Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to hysteresis machines
and more specifically to a hysteresis machine having a
rotor comprising a coil of amorphous metal tape which
has been annealed to increase its coercivity.
Hysteresis machines, such as motors, are
well known selt-starting synchronous machines employing
the hysteresis properties of the rotor. The driving
force is provided by the rotating stator field which
m~gnetizes the rotor. If the power supply
1~ frequency remains constant, rotor speed remains
constant even if there are changes, within limits,
in applied voltage, ambient temperature and attached
torque load. Moreover, the motor speed is not
affected by manufacturing variations, within pre-
determined limits. Consequently, the hysteresis
synchronous machine can be used in virtually any
applciation requiring synchronous motors.
Torque developed by the motor is proportional
to area of the rotor material hysteresis loop, while
exciting current for the motor is determined by coercive
force of the rotor material. Thus, a coercive
force should be selected for a particular hysteresis
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machine application which balances exciting current
against the available torque for the machine.
The cost of hysteresis motor rotor material
is several dollars per pound at the present time.
Use of less expensive material for the hysteresis
motor would be desirable. Amorphous metals have
recently become available which have good magnetic
properties and have a potential cost of one-tenth
at of metals now used for hysteresis motors.
Amorphous metals, however, are not available in a
form convenient for manufacture of conventional
laminated rotors. Thus the metal is in the form of
a tape which is about 0.005 to 0.003 inch thick and
in widths of up to about 2 inches. The amorphous
metal tape also has very low coercive force, of the
order of from 0.01 to 0.1 oersteds.
Amorphous metal taps having magnetic
properties desired for application to electric machines
are disclosed in United States Letters Patents,
3,856,513, dated December 24, 1974, in the name of
Chen et al; 3,881,542, dated May 6, 1975 in the
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RD-10,232
name of Polk et al; 4,052,201, dated October 4, 1977, in the
name of Polk et al; 4,059,441, dated November 22, 1977, in the
name of Ray et al. and 4,067,732, dated January 10, 1978, in
the name of Ray. A survey of metal glass technology is given
in the article "Metallic Glasses" by John J. Gilman, appearing
in Physics Today, May 1975, pages 46 to 53. Some attempts are
being made to exploit the advantages of the properties of
these metal tapes, for example, for acoustic devices as shown
in United States Letters Patent 3,838,365.
An object of the present invention is to provide a low
cost hysteresis machine which employs a coil of amorphous metal
tapes as the rotor, the coil being annealed to substantially
increase its coercive force.
- Brief Descri tion of the Present Invention
P
In accordance with the present invention, a hysteresis
machine rotor is made of a coil of amorphous metal tapes. The
rotor can be wound in either a single continuous strip or a
plurality of parallel overlapping strips, since the machine is
a synchronous machine and there are no induced rotor currents.
Several substantially identical coils may be wound side by side.
The amorphous metal tapes are annealed after winding into the
coil form,at a suitable temperature for a suitable length of
time, up to the point where crystallization of the alloy starts
and its coercive force begins to increase. By annealing the
tapes, coercive force values ranging from 0.02 to 100 oersteds
can be obtained, making the coil useful for hysteresis machine
applications.
Brief Description of the Dr~ s
FIGURE 1 is a cross-sectional view taken along the axis
of a schematically illustrated hysteresis motor fabricated in
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accordance with the present invention.
FIGURE 2 is a cross-sectional view of FIGURE 1 taken
across the section line 2-2 in FIGURE l.
FIGURE 3 is a cross-sectional view of another embodiment
of the hysteresis motor of the present invention.
Detailed Description of the Drawings
Referring now to FIGURES 1 and 2, there is schematically
illustrated therein a typical hysteresis motor (without
housing, supports, or the like) which may be of a general
configuration well known in the art. The basic motor structure
shown comprises a conventional stator 10 which includes a
stack of conventional laminations containing stator winding
slots, such as slots 11 and 12, which receive a conventional
stator winding 13 operable to produce a rotating field.
