Note: Descriptions are shown in the official language in which they were submitted.
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AMORPHOUS ~ETAL ELECTRIC MOTOR WlTH
IN~IL~RAL ~AP CITOR
Backgroun(l o~ th__Invention
This lnvention relates to electric machines with
mag~etic cores made o:E amorphous metal ribbon, and more
particularly to utilization of the amorphous metal material
required or the magnetic circuit to serve also as the plate
material of an integral capacltor.
Most single-phase motors use a capacitor for
starting, running, or both, and this is requirèd
in order to achieve the required phase shift between main
and auxiliary starting currents. The cost of this capacitor
may in some cases exceed the cost of the base motor. There
are other situations where a capacitor is associated with
a motor or generator, such as for power factor correction or
for ~iltering rectified power. In all of -these cases
the capacitor is normally a discrete component,
Motors and inductive components hav-lng laminated
magnetic cores made from long lengths of amorphous me~al
rl~bon, either toothed or ~ith a uniform width, are a
recent development in the art. Amorphous metals are also
known as metall~c glasses and exi~t in many different
.
compositions including a variety of magnetic:~lloys which
~nclude iron group elements and boron or phosphorcus.
Metallic glasses are ormed from metal alloys that can be
quenched without crystallization, and these materials
are mechanically sti~f, strong and ductile, and are low
cost. The f-erromagne~ic types have very low coercive forces
and hlgh permeabilities and are especially attractive
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because of their low losses. Ribbons of the Fe80B20
alloy have one-fourth the losses, at a given induction
for sinusoidal flux, o the best oriented Fe-Si steel.
~dd:itlonal information is given in the article "Potential
. of Amorphous Metals for Application in Magnetic Devices"
by F.E. Luborsky et al, Jr'. of Applied Physics, 49(3),
' Rart II, March 1978, pp. 1769-1774.
~morphous metal is manufactured by extruding the melt
'under pressure onto a rapidly rotating very cold chill surface,
and the liquid al:loy i9 changed lnto a solid ribbon in a
short time measured in micro-seconds before it becomes
cry.stalline. The cooling rate is in the order of 106~C/sec. .
The maximum ribbon thickness at present is two mils or
less; the thickness limit~tion is set by the rate of heat
'' 15 ' transfer through the already solidified material,
which must be rapid enough that the last increment of
'material still avoids crystallization. The inherently
thin'nature of this material and the large number
o~ motor.laminations that are needed-punched steel strip is
commonly 10 mils or ~reater in thickness - is one of ~he assumed
disad~antag~s of using amorphous metal alloys in electric
mot~rs.
Summary of the Invention
The undesirably thin lam~nation thickness (about 1.5-2
mils)~hich is the maximum currently achieveable with amorphous
- metal ribbons is capitalized upon by utilizing the
laminations of a properly configured magnetic core as'the
plates of a capacitor for starting, running, power factor
correcti~n and other.uses in motors and.generators.
Thi9 integral construction is feasible because of the
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txemendously increased interlamination area witll the
thinner core material. Both stator cores and rotor cores can
be constructed with an integral dry capaci.tor. `
The combined laminated core and capacitor has multiple
insulated turns of magne~ic amorphous metal ribbon of
relatively long length,and is comprised of a pair o~ super-
lmposed or parallel ribbons and alternating insulating layers
which are edge-mounted and wound helically or which are wound
spirally like a roll of tape. An energizing winding is
magnetically coupled with the amorphous metal larninated core,
and at least part oE the winding is also conductively or
electrically connected to the pair of amorphous metal ribbons
separated by insualting layers, which function as a
capacitor in circuit relationship wlth the winding. Each
ribbon is capacitively coupled to the other ribbon on either
side so that the t.otal capacitance is proportional to the
total interlaminar area. The magnetic core structure can be
composed of mult:iple helical cores concentric with one another,
or multiple sp:iral cores axially aligned with one another,
each core having a dual function as an isolated capacitor.
