Note: Descriptions are shown in the official language in which they were submitted.
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LAMINATED CORE FOR ELECTRICAL APPARATUS
BACKGROUND OE TH~ INVENTION
Stator cores of dynamoelectric machines are con-
ventionally produced by sta.~ping a plurality of annularly
shaped pieces from sheet met21 and stacking them together
S to form a cylindrical core with a coaxial bore there-
through. Typically, the punchings have teet~ extending
radially inward which are aligned w-t~ similar teeth of
other punchings to form axially running slots in the bore
of the cylindrical core. At a la~er stage of manufacture,
conductors are disposed in these slots to form the stator
wlnding of a dynamoelectric machine.
This process is inherently wasteIul since the
stamping of circular components from sheet metal creates
scrap between adjacent circular punchings and between the
teeth of each punching. In most situations this scrap is
useles~ for any alternate purpose and, thereIore, adverse-
ly affects the manufacturing costs of the stator cores.
A means to avoid this high percentage of waste-
ul scrap has been developed and consists o~ edge rolling
a band of material into a helical shape. This process is
described in U.S. Patent No. 1,920,354 issued to Carpenter
on August 1, 1933i U.S. Patent No. 3,845,647 issued to
Cockin on November S, 1974; U.S. Patent Mo. 3,464,10l
issued to Zubal on September 2, 1969; U.S. Patent No.
3,062,267 issued to Hart et al on November 6, 1962; and
U.S. Patent No. 3,152,629 issued to Rediger on October 13,
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1964. These patents all wind helica~ cores from a contin-
uous strip of material by rolling the strip on its edge.
Some of these devices, such as Carpenter, Zubal, Rediger,
and Hart, utilize a shaping means that exerts a radially
inward force on the strip to bend it into a circular shape
while others, such as Cockin, use forming rolls to cause
the outer edge of the helical winding to be rolled to a
thinner cross-section than the inner edge. This thinning
operation causes the strip to curl into a generally circu-
lar shape.
U.S. Patent No. 4,116,033 issued to Iwaki et al.describes an apparatus and method for forming a wound core
which does not result in an outer lamination edge which is
thinner than its inner portion. This patent also des-
cribes a tooth-slot nesting arrangement for punching its
straight strip to minimize scrap material. An apparatus
for continuously winding helical cores is described in
U.S. Patent No. 3,283,399 issued to Hart et al. on Novcm-
ber 8, 1966. This device, like the other edge winding
devices described above, can be used to produce the cores
made in accordance with the present invention.
Due to the resilience of the strip material, the
wound helices made on these devices t-r.d~ to spring back
to a shape other than that which was intended. Also, due
to variations in the strip's thickness, the outer edge can
be~ro~lled to va~ying degrees of deformation which results
in varying degrees of circular curling. Because of these
problems, various corrective measures have been employed.
U.S. Patent No~ 4,202,196 issued to Asai on May
13, 1980 discloses a method of forminy a core with a
precise inner core diameter. This method is in response
to the inherent instabiLity of heLicaLly wound cores made
in the manner described above. Another aLternative to
this problem is described in U.S. Patent No. 3,436,812
issued to Aoki on April 8, 1969 which punches teeth in the
strip ater it is formed into a helical shape. This
~jraJ
method winds an unslotted strip into a continuous ~c~
~ ~35~
3 49,921
and then cuts the spiral into a plurality of annularly
shaped rings by severing the spiral with a single axial
cut. The indivldual rings are then stamped to form a
plurality of teeth on their inside edge. This process is
intended to avoid the typical misregistration of the teeth
that occurs if they are punched in the strip prior ~o the
helical winding operation described above.
Another m~thod, responsive to the ~imensional
accuracy problems discussed above, is disclosed in U.S.
lOPatent No. 2,058,362 issued to Smally on October 20, 1936.
This patent uses curved laminations which are each approx-
imately 91 arcuate degrees in length. By assembling them
with their ends abutting each other, a core is progres-
sively built.
