U.S. patent application number 12/671387 was filed with the patent office on 2011-01-20 for appliance, rotor and magnet element.
Invention is credited to Kerrin Edmund Burnnand, Gerald David Duncan, Christian John Wade Gianni, Gregory Paul Hill, John Julian Aubrey Williams.
Application Number | 20110012463 12/671387 |
Document ID | / |
Family ID | 40304544 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110012463 |
Kind Code |
A1 |
Duncan; Gerald David ; et
al. |
January 20, 2011 |
APPLIANCE, ROTOR AND MAGNET ELEMENT
Abstract
A magnet element (37) and a method of its manufacture for
assembly into a rotor (38), the magnet element (37) having magnetic
domains aligned anisotropically to form a domain alignment pattern
(42), wherein the magnetic domain alignment pattern (42) in the
magnet element (37) has an orientation that varies substantially
continuously across at least part of the magnet element (37)
between its lateral edges from at least partially radial to at
least partially tangential.
Inventors: |
Duncan; Gerald David;
(Auckland, NZ) ; Gianni; Christian John Wade;
(Auckland, NZ) ; Williams; John Julian Aubrey;
(Auckland, NZ) ; Burnnand; Kerrin Edmund;
(Auckland, NZ) ; Hill; Gregory Paul; (Auckland,
NZ) |
Correspondence
Address: |
CLARK HILL PLC
150 NORTH MICHIGAN AVENUE, SUITE 2700
CHICAGO
IL
60601
US
|
Family ID: |
40304544 |
Appl. No.: |
12/671387 |
Filed: |
August 1, 2008 |
PCT Filed: |
August 1, 2008 |
PCT NO: |
PCT/NZ2008/000195 |
371 Date: |
March 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60953243 |
Aug 1, 2007 |
|
|
|
Current U.S.
Class: |
310/156.43 ;
29/598 |
Current CPC
Class: |
H02K 1/2786 20130101;
H02K 7/14 20130101; Y10T 29/49012 20150115; H02K 15/03
20130101 |
Class at
Publication: |
310/156.43 ;
29/598 |
International
Class: |
H02K 1/27 20060101
H02K001/27; H02K 15/03 20060101 H02K015/03 |
Claims
1. A rotor comprising: a plurality of magnet elements with two
lateral edges each with magnetic domains aligned anisotropically to
form a domain alignment pattern, the plurality of magnets being
arranged to form a permanent magnet ring with an inner face and an
outer face, said permanent magnet ring being between 150 mm and 400
mm in diameter, less than 100 mm in height and less than 20 mm
thick, and a rigid support holding said magnet elements in said
ring arrangement, wherein the magnetic domain alignment pattern in
each magnet element has an orientation that varies substantially
continuously across at least part of the magnet element between its
lateral edges from an orientation that has a predominant radial
component at a pole of the magnet element to an orientation that
has a least some tangential component at one lateral edge of the
magnet element, wherein the magnet elements are magnetised to
produce a resulting magnetic flux field.
2. (canceled)
3. A rotor according to claim 1 wherein each magnet element has the
pole positioned between the magnet element's lateral edges and the
magnetic domain alignment pattern in each magnet element has an
orientation that varies substantially continuously across the width
of the magnet element from an orientation that has a predominant
radial component at the pole of the magnet element to an
orientation that has a least some tangential component at both
lateral edges of the magnet element.
4. (canceled)
5. A rotor according to claim 3 wherein at both lateral edges the
orientation of the magnetic domain alignment pattern has a
significant tangential component, and the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of at least 15 degrees, with respect to the lateral
edges.
6-10. (canceled)
11. A rotor according to claim 1 wherein the radial and tangential
components of the orientation of the magnetic domain alignment
pattern within the magnet element varies sinusoidally according to:
V.sub.R=cos(.theta.), and V.sub.T=sin(.theta.) Where V.sub.R and
V.sub.T are the radial and tangential components of the orientation
respectively and .theta. is the angular position across the magnet
element, varying from substantially -90 degrees at one lateral edge
to substantially +90 degrees at the opposite lateral edge.
12-15. (canceled)
16. A rotor according to claim 1 wherein the resulting magnetic
flux field has poles with alternating polarity spaced around the
ring, the poles being aligned radially with respect to the
permanent magnet ring, and wherein the resulting magnetic flux
field of the permanent magnet ring traverses between adjacent poles
of opposite polarities and between those poles is focused to extend
beyond the boundary defined by the inner face, but remain at least
partially constrained within the boundary defined by the outer face
of the permanent magnet ring.
17. (canceled)
18. A rotor according to claim 16 wherein the portion of the
resulting magnetic flux field in each magnet element has an
orientation that varies substantially continuously over the magnet
element wherein: across the width of the magnet element, the
orientation varies from an orientation that has a predominant
radial component at the pole to an orientation that has a
predominant tangential component at the edges of the magnet element
adjacent other magnet elements in the permanent magnet ring, and
across the depth of the magnet element, the orientation varies from
an orientation that has a predominant radial component at an edge
corresponding to the inner face of the permanent magnet ring to an
orientation that has a predominant tangential component at an edge
corresponding to the outer face of the permanent magnet ring.
19-23. (canceled)
24. A rotor according to claim 1 wherein for each magnet element,
the magnetic domains were aligned during production using a press
or injection moulding tool comprising one or more elements defining
a cavity, and an apparatus for applying a magnetic flux field,
wherein the apparatus produces a magnetic field in the cavity
similar in nature to the desired magnetic domain alignment pattern
in the element.
25. A rotor according to claim 1 wherein the rotor is utilised in
the drive motor of a washing machine comprising an electronically
commutated motor, a stator of the motor having windings energisable
to cause rotation of the rotor, said stator being coupled to a
non-rotating tub or housing of the washing machine, said rotor
being coupled to a rotating drum of the washing machine.
26-29. (canceled)
30. A motor for use in a washing machine, said motor comprising: a
stator having at least three phase windings, each phase winding
being formed on a plurality of radially extending stator teeth, a
rotor as defined in any preceding claim, concentric with said
stator with the permanent magnet ring outside said stator teeth and
said rotor poles facing the ends of said stator teeth.
31. A method of producing a rotor comprising the steps of:
producing a plurality of magnet elements comprising permanent
magnet material with two lateral edges each with magnetic domains
aligned anisotropically to form a domain alignment pattern, wherein
the magnetic domain alignment pattern in each magnet element has an
orientation that varies substantially continuously across at least
part of the magnet element between its lateral edges from an
orientation that has a predominant radial component at a pole of
the magnet element to an orientation that has a least some
tangential component at one lateral edge of the magnet element,
arranging and retaining the magnet elements into a permanent magnet
ring in a rigid support, and magnetising the magnet elements to
produce a resulting magnetic flux field.
32. (canceled)
33. A method according claim 31 wherein the step of producing the
plurality of magnet elements comprises applying an external
magnetic flux field to each magnet element to align the magnetic
domains.
34. A method according to claim 31 wherein each magnet element has
the pole positioned between the magnet element's lateral edges and
applying the external magnetic flux field to a magnet element
aligns its magnetic domains such that the magnetic domain alignment
pattern in the magnet element has an orientation that varies
substantially continuously across the width of the magnet element
from an orientation that has a predominant radial component at the
pole of the magnet element to an orientation that has a least some
tangential component at both lateral edges of the magnet
element.
35. (canceled)
36. A method according to claim 34 wherein at both lateral edges
the orientation of the magnetic domain alignment pattern has a
significant tangential component, and the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of at least 15 degrees, with respect to the lateral
edges.
37-40. (canceled)
41. A method according to claim 31 wherein the radial and
tangential components of the orientation of the magnetic domain
alignment pattern within the magnet element varies sinusoidally
according to: V.sub.R=cos(.theta.), and V.sub.T=sin(.theta.) Where
V.sub.R and V.sub.T are the radial and tangential components of the
orientation respectively and .theta. is the angular position across
the magnet element, varying from substantially -90 degrees at one
lateral edge to substantially +90 degrees at the opposite lateral
edge.
42-50. (canceled)
51. A rotor comprising: a plurality of magnet elements with two
lateral edges each with magnetic domains aligned anisotropically to
form a domain alignment pattern, the plurality of magnets being
arranged to form a permanent magnet arrangement, and a rigid
support holding said magnet elements in said arrangement, wherein
the magnetic domain alignment pattern in each magnet element has an
orientation that varies substantially continuously across at least
part of the magnet element between its lateral edges from an
orientation that has a predominant radial component at a pole of
the magnet element to an orientation that has a least some
tangential component at one lateral edge of the magnet element,
wherein the magnet elements are magnetised to produce a resulting
magnetic flux field.
52. A magnet element for assembly into a ring of magnet elements to
form part of a rotor, the magnet element having two lateral edges
each with magnetic domains aligned anisotropically to form a domain
alignment pattern, wherein the magnetic domain alignment pattern in
the magnet element has an orientation that varies substantially
continuously across at least part of the magnet element between its
lateral edges from an orientation that has a predominant radial
component at a pole of the magnet element to an orientation that
has a least some tangential component at one lateral edge of the
magnet element.
53. (canceled)
54. A magnet element according to claim 52 wherein the pole is
positioned between the magnet element's lateral edges and the
magnetic domain alignment pattern in each magnet element has an
orientation that varies substantially continuously across the width
of the magnet element from an orientation that has a predominant
radial component at the pole of the magnet element to an
orientation that has a least some tangential component at both
lateral edges of the magnet element.
55. (canceled)
56. A magnet element according to claim 54 wherein at both lateral
edges the orientation of the magnetic domain alignment pattern has
a significant tangential component, wherein the significant
tangential component results in the magnetic domain alignment
pattern having an orientation of at least 15 degrees, with respect
to the lateral edges.
57-61. (canceled)
62. A magnet element according to claim 52 wherein the radial and
tangential components of the orientation of the magnetic domain
alignment pattern within the magnet element varies sinusoidally
according to: V.sub.R=cos(.theta.), and V.sub.T=sin(.theta.) Where
V.sub.R and V.sub.T are the radial and tangential components of the
orientation respectively and .theta. is the angular position across
the magnet element, varying from substantially -90 degrees at one
lateral edge to substantially +90 degrees at the opposite lateral
edge.
63-81. (canceled)
82. A rotor according to claim 51 wherein for each magnet element,
the magnetic domains were aligned during production using a press
or injection moulding tool comprising one or more elements defining
a cavity, and an apparatus for applying a magnetic flux field,
wherein the apparatus produces a magnetic field in the cavity
similar in nature to the desired magnetic domain alignment pattern
in the element.
83. An appliance with a drive motor, the drive motor comprising a
stator, and a rotor according to claim 1.
84. A rotor according to claim 3 wherein at both lateral edges the
orientation of the magnetic domain alignment pattern has a
significant tangential component, and the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of at between 20 to 35 degrees, with respect to the
lateral edges.
85. A rotor according to claim 3 wherein at both lateral edges the
orientation of the magnetic domain alignment pattern has a
significant tangential component, and the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of substantially 30 degrees, with respect to the
lateral edges.
86. A method according to claim 34 wherein at both lateral edges
the orientation of the magnetic domain alignment pattern has a
significant tangential component, and the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of between 20 degrees and 35 degrees, with respect
to the lateral edges.
87. A method according to claim 34 wherein at both lateral edges
the orientation of the magnetic domain alignment pattern has a
significant tangential component, and the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of substantially 30 degrees, with respect to the
lateral edges.
88. A magnet element according to claim 54 wherein at both lateral
edges the orientation of the magnetic domain alignment pattern has
a significant tangential component, wherein the significant
tangential component results in the magnetic domain alignment
pattern having an orientation of between 20 degrees to 35 degrees,
with respect to the lateral edges.