A rotor 2Q, described more fully hereinafter,
is provided with a shaft 21 which may be carried in suitable
bearings 22 and 23 which are fixed with respect to the
housing (not shown) supporting rotor 20 and stator 10.
The outer surface of rotor 20 is separated from the
inner surface of stator 10 by a fixed radial gap 14.
In accordance with the present invention, rotor
20 is formed of a plurality of coils of an amorphous metal
tape having a thickness of about 0.002 inch, each coil
comprising a portion of rotor length of about one inch.
Each coil may be formed of a single strip of tape wound on
shaft 21 such that its flat sides are parallel to shaft axis
24 and may have an inner diameter of one-half inch and an
outer diameter of two inches, so as to comprise 375
turns of 0.002 inch thick tape. If a larger power
factor is desired, two or more elongated strips of tape
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laid one on top of another 50 as to introduce capacitance
into the rotor circuit may be simultaneously wound to form the
coil 20. This capacitance introduction by interwinding amorphous
metal tapes in a motor is described and claimed in United States
patent 4,211,944 issued July 8, 1980 to T.R. Haller and assigned
to the present assignee.
FIGURE 1 illustrates five individual coils 30 to 34
which are disposed parallel to one another for forming a rotor
having a length greater than the available width of a single
tape. Since the amorphous metal tape is coated with an
electrically insulating oxide film, side-by-side contact
between adjacent ones of coils 30-34 does not result in an
electrical path therebetween. Rotor eddy currents are thereby
attenuated, resulting in reduced rotor eddy current losses.
Af-ter the rotor 20 has been formed in its coil shape and the
ends of the coils have been secured to prevent unraveling, the
entire rotor may be annealed in order to increase the coercive
force of the rotor.
The coercive force of the metal tapes forming rotor
20 before annealing may be of the order of about 0.01 oersted.
By annealing the tapes, the coercive force can be increased
to at least about 0.02 oersted and up to approximately 100
oersteds. As a specific example, when the tape comprises the
alloy Fe40Ni40P14B6, we have measured the starting coercive
force of the coil to be about 0.015 oersted after the coil is
formed. After this coil is annealed for 120 minutes at 390C,
we have found that the coercive force of the material increases
to about 50 oersteds. Even higher coercive force can be obtained
by longer heating and/or by using a higher annealing
temperature. Saturation magnetization of this alloy
-- 5 --
B
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is about 8,000 gauss. Other alloys using higher or lower
saturations could also be used.
Other alloy materials having other saturation magnetiza-
tions also experience an increase in coercive force when they
are partly crystallized. Thus, the alloy Fe40Ni40B20 has a
saturation magnetization of about 10,000 gauss while the
alloy Fe80B20 has a saturation magnetization of about 16,000
gauss. These amorphous metal strip alloys, when partially
- crystallized, show about the same increase in coercive force -;
as Fe4oNi4opl4B6
The increase in coercive force during annealing is a
general phenomenon exhibited by amorphous metal alloys of the
( )80~10(G)20+lo where TM is any of the
transition metals and their alloys Fe, Co and Ni, and G is
the glass forming atoms usually comprising the metalloids P, B,
C, S, Si and Al.
In the embodiment of FIGURE 3, which is a view similar
to that shown in FIGURE 2, each of the coils 30-34 in a rotor
such as illustrated in FIGURE 1 comprises a pair of amorphous
metal tapes 40 and 41 wound together about longitudinal axis
24 such that a flat side of tape 40 contacts a flat side of
tape 41, and the flat sides o~ both tapes are parallel to
axis 24. The remaining portion of the structure shown in
FIGURE 3 is identical to that shown in FIGURE 2, with like
numerals designating like components.
Thus, in accordance with the present invention, the -
magnetization of a machine rotor is controlled by suitable
choice of alloy used in the rotor, and the coercive force of the
alloy can be controlled by heat treatment to yield a high
quality, low cost rotor structure for a hysteresis machine.
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Although the present invention has been described in
connection with only certain preferred features thereof, many
variations and modifications will now become apparent to those
skilled in the art. It is, therefore, to be understood that
the appended claims are intended to cover all such variations
and modifications as fall within the true spirit of the
invention.