15Individual laminations are discussed in U.S.
Patent No. 4,102,040 issued to Rich on ~ul~ 25, 1978 which
describes a laminated core produced by arranging a plural-
ity of straight strips in a stack and then bending t~e
stack to form a cylindrical core with an axial parting
line formed by its plurality OI aligned s~rip ends.
As should be apparent, helical winding of spiral
cores is a means of effectively minimizing scrap in the
manufacture of stator cores for dynamoelectric machines,
but significant production problems are inherent in the
known methods of winding them. These problems have in-
duced several corrective techniques which, themselves,
increase the cost of manufacture.
It is the object of the present invention to
correct the assembly problems of typical edge winding
methods with minimal increase in their cost and to also
improve the operating characteristics of the finished
core.
SUMMARY OF THE INVENTION
~he present invention relates to the production
of stator cores for dynamoelectric machines and, more
particularly, to the manuacture of edge wound laminated
cores that are dimensionally accurate and have improved
operating characteristics.
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In accordance with the present invention, pre-
punched strip material is wound into a helical shape by
any suitable method such as the those described above.
Instead of a continuous helix, however, the strip can be
wound into segments that are each slightly less than 360
in arcuate length. This can be accomplished by beginning
with straight strips of the proper predetermined length
or, in the alternative, by severing the circular helix at
the proper angular position to result in the generally
circular shapes which comprise approximately 359 of a
complete annular ring.
Rings made in this manner are then stacked to-
gether to form a cylindrical core. Since each individual
ring has prepunched teeth on its inner edge, the teeth can
lS be aligned to form axially running ~roov~s, or slots.
This registration ca~ be accomplished by stacking the
individual laminations on a mandrel which its inside each
ring and has radially extending splines which fit into the
slots between the teeth of the rings.
Since each ring is less than 360 of a circle,
it can easily be deformed to form a dimensionally accurate
cylindrical core when associated with other similarly made
rings. When a core is thus fo~med, the rings can be
~astened together in any suitab~e way to produce a stator
core which is dimensionally accurate and has proper slot
registration.
As a further improvement, the electrical proper-
ties of a core made in zccordance with the present inven-
tion can be significantly improved by producing the
straight strips by stamping them rom rolled sheet metal
in such a way as to have the direction of rolling run in a
parallel direction to the extension of the teeth from the
strip or, in other words, perpendicular to the strip's
length~ As the strip is edge rolled, the outer edge of
the circularly shaped ring is worked so as to orient the
grain structure of this outer edge in a circumferential
direction or generally parallel to the strip's length
while the grain structure of the teeth remains unchanged.
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49,921
A core made in accordance with the present in-
vention can thus comprise a tooth section with radially
oriented grain structure and an outer, or yoke, section
with circumferentially oriented grain structure. ~his
S grain structure orientation results in superior permea-
bility and lower iron losses in the îinished cores.
Since cores made in accordance with the present
invention are made from straight strip material, two
strips can be punched from a thin sheet of metal in such a
way as to further minimize scrap.
The teeth of one strip can be arranged to fit in
the slots of an adjacent strip on a sheet o~ Imaterial
prior to the stamping operation. The strips, by facing in
opposite directions in a nested fashion, minimize the
scrap produced by eliminating the wasted materia1 that
would otherwise be lost from between the teeth. Instead,
this material becomes the teeth of the cooperatively
associated strip.
For many years motor designers have used graded-
slots for single-phase motors. This design principle has
often, but not always, been coupled with the use of some-
what more nearly rectangular laminations to achieve a
general reduction in stamping scrap. Some slots are
graded or varied to achieve greater depth in the radial
direction. Since constant tooth width is used, it is
apparent from the geometry that greater slot width is also
achieved. ~he main, or running, winding of the single-
phase motor is inserted into these deeper and wider slots.
