U.S. patent application number 11/311798 was filed with the patent office on 2007-07-12 for composite magnet structure for rotor.
This patent application is currently assigned to Emerson Electric Co.. Invention is credited to Gary E. Horst.
Application Number | 20070159021 11/311798 |
Document ID | / |
Family ID | 38172621 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070159021 |
Kind Code |
A1 |
Horst; Gary E. |
July 12, 2007 |
Composite magnet structure for rotor
Abstract
An interior permanent magnet electric motor. A rotor comprising
a slot radially spaced from its longitudinal axis of rotation
extending parallel to the axis. First and second magnets are
positioned in the slot and extend parallel to the axis. A first
magnet is positioned between a second magnet and the axis.
Inventors: |
Horst; Gary E.; (Manchester,
MO) |
Correspondence
Address: |
SENNIGER POWERS
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
Emerson Electric Co.
St. Louis
MO
|
Family ID: |
38172621 |
Appl. No.: |
11/311798 |
Filed: |
December 19, 2005 |
Current U.S.
Class: |
310/156.53 |
Current CPC
Class: |
H02K 1/2766
20130101 |
Class at
Publication: |
310/156.53 |
International
Class: |
H02K 21/12 20060101
H02K021/12 |
Claims
1. An electric motor rotor comprising: a core having a central
longitudinal axis and a slot radially spaced from the longitudinal
axis and extending parallel to the axis; and first and second
magnets positioned in the slot and extending parallel to the
longitudinal axis, wherein the first magnet is positioned between
the second magnet and the longitudinal axis.
2. The rotor of claim 1 wherein said core has an outer surface
parallel to said longitudinal axis, said outer surface having a
lobe.
3. The rotor of claim 2 further comprising an air space adjacent to
the first or second magnet.
4. The rotor of claim 1 wherein, when viewed in cross section, the
first magnet is arch-shaped, having a convex surface facing the
central longitudinal axis and a concave surface facing the second
magnet.
5. The rotor of claim 4 wherein at least one of the following: (1)
when viewed in cross section, the second magnet has a convex
surface generally complementary to and in contact with the concave
surface of the first magnet; and (2) when viewed in cross section,
at least a portion of the first magnet contacts the concave surface
of the second magnet.
6. The rotor of claim 1 further comprising a third magnet of the
same material as the second magnet sized and shaped substantially
the same as the second magnet.
7. The rotor of claim 6 wherein, when viewed in cross section, the
second and third magnets are substantially rectangular and at least
a portion of each is in contact with the first magnet.
8. The rotor of claim 1 wherein one of the first or second magnets
is strontium ferrite, the other of the first and second magnets is
neodymium-iron-boron, and the core is steel.
9. A method of producing an electric motor comprising: forming a
slot in a rotor core having a central longitudinal axis; inserting
a first magnet in the slot; inserting a second magnet in the slot,
wherein said first magnet is substantially between the second
magnet and the central longitudinal axis; inserting the rotor core
into a stator having windings; and connecting the windings of the
stator to a commutation circuit.
10. The method of claim 9 wherein the first magnet is strontium
ferrite, the second magnet is neodymium-iron-boron, and the core is
steel.
11. An electric motor comprising: a rotor including: a core having
a central longitudinal axis and a slot radially spaced from the
longitudinal axis and extending parallel to the axis; and first and
second magnets positioned in the slot and extending parallel to the
longitudinal axis, wherein the first magnet is positioned between
the second magnet and the longitudinal axis; a stator in magnetic
coupling relation to the rotor having windings; and a commutation
circuit electrically connected to the windings of the stator.
12. The rotor of claim 11 wherein said core has an outer surface
parallel to said longitudinal axis, said outer surface having a
lobe.
13. The motor of claim 12 further comprising an air space adjacent
to the first or second magnet.
14. The motor of claim 11 wherein, when viewed in cross section,
the first magnet is arch-shaped, having a convex surface facing the
central longitudinal axis and a concave surface facing the second
magnet.
