Title: Method of making a composite electric machine component of a desired magnetic pattern
Abstract: A method of making composite electric machine components. Magnetic segments and non-magnetic segments are separately formed to green strength, and then arranged adjacent to each other in a desired magnetic pattern. A small amount of powder material is added in-between the segments, and the whole assembly is then sintered to form a sinterbonded composite component of high structural integrity.
Patent Number: 6,889,419 Issued on 05/10/2005 to Reiter, Jr., et al.
| Inventors:
|
Reiter, Jr.; Frederick B. (Cicero, IN);
Stuart; Tom L. (Pendleton, IN)
|
| Assignee:
|
Delphi Technologies, Inc. (Troy, MI)
|
| Appl. No.:
|
123804 |
| Filed:
|
April 16, 2002 |
| Current U.S. Class: |
29/596; 29/597; 29/598; 29/605; 29/606; 29/607; 29/608; 29/609; 29/732; 75/246; 310/156.38; 310/156.43; 310/254; 419/6 |
| Intern'l Class: |
H02K 015/00; H02K015/14; H02K015/16 |
| Field of Search: |
29/596-598,605-609,732
419/6
310/156.38,156.43,254
75/246
|
References Cited [Referenced By]
U.S. Patent Documents
| 2913819 | Nov., 1959 | Andreotti et al.
| |
| 3909647 | Sep., 1975 | Peterson.
| |
| 4255494 | Mar., 1981 | Reen et al.
| |
| 4818305 | Apr., 1989 | Steingroever.
| |
| 5554900 | Sep., 1996 | Pop, Sr.
| |
| 5870818 | Feb., 1999 | Bisaga.
| |
| 5982073 | Nov., 1999 | Lashmore et al.
| |
| 6117205 | Sep., 2000 | Krause et al.
| |
| 6437477 | Aug., 2002 | Krefta et al.
| |
| 6455978 | Sep., 2002 | Krefta et al.
| |
| 6538358 | Mar., 2003 | Krefta et al.
| |
| Foreign Patent Documents |
| 19912470 | Oct., 2000 | DE.
| |
| 09117084 | Feb., 1997 | JP.
| |
| WO 9847215 | Oct., 1998 | WO.
| |
Primary Examiner: Arbes; Carl J.
Assistant Examiner: Phan; Tim
Attorney, Agent or Firm: Funke; Jimmy L.
Claims
1. A method of making a composite electric machine component of a desired magnetic
pattern, the method comprising:
placing at least one green-strength magnetically conducting segment and at least
one green-strength magnetically non-conducting segment adjacent in the desired
magnetic pattern;
adding powder metal between the segments; and
sintering the segments and added powder metal whereby the segments are bonded
together by the added powder metal to form the composite electric machine component.
2. The method of claim 1 further comprising forming the at least one green-strength
magnetically conducting segment by pressing a soft ferromagnetic powder metal in
a die and forming the at least one green-strength magnetically non-conducting segment
by pressing a non-ferromagnetic powder metal in a die.
3. The method of claim 2 wherein the added powder metal is the soft ferromagnetic
powder metal.
4. The method of claim 2 wherein the added powder metal is the non-ferromagnetic
powder metal.
5. The method of claim 2 wherein the soft ferromagnetic powder metal is Ni, Fe,
Co or an alloy thereof.
6. The method of claim 2 wherein the soft ferromagnetic powder metal is a high
purity iron powder with a minor addition of phosphorus.
7. The method of claim 2 wherein the non-ferromagnetic powder metal is an austenitic
stainless steel.
8. The method of claim 2 wherein the non-ferromagnetic powder metal is an AISI
8000 series steel.
9. The method of claim 2 wherein pressing comprises uniaxially pressing the powder
in the die.
10. The method of claim 9 wherein pressing comprises pre-heating the powder and
pre-heating the die.
11. The method of claim 1 wherein the added powder metal comprises a magnetically
conducting material.
12. The method of claim 1 wherein the added powder metal comprises a magnetically
non-conducting material.
13. The method of claim 1 wherein sintering includes delubricating the segments
by heating to a first temperature, followed by fully sintering the segments by
heating to a second temperature greater than the first temperature.
14. The method of claim 1 further comprising forming at least one green-strength
permanent magnet segment by pressing a hard ferromagnetic powder metal in a die,
placing the green-strength permanent magnet segments adjacent the magnetically
conducting segments and magnetically non-conducting segments in the desired magnetic
pattern, and after sintering, magnetizing the permanent magnet segments to form
a permanent magnet electric machine component.
15. The method of claim 1 further comprising, after sintering, adding a plurality
of alternating polarity permanent magnets to the composite electric machine component
to form a permanent magnet electric machine component.
