U.S. patent application number 12/409663 was filed with the patent office on 2010-09-30 for optimized electric machine for smart actuators.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Lei Hao, Balarama V. Murty, Chandra S. Namuduri.
Application Number | 20100244613 12/409663 |
Document ID | / |
Family ID | 42669648 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100244613 |
Kind Code |
A1 |
Hao; Lei ; et al. |
September 30, 2010 |
OPTIMIZED ELECTRIC MACHINE FOR SMART ACTUATORS
Abstract
An electric machine includes a plurality of magnets for
generating a first magnetic field. A magnet holder retains the
plurality of magnets. A first stator is disposed radially outward
from the magnet holder for generating a second magnetic field. The
first stator includes a plurality of stator poles separated by
slots with each of the stator poles having a concentrated winding
with a respective number of turns formed around each respective
stator pole. A second stator is disposed radially inward from the
magnet for generating a third magnetic field. The second stator has
a plurality of stator poles separated by slots with each of the
stator poles having a concentrated winding with a respective number
of turns formed around each respective stator pole. The magnet
holder and magnets retained therein are rotatable between the first
stator and second stator.
Inventors: |
Hao; Lei; (Troy, MI)
; Namuduri; Chandra S.; (Troy, MI) ; Murty;
Balarama V.; (West Bloomfield, MI) |
Correspondence
Address: |
MacMillan, Sobanski & Todd, LLC;One Maritime Plaza
720 Water Street, 5th Floor
Toledo
OH
43604
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
DETROIT
MI
|
Family ID: |
42669648 |
Appl. No.: |
12/409663 |
Filed: |
March 24, 2009 |
Current U.S.
Class: |
310/198 |
Current CPC
Class: |
H02K 3/28 20130101; H02K
21/12 20130101; H02K 16/04 20130101 |
Class at
Publication: |
310/198 |
International
Class: |
H02K 16/04 20060101
H02K016/04 |
Claims
1. An electric machine comprising: a plurality of magnets for
generating a first magnetic field; a non-magnetic magnet holder for
retaining the plurality of magnets, the magnet holder having a
circular configuration with the plurality of magnets being
positioned around the circular configuration of the magnet holder;
a first stator disposed radially outward from the plurality of
magnets for generating a second magnetic field, the magnet and the
first stator having a first air gap formed therebetween, the first
stator including a plurality of stator poles separated by slots
with each of the stator poles having a concentrated winding with a
respective number of turns formed around each respective stator
pole, each respective concentrated winding within the first stator
comprising non-overlapping phases; and a second stator disposed
radially inward from the plurality of magnets for generating a
third magnetic field, the magnet and the second stator having a
second air gap formed between, the second stator having a plurality
of stator poles separated by slots with each of the stator poles
having a concentrated winding with a respective number of turns
formed around each respective stator pole, each respective
concentrated winding within the second stator comprising
non-overlapping phases; wherein the magnet holder and magnets
retained therein are rotatable between the first stator and second
stator, wherein the concentrated windings of the first stator and
the second stator increase an active length of the windings of each
respective stator, and wherein the concentrated winding reduces an
overhang of each respective winding with respect to each stator
pole of each stator for improving torque efficiency.
2. The electric machine of claim 1 wherein the magnet holder and
the magnet forms a coreless rotor.
3. The electric machine of claim 1 wherein the inner stator
includes a same number of stator poles as the outer stator.
4. The electric machine of claim 1 wherein each respective magnet
represents a respective rotor pole, wherein a combination of a
number of rotor poles and a number of stator slots have a least
common multiple of at least 36.
5. The electric machine of claim 4 wherein the concentrated
windings include a winding factor of greater than 0.7.
6. The electric machine of claim 4 wherein number of magnet poles
is at least 8.
7. The electric machine of claim 4 wherein the number of stator
slot is an even integer.
8. The electric machine of claim 1 further comprising a shaft
coupled to the magnet holder and is co-axial to the magnet holder,
the shaft being configured for coupling to a driven component,
wherein an electromagnetic force generated by the magnet, first
stator, and second stator is converted into a mechanical torque,
the mechanical torque being applied via the magnet holder and shaft
to the driven component.