89. A magnet element according to claim 54 wherein at both lateral
edges the orientation of the magnetic domain alignment pattern has
a significant tangential component, wherein the significant
tangential component results in the magnetic domain alignment
pattern having an orientation of substantially 30 degrees, with
respect to the lateral edges.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electric motors and magnet
elements for use in such motors, and particularly motors having an
external rotor of a type that are used as the main drive motor for
a domestic laundry machine or other apparatus.
BACKGROUND TO THE INVENTION
[0002] EP 1548171 describes a drive system for washing machines.
The drive system comprises a motor with a large diameter shallow
stator and a rotor with magnets external to the stator. The stator
is supported on the end of a washing tub as shown in FIG. 2 of that
application. The stator has an aperture for a drive shaft to pass
through. As shown in FIGS. 2 and 16 of EP patent application
1548171, a rotor, which is to be fixed to the rotating drum of a
washing machine, has a ring of permanent magnet material supported
on the inside of a steel backing ring. A frame extends between the
hub of the rotor (through which the shaft can extend) and the steel
backing ring. The backing ring and frame may be formed together.
The permanent magnet material is made of a set of curved permanent
magnet elements. The permanent magnet material is magnetised after
physical construction of the rotor. A typical rotor has more than
30 poles magnetised into the ring of magnetic material. The
polarity of the poles alternates proceeding around the ring.
[0003] The magnet elements are typically made of hard ferrite
permanent magnet material. The magnets may be isotropic or
anisotropic. In anisotropic, the magnet elements are formed with
their magnetic domains aligned across the thickness of the magnet
so as to be aligned radially generally as shown by arrow "A" in
FIG. 1 of the present application. Magnetisation of the rotor
follows this pattern to create radial magnetic field lines through
the thickness of the magnet, represented by the magnetic flux lines
or paths in FIG. 1. This results in a pattern of poles on the
outside face of the magnets (adjacent the backing steel) that is
the inverse of the pattern of poles on the inside of the face of
the magnets (facing radial inwards).
[0004] In the case of radial magnetisation, the portion of each
magnet close to the interface between magnets is known to provide
little benefit in terms of the flux coupled from the rotor into the
stator and can typically be removed with little loss in torque
production.
[0005] Halbach arrays have been created to at least partially
alleviate this problem. One example of a Halbach array is an
arrangement of magnets with their respective directions of
magnetisation oriented as shown in FIG. 2a of the present
application. As shown in FIG. 2b of the present application, a
total resulting magnetic flux field is produced that reduces the
magnetic flux that couples out the back face of the magnetic ring.
Isotropic or anisotropic magnetic sections can be used in such an
array. Anisotropic sections have magnetic domains aligned in one
direction, whereas isotropic sections have magnetic domains
arranged randomly. FIG. 2c shows a portion of an "ideal" Halbach
array resulting magnetic flux field where a large or infinite
number of magnetic elements are formed into a Halbach array.
[0006] It has been proposed that a single piece isotropic ring can
be magnetised to produce a Halbach array "style" magnetic field.
The sections of single piece ring are magnetised using an external
magnetic field. Performance of the isotropic ring will be limited
relative to radially magnetised anisotropic magnets due to the
reduced magnetic strength of the isotropic magnets.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a magnet
element, or a rotor or a motor with such an element, or an
appliance that uses such a motor or rotor, where the magnet element
has pre-aligned domains to enable production of an improved
resulting magnetic flux field in a rotor or part of a rotor, or to
at least provide the industry with a useful choice.
[0008] In one aspect the present invention may be said to consist
in a rotor comprising: a plurality of magnet elements with two
lateral edges each with magnetic domains aligned anisotropically to
form a domain alignment pattern, the plurality of magnets being
arranged to form a permanent magnet ring with an inner face and an
outer face, said permanent magnet ring being between 150 mm and 400
mm in diameter, less than 100 mm in height and less than 20 mm
thick, and a rigid support holding said magnet elements in said
ring arrangement, wherein the magnetic domain alignment pattern in
each magnet element has an orientation that varies substantially
continuously across at least part of the magnet element between its
lateral edges from an orientation that has a predominant radial
component at a pole of the magnet element to an orientation that
has a least some tangential component at one lateral edge of the
magnet element, wherein the magnet elements are magnetised to
produce a resulting magnetic flux field.
[0009] Preferably, the magnet elements have a chamfer at the
intersection of each lateral edge with the front edge, wherein the
front edge is the edge at the inner face of the rotor.
[0010] Preferably, each magnet element has the pole positioned
between the magnet element's lateral edges and the magnetic domain
alignment pattern in each magnet element has an orientation that
varies substantially continuously across the width of the magnet
element from an orientation that has a predominant radial component
at the pole of the magnet element to an orientation that has a
least some tangential component at both lateral edges of the magnet
element.
[0011] Preferably, at both lateral edges, the orientation of the
magnetic domain alignment pattern has a significant tangential
component.
[0012] Preferably, at both lateral edges the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of at least 15 degrees with respect to the lateral
edges.
[0013] Preferably, both lateral edges the significant tangential
component result in the magnetic domain alignment pattern having an
orientation of between 20 to 35 degrees, and more preferably
substantially 30 degrees, with respect to the lateral edges.
[0014] Preferably, at both lateral edges, the orientation of the
magnetic domain alignment pattern has a predominant tangential
component.
[0015] Preferably, each magnet element has the pole positioned at
or towards one lateral edge.
[0016] Preferably, the orientation of the magnetic domain alignment
pattern has a significant tangential component at the lateral
edge.
[0017] Preferably, the orientation varies substantially
non-linearly over the magnet element.
[0018] Preferably, the radial and tangential components of the
orientation of the magnetic domain alignment pattern within the
magnet element varies sinusoidally according to:
V.sub.R=cos(.theta.), and
V.sub.T=sin(.theta.)
Where V.sub.R and V.sub.T are the radial and tangential components
of the orientation respectively and .theta. is the angular position
across the magnet element, varying from substantially -90 degrees
at one lateral edge to substantially +90 degrees at the opposite
lateral edge.
[0019] Preferably, one or more spacer elements are arranged between
the lateral edges of one or more proximate magnetic elements
arranged to form the permanent magnet ring.
[0020] Preferably, the spacer elements are magnetic with a magnetic
domain alignment pattern with a substantially tangential
orientation across the spacer element.
[0021] Preferably, the resulting magnetic flux field is created by
applying an external magnetic flux field that has a geometry within
each magnet element that is substantially similar to the magnetic
domain alignment pattern within that element.
[0022] Preferably, the resulting magnetic flux field is a
Halbach-style flux field.
[0023] Preferably, the resulting magnetic flux field has poles with
alternating polarity spaced around the ring, the poles being
aligned radially with respect to the permanent magnet ring, and
wherein the resulting magnetic flux field of the permanent magnet
ring traverses between adjacent poles of opposite polarities and
between those poles is focused to extend beyond the boundary
defined by the inner face, but remain at least partially
constrained within the boundary defined by the outer face of the
permanent magnet ring,
[0024] Preferably, the magnetic domain alignment pattern assists
creation of a stronger resulting magnetic flux field when the
magnet elements are magnetised.
[0025] Preferably, the portion of the resulting magnetic flux field
in each magnet element has an orientation that varies substantially
continuously over the magnet element wherein: across the width of
the magnet element, the orientation varies from an orientation that
has a predominant radial component at the pole to an orientation
that has a predominant tangential component at the edges of the
magnet element adjacent other magnet elements in the permanent
magnet ring, and across the depth of the magnet element, the
orientation varies from an orientation that has a predominant
radial component at an edge corresponding to the inner face of the
permanent magnet ring to an orientation that has a predominant
tangential component at an edge corresponding to the outer face of
the permanent magnet ring.
[0026] Preferably, the orientation varies substantially
non-linearly over the magnet element.
[0027] Preferably, the portion of the resulting magnetic flux field
between adjacent poles extending beyond the boundary defined by the
inner face of the permanent magnet ring magnet element has an
orientation that varies continuously wherein: between the poles,
the orientation varies from an orientation that has a predominant
radial component at the pole to an orientation that has a
predominant tangential component at the mid-point between the
poles, and extending radially from the inner face, the orientation
varies from an orientation that has a predominant radial component
at an inner face to an orientation that has an increasingly
tangential component with distance from the inner face.
[0028] Preferably, the orientation varies substantially
non-linearly between the poles and extending beyond the inner
face.
[0029] Preferably, the radial and tangential components of the
orientation of the resulting magnetic flux field at or proximate
the inner surface of the magnet element varies sinusoidally
according to:
V.sub.R=cos(.theta.), and
V.sub.T=-sin(.theta.)
Where V.sub.R and V.sub.T are the radial and tangential components
of the orientation respectively and .theta. is the angular position
across the magnet element, varying from substantially -90 degrees
at one lateral edge to substantially +90 degrees at the opposite
lateral edge.
[0030] Preferably, for each magnet element, the magnetic domains
were aligned during production of the magnet element.
[0031] Preferably, for each magnet element, the magnetic domains
were aligned during production using a press or injection moulding
tool comprising one or more elements defining a cavity; and an
apparatus for applying a magnetic flux field, wherein the apparatus
produces a magnetic field in the cavity similar in nature to the
desired magnetic domain alignment pattern in the element.
[0032] Preferably, the rotor is utilised in the drive motor of a
washing machine comprising an electronically commutated motor, a
stator of the motor having windings energisable to cause rotation
of the rotor, said stator being coupled to a non-rotating tub or
housing of the washing machine, said rotor being coupled to a
rotating drum of the washing machine.
[0033] Preferably, the washing machine is a top loading washing
machine comprising: an outer wrapper, a tub suspended in the outer
wrapper, and a rotating drum in the tub.
[0034] Preferably, the washing machine is a horizontal axis machine
comprising: an outer wrapper, a rotating drum housing, and a
rotating drum in the housing.
[0035] Preferably, the washing machine is a horizontal axis machine
with top loading access comprising: an outer wrapper, a tub, and a
rotating drum in the tub.
[0036] Preferably, utilised in a power generation apparatus.
[0037] In another aspect the present invention may be said to
consist in a motor for use in a washing machine, said motor
comprising: a stator having at least three phase windings, each
phase winding being formed on a plurality of radially extending
stator teeth, a rotor as defined in any preceding claim, concentric
with said stator with the permanent magnet ring outside said stator
teeth and said rotor poles facing the ends of said stator
teeth.
[0038] In another aspect the present invention may be said to
consist in a method of producing a rotor comprising the steps of:
producing a plurality of magnet elements comprising permanent
magnet material with two lateral edges each with magnetic domains
aligned anisotropically to form a domain alignment pattern, wherein
the magnetic domain alignment pattern in each magnet element has an
orientation that varies substantially continuously across at least
part of the magnet element between its lateral edges from an
orientation that has a predominant radial component at a pole of
the magnet element to an orientation that has a least some
tangential component at one lateral edge of the magnet element,
arranging and retaining the magnet elements into a permanent magnet
ring in a rigid support, and magnetising the magnet elements to
produce a resulting magnetic flux field.
[0039] Preferably, the magnet elements have a chamfer at the
intersection of each lateral edge with the front edge, wherein the
front edge is the edge at the inner face of the rotor.
[0040] Preferably, the step of producing the plurality of magnet
element comprises applying an external magnetic flux field to each
magnet element to align the magnetic domains.