Description
FIELD OF THE INVENTION
This invention relates generally to composite electric machine rotor components
and rotor sense parts, and more particularly, to the manufacture of rotor components
and rotor sense parts by sinterbonding.
BACKGROUND OF THE INVENTION
It is to be understood that the present invention is equally applicable in the
context of generators as well as motors. However, to simplify the description that
follows, reference to a motor should also be understood to include generators.
In the field of electric machine rotor cores, stator cores and generators, the
machine cores are typically constructed using laminations stamped from electrical
steel. The laminations are stacked and pressed onto a shaft. Then, in most electric
machines, windings or permanent magnets are added. These laminations are configured
to provide a machine having magnetic, non-magnetic, plastic and/or permanent magnet
regions to provide the flux paths and magnetic barriers necessary for operation
of the machines. When the shape of the laminations and/or the additional winding/permanent
magnet components are compromised, reduced operating speed and flux leakage may
occur, thus limiting performance of the electric machine. By way of example, synchronous
reluctance rotors formed from stacked axial laminations are structurally weak due
to problems associated both with the fastening together of the laminations and
with shifting of the laminations during operation of their many circumferentially
discontinuous components. This results in a drastically lower top speed. Similarly,
stamped radial laminations for synchronous reluctance rotors require structural
support material at the ends and in the middle of the magnetic insulation slots.
This results in both structural weakness due to the small slot supports and reduced
output power due to magnetic flux leakage through the slot supports. There are
various types of machines utilizing rotors that require non-magnetic structural
support, including synchronous reluctance machines, switched reluctance machines,
induction machines, surface-type permanent magnet machines, circumferential-type
interior permanent magnet machines, and spoke-type interior permanent magnet machines.
Each of these machines utilize rotor components or rotor sense rings of composite
magnetic, non-magnetic, plastic, electric and/or permanent magnet materials that
suffer from the aforementioned problems.
Despite the aforementioned problems, and the general acceptance of conventional
lamination practices as being cost effective and adequate in performance, new powder
metal manufacturing technologies can significantly improve the performance of electric
machines by bonding magnetic (permeable) and non-magnetic (non-permeable) materials
together. Doing so permits the use of completely non-magnetic structural supports
that not only provide the additional strength to allow the rotors to spin faster,
for example up to 80% faster, but also virtually eliminate the flux leakage paths
that the traditionally manufactured electric machines must include to ensure rotor
integrity, but which lead to reduced power output and lower efficiency.
Powder metal manufacturing technologies that allow two or more powder metals
to be bonded together to form a rotor core have been recently disclosed by the
present inventors. Specifically, the following co-pending patent applications are
directed to composite powder metal electric machine rotor cores fabricated by a
compaction-sinter process: U.S. patent application Ser. No. 09/970,230 filed on
Oct. 3, 2001 and entitled "Manufacturing Method and Composite Powder Metal Rotor
Assembly for Synchronous Reluctance Machine"; U.S. patent application Ser. No.
09/970,197 filed on Oct. 3, 2001 and entitled "Manufacturing Method And Composite
Powder Metal Rotor Assembly For Induction Machine"; U.S. patent application Ser.
No. 09/970,223 filed on Oct. 3, 2001 and entitled "Manufacturing Method And Composite
Powder Metal Rotor Assembly For Surface Type Permanent Magnet Machine"; U.S. patent
application Ser. No. 09/970,105 filed on Oct. 3, 2001 and entitled "Manufacturing
Method And Composite Powder Metal Rotor Assembly For Circumferential Type Interior
Permanent Magnet Machine"; and U.S. patent application Ser. No. 09/970,106 filed
on Oct. 3, 2001 and entitled "Manufacturing Method And Composite Powder Metal Rotor
Assembly For Spoke Type Interior Permanent Magnet Machine," each of which is incorporated
by reference herein in its entirety. Additionally, the following co-pending application
is directed to composite powder metal electric machine rotor cores fabricated by
metal injection molding: U.S. patent application Ser. No. 09/970,226 filed on Oct.
3, 2001 and entitled "Metal Injection Molding Multiple Dissimilar Materials To
Form Composite Electric Machine Rotor And Rotor Sense Parts," incorporated by reference
herein in its entirety. Both the compaction-sinter process and the metal injecting
molding process (as disclosed in the above-referenced patent applications) lead
to the advantages described above, such as strong structural support and virtually
non-existent permeable flux leakage paths, and do provide an opportunity to manufacture
an electric machine that costs less, spins faster, provides more output power,
and is more efficient.