9. The electric machine of claim 8 wherein the magnet holder is
adapted to be coupled to an actuator for an active suspension
system.
10. The electric machine of claim 8 wherein the magnet holder is
adapted to be coupled to an actuator for a semi active suspension
system.
11. The electric machine of claim 8 wherein the magnet holder is
adapted to be coupled to an actuator for an electric power steering
system.
12. The electric machine of claim 8 wherein the magnet holder is
adapted to be coupled to an actuator for an electromechanical
braking system.
13. The electric machine of claim 8 can be used as traction machine
for a hybrid propulsion system.
14. The electric machine of claim 8 can be used as traction machine
for a fuel cell propulsion system.
15. The electric machine of claim 8 can be used as traction machine
for an electrical propulsion system.
16. The electric machine of claim 1 wherein the respective inner
stator poles are angularly aligned with respective outer stator
poles.
17. The electric machine of claim 1 wherein the respective inner
stator poles are angularly offset with the respective outer stator
poles.
Description
BACKGROUND OF INVENTION
[0001] An embodiment relates generally to dual stator electric
machines.
[0002] Electric machines are typically designed to achieve a
specific operating characteristic. For example, electric machines
with drag cup rotors have very low inertia properties. Induction
machines typically exhibit torque ripple free properties, whereas
conventional permanent magnet synchronous machines exhibit high
torque to ampere ratios. However, achieving a respective specific
operating characteristic typically results in the sacrifice of
other operating characteristics. While each of the above examples
achieve one of the desired operating characteristics, this is often
done at the expense of not obtaining one of the other respective
desired operating characteristics. That is, none of the devices
described above are capable of exhibiting all of the desired
operating characteristics in a single electric machine.
SUMMARY OF INVENTION
[0003] An advantage of an embodiment of the invention is an
electric machine that provides optimal operating characteristics
such as a high torque to ampere ratio, a high torque to inertia
ratio, and low torque ripple.
[0004] An embodiment contemplates an electric machine. The electric
machine includes a plurality of magnets for generating a first
magnetic field. A magnet holder retains the plurality of magnets.
The magnet holder has a circular configuration with the plurality
of magnets being evenly positioned around the circular
configuration of the magnet holder. A first stator is disposed
radially outward from the magnet for generating a second magnetic
field. The magnet and the first stator have a first air gap formed
therebetween. The first stator includes a plurality of stator poles
separated by slots with each of the stator poles having a
concentrated winding with a respective number of turns formed
around each respective stator pole. Each respective concentrated
winding within the first stator comprises non-overlapping windings.
A second stator is disposed radially inward from the magnet for
generating a third magnetic field. The magnet and the second stator
have a second air gap formed between. The second stator has a
plurality of stator poles separated by slots with each of the
stator poles having a concentrated winding with a respective number
of turns formed around each respective stator pole. Each respective
concentrated winding within the second stator comprises
non-overlapping windings. The magnet holder and magnets retained
therein are rotatable between the first stator and second stator.
The employment of concentrated windings of the first stator and the
second stator increases the active length of the stator within a
package size by reducing the end turn length, and as a result,
increases the torque density. The concentrated winding reduces an
overhang of each respective winding with respect to each stator
pole of each stator for improving machine efficiency.
BRIEF DESCRIPTION OF DRAWINGS
[0005] FIG. 1 is a cross section view of an electric machine along
a diametric plane.
[0006] FIG. 2 is a cross section view of the electric machine along
a transverse plane.
[0007] FIG. 3 is a cross section view of a magnetic holder and
magnet.
[0008] FIG. 4 is an electrical schematic of a concentrated winding
configuration for a 3-phase electric machine.
[0009] FIG. 5 is an electrical schematic of a concentrated winding
configuration for a first phase of the electric machine.
[0010] FIG. 6 is an electrical schematic of a concentrated winding
configuration for a second phase of the electric machine.
[0011] FIG. 7 is an electrical schematic of a concentrated winding
configuration for a third phase of the electric machine.
[0012] FIG. 8 is an electrical schematic of a winding configuration
for a prior art conventional overlapping winding.
[0013] FIG. 9 is a table illustrating optimized rotor pole to
stator slot combinations.
