U.S. patent application number 09/728235 was filed with the patent office on 2002-07-18 for d.c. pm motor with a stator core assembly formed of pressure shaped processed ferromagnetic particles.
Invention is credited to Petersen, Christian C..
Application Number | 20020093268 09/728235 |
Document ID | / |
Family ID | 24925986 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020093268 |
Kind Code |
A1 |
Petersen, Christian C. |
July 18, 2002 |
D.C. PM MOTOR WITH A STATOR CORE ASSEMBLY FORMED OF PRESSURE SHAPED
PROCESSED FERROMAGNETIC PARTICLES
Abstract
A d.c. PM motor having a stator core assembly which is formed of
a pressure shaped processed ferromagnetic particulate material. The
low permeability characteristic of this material is accommodated
for by a stator shape which optimizes the efficiency of the
coupling of the PM field of a rotor into the stator structure.
Efficiency for coupling the applied field into the stator core
structure also is enhanced through the utilization of transitions
in levels between the induction region of each core component and
the field winding support region. A method is described for
assembling the stator core assemblies using discrete core component
pieces in conjunction with back iron linking components or
pieces.
Inventors: |
Petersen, Christian C.;
(Sandwich, MA) |
Correspondence
Address: |
MUELLER AND SMITH, LPA
MUELLER-SMITH BUILDING
7700 RIVERS EDGE DRIVE
COLUMBUS
OH
43235
|
Family ID: |
24925986 |
Appl. No.: |
09/728235 |
Filed: |
December 1, 2000 |
Current U.S.
Class: |
310/216.001 |
Current CPC
Class: |
H02K 1/146 20130101 |
Class at
Publication: |
310/254 |
International
Class: |
H02K 001/00 |
Claims
1. A d.c. motor exhibiting a predetermined torque constant, field
winding resistance, functioning air gap radius extending from a
motor axis, and operable to a predetermined maximum current,
comprising: a rotor having a sequence of generally arcuate regions
of predetermined magnetization and a confronting magnetic surface
of principal dimension in parallel with said motor axis, said
confronting magnetic surface being located in correspondence with
said air gap radius and rotatable about said motor axis; a stator
core assembly having a select number of spaced core components
formed of pressure shaped processed ferromagnetic particles which
are generally mutually insulatively associated, each said core
component being disposed about a radius extending from said motor
axis, having a flux interaction surface located adjacent said rotor
confronting magnetic surface defining a functioning air gap and
having a face length parallel with said motor axis and a face width
selected to provide a magnetic field coupling induction
corresponding with a field turn derived said predetermined torque
constant and said field winding resistance, each said core
component having a winding support region spaced from and in flux
transfer communication with said flux interaction surface, having a
winding region width generally normal to said radius and
cross-sectional area attributes effective for conveyance of
confronting magnetic flux without saturation when said motor is
operated to said maximum current, and said stator assembly
including a back iron assembly formed of pressure shaped processed
ferromagnetic particles which are generally mutually insulatively
associated, said back iron assembly being in flux transfer
association with each said core component adjacent said winding
support region and having cross-sectional area attributes effective
for magnetic flux conveyance without saturation, said face width
having a value less than about 2.5 times said winding region width;
and a field winding assembly configured to exhibit said
predetermined field winding resistance with said field turns,
including winding components located at each said core component
and extending in electromagnetic flux coupling relationship about
said winding support region, said winding components being
controllably electrically excitable for effecting driven rotation
of said rotor about said motor axis.
2. The d.c. motor of claim 1 in which: each said core component
flux interaction surface of said stator core assembly has a said
face length which is about equal to said principal dimension of
said rotor confronting magnetic surface.
3. The d.c. motor of claim 1 in which: each said core component
flux interaction surface of said stator core assembly has a
principal dimension in parallel with said motor axis; and each said
core component winding support region has a principal dimension in
parallel with said motor axis which is less than said face length
of said flux interaction surface.
4. The d.c. motor of claim 3 in which: said stator assembly back
iron assembly has a principal dimension in parallel with said motor
axis which is greater than said principal dimension of said winding
support region.
5. The d.c. motor of claim 3 in which: said stator assembly back
iron assembly has a principal dimension in parallel with said motor
axis which is most equal to the said principal dimension of said
winding support region.
6. The d.c. motor of claim 1 in which: each said core component
includes an induction region extending in flux transfer
relationship between said flux interaction surface and said winding
support region and having a principal dimension in parallel with
said motor axis which corresponds with said face length of said
flux interaction surface.
7. The d.c. motor of claim 6 in which: each said core component
winding support region has a principal dimension in parallel with
said motor axis which is less than said face length of said flux
interaction surface.
8. The d.c. motor of claim 7 in which: each said core component
induction region is configured having first and second oppositely
disposed, parallel induction region surfaces spaced apart said
induction region principal dimension; and each said core component
winding support region is configured having first and second
oppositely disposed, mutually parallel winding support region
surfaces spaced apart said winding region principal dimension,
arranged in parallel relationship and in adjacency with respective
said first and second induction region surfaces, and including a
first forward coupling transition extending a first forward
level-defining distance between said first winding support region
surface and said first induction region surface.
9. The d.c. motor of claim 8 in which said forward level-defining
distance is of an extent to maintain a said winding component below
the level of said first induction region surface.
10. The d.c. motor of claim 8 in which: each said core component
includes a second forward coupling transition extending a second
forward level defining distance between said second winding support
region surface and said second induction region surface.
11. The d.c. motor of claim 8 in which: said stator core assembly
back iron assembly cross-sectional area has a back iron principal
dimension in parallel with said motor axis, is configured having
first and second mutually parallel back iron surfaces spaced apart
said back iron principal dimension, arranged in parallel
relationship and in adjacency with respective said first and second
winding support region surfaces.
12. The d.c. motor of claim 11 in which: said back iron principal
dimension is equal to said winding region principal dimension.
13. The d.c. motor of claim 11 in which: said back iron principal
dimension is greater than said winding region principal dimension;
and including a first rearward coupling transition extending a
first rearward, level-defining distance between said first winding
support region surface and said first back iron surface.
14. The d.c. motor of claim 13 in which said first rearward
level-defining distance is of an extent to maintain a said winding
component below the level of said first back iron surface.
15. The d.c. motor of claim 13 in which: each said core component
includes a second rearward coupling transition extending a second
rearward level-defining distance between said second winding
support region surface and said second back iron surface.
16. The d.c. motor of claim 13 in which: said first back iron
surface is arranged in coplanar relationship with said first
induction region surface.
17. The d.c. motor of claim 16 in which: said second back iron
surface is arranged in coplanar relationship with said second
induction region surface.
18. The d.c. motor of claim 1 in which said stator assembly back
iron assembly comprises: a plurality of discrete back iron linking
members each having at least two, spaced apart first back iron
abutting surfaces; a back iron extension region formed integrally
with and extending from said winding support region of each said
core component to at least two, spaced apart second back iron
abutting surfaces arranged in interkeyed, abutting relationship
with said first back iron abutting surfaces to define said stator
assembly.
19. The d.c. motor of claim 18 in which said stator assembly
includes a tensioning assembly surmounting each said core component
flux interaction surface for effecting a compressive engagement of
said first and second back iron abutting surfaces.
20. The d.c. motor of claim 19 in which said tensioning assembly is
a compression ring.
21. The d.c. motor of claim 18 in which said stator assembly
includes a tensioning assembly surmounting each said back iron
linking member and back iron extension region for effecting a
compressive engagement of said first and second back iron abutting
surfaces.
22. The d.c. motor of claim 19 in which said tensioning assembly is
a compression ring.
23. A d.c. motor system exhibiting a predetermined torque constant,
field winding resistance, functioning air gap radius extending from
a motor axis and operable to a predetermined maximum current,
comprising: a bearing support assembly; an air bearing mounted for
rotation about said motor axis upon said bearing support assembly;
a rotor having a sequence of generally arcuate regions of
predetermined magnetization and confronting surface of first
principal dimension in parallel with said motor axis, mounted for
rotation with said air bearing, said confronting magnetic surface
being located in correspondence with said air gap radius; a stator
core assembly having a select number of spaced core components each
being disposed about a radius extending from said motor axis,
formed of pressure shaped processed ferromagnetic particles which
are generally mutually insulatively associated, each said core
component having an induction region of second principal dimension
in parallel with said motor axis having a value close in value to
the value of said first principal dimension, said induction region
extending to an arcuate flux interaction surface located adjacent
said rotor confronting magnetic surface to define a functioning air
gap and having a face length parallel with said motor axis and an
arcuate face width generally normal to said radius, said face
length exhibiting said second principal dimension selected to
provide a coupling induction of the magnetic flux derived from said
rotor regions of predetermined magnetization, each said core
component having a winding support region extending in flux
transfer communication from said induction region having a third
principal dimension parallel with said motor axis, and a winding
region width generally normal to said radius, and said stator
assembly including a back iron assembly formed of pressure shaped
processed ferromagnetic particles which are generally mutually
insulatively associated, said back iron assembly being in flux
transfer association with each said core component adjacent said
winding support region; a field winding assembly configured with
multiple field turns exhibiting said predetermined field winding
resistance, said field turns being located at each said core
component and extending in electromagnetic flux coupling
relationship about said winding support region, said field turns
being controllably electrically excitable for effecting driven
rotation of said rotor upon said air bearing; and each said core
component induction region and winding support region, and said
back iron assembly having cross sectional area attributes effective
for conveyance of magnetic flux derived from said regions of
predetermined magnetization and from said field winding assembly
without saturation.