[0041] Preferably, each magnet element has the pole positioned
between the magnet element's lateral edges and applying the
external magnetic flux field to a magnet elements aligns its
magnetic domains such that the magnetic domain alignment pattern in
the magnet element has an orientation that varies substantially
continuously across the width of the magnet element from an
orientation that has a predominant radial component at the pole of
the magnet element to an orientation that has a least some
tangential component at both lateral edges of the magnet
element.
[0042] Preferably, at both lateral edges, the orientation of the
magnetic domain alignment pattern has a significant tangential
component.
[0043] Preferably, at both lateral edges the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of at least 15 degrees with respect to the lateral
edges.
[0044] 37. A method according to claim 34 or 35 wherein at both
lateral edges the significant tangential component result in the
magnetic domain alignment pattern having an orientation of between
20 to 35 degrees, and more preferably substantially 30 degrees,
with respect to the lateral edges.
[0045] Preferably, at both lateral edges, the orientation of the
magnetic domain alignment pattern has a predominant tangential
component.
[0046] Preferably, each magnet element has the pole positioned at
or towards one lateral edge.
[0047] Preferably, the orientation varies substantially
non-linearly over the magnet element.
[0048] Preferably, the radial and tangential components of the
orientation of the magnetic domain alignment pattern within the
magnet element varies sinusoidally according to:
V.sub.R=cos(.theta.), and
V.sub.T=sin(.theta.)
Where V.sub.R and V.sub.T are the radial and tangential components
of the orientation respectively and .theta. is the angular position
across the magnet element, varying from substantially -90 degrees
at one lateral edge to substantially +90 degrees at the opposite
lateral edge.
[0049] Preferably, the resulting magnetic flux field is created by
applying an external magnetic flux field that has a geometry within
each magnet element that is substantially similar to the magnetic
domain alignment pattern within that element.
[0050] Preferably, the resulting magnetic flux field is a
Halbach-style flux field.
[0051] Preferably, the resulting magnetic flux field has poles with
alternating polarity spaced around the ring, the poles being
aligned radially with respect to the permanent magnet ring, and
wherein the resulting magnetic flux field of the permanent magnet
ring traverses between adjacent poles of opposite polarities and
between those poles is focused to extend beyond the boundary
defined by the inner face, but remain at least partially
constrained within the boundary defined by the outer face of the
permanent magnet ring,
[0052] Preferably, the magnetic domain alignment pattern assists
creation of a stronger resulting magnetic flux field when the
magnet elements are magnetised.
[0053] Preferably, the portion of the resulting magnetic flux field
in each magnet element has an orientation that varies substantially
continuously over the magnet element wherein: across the width of
the magnet element, the orientation varies from an orientation that
has a predominant radial component at the pole to an orientation
that has a predominant tangential component at the edges of the
magnet element adjacent other magnet elements in the permanent
magnet ring, and across the depth of the magnet element, the
orientation varies from an orientation that has a predominant
radial component at an edge corresponding to the inner face of the
permanent magnet ring to an orientation that has a predominant
tangential component at an edge corresponding to the outer face of
the permanent magnet ring.
[0054] Preferably, the orientation varies substantially
non-linearly over the magnet element.
[0055] Preferably, the portion of the resulting magnetic flux field
between adjacent poles extending beyond the boundary defined by the
inner face of the permanent magnet ring magnet element has an
orientation that varies continuously wherein: between the poles,
the orientation varies from an orientation that has a predominant
radial component at the pole to an orientation that has a
predominant tangential component at the mid-point between the
poles, and extending radially from the inner face, the orientation
varies from an orientation that has a predominant radial component
at an inner face to an orientation that has an increasingly
tangential component with distance from the inner face.
[0056] Preferably, the orientation varies substantially
non-linearly between the poles and extending beyond the inner
face.
[0057] Preferably, the radial and tangential components of the
orientation of the resulting magnetic flux field at or proximate
the inner surface of the magnet element varies sinusoidally
according to:
V.sub.R=cos(.theta.), and
V.sub.T=-sin(.theta.)
Where V.sub.R and V.sub.T are the radial and tangential components
of the orientation respectively and .theta. is the angular position
across the magnet element, varying from substantially -90 degrees
at one lateral edge to substantially +90 degrees at the opposite
lateral edge.
[0058] In another aspect the present invention may be said to
consist in a rotor comprising: a plurality of magnet elements with
two lateral edges each with magnetic domains aligned
anisotropically to form a domain alignment pattern, the plurality
of magnets being arranged to form a permanent magnet ring with an
inner face and an outer face, and a rigid support holding said
magnet elements in said ring arrangement, wherein the magnetic
domain alignment pattern in each magnet element has an orientation
that varies substantially continuously across at least part of the
magnet element between its lateral edges from an orientation that
has a predominant radial component at a pole of the magnet element
to an orientation that has a least some tangential component at one
lateral edge of the magnet element, wherein the magnet elements are
magnetised to produce a resulting magnetic flux field.
[0059] In another aspect the present invention may be said to
consist in a magnet element for assembly into a ring of magnet
elements to form part of a rotor, the magnet element having two
lateral edges each with magnetic domains aligned anisotropically to
form a domain alignment pattern, wherein the magnetic domain
alignment pattern in the magnet element has an orientation that
varies substantially continuously across at least part of the
magnet element between its lateral edges from an orientation that
has a predominant radial component at a pole of the magnet element
to an orientation that has a least some tangential component at one
lateral edge of the magnet element.
[0060] Preferably the element has a chamfer at the intersection of
each lateral edge with a front edge, wherein the front edge is the
edge at the inner face of the rotor.
[0061] Preferably, the pole is positioned between the magnet
element's lateral edges and the magnetic domain alignment pattern
in each magnet element has an orientation that varies substantially
continuously across the width of the magnet element from an
orientation that has a predominant radial component at the pole of
the magnet element to an orientation that has a least some
tangential component at both lateral edges of the magnet
element.
[0062] Preferably, at both lateral edges, the orientation of the
magnetic domain alignment pattern has a significant tangential
component.
[0063] Preferably, at both lateral edges the significant tangential
component results in the magnetic domain alignment pattern having
an orientation of at least 15 degrees with respect to the lateral
edges.
[0064] Preferably, at both lateral edges the significant tangential
component result in the magnetic domain alignment pattern having an
orientation of between 20 to 35 degrees, and more preferably
substantially 30 degrees, with respect to the lateral edges.
[0065] Preferably, at both lateral edges, the orientation of the
magnetic domain alignment pattern has a predominant tangential
component.
[0066] Preferably, each magnet element has a pole positioned at or
towards one lateral edge.
[0067] Preferably, the orientation of the magnetic domain alignment
pattern has a significant tangential component at the lateral
edge.
[0068] Preferably, the orientation varies substantially
non-linearly over the magnet element.
[0069] Preferably, the radial and tangential components of the
orientation of the magnetic domain alignment pattern within the
magnet element varies sinusoidally according to:
V.sub.R=cos(.theta.), and
V.sub.T=sin(.theta.)
Where V.sub.R and V.sub.T are the radial and tangential components
of the orientation respectively and .theta. is the angular position
across the magnet element, varying from substantially -90 degrees
at one lateral edge to substantially +90 degrees at the opposite
lateral edge.
[0070] Preferably, the resulting magnetic flux field is created by
applying an external magnetic flux field that has a geometry within
each magnet element that is substantially similar to the magnetic
domain alignment pattern within that element.
[0071] Preferably, the resulting magnetic flux field is a
Halbach-style flux field.
[0072] Preferably, the resulting magnetic flux field has poles with
alternating polarity spaced around the ring, the poles being
aligned radially with respect to the permanent magnet ring, and
wherein the resulting magnetic flux field of the permanent magnet
ring traverses between adjacent poles of opposite polarities and
between those poles is focused to extend beyond the boundary
defined by the inner face, but remain at least partially
constrained within the boundary defined by the outer face of the
permanent magnet ring,
[0073] Preferably, the magnetic domain alignment pattern assists
creation of a stronger resulting magnetic flux field when the
magnet elements are magnetised.
[0074] Preferably, the portion of the resulting magnetic flux field
in each magnet element has an orientation that varies substantially
continuously over the magnet element wherein: across the width of
the magnet element, the orientation varies from an orientation that
has a predominant radial component at the pole to an orientation
that has a predominant tangential component at the edges of the
magnet element adjacent other magnet elements in the permanent
magnet ring, and across the depth of the magnet element, the
orientation varies from an orientation that has a predominant
radial component at an edge corresponding to the inner face of the
permanent magnet ring to an orientation that has a predominant
tangential component at an edge corresponding to the outer face of
the permanent magnet ring.
[0075] Preferably, the orientation varies substantially
non-linearly over the magnet element.
[0076] Preferably, the portion of the resulting magnetic flux field
between adjacent poles extending beyond the boundary defined by the
inner face of the permanent magnet ring magnet element has an
orientation that varies continuously wherein: between the poles,
the orientation varies from an orientation that has a predominant
radial component at the pole to an orientation that has a
predominant tangential component at the mid-point between the
poles, and extending radially from the inner face, the orientation
varies from an orientation that has a predominant radial component
at an inner face to an orientation that has an increasingly
tangential component with distance from the inner face.
[0077] Preferably, the orientation varies substantially
non-linearly between the poles and extending beyond the inner
face.
[0078] Preferably, the radial and tangential components of the
orientation of the resulting magnetic flux field at or proximate
the inner surface of the magnet element varies sinusoidally
according to:
V.sub.R=cos(.theta.), and
V.sub.T=-sin(.theta.)
Where V.sub.R and V.sub.T are the radial and tangential components
of the orientation respectively and .theta. is the angular position
across the magnet element, varying from substantially -90 degrees
at one lateral edge to substantially +90 degrees at the opposite
lateral edge.
[0079] In another aspect the present invention may be said to
consist in a method of producing a magnet element comprising
aligning the magnetic domains of the element in the manner defined
above.
[0080] Preferably, comprising producing a magnet element in a press
or injection moulder from magnetic material, and applying a
magnetic flux field approximately in the direction of the desired
magnetic domain alignment pattern.
[0081] In another aspect the present invention may be said to
consist in a rotor comprising: a plurality of magnet elements with
two lateral edges each with magnetic domains aligned
anisotropically to form a domain alignment pattern, the plurality
of magnets being arranged to form a permanent magnet arrangement,
and a rigid support holding said magnet elements in said
arrangement, wherein the magnetic domain alignment pattern in each
magnet element has an orientation that varies substantially
continuously across at least part of the magnet element between its
lateral edges from an orientation that has at least some tangential
component at a point in the magnet element to an orientation that
has a predominant radial component at poles positioned at the
lateral edges of the magnet element, wherein the magnet elements
are magnetised to produce a resulting magnetic flux field.
[0082] In another aspect the present invention may be said to
consist in a magnet element for assembly into a ring of magnet
elements to form part of a rotor, the magnet element having two
lateral edges each with magnetic domains aligned anisotropically to
form a domain alignment pattern, wherein the magnetic domain
alignment pattern in the magnet element has an orientation that
varies substantially continuously across at least part of the
magnet element between its lateral edges from an orientation that
has at least some tangential component at a point in the magnet
element to an orientation that has a predominant tangential
component at poles positioned at the lateral edges of the magnet
element.
[0083] In another aspect the present invention may be said to
consist in a rotor comprising: a plurality of magnet elements with
two lateral edges each with magnetic domains aligned
anisotropically to form a domain alignment pattern, the plurality
of magnets being arranged to form a permanent magnet ring with an
inner face and an outer face, and a rigid support holding said
magnet elements in said ring arrangement, wherein the magnetic
domain alignment pattern in each magnet element has an orientation
that varies substantially continuously across at least part of the
magnet element between its lateral edges from an orientation that
has a predominant radial component at a pole of the magnet element
positioned between the lateral edges to an orientation that has a
least some tangential component at the lateral edges of the magnet
element, wherein the magnet elements are magnetised to produce a
resulting magnetic flux field.