In the compaction-sinter process described in the above-identified co-pending
applications, the magnetic and non-magnetic metal powders are poured into respective
sections of a disk-shaped die insert. Upon removal of the die insert, the powders,
after some settling and mixing along their boundaries, are compressed to a "green"
strength, which is usually on the order of 2-6 ksi (13.8-41.4 MPa). The green part
is then sintered, such as at about 2050° F. (1121° C.), for about one
hour to obtain full strength, typically on the order of 30-50 ksi (207-345 MPa).
One disadvantage of this compaction process is that the mixing that occurs after
the die insert is removed can lead to blurred boundaries between permeable and
non-permeable materials thereby reducing performance. Further, the blurring of
boundaries is often particularly pronounced near the top and bottom of the pressed
disks such that these sections of the machine do not adequately perform their intended
function. To overcome this disadvantage, approximately one-third to two-thirds
of the disk's thickness is ground away to leave a middle section having minimal
blurring of boundaries that can be effectively utilized as an electric machine component.
The composite metal injection molding process described in the above-identified
co-pending application does not exhibit the problem of boundary blurring like the
composite compaction-sintering manufacturing process because the magnetic and non-magnetic
materials are injection-molded separately into molds that provide definitive edges.
However, the injection molding process can be expensive because liquifying the
metals generally requires the use of powders that are more expensive and of finer
grain size than the powders that can be used in the compaction process. Thus, composite
metal injection molding may not be cost effective for a broad range of electric
machine applications.
There is thus a need to provide a powder metallurgy manufacturing process that
is cost effective and provides definitive boundaries between magnetic (permeable)
and non-magnetic (non-permeable) portions of the electric machine components.
SUMMARY OF THE INVENTION
The present invention provides a method of making composite electric machine
components using powder metal for magnetic and non-magnetic portions of the component.
To this end, and in accordance with the present invention, one or more magnetically
conducting segments are formed to a green strength by pressing soft ferromagnetic
powder metal in a die of desired shape. Similarly, one or more magnetically non-conducting
segments are formed to a green strength by pressing non-ferromagnetic powder metal
in a die of desired shape. The green strength segments are positioned adjacent
each other in a desired magnetic pattern, and powder metal is added between adjacent
segments. The assembly is then sintered, advantageously to full strength, whereby
a bond is formed between segments by the added powder metal.
In an exemplary embodiment for forming a rotor assembly, the segments are positioned
to form a disk having the desired magnetic pattern, and a plurality of sinterbonded
disks are stacked on a shaft with their magnetic patterns aligned. In an embodiment
of the present invention, permanent magnets may be affixed to the composite component
to form a permanent magnet electric machine component. Alternatively, permanent
magnet segments may be formed to a green strength by pressing hard ferromagnetic
powder metal in a die of desired shape, and then placing the permanent magnet segments
in the desired magnetic pattern followed by sintering and magnetizing to form a
permanent magnet electric machine component. By the method of the present invention,
there is provided a structurally robust electric machine component having definite
boundaries between magnetic regions that costs less, spins faster, provides more
output power, and is more efficient.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of
this specification, illustrate embodiments of the invention and, together with
a general description of the invention given above, and the detailed description
given below, serve to explain the invention.
FIG. 1 is a perspective view of a sinterbonded powder metal surface type permanent
magnet rotor assembly of the present invention having a rotor positioned on a shaft,
the rotor comprising a plurality of sinterbonded disks;
FIG. 2 is a partially exploded plan view of a partially assembled disk for the
rotor assembly of FIG. 1 prior to sinterbonding;
FIG. 2A is an enlarged view of encircled area 2A of FIG. 2;
FIG. 3A is a partially exploded plan view of a partially assembled disk for
a sinterbonded powder metal switched reluctance rotor assembly prior to sinterbonding;
FIG. 3B is a perspective view of the assembled and sinterbonded disk of FIG. 3A;
FIG. 4A is an exploded plan view of a disassembled disk for a sinterbonded powder
metal synchronous reluctance rotor assembly prior to sinterbonding;
FIG. 4B is a plan view of the assembled and sinterbonded disk of FIG. 4B;
FIG. 5A is an exploded perspective view of a disassembled disk for a sinterbonded
powder metal induction rotor assembly prior to sinterbonding and prior to adding
the rotor conductors;
FIG. 5B is a plan view of the assembled disk of FIG. 5A after sinterbonding;
FIG. 5C is a plan view of a rotor assembly including the disk of FIG. 5B after
adding the rotor conductors;
FIG. 6A is a partially exploded plan view of a partially assembled disk for
a sinterbonded powder metal spoke type interior permanent magnet rotor assembly
prior to sinterbonding;
FIG. 6B is a plan view of the assembled and sinterbonded disk of FIG. 6A;
FIG. 7A is an exploded plan view of a disassembled disk for a sinterbonded powder
metal circumferential type interior permanent magnet rotor assembly prior to sinterbonding; and
FIG. 7B is a plan view of the assembled and sinterbonded disk of FIG. 7A.