24. The d.c. motor system of claim 23 in which said face width has
a value less than about 2.5 times the value of said winding region
width.
25. The d.c. motor system of claim 23 in which: each said core
component induction region is configured having first and second
oppositely disposed, parallel induction region surfaces spaced
apart said second principal dimension; said third principal
dimension is less than said second principal dimension; and each
said core component winding support region is configured having
first and second oppositely disposed, mutually parallel winding
support region surfaces spaced apart said third principal
dimension, arranged in parallel relationship and in adjacency with
respective said first and second induction region surfaces, and
including a first forward coupling transition extending a first
forward level-defining distance between said first winding support
region surface and said first induction region surface.
26. The d.c. motor system of claim 25 in which: said back iron
assembly has a fourth principal dimension paralleled with said
motor axis; and said second principal dimension is less than said
fourth principal dimension.
27. The d.c. motor of claim 25 in which said forward level-defining
distance is of an extent to maintain a said winding component below
the level of said first induction region surface.
28. The d.c. motor of claim 25 in which: each said core component
includes a second forward coupling transition extending a second
forward level defining distance between said second winding support
region surface and said second induction region surface.
29. The d.c. motor of claim 25 in which: said stator core assembly
back iron assembly cross-sectional area has a fourth principal
dimension in parallel with said motor axis, is configured having
first and second mutually parallel back iron surfaces spaced apart
said fourth principal dimension, arranged in parallel relationship
and in adjacency with respective said first and second winding
support region surfaces.
30. The d.c. motor of claim 29 in which: said fourth principal
dimension is equal to said third principal dimension.
31. The d.c. motor of claim 29 in which: said fourth principal
dimension is greater than said third principal dimension; and
including a first rearward coupling transition extending a first
rearward, level-defining distance between said first winding
support region surface and said first back iron surface.
32. The d.c. motor of claim 31 in which said first rearward
level-defining distance is of an extent to maintain a said winding
component below the level of said first back iron surface.
33. The d.c. motor of claim 31 in which: each said core component
includes a second rearward coupling transition extending a second
rearward level-defining distance between said second winding
support region surface and said second back iron surface.
34. The d.c. motor of claim 31 in which: said first back iron
surface is arranged in coplanar relationship with said first
induction region surface.
35. The d.c. motor of claim 34 in which: said second back iron
surface is arranged in coplanar relationship with said second
induction region surface.
36. The method of forming a stator and field winding assembly for a
d.c. motor having a rotor supporting a multiple pole permanent
magnet assembly drivably rotatable about a motor axis, comprising
the steps of: (a) providing a predetermined number of core
components, each being formed of pressure shaped processed
ferromagnetic particles which are generally mutually insulatively
associated, each said core component having an induction region
extending along a radius from said axis to an arcuate flux
interaction surface, said induction region extending to and being
integrally formed with a winding support region of predetermined
winding region width, said winding support region extending to and
being integrally formed with a back iron extension region having
two, spaced apart core component back iron abutting surfaces; (b)
providing a predetermined number of discrete back iron linking
members each having two, spaced apart linking abutting surfaces and
each being formed of pressure shaped processed ferromagnetic
particles; (c) positioning a core component winding over said
winding support region; and (d) then attaching said back iron
linking members to said core components in a manner wherein said
back iron abutting surfaces are in intimate abutting contact with
said linking abutting surfaces.
37. The method of claim 36 in which: said step (c) of positioning a
core component winding over said winding support region includes
the step of: (c1) providing an electrically insulative bobbin; (c2)
winding a predetermined number electrically conductive wire turns
upon said bobbin; and (c3) inserting said bobbin with said wound
wire turns over said winding support region by insertion over said
back iron extension region.
38. The method of claim 36 in which said step (d) is carried out by
adhesively joining said back iron abutting surfaces with said
linking abutting surfaces.
39. The method of claim 36 in which said step (d) for attaching
said back iron linking members to said core components includes the
steps of: (d1) providing a tensioning assembly; and (d2 positioning
said tensioning assembly over each said core component flux
interaction surface to effect a compressive abutment of said back
iron abutting surfaces against said linking abutting surfaces.
40. The method of claim 36 in which said step (d) for attaching
said back iron linking members to said core components includes the
steps of: (d1) providing a tensioning assembly; and (d2)
positioning said tensioning assembly over each said core component
back iron linking member and back iron extension region to effect a
compressive abutment of said back iron abutting surfaces against
said linking abutting surfaces.
41. A d.c. motor, comprising: a rotor rotatable about a motor axis
having a sequence of generally arcuate regions of predetermined
magnetization and confronting magnetic surface of first principal
dimension in parallel with said motor axis; a stator core assembly
having spaced core components formed of pressure shaped processed
ferromagnetic particles which are generally mutually insulatively
associated, each said core component having an induction region of
second principal dimension in parallel with said motor axis between
first and second induction region surfaces and extending to an
arcuate flux interaction surface located adjacent said rotor
confronting magnetic surface to define a functioning air gap and
having a face length parallel with said motor axis of value about
equal to said first principal dimension, said induction region
extending to an integrally formed winding support region having
oppositely disposed first and second support region surfaces spaced
apart a third principal dimension less than said second principal
dimension, a first forward coupling transition extending a first
forward level-defining distance between said first winding support
region surface and said first induction region surface, and
including a back iron assembly formed of pressure shaped processed
ferromagnetic particles which are generally mutually insulatively
associated, said back iron assembly being in flux transfer
association with each said core component adjacent said winding
support region and having a fourth principal dimension parallel
with said motor axis extending between first and second spaced
apart back iron surfaces; and a field winding assembly including
winding components located at each said core component and
extending in electromagnetic flux coupling relationship about said
winding support region, said winding components being controllably
electrically excitable for effecting driven rotation of said rotor
about said motor axis.
42. The d.c. motor of claim 41 in which said forward level-defining
distance is of an extent to maintain a said winding component below
the level of said first induction region surface.
43. The d.c. motor of claim 41 in which: each said core component
includes a second forward coupling transition extending a second
forward level defining distance between said second winding support
region surface and said second induction region surface.
44. The d.c. motor of claim 41 in which: said back iron principal
dimension is equal to said winding region principal dimension.
45. The d.c. motor of claim 41 in which: said back iron principal
dimension is greater than said winding region principal dimension;
and including a first rearward coupling transition extending a
first rearward, level-defining distance between said first winding
support region surface and said first back iron surface.
46. The d.c. motor of claim 45 in which said first rearward
level-defining distance is of an extent to maintain a said winding
component below the level of said first back iron surface.
47. The d.c. motor of claim 45 in which: each said core component
includes a second rearward coupling transition extending a second
rearward level-defining distance between said second winding
support region surface and said second back iron surface.
48. The d.c. motor of claim 45 in which: said first back iron
surface is arranged in coplanar relationship with said first
induction region surface.
49. The d.c. motor of claim 48 in which: said second back iron
surface is arranged in coplanar relationship with said second
induction region surface.
50. The d.c. motor of claim 41 in which said stator assembly back
iron assembly comprises: a plurality of discrete back iron linking
members each having at least two, spaced apart first back iron
abutting surfaces; a back iron extension region formed integrally
with and extending from said winding support region of each said
core component to at least two, spaced apart second back iron
abutting surfaces arranged in interkeyed, abutting relationship
with said first back iron abutting surfaces to define said stator
assembly.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0001] Not applicable.
BACKGROUND OF THE INVENTION
[0002] Investigators in the electric motor arts have been called
upon to significantly expand motor technology from its somewhat
static status of many decades. Improved motor performance
particularly has been called for in such technical venues as
computer design and secondary motorized systems carried by
vehicles, for example, in the automotive and aircraft fields. With
progress in these fields, classically designed electric motors, for
example, utilizing brush-based commutation, have been found to be
unacceptable or, at best, marginal performers.
[0003] From the time of its early formation, the computer industry
has employed brushiess d.c. motors for its magnetic memory systems.
The electric motors initially utilized for these drives were
relatively expensive and incorporated a variety of refinements
particularly necessitated with the introduction of rotating disc
memory. For example, detent torque phenomena has been the subject
of correction. The phenomena occurs as a consequence of the nature
of motors configured with steel core stator poles and associated
field windings performing in conjunction with permanent magnets.
With such component combinations, without correction, during an
excitation state of the motor windings which create motor drive,
this detent torque will be additively and subtractively
superimposed upon the operational characteristics of the motor
output to distort the energized torque curve, increase ripple
torque, reduce the minimum torque available for starting and,
possibly develop instantaneous speed variations. Such instantaneous
speed variations generally have not been correctable by
electronics. Particularly over the recent past, the computer
industry has called for very low profile motors capable of
performing in conjunction with very small disc systems and at
substantially elevated speeds.