DETAILED DESCRIPTION
[0014] Referring to both FIGS. 1 and 2 there is shown a
cross-section section views of an electric machine 10 along a
diametric plane and a transverse plane, respectively. The electric
machine 10 as described herein is used for devices and systems that
require high torque and fast response times such as semi-active or
active suspension systems, electric power steering systems,
electromechanical braking systems or like systems. The electric
machine 10 is a dual stator electric machine having a first stator
12 and a second stator 14 fixed within in a machine housing 15. The
first stator 12 and the second stator 14 are coaxial to one another
within the machine housing 15, and have different diameters. The
first stator 12 and the second stator 14 have concentrated
windings. Concentrated windings are non-overlapping windings which
will be described in detail later.
[0015] A plurality of magnets 16 are radially disposed between the
first stator 12 and second stator 14. The plurality of magnets 16
are retained by a magnet holder 18 in a cylindrical configuration
that are rotatable in the space created between the first stator 12
and the second stator 14. A cross section view of the magnet holder
18 and a respective magnet are shown generally in FIG. 3. It should
be understood the magnet holder is only one configuration and is
not limited to the magnet holder as illustrated. The first stator
12 is disposed radially outward from the plurality of magnets 16 by
a respective distance thereby forming a first air gap 20
therebetween. The second stator 14 is disposed radially inward from
the magnet holder 18 by a respective distance thereby forming a
second air gap 22 therebetween. The first stator 12 in cooperation
with the second stator 14 and plurality of magnets 16 generate a
flux path, as shown, for creating an electromagnetic field which is
converted into mechanical energy in the form of a torque. The
alignment of the stator poles of the first stator 12 to the stator
poles of the second stator 14 are angularly offset from one
another. It should be understood that depending upon the specific
electric machine operating requirements, the respective stator
poles of both respective stators may be angularly aligned with one
another or angularly offset with one another as illustrated.
[0016] The magnet holder 18 is coupled to a shaft 24 at a first end
of the magnet holder 18. The magnet holder 18 is supported by a
bearing surface 25 at second end of the magnet holder 18. The shaft
extends axially through the electric machine 10 and is co-axial to
the plurality of magnets 16. A first bearing 26 and a second
bearing 28 supports the shaft 24 as it extends through the machine
housing 15. The shaft extends through apertures in the machine
housing 15 and is configured for coupling to a respective component
29 exterior of the electric machine 10 for applying torque to the
respective component 29. The component may include an actuator for
the active suspension system, electric steering system, electric
braking system or like system. The magnet holder 18 is preferably
made from non-magnetic stainless steel. Alternatively, the magnet
holder 18 may be produced from other non-magnetic materials which
provide adequate strength for transmitting mechanical torque to the
respective vehicle system. The magnetic holder 18 in cooperation
with the bearing surface 25 and the coupling to shaft 24 which is
supported by bearings 26 and 28 maintain a spatial relationship
between the first and second stators 12 and 14. The respective
bearings allow the magnet holder 18 and plurality of magnets 16 to
rotate in the space formed radially between the first stator 12 and
second stator 14.
[0017] The electric machine 10 as shown in FIG. 1 eliminates the
conventional rotor with an integrally formed rotor shaft typically
used in conventional electric motors such as permanent magnet
electric machines. The second stator 14 in cooperation with the
second air gap 22 not only functions as the rotor core for
providing the magnetic flux path that would otherwise be provided
by the rotor core in a standard permanent magnet motor, but also
generates torque to increase torque density. The elimination of the
conventional rotor core and integral formed shaft reduces the
overall weight of the rotary part of electric machine thereby
reducing the inertia of the electric machine 10. At the same time,
in addition to the torque generated by the first stator and
coreless PM rotor, the second inner stator in cooperation with
coreless rotor can generate additional torque to increase the
torque density within package size.
[0018] As discussed earlier, both the first stator 12 and second
stator 14 have non-overlapping concentrated windings. FIGS. 4-7
show winding configurations illustrating the concentrated winding.
It should be understood that the winding concentrated winding
configuration is for exemplary purposes and that any configuration
of concentrated windings may be used herein. The electric motor 10
is a three phase motor having a first phase (A), a second phase
(B), and a third phase (C).
