U.S. patent application number 15/340131 was filed with the patent office on 2017-02-23 for system and method for smoothing a salient rotor in electrical machines.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is General Electric Company. Invention is credited to James Pellegrino Alexander, Aymam Mohamed Fawzi EL-Refaie, Tsarafidy Raminosoa, David A. Torrey.
Application Number | 20170054335 15/340131 |
Document ID | / |
Family ID | 51178806 |
Filed Date | 2017-02-23 |
United States Patent
Application |
20170054335 |
Kind Code |
A1 |
Raminosoa; Tsarafidy ; et
al. |
February 23, 2017 |
SYSTEM AND METHOD FOR SMOOTHING A SALIENT ROTOR IN ELECTRICAL
MACHINES
Abstract
An electrical machine exhibiting reduced friction and windage
losses is disclosed. The electrical machine includes a stator and a
rotor assembly configured to rotate relative to the stator, wherein
the rotor assembly comprises a rotor core including a plurality of
salient rotor poles that are spaced apart from one another around
an inner hub such that an interpolar gap is formed between each
adjacent pair of salient rotor poles, with an opening being defined
by the rotor core in each interpolar gap. Electrically
non-conductive and non-magnetic inserts are positioned in the gaps
formed between the salient rotor poles, with each of the inserts
including a mating feature formed an axially inner edge thereof
that is configured to mate with a respective opening being defined
by the rotor core, so as to secure the insert to the rotor core
against centrifugal force experienced during rotation of the rotor
assembly.
Inventors: |
Raminosoa; Tsarafidy;
(Niskayuna, NY) ; Alexander; James Pellegrino;
(Ballston Lake, NY) ; EL-Refaie; Aymam Mohamed Fawzi;
(Niskayuna, NY) ; Torrey; David A.; (Ballston Spa,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
51178806 |
Appl. No.: |
15/340131 |
Filed: |
November 1, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13949406 |
Jul 24, 2013 |
9520751 |
|
|
15340131 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 15/022 20130101;
H02K 1/22 20130101; Y10T 29/49012 20150115; H02K 1/24 20130101;
H02K 15/02 20130101; H02K 2205/12 20130101; H02K 1/246 20130101;
H02K 1/146 20130101 |
International
Class: |
H02K 1/24 20060101
H02K001/24; H02K 15/02 20060101 H02K015/02; H02K 1/14 20060101
H02K001/14 |
Goverment Interests
GOVERNMENT LICENSE RIGHTS
[0001] This invention was made with Government support under
contract number DE-EE0005573 awarded by the United States
Department of Energy. The Government has certain rights in the
invention.
Claims
1. An electrical machine comprising: a stator; a rotor assembly
disposed within the stator and configured to rotate relative to the
stator, wherein the rotor assembly comprises: a rotor core
constructed of a stack of laminations, the rotor core comprising a
plurality of salient rotor poles that are spaced apart from one
another around an inner hub such that an interpolar gap is formed
between each adjacent pair of salient rotor poles; and a plurality
of inserts positioned in the gaps formed between the plurality of
salient rotor poles, the inserts each formed as a single piece
extending axially through the stack of laminations of the rotor
core and each being entirely formed of nonconductive and
non-magnetic material.
2. The electrical machine of claim 1 wherein the inserts each
comprise a mating feature forming an axially inner edge thereof
configured to mate with a corresponding opening in each interpolar
gap defined by the rotor core.
3. The electrical machine of claim 2 wherein the mating feature
comprises a dovetail feature configured to mate with an opening
formed in the inner hub of the rotor core.
4. The electrical machine of claim 1 wherein the rotor assembly
further comprises a pair of non-conductive and non-magnetic end
plates positioned on axially opposing ends of the rotor core.
5. The electrical machine of claim 4 wherein opposing ends of each
insert comprise an additional mating feature formed on each end
thereof configured to mate with a corresponding opening on each end
plate.
6. The electrical machine of claim 1 wherein the plurality of
salient rotor poles comprises a plurality of rotor teeth.
7. The electrical machine of claim 1 wherein each of the plurality
of inserts comprises a T-shaped insert comprising: a lengthwise
member extending in a radial direction; and a crosswise member
extending normally between two adjacent rotor poles.