15. The motor of claim 14 wherein at least one of the following:
(1) when viewed in cross section, the second magnet has a convex
surface generally complementary to and in contact with the concave
surface of the first magnet; and (2) when viewed in cross section,
at least a portion of the first magnet contacts the concave surface
of the second magnet.
16. The motor of claim 11 further comprising a third magnet of the
same material as the second magnet sized and shaped substantially
the same as the second magnet.
17. The motor of claim 16 wherein, when viewed in cross section,
the second and third magnets are substantially rectangular and at
least a portion of each is in contact with the first magnet.
18. The motor of claim 17 wherein, when viewed in cross section,
the second and third magnets are spaced apart.
19. The motor of claim 11 wherein the rotor has at least two slots
equally spaced radially and circumferentially about the
longitudinal axis.
20. The motor of claim 11 wherein one of the first or second
magnets is strontium ferrite, the other of the first and second
magnets is neodymium-iron-boron, and the core is steel.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to an electric motor
rotor design. More particularly, the present invention relates to
an interior permanent magnet rotor design wherein strontium ferrite
and neodymium-iron-boron are positioned in a common slot in the
rotor core.
BACKGROUND OF THE INVENTION
[0002] Interior permanent magnet (IPM) rotor designs using
strontium ferrite (ferrite) and neodymium-iron-boron (neo) are
known in the art.
[0003] In one prior art design, the rotor has a core with long thin
slots having neo in each slot. This design does not make use of
ferrite. The slots are formed by using a punch press on the rotor
core. In order to increase die life, decrease the core weight, and
reduce flux leakage, the slots are oversized. The oversized slots
allow air spaces around the neo which cause the motor to have high
windage noise at high speeds. These motors can have a sinusoidal
back electromagnetic flux (EMF) which is desirable.
[0004] Another option is to use ferrite in an IPM rotor design.
Ferrite is less expensive and can be used to fill large slots. This
results in very small air spaces which correspond to a quieter
motor. The problem with ferrite is that it does not have a
sufficiently high flux density to make an efficient motor.
[0005] The combination of neo and ferrite in a single rotor design
has been the solution. Large slots near the center of the rotor are
filled with ferrite, and smaller slots closer to the edge of the
rotor have pieces of neo in them. A motor employing this design is
somewhat quieter than a motor using neo alone (i.e. has less
windage noise), but generally has a non-sinusoidal back EMF (i.e.,
it is harmonically rich). Also, the die used in manufacturing this
type of rotor has a short lifespan due to the small size of the neo
slot.
SUMMARY OF THE INVENTION
[0006] Embodiments of the invention include IPM rotor designs with
small air spaces and large slots in order to achieve a quiet motor
and improved die life. Embodiments of the invention also include
IPM rotor designs that demonstrate a near sinusoidal back EMF.
[0007] In accordance with one aspect of the invention, an electric
motor rotor is provided. A core has a central longitudinal axis and
a slot radially spaced from the longitudinal axis extending
parallel to the axis. First and second magnets are positioned in
the slot and extend parallel to the longitudinal axis. The first
magnet is positioned between the second magnet and the longitudinal
axis.
[0008] In accordance with another aspect of the invention, a method
is provided for producing an electric motor. A slot is formed in a
rotor core material having a central longitudinal axis. A first
magnet is inserted in the slot. A second magnet is inserted in the
slot such that the first magnet is substantially between the second
magnet and the central longitudinal axis. The rotor core is
inserted into a stator having windings. The windings of the stator
are connected to a commutation circuit.
[0009] In accordance with another aspect of the invention, an
electric motor is provided. A rotor includes a core and first and
second magnets. The core has a central longitudinal axis and a slot
radially spaced from the longitudinal axis extending parallel to
the longitudinal axis. The first and second magnets are positioned
in the slot and extend parallel to the longitudinal axis. The first
magnet is positioned between the second magnet and the longitudinal
axis. A stator having windings is in magnetic coupling relation to
the rotor. A commutation circuit is electrically connected to the
windings of the stator.
[0010] Alternatively, the invention may comprise various other
methods and apparatuses.
[0011] Other objects and features will be in part apparent and in
part pointed out hereinafter.