The preferrea embodiment is a single phase permanent
split-capacitor motor with a laminated stator core in
which the two superimposed amorphous metal ribbons are
helically wound and permanently electrically connec~ed to
function as`a dr~; capacitor in series circuit relationship
with the auxiliary winding. An3ther embodiment is a poly-
phase motor having plural concentric h~lical stator cores
each magnetically coupled to the stator winding and also
electrically connected across the windings to ~unction
as isolated power factor correction capacitors. Utilization
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of the coxe interlaminar capacitance results in cost,
wei~ht, and space savings.
Brief Descr_~tion_of the Dra~-ln~
FIG. 1 .is a slmplified diagram of a prior art permanent-
split-capacitor motor with separate capacitor;
FIG. 2 is an expanded partial view of a two-in-hand
helically wound amorphous metal core having a dual function
as a capacitor and showing connections to the auxiliary winding;
FIG. 3 is a fragmentaxy cross section of the assembled
laminated coxe structure of FIG. 2;
FIG. ~ i~, a perspective view of a slotless motor with a
helical stator core serving as an integral capacitor;
FIG~ 5 shows an edge-wound stator aore made from toothed
amorphous me-tal ribbon;
FIG. 6 is a partially expanded perspective view of a
two-in-hand spirally wound amorphous metal stator or rotor
- core and integral capacitor;
FIG. 7 is a circuit diagram of a prior art polyphase
motor with separate power factor correction capacitors;
FIG. 8 is a ragmentary cross section of the slotl~ss
motor of FIG. 4 with plural edge-wound cores and i~tegral
capacitors; and
FIG. 9 is a fragmentary cross section of a rotor with
multiple spirally wound cores and integral capacitors.
~ he Preferred Embodiments
To achieve a rotating magne~lc field ln a single phas~
electric motor it is necessary to have a phase difference
between the motor currents in two windings, and the most
efficient way to accomplish this is to use a capacitor.
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The ob]ective is to produce a current in the auxiliary
or start winding which is 90 displaced in phase from the
current in the maill wlnding, and this results in a uniform,
balanced rotating field. There are three basic types of
single phase motors with capacitors, and the permanent
split-capacitor motor is the most e:E:Eicient and ordinarily
the most expensive. The prior art motor in FIG.,l has
a separate, ex-ternal capacitor 11 in series with auxiliary
stator winding 12, and the capacitor is permanently
connected so that it is in the auxiliary winding circuit
for starting and then remains for running to achieve good
eficiency and improved performance. The pulsating flux
of double frequency which is characteristic of si.ngle
phase motors is reduced. The main or running winding at
right angles to the auxi:liary winding is indicated at 13,
and ~he rotor and shaft at 14 and ].5. Other types of
single phase motors with capacitors are the capacitor-
start motor, which has high starting torque but has a
swi.~.ch to disconnect the capacitor and start winding after
. getting up to speed, and the capacitor-start capacitor-
run motor which switches.betwèen two.values of capacltance,
high for starting and low for running. There is ~ large .:
class of motors where.'efficiency is important and the
permanent split-capacitor motor is the best cholce, such
5 as aompressors and fans in refrigerators and air condi~ioners.
The permanent split-capacitor motor illustrated in
FIGS. 2-4 has a stator core,made of magnetic amorphous
metal ribbon which is specially cons~ructed to also be
a dry capacitor. This invention permits utilization of
stator core material which is required for the magn~tic
circuit to serve also as the pla~ material of an integral
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capacitor, resulting in cost, weight, and space savings.
The lam:inated stator core :is magnetically coupled with
the main and au~iliary stator wlnclings to generate a
rotatLng magne~ic fielcl in the a~.r gap, ancl the ribbon
core material in its dua:L lmction as a capacitor is
conductively or el.ectrlcally eonnected in series circuit
relationship with the auxiliary winding. The total
capacitance is more than enough or is adequate to provide
proper phase shift and excellent power factor in such a
motor. One of the previously ass~lmed disadvantages of
using amorphous metal alloys in electric motors has
been the large number of laminations that have been
required due to the inhererltly thin nature of this material.