8. The electrical machine of claim 7 wherein the crosswise member
forms a smooth outer surface on the rotor in combination with a
pair of adjacent rotor poles.
9. The electrical machine of claim 7 wherein each of the plurality
of rotor poles comprises a pair of flange-like protrusions formed
at a radially outermost portion thereof, wherein the crosswise
member includes a shoulder on each end thereof configured to mate
with the pair of flange-like protrusions.
10. The electrical machine of claim 7 wherein each of the plurality
of rotor poles comprises a pair of axially-extending notches formed
in proximity to the radially outermost portion thereof, wherein the
crosswise member includes a shoulder on each end thereof configured
to mate with the pair of axially-extending notches.
11. A rotor assembly for an electrical machine comprising: a rotor
core constructed of a stack of laminations, the rotor core
comprising a plurality of salient rotor poles that are spaced apart
from one another around an inner hub such that an interpolar gap is
formed between each adjacent pair of salient rotor poles; and a
plurality of inserts positioned in the gaps formed between the
plurality of salient rotor poles, the inserts each formed as a
single piece extending axially through the stack of laminations of
the rotor core and each being entirely formed of nonconductive and
non-magnetic material.
12. The rotor assembly of claim 11 wherein the rotor assembly
further comprises a pair of non-conductive and non-magnetic end
plates positioned on axially opposing ends of the rotor core.
13. The rotor assembly of claim 12 wherein opposing ends of each
insert comprise an additional mating feature formed on each end
thereof configured to mate with a corresponding opening on each end
plate.
14. The rotor assembly of claim 11 wherein each of the plurality of
inserts comprises a T-shaped insert comprising: a lengthwise member
extending in a radial direction; and a crosswise member extending
normally between two adjacent rotor poles.
15. The rotor assembly of claim 14 wherein the crosswise member
forms a smooth outer surface on the rotor in combination with a
pair of adjacent rotor poles.
16. The rotor assembly of claim 14 wherein each of the plurality of
rotor poles comprises a pair of flange-like protrusions formed at a
radially outermost portion thereof, wherein the crosswise member
includes a shoulder on each end thereof configured to mate with the
pair of flange-like protrusions.
17. The rotor assembly of claim 14 wherein each of the plurality of
rotor poles comprises a pair of axially-extending notches formed in
proximity to the radially outermost portion thereof, wherein the
crosswise member includes a shoulder on each end thereof configured
to mate with the pair of axially-extending notches.
18. An electrical machine comprising: a stator; a rotor assembly
disposed within the stator and configured to rotate relative to the
stator, wherein the rotor assembly comprises: a rotor core
comprising a plurality of salient rotor poles that are spaced apart
from one another around an inner hub such that an interpolar gap is
formed between each adjacent pair of salient rotor poles; and a
plurality of inserts positioned in the gaps formed between the
plurality of salient rotor poles, the inserts each formed as a
single piece extending axially through the rotor core and each
being entirely formed of nonconductive and non-magnetic
material.
19. The electrical machine of claim 19 wherein the rotor core is
formed as a single piece of material.
20. The electrical machine of claim 19 wherein the rotor assembly
further comprises a pair of non-conductive and non-magnetic end
plates positioned on axially opposing ends of the rotor core.
21. The electrical machine of claim 20 wherein opposing ends of
each insert comprise an additional mating feature formed on each
end thereof configured to mate with a corresponding opening on each
end plate.
Description
BACKGROUND OF THE INVENTION
[0002] The invention relates generally to electrical machines and,
more particularly, to a system and method for smoothing a salient
rotor of an electrical machine in order to reduce friction and
windage losses in the machine, while providing for a mechanically
robust rotor assembly that can withstand centrifugal forces at high
speeds.
[0003] The usage of electrical machines in various industries has
continued to become more prevalent in numerous industrial,
commercial, and transportation industries over time. Several types
of such electrical machines, such as reluctance motors and stator
permanent magnet motors for example, require the use of salient
poles or protruding teeth on the rotor. These types of rotors are
generally passive and robust and thus suitable for high-speed
applications. It is recognized, however, that the salient structure
of such rotors contributes to the creation of excessive windage
losses due to the tendency of the protrusions to catch air as the
rotor rotates.