[0004] Petersen, in U.S. Pat. No. 4,745,345, entitled "D.C. Motor
with Axially Disposed Working Flux Gap", issued May 17, 1988,
describes a PM d.c. motor of a brushless variety employing a
rotor-stator pole architecture wherein the working flux gap is
disposed "axially" wherein the transfer of flux is parallel with
the axis of rotation of the motor. This "axial" architecture
further employs the use of field windings which are simply
structured, being supported from stator pole core members, which,
in turn, are mounted upon a magnetically permeable base. The
windings positioned over the stator pole core members
advantageously may be developed upon simple bobbins insertable over
the upstanding pole core members. Such axial type motors have
exhibited excellent dynamic performance and efficiency and,
ideally, may be designed to assume very small and desirably
variable configurations.
[0005] Petersen in U.S. Pat. No. 4,949,000, entitled "D.C. Motor",
issued Aug. 14, 1990 describes a d.c. motor for computer
applications with an axial magnetic architecture wherein the axial
forces which are induced by the permanent magnet based rotor are
substantially eliminated through the employment of axially
polarized rotor magnets in a shear form of flux transfer
relationship with the steel core components of the stator poles.
The dynamic tangentially directed vector force output (torque) of
the resultant motor is highly regular or smooth lending such motor
designs to numerous high level technological applications such as
computer disc drives which require both design flexibility,
volumetric efficiency, low audible noise, and a very smooth torque
output.
[0006] Petersen et al, in U.S. Pat. No. 4,837,474 entitled "D.C.
Motor", issued Jun. 6, 1989, describes a brushless PM d.c. motor in
which the permanent magnets thereof are provided as arcuate
segments which rotate about a circular locus of core component
defining pole assemblies. The paired permanent magnets are
magnetized in a radial polar sense and interact without back iron
in radial fashion with three core components of each pole assembly
which include a centrally disposed core component extending within
a channel between the magnet pairs and to adjacently inwardly and
outwardly disposed core components also interacting with the
permanent magnet radially disposed surface. With the arrangement,
localized rotor balancing is achieved and, additionally, discrete
or localized magnetic circuits are developed with respect to the
association of each permanent magnet pair with the pole
assembly.
[0007] Petersen in U.S. Pat. No. 5,659,217, issued Feb. 10, 1995
and entitled "Permanent Magnet D.C. Motor Having Radially-Disposed
Working Flux-Gap" describes a PM d.c. brushless motor having
outstanding performance characteristics which is producible at
practical cost levels commensurate with the incorporation of the
motors into products intended for the consumer marketplace. These
motors exhibit a highly desirable heat dissipation characteristic
and provide improved torque output in consequence of a relatively
high ratio of the radius from the motor axis to its working gap
with respect to the corresponding radius to the motors' outer
periphery. The torque performance is achieved with the design even
though lower cost or, lower energy product permanent magnets may be
employed with the motors. See also: Petersen, U.S. Pat. No.
5,874,796, issued Feb. 23, 1999.
[0008] Over the years of development of what may be referred to as
the Petersen motor technology, greatly improved motor design
flexibility has been realized. Designers of a broad variety of
motor driven products including household implements and
appliances, tools, pumps, fans and the like as well as more complex
systems such as disc drives now are afforded a greatly expanded
configuration flexibility utilizing the new brushless motor
systems. No longer are such designers limited to the essentially
"off-the-shelf" motor variety as listed in the catalogues of motor
manufacturers. Now, motor designs may become components of and
compliment the product itself in an expanded system design
approach.
[0009] During the recent past, considerable interest has been
manifested by motor designers in the utilization of processed
ferromagnetic particles in conjunction with pressed powder
technology as a substitute for the conventional laminar steel core
components of motors. With this technology, the fine particles
which are pressed together essentially are mutually electrically
insulated. So structured, when utilized as a motor core component,
the product will exhibit very low eddy current loss which will
represent a highly desirable feature, particularly as higher motor
speeds and resultant core switching speeds are called for. As a
further advantage, for example, in the control of cost, the pressed
powder assemblies may be net shaped wherein many intermediate
manufacturing steps and quality considerations are avoided. Also,
tooling costs associated with this pressed powder fabrication are
substantially low as compared with the corresponding tooling
required with typical laminated steel fabrication. The desirable
molding approach provides a resultant magnetic particle structure
that is 3-dimensional magnetically and avoids the difficulties
encountered in the somewhat two-dimensional magnetic structure
world of laminations. See generally U.S. Pat. No. 5,874,796
(supra).
[0010] The high promise of such pressed power components, however,
currently is compromised by the unfortunate characteristic of the
material in exhibiting relatively low permeability as contrasted at
least with conventional laminar core systems. Thus the low
permeability has called for 11/2 to 2 times as many ampere turn
deriving windings. In order to simultaneously achieve acceptable
field winding resistance values, the thickness of the winding wire
must be increased such that the wire gauge now calls for bulksome
structures which, in turn, limit design flexibility. Indeed,
designers confronting the permeability values available with
processed ferromagnetic particle technology will, as a first
inclination, return to laminar structures. This is particularly
true where control over the size of the motors is mandated as, for
example, in connection with the formation of brushless d.c. motors
employed with very miniaturized packaging. However, the disc drive
industry now seeks such compact packaging in conjunction with high
rotational speeds. In the latter regard, speed increases from
around 7200 rpm to 15000 rpm and greater now are contemplated for
disc drives which, in turn, must perform with motors the profile of
which is measured in terms of a small number of millimeters. In
general, lamination-based core structures cannot perform as
satisfactorily at the higher core switching speeds involved, while
particulate core-based structures are defeated by the size
restraints.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention is addressed to PM d.c. motors having
stator core assemblies formed of processed ferromagnetic particles
and created by molding or pressing procedures. Practical
configurations for these motors are developed with architectures
which accommodate for the lower permeability characteristics of
their stator forming material through the application of a higher
level of P.M. induced fields and larger cross sectional area of the
winding support region to achieve the required performance
comparable to conventional laminated stator core structures. To
make optimum use of the form pressed particulate material, a stator
assembly shape is provided which maximizes the efficiency of
coupling of the permanent magnet field into each stator core
component, as well as improves the coupling efficiency of the
applied field at the field winding support region. The latter
coupling efficiency is developed through the utilization of
ramp-shaped transitions from one level at an induction region to a
next adjacent level at the field winding support region of each
core component of the stator core assembly. Efficiency further is
realized by adherence to a criteria wherein the widthwise extent or
width of each core component of the stator assembly at the field
winding region and the arcuate or circumferential length of the
flux interaction surface at each induction region meet a
requirement wherein their ratio cannot exceed about 2.5. Enhanced
induction of the permanent magnet field at the induction region of
each core component is evolved by an enlarged face length or length
of the flux confronting surface of each core component taken in
parallel with the motor axis. That length will be about coextensive
with the corresponding length of the permanent magnet assembly in
the motor rotor.
[0012] By meeting these design criteria, motors can be designed
which meet severe size and/or shape limitations and which may take
advantage of the lower eddy current losses evidenced by pressed
processed ferromagnetic particulate materials. The resultant stator
cores will sustain very high field switching rates without
otherwise unacceptable losses, which typically are manifested in
excessive and generally unacceptable heat development.
[0013] In one approach of the invention, further advantage is taken
of these processed ferromagnetic particulate structures in that the
stator core assemblies can be formed of discrete core components
which are interkeyed to form a plurality of core components
interconnected by a back iron assembly formed of the same type
material. Alternately the back iron assembly can be formed from
stamped laminations albeit with some accompanying increase in
losses at higher switching frequencies. Compression stamped
laminations Tensioning assemblies are utilized in retaining these
assemblies together and further, they can be interkeyed and
assembled together with adhesives.
[0014] Another feature of the invention is to provide a d.c. motor
exhibiting a predetermined torque constant, field winding
resistance and functioning air gap radius extending from a motor
axis. The motor includes a rotor having a sequence of generally
arcuate regions of predetermined magnetization and confronting
magnetic surface of principal dimension in parallel with the motor
axis. This confronting magnetic surface is located in
correspondence with the air gap radius and is rotated about the
motor axis. A stator core assembly is provided having spaced core
components formed of the noted pressure shaped processed
ferromagnetic particles which are generally mutually insulatively
associated. Each core component of the stator core assembly is
disposed about a radius extending from the motor axis and has a
flux interaction surface located adjacent the rotor confronting
magnetic surface to define a functioning air gap. The flux
interaction surface has a face length parallel with the motor axis
and a face width selected to provide a magnetic field coupling
induction acting with a selected core component winding support
region area and winding turns that corresponds with the
predetermined torque constant and field winding resistance. Each
core component has the winding support region radially spaced from
and in flux transfer communication with the flux interaction
surface and has a flux interacting pole region which exhibits a
cross-sectional area effective for conveying of confronting
magnetic flux and coil generated electromagnetic flux without
saturation. The stator assembly includes a back iron assembly
formed of pressure shaped processed ferromagnetic particles which
are generally mutually insulatively associated. This back iron
assembly is radially spaced from and in flux transfer association
with each core component winding support region and has
cross-sectional area attributes effective for magnetic flux
conveyance without saturation. The noted core component flux
interaction surface face width has a value less than about 2.5
times the winding region width. A field winding assembly is
provided which is configured to exhibit the predetermined field
winding resistance and which includes winding components located at
each core component, extending in electromagnetic flux coupling
relationship about the winding support region, the winding
components being controllably electrically excitable for effecting
driven rotation of the rotor about the motor axis.