DETAILED DESCRIPTION
The present invention is directed to sinterbonding electric machine components
by pressing magnetically conducting and magnetically non-conducting rotor or stator
segments separately to a green state, arranging the green-strength segments adjacent
to each other with a small amount of powder material in between green-strength
segments, and then sintering the whole assembly. The small amount of powder material,
such as high purity iron powder, facilitates bond formation between the separate
green-strength segments during sintering. By way of example and not limitation,
the sinterbonding process of the present invention may be used on induction, permanent
magnet, switched reluctance and synchronous reluctance rotors, as well as permanent
magnet and reluctant sensor wheels. Sinterbonding combines the cost advantage of
composite powder metal compaction manufacturing processing with the performance
advantage of metal injection molding processing by allowing the magnetically conducting
and magnetically non-conducting electric machine segments to be pressed separately
and then bonded together during the sintering process. The sinterbonded product
yields bond strengths equal to either of the prior powder metal processes, while
at the same time reducing tooling costs because the tooling only has to be large
enough to accommodate the individual segments and not the whole rotor or stator
component. For example, on a ring machine used for an integral-starter generator
application, the tooling for compaction or molding processes must be large enough
to construct a 360 mm outer diameter core, whereas with the sinterbonding of the
present invention, the largest tooling required would be for a 50 mm wide by 20
mm thick part.
An additional advantage of sinterbonding in accordance with the present invention
is that less post-machining is required than with composite powder metal compaction-sinter
processes. During material fill for the compaction-sinter process, the permeable
and non-permeable materials may detrimentally mix along their boundaries prior
to compaction, particularly near the top and bottom of the rotor disks. After the
disks are sintered, the tops and bottoms often must be ground to leave only permeable
and non-permeable materials that are clearly bonded together but distinct from
each other. With sinterbonding, the materials are always distinct from each other
because they are pressed separately, then sintered together. Thus, the sinterbonding
process of the present invention eliminates the need for extensive bottom and top
grinding of the disks that comprise the rotor or stator assembly. In addition,
sinterbonding is less expensive than metal injection molding because it does not
require the finer and more expensive powders generally required to liquify for
the injection molding process.
Composite powder metal parts, whether they are compacted or injection-molded
as described in the co-pending applications referred to above or whether they are
sinterbonded in accordance with the present invention, have a cost, strength and
performance advantage over traditional stamped electric machine cores. Composite
powder metal components are less expensive because they can be formed in greater
piece thicknesses and can be formed into near-net shape parts with little or no
scrap material. Composite powder metal cores are stronger than traditional stamped
electric machine cores because most electric machine components must minimize the
use of non-permeable materials used as structural elements to avoid flux leakage
and lower machine performance, whereas composite powder metal components may utilize
relatively large amounts of non-permeable material, for example stainless steel,
for the structural elements while minimizing or eliminating the magnetic flux leakage
pathways. With less or no flux leakage, they also perform better in terms of output
power, power factor and efficiency. By way of example, a four-inch diameter induction
rotor comprising stamped laminations and aluminum bars and end rings, when subjected
to spin testing, fails at about 28,000 rpm, whereas a four-inch diameter synchronous
reluctance rotor of the present invention does not fail until about 44,600 rpm.
Thus, the sinterbonding process of the present invention reduces tooling costs
and produces electric machine components that are less expensive, stronger, faster
and more efficient than those produced by prior techniques.
In general, a rotor assembly comprises an annular core having at least one magnetically
conducting segment and at least one magnetically non-conducting segment. The magnetically
conducting segments comprise soft ferromagnetic materials, also referred to as
permeable or magnetic materials. The magnetically non-conducting segments comprise
non-ferromagnetic material, also referred to as non-permeable or non-magnetic materials.
In the present invention, the magnetically conducting segments and magnetically
non-conducting segments are fabricated from pressed and sintered soft ferromagnetic
and non-ferromagnetic powder metals. In permanent magnet rotor assemblies, the
assembly further comprises permanent magnets, which are formed from hard ferromagnetic
materials. In the present invention, the permanent magnets may be formed from pressed
and sintered hard ferromagnetic powder metal, or may be prefabricated magnets that
are affixed to the sinterbonded component. In induction rotor assemblies, the assembly
further comprises conductors that are generally made of aluminum or copper. For
example, aluminum conductors may be cast into slots in the sinterbonded rotor assembly,
or prefabricated copper bars may be inserted into the slots and affixed to axial
end rings.