[0004] One manner of addressing the issue of windage losses that
accompany the use of salient rotors is to "smooth" the outer
surface of the rotor by filling the interpolar spaces between the
rotor teeth. One prior art mechanism for filling in the interpolar
spaces is magnetic bridges that are positioned between the rotor
poles so as to connect adjacent rotor pole tips, thereby smoothing
the rotor. Such magnetic bridges, however, negatively affect the
magnetic saliency and thus serve to reduce the performance of the
electrical machine. Another prior art mechanism for filling in the
interpolar spaces is segments of a non-magnetic material (e.g.,
stainless steel) positioned between the rotor poles, such as
described in U.S. Pat. No. 4,916,346, that provide smoothing to the
rotor and do not affect the magnetic saliency. However, in the
prior art, such non-magnetic segments have been formed as solid,
plain metallic inserts that greatly increase the overall mass of
the electrical machine. Additionally, such non-magnetic segments
have been either welded to the rotor poles or secured thereto
solely via a notch formation, both of which may not be ideal for
retaining the segments between the rotor poles and/or provide a
desired robustness for the rotor assembly. Further, metallic
inserts and their associated welds are subject to eddy current
losses that reduce the efficiency of the machine.
[0005] Therefore, it would be desirable to provide inserts for
smoothing a salient rotor that address the issue of windage losses
without affecting the magnetic performance. It would further be
desirable for such inserts to be assembled with the salient rotor
in a mechanically robust way that can withstand centrifugal forces
at high speeds, while minimizing the mass that is added to the
rotor.
BRIEF DESCRIPTION OF THE INVENTION
[0006] In accordance with one aspect of the invention, an
electrical machine includes a stator and a rotor assembly disposed
within the stator and configured to rotate relative to the stator,
wherein the rotor assembly comprises a rotor core comprising a
plurality of salient rotor poles that are spaced apart from one
another around an inner hub such that an interpolar gap is formed
between each adjacent pair of salient rotor poles, with an opening
being defined by the rotor core in each interpolar gap, and a
plurality of inserts positioned in the gaps formed between the
plurality of salient rotor poles, the plurality of inserts being
formed of electrically non-conductive and non-magnetic material.
Each of the plurality of inserts comprises a mating feature formed
an axially inner edge thereof that is configured to mate with a
respective opening being defined by the rotor core, so as to secure
the insert to the rotor core against centrifugal force experienced
during rotation of the rotor assembly.
[0007] In accordance with another aspect of the invention, a method
for manufacturing an electrical machine includes providing a stator
and providing a rotor assembly that is positionable within the
stator and is mountable for rotation about a central axis, wherein
providing the rotor assembly comprises providing a salient rotor
core comprising a plurality of salient rotor poles that are spaced
apart from one another around an inner hub such that an interpolar
gap is formed between each adjacent pair of salient rotor poles,
with a dovetail-shaped opening being defined by the rotor core in
each interpolar gap. Providing the rotor assembly further comprises
providing a plurality of inserts formed of electrically
non-conductive and non-magnetic material and securing the plurality
of inserts in the interpolar gaps formed between the plurality of
salient rotor poles, wherein, in securing each of the plurality of
inserts in an interpolar gap formed between an adjacent pair of
salient rotor poles, a mating feature of the insert is mated with a
respective opening being defined by the rotor core, so as to secure
the insert to the rotor core against centrifugal force experienced
during rotation of the rotor assembly.
[0008] In accordance with yet another aspect of the invention, a
rotor assembly for an electrical machine includes a salient rotor
comprising a plurality of salient rotor poles that are spaced apart
from one another around an inner hub such that an interpolar gap is
formed between each adjacent pair of salient rotor poles and a
plurality of inserts positioned in the interpolar gaps formed
between the plurality of salient rotor poles and being constructed
such that the plurality of inserts in combination with the
plurality of salient rotor poles forms a smooth outer surface on
the rotor assembly. The plurality of inserts comprise one of
T-shaped inserts formed of an electrically non-conductive and
non-magnetic material, hollow inserts having an outer shell formed
of an electrically non-conductive and non-magnetic material, or
dovetail-shaped inserts formed of an electrically non-conductive
and non-magnetic material. Each of the plurality of inserts is
configured to mate with the salient rotor so as to secure the
insert to the salient rotor against centrifugal force experienced
during rotation of the rotor assembly.