Conversely, the auxiliary, or starter winding
operates only during the starting of the motor and may
have signi~icantly less thermal mass. It is inserted into
slots which have been graded in ~he opposite manner, that
is, shallower and narrower. In the typicaL graded-slot
design, tooth pitch is not altered. Both main and starter
teeth have identical and constant tooth pitch.
With study of the geometry, it becomes apparent
that graded-slots, as just described above, are physically
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impo~sible to produce while using the tooth/slot nesting
principle to yield minimum scrap. However, in accordance
with the present invention, if the grading is done in the
opposite manner, using variable tooth and slot pitch, a
variable slot and tooth width is obtained and the advan-
tages of graded-slots can be maintained. In order to
allow the straight strips to be stamped in a nested man-
ner, each tooth of a specific straight strip is matched by
a slot in the same strip with a generally equal width.
This allows the teeth to be associated in a nested manner
. in ~ generally equal slot in another straight strip
. . ~
which can be punched simultaneously. According to the
present invention, graded slots can therefore be produced
in continuous strips of material in a way to minimize
scrap and make possible them being edge wound to form
helical cores.
It is therefore an object of the present inven-
tion to provide a laminated core which can be manufactu~ed
with a minimal amount of scrap but which has superior
magnetic characteristics to conventionally produced cores.
It is a further object of the present invention to provide
a core which can be manufactured with dimensional accur-
acy.
BRIEF DESCRIPTION OF THE DRAWINGS
. __
The present invention will be better understood
from a reading of the description of the preferred embodi-
ment in conjunc:tion with the figures, in which:
Figure 1 is an isometric view of a core made in
accordance with the present invention;
Figure 2 is a view of a single laminatlon of the
present invention;
Figure 3 illustrates the way the strips of the
present invention may be nested during a stamping opera-
tion in which they are punched from a continuous sheet of
magnetic material;
Figures aA and 4B further illustrate the nested
relationship of two straps of magnetic material along with
their grain structure orientation;
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Figure 5 demonstrates a straight strip as it is
edge rolled to form an annular lamination; showing the
resultant changes in its grain structure orientation;
Figu.res 6A and 6B illustrate two straight strips
of magnetic material which have been punched with an
graded-slot ~ooth configuration; and
Figure 7 depicts a graded-slot lamination made
in accordance with presently known stamping techniques.
DESCRIPTION OF T~E PR~FERRED EMBODIMENT
A laminated stator core, made in accordance with
the present invention, is shown in Figure 1. The core 10
comprises a plurality of generally annular laminations 1~
with each of these laminations 12 comprising a plurality
of teeth 14 which extend radially inward ~rom a yoke
portion 16 thereof. Each circular lamination 12 extends
circumferentially around the cylindrical core 10 for an
arcuate distance which is slightly less than 360. It has
been determined that a lamination which comprises from
355~ to 359 of a circle can satisfactorily produce a core
10 made in accordance with the present invention. The
remaining arcuate distance that is not traversed by the
lamination 12 forms a slight gap 18 between the two adja-
cent ends of each lamination. As shown in figure 1, the
laminations 12 are stacked in such a way as to randomly
distribute their gaps 18 around the periphery of the core
10 .
After the laminations 12 are s.acked with their
teeth 14 and slots 20 aligned to form axially running
grooves, the outside diameter of the core 10 can be formed
to a preselected dimension by compressing it radially
inwardly while the laminations are mounted on a mandrel to
produce the desired dimensions of the inside diameter of
the core. Any deformation in an individual lamination 1
will be compensated by an associated change in its gap 18.
Therefore, it should be understood that the core can be
formed in such a way as to correct for any individual
variation in laminations.
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This ability to form the outside diameter of the
core enables dimensionally oversized or ~mdersized lamin-
ations to be corrected during assembly. It has been found
that conventional edge winding equipment does no-t produce
circular laminations 12 to precise tolerances and a cer-
tain amount of resiliency in the shaped lamina~ion is to
be expected.
By stacking the individual laminations 12, as
shown in Figure 1, they can also be aligned over a splined
mandrel which fits into the inside diameter of the lamina-
tions 12. This allows proper tooth 14 registration to be
maintained during ~he forming process.