[0084] Preferably, the magnetic domains are substantially aligned
as shown in one of FIGS. 4a to 4f or 15a to 15d.
[0085] Preferably, the magnetic domain alignment pattern deviates
from the Halbach-style resulting magnetic flux field.
[0086] Preferably the magnetic domain alignment pattern deviates
from the Halbach-style resulting magnetic flux field.
[0087] Preferably, the magnetic domain alignment pattern deviates
from the Halbach-style resulting magnetic flux field.
[0088] Preferably, for each magnet element, the magnetic domains
were aligned during production of the magnet element.
[0089] Preferably, for each magnet element, the magnetic domains
were aligned during production using a press or injection moulding
tool comprising one or more elements defining a cavity, and an
apparatus for applying a magnetic flux field, wherein the apparatus
produces a magnetic field in the cavity similar in nature to the
desired magnetic domain alignment pattern in the element.
[0090] An anisotropic magnet element in accordance with the present
invention can, when arranged in a rotor, result in or allow
production of a Halbach-style resulting magnetic flux field that is
much stronger than such a flux field produced in an isotropic or
radially aligned anisotropic magnet. Therefore, in aligning the
magnetic domains as described to create an anisotropic Halbach
magnetised rotor, the resulting flux field is much stronger than
that achievable by the previously alternatively proposed isotropic
magnet ring or an equivalent radially magnetised anisotropic
ring.
[0091] This provides a higher performance rotor/motor. Low togging
is also obtainable.
[0092] In this specification where reference has been made to
patent specifications, other external documents, or other sources
of information, this is generally for the purpose of providing a
context for discussing the features of the invention. Unless
specifically stated otherwise, reference to such external documents
is not to be construed as an admission that such documents, or such
sources of information, in any jurisdiction, are prior art, or form
part of the common general knowledge in the art.
[0093] The term "comprising" as used in this specification means
"consisting at least in part of". Related terms such as "comprise"
and "comprised" are to be interpreted in the same manner.
[0094] It is intended that reference to a range of numbers
disclosed herein (for example, 1 to 10) also incorporates reference
to all rational numbers within that range (for example, 1, 1.1, 2,
3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of
rational numbers within that range (for example, 2 to 8, 1.5 to 5.5
and 3.1 to 4.7).
[0095] To those skilled in the art to which the invention relates,
many changes in construction and widely differing embodiments and
applications of the invention will suggest themselves without
departing from the scope of the invention as defined in the
appended claims. The disclosures and the descriptions herein are
purely illustrative and are not intended to be in any sense
limiting
BRIEF DESCRIPTION OF THE DRAWINGS
[0096] FIG. 1 shows a typical magnet element for a rotor,
[0097] FIG. 2a shows a Halbach array with a finite number of
elements,
[0098] FIG. 2b shows the resulting magnetic flux field of the
Halbach array in FIG. 2a,
[0099] FIG. 2c shows a portion of a resulting magnetic flux field
of an ideal Halbach array with a large or infinite number of
elements,
[0100] FIGS. 3a-3c show a rotor and stator, where the rotor
incorporates a magnet element according to an embodiment of the
invention,
[0101] FIGS. 3d and 3e show another rotor and stator, where the
rotor incorporates a magnet element according to an embodiment of
the invention,
[0102] FIG. 3f shows another rotor that incorporates a magnet
element according to an embodiment of the invention,
[0103] FIG. 4a shows a magnetic domain alignment pattern formed in
a magnet element according to an embodiment of the invention,
[0104] FIG. 4b shows a magnetic domain alignment pattern formed in
a pair of magnet elements according to one embodiment,
[0105] FIGS. 4c-4f show magnetic domain alignment patterns
according to alternative embodiments,
[0106] FIG. 5a shows a portion of a rotor comprising a number of
magnet elements as shown in FIG. 4a, and the resulting magnetic
flux field,
[0107] FIG. 5b shows a predicted resulting magnetic flux field of
the portion of the rotor with a stator present,
[0108] FIG. 6a shows a resulting magnetic flux field existing in a
magnet element of a ring when magnetised,
[0109] FIG. 6b shows the magnet element of FIG. 6a with its
magnetic domain alignment pattern superimposed on the resulting
magnetic flux field,
[0110] FIG. 6c shows a graph indicating the relationship between
the flux linkage and orientation of the magnetic flux field at the
edge of a magnet element,
[0111] FIGS. 6d, 6e show graphs of the tangential and radial
components of the resulting magnetic flux field along the inner
surface of a magnet element, along with a comparison of tangential
and radial components of the resulting magnetic flux field in
standard elements with radially aligned magnetic domains,
[0112] FIG. 7a shows a first apparatus for producing a magnet
element with a magnetic domain alignment pattern the same as or
similar to one of those shown in FIG. 4a-4e,
[0113] FIGS. 7b and 7c show the magnetic domain alignment pattern
during production of a magnet element using the apparatus in FIG.
7a,
[0114] FIG. 8a shows a second apparatus for producing a magnet
element with a magnetic domain alignment pattern the same as or
similar to one of those shown in FIG. 4a-4e,
[0115] FIGS. 8b and 8c show the magnetic domain alignment pattern
during production of a magnet element using the apparatus in FIG.
8a,
[0116] FIG. 9 shows a diagrammatic cutaway view of a washing
machine of a vertical axis type that may incorporate a rotor and/or
motor according to the present invention,
[0117] FIG. 10 shows a diagrammatic view of a horizontal axis
washing machine with front access that may incorporate the rotor
and/or motor according to the present invention,
[0118] FIG. 11 shows a diagrammatic view of a horizontal axis
washing machine with top or tilt access that may incorporate the
rotor and/or motor according to the present invention,
[0119] FIG. 12 shows a diagrammatic view of a horizontal axis
laundry machine with tilt access that may incorporate the rotor
and/or motor according to the present invention,
[0120] FIG. 13 shows a graph of the relative cogging performances
of Halbach and standard magnetic field patterns,
[0121] FIG. 14 shows two graphs indicating the desired B--H
characteristics of a magnetic material used for a magnet
element,
[0122] FIGS. 15a-15d show alternative magnet elements with magnetic
domain alignment patterns,
[0123] FIG. 16 shows a diagrammatic view of a magnetiser for
magnetising the rotor,
[0124] FIG. 17 shows a magnet element with a chamfer according to
another embodiment,
[0125] FIGS. 18a to 18c show resulting magnetic flux fields for
adjacent magnet elements with chamfers and magnetic domain edge
angles of 30, 60 and 90 degrees respectively,
[0126] FIG. 19 shows a graph of the cogging torque for chamfered
and non-chamfered magnet elements,
[0127] FIG. 20 shows a perspective view of a chamfered magnet
element,
[0128] FIG. 21 shows chamfered magnet elements keyed onto a core
ring,
[0129] FIG. 22 shows a demagnetisation curve for three different
magnet materials,
[0130] FIG. 23 shows the flux linkage versus angle and magnet grade
required to avoid demagnetisation,
[0131] FIG. 24 shows an alternative arrangement for the backing
steel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0132] In one embodiment of the invention, a motor is provided such
as that shown diagrammatically in FIGS. 3a to 3c. FIGS. 3a, 3b show
the top and bottom of the rotor 36, while FIG. 3c shows the stator
31. The motor could be used in a washing machine, for example. The
stator 31 comprises a number of poles e.g. 32, each pole comprising
a coil or winding 33 wound around a radially extending core or
tooth 34. The windings are typically arranged to form multiple sets
of windings, or phases. Three phases are commonly used. Each tooth
extends from an annular ring 35 or other suitable support frame.
Each winding may be independently energised. The stator core can be
formed from any suitable material.
[0133] The rotor 36 comprises a number of, hard ferrite or
neodymium-iron-boron permanent magnet elements, e.g. 37, arranged
to form a permanent magnet ring 38 of such elements. The permanent
magnet elements 37 could also be comprised of a blend of hard
ferrite and neodymium-iron-boron material or other magnetic
material such as, but not limited to, Samarium-cobalt.
Alternatively the permanent magnet elements 37 could comprise a
blend of these magnet materials and plastic material. The ring 38
of magnetic material can be supported by a rigid rotor support or
housing 39. This may comprise an over moulded plastics annular
ring, with a plastics hub. Alternatively, the housing could
comprise pressed steel 39a (as in the rotor of FIG. 3e) with the
magnet elements attached therein. A single or multiple piece or
multiple layer laminated backing ring 40 (see FIG. 3a) could
optionally be provided to increase the resulting magnetic flux
field produced by the magnetic material. Preferably, the ring of
permanent magnetic material 38 has a diameter of between 150 mm and
400 mm, a height being less than 100 mm. Each said section (and
said ring) is preferably less than 20 mm thick. It will be
appreciated by those skilled in the art that there are many
possible variations on the construction of a stator 31 and rotor 36
for use in a washing machine motor.
[0134] FIGS. 3a-3c show just one possibility in a general form for
exemplary purposes. FIGS. 3d-3e show an alternative possible rotor.
It should be noted that FIG. 3a-3c shows a magnet to stator ratio
of 4:3. Other ratios are possible also, for example 6:7, 9:10 or
any other suitable ratio. It should also be noted that the number
of stators and magnets shown in FIGS. 3d and 3e are illustrative
only to demonstrate the physical nature of the rotor/stator. The
actual number of stator poles and magnets might be different. The
rotor 36 can be magnetised to produce a Halbach-style resulting
magnetic flux field the same or similar to that produced by a
standard Halbach array.
[0135] Each permanent magnet element 37 in the rotor is produced in
a manner such that it comprises magnetic domains, e.g. 41,
pre-aligned into a magnetic domain alignment pattern 42 as shown
generally in FIG. 4a. The term "magnetic domain alignment pattern"
refers to the orientation of the magnetic domains 41 occurring as a
result of the manufacture process. Multiple magnet elements 37 can
be arranged together, such as shown in FIG. 4b, where two permanent
magnet elements 37 with magnetic domains 41 pre-aligned into the
domain alignment pattern 42 shown have been arranged side-by-side.
This creates magnetic material with pre-aligned magnetic domains 41
that enable production of a Halbach-style resulting magnetic flux
field when the magnet material is subsequently magnetised by a
magnetisation pattern. A ring of such magnet elements 37 can be
assembled to produce a permanent magnet ring 38 of the rotor 36.
This can be magnetised to have a Halbach-style resulting magnetic
flux field. This field is stronger than if isotropic or radially
aligned anisotropic magnetic material is magnetised with the same
flux field. A rotor 36 with Halbach-style resulting magnetic flux
field is the desired field in order to produce improved operating
characteristics of the motor. The magnet elements 37 of the
permanent magnet ring 38 might be curved commensurate with the
curvature of the rotor 36.
[0136] "Halbach style" refers to a resulting magnetic flux field
that is the same as or is similar to a magnetic flux field produced
by a traditional Halbach array magnet arrangement. The term
"magnetisation pattern" refers to the external magnetic flux field
employed to energise the magnet element according to the domain
alignment pattern, causing the magnets to become magnetised. The
term "resulting magnetic flux field" refers to the magnetic flux
field that exists in the magnet elements 37 (and surrounding
structure, where applicable) after production, assembly and
magnetisation.
[0137] FIGS. 4c to 4e show alternative domain alignment patterns,
which will be described in detail later.