[0009] Various other features and advantages will be made apparent
from the following detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The drawings illustrate preferred embodiments presently
contemplated for carrying out the invention.
[0011] In the drawings:
[0012] FIG. 1 is a schematic view of an electrical machine useable
with embodiments of the invention.
[0013] FIG. 2 is a side view of a rotor of an electrical machine
useable with embodiments of the invention.
[0014] FIG. 3 is a schematic diagram of a toothed rotor useable
with embodiments of the invention.
[0015] FIG. 4 is a schematic diagram of a segmented rotor useable
with embodiments of the invention.
[0016] FIGS. 5, 6, and 7A-7C are schematic diagrams of a rotor
assembly including a toothed rotor and electrically non-conductive,
non-magnetic rotor inserts according to embodiments of the
invention.
[0017] FIG. 8 is a schematic diagram of a rotor assembly including
a segmented rotor and electrically non-conductive, non-magnetic
rotor inserts according to an embodiment of the invention.
[0018] FIG. 9 is a schematic diagram of a rotor assembly including
a toothed rotor, electrically non-conductive, non-magnetic rotor
inserts, and electrically non-conductive, non-magnetic end plates
according to an embodiment of the invention.
[0019] FIG. 10 is a schematic diagram of a rotor assembly including
a segmented rotor, electrically non-conductive, non-magnetic rotor
inserts, and electrically non-conductive, non-magnetic end plates
according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] Embodiments of the invention are to electrical machines
incorporating a salient rotor, with inserts being provided for the
salient rotor for smoothing the rotor so as to address issues of
friction and windage losses without affecting the magnetic
performance. While embodiments of the invention are discussed with
respect to an electrical machine in which the rotor and stator
interact through radial magnetic fields, it will be appreciated by
one skilled in the art that embodiments of the invention can also
be used for electrical machines that use axial fields for
rotor/stator interaction, with the inserts oriented in the radial
direction.
[0021] Referring to FIG. 1, a typical electrical machine 1 that may
benefit from embodiments of the present invention is shown. The
electrical machine 1 includes a stator 2 (e.g., laminated iron
stator) that surrounds a rotor 3 in the radial direction and
extends axially along rotor 3. The stator 2 further includes a
plurality of stator poles 4, with each stator pole 4 being matched
with a radially opposite stator pole to form a stator pole pair.
Stator pole pairs 4a and 4b are wound with a phase winding 5 that
may be driven in a conventional manner from a remote source (not
shown). Separate phase windings, (not shown), are also included on
the other stator poles 4 in a like manner.
[0022] As shown in FIG. 1, the rotor 3 is formed as a salient rotor
having a plurality of salient pole pieces 6. According to one
embodiment, the rotor 3 is constructed of a stack of integral
laminations 7, as can be seen in the view of the rotor 3 provided
in FIG. 2, although it is recognized that the rotor core could also
be formed as a single piece--with the core being machined out of
steel or formed from sintered magnetic materials, for example. The
rotor 3 includes multiple projections/teeth 6 acting as salient
magnetic poles. A central portion of the rotor 3 includes a rotor
bore 8 through which a drive shaft may be inserted, about which the
rotor 3 can rotate.
[0023] The exact structure of the electrical machine may take one
of numerous forms, according to embodiments of the invention. For
example, the electrical machine may be configured as a reluctance
motor that induces non-permanent magnetic poles, with the phase
windings 5 of the stator 3 being driven in a predetermined sequence
to cause rotor 3 to rotate. The reluctance motor may be a
synchronous reluctance motor having equal numbers of stator and
rotor poles or a switched reluctance motor where the number of
stator pole pairs exceeds the number of rotor pole pairs by one. As
another example, the electrical machine may be configured as a
stator permanent magnet machine (e.g., permanent magnet flux
switching machine, permanent magnet flux reversal machine, or
doubly-salient permanent magnet machine, for example) that includes
permanent magnets 9 (shown in phantom) embedded in the stator. In
such stator permanent magnet machines, electric current in the
windings 5, interacts with magnetic fields associated with the
magnets 9 to cause rotation of the rotor 3.