The electric machine components may be fabricated by sinterbonding magnetically
conducting and magnetically non-conducting segments to form a plurality of composite
disks of a desired magnetic pattern, and stacking the disks axially along a shaft
and affixing the disks to the shaft to form the rotor assembly. The shaft is typically
equipped with a key and the individual disks have a keyway on an interior surface
to mount the disks to the shaft upon pressing the part to the shaft. The magnetic
patterns of the individual disks are aligned with respect to each other along the
shaft such that the magnetic flux paths are aligned along the shaft. In the present
invention, there is no limit to the thickness of each composite powder metal disk
or the number of disks that may be utilized to construct a rotor assembly.
In an embodiment of the present invention, the soft ferromagnetic powder metal
used to form magnetically conducting segments is nickel, iron, cobalt or an alloy
thereof. In another embodiment of the present invention, this soft ferromagnetic
metal is a low carbon steel or a high purity iron powder with a minor addition
of phosphorus, such as covered by MPIF (Metal Powder Industry Federation) Standard
35 F-0000, which contains approximately 0.27% phosphorus. In general, AISI 400
series stainless steels are magnetically conducting, and may be used in the present invention.
In an embodiment of the present invention, the non-ferromagnetic powder metal
used to form magnetically non-conducting segments is austenitic stainless steel,
such as SS316. In general, the AISI 300 series stainless steels are non-magnetic
and may be used in the present invention. Also, the AISI 8000 series steels are
non-magnetic and may be used.
In an embodiment of the present invention, the soft ferromagnetic metal and the
non-ferromagnetic metal are chosen so as to have similar densities and sintering
temperatures, and are approximately of the same strength, such that upon compaction
and sinterbonding, the materials behave in a similar fashion. In an embodiment
of the present invention, the soft ferromagnetic powder metal is Fe-0.27% P and
the non-ferromagnetic powder metal is SS316.
In an embodiment of the present invention, the small amount of powder metal added
between the green-strength segments is a soft ferromagnetic material, such as described
above. For example, the small amount of added powder metal may be high purity iron
powder, such as covered by MPIF Standard 35 F-0000. In another embodiment of the
present invention, the small amount of added powder metal is the same powder metal
as used to form the magnetically conducting segments of the rotor or stator components.
Alternatively, the small amount of added powder metal may be a non-ferromagnetic
material, such as described above. For example, the small amount of added powder
metal may be an austenitic stainless steel, such as SS316. In yet another embodiment
of the present invention, the small amount of added powder metal is the same powder
metal as used to form the magnetically non-conducting segments of the rotor or
stator components.
In an embodiment of the present invention relating to permanent magnet machines,
the hard ferromagnetic powder metal used to form permanent magnet segments is ferrite
or rare earth metals. Alternatively, the permanent magnets may be prefabricated
magnets that are affixed to adjacent segments in the rotor component after sinterbonding.
In accordance with the present invention, the ferromagnetic and non-ferromagnetic
powder metals are pressed separately in individual dies to form the compacted powder
metal segments, or green-strength segments. The compacted powder metal segments
are then positioned adjacent to each other in the desired magnetic pattern. A small
amount of powder metal is then provided between the green-strength segments, and
the arrangement is then sintered to form a sinterbonded powder metal component
or lamination having at least one region of magnetically non-conducting material
and at least one region of magnetically conducting material, the component exhibiting
high structural stability and definitive boundaries between regions. The component
may be an annular disk-shaped component for affixing to a shaft to form a rotor
assembly. The amount of powder metal provided between green-strength segments may
be any amount deemed necessary or adequate for a bond to form between the segments.
The pressing or compaction of the filled powder metal to form the green-strength
segments may be accomplished by uniaxially pressing the powder in a die, for example
at a pressure of about 45-50 tsi (620-689 MPa). The die is shaped to correspond
to the particular segment being fabricated. It should be understood that the pressure
needed is dependent upon the particular powder metal materials that are chosen.
In a further embodiment of the present invention, the pressing of the powder metal
involves heating the die to a temperature in the range of about 275° F. (135°
C.) to about 290° F. (143° C.), and heating the powder within the die
to a temperature in the range of about 175° F. (79° C.) to about 225°
F. (107° C.).
In an embodiment of the present invention, the sintering together of the green-strength
segments with added powder therebetween comprises heating the green-strength segments
and added powder metal to a first temperature of about 1400° F. (760°
C.) and holding at that temperature for about one hour. Generally, the powder metals
used to fabricate the segments include a lubricating material, such as a plastic,
on the particles to increase the strength of the material during compaction. The
internal lubricant reduces particle-to-particle friction, thus allowing the compacted
powder to achieve a higher strength after sintering. The lubricant is then burned
out of the composite during this initial sintering operation, also known as a delubrication
or delubing step. A delubing for one hour is a general standard practice in the
industry and it should be appreciated that times above or below one hour are sufficient
for the purposes of the present invention if delubrication is achieved thereby.