[0012] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a partial cross sectional view perpendicular to an
axis of rotation of a motor according to one embodiment of the
invention having a rectangular first magnet, a rectangular second
magnet, and a trapezoidal slot.
[0014] FIG. 2 is a cross sectional view perpendicular to an axis of
rotation of a rotor according to one embodiment of the invention
having an arc shaped first magnet, a rectangular second magnet, and
a trapezoidal slot.
[0015] FIG. 3 is a cross sectional view perpendicular to an axis of
rotation of a rotor according to one embodiment of the invention
having an arc shaped first magnet, two contiguous rectangular
pieces of a second magnetic material, and a trapezoidal slot.
[0016] FIG. 4 is a cross sectional view perpendicular to an axis of
rotation of a rotor according to one embodiment of the invention
having an arc shaped first magnet, two separated rectangular pieces
of a second magnetic material, and a trapezoidal slot.
[0017] FIG. 5 is a cross sectional view perpendicular to an axis of
rotation of a rotor according to one embodiment of the invention
having an arc shaped first magnet, a bread loaf shaped second
magnet, and a precision slot.
[0018] FIG. 6 is a cross sectional view perpendicular to an axis of
rotation of a rotor according to one embodiment of the invention
having an arc shaped first magnet, two separated bread loaf shaped
pieces of a second magnetic material, and a trapezoidal slot.
[0019] FIG. 7 is a cross sectional view perpendicular to an axis of
rotation of a rotor according to one embodiment of the invention
having an arc shaped first magnet and a rectangular second magnet
wherein the second magnet is between the arc shaped first magnet
and the axis of rotation.
[0020] FIG. 8 is a cross sectional view perpendicular to an axis of
rotation of a lobed rotor according to one embodiment of the
invention having a composite slot for a first and second magnet
wherein the slot is trapezoidal in the area of the second
magnet.
[0021] Corresponding reference characters indicate corresponding
parts throughout the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Referring to FIG. 1, one embodiment of a motor 100 of the
invention is illustrated in cross section including a rotor 102
having a central shaft 104 rotating about an axis of rotation A.
The rotor 102 comprises a cylindrical core of steel (or other
material) having a slot 110 extending parallel to the shaft.
Positioned within the slot 110 are a ferrite magnet 106 and a neo
magnet 108. The rotor is positioned within a stator 112 having
windings 114. The windings are connected to a commutation circuit
116. Commutation circuit 116 energizes the windings 114 causing the
rotor 102 to rotate about the central shaft 104. FIG. 1 illustrates
one embodiment in which a single, unitary slot 110 has located
therein neo and ferrite magnets each having a generally rectangular
cross section perpendicular to the axis of rotation A. The magnets
each have a longer rectangular dimension which is generally
parallel to each other and the ferrite magnet 106 is positioned
between the neo magnet 108 and the central shaft 104. In one
embodiment, the slot 110 has a partial trapezoidal cross section
perpendicular to the axis of rotation at the ends of the neo magnet
108. This results in generally triangular air spaces 118 bounded by
the short side of the neo magnet 108, the long side of the ferrite
magnet 106, and the core 102. Other rotor configurations are
contemplated. For example, see the configurations illustrated in
FIGS. 2-7.
[0023] Generally, motors employing the invention have a
substantially sinusoidal back EMF whereas motors known in the art
using ferrite and neo magnets have a harmonically rich back EMF.
Motors employing the invention generally have a lower minimum
inductance than motors known in the art, and the ratio of maximum
inductance to minimum inductance is generally higher which improves
the contribution of reluctance torque. Motors employing the
invention also generate less noise at high speeds than motors known
in the art because there are less air spaces in the rotor.