[0015] Other objects of the invention will, in part, be obvious and
will, in part, appear hereinafter. The invention, accordingly,
comprises the method, system and apparatus possessing the
construction, combination of elements, arrangement of parts and
steps which are exemplified in the following detailed
description.
[0016] For a fuller understanding of the nature and objects of the
invention, reference should be made to the following detailed
description taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a chart demonstrating the variation of
permeability between a conventional laminar stator core structure
and a stator core structure according to the invention;
[0018] FIG. 2 is a perspective view of a disc drive with portions
broken away to reveal internal structure;
[0019] FIG. 3 is a sectional view taken through the plane 3-3 shown
in FIG. 2;
[0020] FIG. 4 is a partial sectional view of a rotor and stator
core component described in connection with FIG. 3;
[0021] FIG. 5 is a partial sectional view of a laminar stator core
structured implementation of the motor of FIG. 4;
[0022] FIG. 6 is a top view of a stator core assembly shown in
connection with a schematic representation of a rotor and showing
flux flow paths;
[0023] FIG. 7 is a sectional view taken through the plane in 7-7 in
FIG. 6;
[0024] FIG. 8 is a top view of a second stator core assembly
according to the invention;
[0025] FIG. 9 is a sectional view taken through the plane 9-9 in
FIG. 8:
[0026] FIG. 10 is a top view of another stator core assembly
embodiment of the invention;
[0027] FIG. 11 is a sectional view taken through the plane 11-11
shown in FIG. 10;
[0028] FIG. 12 is a sectional view of another embodiment of a motor
according to the invention showing its implementation with a disc
drive;
[0029] FIG. 13 is a top view of the stator core assembly employed
with the motor shown in FIG. 12;
[0030] FIG. 14 is a top view of a stator core assembly and
associated rotor utilizing interkeyed discrete processed
ferromagnetic particle structures; and
[0031] FIG. 15 is a top view of another embodiment for a stator
core structure and rotor assembly utilizing interkeyed processed
ferromagnetic particle components.
DETAILED DESCRIPTION OF THE INVENTION
[0032] In the discourse to follow, the structuring of pressed
powder metal (PPM) permanent magnet (PM) d.c. motors according to
the invention is evolved in consonance with a discovery that for
implementing such motors in a system design approach associated
with a product, the designer will necessarily always have a
pre-selected or specified torque constant required of the motor to
evoke requisite speed, and a field winding resistance which can be
tolerated both in terms electrical circuit requirements and
starting torque needs in achieving such speeds at the required
load. Additionally, the outside diameter of the motor is often
specified which indirectly defines the radius from the motor axis
to its functioning or working air gap. These motors all employ
stator assemblies which are formed, for example, by pressure
shaping processed ferromagnetic particles formed of a very pure
iron powder which is coated with an inorganic material. The
advantages of being able to use these materials while still meeting
system packaging or envelope requirements reside in their net
shaping capabilities and lower cost tooling, which cost will be
substantially below the tooling required for creating conventional
core laminations. While the very low eddy current loss exhibited by
stator core components formed with this material is highly
advantageous, the permeability parameter for the material,
typically expressed in Gauss per Oersted (G/Oe) is remarkably low
for currently available materials.
[0033] The lower permeability of a resultant stator configured with
the processed ferromagnetic particle material is accommodated for
through the utilization of a higher applied or electromagnetic
field which achieves an adequate level of induction. These
materials also exhibit a lower level of maximum induction. In this
regard, the highest level of possible induction of the material is
lower than that of steel lamination material when utilized in its
preferred direction. This means that the powdered material may
saturate at a lower flux density. To make optimum use of the
processed ferromagnetic particulate material the principal coplanar
dimension or face length along the axis of the arcuate flux
interaction surface is made as long as possible. In this regard, it
is made about the same length taken in the sense of the axis of the
motor as the length of the permanent magnets available to be
installed in the rotor. The term "about" the same length is
utilized inasmuch as it is desirable to permit a slight overlap of
the permanent magnet component with respect to that flux
interaction surface. Another feature of motors of the invention
resides in the arcuate circumferential length of the typically
flared flux interaction surface. It is desirable that that length
be minimized and such minimization can be realized by increasing
the number of core components and, typically, increasing the number
of north-south pole pairs on the rotor. For example, by increasing
the number of core components from six to twelve for a given rotor
structure that arcuate length can be lessened and the number of
field winding turns required is diminished to give the designer
more flexibility in achieving control over the height along the
axis or profile of the motor. With the motor design of the
invention, it further is desirable that the widthwise extent of
that portion of pole components referred to as a winding support
region be as wide as possible with respect to the arcuate length of
the flux interaction surface. In this regard, the circumferential
extent of the flux interaction surface should be no more than about
2.5 times the widthwise extent of the winding region of a core
component.
[0034] With the design of the invention, advantage also is taken of
the capability for pressure shaping the core components or stator
assemblies, for example, utilizing net shaping procedures. In this
regard, transitions effecting changes in levels between the
induction region of a core component leading to the flux
confronting face and that region supporting a winding are provided.
These transitions appear as ramps leading to widened field winding
support regions which function as coupling enhancers improving the
coupling of the applied or electromagnetic flux field into the core
component and also reduce the overall height of the motor over the
windings along the axis.
[0035] FIG. 1 illustrates the immediately apparent design
disadvantage occasioned by the low permeability design parameter as
it is compared with a quality lamination material. In the figure,
curves are shown which plot permeability with respect to induction
in kilogauss (kG). Curve 10 is developed from a conventionally
available laminar material identified as M-19FP having a 24 gauge
thickness. The reader may now contrast the permeability
characteristics of this conventional material with the
corresponding permeability characteristics of processed
ferromagnetic materials as are employed with the motors of the
invention, as represented at curve 12. The material deriving curve
12 is identified as SM-2HB marketed by Mii Technologies, LLC of
West Lebanon, NH. This material is described as having low eddy
current losses as a percentage of hysteresis loss. For example, at
60 Hz, and an induction of 1.5 Tesla, the material exhibits 9% eddy
current loss and 91% hysteresis loss. Thus, the material is capable
of providing a significant advantage for electrically commutated
motors that operate at frequencies higher than line frequencies.
However, its permeability characteristics would, at first
observation, render it unfit to meet the packaging and performance
criteria sought in many applications.
[0036] The motor architecture of the invention is described in
conjunction with a severe application of criteria associated with
small but very high speed disc drive applications. In this regard,
the motor illustrated was designed for a disc drive operating at
15,000 rpm and with a profile or height above the base or reference
surface of the disc drive wherein the combination of rotor borne
permanent magnet and an associated stator core assembly including
field winding is slightly more than 3 mm and the noted radius from
the center line to the functioning air gap, i.e., to the
confronting surface of the permanent magnet components was about
171/2 mm. Further contemplated for this same architecture is a disc
drive of essentially the same dimensional requirement performing at
40,000 rpm. For all of such high speed embodiments, the core
switching frequencies typically will exceed 1000 Hz, representing
values which are highly difficult to accommodate for with
conventional laminar core structures, inasmuch as the core losses
encountered become more severe at such elevated frequencies.
[0037] In the instant discussion, the parameter, "torque constant"
may be represented by the following expression: 1 K T = E S N NL (
K ) ( 1 )
[0038] where;
[0039] Kr=Torque Constant E.sub.s=Motor Supply Voltage
N.sub.NL=Ideal No-Load Speed, and K=A Conversion Constant. The term
voltage constant (K.sub.E) is the reciprocal of the torque constant
when the torque constant is expressed in Newton Meters/A and the
voltage constant is then expressed as volt-sec./radian.
[0040] The parameter "field winding resistance" means the d.c.
resistance of the motor winding that is presented to the electrical
driving circuit.
[0041] The term "functioning air gap radius" is intended to mean
the radial length from the motor axis to the midpoint of the
working air gap which is driven.
[0042] Referring to FIG. 2, a rotating element magnetic storage
device employing rigid storage media, generally referred to as a
"disc drive" is shown in general at 20. Drive 20 is one exhibiting
a highly compact size and which functions in conjunction with
memory discs which are rotated at 15,000 rpm. The diminutive
packaging features of the drive 20 impose severe envelope
restraints upon the spindle motor which functions to carry out the
high speed rotation of the rigid disc media, particularly in terms
of its "profile". The latter term refers to the height of the motor
above the base and associated reference surface 22 upon which the
motor is mounted. Device 20 is seen to include side walls 24 and 26
extending from the base 22 and a removable upper cover 28. A
sequence of rigid magnetic memory discs is shown in general at 30
which are retained over a motor spindle or hub by a spindle clamp
represented generally at 32. Accessing the disc sequence 30 are
multiple magnetic heads, one for each disc surface, each supported
from an arm or suspension assembly the top arm of which is shown at
36. All the head suspension arms are in turn, rotated around a
pivot 44 by an angular movement motor represented generally at 38,
conventionally referred to as a head positioner motor. Peripheral
support devices are represented generally at 40 supported from base
22 and a multilead connector is shown generally at 42.