Likewise, the temperature may be varied from the general industry standard if the
ultimate delubing function is performed thereby.
After delubing, the sintering temperature is raised to a full sintering temperature,
which is generally in the industry about 2050° F. (1121° C.). During
this full sintering, the compacted powder shrinks, and particle-to-particle bonds
are formed, generally between iron particles. For the particles that comprise the
small amount of powder metal added between green-strength segments, the particles
bond to each other and to particles that comprise the magnetically conducting and
non-conducting segments to thereby bond the segments to each other. Standard industry
practice involves full sintering for a period of one hour, but it should be understood
that the sintering time and temperature may be adjusted as necessary. The sintering
operation may be performed in a vacuum furnace, and the furnace may be filled with
a controlled atmosphere, such as argon, nitrogen, hydrogen or combinations thereof.
Alternatively, the sintering process may be performed in a continuous belt furnace,
which is also generally provided with a controlled atmosphere, for example a hydrogen/nitrogen
atmosphere such as 75% H
2/25% N
2. Other types of furnaces
and furnace atmospheres may be used within the scope of the present invention as
determined by one skilled in the art.
The sinterbonded powder metal components of the present invention typically exhibit
magnetically conducting segments having at least about 95% of theoretical density,
and typically between about 95%-98% of theoretical density. Wrought steel or iron
has a theoretical density of about 7.85 gms/cm
3, and thus, the magnetically
conducting segments exhibit a density of around 7.46-7.69 gms/cm
3. The
non-conducting segments of the powder metal components of the present invention
exhibit a density of at least about 85% of theoretical density, which is on the
order of about 6.7 gms/cm
3. Thus, the non-ferromagnetic powder metals
are less compactable than the ferromagnetic powder metals. The pressed and sintered
hard ferromagnetic powder metal magnets of certain embodiments of the present invention
exhibit a density of at least 95.5% ± about 3.5% of theoretical density, depending
on fill factor, which is on the order of about 3.8-7.0 gms/cm
3. The
sinterbonding method for forming these rotor components provides increased mechanical
integrity, reduced flux leakage, more efficient flux channeling, reduced tooling
cost, and simpler construction.
To further explain the method of the present invention and the composite powder
metal components formed thereby, reference is made to the following figures in
which there are depicted exemplary components for various electric machines. The
components depicted are by no means exhaustive of the range of applicability of
the present invention. All green-strength segments described in reference to the
figures are fabricated individually by compacting an appropriate powder metal in
a die having the desired segment shape, as described above.
FIG. 1 depicts in perspective view a powder metal surface permanent magnet rotor
assembly
10 of the present invention having a plurality of sinterbonded
powder metal composite disks
12 aligned and mounted on a shaft
14,
the disks
12 each having an inner annular magnetically conducting segment
16 and a plurality of spaced magnetically non-conducting segments
18
separated by a plurality of alternating polarity permanent magnets
20. The
magnetically non-conducting segments
18 provide insulation that in part
directs the magnetic flux from one permanent magnet
20 to the next alternating
polarity permanent magnet
20.
A partially assembled, unsintered disk
12a is depicted in FIG. 2
in a partially exploded plan view. The inner annular segment
16 is formed
by compacting a soft ferromagnetic powder metal in a die to form a green-strength
conducting segment
16a. The magnetically non-conducting segments
18 are each formed by compacting a non-ferromagnetic powder metal in a die
to form green-strength non-conducting segments
18a. In the particular
embodiment of the present invention depicted in FIG. 2, the permanent magnets
20
are each formed by compacting a hard ferromagnetic powder metal in a die to form
green-strength permanent magnets
20a. The alternating polarity may
be created after sinterbonding. The green-strength magnetically non-conducting
segments
18a and green-strength permanent magnet segments
20a
are placed adjacent the green-strength inner annular magnetically conducting
segment
16a in alternating relation, as indicated by the arrows.
FIG. 2A depicts, in an enlarged view, a portion of disk
12a to show
the green-strength segments
16a,
18a,
20a
that are individually fabricated and then positioned adjacent each other with
powder metal
22 added between segments for sintering to form the sinterbonded
disk
12 of FIG.
