U.S. patent application number 12/393582 was filed with the patent office on 2009-09-24 for brushless machine with tapered poles.
This patent application is currently assigned to UT-BATTELLE, LLC. Invention is credited to John S. Hsu.
Application Number | 20090236924 12/393582 |
Document ID | / |
Family ID | 46322722 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090236924 |
Kind Code |
A1 |
Hsu; John S. |
September 24, 2009 |
BRUSHLESS MACHINE WITH TAPERED POLES
Abstract
A method and apparatus in which a rotor (11) and a stator (17)
define a radial air gap (20) for receiving AC flux and at least one
DC excitation coil (23, 24) positioned near the stator end turn to
produce DC flux in axial air gaps (21, 22) additive to the AC flux.
Side magnets (16) and flux-guiding magnets (14) are provided as
boundaries separating the side poles (12a, 12b) of opposite
polarity from other portions of the rotor (11) and from each other
to define PM poles (12a, 12b) for conveying the DC flux to or from
the primary air gap (20) and for inhibiting flux from leaking from
said pole portions prior to reaching the primary air gap (20). Side
magnets (16), side poles (12a and 12b), flux-guiding magnets (14),
ferromagnetic end plates (11c), non-magnetic end plates (12c), and
ring bands (37) are optionally provided for performance
improvement.
Inventors: |
Hsu; John S.; (Oak Ridge,
TN) |
Correspondence
Address: |
ORNL-UTB-LUEDEKA, NEELY & GRAHAM
P.O. BOX 1871
KNOXVILLE
TN
37901
US
|
Assignee: |
UT-BATTELLE, LLC
Oak Ridge
TN
|
Family ID: |
46322722 |
Appl. No.: |
12/393582 |
Filed: |
February 26, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11162753 |
Sep 21, 2005 |
7518278 |
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12393582 |
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11019075 |
Dec 21, 2004 |
6972504 |
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11162753 |
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10848450 |
May 18, 2004 |
6989619 |
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11019075 |
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60675419 |
Apr 27, 2005 |
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Current U.S.
Class: |
310/156.53 ;
310/181 |
Current CPC
Class: |
H02K 1/2766 20130101;
H02K 21/046 20130101 |
Class at
Publication: |
310/156.53 ;
310/181 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 21/04 20060101 H02K021/04 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under
Contract No. DE-AC05000R22725 awarded to UT-Battelle, LLC, by the
U.S. Department of Energy. The Government has certain rights in
this invention.
Claims
1.-4. (canceled)
5. A brushless electric machine comprising: a cylindrical stator; a
rotor having an axis of rotation, the rotor being spaced from the
stator to define an annular primary air gap that receives an AC
flux from the stator, the rotor having longitudinal pole portions
running parallel to the axis of rotation and alternating in
polarity around a circumference of the rotor; wherein portions of
permanent magnet (PM) material are positioned to form boundaries
separating the rotor pole portions of opposite polarity from an
interior of the rotor and from each other to define PM poles for
conveying the DC flux to or from the primary air gap and for
inhibiting flux from leaking from said pole portions prior to
reaching the primary air gap when said direct current is of the
first polarity; wherein at least one pole portion in each pair of
rotor pole portions is provided by ferromagnetic pole material and
extends longitudinally from the axial air gap towards a middle of
the rotor; wherein the pole material has a relative greater cross
section at the axial air gap and tapers to a relatively narrower
cross section proximate the middle of the rotor to conduct flux
that turns ninety degrees from the secondary air gap to reach the
primary air gap; and at least one device selected from the group
consisting of side magnets, side poles, flux-guiding magnets,
ferromagnetic end plates, non-magnetic end plates, and ring
bands.
6. The brushless machine of claim 5 further comprising at least one
stationary excitation coil and at least one stationary flux
collector for receiving direct current from an external source and
being positioned across an axial air gap from one end face of the
rotor so as to induce a DC flux in the rotor which increases a
resulting flux in the primary air gap when said direct current is
of a first polarity and which reduces the resulting flux in the
primary air gap when said direct current is of a second polarity
opposite said first polarity.
7. The brushless machine of claim 6, wherein a return path for the
DC flux to the excitation coil is provided by the magnetic stator
frame and stator core.
9. (canceled)
10. The brushless machine of claim 5 further comprising side
magnets in place of said side poles.
