U.S. patent number 3,699,372 [Application Number 05/154,183] was granted by the patent office on 1972-10-17 for rotor for dynamo-electric machine of the axial airgap type.
This patent grant is currently assigned to Tokai Cold Forming Co., Ltd.. Invention is credited to Michio Abe, Naoyuki Maeda.
United States Patent |
3,699,372 |
Abe , et al. |
October 17, 1972 |
ROTOR FOR DYNAMO-ELECTRIC MACHINE OF THE AXIAL AIRGAP TYPE
Abstract
A dynamo-electric machine of the axial airgap type has a rotor
comprising a plurality of wedge-shaped grain oriented core segments
arranged in a circular array, each core segment having a
crystallographic orientation such that the directivity of magnetic
orientation thereof, in directions parallel to the rotor axis, is
high at and around the inner portion of the lamination, proximate
to the rotor periphery, and is low at and around the inner portion
of the lamination, proximate to the rotor shaft. Preferably, the
core segments are made of iron having a degree of purity of at
least 99.6 percent.
Inventors: |
Abe; Michio (Kasugai,
JA), Maeda; Naoyuki (Inuyama, JA) |
Assignee: |
Tokai Cold Forming Co., Ltd.
(Kasugai-shi, Aichi-ken, JA)
|
Family
ID: |
12684416 |
Appl.
No.: |
05/154,183 |
Filed: |
June 17, 1971 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
773738 |
Nov 6, 1968 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Jun 27, 1968 [JA] |
|
|
43/44182 |
|
Current U.S.
Class: |
310/268 |
Current CPC
Class: |
B22D
19/0054 (20130101); H02K 17/16 (20130101); H02K
15/0012 (20130101) |
Current International
Class: |
H02K
17/16 (20060101); H02K 15/00 (20060101); H02k
001/00 () |
Field of
Search: |
;310/216,268,179,193,155 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sliney; D. X.
Parent Case Text
The present invention relates to dynamo-electric machines, and more
particularly to improvements in the rotor of induction motors of
the axial airgap type, such as described, for instance, in U. S.
Pat. No. 3,296,475 and/or U. S. application Ser. No. 643,171, filed
June 2, 1967 and copending with our application Ser. No. 773,738,
filed Nov. 6, 1968, of which this is a continuation-in-part.
Claims
What is claimed is:
1. In a dynamo-electric machine of the axial airgap type,
comprising rotor means including a rotor shaft, a plurality of
wedge-shaped core segments arranged in a circular array about the
rotor shaft, the core segments having wider ends adjacent the outer
periphery of said circular array and narrower ends adjacent the
axial center of the array, and supporting means for the array of
core segments including a secondary conductor forming radially
extending supporting members between the wedge-shaped core segments
and a rim surrounding the core segments adjacent the outer
periphery of said array, the improvement of each of said core
segments having a crystallographic orientation such that the
directivity of magnetic orientation thereof, in directions parallel
to the rotor axis, is high at and around the outer portion of the
core segment, proximate to the rotor periphery, and is low at and
around the inner portion of the core segment, proximate to the
rotor shaft.
2. In the dynamo-electric machine of claim 1, each of the core
segments being of electromagnetic pure iron having a degree of
purity of at least 99.6 percent.
3. In the dynamo-electric machine of claim 1, the secondary
conductor being a die-cast metal disc member fixing and bonding the
core segments and the rotor shaft together to form an integral disc
type rotor.
4. In the dynamo-electric machine of claim 3, each of the core
segments having flange portions extending in planes parallel to the
faces of the disc member.
5. In the dynamo-electric machine of claim 1, the secondary
conductor being a conductive metal disc member having a plurality
of core segment receiving windows arranged circularly about a
central bore receiving the rotor shaft, and the core segments
having flange portions riveted to the disc windows.
6. In the dynamo-electric machine of claim 1, the secondary
conductor comprising an inner circular disc portion, the rim being
fitted around the periphery of the disc portion, and the disc
portion having radially extending teeth wherebetween the core
segments are received.
Description
Dynamo-electric machines of the axial airgap type have motor means
comprising a plurality of wedge-shaped and core segments arranged
in a circular array. The core segments have their wider ends
adjacent the outer periphery of the circular array and their
narrower ends adjacent the axial center of the array. Supporting
means for the array comprises a secondary conductor forming
radially extending supporting members between the wedge-shaped core
segments and a rim surrounding the core segments adjacent the outer
periphery of the array.