[0024] Motors employing the invention are generally less expensive
to manufacture than those known in the art, but there are
compromises between cost and noise. Rectangular neo magnets are
less expensive than neo magnets of other shapes, but they allow
some air spaces when used with an arc shaped ferrite magnet. Two
small neo magnets generally conform to the arc shaped ferrite
magnet better than one large neo magnet. However, using two small
magnets may require a die used to form slots in a rotor core to
have intricate details which means that the die will not last as
long as a die that has less intricate details. Die life can be
increased by not conforming to every detail of the magnets, but
this will allow for air spaces which will increase acoustic noise
when the motor is operating at high speeds. Because of their
reduced cost, reduced acoustic noise, and reduced electrical noise,
motors according to the invention may be advantageously applied in
consumer appliances such as horizontal washing machines, dish
washers and clothes dryers.
[0025] Referring now to FIG. 2, an embodiment of the invention
using a rectangular neo magnet 208, an arc shaped ferrite magnet
206, and a trapezoidal slot is shown. A cylindrical core 202 has a
central shaft 204 about which it rotates and a slot extending
parallel to the shaft 204. The arc shaped ferrite magnet 206 has a
convex surface 214 facing the central shaft 204 and a concave
surface 216 facing away from the central shaft 204. The rectangular
neo magnet 208 has a longer dimension facing the ferrite magnet
206, and the corners of the neo magnet 208 contact the concave face
216 of the ferrite magnet 206. The concave surface 216 of the
ferrite magnet 206 facing the flat surface of the neo magnet 208
results in an air space 212 between the ferrite magnet 206 and the
neo magnet 208. The slot is not precision cut, but is trapezoidal
in the area that contains the neo magnet 208. That is, instead of
fitting tightly against the outline of the combined ferrite and neo
magnets, the core is cut so that it does not fit against the
shorter edges of the neo magnet 208. A trapezoidal slot results in
generally triangular air spaces 210 bounded by the short sides of
the rectangular neo magnet 208, the concave face 216 of the ferrite
magnet 206, and the core 202. This trapezoidal style slot reduces
intricate details of the slot cross section which can increase the
life of a die used to make the slot, making a trapezoidal slot
desirable when die life is more important to the manufacturer than
motor noise is to the end user. The trapezoidal slot also reduces
leakage flux which contributes to a motor with a higher maximum
inductance, and thus a potentially better ratio of maximum
inductance to minimum inductance.
[0026] Referring now to FIG. 3, an embodiment of the invention
using two rectangular neo magnets 308, an arc shaped ferrite magnet
306, and a trapezoidal slot is shown. A cylindrical core 302 has a
central shaft 204 about which it rotates and a slot extending
parallel to the shaft 304. The arc shaped ferrite magnet 306 has a
convex surface facing the central shaft 304 and a concave surface
facing away from the central shaft 304. Each rectangular neo magnet
208 has a longer dimension facing the ferrite magnet 206, and the
corners of the neo magnet 308 contact the concave face of the
ferrite magnet 306. The neo magnets 308 contact each other at one
corner. The concave surface of the ferrite magnet 306 facing the
flat surface of the neo magnets 308 results in air spaces 310
between the ferrite magnet 306 and each neo magnet 308. There is
also a generally triangular air space 312 between the two neo
magnets 308 bound by the concave surface of the ferrite magnet 306
and the shorter sides of each neo magnet 308. The slot is generally
trapezoidal in cross section and triangular in cross section in the
area that contains the neo magnets 308. That is, instead of fitting
tightly against the outline of the combined ferrite and neo
magnets, the core may be cut so that it does not have a precision
fit with the shorter edges of the neo magnet 208. A trapezoidal
slot results in generally triangular air spaces 314 bounded by the
short side of the rectangular neo magnet 308, the concave face of
the ferrite magnet 306, and the core 302. Air spaces 310 and 312
may be smaller than air space 212 (see FIG. 2) because two smaller
neo magnets conform to the face of the ferrite magnet better than
one large neo magnet. The rotor design of FIG. 3 has different
acoustic characteristics than that of the design in FIG. 2 because
of the difference in air spaces. The two rotors (see FIGS. 2 and 3)
may be employed in different applications with different operating
speeds because of their differing acoustical characteristics (i.e.,
reduced windage noise at certain speeds).