[0138] FIG. 5a shows the Halbach-style resulting magnetic flux
field 60, in diagrammatic form, of a part of the rotor 36 of FIGS.
3a, 3b with a magnetic material ring 38 formed using the magnet
elements 37 with the pre-aligned magnetic domain alignment pattern
42 as shown in FIG. 4a. This is the resulting magnetic flux field
60 when no stator 31 is present. In this case the rotor 36 has a
backing ring 40. The rotor comprises magnet elements, e.g. 37,
arranged side-by-side continuing the arrangement as shown in FIG.
4b. Only some of the magnetic elements 37 of the rotor are shown,
but it will be appreciated that the rotor contains enough elements
to form a full permanent magnet ring 38. The ring 38 has been
magnetised. Once magnetised, each magnet element 37 forms a magnet
that has a magnetic pole located on the stator side (E) of the
magnet element 37. By arranging a number of such magnet elements 37
in a permanent magnet ring 38 as shown in FIG. 5a, a multiple pole
magnet ring 38 is created where more than one magnetic pole (B or
F) is located on the stator side E of the ring 38. This is done by
duplicating the domain alignment pattern 42 shown in FIG. 4a but
with reversed domain magnetisation directions for each subsequently
added pole or element 37.
[0139] When a magnet element 37 is arranged in a ring 38 of similar
magnet elements as shown in FIG. 5a, face D of the magnet element
37 (and entire ring 38) is the external (outer) face, pointing away
from the rotational centre of the rotor 36. Face E of the magnet
element 37 (and entire ring 38) is the internal (inner) face,
pointing towards the rotational centre of the rotor. It should be
noted that a magnet element 37 might have curved faces D, E
commensurate with the curvature of the permanent magnet ring 38. In
FIG. 4a, the faces D, E are shown flat for clarity. Poles B and F
could either be north/south or south/north poles.
[0140] When a magnet element 37 forms part of a ring of such
elements that has been magnetised to produce a Halbach-style
resulting magnetic flux field 60, each element 37 contains a
portion 60a of that resulting magnetic flux field 60. The portion
of the resulting magnetic flux field is like that shown
diagrammatically by the magnetic flux field (comprising flux lines
or paths) in FIG. 6a. The magnetic flux 60b existing outside the
element 37 is also shown for completeness. The lines represent the
portion of the resulting magnetic flux field 60a in each magnet
element 37 after magnetisation. The pre-aligned magnetic domains 41
of each element are generally aligned in a direction similar, but
not exactly the same, as the portion of resulting magnetic flux
field 60a that is ultimately created in each magnet element 37. The
pre-aligned magnetic domains of each element do not need to be
aligned in the same manner as the desired Halbach-style resulting
magnetic flux field 60a. In fact, deviation in the magnetic domain
alignment pattern (from the ideal Halbach-style resulting magnetic
flux field) is possible, while still allowing or assisting the
creation of the desired Halbach-style resulting magnetic flux
field. This result is counter-intuitive. FIG. 6b shows a
superposition of the portion of the resulting magnetic flux field
60a and the magnetic domain alignment pattern 42 existing in each
element 37--this illustrates the differences between the two. When
applying the magnetisation pattern to magnetise the permanent
magnet ring 38 of the rotor 36, the magnetic domain alignment
pattern 42 shown in FIG. 4a which exists in each magnet element 37
produces a desired Halbach-style resulting magnetic flux field that
is stronger at the poles B, F on the inner face E than what would
be achieved with an isotropic element or magnet elements in which
the domains are aligned radially.
[0141] Referring now to FIGS. 4a to 6c in general, the nature of
the magnetic domain alignment pattern 42 and resulting magnetic
flux field 60 will be described in more detail. Note that these
Figures show flux fields and domain alignment in diagrammatic form
for illustrative purposes.
[0142] Each magnet element comprises magnetic domains 41 as noted
earlier. The preferred orientation direction of each magnetic
domain 41 is a function of its angular position around the
circumference of the rotor 36 and does not vary with radial
position, as shown in FIG. 4a. It should be noted that FIG. 4a
shows the ideal preferred magnetic domain alignment pattern. In
practice, not all magnetic domains will necessarily be aligned as
shown, as some might vary from the ideal due to random
fluctuations. Also, other patterns, as will be described later, are
also possible. The differing orientations of the magnetic domains
in an element 37 produces a magnetic domain alignment pattern 42
that preferably varies continuously with tangential position in
direction C. Tangential position refers to the position across the
width of the element 37, or more particularly across the element 37
between the lateral edges 37a, 37b. The lateral edges 37a, 37b are
those edges that are adjacent or proximate other elements 37
arranged in the permanent magnet ring. The orientation of the
magnetic domain alignment pattern 42 at any position corresponds to
the orientation of the magnetic domain(s) 41 at that position. The
magnetic domain alignment pattern 42 is substantially radially
aligned in the centre of the pole B, F and substantially
tangentially aligned on each edge of each magnet element 37.
Radially aligned refers to the direction pointing towards or away
from the centre of the permanent magnet ring 38 when the element 37
is arranged in such a ring, generally in the direction of arrow G.
Tangentially aligned refers to the direction perpendicular to the
lateral edge, generally in the direction of arrow C.
[0143] It will be appreciated that the magnet elements have a
three-dimensional thickness, not depicted in the two-dimensional
representations. It will be appreciated that the domain alignment
pattern described and shown in two dimensions will exist throughout
the thickness of the magnet element. If a cross section were
hypothetically taken through any part of the thickness of the
magnet element, substantially the same domain alignment patterns
depicted would exist. Following on from this, the term "lateral
edge" more generally refers to the lateral edge of the magnet
element at any point throughout the thickness, such that the
lateral edge in fact exists as a lateral edge surface. For
simplicity, this is referred to as the lateral edge.
[0144] To produce such a magnetic domain alignment pattern 42, the
radial and tangential components of the orientation of the magnetic
domains 41 within each magnet element 37 are aligned according to
sinusoidal functions of the tangential position along the magnet
element 37, according to the following relations:
V.sub.R=cos(.theta.) (1)
V.sub.T=sin(.theta.) (2)
where V.sub.R and V.sub.T are the radial and tangential components
of the alignment direction vector of a magnetic domain respectively
and .theta. is the angular position across the magnet, varying from
-90 degrees at lateral edge 37a to +90 degrees at lateral edge
37b.
[0145] The resulting magnetic domain alignment vector preferably
rotates smoothly with the angular position across each magnet
element 37, being substantially radially aligned in the centre of a
magnet element (.theta.=0, at the pole) and being substantially
tangentially aligned at the magnet element 37 edges 37a and 37b,
but being of opposite polarity.
[0146] In this arrangement, the magnetic domains 41 of each magnet
element 37 are aligned, prior to magnetisation, approximately in
the direction of the portion of the resulting magnetic flux field
60a that exists in that magnet element 37 after magnetisation.
However, they are not exactly aligned, as is evident from FIG. 6b,
which shows a superposition of the domain alignment 42 and
resulting magnetic flux field in the magnet element. The preferred
magnetic domain alignment pattern 42 and the preferred
Halbach-style resulting magnetic flux field 60 are different in
geometry.
[0147] It will be appreciated that while the above describes the
preferred magnetic domain alignment pattern 42, exact conformance
to the preferred alignment pattern is not essential for producing a
Halbach-style resulting magnetic flux field 60. Any magnetic domain
alignment pattern 42 could be used in which the magnetic domains 41
are aligned, prior to magnetisation, approximately in the direction
of the preferred magnetic domain alignment pattern that assists in
producing a stronger Halbach-style resulting magnetic flux
field.
[0148] In the general case, the magnetic domain alignment pattern
42 can be any pattern that improves or assists the production of a
Halbach-style flux field during magnetisation. The inventors have
found that aligning the domain alignment pattern in the manner
described above improves the strength per unit of magnet material
of the Halbach-style resulting magnetic flux field 60 ultimately
linked through the stator. Counter-intuitively, this domain
alignment pattern 42 is not the same as the actual resulting
magnetic flux 60a in the magnet element 37, after magnetisation, as
can be seen in FIG. 6b. This improvement in flux field strength per
unit of magnetic material provides an ultimate increase in torque
provided by the motor in which the rotor is used.
[0149] However, some gains can be achieved even without using the
ideal preferred domain alignment pattern shown in FIG. 4a.
Non-ideal (e.g. with random fluctuations from the ideal) alignment
patterns provide some gain, as well as the alternative embodiments
described below, or acceptable deviations from those alternative
embodiments, which will be appreciated by those skilled in the
art.
[0150] For example, more generally, the orientation of the magnetic
domain alignment pattern 42 might not be substantially radial at
the poles B, F and might not be substantially tangential at the
edges of the element 37. The orientation might, instead, have a
predominant radial component and at least some tangential component
at the poles and edges respectively. By predominant radial
component, it is meant that the magnitude of the radial component
dominates the orientation vector such that the vector points more
in a radial direction than a tangential direction. This means that
the orientation points predominantly, although not necessarily
entirely, in the radial direction. Predominant radial component
also covers the preferred case where there is only a radial
component of the orientation vector, such that the orientation
vector points solely or substantially in a radial direction.
[0151] By at least some tangential component, it is meant that the
orientation vector has at least some tangential component so that
the orientation vector points at least partially in a tangential
direction. This can also cover where the orientation vector points
completely tangentially.
[0152] The more tangential the angle of the orientation vector at
the edge, the larger the increase in flux linkage through the
stator, and the greater the benefits. The orientation angle is
measured between the radially aligned edge 37a, 37b of the magnet
element 37 and the orientation vector (see, for example .theta. in
FIG. 4c). For example, FIG. 6c shows the relationship between a)
the angle of the orientation of the domain alignment pattern 42 at
the edge 37a, 37b of a magnet element 37 and b) the percentage of
magnetic flux linking with the stator pole (relative to a magnet
element with radially aligned domains) when the magnet element 37
is used in a rotor. As can be seen, where the orientation angle at
the magnet element 37 edge is 0 degrees (i.e. the orientation at
the edge is radially aligned), the percentage of flux linking is
the same (100%) as for a magnet element with radial domain
alignment. Where the orientation at the magnet element 37 edge is
90 degrees (completely tangential), the percentage flux linking
compared with the radially aligned element is 130%. Noticeably,
there is gain at even relatively small angles. For example, an
orientation angle of 15 degrees at the edge 37a, 37b still gives a
flux linking of around 105%, and there is a significant advantage
at 30 degrees. Therefore, any suitable angle of domain alignment
orientation 42 at the edge 37a, 37b could be used, as shown
generally in FIG. 4c.
[0153] More specifically, referring to FIG. 4d, a domain alignment
orientation at the edge (also called a "magnetic domain edge
angle") 37a, 37b of around 15 degrees could be used. This is
provided a vector with at least some tangential component. In a
more preferable case, the orientation vector at the edge has a
significant tangential component. By this it means that the
orientation vector has an angle of at least 30 degrees with respect
to the respective edge 37a, 37b. In a yet more preferable case, the
orientation vector at the edge 37a, 37b has a predominant
tangential component. By this it means that the tangential
component dominates the orientation vector such that the vector
points more in a tangential direction than in a radial direction.
By this it means that the orientation of the magnetic domain
alignment pattern at the edges could have components that are
sufficient in magnitude to produce an orientation that differs by
up to 45 degrees (or greater--towards 90 degrees) from the radial
direction, which can be seen in FIG. 4e.
[0154] A preferred magnetic domain edge angle is 30 degrees, as
shown in FIG. 4f. As edge angles increase, it has been found that
the yield of the magnet elements during production decreases. It
has been found that a 30 degree magnetic domain edge angle provides
an acceptable yield, while still providing the required flux
linking. Clearly, other edge angles might be found to be more
suitable in different applications, where there are different
acceptable levels of yield and flux linkage.