Induction motors of this type are seldom found in practical use,
and methods of manufacturing the rotor core segments have improved
little over the years. This type of induction motor has, therefore,
rarely been used in industry, its characteristics being very poor
in comparison with the radial airgap type induction motors. In
recent years, however, some advantages of the axial airgap type of
motor have been recognized, for example the fact that the length in
the axial direction is shorter, the airgap may be narrowed since
the rotor is of a disc type, and the total weight of the motor is
considerably less than that of radial airgap type machines.
Notwithstanding these advantages, no satisfactory axial airgap type
induction motor has been placed on the market.
One object of the invention is to provide a novel rotor lamination
structure for axial airgap type of dynamo-electric machines.
Another object of this invention is to provide a novel structure
for the secondary conductor of the rotor.
A further object is the provision of an axial airgap type induction
motor having a higher power factor and superior starting
characteristics than those of radial airgap type induction
motors.
Broadly, these and other objects are accomplished in accordance
with the present invention by giving each core segment a
crystallographic orientation such that the directivity of magnetic
orientation thereof, in directions parallel to the rotor axis, is
high at and around the inner portion of the lamination, proximate
to the rotor periphery, and is low at and around the inner portion
of the lamination, proximate to the rotor shaft.
More specifically, this may be accomplished in accordance with a
preferred embodiment of this invention by making the core segments
of iron having a degree of purity of at least 99.6 percent.
According to one feature of the invention, the secondary conductor
fixes and bonds the core segments and rotor shaft together to form
an integral disc type rotor, each of the core segments preferably
having flange portions extending in planes parallel to the rotor
disc faces.
According to another feature, the secondary conductor is a disc
having a plurality of core segment-receiving windows arranged
circularly thereabout and a rotor shaft bore, the core segments
having flange portions secured in the windows by rivets.
According to yet another feature, the secondary conductor is of
metal and comprises an inner circular disc and the rim is adapted
to fit around the periphery of the inner disc, the inner disc being
formed with teeth to receive the core segments having flange
portions.
In the drawing,
FIG. 1 is a longitudinal cross sectional view of one embodiment of
an induction motor according to the present invention;
FIG. 2 is a perspective view showing the relationship between the
rotor core segments and a rotor shaft arranged in position;
FIG. 3 is a perspective view of a rotor assembled according to this
invention;
FIG. 4 is a schematic diagram showing a cold-forming process for
the manufacture of the core segments;
FIGS. 5A-D are schematic diagrams showing the metal structure of a
core segment manufactured according to the process illustrated in
FIG. 4;
FIG. 6 is a side view, partly in cross section, showing the
magnetic flux path passing through the core segments of an axial
airgap type motor;
FIGS. 7 and 8 show a simplified die-casting machine for securing
the core segments to each other and to the rotor shaft;
FIGS. 9A and 9B are plan and cross-sectional views, respectively,
of another embodiment of the secondary conductor;
FIG. 10 is a perspective view of a core segment of modified
shape;
FIGS. 11A-D and 12A-D are side, plan, perspective and top views,
respectively, of core segments made in a cold-forming operation
from the shape of FIG. 10;
FIGS. 13A and 13B are plan and cross-sectional views, respectively,
of yet another embodiment of the secondary conductor and several
core segments aligned therein;
FIGS. 14A and 14B show processes for securing the core segments of
FIGS. 11 and 12, respectively, to the secondary conductor
support;
FIG. 15 shows the completed arrangement of FIGS. 14A and 14B;
and
FIG. 16 is a Hyland's circle diagram of the operation of an
induction motor with the secondary conductor of FIGS. 9A and
9B.
Referring now to the drawing and first to FIG. 1, the rotor core
segments 5 shown therein comprise "pure iron," e.g. iron having a
degree of purity of 99.98 percent, of high permeability, rather
than the "wrought" iron commercially available.
FIG. 1 shows a rotor mounted within motor casing 12. The rotor
comprises a rotor shaft 7, a secondary conductor 6, and a plurality
of wedge-shaped core segments 5 arranged in a circular array and
supported in the secondary conductor. The rotor shaft 7 is
supported by two ball bearings 16, 16 secured in bearing housings
15, 15. Left and right stators each comprising stator core 2 and
stator windings 3 are mounted adjacent the rotor core segments.
FIG. 2 shows the relationship between alignment of shaft 7 and the
core segments 5 of the rotor, and FIG. 3 shows the assembled rotor
after the core segments have been secured in the secondary
conductor support.