11-22. (canceled)
23. A brushless electric machine comprising: a cylindrical stator;
a rotor having an axis of rotation, the rotor being spaced from the
stator to define an annular primary air gap that receives an AC
flux from the stator, the rotor having a plurality of longitudinal
pole portions disposed parallel to the axis of rotation and
alternating in polarity around a circumference of the rotor;
wherein each longitudinal pole portion comprises portions of
permanent magnet (PM) material positioned to form boundaries
separating the longitudinal pole portions of opposite polarity from
an interior of the rotor and from each other to define PM poles and
wherein at least one of the longitudinal pole portions has a first
end and a side magnet is disposed adjacent the first end; and a
ferromagnetic end plate disposed adjacent the side magnet wherein
the side magnet is disposed between the ferromagnetic side plate
and the first end of the at least one longitudinal pole portion.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Divisional Application of currently
pending and allowed U.S. patent application Ser. No. 11/162,753
filed Sep. 21, 2005, entitled: "IMPROVEMENTS FOR HIGH STRENGTH
UNDIFFUSED BRUSHLESS MACHINE AND METHOD," which is a
continuation-in-part of U.S. patent application Ser. No. 11/019,075
filed Dec. 21, 2004, which issued as U.S. Pat. No. 6,972,504 on
Dec. 6, 2005, which is a continuation-in-part of U.S. patent
application Ser. No. 10/848,450 filed May 18, 2004, which issued as
U.S. Pat. No. 6,989,619 on Jan. 24, 2006. Application Ser. No.
11/162,753 claims priority to U.S. Provisional Patent Application
60/675,419, filed Apr. 27, 2005 and is herein incorporated by
reference in its entirety. This application is related to Hsu's
previous U.S. Pat. Nos. 6,310,417 issued Oct. 30, 2001; 6,573,634
issued Jun. 3, 2003; and 6,700,297 issued Mar. 2, 2004, all herein
incorporated by reference.
TECHNICAL FIELD
[0003] The field of the invention is brushless machines, including
both AC and DC machines, including both motors and generators, and
including permanent magnet (PM) machines and PM-reluctance
machines. This invention specifically teaches flux guide technology
for a High Strength Undiffused Brushless (HSUB) motor.
DESCRIPTION OF THE BACKGROUND ART
[0004] There are three major types of brushless electric machines
available for the electric vehicle (EV) and hybrid electric vehicle
(HEV) drive systems. These are the induction machine, the PM
machine, and the switched-reluctance machine.
[0005] Permanent magnet (PM) machines with and without reluctance
paths have been recognized for having a high power density
characteristic. A PM rotor does not generate copper losses. One
drawback of the PM motor for the above-mentioned application is
that the air gap flux produced by the PM rotor is limited, and
therefore, a sophisticated approach is required for high speed,
field weakening operation. Another constraint is that inductance is
low, which means that current ripple must be controlled.
[0006] It is understood by those skilled in the art that a PM
electric machine has the property of high efficiency and high power
density. However, the air gap flux density of a PM machine is
limited by the PM material, which is normally about 0.8 Teslas and
below. A PM machine cannot operate at an air gap flux density as
high as that of a switched reluctance machine. When the PM motor
needs a weaker field with a reasonably good current waveform for
high-speed operation, a sophisticated power electronics inverter is
required.
[0007] When considering a radial gap configuration for undiffused,
high strength operation, several problems have to be overcome. It
is desirable to provide a compact design with a shape similar to a
conventional radial gap machine and to include laminated rotor-core
structure.
[0008] It would also be beneficial to further enhance the control
of the field above that which is available with known PM rotor
constructions. This would increase the motor torque. It is also an
objective to accomplish this while retaining the compactness of the
machine.
[0009] The enhanced field weakening can reduce the field strength
at high speed to lower the back EMF produced in the winding.
Therefore, for a specified DC link voltage, the speed range of the
machine can be increased over what it otherwise would be. This will
meet the compactness objective and allow simplification of the
drive system requirements.
[0010] The permanent magnet (PM) motor is known to have higher
power density among motors. However, the air-gap flux density of a
PM motor is fixed due to the "permanent" nature of the magnet. The
HSUB motor with the field enhancement and weakening capabilities
can overcome the drawbacks of the PM motors.
SUMMARY OF THE INVENTION
[0011] The electric machine may have at least one improved feature
selected from the group consisting of at least one device selected
from the group consisting of side magnets, side poles, flux-guiding
magnets, ferromagnetic end plates, and ring bands.
[0012] The electric machine may have at least one improved feature
selected from the group consisting of flux-guiding magnets, side
magnets, side poles, side ring, retaining rings, axial stationary
flux path, and stationary excitation coils. Embodiments of the
invention may incorporate a method and apparatus in which a rotor
and a stator define a radial air gap for receiving AC flux.
[0013] Embodiments of the invention provide increased power and
torque without increasing the size of the machine.
[0014] Embodiments of the invention are applicable to both AC and
DC machines, and to both motors and generators.