1. Alternatively, the permanent magnets
20
may be prefabricated magnets that are added after sinterbonding green-strength
magnetically non-conducting segments
18a to green-strength magnetically
conducting segment
16a. Spacing inserts (not shown) may be temporarily
placed between segments
18a to facilitate proper positioning around
segment
16a. The inserts are removed, and prefabricated magnets
20
may then be adhesively affixed to sinterbonded segments
18 and/or
16.
FIG. 3A depicts in partially exploded plan view a partially assembled unsintered
disk
30a for a composite powder metal switched reluctance rotor assembly
of the present invention (not shown). The disk
30a includes a green-strength
magnetically conducting segment
32a that has a yoke portion
34a
and a plurality of equiangular spaced, radially extending teeth
36a
defining channels there between. Green-strength magnetically non-conducting
segments
38a are placed, as indicated by the arrows, in the channels
between the teeth
36a. Added powder metal (not shown) is added between
adjacent segments
32a and
38a. The segments are then
subjected to sintering to bond the segments together. FIG. 3B depicts in perspective
view the fully assembled and sintered disk
30 from FIG. 3A having magnetically
non-conducting segments
38 sinterbonded to magnetically conducting segment
32. A plurality of disks
30 may be affixed to a shaft to form a rotor
assembly. The non-conducting segments
38 function to cut down on windage
losses, and more particularly, a switched reluctance machine incorporating the
powder metal rotor disks
30 of the present invention exhibits low windage
losses as compared to assemblies comprising stamped laminations.
FIG. 4A depicts in partially exploded plan view an unassembled, unsintered disk
40a for a composite powder metal synchronous reluctance rotor assembly
of the present invention (not shown). The disk
40a includes a plurality
of alternating green-strength magnetically conducting arcuate segments
42a
and non-conducting arcuate segments
44a, which are placed, as
indicated by the arrows, in stacked arrangements adjacent a green-strength magnetically
non-conducting segment
46a. This segment
46a essentially
forms four equiangular spaced, radially extending arm portions
48a that
define axially extending channels there between, in which segments
42a,
44a, are alternately placed. Added powder metal (not shown) is added
between adjacent segments
42a,
44a, and
46a.
The segments are then subjected to sintering to bond the segments together. FIG.
4
b depicts in plan view the fully assembled and sintered disk
40
from FIG. 4A having magnetically non-conducting segment
46 with arm portions
48 forming channels, and within those channels are alternating layers of
magnetically conducting segments
42 and magnetically conducting segments
44. It should be understood, however, that a disk for a synchronous reluctance
rotor assembly may be formed of an opposite magnetic pattern in which the segment
having the arm portions may be conducting, with alternating magnetically nonconducting
segments and magnetically conducting segments in the channels. A variety of other
magnetic configurations are known and well within the skill of one in the art.
A plurality of disks
40 may be affixed to a shaft to form a powder metal
rotor assembly. A synchronous reluctance machine incorporating the powder metal
rotor disks
40 of the present invention exhibits power density and efficiency
comparable to induction motors and improved high speed rotating capability, yet
may be produced at a lower cost.
FIG. 5A depicts in partially exploded perspective view an unassembled, unsintered
disk
50a for a composite powder metal induction rotor assembly of
the present invention (not shown), the disk
50a having a green-strength
magnetically conducting segment
52a and a plurality of slots or slot
openings
54 extending along the axial length of the segment
52a
for receiving a plurality of conductors
55. A green-strength magnetically
non-conducting segment
56a is placed in each slot
54, as indicated
by the arrow, to thereby cap or enclose the slot opening
54. Powder metal
(not shown) is added between adjacent segments
52a and
56a,
and the segments are then subjected to sintering to bond the segments together.
FIG. 5B depicts in plan view a fully assembled and sintered disk
50 from
FIG. 5A having a magnetically conducting segment
52 with spaced axially
extending slots
54 around the exterior surface of the segment
52
for receiving a plurality of conductors
55, and magnetically non-conducting
segments
56 enclosing each slot opening
54 adjacent the exterior
surface of the segment
52. A plurality of disks
50 may be affixed
to a shaft
58 with the slots
54 aligned axially along the shaft,
and conductors
55 are then added in the aligned slots
54, as indicated
by the arrow in FIG. 5A, to form a composite powder metal rotor assembly
59,
as depicted in FIG.
5C. The conductors
55 may be cast into the aligned
slots
54 of the composite disks
50 or may be prefabricated bars inserted
into the slots
54. Thus, each slot
54 receives a conductor
55
in a radially inner portion of the slot
54, and a radially outer portion
of the slot
54 comprises the non-conducting segment
56 such that
the conductors
55 are embedded within the rotor assembly
59. An induction
machine incorporating the powder metal rotor assembly
59 of the present
invention can obtain high speeds with low flux leakage, and yet may be produced
at a lower cost.