According to a preferred feature of the present invention, high
permeability iron of a degree of purity of at least 99.6 percent is
used for the core segments 5. Iron of such purity is, for example,
discussed on page 786 of "Metals Handbook," 8th ed., Vol. 1, in the
following words:
"For experimental uses, 99.99 percent pure iron can be obtained
with maximum permeability of about 100,000; this grade of iron has
a hysteresis loss of about 100 ergs per cu.cm. per cycle for a flux
density of 10,000 gausses. The saturation value of iron is given as
4.pi.Is = 21,580 .+-. 10 gausses, based on a density of 7.878,
where Is is the intensity of magnetization or magnetic moment per
unit volume."
However, the industrially attainable purity of iron is limited to
99.6 percent to 99.8 percent and, to facilitate melting, elastic
working, and plastic deformation, a small amount of alloy is
generally added to pure iron, the amount being insufficient to
degrade the magnetic property of the iron. We have found that the
magnetic characteristic of iron having a purity of at least 99.6
percent is excellent in the directions along the crystal flow, as
will become apparent herein. Thus, the objects of this invention
may be achieved well with iron of a purity no lower than 99.6
percent, which is referred to as "electromagnetic pure iron" in the
present-day industry. The motors hereinbelow more fully described
and tested were constructed with core segments made of such
electromagnetic pure iron commercially available in Japan.
As shown in FIG. 2, each core segment 5 has an I-shaped cross
section, one face 5a thereof being wedge-shaped, the flange portion
5c being a projection of the wedge-shaped face 5a and defining an
air duct 5f with a corresponding flange portion of the adjacent
core segment. The cylindrical faces 5d and 5e of each core segment
contact the rim 6a and the inner disc 6c, respectively, of the
secondary conductor 6, as shown in FIG. 3.
The rotor shaft 7 has two ratchet portions 7a, 7a for receiving
torque, a reduced diameter portion 7b being defined between the
ratchet portions for receiving thrust. A curved shaft portion 7c is
adjacent the ratchet portions.
FIG. 4 shows a method of manufacturing the core segments. In this
method, a cylindrical iron bar d1 which has a cross sectional area
corresponding to the cross sectional area of the inner cylindrical
face 5e of the core segment shown in FIG. 2 is first cut down to
have the same volume as that of the completed core segment. This is
done by feeding the bar d1 into a header where it is cut to form
blank d2 of a predetermined length. This blank is then worked in a
compression die and a preforming punch to form, in the first stage,
an element d3 and, in the second stage, the finished form d4 in a
subsequent die and punch. This is a cold-forming operation in which
the normal crystallographic structure of the metal receives
compression, reduction and expansion working. As a result, crystal
flow occurs, resulting in the metal structure schematically shown
in FIGS. 5A-D.
A double blow cold header or progressive header may be used in this
process to manufacture 100 to 200 core segments per minute, each
exhibiting the superior magnetic properties hereinafter
described.
FIGS. 5A-D illustrate the crystal flow which occurs in a core
segment formed in the above-described cold-forming process. Since
the core segment is reduced and shaped from a circular iron blank
having a cross section as large as that of the cylindrical face 5e,
the crystal flow occuring in channel 5b adjacent the inner
cylindrical face 5e results in a grain structure which is somewhat
narrower and longer along the X-axis that that which occurs near
the outer cylindrical face 5d. Upon reaching the outer face 5d,
this tendency decreases and, at the upper portion adjacent the
outer face, the effects of compression being to appear and the
crystallographic orientation is compressed and flattened along the
Y- and Z-axes. Further, at the flange portions 5c, the
crystallographic orientation is aligned along the Z-axis, due to
the method of forming the projections 5c, and at the upper channel
portion 5b the grain structure is aligned along the Y-axis.
Because of the crystallographic orientation in the metal of the
rotor core segments, the intensity of any magnetic flux induced in
the rotor core is greater along the Y-axis at and around the outer
cylindrical face 5d whereas, in channel 5b, near the inner face 5e,
the magnetic flux intensity along the Y-axis is reduced. As a
result, the flux distribution along the Y-axis is improved, as will
be explained hereinafter.
FIG. 6 is a simplified cross sectional view of FIG. 1 and
illustrates, in dotted lines, the magnetic flux path in the motor.