[0155] This means that the orientation points predominantly,
although not necessarily entirely in the respective tangential or
radial directions. The terms "predominant" and "significant"
tangential component also covers the case where there is only a
tangential component of the orientation vector, such that the
orientation vector points solely in a tangential direction.
[0156] Therefore, in general, the domain alignment pattern of a
magnet element 37 can be any where the orientation varies
substantially continuously across at least part of the magnet
element 37 (e.g. from a pole to an edge) from an orientation that
has a predominant radial component at a pole of the magnet element
to an orientation that has a least some tangential component at
least one lateral edge 37a, 37b of the magnet element. Clearly, the
same orientation variance might take place from the pole to the
other lateral edge 37a, 37b also. FIG. 4c shows a magnet element in
the general case with one possible alternative domain alignment
pattern in which the edge orientations are not tangential, but
rather some arbitrary angle .theta. with respect to the lateral
edges of the element. In this case, .theta. is greater than 45
degrees, but it could be 45 degrees or less or even as low as 15
degrees, as described above.
[0157] Further, the variance across the element 37 might only be
quasi-sinusoidal. Also, the variance of orientation might only be
predominantly continuous, due to random fluctuations in magnetic
domain orientations.
[0158] It should also be noted that FIGS. 4a and 4c to 4e show the
magnetic domains aligned in a manner pointing "away" from the front
face E. The magnetic domains could be aligned with the domains
pointing "towards" the front face E, like the right hand element in
FIG. 4b. As can be seen, the "flipped" magnetic domain direction is
due to the existence of a north or south pole at face E, as shown
in FIG. 4b. Predominantly, the magnetic domains are shown in
respect of one pole for clarity reasons.
[0159] The magnetic domains of each magnet element are pre-aligned
as described above and as shown in FIGS. 4a-4e by applying an
external magnetic field during production of the magnet element 37.
The pre-aligning of the magnetic domains creates an anisotropic
element. Pre-aligning the magnetic domains enables more efficient
creation of a permanent magnetic field in the element. Creation of
the magnet element 37 is described further later with respect to
FIGS. 7a to 8c.
[0160] The resulting magnetic flux field 60 will now be described
in further detail. The rotor 36 has a preferred resulting magnetic
flux field as shown in solid lines in FIG. 6a, which is the
Halbach-style resulting magnetic flux field as mentioned
previously. Each magnet element 37 in the rotor 36 has a magnetic
pole with a polarity as shown by arrow "B" or "F", in FIG. 5a. The
pole is radially aligned. That is, the pole creates a resulting
magnetic flux field in its vicinity that is aligned substantially
radially towards or away (direction of arrow G) from the centre of
the rotor 36 when the magnet element 37 is arranged in a permanent
magnet ring 38 with other magnet elements 37. When arranged in a
ring 38, each magnet element 37 will have a pole in the same place
but with an opposite polarity to adjacent magnet elements 37, as
shown by the arrows "B" and "F" in FIG. 5a. Therefore, the
permanent magnet ring formed from the magnet elements 37 will have
poles with alternating polarity spaced around the ring.
[0161] The portion of the resulting magnetic flux field 60a in a
magnet element 37 traverses from its pole (B or F) to the
respective adjacent opposite poles (F or B) in each adjacent
element. That is, in the preferred embodiment, the portion of the
resulting magnetic flux field 60a in a magnet element 37 is aligned
substantially tangential to faces D and E at the edges of the
magnet element 37, as shown in FIG. 6a. At the poles B, F (FIG.
5a), the resulting magnetic flux field 60 is substantially aligned
radially towards or away from the centre of the rotor 36.
Therefore, in each element, the alignment of the resulting magnetic
flux field 60a changes from substantially radially aligned to
substantially tangentially aligned along the tangential direction,
from the pole to the edges, 37a and 37b, shown by arrow "C" in FIG.
6a.
[0162] The resulting magnetic flux field 60 produced in and around
the magnetised permanent magnet ring 38 is substantially or at
least partially constrained within the boundary defined by outer
faces D of the magnet elements 37 forming the ring. However, the
resulting magnetic flux field is not necessarily totally
constrained, as some might enter the backing ring 40 (e.g. see FIG.
5b). Therefore, the resulting magnetic flux field 60 is
significantly reduced on the external side (outer face D) of the
ring 38 (and the backing ring 40, if one exists). The predominant
part of the resulting magnetic flux field 60 traversing the poles
B, F of opposite polarity in the permanent magnet ring 38 exist
within the permanent magnet ring 38 and extend beyond the boundary
defined by inner faces E towards the stator poles 32 in a radial
direction. That is, the resulting magnetic flux field 60 extends
beyond inner faces E and can couple with the magnetic flux field of
the stator poles 32 (see FIG. 5b). The predicted actual resulting
magnetic flux field 60 in the elements when a stator 31 is
introduced to the rotor 36, is shown in FIG. 5b. The magnetic
domain alignment pattern allows for more magnetic material to be
utilised in creating the resulting magnetic flux field. The
magnetic flux field 60 is focussed towards and into the stator 31
poles 32. This increases the magnetic flux field beyond the inner
faces E of magnet elements 37 of the ring 38 to increase the torque
on the rotor 36 and, if this field is sinusoidal, can also minimise
cogging. This resulting magnetic flux field 60 is effectively
created by focussing the flux in the magnet elements 37 themselves,
and outside the magnet elements radially towards the stator poles
32. This focussing reduces the amount of magnetic flux passing out
the external side D of the magnet ring 38. As can be seen, only a
small portion of the magnetic flux field 60 passes out the back
face D and into the backing ring 40. The pre-alignment of the
magnetic domains 41 as described above produces the desired
resulting magnetic flux field 60 when magnetisation of the rotor
ring 38 or elements 37 of the rotor ring 38 takes place.
[0163] The above description of the resulting magnetic flux field
60 relates to the preferred Halbach-style resulting magnetic flux
field that is to be achieved using the magnetic domain alignment
pattern 42 described above. This preferred flux field mimics as
much as possible a flux field produced by a large or infinite
number of magnet elements formed into a Halbach array of magnets.
The magnet elements 37 are oriented in the rotor according to their
pole orientation order to obtain this flux "focussing" towards the
centre of the rotor. This is in contrast to placing the magnet
elements so that flux is "defocused" away from the centre of the
rotor. In practice, this preferred flux field might not be fully
achieved by the magnetic domain alignment pattern 42. In the more
general case, the resulting magnetic flux field 60 can be described
as follows.
[0164] Referring to FIG. 6a, each portion of the resulting magnetic
flux field 60a that exists in each magnet element 37 has an
orientation that varies continuously over the magnet element. The
orientation of the resulting magnetic flux field 60 at any point
can be described as a vector with a tangential component (as shown
by arrow C in FIG. 6a) and a radial component (as shown by arrow G
in FIG. 6a). Across the width of a magnet element 37, that
orientation varies from an orientation that has a predominant
radial component at the pole (B or F) to an orientation that has a
predominant tangential component at the edges of the magnet element
37 adjacent other magnet elements 37 in the permanent magnet ring
38. Further, across the depth (from face E to face D) of the magnet
element 37, the orientation varies from an orientation that has a
predominant radial component at an edge corresponding to the inner
face E of the permanent magnet ring 38 to an orientation that has a
predominant tangential component at an edge corresponding to the
outer face D of the permanent magnet ring 38. The orientation
typically varies non-linearly over the magnet element 37.
[0165] By predominant radial component, it is meant that the
magnitude of the radial component dominates the orientation vector
such that the vector points more in a radial direction than a
tangential direction. Predominant radial component also covers the
case where there is only a radial component of the orientation
vector, such that the orientation vector points solely in a radial
direction. By predominant tangential component, it is meant that
the magnitude of the tangential component dominates the orientation
vector such that the vector points more in a tangential direction
than in a radial direction. Predominant tangential component also
covers the case where there is only a tangential component of the
orientation vector, such that the orientation vector points solely
in a tangential direction.
[0166] Preferably, when no stator 31 is present, the radial and
tangential components of the resulting magnetic flux field 60 at
the inner surface E varies substantially sinusoidally proceeding
along the magnet in direction C, according to the following
relations:
V.sub.R=cos(.theta.) (3)
V.sub.T=-sin(.theta.) (4)
where V.sub.R and V.sub.T are the radial and tangential components
of the flux field direction vector respectively and .theta. is the
angular position across the magnet element 37, varying from -90
degrees at one edge 37a to +90 degrees at the opposite edge
37b.
[0167] FIGS. 6d and 6e show the comparison of the tangential and
radial components of the resulting flux field along the inner
surface of the magnet element 37. As can be seen, they follow sine
and cosine forms. The graphs in FIGS. 6d, 6e also shows a
comparison to the tangential and radial components of the resulting
magnetic flux field along the inner surface when using standard
elements with radially aligned magnetic domains.
[0168] In addition, the portion of the resulting magnetic flux
field 60b outside each magnet element 37 and between adjacent poles
B, F extending beyond the boundary defined by the inner face E of
the permanent magnet ring 38 has an orientation that varies
continuously. Again, the orientation of the resulting magnetic flux
field 60 at any point outside the inner face E of each magnet
element 37 can be described as a vector with a tangential component
(as shown by arrow C in FIG. 6a) and a radial component (as shown
by arrow G in FIG. 6a). Between the poles B, F, the orientation
varies from an orientation that has a predominant radial component
at the pole to an orientation that has a predominant tangential
component at the mid-point between the poles. Further, extending
radially inwards from the inner face E to the centre of rotation of
the rotor 36, the orientation varies from an orientation that has a
predominant radial component at the inner face E to an orientation
that has an increasingly tangential component with distance from
the inner face E. The orientation typically varies non-linearly
between the poles B, F and extending beyond the inner face E.
[0169] During use, when current is applied to the stator, a net
torque is generated between the rotor 36 and stator 31, causing the
rotor 36 to rotate with respect to the stator 31. In addition to
this net torque, the motor will also experience a rotor position
dependent torque that causes the rotor 36 to rotate in the
direction in which the reluctance of the magnet flux path is
reduced. Likewise the rotor 36 will oppose movement in the
direction that increases reluctance. This torque is commonly
referred to as cogging, or reluctance, torque. Cogging torque
occurs because there are variations in the reluctance as the
angular position of the rotor 36 changes, and the effect of this
variation in torque can lead to unwanted vibrations. The resulting
magnetic flux field 60 of the present invention alleviates this to
at least some extent. In the present invention, a sinusoidal flux
distribution is produced by the magnet rotor ring 38 on the stator
side E of the rotor 36. A sinusoidal flux distribution makes it
easier to cancel cogging forces through manipulation of the stator
pole 32 tip geometry since there are no higher order torque
harmonics, cancellation of the fundamental frequency being
required.
[0170] Each element could be produced by a press 78 as shown in
FIG. 7a. The press comprises a die 70 formed of a first portion 70a
made of non-magnetic steel and a second portion 70b, made of
magnetic steel. The die can preferably have a tungsten carbide
layer 70c to provide wear resistance. Magnetic steel inserts 79a,
79b are placed in the first portion 70a to avoid saturation in the
steel of the punch during domain alignment. The die 70 defines a
magnet cavity 72. The press 78 also comprises a two part lower
hydraulic punch 71, and a two part upper hydraulic punch 73. The
upper and lower punches 71, 73 are formed of magnetic steel. Punch
71 has a non-magnetic cap 71a. The upper punch has a non-magnetic
insert 79c. Preferably, both the non-magnetic cap 71a and
non-magnetic insert 79c are made of tungsten carbide for wear
resistance. An electromagnetic coil 74 resides around the upper
punch. A top plate 75, base plate 76 and two posts 77a, 77b provide
the press structure. These are made of magnetic steel.