[0024] It is recognized that FIGS. 1 and 2 are meant to only
illustrate examples of electrical machines that can benefit from
incorporating embodiments of the invention. That is, embodiments of
the invention can be implemented in a plurality of different types
of electrical machines that require the use of salient poles or
protruding teeth on the rotor. As such, embodiments of the
invention are not meant to be limited only to the types of
electrical machines shown and described herein.
[0025] Referring now to FIGS. 3 and 4, embodiments of salient
rotors with which embodiments of the invention can be incorporated
are shown. Referring first to FIG. 3, a construction of a toothed
rotor 10 is shown, where a plurality of rotor teeth or poles 12
extends radially outward from an inner hub 14 or portion of the
rotor with which the teeth 12 are integrally formed. Referring to
FIG. 4, a construction of a segmented rotor 20 is shown, where each
salient rotor pole 22 is formed as a separate component from the
other rotor poles. As shown in FIG. 4, the separate rotor poles are
arranged circumferentially around a non-magnetic rotor hub 26, with
each rotor pole 22 mating with the rotor hub 26 via a mating
feature 28 formed on the bottom of the rotor pole (i.e., on each
lamination of the rotor pole). A recess 30 between each rotor pole
22 of the segmented rotor 20 is configured to receive an insert
therein to be held radially between the rotor poles 22 against
centrifugal force caused by rotation of the rotor, as will be
described in detail further below.
[0026] According to embodiments of the invention, salient rotors
10, 20 such as those shown in FIGS. 3 and 4 can be made
mechanically smooth by providing electrically non-conductive and
non-magnetic inserts that partially fill the interpolar spaces
between the rotor poles and that, in conjunction with the rotor
poles, form a mechanically "smooth" outer surface on the
rotor--with it being understood that "smooth" as used herein does
not necessarily require that the rotor assembly outer surface to be
round or completely smooth, just that the inserts traverse a
distance between adjacent rotor poles to present an essentially
closed surface therebetween. Thus, for example, it is envisioned
that the inserts could be constructed as having a linear outer
face/segment rather than an are segment bridging adjacent rotor
poles (in order to provide a cheaper insert) and that this would
still be considered to present a mechanically smooth outer surface
on the rotor. The non-conductive and non-magnetic rotor insert
pieces address the issue of windage losses associated with salient
rotors without affecting the magnetic performance. The
non-conductive and non-magnetic inserts are constructed and
assembled with the salient rotor in a mechanically robust way that
can withstand centrifugal forces at high speeds, while minimizing
the mass that is added to the rotor. According to an exemplary
embodiment, each of the inserts is formed as a solid integral piece
that extends axially through the entire length of the salient
rotor.
[0027] Referring now to FIGS. 5-7, portions of a rotor assembly
according to various embodiments of the invention are shown. The
rotor assembly of each embodiment includes a toothed rotor and a
non-conductive, non-magnetic insert inserted in an interpolar space
between each pair of adjacent rotor teeth in the toothed rotor. As
can be seen, the rotor insert can have various
shapes/cross-sections according to embodiments of the invention,
with the shape of the inserts being adapted to the shape of the
rotor poles of the particular salient rotor that is employed and
the amount of centrifugal strength required to support the speed of
the rotor.
[0028] As shown in FIG. 5, a rotor assembly 32 is provided having a
toothed rotor 34 that includes rotor teeth 36 having a flange-like
protrusion 38 at the radially outermost portion of each of rotor
tooth 36, with the protrusion 38 extending normal to the tooth 36
on each side thereof. An electrically non-conductive, non-magnetic
insert insert 40 is formed as a T-shaped insert positioned in an
interpolar space 41 between adjacent teeth 36, with the T-shaped
insert 40 having a lengthwise member 42 extending in the axial
direction and a crosswise member 44 extending normally between two
adjacent rotor teeth 36, with the crosswise member 44 forming a
smooth outer surface on the toothed rotor 34 in combination with a
pair of adjacent rotor teeth 36. The crosswise member 44 is formed
to include a shoulder 46 on each end thereof that abuts a
respective protrusion 38 on a rotor tooth, such that the
protrusions 38 mate with the shoulders 46 on the T-shaped insert 40
to hold the insert in place against centrifugal forces experienced
during rotor rotation. Also included on the T-shaped insert 40 is a
mating feature 48 formed on an inner end of the lengthwise member
42. The mating feature 48 is configured to mate with an opening 50
formed in the back iron/inner hub 52 of the toothed rotor 34, such
that the mating of the insert 40 to the toothed rotor 34 is further
reinforced and the rotor assembly 32 is made more robust to
centrifugal forces acting thereon. According to an exemplary
embodiment, the mating feature 48 is configured as a dovetail
feature that mates with a dovetail-shaped opening 50 to provide the
increased robust to centrifugal forces; however, it is recognized
that mating features of other shapes/configurations are also
envisioned as being used.