[0043] FIG. 3 reveals that the sequence of discs 30 includes discs
44-47 which are mounted upon a spindle or hub represented generally
at 50 and are retained in place by the spindle clamp 32. That clamp
32 is formed with an externally threaded collar 52 and a spring
retainer 54 which engages the disc sequence 30. These discs, for
example, will be about 0.031 inch thick and their mutual spacing is
approximately 0.073 inch. To achieve the high rotational speeds
called for, a low friction bearing system is required for the
spindle 50. For example, an air bearing is represented in general
at 56 which provides for rotation about a motor axis 58 at a
stationary axle or spindle 59 fixed to base 22 and top cover 28.
Such air bearings as at 56 ride on a thin film of gas which
provides lubrication. In the case of aerodynamic or self-acting
bearings, the air film or gas film is created by the relative
motion of two mating surfaces separated by a small distance or
clearance. From rest, as rotational speed is increased, a velocity
induced pressure gradient is formed across the clearance. The
increased pressure between the surfaces creates the load carrying
effect of the mechanism. Such bearings are marketed, for example,
by Specialty Components, Inc. of Wallingford, Conn. Self-acting gas
bearings also are described in the publication, "BEARINGS" edited
by M. J. Neale, published by the Society of Automotive Engineers,
Inc. of Warrendale, Pa.
[0044] The high speed d.c. PM motor which drives the disc sequence
30 about this air bearing 56 is represented generally at 60. Motor
60 is called upon to achieve the noted high speeds while
maintaining a very low profile. That profile is measured from its
bottom which abuts against the reference plane at base 22 to the
top of the uppermost field winding wire and will, for example, be
about 4 mm. For the stator shown in FIG. 8 or 3.4 mm for the stator
shown in FIG. 6. The rotor of motor 60 is shown generally at 62
representing a portion of hub 82. Rotor 62 is rotationally
supported by the air bearing 56 and carries an arcuate magnet
assembly represented generally at 64 which is configured having a
sequence of eight generally arcuate regions of alternating magnetic
polarity. Those magnet regions present a confronting magnetic
surface 66 facing inwardly toward the axis 58 of the motor. Motor
60, in order to achieve the high speed called for, must exhibit a
predetermined relatively low torque constant. Because of the low
torque constant a relatively high starting current will be required
in order to accelerate the disks rapidly enough to get head lift
off in the required time. To maximize space for the disks the motor
is required to have a very low profile because the interior of the
hub 82 is occupied by the air bearing system so the motor must fit
below the disks. The motor must therefore be short radially as well
as axially. Shown in FIG. 3 the motor air gap radius is {fraction
(1/2)} of the diametric extent of the magnetic surface 66. The
latter dimension is represented by arrow pair 68. For the instant
motor embodiment that diametric extent is 34.85 mm. Located
inwardly from the magnet assembly 64 and supported upon the
reference plane or non-conductive base 22 is an annular stator core
assembly represented generally at 70. Formed of the above-discussed
processed ferromagnetic particles using pressed powdered metal
technology, the multiple core components of the assembly 70 extend
from a flux interaction surface 72 spaced from the confronting
magnetic surface 66, to define the functioning air gap of motor 60,
to a back iron assembly represented generally at 74. Because of the
air bearing requirements, the back iron assembly 74 is radially or
diametrically restricted in an inward sense to a diameter of 22.3
mm as represented by the arrow pair 76. The stator core assembly 70
is seen to be positioned and supported at this back iron assembly
region 74 by an annular collar 78 formed with the base 22.
[0045] Each of the core components of the stator core assembly 70
includes a winding support region, each of which, in turn, supports
and is in flux transfer communication with the winding components
of a field winding assembly represented generally at 80. This field
winding assembly will exhibit a predetermined field winding
resistance that is low enough to permit the aforementioned starting
current and represents a third parameter involved in achieving a
design flexibility including the low profile, as well as the high
speed characteristic of the motor 60. In general, the profile or
height of the motor 60 is predicated upon the uppermost height of
these windings with respect to the reference surface or base 22. In
this regard, the stator core assembly 70 is seen to rest in flat
abutting relationship against that reference surface 22. Because
the magnet assembly 64 extends slightly below the plane of that
surface 22, a shallow annular groove 82 is formed therein.
[0046] Referring to FIG. 4, an enlarged representation of a core
component of the stator core assembly and its association with the
rotor carried permanent magnet is revealed. FIG. 4 illustrates the
rightward section of the rotor and stator assembly as shown in FIG.
3 in enlarged fashion. In the figure, the flux interaction surface
72 of the stator core assembly 70 again is seen to be spaced from
the corresponding confronting magnetic surface 66 of permanent
magnet 64 to define a functional or working air gap 90. The flux
interaction surface 72 of the stator core assembly core component
will have a principal dimension or face height represented by
paired arrows 92. For the embodiment described, that height or
principal dimension became 3 mm. That dimension is slightly less
than the corresponding principal dimension or height of the
permanent magnet 64 which additionally is shown in FIG. 5 by paired
arrows 94. The latter height or principal dimension is 3.4 mm for
the instant embodiment. Note the symmetrical alignment of the
confronting faces or surfaces 66 and flux interaction surface 72.
Thus there is permitted a slight overlap of flux transfer from the
permanent magnet 64, as represented by the dashed flux
representation lines 96 and 98. Located immediately inwardly from
the surface 72 is an induction region represented in general at
100. Induction region 100 extends in flux transfer relationship
from the flux interaction surface 72 inwardly and is formed between
mutually parallel oppositely disposed surfaces 102 and 104 which
are spaced apart the same principal dimension or height as the flux
interaction surface 72. In this regard, note that the flat surface
104 is shown supported adjacent the reference plane 22 of the motor
and that the vertical principal dimensions involved are in parallel
relationship with the axis 58 of motor 60.
[0047] Located next inwardly from the induction region 100 is a
winding support region represented generally at 106. Support region
106 is seen to be formed with oppositely disposed mutually parallel
surfaces 108 and 110. Note that surface 108 is in parallel
relationship with induction region surface 100, while support
surface 110 is similarly arranged in parallel relationship with
induction region surface 104. Support surfaces 108 and 110 are
spaced apart a principal dimension taken parallel with motor axis
58 which is seen to be less than the corresponding principal
dimension spacing apart induction region surfaces 102 and 104. This
lessened dimension creates what appears as a double sided notch
structure at the winding support region 106. However, region 106
will be seen to be quite wide in consonance with the
above-discussed ratios. The planar surface 108 is established by a
ramp-shaped forward coupling transition 112 slopping downwardly and
inwardly from the edge of surface 102 to corresponding edge of
surface 108. Another ramp-shaped forward coupling transition is
shown at 114 extending inwardly and upwardly from the edge of
surface 104 to the corresponding edge of surface 110. Transitions
112 and 114 serve, inter alia, to define the level of respective
surfaces 108 and 110 and further function in the improvement of
flux transfer or coupling the applied field between the winding
components of the field winding assembly 80 and adjacent induction
region 100. Note that the amount of transition between surfaces 102
and 108 is less than that between surfaces 104 and 110. In the
embodiment shown, the level change to surface 108 is 0.25 mm, while
the level change between surfaces 104 and 110 is 0.65 mm.
[0048] The mutually parallel winding support region surfaces 108
and 110 extend inwardly to the back iron assembly 74 which, for the
present embodiment, is formed with upper and lower mutually
parallel back iron surfaces 116 and 118. A ramp-shaped rearward
coupling transition 120 extends between the winding support surface
108 and back iron surface 116. In similar fashion, a ramp-shaped
rearward coupling transition 122 extends between the winding
support surface 110 and back iron surface 118. Transitions 112,
114, 120 and 122 function to establish oppositely disposed wide
valleys for the winding support region 106 and, thus, function to
lower the overall winding height. It will be seen that the winding
support regions are expanded in the opposite or widthwise dimension
to accommodate for magnetic flux transfer without core saturation.
As in the case of transitions 112 and 114, transitions 120 and 122
also function to improve flux transfer or coupling between an
associated, i.e., supported, winding component and the processed
ferromagnetic particle core structure. Note that lower induction
surface 104 and lower back iron surface 118 are coplanar and are
supported at the reference plane of base 22. Transitions 114 and
122 are so dimensioned as to provide a surface 110 level adjustment
wherein all of the windings are retained interiorally, i.e., above
the base 22 reference surface. At the opposite surface, however,
the windings can build slightly above coplanar surfaces 102 and 116
due to the necessary clearance provided by the hub defining
structuring of rotor 62. The winding component for the instant core
component is represented in the figure schematically at 124 and for
a twelve pole embodiment, will be provided with 19 turns of 0.16 mm
wire. This embodiment gives the lowest overall height of the stator
assembly over the wire of 3.4 mm, a highly desirable feature for
this application.
[0049] Permanent magnet assembly 64 may be formed, for example, of
a neodymium magnetic material. Its size, while important to the
performance of the motor, is selected from the standpoint of a
criteria of maintenance of a compact or miniaturized shape or
envelope as well as by important considerations of cost. The
assembly 64 performs in conjunction with a back iron function
provided by the portion or region 126 of the hub or spindle
defining rotor 62. That component 62 with region 126 typically is
formed of a machined magnetically responsive stainless steel. For
all embodiments of the magnet assembly 64, an eight-pole rotor is
utilized. In this regard, each such rotor will have a sequence of
eight generally arcuate regions of predetermined and alternating
magnetization. Because of the noted cost and sizing constraints,
the selection of a magnet assembly as at 64 typically will result
in the same magnet structure and formulation, whether laminar or
processed ferromagnetic particle stator core structures are
employed. FIG. 5 reproduces the principal components of the motor
60 but with a sizing geometry and proportioning which would be
employed utilizing conventional laminar steel core material. Thus,
where the eddy current losses under high speed switching are
dismissed for purposes of comparison, the size proportioning of
components of FIG. 5 can be contrasted with the above-described
components of FIG. 4. In the former figure, where the components
generally are the same, they are identified with the same
numeration utilized in FIGS. 3 and 4 but in primed fashion. In FIG.