FIG. 6A depicts in partially exploded plan view a partially assembled, unsintered
disk
60a for a composite powder metal spoke type interior permanent
magnet rotor assembly of the present invention (not shown). The disk
60a
includes an inner annular green-strength magnetically non-conducting segment
62a around which is placed, as indicated by the arrows, a plurality
of green-strength permanent magnet segments
64a separated by green-strength
magnetically conducting segments
66a. A radially outer green-strength
magnetically non-conducting segment
68a is placed adjacent each permanent
magnet segment
64a for embedding the permanent magnet segment
64a
in the disk
60a. Powder metal (not shown) is added between adjacent
segments
62a,
64a,
66a and
68a.
The segments are then subjected to sintering to bond the segments together. FIG.
6B depicts in plan view the fully assembled and sintered disk
60 from FIG.
6A having an inner annular magnetically non-conducting segment
62, a plurality
of alternating polarity permanent magnets
64 (polarized subsequent to sinterbonding)
separated by magnetically conducting segments
66 and radially embedded by
magnetically non-conducting segments
68. Two adjacent permanent magnets
64 direct their magnetic flux into the intermediate conducting segment
66,
which forms one rotor pole, and the next adjacent rotor pole will be of opposite
polarity. As with FIG. 2 above, permanent magnets
64 are depicted as compacted
and sinterbonded hard ferromagnetic powder metal segments, but may alternatively
be prefabricated and affixed to adjacent segments after sinterbonding. A plurality
of disks
60 may be affixed to a shaft to form a powder metal rotor assembly.
A spoke type interior permanent magnet machine incorporating the powder metal rotor
disks
60 of the present invention exhibits flux concentration, minimal flux
leakage and permits the motor to produce more power than a circumferential interior
permanent magnet motor or to produce the same power using less powerful and less
expensive magnets, and may be produced at a lower overall cost.
FIG. 7A depicts in exploded plan view an unassembled, unsintered disk
70a
for a composite powder metal circumferential type interior permanent magnet
rotor assembly of the present invention (not shown). Disk
70a includes
a green-strength inner annular magnetically conducting segment
72a,
around which is placed, as indicated by the arrows, a plurality of green-strength
permanent magnet segments
74a and a plurality of green-strength magnetically
non-conducting barrier segments
76a for separating the permanent
magnet segments
74a. A plurality of radially outer green-strength
magnetically conducting segments
78a are placed adjacent each permanent
magnet segment
74a for embedding the permanent magnet
74a
in the disk
70a. FIG. 7A further depicts placing an optional
green-strength inner annular magnetically non-conducting insert
80a within
segment
72a. Added powder metal (not shown) is added between adjacent
segments
72a,
74a,
76a,
78a
and
80a. The segments are then subjected to sintering to bond
the segments together. FIG. 7B depicts in plan view the fully assembled and sintered
disk
70 from FIG. 7A having an inner annular magnetically conducting segment
72 and an inner annular magnetically non-conducting insert
80 therein.
Positioned around segment
72 is a plurality of circumferentially extending
alternating polarity permanent magnets
74 (polarized after sinterbonding)
separated in between by magnetically non-conducting barrier segments
76.
The non-conducting segments
76 provide insulation that in part directs the
magnetic flux from one permanent magnet
74 to the next alternating polarity
permanent magnet
74. The insert
80 blocks magnetic flux from being
channeled into the shaft (not shown) when the rotor assembly (not shown) is operating.
The permanent magnets
74 are also circumferentially embedded by radially
outer magnetically conducting segments
78. As with FIG. 2 above, the permanent
magnets are depicted as compacted and sinterbonded hard ferromagnetic powder metal
segments, but may alternatively be prefabricated magnets affixed to adjacent segments
after sinterbonding. A plurality of disks
70 may be affixed to a shaft to
form a powder metal rotor assembly. A circumferential type interior permanent magnet
machine incorporating the powder metal rotor disks
70 of the present invention
exhibits increased power and speed capabilities, lower flux leakage, and may be
produced at a lower cost.
While the present invention has been illustrated by the description of one
or more embodiments thereof, and while those embodiments have been described in
considerable detail, they are not intended to restrict or in any way limit the
scope of the appended claims to such detail. Additional advantages and modifications
will readily appear to those skilled in the art. The invention in its broader aspects
is therefore not limited to the specific details, representative apparatus and
method and illustrative examples shown and described. Accordingly, departures may
be made from such details without departing from the scope or spirit of applicant's
general inventive concept.
*