[0171] A possible process for promoting the domain alignment
pattern 42 within a magnet using a wet slurry of ferrite material
is as follows. The press 78 is set to the open position. In such a
state the upper punch 73 is moved up some distance away from die 70
providing access to the magnet cavity 72. The lower punch 71
retracts downwards a short distance. A wet slurry of magnetic
material (not shown) such as that typically used in industry for
the moulding of high strength ferrite magnets is placed in the
magnet cavity 72. The individual magnetic domains to be aligned are
defined by the very finely ground magnetic material. A permeable
gauze material 79 is placed in the gap between the faces of the
stationary die 70 and the upper punch 73. The upper punch 73 moves
down to close the gap between the stationary die 70 and upper punch
73 face. A DC current is applied to the electromagnetic coil 74,
which acts to generate a magnetic flux field in the magnetic
circuit provided by the press 78 components. This is described
further below in respect of FIGS. 7b, 7c. The combination of the
geometry and the location of the magnetic and non-magnetic material
is such that the intended magnetic domain alignment pattern is
promoted within the magnet cavity.
[0172] The lower punch 71 is then extended steadily upwards,
compressing the material. The applied pressure forces liquids
within the material out through the permeable gauze material
located between the die 70 and upper punch 73 faces. The quantity
of liquid within the magnet cavity is significantly reduced during
this step. When the magnetic material has been sufficiently
compressed, the lower punch 71 is no longer extended but is held in
position. At this stage the magnet has reached the green state. In
this state the magnetic domains are aligned and are no longer free
to rotate relative to each other. To ensure that both the press 78
and magnet element 37 are demagnetised to enable further
processing, the constant DC current is changed to be time varying
such that it is sinusoidal in nature and whose magnitude diminishes
towards zero. When the peaks of the current have been reduced to
zero the magnet and press 78 can be considered to be demagnetised.
The element is demagnetised to avoid the possibility of the element
disintegrating. The upper punch 73 is then retracted upwards and
the gauze material 79 removed to leave the upper surface of the
magnet exposed. The lower punch 71 is then further extended a short
distance so that the green magnet is separated from the die 70 and
can be removed. The green magnets are then left to dry for a period
of time. The green magnets are then sintered within a kiln at high
temperatures. The remaining liquid is extracted from the magnet
during this stage. After cooling the magnet is ready for use or if
necessary additional operations such as grinding are possible.
[0173] FIG. 7b shows the applied magnetic flux field to the press
78, and in particular the cavity 72 in order to align the magnetic
domains of the magnet element 37 in the desired manner. FIG. 7c
shows the magnetic flux field in the cavity 72 in more detail. The
top plate 75, base plate 76 and posts 77a, 77b along with the
insert 79a, 79b, lower punch 71, magnetic portion of die 70b and
upper punch 73 combine to form a loop that directs magnetic field
flux through the tool and into the cavity in such a way as to
produce a resulting magnetic flux field in the cavity 72 (and
magnet element 37). This flux field is generally in the same
direction as the desired domain alignment pattern 42. This flux
field promotes the desired alignment of the magnetic domains 41
within the magnet element. For ferrite material, a flux density
throughout the magnet cavity 72 equal to the remanence flux density
B.sub.r of the magnet element is typically sufficient to ensure
that the magnet domains of the material are well aligned. However,
a flux density less than B.sub.r could still be applied although in
such a case the magnetic domains 41 may not be fully aligned with
the magnetic field that exists within the cavity and therefore
being less desirable but still acceptable. Though only one magnet
cavity 72 is shown, for economic manufacture multiple magnet
cavities 72 could be readily created within a single die 70 with
the process for producing the alignment pattern within a magnet
replicated for each cavity.
[0174] Alternatively each magnet element 37 could be produced in an
injection moulding tool 80 as shown in FIG. 8a. The injection
moulding tool 80 comprises two main sections 81, 82. The first
section 81 is the fixed portion of the tool and the second section
82 is the moving portion of the tool. The first section comprises a
fixed magnetic steel plate 83a, 83b, a fixed non-magnetic steel
insert 84 and a fixed plastic injection runner 85. The second
section 82 comprises a moving magnetic steel insert 86, a moving
magnetic steel plate 89, moving permanent magnet material 87a, 87b,
moving flux directing plates 90a, 90b and a moving non-magnetic
steel 88. The first and second sections 81, 82 are arranged to form
a mould cavity 91 for producing a magnet element 37. The moving
permanent magnet material 87a, 87b can be Samarium cobalt permanent
magnet material.
[0175] The magnetic steel plate 83a, 83b is attached to an
injection moulding machine, with the injection moulding machine
being capable of injection moulding blends of plastic and particles
of magnetic material into the cavity 91.
[0176] FIG. 8b show the magnetic domain alignment flux field
applied to the magnetic element 37. FIG. 8c shows the cavity 91 and
magnetic domain alignment flux field in more detail. This flux
field is generally in the same direction as the desired domain
alignment pattern 42. After producing the magnetic element 37 using
the injection moulding tool 80, the magnetic element 37 is fully
magnetised ready for assembly into the magnet ring 38 without the
need for demagnetising for further processing. The magnet element
37 may be optionally demagnetised to enable easy assembly into the
magnet ring 38 and then the assembled magnet ring 38
re-magnestised.
[0177] The magnetic steel 83a, 83b, permanent magnet material 87a,
87b, flux directing plates 90a, 90b and moving magnetic steel 86,
89 combine to form a loop that directs magnetic field flux through
the tool 80 in such a way as to produce a magnetic flux field in
the cavity 91 and magnetic element 37. This flux field promotes the
desired alignment of the magnetic domains 41 within the plastic
material with particles of magnetic material in the cavity 91. As
can be seen in FIG. 8c, the magnetic flux field that is set up
within the cavity 91 and magnet element 37 is such that it
pre-aligns the magnetic domains 41 in the desired magnetic domain
alignment pattern 42. Though only one magnet cavity 91 is shown,
for economic manufacture multiple magnet cavities 91 could be
readily created within a single die 80 with the process for
producing the alignment pattern within a magnet replicated for each
cavity.
[0178] The press shown in FIG. 7a could be used to produce ferrite
magnetic elements from dry ferrite powder or wet ferrite slurry, or
alternatively magnet elements from neodymium wet or dry powder or
slurry. A combination of these two magnetic materials, or others
could also be used in the press of FIG. 7a.
[0179] The injection moulding tool 80 of FIG. 8a could produce
magnetic elements of polymer bonded ferrite, or
neodymium-iron-boron, or a blend of ferrite and
neodymium-iron-boron or any other polymer bonded magnetic
material.
[0180] It should be noted that slurry of ferrite and/or
neodymium-iron-boron material or alternatively polymer bonded
ferrite and/or neodymium-iron-boron is made up of micron sized
magnetic particles. The particles are this small so that they
essentially contain only a single magnetic domain, which is
effectively the building block of a completed magnet that looks
like the diagrammatic magnet element 37 of FIGS. 4a to 4e. In an
isotropic magnet element, these domains are randomly aligned. In
the slurry of ferrite and/or neodymium material, the domains are
free to rotate in the water, unless aligned by a magnetic field,
until the water is pressed out and the particles, or domains, are
"squashed" together to form a solid--then this results in an
anisotropic magnetised magnet. When magnetized, the anisotropic
magnet element will have a higher magnetic flux density than an
equivalent isotropic magnet element.
[0181] In the injection moulding process, the domains are mixed
with a polymer binder that is melted in the barrel of an injection
moulder prior to injection into the cavity. The particles are
relatively free to rotate in the molten polymer binder, unless
aligned by a magnetic field. If the magnetic domains are aligned by
a magnetic field until the binder freezes in the cavity, they are
locked in place and then this again results in an anisotropic
magnetised magnet.
[0182] In the case of the pressed magnet the magnet is green and is
mechanically very weak. To enable the magnet to be handled after
pressing and through the sintering process without disintegrating,
the green magnet is demagnetised before removal from the cavity
72.
[0183] To prevent demagnetisation of the magnet element 37 once
produced, a grade of magnetic material should be used that shows
good demagnetisation characteristics. That is, preferably a grade
that exhibits a B-H curve with a knee in the third quadrant, such
as shown in FIG. 14.
[0184] Once the magnet elements have been produced, they can be
assembled in any suitable manner to form the magnetic ring for the
rotor 36 as described above. The ring can be magnetised using any
suitable method, to produce the desired Halbach-style resulting
magnetic flux field 60. For example, the rotor 36 could be placed
on and mechanically aligned with a magnetising head. The head would
be a strengthened fixture capable of high current and field. A bank
of capacitors would then be discharged through the windings of the
head, producing the magnetising alignment field necessary to
produce the resulting magnetic flux field.
[0185] FIG. 16 shows one possible magnetiser 169. This produces
flux lines designed to match up with FIG. 5a. FIG. 16 shows an all
steel back iron (laminated silicon steel) 170 with high saturation
flux density 160, a set of slots between the poles 161, coil
windings 162 in the slots, and air gap 163 between the magnetiser
poles 161 and the magnet elements 37. A backing steel 40 is behind
the magnet elements 37, and there is a small air gap 164 between
the elements 37. This magnetiser 169 produces the resulting
magnetic flux field in the rotor.
[0186] Magnetisation of the overall rotor is used when individual
elements 37 are demagnetised during the production process to avoid
disintegration. If the elements 37 are not demagnetised during
production, then it is not necessary to magnetise the rotor as
described above. That is, the rotor could be assembled from
magnetised elements 37, such that when arranged in a ring for the
rotor, the Halbach-style resulting magnetic flux field is already
present. The benefits of having pre-aligned domains will still
apply, in that the magnets will provide an overall stronger
Halbach-style resulting magnetic flux field per unit of magnet
material.
[0187] An embodiment of the invention might comprise a washing
machine with a motor as described above, or another embodiment
might comprise the motor itself, or the rotor itself.
Alternatively, the rotor could be used in another application, such
as a power generation apparatus. Another embodiment of the
invention could comprise a magnet element, as described above.
[0188] A washing machine using the motor described could take one
of many forms. For example, referring to FIG. 9, one embodiment
comprises a top loading washing machine with an outer wrapper and a
tub suspended within the wrapper. A rotating drum with perforated
walls is disposed in and rotatable within the suspended tub. A
motor, comprising a stator and rotor as previously desired, is
coupled to the rotating drum via a rotational shaft. The motor can
be operated by a controller to spin and oscillate the rotating drum
to carry out washing of clothes. The magnetic elements used in the
rotor reduce cogging of the motor and the magnetic field in the
rotor increases the torque of the motor relative to the rotor size,
weight and volume of ferrite. These make the motor as a whole less
expense and operate more efficiently.
[0189] Referring to FIG. 10, another embodiment comprises a front
loading horizontal axis washing machine with an outer wrapper and a
rotating drum housing suspended in the outer wrapper. A rotating
drum is disposed in and rotatable within the rotating drum housing.
A door provides access to the rotating drum for introducing or
removing clothing to be washed. A gasket provides a seal between
the door and the rotating drum. A motor, comprising a stator and
rotor as previously desired, is coupled to the rotating drum via a
rotational shaft. The motor can be operated by a controller to spin
and oscillate the rotating drum to carry out washing of clothes.