[0019] A respective pair of successively wound stator poles is
represented by stator pole 32 and stator pole 34 illustrates
concentrated winding configurations. Windings around stator poles
32 and 34 are electrically coupled to phase A. A first winding 36
is formed around stator pole 32 in a concentrated configuration,
which includes continuously wrapping stator pole 32 with a
predetermined number of turns before an exit wire 38 exits the
stator pole 32 and continues uninterrupted to the next stator pole
34. At stator pole 34, a second winding 40 is formed by
continuously winding stator pole 34 with the predetermined number
of turns. The second winding 40 thereafter electrically couples to
a neutral point 30. A next successive pair of stator poles is
electrically coupled to phase B using the concentrated winding
configuration. Similarly, the next successive pair of stator poles
is electrically coupled to phase C using the concentrated winding
configuration. The winding pattern is repeated for each of the
remaining successive pair of stator poles of the respective stator.
In contrast, a conventional lapping winding configuration includes
winding a respective pole using only a single turn before
proceeding to a next pole. The winding of the conventional lapping
configuration is continued in succession thereby ultimately
returning to each previously wound pole to add additional turns
around the stator pole. As a result, the number of exit wires that
electrically connect the successive stator poles will be equal to
the number of turns formed on each stator pole. The plurality of
exit wires between successive poles lap one another thereby
creating an overhang extending radially outward from the respective
stator as illustrated in FIG. 8. In the preferred embodiment, shown
in FIG. 4, only a single exit wire electrically connects a
respective pair of stator poles. The single non-overlapping exit
wire results in a significantly reduced overhang in comparison to
the conventional lap winding configuration. The reduction in the
overhang results in an increase in the active length of the stator
within package size for increasing the torque density and the fill
factor of the winding which provides for high power density with
fast response times. That is, in the concentrated winding
configuration, the majority of the overall winding is formed as
part of the turns as opposed to the exit wires coupling the
respective turns, thereby concentrating the length of the entire
winding to each of the respective stator poles. This results in
reducing the stator copper loss and improving efficiency of the
electrical machine. For same package size, the reduced length of
end turns results in longer active stator length thereby achieving
a high torque to ampere ratio or high power density for the same
operating range. Due to the improved efficiency, the increased
machine power density does not affect its thermal performance.
[0020] In utilizing the electric machine with concentrated
windings, an increased number of rotor poles (i.e., magnets) in
comparison to a conventional rotor may be preferably used.
Increasing the number of poles allows the thickness of the stator
core to be reduced. Reduction of the stator core thickness, in
addition to eliminating the conventional integral formed rotor core
and shaft, results in an overall weight reduction of the electrical
machine. Moreover, the increase in the number of poles in the
electrical machine also generates sinusoidal back emf which
provides an advantage of reducing torque ripple.
[0021] It should be understood that a respective pole/slot
combination may be selected for optimizing the torque output of the
electric machine in addition to decreasing the current draw and
torque ripple. FIG. 9 illustrates a table identifying a rotor pole
(i.e., magnets) to stator slot combination. The table identifies a
least common multiple (LCM) factor between the rotor pole and
stator slot combination, and in addition, a winding factor is shown
in certain combinations. The (LCM) is the smallest whole number
that is divisible by each of the combination values. The higher the
LCM factor, the lower torque ripple that is generated. Preferably,
a rotor pole number of greater than 8 is selected and rotor pole
and slot combination having a LCM of at least 36 has to be
selected.
[0022] The winding factor is defined by the ratio of flux linked by
an actual winding to flux that would have been linked by a full
pitch concentrated winding with the same number of turns. The
higher the winding factor value, the higher the torque density.
Preferably, a winding factor of greater than 0.7 is selected.
[0023] When selecting a combination which affords the advantages
described herein, a combination offering the highest LCM and the
highest winding factor should be selected. However, selecting the
combination with the highest LCM and winding factor has drawbacks.
For example, those combinations having an odd number of stator
slots can induce unbalanced magnetic pull which results in
vibration. Combinations that are acceptable selections are those
identified with an asterisk notation. Those combinations having a
high LCM values and winding factors but are suspect to vibration
are those with an odd number of slots and are represented with a #
notation.
[0024] While certain embodiments of the present invention have been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
* * * * *