[0027] Referring now to FIG. 4, an embodiment of the invention
using two rectangular neo magnets 408, an arc shaped ferrite magnet
406, and a trapezoid slot is shown. A cylindrical core 402 has a
central shaft 404 about which it rotates and a slot extending
parallel to the shaft 404. The arc shaped ferrite magnet 406 has a
convex surface facing the central shaft 404 and a concave surface
facing away from the central shaft 404. The two rectangular neo
magnets 408 each have a longer dimension facing the ferrite magnet
406, and the corners of the neo magnets 408 contact the concave
face of the ferrite magnet 406. The concave surface of the ferrite
magnet 406 facing the flat surfaces of the neo magnets 408 results
in air spaces 412 between the ferrite magnet 406 and the neo
magnets 408. Two small neo magnets 408 conform to the concave face
of the ferrite magnet 406 better than one large neo magnet thus
reducing the air spaces 412 between the neo magnets 408 and the
ferrite magnet 406 which tends to provide a quieter rotor design.
The neo magnets 408 are spaced apart from each other by a portion
of the core 414. Spacing the neo magnets 408 apart from each other
allows them to be positioned in the slot more securely. The slot is
trapezoidal in each area that contains each neo magnet 408. That
is, instead of fitting tightly against the outline of the combined
ferrite and neo magnets, the core is cut so that it does not fit
against the shorter edges of the neo magnets 408. The trapezoidal
slot results in generally triangular air spaces 410 bounded by the
short sides of the rectangular neo magnets 408, the concave face of
the ferrite magnet 406, and the core 402. This trapezoidal style
slot reduces intricate details of the slot cross section which can
increase the life of a die used to make the slot, making a
trapezoidal slot desirable when die life is more important to the
manufacturer than motor noise is to the end user. This embodiment
thus allows longer die life and secure positioning of two
relatively small neo magnets 408 which is cost effective regarding
die life and minimizes motor noise (as compared to a design
utilizing one large neo magnet).
[0028] Referring now to FIG. 5, an embodiment of the invention
using a bread-loaf shaped neo magnet 508, an arc shaped ferrite
magnet 506, and a precision cut slot is shown. A cylindrical core
502 has a central shaft 504 about which it rotates and a slot
extending parallel to the shaft 504. The arc shaped ferrite magnet
506 has a convex surface 510 facing the central shaft 504 and a
concave surface 512 facing away from the central shaft 504. A
bread-loaf shaped neo magnet 508 is generally rectangular, however,
one of the longer sides is generally complementary to the concave
face 512 of the ferrite magnet 506. The curved side of the neo
magnet 508 is substantially in contact with the concave face 512 of
the ferrite magnet 506. The precision cut slot is an alterative to
a slot that is trapezoidal or triangular in the area of the neo
magnet. The slot is precision cut to accept the ferrite magnet 506
and neo magnet 508 while maintaining a minimum air space between
the ferrite and neo magnets and between each magnet and the rotor
core. This means that the core 502 fits tightly against the outline
of the combined neo and ferrite magnets. This embodiment has
essentially no air spaces either between the two magnets or between
the magnets and the core and thus is quiet when operating at high
speeds. However, the large bread-loaf shaped neo magnet 508 and
precision slot mean that this embodiment may be one of the more
expensive to manufacture due to shortened die life and increased
neo magnet expense. Also, embodiments utilizing a precision slot
generally have a lower maximum inductance than embodiments
utilizing a trapezoidal slot which means that such embodiments may
not be as efficient as other embodiments.