The magnetic elements used in the rotor reduce cogging of the motor
and the magnetic field in the rotor increases the torque on the
rotor. These make the motor as a whole operate more
efficiently.
[0190] Referring to FIG. 11, another embodiment comprises a top
loading or tilt access horizontal axis washing machine. The washing
machine has an outer wrapper and a tub suspended within the outer
wrapper. A rotating drum can rotate within the tub. Clothes can be
introduced and taken from the rotating drum through an opening in
the top of the drum. A motor, comprising a stator and rotor as
previously desired, is coupled to the rotating drum via a
rotational shaft. The motor can be operated by a controller to spin
and oscillate the rotating drum to carry out washing of clothes.
The magnetic elements used in the rotor reduce cogging of the motor
and the magnetic field in the rotor increases the torque on the
rotor. These make the motor as a whole operate more
efficiently.
[0191] FIG. 12 shows a tilt loading horizontal axis washing
machine. The washing machine has an outer wrapper and a tub
suspended within the outer wrapper. A rotating drum can rotate
within the tub. Clothes can be introduced and taken from the
rotating drum by tilting the drum. A motor, comprising a stator and
rotor as previously desired, is coupled to the rotating drum via a
rotational shaft. The motor can be operated by a controller to spin
and oscillate the rotating drum to carry out washing of clothes.
The magnetic elements used in the rotor reduce cogging of the motor
and the magnetic field in the rotor increases the torque on the
rotor. These make the motor as a whole operate more
efficiently.
[0192] It will be appreciated that FIGS. 9 to 12 show just four
examples of washing machines that could utilise a motor with a
rotor containing magnetic elements produced in the manner described
above. Other embodiments of the present invention could comprise
other washing machines be envisaged by those skilled in the art,
operated by a motor as described above.
[0193] FIG. 13 shows the predicted relative togging performance of
a) rotors with standard magnetic field patterns and radially
oriented magnetic domains, and b) rotors with equal size and volume
of magnet material with magnetic domains oriented to follow the
Halbach type field patterns.
[0194] It will be appreciated that magnet elements made from
material other than hard ferrite are possible. For example,
neodymium-iron-boron or Samarium-Cobalt or other magnet material
could be used, or a combination of magnetic materials. Further,
magnetic material(s) bonded into a polymer could be used.
[0195] It will be appreciated the rotor or motor according to the
embodiments above could be used in another applications, such as a
power generation apparatus.
[0196] It will be appreciated that the magnet element 37 described
is preferred, although other configurations of magnet element with
domain alignment patterns are possible, that when combined form an
equivalent domain alignment pattern like that shown in FIGS. 4a, 4b
or FIGS. 4c to 4e. For example, a magnet element might in fact
comprise just one half of the magnet element 37 shown in FIG. 4a.
This is shown in FIG. 15a. This alternative magnet element 150 has
a magnetic domain alignment pattern 151 from one half of the magnet
domain alignment pattern 42 shown in FIG. 4a. The magnetic domain
alignment pattern 151 has a pole 153 at one lateral edge 154b of
the element 150. The orientation varies substantially continuously
across the magnet element 150 between its lateral edges 154b, 154a
from an orientation that has a predominant radial component at the
pole 153 of the magnet element at one lateral edge 154b to an
orientation that has a least some tangential component on the other
lateral edge 154a of the magnet element 150. It will be appreciated
that the nature of the magnetic domain alignment pattern is exactly
the same as one half of the alignment pattern shown in FIG. 4a, and
the description there can be extended to apply to this embodiment.
The alternative embodiments of domain alignment patterns described
in relation to the magnet element 37 (see e.g. FIGS. 4c to 4e) can
also apply to the magnet element 150. that is, in such a element as
150, its domain alignment pattern has an orientation that varies
substantially continuously across the magnet element between its
lateral edges from an orientation that has a predominant radial
component at a pole of the magnet element at one lateral edge to an
orientation that has a least some tangential component the other
lateral edge of the magnet element.
[0197] It will also be appreciated that an alternative magnet
element could also be made that has a domain alignment pattern that
is the mirror image of that shown in FIG. 15a, as shown in FIG.
15b. Elements 150 and a mirror image element could be assembled
resulting in an element like that in FIG. 4a. Alternatively,
Element 150 could be assembled with another element 150 rotated 180
degrees around the radial axis, resulting in an element like that
of FIG. 4a.
[0198] The elements 150 of FIGS. 15a, 15b could be arranged
together to produce a rotor as described above. For example, as
shown in FIG. 15c, two such elements could be brought together
arranged side-by-side in a rotor ring, to effectively produce an
element 37 like that shown in FIG. 4a. Alternatively, as shown in
FIG. 15d, the position of the elements 150 could be reversed. Any
such combination of elements 150 could then be arranged in a ring
38 to produce the required domain alignment pattern. The magnet
elements of alternative embodiments could be made in the press 78
or injection moulder 80 described above.
[0199] Alternatively, a magnet element 37 could have poles at the
edges, and tangentially aligned domains in the centre. A ring could
be assembled from such elements.
[0200] In the preferred embodiment described above, when the magnet
elements 37 are arranged in a ring, they are arranged directly
adjacent to each other, such that a lateral edge of one magnet
elements is touching or very near the corresponding lateral edge of
an adjacent magnet element 37. In an alternative embodiment as
shown in FIG. 3f, there could be spacer elements e.g. 171 between
the lateral edges of one or more adjacently arranged magnet
elements 37. Each spacer element could be made from magnetic steel,
or other magnetic material such as hard ferrite,
neodymium-iron-boron or a combination, or a bonded magnetic
material, or other magnetic or non-magnetic material. Where
magnetic material is used, the magnetic domains could be aligned in
a suitable domain alignment pattern to assist the production of a
stronger Halbach-style magnetic flux field per unit magnet in the
rotor overall. Such a flux field could be an anisotropic
tangentially aligned domain pattern. It will be appreciated that in
this specification that when referring to adjacently arranged or
proximate magnetic elements 37, this does not preclude having a
spacer elements between the corresponding lateral edges of such
adjacently arranged or proximate magnetic elements 37.
[0201] FIG. 17 shows an alternative embodiment of a magnet element
170, which comprises a chamfer 171. The chamfer is placed on each
intersection of the inner face E of the element and its lateral
edge 175. Only one chamfer is shown, but a magnet element could
have a chamfer on both lateral edges 175. Multiple elements 170 can
be arranged in an adjacent fashion with their respective chamfers
aligned. The chamfer 171 reduces cogging.
[0202] The chamfer has an angle 172, and a cross-sectional area "A"
173. The exact shape of the chamfer (in terms of chamfer size and
angle) is not critical. The effect of the chamfer is approximately
correlated to the cross-sectional area A 173 of the chamfer. For a
given magnetic domain edge angle there are multiple chamfer sizes
and angles that all provide a low cogging solution.
[0203] Possible chamfer areas for particular edge angles are as
follows:
TABLE-US-00001 Magnetic Domain Area removed by chamfer Edge Angle
to reduce cogging 15.degree. 1.5 mm.sup.2 30.degree. 1.0 mm.sup.2
45.degree. 0.5 mm.sup.2 60.degree. 0.05 mm.sup.2
[0204] The above chamfer 171 dimensions are suitable for one type
of rotor. It will be appreciated by those skilled in the art that
the area 173 of chamfer 171 for any particular edge angle will
differ depending on rotor/magnet element specifications. Those
skilled in the art would be able to determine the correct area of
chamfer 171 by selecting that which provides the required cogging
performance.
[0205] FIGS. 18a to 18c show various magnet elements 170 with
chamfers 171 arranged in an adjacent manner. The Figures show
adjacent magnet elements with 30.degree., 60.degree. and 90.degree.
magnetic domain edge angles respectively. For completeness, the
magnetic domain alignment patterns 42 and resulting magnetic flux
fields 60 are shown on each.
[0206] FIG. 19 indicates how utilising magnet elements with
chamfers improves cogging performance over using magnet elements
without chamfers. The graph in FIG. 19 shows the relative cogging
torque produced in a rotor constructed from magnet elements with
chamfers as described above, versus the relative cogging torque
produced in a rotor constructed from magnet elements without
chamfers. In this case, the chamfer has radial and tangential
chamfer dimensions equal to 1.45 mm and each magnet element has a
30.degree. magnet domain edge angle. The graph indicates that
cogging torque is significantly reduced in the case where chamfered
magnets are utilised.
[0207] FIG. 20 shows a perspective view of a magnet element 200
with chamfered edges 201.
[0208] The chamfers provide an additional advantage of enabling the
magnet elements 200 to key into place on the core ring 210 of a
rotor during production, as shown in FIG. 21. Protrusions 211 in
the core ring assist keying and enable accurate positioning of the
magnets. The chamfers also improve the retention of magnet elements
in place via overmoulding.
[0209] The type of magnetic material used to construct a magnet
element can be selected according to the magnetic domain edge
angle. As described previously, FIG. 6c shows the ideal
relationship between flux linkage and magnetic domain edge angle.
As the magnetic domain edge angle increases towards 90.degree., the
flux linkage increases. But, in practice, as the magnetic domain
edge angle increases towards 90.degree., the resulting magnetic
flux density decreases at the back edge of the rotor ring (side "D"
in FIG. 5a). If the level of flux density is too small,
demagnetisation occurs, which is undesirable. Selecting a different
magnetic material for the magnetic element can reduce the
susceptibility to demagnetisation, thus enabling a higher magnetic
domain edge angle to be used.
[0210] FIG. 22 shows the demagnetisation curve for three types of
magnet materials, being N, B and H materials. As the magnetic
domain edge angle increases, the operating point of the magnetic
material at the back edge of the rotor ring will move to a more
negative H region in the BH curve, resulting in a lower B value.
Once the knee of the BH curve is reached, magnetisation drops off
rapidly, resulting in demagnetisation. By selecting another
magnetic material, the "operating" region of the magnetic material
before encountering the knee is increased for a particular edge
angle. Therefore, by selection of another material, demagnetisation
can be avoided for higher edge angles. Typically, for lower edge
angles an N magnet material will be selected, moving towards a B
and then H magnet material for higher edge angles. Materials with
knees that occur at a more negative B value typically have a lower
magnetic strength. Therefore, a material will be selected to
maximise flux coupling while avoiding demagnetisation at the
desired edge angle.
[0211] FIG. 23 is a graph showing generically the effect of flux
linkage versus magnetic domain edge angle using different magnet
material. An N grade material provides an increase of flux linkage
between 0 and edge angle 1 (EA1). At EA 1 the demagnetisation is
unacceptable, so for edge angles between EA1 and EA2 a B grade
material is used. The flux linkage is less than for the equivalent
edge angle than if the N grade material were used, but the B grade
material provides a more acceptable level of magnetisation. Above
an edge angle EA 2, a H grade material can be used. Again, it has
lower flux linkage, but provides acceptable magnetisation
characteristics. The appropriate type of material can be selected
based on the desired magnetic domain edge angle for the magnet
element. However, it has been found that the gain in flux linkage
for higher edge angles has diminishing returns. Therefore, in many
cases, a lower edge angle might be selected, as it allows for a
magnet grade of higher strength to be used, while still providing
an acceptable flux linkage.
[0212] FIG. 24 shows a possible arrangement of the backing steel of
the rotor. Here the backing steel 240 is overlayed to create a
"joggle" 241. The joggle reduces the airgap behind one magnet as
the steel strip 240 from the second layer 240b ramps up over the
start of the first layer 204a. Benefits are:
[0213] a) a better retention of magnets on the core ring, and
[0214] b) avoidance of an increased reluctance path for the flux
passing through the magnet into the backing ring.
* * * * *