Since an axial airgap type induction motor has a core or pole face
which expands radially outwardly towards the periphery, the length
of the magnetic path increases as one moves from the rotor shaft to
the periphery. Therefore, the magnetic flux density within the core
is high, at or near the center of the rotor, and low at and around
the periphery thereof. Moreover, when the fan-shaped core segments
are used, the magnetic flux density generally induced therein
varies over a wide range and is non-uniform so that the efficiency
of the motor is poor. That is to say, as the magnetic flux passing
through the center of the rotor shaft increases, the torque being
generated decreases.
Although the total permeability of the core segments manufactured
by the above-described cold-forming operation decreases a little,
the crystal flow around the outer portion 5d of the rotor core is
such that a decrease in permeability thereabout is substantially
prevented and the magnetic flux passes easily through the outer
periphery of the rotor. As a result, the magnetic flux density
about the center of the rotor shaft decreases, relatively speaking,
and the flux density in the outer periphery increases
correspondingly so that the motor torque increases.
One method of manufacturing the rotor of FIG. 3 is described with
reference to FIGS. 7 and 8.
FIG. 7 shows four core segments 5 and the rotor shaft 7 arranged in
a die 18 including a plurality of recesses 18a each having a depth
corresponding to the thickness of flange portion 5c (FIG. 2) of the
core segment 5, and a shape to match that of fan-shaped face 5a
thereof. A face 18b of the die is utilized to form disc face 6b of
the secondary conductor 6 which is a part of the rotor. A
projection 18c of the die is provided for sealing upon die-casting,
and a port 19 is provided as an inlet for molten metal.
FIG. 8 simply illustrates the die-casting operation using a fixed
die 18 and a movable die 20 having portions 20a, 20b and 20c which
correspond to, or match with, the conforming portions of fixed die
18 described hereinabove. Curved portions 18d and 20d of the dies
engage with the correspondingly curved portion 7c of rotor shaft 7.
The dies are mounted on base 23.
The right half of FIG. 8 shows the core segments 5 being inserted
in the apertures 24a in an aligning frame 24 placed on a slidable
plate 25 on a table 26. The core segments may be inserted manually
or by an automatic feeding device. Apertures 24a have the same
arrangement as recesses 18a of die 18. Distributed in apertures 24a
of frame 24, the core segments 5 are advanced into the die 18,
together with slidable plate 25 and frame 24. They are then dropped
into the corresponding recesses 18a by withdrawing plate 25. After
that, frame 24 is also withdrawn from die 18 to its original
position on Table 26. The rotor shaft 7 is then inserted in the
shaft supporting portion 18d of the die 18, and the upper die 20 is
lowered along guide cylinder 22 until the dies engage the shaft,
leaving a space therebetween for die-casting the secondary
conductor while the rotor shaft and the core segments are firmly
held in position between the dies to form the integral rotor
structure shown in FIG. 3. The channels 5f (FIG. 2) between the
flange portions 5c of adjacent core segments function as air ducts
so that a cooling effect is obtained.
An alternative method of manufacturing the rotor without a
die-casting operation is described hereinbelow.
FIGS. 9A and 9B show another embodiment of a secondary conductor
wherein a sheet of copper is employed instead of a die-cast core
segment support. As shown, the copper sheet has an inner disc
portion 6c wherefrom there extend radially projecting teeth 6b
machined into the copper sheet in a finishing lathe, the teeth
being finished by broach working after punching. Thereafter, core
segments 5 are inserted, with a friction fit, between the teeth of
the sheet. The outer secondary conductor ring 6a has a tapered face
6d so that it may be easily secured to the periphery of the inner
conductor portion and, after the core segments have been aligned
between the teeth of the inner portion, the outer ring is engaged
therewith to form the rotor body. When the rotor shaft is secured
in the central bore of the copper sheet by friction fit, a
mechanically strong rotor similar to that of FIG. 3 is
produced.
An alternative method of manufacturing the core segments will be
described hereinbelow. FIG. 10 shows a core blank which has been
roughly drawn from electromagnetic pure iron of normal crystalline
structure by means of a drawing die. The blank has a fan-shaped
cross section and is subjected to working by means of a cold header
to assume the shapes shown in FIGS. 11A-D and 12A-D.
The difference between the shapes of the core segments of FIGS.
11A-D and 12A-D and that of FIGS. 5A-D is that the former have
fringe portion 5a' which may be rivetted to the secondary conductor
of the rotor. Here again, it is possible to provide an advantageous
crystallographic orientation in the metal by appropriately
selecting the cross sectional area of the blank.