[0029] FIG. 6 shows a rotor assembly 54 similar to that of FIG. 5
(with like elements numbered the same as in FIG. 5), but with the
teeth 56 of a toothed rotor 58 and T-shaped inserts 60 having
different features formed thereon. That is, the rotor teeth 56 are
formed to each include axially-extending notches 62 formed therein
in proximity to the radially outermost portion of each rotor tooth
56. The crosswise member 64 of the T-shaped insert 60 is formed to
include a shoulder 66 on each end thereof that mates with the
notches 62 of adjacent teeth 56 to hold the insert 60 in place
against centrifugal force experienced during rotor rotation. Also
included on the T-shaped insert 60 is a mating feature 48 formed on
an inner end of the lengthwise member 42. The mating feature 48 is
configured to mate with an opening 50 formed in the back iron/inner
hub 52 of the toothed rotor 58, such that the mating of the insert
60 to the toothed rotor 58 is further reinforced and the rotor
assembly 54 is made more robust to centrifugal forces acting
thereon.
[0030] Referring now to FIG. 7A, a rotor assembly 68 is shown
having a toothed rotor 58 identical to that of the toothed rotor in
FIG. 6, with the toothed rotor 58 having rotor teeth 56 formed to
each include axially-extending notches 62 formed therein in
proximity to the radially outermost portion of each rotor tooth 56.
The non-conductive, non-magnetic insert 70 of rotor assembly 68,
however, differs from the insert 60 of rotor assembly 54 (FIG.
6)--in that the insert 70 is configured to fill an entire
interpolar space or gap 41 between adjacent rotor teeth 56 rather
than having a T-shape that leaves part of the gap 41 open. As the
insert 70 is larger in size than the T-shaped inserts 40, 60 (FIGS.
5 and 6), it is recognized that the mass thereof may be greater
than that of the T-shaped inserts--which may be undesirable with
respect to the centrifugal forces generated by the insert during
rotor rotation. In order to minimize the mass of the insert 70 to
the extent possible, the non-conductive, non-magnetic insert is
formed as what is referred to here as a "hollow" insert, in that it
includes an interior region that is not formed of a material of
higher density. The "hollow" insert includes an outer shell 72
formed of a non-conductive, non-magnetic material, with the outer
shell 72 defining an area or opening 73. According to an exemplary
embodiment, the outer shell 72 is formed of a non-conductive,
non-magnetic material that provides a high mechanical strength and
rigidity to the insert. According to one embodiment of the
invention, the opening 73 includes an inner filler 74 formed of a
non-conductive, non-magnetic material different from that used to
form outer shell 72, such that the insert 70 is formed as a
multi-material insert. The inner filler 74 is formed of
non-conductive, non-magnetic material having a lower density than
the outer shell material--and may be formed, for example, of a
dielectric foam that is very light weight. The inclusion of inner
filler 74 in the insert 70 in an interior of outer shell 72
functions to greatly reduce the overall weight of the insert 70,
such that the centrifugal forces generated by the inserts 70 are
greatly reduced--thereby improving the functioning and longevity of
the rotor assembly 68. Additionally, inclusion of the inner filler
74 within the outer shell 72, prevents air churning and distortion
during operation of the rotor assembly 68, thereby improving an
efficiency thereof.