[0029] Referring now to FIG. 6, an embodiment of the invention
using two bread-loaf shaped neo magnets 608, an arc shaped ferrite
magnet 606, and a trapezoidal slot is shown. A cylindrical core 602
has a central shaft 604 about which it rotates and a slot extending
parallel to the shaft 604. The arc shaped ferrite magnet 606 has a
convex surface facing the central shaft 604 and a concave surface
facing away from the central shaft 604. Bread-loaf shaped neo
magnets 608 are generally rectangular, however, one of their longer
sides is complementary to the concave face of the ferrite magnet
606. The curved side of each neo magnet 508 is substantially in
contact with the concave face of the ferrite magnet 606. The neo
magnets 608 are spaced apart from each other. The slot is not
precision cut, but is trapezoidal in the area that contains the neo
magnets 608. That is, instead of fitting tightly against the
outline of the combined ferrite and neo magnets, the core is cut so
that it does not fit tightly against the shorter edges of the neo
magnets 608. The trapezoidal slot results in generally triangular
air spaces 610 bounded by the short sides of the rectangular neo
magnets 608, the concave face of the ferrite magnet 606, and the
core 602. This trapezoidal style slot reduces intricate details of
the slot cross section which can increase the life of a die used to
make the slot, making a trapezoidal slot desirable when die life is
more important to the manufacturer than motor noise is to the end
user. This embodiment allows for longer die life, secure
positioning of two relatively small neo magnets, and reduced air
spaces as compared to the embodiment illustrated in FIG. 4.
[0030] Referring now to FIG. 7, an embodiment of the invention
using a rectangular neo magnet 708, an arc shaped ferrite magnet
706, and a precision slot is shown. A cylindrical core 702 has a
central shaft 704 about which it rotates and a slot extending
parallel to the shaft 704. The generally arc shaped ferrite magnet
706 has a convex surface facing the central shaft 704 and a concave
surface facing away from the central shaft 704. The rectangular neo
magnet 708 is positioned with a longer edge in contact with the
convex surface of the ferrite magnet 706. The neo magnet 708 is
offset from the center of the convex face of the ferrite magnet
706. The slot is precision cut to fit against the outline of the
combined neo and ferrite magnets. However, generally triangular air
spaces 710 exist bound by the convex surface of the ferrite magnet
706, a portion of the long side of the neo magnet 708, and the core
702. This embodiment allows for a long die life and relatively
small air spaces as compared to certain other embodiments. However,
locating the neo magnet 708 closer to the shaft 704 than the
ferrite magnet 706 reduces the maximum inductance of the rotor.
[0031] Referring to FIG. 8, an embodiment of the invention shows a
lobed core using either a rectangular neo magnet or bread-loaf neo
magnet, an arc shaped ferrite magnet, and a trapezoidal slot is
shown. This embodiment is shown without the magnets to better
depict the cross section of a composite slot 808. A cylindrical
core 802 has a central shaft 806 about which it rotates and the
composite slot 808 extends parallel to the shaft 806. An arc shaped
ferrite magnet for use with this embodiment has a convex surface
facing the central shaft 806 and a concave surface facing away from
the central shaft 806. A neo magnet for use with this embodiment
has a longer dimension facing the ferrite magnet, and either has
the corners of the neo magnet contacting the concave face of the
ferrite magnet 206 (if the neo magnet is rectangular), or has one
of the longer sides generally complementary to the concave face of
the ferrite magnet and substantially in contact with the concave
face of the ferrite magnet (if the neo magnet is bread-loaf
shaped). The composite slot 808 is trapezoidal in cross section
perpendicular to the axis of rotation forming generally triangular
air spaces with the shorter edges of a neo magnet used in this
embodiment. This trapezoidal slot reduces intricate details of the
slot cross section which can increase the life of a die used to
make the slot, making a trapezoidal slot desirable when die life is
important to the manufacturer.
[0032] In the embodiment of FIG. 8, the core 802 is lobed. A rotor
with lobes generally has reduced cogging torque and a more
sinusoidal back EMF. The cross section of the core 802 is shown
surrounded by a perfect circle 804. The outer edge 812 of the core
802 varies in distance from the perfect circle 804. The distance
810 from the outer edge 812 of the core 802 to the perfect circle
804 is generally less than the distance 814 from the outer edge 812
of the core 802 to the perfect circle 804 over a slot 808. In one
embodiment, the distance 810 over a slot is 0.020'' and the
distance 814 not over a slot is 0.040''. Embodiments of the
invention may have lobes over each slot in the rotor, or lobes over
selected slots in the rotor.