Ribbons of about 1.5 to 2 mils is the maximum thickness
attainable in the forseeable future. This constraint is
a result of the rapid cooling rate or quench rate of 105
to 108 C/sec. that is required to prevent
formation of crystal structure. In spite of this thickness
ltm~tation, a number of ways are known for handling such
material, and once assemb~dsuch a core has a significant
interlaminar area. The capacitance of a capacitor is
directly proportional to the area of the plates and
to the dielectric constant of the insulator separating
the plates, and is inversely p~oportional to the distance
between plates. There is not too much that can be done
about the dielectric constant and distance between plates,
but the plate area is many times greater where the
core laminations are made of very thin amorphous metal
rather than the much thicker punched steel skrip.
FIG. 2 shows to an expanded scale a few turns of an
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edge-wound or helical laminated core made essentially of a
pair of superimposed magnetic amorphous metal ribbons 16 and 17
of relatively ]ong length that alternate with insulating
layers 18 and 19 and are wound hellcally similar to a Slinky E~
spring toy. The capacitor connections are made to the ends of
' amorphous helices 16 and 17. Viewed as a capacitor, this
structure can be called a dry parallel-plate capacitor. When
the core is assen~led and successive turns are contacting as
in FIG. 3, each ribbon is capacitively coupled to the other
ribbon on either side and the total capacitance is proportional
to the totaI interlaminar area. One way of fabricating the
helical stator core is to coat one surface of Fe80B20 alIoy
ribbon with varnish, and then take two such ribbons and wind ''
them helically two~in-hand. Alternatively, one amorphous metal
ribbon can he coated with varniæh on both sides and wound
two-in-hand with a plain ribbon. Other dielectrics such as
Mylar R polyester film'can be employed.
The'amorphous metal can be any of the magnetic alloys, and
many different compositions for magnetic applications are '
presently known having iron, nickel, or cobalt, or any combina-
tion of these three metals,'with boron and possibly phosphorous.
~he'preferred composition because of its high induction
characteristics is the Fe80B20 alloy, and another suitable
amorphous metal is Fe40Ni40P14B6 or the variation of this
material sold as METGLAS(~ Alloy Ribbon 2826MB by ALlied
Chemical Corporation. In power frequency applica~ions these
materials are capable of exceeding to a substantial degree the
properties of conventional Fe--Ni, Fe-Co, and Fe-Si alloys, and
` to offer a substan~ial cost saving. The Fe80B20 alloy ribbons
have one-fourth the losses, at a given induction, for
sinusoidal flux, of the best oriented Fe-Si sheet steel.
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The saturation magnetization o~ ~e80B20~ however, is
lower than that of maTIy commonly used iron-based magnetic
materials Since the stri.p is very thin, the eddy current
losses are smallel- than Eor convellt:ional. laminations.
The slotle.ss permanen~ split-capacitor (induction or other
type) motor with int~gral capacitor in FIG . 4 has the stator
windings 20 lying in the air gap be-tween the unsolotted helical
stator core 21 and rotor structure 22. The combined core
and dry capacitor is made from amorphous metal tape
o~ uniform width as shown in FIG. 2 and is a simple
cylindrical shell. Such a shape is ideally suited to
manufacture wi.th continuous helical strips of magnet.ic
material. The main and auxiliary windings are displaced
from one another as in a ~wo-phase machine and can be
of the single layer concentric type. The dual function
stator core and capacitor can be made from toothed
slotted amorphous metal ribbon as shown in FIG. 5,
and in this case the motor windings are inserted in~o
the s~ator slots. The toothedStrip of motor laminations,
either curled or naturally straight, can be manufac~ured
d~ree~ly from a~orphous me~al alloy melt in one process
as described and ~laimed in ~nl~ed States Patent 4,155,397
issued May 22, 1979 by V.B. Honsinger and R.E. Tompkins,
entitled "Method and Apparatus for Fabricating Amorphous
Metal Laminations for Motors and Transformers", and assigned
to the same assignee as this invention.
To demonstrate that an assembled helical core
has a significant interlaminar areaj an example will be
given. If a standard four horsepower hermetic compressor
3a motor with a 6" outer di.ameter, 3" inner diameter, and a 5"
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length were fabricated in this fas~ion from 1.5 mil
materl~l having a 0.5 rnil insulation thickness, 2250 layers
with a total area of 35,000 in.~ would be,provided
assuming a 90% packing factor and 20% slot area.