5, a stator core assembly is represented in general at 140.
Assembly 140 is formed with a stack 142 of laminar magnetically
responsive sheets. These sheets extend to a flux interaction
surface 144 positioned in adjacency with the confronting magnetic
surface 66' of magnet assembly 64'. Because of the more desirable
permeability characteristics of the core stack 142, its profile or
height is lessened as compared to that of assembly 70 and the
extent of field winding components required for each core component
142, as shown at 146, is slightly increased with respect to 6 pole
embodiment of the pressed powdered metal stator shown in FIG. 4.
The addition of a sixth lamination to core stack shown at 142 would
reduce the required turns 146 but the overall height of stator
assembly over the wire would probably suffer as well as creating a
cost increase and potentially adversely affecting the copper iron
ratio. For the laminated stator assembly shown in FIG. 5, the
number of turns provided is 39 with a gauge of 0.16 mm. The
resulting overall stator height is 4.1 mm. This compares to the 6
pole pressed powdered metal stator requirement of 35 turns of 0.16
mm wire and an overall stator height of 4.1 mm. The laminated
stator assembly of FIG. 5 achieves a physical winding height such
that the stack 142 can be mounted over a step 147 formed within an
inner collar 148. As in the embodiment of FIG. 4, a flux overlap
between the confronting surface 66' and the core stack 142 is
provided, as represented at dashed flux line representations 148
and 150.
[0050] A comparison of FIGS. 4 and 5 reveals that by a
configuration of the induction region 100 and its flux interaction
surface 72 with their principal dimension 92, the highly restricted
packaging envelope for the motor can be maintained along with the
necessary torque constant. Because of the realized increase in
induction coupling from the permanent magnet assembly 64 provided
by this feature, and by adherence to the noted ratio requirement,
the number of windings required, for example, at winding of
assembly 80 in the embodiment of FIG. 4, can actually be slightly
reduced when comparing 6 pole configurations. This is achieved
without a stator overall height penalty and is based upon the
disparities of permeability between the two stator core structures.
With this achievement, requisite rotational and core switching
speeds can be realized with the embodiment in FIG. 4 without an
attendant severe increase in eddy current losses and with a
reduction in the cost of the motor. As noted earlier, the 12 pole
stator configuration shown in plain view in FIG. 6, yields a
significant reduction in winding turns 80 and a significant
reduction in overall stator height from 4.1 mm to 3.4 mm.
[0051] Two implementations of the stator core assembly 70 of motor
60 are illustrated in connection with FIGS. 6 through 9. FIGS. 6
and 7 reveal a twelve stator core component or twelve pole
embodiment of the assembly 70 and a configuration wherein the
entire stator assembly is integrally formed using pressed powdered
metal technology. An important aspect of these structures including
the design of the induction region, winding support region and back
iron assemblies is a criterion that the structure presents or has a
cross sectional area attribute which is effective to convey the
path of magnetic flux confronting that cross section, understanding
that a variety of flux paths will occur. Further, the ratio of the
arcuate or circumferential length of the flux interaction surface
to the width of the winding support region should not exceed about
2.5. Maintaining this ratio yields optimum results when
implementing pressed powdered metal in electric motor applications
where performance, space and cost are at a premium. The twelve pole
implementation shown in the figure is a desirable architecture from
the standpoint of that ratio criteria. An aspect of the instant
design resides in a recognition that the flux path directions are
primarily two-dimensional in nature in that the flux paths, for
instance, remain in the plane of the paper carrying the figures at
hand. No principal flux paths deviate from that plane or aspect
other than the compression that occurs in the winding region 166.
The twelve pole implementation of the assembly 70 is shown in FIG.
6 as having twelve spaced apart core components 160a-160l, each
incorporating a respective induction region 162a-162l. These
induction regions extend to and support respective flux interaction
surfaces 164a-164l. Formed integrally with and extending inwardly
from the induction regions 162a-162l are the earlier-described
winding support regions identified respectively at 166a-166l. The
back iron region remains identified in general at 74. As noted,
each of these regions is configured such that it will exhibit the
above cross-sectional area attribute which is effective for the
non-saturation conveyance of confronting magnetic flux both from
the coil winding as well as the magnet.
[0052] Because of the earlier-described performance characteristics
of the processed ferromagnetic particle structuring, there is an
enlargement of the flux interaction surface area and the provision
of an induction region which confronts flux from the permanent
magnets, i.e. an adjustment of the induction characteristic. This
alteration is manifested by the above comparison made with
equivalent laminar or stacked cores as discussed in general in
connection with FIG. 5.
[0053] To gain some insight as to how the above confronting cross
sectional area attributes are considered, a partial schematic
representation of the permanent magnet assembly 64 and its
associated permanent magnet back iron 126 is presented in FIG. 6.
That presentation is made in conjunction with a tracing of certain
of the flux path directions which will be encountered in the
operation of motor 60. Effective presentation of this cross
sectional area attribute is one which avoids any core saturation
phenomena over the desired operating range of the motor. In the
figure, the boundary between adjacent polar designated regions of
the permanent magnet 64 are represented, for example, by the
boundary lines 170-172. Arbitrary polar designations north (N) and
south (S) are labeled within certain of these sections, as well as
at locations upon stator core assembly 70. With this representative
arrangement it may be observed that one path is represented by flux
path arrows 176 and 177 extending from a north segment of permanent
magnet 64 into the flux interaction surface 164c and induction
region 162c of a core component 160c which is excited from an
associated winding to evoke a north designated induction region.
Path arrow 177 shows the flux path being satisfied by return to the
next adjacent permanent magnet segment having a south (S) polar
designation. Another flux path is from one induction region to a
next adjacent one as represented by the flux path arrows 178 and
179 extending from core components 160c to components 160b and
160d. Field excitation of core component 160c will develop a flux
path as shown at arrow 180. Additional field winding flux passes
through magnet 64 to back iron region 126 and returns back through
the magnet to oppositely polarized stator poles. A flux path also
is represented at arrows 181 coursing about the permanent magnet
back iron 126 for purposes of magnet flux circuit satisfaction.
Where the stator core components are not excited, flux from the
rotor carried permanent magnets, may follow paths such as
represented by the flux entry arrow 182 and exit arrows 183 and
184. The cross sectional area confronting such flux paths must be
of adequate extent, i.e., representing a cross sectional attribute
which is effective to pass these flux paths without saturation. PPM
materials generally have a lower saturation level than steel
laminations, requiring commensurately larger cross sectional areas
to avoid saturation. Where a diminution in cross section is
provided as illustrated in connection with FIG. 7 at winding
support regions 166j and 166d, then the widthwise aspect of those
regions is increased well over what it would be, for example, in
conjunction with a laminar core system. This is represented, for
example, by a plane passing perpendicularly to a radius
intersecting a given core component. Such a radius is represented
in the figure at 190 and the cross sectional attribute showing such
expansion is represented at arrow pair 192. That width or widthwise
extent represented by arrow pair 192 preferably is as wide as
possible and forms the denominator of the above-noted maximum ratio
criteria. In this regard, the arcuate length or circumferential
length of the flux interaction surfaces 164 are represented by the
arc-shaped arrow 194. Recall that the ratio of that circumferential
or arc value to the widthwise extent of flux interaction region
represented at arrow pair 192 should not exceed about 2.5. It may
be further observed that the type of motors described herein
generally are referred to as "radial". In this regard, flux passage
between the permanent magnet and the flux interaction surfaces 164
is generally in the direction of a radius from the motor axis 58 as
represented at 190. For the embodiment of the FIGS. 6 and 7, the
noted ratio is about 1.6.
[0054] FIGS. 8 and 9 illustrate a six core component implementation
of stator core assembly 70. The discrete core components of this
assembly 70 shown in FIG. 8 are identified in general at 200a-200f.
Each of the latter components is formed with an induction region
shown respectively at 202a-202f which, in turn, extends and is
integrally formed with a respective winding support region
204a-204f. The latter regions, in turn, are integrally formed with
the back iron region, again identified at 74. Note that the core
components 200a-200f exhibit much wider flux interaction surfaces,
shown respectively at 206a-206f, to gain adequate induction
coupling from the permanent magnet flux and, additionally, wider
winding support regions 204a-204f to avoid core saturation, for
example, as represented by the arrow pair 208. This width may be
contrasted in a manner similar to that set forth in the discussion
concerning FIGS. 4 and 5 by indicating a corresponding width of a
higher permeability stator core stack which is represented by
spaced apart dashed lines 210. As before, a criterion for all
components including the induction regions, winding support regions
and back iron regions is that any given flux path region must have
cross-sectional attributes which are effective for conveyance of
confronting magnetic flux without saturation. That criterion is
further evidenced by the principal dimension parallel to motor axis
58 of region 74, which is commensurate with, here equal to, the
corresponding dimension of the induction regions as at 162a-162l
(FIGS. 6 and 7) and 202a-202f (FIGS. 8, 9). The width represented
by arrow pair 208 of the winding support region 204a-204f again is
selected in conjunction with the arcuate length of the flux
interaction surfaces 206a-206f to meet the maximum ratio criterion
of 2.5. That latter arcuate length is represented by the curved
arrow 212 in FIG. 8. For the six pole embodiment shown when
utilized in the motor discussed above, the ratio becomes about 1.9.