[0015] Embodiments of the invention are applicable to both PM
machines with and without reluctance paths, respectively. The
reluctance paths are known for producing reluctance torque
components.
[0016] Embodiments of the invention are applicable to both PM
machines with and without stationary excitation field coils and
stator axial flux paths.
[0017] Embodiments of the invention provide a compact electric
machine structure for application to electric or hybrid
vehicles.
[0018] Other objects and advantages of the invention, besides those
discussed above, will be apparent to those of ordinary skill in the
art from the description of the preferred embodiments which
follows. In the description reference is made to the accompanying
drawings, which form a part hereof, and which illustrate examples
of the invention. Such examples however are not exhaustive of the
various embodiments of the invention, and therefore reference is
made to the claims which follow the description for determining the
scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a longitudinal section view of a HSUB machine with
brushless excitation;
[0020] FIGS. 2 and 3 are end views of the rotor incorporated in the
assembly in FIG. 1;
[0021] FIGS. 2a and 3a are close-ups of the rotor face at the axial
gaps;
[0022] FIG. 4 is a longitudinal section view of a HSUB machine
without brushless excitation;
[0023] FIGS. 5 and 6 are end views of the rotor incorporated in the
assembly in FIG. 4;
[0024] FIGS. 5a and 6a are close-ups of the rotor face at the axial
gaps;
[0025] FIG. 7 shows the flux-guide magnets on the rotor. As an
option, the magnet strength on the left hand side can be chosen to
be different from the right hand side.
[0026] FIG. 8 is an end view of the rotor seen in FIG. 7;
[0027] FIG. 8a is an end view of a pole having multiple sets of
flux-guide magnets for improving reluctance-torque production.
[0028] FIGS. 9 and 10 show the rotor with and without both
reluctance poles and additional side magnets, respectively;
[0029] FIGS. 11, 12, and 13 are another view of the improved
features of the invention with the excitation coil flux shown.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The principle of a high strength, undiffused brushless
machine has been previously disclosed in the Hsu, U.S. Pat. No.
6,573,634, issued Jun. 3, 2003, Hsu, U.S. patent application Ser.
No. 10/688,586 filed Sep. 23, 2003, and Hsu U.S. patent application
Ser. Appl. No. 10/848,450 filed May 18, 2004, the disclosures of
which are hereby incorporated by reference.
[0031] For a conventional PM machine the air-gap flux density is
about 0.6 to 0.8 Teslas and cannot be weakened without the aid of
some sophisticated power electronics. Both the stationary
excitation coil and the PM material in the rotor maximize rotor
flux in the PM machines of the embodiments of the present
invention. These embodiments can produce two to three times the air
gap flux density of a conventional PM machine. Because the PM
torque produced by an electric machine is directly proportional to
the air gap PM flux density, a higher torque, more powerful machine
is provided with only small additions to size and weight.
[0032] FIG. 1 shows a longitudinal section view of a radial gap,
high strength undiffused machine 10 with eight side poles 12a, 12b
in a rotor assembly 11. FIGS. 2 and 3 each show the eight side
poles 12a and 12b attached to the sides of the rotor core in an
area bounded by eight sets of flux-guiding magnets 14 that consist
of three pieces of magnets for guiding flux towards the radial air
gap 20 for the sample eight-pole machine. The eight side magnets 16
help to prevent leakage flux at the rotor sides. Optionally,
reluctance side poles 15 are provided by the portions of the rotor
positioned in between the side magnet 16 and side pole 12a and 12b
and between the flux-guiding magnets 14 without contacting the
flux-guiding magnets 14. The reluctance side poles 15 allow the
flux produced by a stator 17 to go through these reluctance side
poles 15 easier than the path going through the side poles 12a and
12b.
[0033] The rotor assembly 11 is preferably made as described in the
disclosures cited above, namely, the rotor has a hub 11a and a
plurality of laminations 11b of ferromagnetic material are mounted
and stacked on the hub 11a and clamped by non-magnetic end plates
12c. The rotor laminations 11b and ferromagnetic end plates 11c
have keyed projections 11d for insertion in keyways in the rotor
hub 11a. The ferromagnetic end plates 11c can be made of solid mild
steel or stacked laminations.
[0034] The side poles 12a, 12b are made of ferromagnetic material.
The flux-guiding magnets 14 can be pre-formed pieces or the
injected type. Between pieces of flux-guiding magnets 14, an epoxy
material can be used to fill gaps. Side magnets 16 are separate
pieces attached to the ends of the rotor assembly 11. Bolts (not
shown) are used to hold the side poles 12a, 12b and ferromagnetic
end plates 11c in position. Ring band 37 can hold the side poles
12a, 12b, side magnets 16, and ferromagnetic end plate 11c in place
to withstand the centrifugal force.