When the diameters are ~ormed with dimensional
accuracy and the teeth 14 are properly aligned, the lamina-
tions 12 can then be fastened together by any suitablemeans such as welding or potting.
Figure 2 shows a single lamination 12 with its
teeth 14, slots 20 and gap 18. The teeth 14 extend radi-
ally inward from the lamination's yoke portion 16. Be-
tween each adjacent pair of teeth 14, a slot 20 is formedwhich is sized to accept a stator conductor after the lam-
ination is stacked with others to form a core. It should
be apparent that the gap 18 allows the lamination 12 shown
in Figure 2 to be radially compressed to a smaller diameter
than illustrated in Figure 2, limited only by the size
of the gap 18.
The armular lamination 12, or ring, shown in
Figure 2 can be manufactured by any of the edge winding
techniques described above. It can be severed from a con-
tinuous helical coil or rolled from a precisely measuredstraight strip whose length has been determined to result
in the proper circumferential dimension required to pro-
duce a lamination which has a predetermined gap and is of
a preselected circular configuration. A representative
apparatus on which the rlng 12 can be produced is des-
cribed in copending Canadian application Serial Number
410,253 filed August 26, 1~81 assigned to the assignee of
the present application.
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When each of the laminations are rolled from in-
dividual straight strips of material, as discussed above,
additional advantages can be realized in the magnetic
characteristics of each lamination and therefore of the
completed core. Figure 3 shows a sheet 30 of rolled sheet
material from which laminations are to be made. Sheet
material of this type is normally rolled in the direction
,~t shown by the arrow R1. This rolling, which is inherent in
the manufacture of rolled sheet material of this~e~sults
in a grain orientation of the material which is in the
direction of the arrow R1.
Also shown in Figure 3 are four typical straight
strips 32a, 32b, 32c and 32d, which are to be eventually
edge-wound into circular laminations. The strips are
stamped from the sheet in such a way that their individual
lengths are perpendicular to the direction of grain orien-
tation Rl. Figure 3 also demonstrates the cooperative
association of strip 32a with 32b and of strip 32c with
32d. Each of these pairs comprises two nested strips
wherein the teeth of one strip ~ disposed in the slot of
its associated strip to minimize scrap. It should be
understood that, for teeth which are not rectangular,
total eliminatlon of scrap is not possible. However, the
nesting of associated strips, as shown in Figure 3, mini-
.25 mizes the amount of scrap produced for any particulartooth design.
It should be understood that many tooth designs
are not rectangular as shown in Figure 3. Instead, some
are shaped with rounded bottoms as shown ln Figure 2.
However, since the present invention is not dependent on a
particular tooth configuration, rectangular tooth shapes
will be illustratively used herein.
Using straight strips 32a and 32b from Figure 3,
Figures 4A and 4B further show their nested relationship
as the two are parted. Arrows R1 illustrate the original
direction of grain orientation, as described in conjunc
tion with Figure 3 and the discussion above. As Figures
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49,921
4A and 4B clearly show, the grain orientation is the same
throughout both straight s~rips and is consistent in both
the tooth 14 and yoke 16 portions of the strips. It
should be understood that this particular orientation of
grain structure in the straight strips is due to both the
rolling direction by which the roll of sheet metal (ref-
erence numeral 30 of Figure 3) was produced and the orien
tation of the straight strips on that sheet metal. As
Figure 3 illustrates, the straight strips 32a, 32~, 32c
and 32d were punched from the sheet 30 so that their
lengths were perpendicular to the direction of rolling R.
Figure 5 illustrates a strip 32b of material as
it is being formed into a circular, edge wound shape. It
should be understood that, although no winding e~uipment
lS is shown in Figure 5, any device that is capable of edge
winding a straight strip, such as 32b, of prepunched
material into an annular shape can be utilized.