It should be noted in connection with FIGS. 6 through 9 that the
earlier-discussed forward and rearward coupling transitions as
discussed in connection with FIG. 4 are retained for the same
purposes of improving the coupling of the applied field and
confining the winding components associated with the winding
association region generally within the mandated planar top and
bottom envelope of the stator assemblies. Additionally, FIGS. 7 and
9 reveal that the same variation in winding support surface level
is achieved with these coupling transitions.
[0055] FIGS. 10 and 11 reveal an embodiment which corresponds with
that of FIGS. 8 and 9 but without the noted internal diametric
restraint. FIG. 10 shows a stator core assembly represented
generally at 220 which is somewhat similar to that described in
connection with FIGS. 8 and 9 in that it is of a six core component
architecture. In this regard, the six core components are
represented in general at 222a-222f. Each of these core components
222a-222f extends from an outwardly disposed flux interaction
surface shown respectively at 224a-224f which, in turn, are
integrally formed with and extend inwardly into respective
induction regions 226a-226f. Integrally formed with and extending
inwardly from those induction regions are respective winding
support regions 228a-228f. Formed with those winding support
regions 228a-228f is the annular shaped back iron assembly or
region represented generally at 230 and which is seen to extend to
an inwardly disposed annular boundary 231. Looking to FIG. 11, it
may be seen that induction region 226e is configured with
oppositely disposed mutually parallel induction surfaces 232e and
234e and, in similar fashion, induction region 226b is configured
with corresponding surfaces 232b and 234b. In similar fashion, the
winding support regions 228a-228f are configured with spaced apart
mutually parallel winding support surfaces otherwise generally
identified with numbers 236 and 238 as are revealed in FIG. 11 at
236e and 238e as well as at 236b and 238b. As in the earlier
embodiments, the structuring represented in the instant figures is
one meeting the noted maximum ratio criterion. That is, the arcuate
or circumferential length of the flux interaction surfaces
224a-224f when compared to the width of the winding support regions
228a-228f does not exceed a value of about 2.5.
[0056] As in the earlier embodiments, forward coupling transitions
are provided as at 240a-240f otherwise identified generally with
the number 242. These are seen in FIG. 11 at 240e and 242e as well
as at 240b and 242b. However, no rearward coupling transitions are
provided and the winding support surfaces 236a-236f otherwise
identified generally by the number 238 (see 238e and 238b in FIG.
11) simply extend rearwardly to assume the function of the back
iron assembly represented generally at 230 and extending to the
inward boundary 231. The forward coupling transitions 240 and 242
establish the same relative levels for the winding support surfaces
in the same manner described above in connection with the earlier
embodiments. Note, however, that the stator core assembly 220 may
be supported at a reference plane or base by the six induction
region lower surfaces identified generally with the number 234 and
shown at 234e and 234b in FIG. 11.
[0057] As is apparent, a design flexibility is present with respect
to the configuration of the back iron assembly. For example the
principal dimension of that assembly taken parallel with the motor
axis may be enlarged to a value greater than the corresponding
dimension of the induction region while its radial dimension is
shortened. This flexibility may aid a given packaging requirement
and takes advantage of the noted net shaping characteristic of the
pressed processed ferromagnetic particulate materials.
[0058] The design flexibility of the instant motors is demonstrated
in connection with FIGS. 12 and 13. In those figures, an embodiment
is presented wherein the functioning or working gap between the
rotor borne permanent magnet and the stator core assembly is
disposed inwardly radially from the base of that latter assembly.
While a performance penalty is paid by virtue of the lower radius
values to the working gap, the motor can be designed to meet a
compactness envelope. To illustrate the similarity of structuring,
the motor of FIGS. 12 and 13 is shown associated with a disc drive
application resembling that discussed earlier in connection with
FIG. 3. In FIG. 12 the disc drive is represented generally at 250.
As before, the drive 250 includes a non-conductive base 252 with
associated upwardly disposed reference surface from which
integrally formed side walls 254 and 256 extend upwardly for
attachment to an upperly disposed cover 258. The disc drive 250
functions to rotate and access a sequence of memory discs
represented generally at 260 which are mounted upon a hub or
spindle represented generally at 262. Four discs, of the sequence
260, identified at 264-267 are mounted for rotation on the hub 262
in conjunction with three ring-shaped spacers and the sequence 260
is retained in position by a clamp including externally threaded
collar 268 performing in conjunction with a spring retainer 270.
The hub 262 and disc sequence 260 rotate about a stationary axle
272 and are supported therefrom by an air bearing or similar low
friction rotational mount as represented in general at 274. Hub or
spindle 262 functions as a PM rotor, providing back iron for and
supporting a ring shaped permanent magnet assembly 276 which is
formed having a sequence of generally arcuate regions of
predetermined and alternating magnetization. Each of those regions
presents a confronting magnetic surface 278 of arcuate shape at a
radius spaced from a centrally disposed motor axis 280, an air gap
radius. Magnet 276 extends slightly below the reference surface of
base 252 and to accommodate for this slight extension, an annular
groove 282 is formed within that base.
[0059] The hub defining rotor 262 is surmounted by a stator core
assembly represented generally at 284 which is configured having
spaced core components formed of pressure shaped processed
ferromagnetic particles which are generally mutually insulatively
associated. Looking additionally to FIG. 13, this assembly 284 is
revealed having a six core component configuration, those
components being represented generally at 286a-286f. Each core
component 286a-286f presents a flux interaction surfaces shown
respectively at 288a-288f toward the motor axis 280 to define the
noted functional gap of the motor with the permanent magnet
confronting magnetic surface 278. As before, these flux interaction
surfaces have a surface area including a principal dimension in
parallel relationship with the motor axis 280 to provide a magnetic
field coupling induction with the selected permanent magnet which
acts in conjunction with the energized field generated by the
appropriate field winding turns to provide the predetermined torque
constant. That vertical dimension and area requirement is repeated
in conjunction with the immediately adjacent induction regions
shown respectively at 290a-290f.
[0060] As in the earlier embodiment, the induction regions
290a-290f are formed with parallel flat upper and lower surfaces
with a principal dimension parallel to the motor axis 280. The
functioning air gap established by them with the permanent magnet
is created such that the permanent magnet slightly overlaps these
two parallel surfaces. Next radially outwardly in the core
component structure are winding support regions shown respectively
at 292a-292f each being formed having upper and lower support
surfaces which, as in the earlier embodiments described in
connection with FIGS. 4, 7 and 9, are configured with forward
coupling and rearward coupling transitions to provide upper surface
and lower surface defined notch-like configurations functioning to
control total field winding height, as well as to enhance magnetic
coupling between the field winding component and the core
component. As described in FIG. 8, the "circumferential" width or
width taken normally to the centrally disposed radius extending
from motor axis 280 is enhanced within the winding support region
to exhibit cross-sectional area attributes which when confronting
flux path activity, will avoid core saturation. The enhanced
widthwise dimensioning, however, permits a control over the
vertical dimension or profile of the stator assembly. As in the
early embodiments the width dimension at the winding support
regions 292a-292f when compared with the arcuate or circumferential
length of the flux interaction surfaces 288a-288f continues to meet
the noted ratio criterion. In this regard, the latter arcuate
length divided by the width of the winding support region should
not exceed a value of about 2.5.
[0061] Integrally formed with the winding support regions 292a-292f
is the annular-shaped back iron assembly represented generally at
294. FIG. 12 reveals that this assembly 294 is configured with a
height or principal dimension commensurate with or equal to the
height of the induction regions 290a-290f. This is to provide
improved coupling from the winding and a cross-sectional area
attribute effective for magnetic flux conveyance without
encountering saturation.
[0062] While the winding excitation approaches for operating
brushless motors such as those described herein vary somewhat, the
windings typically are interconnected in either a "Y" or a "Delta"
configuration for three phase operation Description of such
excitation circuits is provided in the above-referenced United
States patents including, for example, U.S. Pat. No. 5,874,796
incorporated herein by reference.
[0063] Current analysis of the processed ferromagnetic particles
which are used in providing the stator core assemblies of the
motors of the invention from a microscopic standpoint, looks at
them as the surface of each particle providing a path for eddy
current flow which is relatively insulated from adjacent particles.
Such a flow aspect can be contrasted with the eddy current activity
in a laminar core structure. In such laminar core structures, the
eddy currents, being surface phenomena, reside at the surfaces of
each of the laminar sheets of the core. In another approach to
considering the processed ferromagnetic particle stator core
structures, they are considered from a macroscopic standpoint
wherein the entire structure is treated somewhat as an insulator.