[0031] According to other embodiments, the area 73 defined by outer
shell 72 may be left open (or partially open)--such that the mass
of the insert 70 is reduced. That is, in one embodiment, the
opening 73 may be left entirely unfilled, as shown in FIG. 7B. In
another embodiment, and as shown in FIG. 7C, the hollow area 73
defined by outer shell 72 could include a weight reduced structure
formed therein, such as a honeycomb structure 75 extruded with the
shell 72 that provides rigidity to the insert 70 while still
serving to reduce the overall mass of the insert. The interior of
the honeycomb structure 75 could be left unfilled or could include
a foam material therein.
[0032] As shown in FIG. 7, the outer shell 72 of the insert 70
includes retaining features thereon similar to those formed on
T-shaped insert 60 (FIG. 6). That is, outer shell 72 includes a
shoulder 66 on each end thereof that mates with the notches 62 of
adjacent rotor teeth 56, as well as a mating feature 48 (e.g., a
dovetail) formed on an axially inner surface thereof that mates
with a corresponding opening 50 formed in the back iron/inner hub
52 of the toothed rotor 58. The shoulders 66 and mating feature 48
hold the insert 70 in place against centrifugal force experienced
during rotor rotation and help form a rotor assembly 68 that is
robust to centrifugal forces acting thereon.
[0033] Referring now to FIG. 8, a portion of a rotor assembly 76 is
shown according to another embodiment of the invention, with the
rotor assembly 76 having a segmented rotor 78 formed of a plurality
of separate rotor poles 80 that are mated circumferentially around
a non-magnetic rotor hub 82 by way of a mating feature (e.g.,
dovetail feature) 84 on the rotor poles 80 that mates with an
opening/receptacle 86 formed in the hub 82. The rotor assembly 76
also includes non-conductive, non-magnetic inserts 88 inserted
between each pair of adjacent rotor poles 80--in an interpolar gap
90 formed by the adjacent rotor poles 80. As shown in FIG. 8, the
non-conductive, non-magnetic inserts 88 are formed as inserts that
are configured to be received in the interpolar gap 90 formed
between each adjacent pair of rotor poles 80--with the inserts 88
having a shape that conforms to that of the gaps 90. According to
an exemplary embodiment, the inserts have a dovetail construction
that enables the inserts to be held radially between the rotor
poles 80 against centrifugal force caused by rotor rotation.
[0034] According to an exemplary embodiment, the insert 88 is
formed as a multi-material insert having an outer shell 90 formed
of a first non-conductive, non-magnetic material and an inner
filler 92 formed of a second non-conductive, non-magnetic material.
According to an exemplary embodiment, the outer shell 90 is formed
of a non-conductive, non-magnetic material that provides a high
mechanical strength and rigidity to the insert. The inner filler 92
is formed of non-conductive, non-magnetic material having a lower
density than the outer shell 90 material--and may be formed, for
example, of a dielectric foam that is very light weight. The
inclusion of inner filler 92 in the insert in an interior thereof
functions to greatly reduce the overall weight of the insert 88,
such that the centrifugal forces generated by the inserts 88 are
greatly reduced--thereby improving the functioning and longevity of
the rotor assembly 76. Alternatively, it is recognized that the
insert 88 could also be formed as an extrusion with internal
features that provide for increased strength, without the weight
penalty of being solid, as discussed above.
[0035] Referring now to FIGS. 9 and 10, rotor assemblies 94, 96 for
a toothed rotor and a segmented rotor are shown, respectively,
according to additional embodiments of the invention. In each of
the rotor assemblies 94, 96, a "cage-like" assembly is provided for
fastening of the rotor assembly 94, 96 and for providing additional
retaining strength for the non-conductive, non-magnetic inserts 98,
100 positioned between the salient rotor poles 102, 104 of the
rotors in order to make the assembly more robust. For forming the
cage-like assembly, non-conductive, non-magnetic end plates 106 are
positioned at opposing ends of the rotor assembly 94, 96--on
opposite sides of a toothed rotor or segmented rotor 112, 114 that,
according to one embodiment, may be formed of a stack(s) of rotor
laminations 108, 110 (or that alternatively may be formed as a
single piece). As shown in FIGS. 9 and 10, the non-conductive,
non-magnetic inserts 98, 100 that extend axially through the entire
length of the stack of rotor laminations 108, 110 include a mating
feature 116 formed on each end thereof that is constructed to mate
with a corresponding opening 118 formed in the end plates 206. The
mating features 116 formed on the inserts 98, 100 are received in
the openings 118 formed in the end plates 106 so as to mate the
inserts to the end plates and thereby form the "cage-like" rotor
assembly. The end plates 106 function to both provide fastening of
the rotor assembly 94, 96 (i.e., fastening of the stack(s) of rotor
laminations 108, 110 of the toothed rotor 112 or segmented rotor
114, if the rotors are formed of laminations) and to provide
additional retaining strength for the inserts 98, 100, making the
rotor assemblies 94, 96 more robust.