[0033] In yet another embodiment, the present invention is a method
of manufacturing an IPM motor having a rotor wherein a ferrite
magnet and a neo magnet are both located in the same slot. One or
more slots are formed in a cylindrical rotor core having a central
longitudinal axis about which the core rotates. The neo magnet is
inserted in the slot. The ferrite magnet is placed in the slot
between the neo magnet and the central longitudinal axis of the
cylindrical core. The ferrite magnet is arc shaped when viewed in
cross section relative to the central longitudinal axis. The neo
magnet is rectangular when viewed in cross section relative to the
central longitudinal axis. The slot may be precisely complementary
to the outline of the combined ferrite and neo magnets so as to
minimize air spaces, or it may have a trapezoidal area around the
rectangular neo magnet. The rotor core is secured within a stator
having windings, and a commutation circuit energizes the windings.
A magnetic field of the stator interacts with the magnets in the
rotor causing the rotor to turn.
[0034] It is contemplated that aspects of the embodiments described
above may be combined in numerous ways without deviating from the
invention. For example, the embodiment shown in FIG. 6 may use a
precision slot instead of a trapezoidal slot, or the embodiment
shown in FIG. 5 may use a trapezoidal slot. FIGS. 1-7 show 4 slots
having magnets in them, but the rotor may have any number of slots,
some of which may be empty. Also, the same rotor may contain more
than one configuration of neo and ferrite magnets. The central
shaft shown in the above embodiments may be cast, forged, or
machined as part of the core or engage the core by some other means
such as splining. Additionally, any of the rotor configurations may
have lobed cores as shown in FIG. 2.
[0035] Some embodiments of the invention have advantages over other
embodiments. For example, using two rectangular (i.e., viewed in
cross section) pieces of neo magnet allows small air spaces than
one larger piece of neo magnet because they better conform to the
curvature of the ferrite magnet. Embodiments of the invention
utilizing a trapezoidal slot will generally have a higher maximum
inductance than embodiments utilizing a precision slot because a
precision slot tends to increase leakage flux. Embodiments using
lobed rotor cores generally have a lower cogging torque and more
sinusoidal back EMF than embodiments using cylindrical rotor cores.
Also, embodiments with a neo magnet further from the center of the
rotor than the ferrite magnet tend to develop a higher maximum
inductance than embodiments with neo magnets closer to the center
than the ferrite magnet.
[0036] The above description is also applicable to other motor
configurations such as inside out motors and/or motors having
windings in the rotor and permanent magnets in the stator, and visa
versa. For example, embodiments of the invention in an inside out
motor include neo and ferrite magnets located in a single slot.
Magnet configurations and air space considerations are similar to
those of the above described rotor designs.
[0037] This description refers to ferrite and neo throughout, but
one skilled in the art will recognize that magnetic materials other
than neo and ferrite may be used without deviating from the
invention and more than one piece of neo and/or ferrite may be used
in each slot. One skilled in the art will also notice that
different shapes of neo magnets, ferrite magnets, and slots are
possible without deviating from the invention. The cylindrical
rotor core may be made with steel or some other material. The
description refers to an IPM motor rotor throughout, but one
skilled in the art knows that an electric motor may be configured
as a generator.
[0038] Having described the invention in detail, it will be
apparent that modifications and variations are possible without
departing from the scope of the invention defined in the appended
claims.
[0039] The order of execution or performance of the methods
illustrated and described herein is not essential, unless otherwise
specified. That is, it is contemplated by the inventors that
elements of the methods may be performed in any order, unless
otherwise specified, and that the methods may include more or less
elements than those disclosed herein. For example, it is
contemplated that executing or performing a particular element
before, contemporaneously with, or after another element is within
the scope of the various embodiments of the invention.
[0040] When introducing elements of the present invention or the
preferred embodiments(s) thereof, the articles "a", "an", "the" and
"said" are intended to mean that there are one or more of the
elements. The terms "comprising", "including" and "having" are
intended to be inclusive and mean that there may be additional
elements other than the listed elements.
[0041] In view of the above, it will be seen that the several
objects of the invention are achieved and other advantageous
results attained.
[0042] As various changes could be made in the above products and
methods without departing from the scope of the invention, it is
intended that all matter contained in the above description and
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
* * * * *