These aspects of this material lead to a desirable constructional
feature of the stator core assemblies employed with the motors of
the invention. In this regard, the back iron assemblies can be
fabricated as a compilation of discrete components which are
abuttably joined together. Such juncture-based formation is done
with compression, inasmuch as it is the property of the materials
at hand they are structurally sound under compression but
structurally weaker in tension. In general, such multi-component
back iron structuring for stator core assembly is not available
with conventional laminar structures due to the disposition of flux
coupling between adjacent structures and eddy currents within them.
However, with the instant motors, a substantial manufacturing
advantage accrues. In this regard, the winding support regions can
retain field winding components which have been wound about
insulated bobbins. Those bobbins then can be inserted into position
from the back iron region onto the winding support region prior to
its interlocking assembly with the core component portions.
[0064] Referring to FIG. 14, a stator assembly and rotor
combination incorporating one version of this interlocking back
iron assembly feature is represented generally at 300. Assembly 300
emulates the six core component structure of FIGS. 10 and 11
wherein the back iron assembly exhibits a principal dimension
parallel with the motor axis which corresponds with the principal
dimension of the winding support region. The rotor component of
assembly 300 is represented generally at 302 and includes the PM
magnet back iron component schematically represented as an annulus
304 which supports or carries a PM magnet 306 formed as a sequence
of generally arcuate regions of alternating predetermined
magnetization. The inwardly disposed face exposing these magnetic
regions provides an arcuate confronting magnetic surface 308
serving as one side of a functioning or working air gap.
[0065] A stator core assembly is represented in general at 310 and
is seen to comprise six spaced core components represented
generally at 312a-312f. As in the embodiment of FIGS. 10 and 11,
core components 312a-312f are formed with respective flux
interaction surfaces 314a-314f representing the forward face of
corresponding respective induction regions 316a-316f. As in the
earlier embodiments, the principal dimension of the flux
interaction surfaces taken parallel to the motor axis 318, as well
as the corresponding principal dimension of induction regions
316a-316f provides a flux interaction surface located in spaced
adjacency with the rotor confronting magnetic surface 308 to define
a functioning air gap 320. However, as part of that air gap 320
there is provided a tensioning assembly 322, here implemented as a
tension ring formed of non-magnetically responsive material such as
a polymeric material or aluminum.
[0066] Returning to the core components 312a-312f, formed
integrally with the induction regions 316a-316f are respective
winding support regions 324a-324f, support region 324e being
referred to in general fashion. Configured in consonance with the
cross section illustrated in FIG. 11, the winding support regions
324a-324f are formed having parallel, oppositely disposed surfaces
spaced apart and a principal dimension parallel with the motor axis
318 which is less than the corresponding principal dimension of the
induction region associated therewith and described at 316a-316f.
The upper and forward coupling transition for core components
312a-312f are shown in FIG. 14 respectively at 326a-326f. With this
arrangement, the parallel, spaced apart upper and lower surfaces of
both the winding support region and the associated back iron
assemblies have a coplanar relationship particularly suited for
inserting an insulated bobbin pre-wound with a field winding
component over the field winding support region by placement from
the back iron assembly region. Such a bobbin and winding assembly
is shown positioned over winding support region 324e at 328. As is
apparent, each of the winding support regions 324a-324f, depending
upon the design involved, will receive one such winding component
and bobbin assembly.
[0067] To provide for this winding component insertion or mounting
arrangement, a back iron extension region as represented at
330a-330f is formed integrally with each respective winding support
region 324a-324f. Each back iron extension region 330a-330f is
configured with two, spaced apart back iron abutting surfaces 332a,
333a-332f, 333f. Note that with this geometrical structuring the
back iron abutting surfaces 332a, 333a-332f, 333f provide a
keystone form of structural configuration. This permits an
inter-keyed abutting relationship with six discrete back iron
linking members 336a-336f. Each of those back iron linking members
336a-336f is formed having two, spaced apart back iron abutting
surfaces which are co-identified with the back iron abutting
surfaces of the back iron extension regions 330a-330f at 332a,
333a-332f,333f. Due to the compressive structural action asserted
from the tensioning assembly 322, a close and intimate abutment
providing the noted inter-keyed abutting relationship is achieved
at each of these abutting unions identified at 332a, 333a-332f,
333f. Because of the above-noted nature of the processed
ferromagnetic particle configuration, electromagnetically generated
and permanent magnet generated flux readily is transferable along
the back iron assembly and the advantage of an enhanced assembly
procedure for providing winding components is made available.
[0068] Another advantage realized in connection with the assembly
of the discrete core components with correspondingly discrete back
iron linking members stems from a determination that these
components can be adhesively connected together while retaining
requisite flux transfer characteristics. Preferably, this
adhesive-implemented assembly is combined with the noted tensioning
assembly to provide a compressive-adhesive combination. A suitable
adhesive has been found to be, for example, #4210, marketed by
Loctite of Newington, Conn.
[0069] In addition to the keystone structuring shown in the instant
figure, interlocking geometrys at the back iron abutting surfaces
can be employed. One such arrangement is presented in connection
with the assembly 340 shown in FIG. 15. Assembly 340 emulates the
structure discussed above in connection with FIGS. 12 and 13 in
that the flux interaction surfaces of the core components of the
stator core assembly face inwardly toward the motor axis shown at
342. The rotor of assembly 340 is represented generally at 344 and
is seen to include a PM back iron component schematically
represented as an annulus at 346. Component 346 supports an annular
magnet material 348 which is provided with a sequence of generally
arcuate regions of predetermined magnetization alternating between
north and south polarities and which presents a confronting
magnetic surface 350 of principal dimension in parallel with the
motor axis 342. Extending around this confronting magnetic surface
350 is a stator core assembly represented generally at 352.
Assembly 352 is configured with six spaced apart core components
formed as the noted pressure shaped processed ferromagnetic
particles and represented generally at 354a-354f. Similar to stator
assembly 284, the stator assembly 352 of the core components
354a-354f each are configured with a flux interaction surface shown
respectively at 356a-356f. Surfaces 356a-356f combine with the
confronting magnetic surface 350 to define a functioning or working
air gap 358. As before, the functioning air gap radius extends from
the motor axis 342 to the surface 350. Extending radially outwardly
from the flux interaction surfaces 356a-356f are respective
induction regions 360a-360f. As before the flux interaction
surfaces 356a-356f, as well as the associated induction regions
360a-360f, will exhibit a principal dimension parallel with motor
axis 342 and a corresponding surface area selected to provide the
magnetic field coupling induction with the selected permanent
magnet which acts in conjunction with the energized field generated
by the appropriate field winding turns to provide the predetermined
torque constant.
[0070] Formed integrally with the induction regions 360a-360f are
respective winding support regions 362a-362f. Support regions
362a-362f are configured in the manner described in connection with
FIGS. 12 and 13, having mutually parallel upper and lower winding
support surfaces, the levels of which are defined by forward and
rearward coupling transitions to evolve the radial cross section
shown in FIG. 12. As before, the diminished principal dimension in
parallel with the motor axis 342 of the winding support regions
362a-362f is accommodated for in terms of the cross-sectional area
confronting magnetic flux paths by expanding the widthwise
dimension of this region, i.e., the width extending perpendicularly
to a radius through the center of the core component. The rearward
coupling transitions then also provide for re-establishing a larger
principal dimension parallel to the motor axis 342 at the
integrally formed back iron extension regions shown respectively at
364a-364f. These regions 364a-364f exhibit a principal dimension in
parallel with motor axis 342 which corresponds with the principal
dimension of the flux interaction surfaces 356a-356f such that the
overall diameter of the assembly 340 may be controlled by the
designer. Note at this juncture, that each of the core components
354a-354f may be treated as a discrete member for purposes of
providing winding components about their winding support regions
362a-362f. This flexibility in assembly, permitting a much more
facile winding procedure is beneficial.
[0071] Each of the back iron extension regions 364a-364f is seen to
extend to a curved outer periphery engaged by the inwardly disposed
surface of a tensioning assembly 366 which here is implemented as a
tension ring which may be formed of a magnetic or non-magnetic
material. Note additionally, that each back iron extension region
is formed with back iron abutting surfaces which are formed with a
notched shape of obtuse angular profile. For the instant
embodiment, this profile is concave with respect to a radius
extending from motor axis 342 through the center of a given core
component. The back iron abutting surfaces with respect to each
core component 354a-354f are shown positioned at opposite sides of
a respective back iron extension region 364a-364f at 368a,
369a-368f,369f. A generally angularly shaped back iron assembly
represented generally at 370 is completed with the addition of six
discrete back iron linking members 372a-372f. Each of those linking
members extends between two spaced apart back iron abutting
surfaces which are formed with an obtuse angular profile of a
convex nature configured to compliment the corresponding abutting
surfaces of the back iron extension regions 364a-364f. These
profiles are illustrated at 368a, 369a-368f, 369f. With the back
iron assembly 370 thus constructed with its discrete components and
extension regions, the assembly can be retained in place
compressibly by the tension assembly 366. However, as discussed in
connection with FIG. 14, the components forming the back iron
assembly 370 may be adhesively connected in mutual abutment, but
preferably in connection with the tensioning assembly 366
subsequent to the provision of winding components to each of the
winding support regions 362a-362f. One such winding component is
shown in connection with winding support region 362e at 374, only a
sectional portion of these windings being represented in the
interest of clarity.
[0072] Since certain changes may be made in the above apparatus and
method without departing from the scope of the invention herein
involved, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
* * * * *