Chooslng a varnish w~th dielectri.c constant of 4 results
in a total capacitance of 64 microfarads which is more
than enough.to provide proper phase shift and excellent
power factor in such a motor.
'Another technique for building magnetic cor.es
. lO from long continuous strips o amorphous metal coated
, ' w~th insulation is to wind -the material spirally like
a roll of tape. The stator. or rotor core in FIG. 6
is wound two-in-hand spirally, and every turn at a successively
' greater diameter has the four-layered cross sec~ion of
~IG, 3 comprised of alternatin~ metal strips and insulating
layers. The two parallel metal stri.ps 25 and 26 are the
capacitor plates, and the insulating layers 27 and 28 between
are the capacitor dielectric. Metallic gl.ass material is
strong and ductile and in practice'it is possible to pull the
strips during winding and produce a tightiy wound cylindrical
or d'isk-shaped core structure with a high packing ~actor.
Electrical connections to the.pair of spirally wound capacitor
plates are made at the ends of the.metal strips, which can be
. of uniform width or slotted. The insulating layer is coated
onto the ribbon or ls a separate film of material, and for
some applica~ions may be an oxide fol~ed on the surface of the
ribbon.
. A conventional prior art polyphase induction motor 30
is illu~trated in FIG. 7 with three power factor correction
capacitors 31 across the mo~or terminals. Plural
isolated inte~ral capacitors are realized by using plural
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amorphous metal cores or core sections that are concentric
with one another or axially aligned with one another.
Another embodiment of the inventioIl in FI~ 8 is a
slotless motor similar t.o FIG. 4 but with three concentric
helical cores 32, 33 and 34~ The three core sections are
magnetically coupled with the stator w:indings but are
electrically isolated in their functions as power factor
correction capacitors. The three capacitors are connected
across the three different pairs of stator windings
the same as in FIG. 7. Core sections 32, 33 and 34
are identical to one another and assembled as taught
in FIGS. 2 and 3, and can be made ~rom narrower widths
of amorphous metal tape. Ribbon widths of one half inch
are available con~ercially at present and wider widths
have been reported.
Similar schemes are employed to utilize the
interlaminar capacitance of an amorphous metal rotor core.
FIG, 9 depicts a relatively long magnetic core structure
composed of two (or more~ axially aligned rotor core
sectiQns 35 and 36 which can be identical to one another
and ~ound spirally as taught in FIG. 6. The dry
capacit~r integral with each core section is electrically
connected in circuit relationship with rotor winding 37
or a portion of the rotor winding, or can be coupled to the
outside by means of slip rings. It is also possible
to construct the stator core with multiple spirally wound
and axially aligned core sections. Disk type motors
can have spiral.ly wound amorphous metal cores with
radial slots at one or both sides of the core to receive
the ~indings, and these can be made with an integral
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,capacitor. ~ multiple disk amorphous metal motor is
disclosed and claimed in ~Canadian application S.N. 299,981
Eiled March 29, 1978 - by W.R. Oney, entitled "High
Power Density Brushless DC Motor", and assigned to the same,
assignee.
The invention as broadly defined has application to
generators and other types of motors than those that
have'been mentioned specifically. The capacitor integral
with the amorphous metal mag~etic circuit may in some
circumstances find utility to provide commutating capacitance '
in an associated solid state converter or to smooth
rectified currents. The prime consideration, however, is
the magnetic area needed to carry the magnatic flux and
the amount of available capacitance depends on the inter-
laminar capacitance of this magnetic circuit. The reduction
in costj weight and space by having the magnetic core
serve in a dual'capacity is compounded with the low
losses and potential'low cost of amorphous metal magnetic
materials. '
While the invention has been particularly shown ,and
described with reference to several preferred embodiments
thereof, it will be understood,by those skilled in the art
that the foregoing and other changes in'form and details
may be made therein without departing from ~he spirit and
scope o, the in~ention.
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