[0036] Beneficially, embodiments of the invention thus provide
non-conductive, non-magnetic rotor inserts that provide smoothing
for various types of salient rotors. The rotor inserts enable
significant reduction of friction and windage losses, as the rotor
surface becomes mechanically smooth based on the positioning of the
inserts between adjacent pairs of rotor poles, so as to provide a
significant efficiency improvement (i.e., better efficiency than a
non-smooth rotor), especially for high-speed applications. The
non-conductive, non-magnetic rotor inserts are assembled with the
salient rotor in a mechanically robust way, such as via the use of
mating (e.g., dovetail) features on the inserts, that enable the
inserts to withstand centrifugal forces at high speeds. The
non-conductive, non-magnetic rotor inserts are further constructed
to minimize the mass that is added to the rotor, with the inserts
being formed to fill only a portion of an interpolar between
adjacent rotor poles and/or being formed partially of a low-density
material.
[0037] Therefore, according to one embodiment of the invention, an
electrical machine includes a stator and a rotor assembly disposed
within the stator and configured to rotate relative to the stator,
wherein the rotor assembly comprises a rotor core comprising a
plurality of salient rotor poles that are spaced apart from one
another around an inner hub such that an interpolar gap is formed
between each adjacent pair of salient rotor poles, with an opening
being defined by the rotor core in each interpolar gap, and a
plurality of inserts positioned in the gaps formed between the
plurality of salient rotor poles, the plurality of inserts being
formed of electrically non-conductive and non-magnetic material.
Each of the plurality of inserts comprises a mating feature formed
an axially inner edge thereof that is configured to mate with a
respective opening being defined by the rotor core, so as to secure
the insert to the rotor core against centrifugal force experienced
during rotation of the rotor assembly.
[0038] According to another embodiment of the invention, a method
for manufacturing an electrical machine includes providing a stator
and providing a rotor assembly that is positionable within the
stator and is mountable for rotation about a central axis, wherein
providing the rotor assembly comprises providing a salient rotor
core comprising a plurality of salient rotor poles that are spaced
apart from one another around an inner hub such that an interpolar
gap is formed between each adjacent pair of salient rotor poles,
with a dovetail-shaped opening being defined by the rotor core in
each interpolar gap. Providing the rotor assembly further comprises
providing a plurality of inserts formed of electrically
non-conductive and non-magnetic material and securing the plurality
of inserts in the interpolar gaps formed between the plurality of
salient rotor poles, wherein, in securing each of the plurality of
inserts in an interpolar gap formed between an adjacent pair of
salient rotor poles, a mating feature of the insert is mated with a
respective opening being defined by the rotor core, so as to secure
the insert to the rotor core against centrifugal force experienced
during rotation of the rotor assembly.
[0039] According to yet another embodiment of the invention, a
rotor assembly for an electrical machine includes a salient rotor
comprising a plurality of salient rotor poles that are spaced apart
from one another around an inner hub such that an interpolar gap is
formed between each adjacent pair of salient rotor poles and a
plurality of inserts positioned in the interpolar gaps formed
between the plurality of salient rotor poles and being constructed
such that the plurality of inserts in combination with the
plurality of salient rotor poles forms a smooth outer surface on
the rotor assembly. The plurality of inserts comprise one of
T-shaped inserts formed of an electrically non-conductive and
non-magnetic material, hollow inserts having an outer shell formed
of an electrically non-conductive and non-magnetic material, or
dovetail-shaped inserts formed of an electrically non-conductive
and non-magnetic material. Each of the plurality of inserts is
configured to mate with the salient rotor so as to secure the
insert to the salient rotor against centrifugal force experienced
during rotation of the rotor assembly.
[0040] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
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