US 20030122439A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2003/0122439 A1
(43) Pub. Date:
Horst
(54)
DOUBLY SALIENT MACHINE WITH
ANGLED PERMANENT MAGNETS IN
STATOR TEETH
(52)
Jul. 3, 2003
US. Cl. ...................................................... .. 310/154.11
(57)
ABSTRACT
(75) Inventor: Gary E. Horst, Manchester, MO (US)
Correspondence Address:
MICHAEL J. THOMAS
HARNESS, DICKEY & PIERCE
7700 Bonhomme Avenue
Suite 400
St. Louis, MO 63105 (US)
(73)
Assignee: Emerson Electric Co.
(21) Appl. No.:
(22)
Filed:
10/035,366
Dec. 28, 2001
Publication Classi?cation
(51)
Int. Cl.7 .................................................. .. H02K 21/26
Permanent magnet machines including doubly salient
machines having one or more permanent magnets located at
least partly and preferably entirely Within the stator teeth,
thereby avoiding weakening of the stator structure While
reducing acoustic noise. The magnets may be located in only
a subset of the stator teeth, thereby loWering magnet material
and manufacturing costs, and all such magnets may have
north poles directed toWard an interior of the machine,
resulting in reduced cogging and negative torques With
improved torque densities. The permanent magnets may also
extend Within the stator teeth on an angle or diagonal,
thereby alloWing use of magnets Which are Wider than the
teeth themselves to produce greater ?ux. Further, a magne
tizing device having a single coil may be used to simulta
neously magnetiZe all the stator magnets With a common
polarity.
Patent Application Publication
FIG. 1
Jul. 3, 2003 Sheet 1 0f 18
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FIG. 6
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Patent Application Publication
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DOUBLY SALIENT MACHINE WITH ANGLED
PERMANENT MAGNETS IN STATOR TEETH
FIELD OF THE INVENTION
[0001] The present invention relates generally to electric
machines, and more particularly to doubly salient machines
having stator teeth With angled permanent magnets therein.
BACKGROUND OF THE INVENTION
[0002] A variety of permanent magnet machines, includ
ing doubly salient machines, are knoWn in the art in Which
permanent magnets are positioned Within the frame or back
iron of a stator. This is typically done to accommodate
relatively large magnets capable of producing signi?cant
?ux. As recogniZed by the inventor, hoWever, positioning
permanent magnets each having inWardly facing north
poles, a ?rst plurality of stator teeth each extending along a
radial axis from the frame’s inner peripheral edge toWard the
central axis, and a second plurality of stator teeth extending
from the frame’s inner peripheral edge toWard the central
axis. Each of the ?rst plurality of stator teeth has one of the
permanent magnets located at least partly therein, While the
second plurality of stator teeth each have no permanent
magnets located therein. The ?rst plurality of stator teeth are
each positioned directly betWeen tWo of the second plurality
of stator teeth. The north poles of the permanent magnets are
each oriented at an oblique angle relative to the radial axis
along Which its corresponding one of the stator teeth
extends. Each permanent magnet and its corresponding one
of the stator teeth has a Width extending in a direction of
rotation of a rotor When the rotor is mounted for rotation
structure, including along those portions Where the stator
about the central axis. The Width of each permanent magnet
is greater than the Width of its corresponding one of the
magnets in the stator frame tends to Weaken the stator
teeth meet the stator frame, and often leads to acoustic noise
stator teeth.
problems. In many designs, permanent magnets are associ
ated With each stator pole, often With an alternating polarity
for each adjacent stator tooth. As recogniZed by the inventor,
hoWever, such a con?guration requires an excessive number
[0006] In accordance With a further aspect of the inven
tion, a permanent magnet machine includes a stator of the
type described herein.
of permanent magnets as Well as a relatively complex device
[0007]
for magnetiZing the stator magnets, thus increasing the
complexity and manufacturing cost of the permanent magnet
machine.
In accordance With yet another aspect of the inven
tion, a method is provided for magnetiZing a stator of an
electric machine having a plurality of stator teeth spaced
about a central axis, and a plurality of magnets, using a
magnetiZing device Which includes a post and a coil extend
SUMMARY OF THE INVENTION
[0003] In order to solve these and other needs in the art,
the inventor hereof has succeeded at designing and devel
oping permanent magnet machines, including doubly salient
machines, having one or more permanent magnets located at
least partly and preferably entirely Within the stator teeth,
thereby avoiding Weakening of the stator back iron structure
While reducing acoustic noise. In one embodiment, perma
nent magnets are located in only a subset of the stator teeth,
thereby loWering magnet material and manufacturing costs.
In another embodiment, all such magnets are oriented With
their north poles facing inWardly (i.e., toWard an interior of
the machine), resulting in reduced cogging and negative
torques With an improved torque density. The permanent
ing around a central axis. The method includes positioning
the stator relative to the magnetiZing device With the central
axis of the stator generally parallel to the central axis of the
coil, and With the post extending adjacent the plurality of
stator teeth, and energiZing the coil to induce ?ux through
the post, through at least some of the stator teeth, and
through at least some of the magnets to thereby magnetiZe
at least some of the magnets.
[0008] While some of the principal features and advan
tages of the invention have been described above, a greater
and more thorough understanding of the invention may be
attained by referring to the draWings and the detailed
description of preferred embodiments Which folloW.
magnets may also extend Within the stator teeth on an angle
or diagonal, thereby alloWing use of magnets Which are
BRIEF DESCRIPTION OF THE DRAWINGS
Wider than the teeth themselves to produce greater ?ux.
Further, a magnetiZing device having a single coil may be
used to readily and simultaneously magnetiZe all the stator
[0009] FIG. 1 is a cross-sectional vieW of a doubly salient
machine according to one embodiment in Which permanent
magnets are positioned Within the stator teeth.
magnets With a common polarity.
[0004]
In accordance With one aspect of the present inven
tion, a stator for use in a permanent magnet machine
includes a frame having an outer peripheral edge and an
inner peripheral edge extending about a central axis, a
plurality of stator teeth each extending along a radial axis
from the frame’s inner peripheral edge toWard the central
axis, and at least one permanent magnet located at least
partly Within one of the stator teeth, Wherein said one
permanent magnet is oriented at an oblique angle relative to
the radial axis along Which said one of the stator teeth
extends.
[0005]
In accordance With another aspect of the invention,
[0010] FIG. 2 illustrates torque curves for the doubly
salient machine of FIG. 1.
[0011]
FIG. 3A illustrates a prior art sWitched reluctance
motor having no stator magnets.
[0012] FIG. 3B illustrates a torque curve for the conven
tional sWitched reluctance motor of FIG. 3A.
[0013]
FIG. 4 is a cross-sectional vieW of a doubly salient
machine having permanent magnets in only every other
stator tooth.
[0014] FIG. 5 illustrates torque curves for the doubly
salient machine of FIG. 4.
a stator for use in a permanent magnet machine includes a
frame having an outer peripheral edge and an inner periph
eral edge extending about a central axis, a plurality of
[0015] FIG. 6 illustrates an exemplary stator coil for the
doubly salient machine of FIG. 4.