~ s the strip is rolled into a circle, i~s outer
edge is elongated and becomes thinner. This elongation is
a physical necessity because of the greater circumferen-
tial distance around which the outer edge extends. When a
prepunched strip is edge-rolled, it typically experiences
elongation from its outer edge S0 to a point 52 just below
the root of the slot 20. Betwesn this point 52 and the
root of the slot 20, the strip experiences a slight com-
pression and, in the tooth 14 region, no material deforma-
tion occurs.
Tha elonbgation of the outer portion, or yoke 16,
of the strip ~ causes the grain structure in that por-
tion of the strip to become oriented in the direction ofelongation of the strip. Arrows R2 show this new direc-
tion of grain orientation in Eigure 5. It should be
apparent that, since the yoke 16 is elongated and the
tooth 14 portion is not deformed, the result of the edge
rolling operation is to orient the grain structure of the
yoke 16 in a circumferential direction R2 whiLe leaving
the grain structure of the teeth 14 unchanged and oriented
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in a radial direction in the annular lamination that is
produced by the edge rolling operation. It should further
be apparent tc one skilled in the art that this selective
grain orientation of the tooth 14 and yoke 16 portions of
each lamination improve the magnetic characteristics,
increasing permeability and reducing iron losses.
Figures 6A and 6B illustrate a variation of the
present invention in which the slots 20 and the teeth 14
do not comprise a uniform pitch. This type of construc-
tion, referred to herein as a graded-slot design, selec
tively provides larger slots for the main wi~ding and
smaller slots for the auxiliary winding of a single phase
motor. It should be apparent from a viewing of Figures 6
and 6B together that the elements and methods of the
present invention are equally applicable in graded-slot
designs. Of course, in order to permlt the eco~omical
nesting described above, the tooth widths and slot widths
must be coordinated so that the teeth 14 of one strip 6~a
are cooperatively associated wi~h ~he slots 20 of another
strip 60b, and vice versa. It sho~ld be apparent from
these figures that, even in graded-slot designs, the
material saving nesting techniques described above and
shown in Figures 3, 4A and 4B are appl cable. It should
further be apparent that the selective grain orientation,
also describecl above, can be achieved in an graded-slot
design.
Figure 7 depicts a graded-slot lamination de-
signed for manufacture by presently used stamping tech~
niques. It ccnsists of slots of variable depth in order
to provide slots with variable area. .~s e~plained above,
the purpose of this variability is to provide large slots
for the maln windings and small slots for the auxiliary
winding. The auxiliary winding slot 71 is clearly smaller
than the main winding slot 72 with gradations therebe-
tween. It should be obvious, by studying the geometry
involved, that a pattern of varying slot depths, as shown
in Fig. 7, is not physically possible to manufacture while
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achieving the maximum savings obtained in a double width
strip having full slot to tooth meshing as shown in Fig
ures 3, 4a and 4b. The graded-slot design of the present
invention, as shown in Figs. 6A and 6B, in contrast,
utilizes slots which have a constant depth and is thus
manufacturable. This geometric advantage, which results
in reduced material usage, accrues irrespective of the
method used for edge winding or forming the strip and
irrespective of the usage of the grain orientation advan-
tage illustrated in Figures 3, ~a and 4b.
The present invention provides a laminatedstator core that utilizes edge rolled laminations which
result in significant material savings. It further pro-
vides a means of correcting typical malformations expari-
enced in most conventional roll-forming methods by employ-
ing single laminated rings ~ith a gap within each lamina-
tion. Also, ~he present invention makes possi~le a selec-
tive grain orientation within each lamination which si~g-
nificantly improves the magnetic characteristics of the
core and the electrical performance of ~he resulting
dynamoelectric machine. Furthermore, it is applicable to
both uniform and graded-slot designs.
It should be apparent to one skilled in the art
that the present invention provides a stator core that
reduces manufacturing costs and improves the electrical
characteristics of a dynamoelectric machine comprising it.
It should also be understood that, although the present
invention has been described in considerable detail and
with particularity, it should not be considered to be so
limited.
