magnetic flux lines
24
which accompany the current
21
.
FIG. 2C
is a cross-sectional view of
FIGS. 2A and 2B
, with some of the flux lines
24
removed, and with the brushes
15
shown in contact with the commutator
12
.
FIGS. 3A through 3F
show the components of
FIG. 2C
in assembled form, and show how the magnetic flux
24
, produced by the armature
6
, rotates as the armature
6
rotates. In
FIG. 3A
, the flux
24
is directed to the left, and does not cross the south pole S. (In actual practice, some leakage flux may cross the south pole, but
FIG. 3A
is a simplification, used to illustrate major principles.)
In
FIG. 3B
, the armature
6
has rotated clockwise, and the armature's flux
24
occupies the position shown. In
FIG. 3C
, the armature flux
24
penetrates the south pole S.
In
FIG. 3D
, the armature flux
24
has disappeared, because the commutator
12
is no longer in contact with the brushes
15
. In
FIG. 3E
, the armature flux
24
has re-appeared, because the commutator re-contacts the brushes
15
. However, the flux
24
has reversed in direction, as indicated by a comparison of
FIG. 3E
with FIG.
3
C.
FIG. 3F
indicates the position of the armature flux
24
a time later than in
FIG. 3E
, wherein the flux does not penetrate the north pole N.
The sequence of
FIG. 3
provides a simple explanation of one cause of vibration. The sequence of
FIGS. 3B through 3F
show the following events:
Figure
Event
3B
No penetration of south pole.
3C
Penetration.
3D
No penetration.
3E
Penetration, but reversed in
direction.
3F
No penetration.
The sequence can be characterized as a repeated sequence of two events: flux penetration of the south pole S, followed by removal of penetration.
In effect, a magnetic field is repeatedly applied, and then removed, from the south pole S. The application of the magnetic field applies a force to the south pole S. The removal of the magnetic field removes the force. The sequence of
. . . force . . . no force . . . force . . . no force
is believed to cause vibration of the south pole S. Similar events occur with respect to the north pole N.
A second cause of vibration can be explained with reference to
FIGS. 4 and 5
. In
FIG. 4A
, an actual armature
6
comprises a rotor
30
containing slots
33
, which hold conductive bars
36
(also called armature windings). Additional conductors, indicated by the dashed lines
39
, form a conductive loop, analogous to loop
9
in FIG.
1
B.
FIG. 4B
shows the slotted rotor
30
in cross section, and includes the conductive bars
36
. When current passes through the loop comprising bars
36
and dashed lines
39
in
FIG. 4A
, the flux lines
40
shown in
FIG. 5A
are generated. Two positions which the slotted rotor occupies during rotation are shown in
FIGS. 5B and 5C
.
A significant feature of these two positions is that the flux lines must traverse different numbers of slots en route to the south pole S. That is, different flux lines follow paths through different materials. Consequently, different flux lines apply different forces to the south pole S. These differences can also cause vibration, as will now be explained.
The slots
33
in
FIG. 5A
act as an air gap, and reduce the strength of the flux lines
40
. (Even though the slots
33
contain the conductive bars
36
, the slots can be viewed, for present purposes, as being filled with air, because the magnetic permeability of the conductive bars is close to that of air, when compared with the permeability of the material of which the rotor
30
is itself constructed.
How an air-gap can change a magnetic field can be explained by an analogy. When a hand-held magnet is brought two inches from a steel nail, the nail hardly “feels” the magnet, because of the large, two-inch, air gap. However, when the magnet is brought sufficiently close to the nail, the nail snaps into contact with the magnet. The very small air gap, created when the magnet approached the nail, caused the strength of the flux lines (more precisely, the magnetic flux density) to increase.
Similarly, when the rotor
30
is in the position shown in
FIG. 5B
, the flux lines must pass through three slots, or air gaps, indicated in insert I, en route to the south pole S. In contrast, in
FIG. 5C
, the number of slots increases from three to four, as indicated in insert I
2
.
In effect, the air gap between the armature and the south pole S has increased from
FIG. 5B
to FIG.
5
C. Consequently, the “pull” which the rotor
30
applies to the south pole S, because of the flux lines
40
, decreases in FIG. C, compared with
FIG. 5B
, because of the increased air gap, similar to the case of the steel nail.
Therefore, as the armature
30
rotates, the number of slots, through which the flux lines must travel en route to the south pole S, changes, thereby changing the magnetic force applied to the south pole S. This changing magnetic force induces vibration. Some components of the vibration lie within the range of human hearing, and are perceived as audible noise.
A similar analysis applies to the north pole N.
SUMMARY OF THE INVENTION
An object of the invention is to reduce noise and vibration in electric motors.
A further object of the invention is to reduce noise and vibration caused by a changing magnetic flux applied to internal components of a permanent magnet electric motor.
In one form of the invention, a conductive ring surrounds a stationary pole of a magnet in an electric motor. When armature flux through the hole in the ring changes, a current is induced, which generates a magnetic field which compensates for the change in the armature flux, thereby tending to keep the overall flux constant.


REFERENCES:
patent: 3566251 (1971-02-01), Hoglund
patent: 3663851 (1972-05-01), Persson
patent: 3686524 (1972-08-01), Hall
patent: 3793546 (1974-02-01), King, Jr.
patent: 3929390 (1975-12-01), Simpson
patent: 4024458 (1977-05-01), Templin
patent: 4329609 (1982-05-01), Allegre et al.
patent: 5000524 (1991-03-01), Savage
patent: 5130591 (1992-07-01), Sato
patent: 5177383 (1993-01-01), Sim
patent: 5219214 (1993-06-01), Savage et al.
“Theory of Alternating-Current Machinery,” by Alexander S. Langsdorf, Second Edition, McGraw Hill, 1955; pp. 203-204.
“Control of Mechanical Vibrations in DC Machines,” by A. Foggia, et al., 1990 IEEE Industry Applications Society Annual Meeting, Seattle, WA, pp. 99-101.
“Flux Augmentation of Permanent Magnet Direct Current Machines,” by Donald F. Harker IV, M.S. Thesis, University of Missouri-Rolla, 1991.

Affiliated with

Also associated with

Rating

Flux damper for permanent magnet electric motors does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Flux damper for permanent magnet electric motors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flux damper for permanent magnet electric motors will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2513711