CA1125344A - Amorphous metal electric motor with integral capacitor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An electric machine with a laminated stator or rotor core made of magnetic amorphous metal ribbon takes advantage of the increased lamination area due to the inherent thinness of the material to utilize the laminations as the plates of a capacitor for starting, running, and/or power factor correction. Two amorphous metal ribbons with alternate insulating layers are wound two-in-hand either helically or spirally to fabricate the cores. Additional amorphous metal cores can be provided and connected as additional capacitors. The preferred embodiment is a single phase permanenet split-capacitor motor with integral capacitor.

Description

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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 -1 ~

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. RD-10446 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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RD-104~6 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 ... . . .. .

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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~D-10446 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 _g _ ~fZ,53~
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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 -lQ

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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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Claims (12)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. An electric machine comprising: a stator and a rotor mounted for relative rotation at least one of which has a laminated magnetic core that has a dual function as a capacitor and is constructed of multiple insulated turns of magnetic amorphous metal ribbon of relatively long length; an energizing winding on and magnetically coupled with said laminated core;
at least part of said winding also being electrically connected to the ribbon such that said insulated turns of amorphous metal ribbon are said capacitor which is in circuit relationship with said winding.

2. An electric machine comprising: a stator and a rotor mounted coaxially for relative rotation at least one of which has a laminated magnetic core that has a dual function as a capacitor and is constructed of multiple insulated turns of a pair of superimposed magnetic amorphous metal ribbons of relatively long length separated by alternating insulating layers; an energizing winding on and magnetically coupled with said laminated core; at least part of said winding also being electrically connected to said pair of amorphous metal ribbons separated by insulating layers which function as said capacitor in circuit relationship with said winding.

3. The electric machine of claim 2 wherein said pair of ribbons both have a thickness of about 2 mils and wherein said pair of ribbons are permanently connected in circuit relationship with at least part of said winding.

4. The electric machine of claim 2 wherein said pair of amorphous metal ribbons separated by insulating layers are edge-mounted and wound helically in said laminated core.

5. The electric machine of claim 2 wherein said pair of amorphous metal ribbons separated by insulating layers are wound spirally so that successive turns have a larger diameter in said laminated core.

6. The electric machine of claim 4 or claim 5 further including at least one additional laminated core comprised of multiple turns of another pair of magnetic amorphous metal ribbons separated by insulating layers; at least part of said winding being magnetically coupled with said additional laminated core and also electrically connected to said other pair of amorphous metal ribbons separated by insulating layers which function as another capacitor in circuit relationship with said winding.

7. A single phase electric motor with an integral capacitor comprising: a stator and a rotor mounted coaxially for relative rotation with an air gap therebetween; said stator having a laminated magnetic core that is comprised of multiple turns of a pair of parallel magnetic amorphous metal ribbons separated by alternating insulating layers; a main stator winding and an auxiliary stator winding on and magnetically coupled with said laminated core and producing an air gap magnetic field for rotating said rotor; said auxiliary winding further being electrically connected in series circuit relationship with said pair of amorphous metal ribbons separated by insulating layers which function as the capacitor in an auxiliary winding circuit.

8. The electric motor of claim 7 wherein said pair of amorphous metal ribbons separated by insulating layers are edge-mounted and wound helically in said laminated core.

9. The electric motor of claim 7 wherein said pair of amorphous metal ribbons separated by insulating layers are wound spirally so that successive turns have a larger diameter in said laminated core.

10. An electric motor with an integral capacitor comprising: a stator and a rotor mounted coaxially for relative rotation with an air gap therebetween; said stator having a laminated magnetic core that is comprised of multiple insulated turns of a pair of parallel magnetic amorphous metal ribbons separated by insulating layers; a stator winding on and magnetically coupled with said laminated core and producing an air gap magnetic field for rotating said rotor; said stator winding also being electrically connected in circuit relationship with said pair of amorphous metal ribbons separated by insulating layers which function as said capacitor to effect power factor correction.

11. The electric motor of claim 10 wherein said pair of amorphous metal ribbons separated by insulating layers are edge-mounted and wound helically in said laminated core; and at least one additional laminated helical core concentric with said first-mentioned core and constructed in similar fashion from another pair of helically wound magnetic amorphous metal ribbons separated by insulating layers; said stator winding being magnetically coupled with said additional helical core and also electrically connected in circuit relationship with said other pair of amorphous metal ribbons separated by insulating layers which function as an additional capacitor for power factor correction.
12. The electric motor of claim 10 wherein said pair of amorphous metal ribbons separated by insulating layers are wound spirally so that successive turns have a larger diameter in said laminated core; and at least one additional laminated spiral core axially aligned with said first mentioned core and constructed in similar fashion from another pair of spirally wound magnetic amorphous metal ribbons separated by insulating layers; said stator winding being on and magnetically coupled with said additional spiral core and also electrically

Claim 12 continued:
connected in circuit relationship with said other pair of amorphous metal ribbons separated by insulating layers which function as an additional capacitor for power factor correction.