A secondary conductor suitable for riveting comprises a punched
metal disc, as shown in FIGS. 13A and 13B. The disc may be an
aluminum or copper sheet having a plurality of radially extending
windows 27 around its periphery in which the correspondingly shaped
core segments may be inserted. The central bore 28 in the metal
disc receives the rotor shaft. The insertion of a fan-shaped core
segment of the type shown in FIGS. 11A-D in window 27 is
illustrated in FIG. 14A, the core segment then being riveted on
both sides thereof to the metal disc. Insertion of a core segment
of the type shown in FIGS. 12A-D in window 27 is illustrated in
FIG. 14B but, in this case, only one side thereof is riveted. FIG.
15 shows the core segment secured to the disc.
The results of a test performed on an induction motor constructed
in accordance with the present invention are given hereinbelow, the
tested motor being of the type shown in FIG. 1 wherein the core
segments of electromagnetic pure iron were manufactured in a
cold-forming operation shown in FIGS. 5A-D, and the secondary
conductor was that of FIG. 9. Both stators comprised conventional
coiled cores.
The ratings of the tested motor were as follows:
Output 2.2 KW Voltage 200 V Frequency 60 cps Phases 3
Design factors were as follows:
Number of core segments 29 Segment thickness in the direction of
the shaft 16 mm Diameter of the rotor including outer face 5d 165
mm Diameter of the rotor including inner face 5e 90 mm Weight of
core segments 0.84 kg Weight of secondary conductor 1.32 kg Total
weight of rotor 2.83 kg
By comparison, the weight of an "A" class motor of the same ratings
specified in the JIS (Japan Industrial Standard) is 10 kg. Thus,
the weight of the rotor of the invention is less than a third of
that of a conventional radial airgap type induction motor.
Following are the test results:
Item Effi- Power Output Torque Measurement ciency factor Sync.watt
Kg-m point % % KW KW
__________________________________________________________________________
Max. efficiency (79.7) 86.0 2.12 2.20 1.185 Max. power factor 77.0
(90.0) 2.80 3.00 1.620 Max. output 61.9 83.0 (3.90) 4.74 2.560 Max.
torque 53.5 78.0 3.72 (4.90) (2.650)
Input Slip Current KW % A
__________________________________________________________________________
2.66 4.3 8.7 3.64 6.7 11.7 6.30 17.0 21.8 6.97 23.2 25.7
__________________________________________________________________________
the Hyland's circle diagram for the above results is shown in FIG.
16.
A comparison between the characteristics of the motor of the
present invention, which were calculated by the Hyland's circle
diagram method, and of conventional motor of the same ratings is as
follows:
Output Efficiency Power Synchronous factor watt KW % % KW
__________________________________________________________________________
Subject motor 2.2 79.5 89.0 2.31 JIS "A" motor 2.2 80.5 79.0
2.36
Input Slip Current Starting Current KW % A A
__________________________________________________________________________
2.77 4.8 9.1 37.3 2.73 6.5 9.5 60
__________________________________________________________________________
thus, it has been shown that the core segments made by a
cold-forming operation have a superior crystallographic orientation
while exhibiting only a slight degradation of magnetic
characteristics. This degradation is shown more in an increase in
the hysteresis loss than in a decrease of permeability. Since the
former has little effect on the properties of the motor, only the
advantages of the latter remain.
In a rotor which includes soft iron core segments according to the
present invention, when the slip is large (i.e. at starting), a
large starting torque is obtained because the eddy current loss
appearing within the core segments is large. When rotation
approaches the synchronous speed, the iron loss within the core
segment decreases because the secondary frequency decreases.
Therefore, even if it has a secondary conductor of low resistance
and provides a small slip, such a motor exhibits characteristics
similar to those of a cage type having an increased starting
torque.
A rotor according to this invention, which is thin in the axial
direction, has an improved power factor since the exciting
ampere-turns can be decreased and, thus, a large magnetic flux may
be obtained for the same magnetomotive force. Further, since it is
possible to increase magnetic flux density by using magnetic
material of high permeability, the core weight can be substantially
reduced over conventional motors of the radial airgap type. Thus,
the motor may be miniaturized and made so light that its moment of
inertia is extremely small, resulting in considerably shortened
starting and stopping times.
In the event that the core segments and the rotor shaft are secured
by die-casting, the core segments and the rotor shaft are fixed
very tightly to each other and a very thin rotor of the disc type
can be produced.
* * * * *