[0035] The machine 10 optionally has brushless excitation as shown
in FIGS. 1 and 4. Brushless excitation of FIG. 1 is provided by
stationary coils 23 and 24 and stationary flux collectors 25 and
26. No brushless excitation is used in FIG. 4 wherein the machine
10 is absent stationary coils and stationary flux collectors.
[0036] The rotor assembly 11 rotates with a main drive shaft 19
around an axis of rotation 19a. The stator 17 is disposed around
the rotor 11 and has a laminated core 17a and windings 17b as seen
in a conventional AC machine. The rotor assembly 11 is separated
from the stator 17 by a radial air gap 20, which is also referred
to herein as the primary air gap. AC flux is produced in this air
gap 20 by the stator field. With brushless excitation, the rotor
assembly 11 is separated from the stationary flux collectors 25 and
26 by axial air gaps 21 and 22, respectively. These air gaps 21, 22
are oriented perpendicular to the axis 19a of the rotor 11. DC flux
will be produced in these air gaps 21, 22 by excitation coils 23
and 24. Stationary flux collectors 25 and 26 are disposed at the
axial air gaps 21, 22. The laminated option of stationary flux
collector can further smooth the DC flux component and reduce the
possible occurrence of eddy currents.
[0037] The drive shaft 19 is supported by bearings 31 and 32. A
short internal shaft 30 is also coupled to the rotor 11. A shaft
encoder 33 and a pump 34 for lubricant for the motor 10 are
situated inside a passageway 35 through the hollow center of the
excitation coil 24. A housing cover 36 closes the passageway
33.
[0038] Referring to FIG. 2, the DC flux produced by the excitation
coils 23, 24 is conducted into the rotor from one set of the
ferromagnetic side poles 12a attached to the N polarity of the
rotor, and then turns to flow radially outward across the main air
gap 20 into the stator core 17a, then loops and returns radially
inward and is conducted axially outward through adjacent side poles
12b attached to the S polarity at the other end of the rotor 11
(FIG. 3). The DC flux produced by the excitation coils does not
pass through the reluctance side poles 15. The DC flux return path
38 (labeled in FIG. 11) goes through the frame that is made of
magnetically conducting material.
[0039] Referring to FIGS. 2 and 3, the flux-guiding magnets 14
together with the excitation current going through the excitation
coils 23 and 24 produce the north (N) and south (S) poles on the
exterior of rotor 11 that faces the stator 17 and the radial air
gap 20. This rotor flux in the radial air gap 20 can be either
enhanced or weakened according to the polarity of the DC excitation
in the excitation assemblies 23, 24 that face the ends the rotor
11. Subsequently, the radial air gap 20 receives the rotor flux
from the rotor 11, which interacts with the primary flux induced by
the stator windings 17b to produce a torque.
[0040] FIGS. 7 and 8 show the flux-guiding magnets 14 inside the
rotor lamination 11b. As an option, a strong flux guiding magnet
set 14a and a weak magnet 14b can be chosen.
[0041] FIG. 8a shows a rotor assembly 11' illustrating that the
flux-guiding magnets 14 can be modified to consist of multiple sets
of magnets for each pole disposed on multiple grooves to increase
the reluctance torque value.
[0042] FIGS. 9 and 10 show the rotor with and without reluctance
side poles 15 installed, respectively.
[0043] FIGS. 11, 12 and 13 illustrate an embodiment of the
improvements of the current invention.
[0044] The functions of each optional improvement are described as
follows. The flux-guiding magnets 14 and side magnets 16 are used
to conduct the axial fluxes and to block the unwanted axial leakage
flux during field enhancement. The flux-guiding magnets 14 are
typically thin with respect to the width of the grooves in which
they are situated. A thinner magnet can reduce the cost of
permanent magnets. During field enhancement the higher air-gap flux
density is produced by the brushless field excitation. Therefore, a
weaker and thinner PM can do the job as part of the flux-guiding
barriers to discourage the flux going across the grooves. The
ferromagnetic end plate 11c smoothes the axial flux and produces a
return path for the side magnets 16. The ring band 37 prevents the
side poles, side magnets and end pieces from flying apart due to
the centrifugal force.
[0045] The HSUB technology is for electric vehicle and hybrid
electric vehicle applications. However, the HSUB technology
certainly can be used for other applications where the use of
electricity to produce torque and motion is involved.
[0046] The invention is applicable to both AC synchronous and DC
brushless machines and to both motors and generators.
[0047] This has been a description of the preferred embodiments of
the invention. The present invention is intended to encompass
additional embodiments including modifications to the details
described above which would nevertheless come within the scope of
the following claims.
* * * * *