MOTOR BASED ON THE DIFFERENCE OF PHASE IN THE MAGNETIZATION OF THE INNER
AND OUTER PARTS OF AN IRON CORE.
It is well known that if a magnetic core, even if laminated or
subdivided, be wound with an insulated coil and a current of electricity
be directed through the coil, the magnetization of the entire core does
not immediately ensue, the magnetizing effect not being exhibited in all
parts simultaneously. This may be attributed to the fact that the action
of the current is to energize first those laminae or parts of the core
nearest the surface and adjacent to the exciting-coil, and from thence
the action progresses toward the interior. A certain interval of time
therefore elapses between the manifestation of magnetism in the external
and the internal sections or layers of the core. If the core be thin or
of small mass, this effect may be inappreciable; but in the case of a
thick core, or even of a comparatively thin one, if the number of
alternations or rate of change of the current strength be very great,
the time interval occurring between the manifestations of magnetism in
the interior of the core and in those parts adjacent to the coil is more
marked. In the construction of such apparatus as motors which are
designed to be run by alternating or equivalent currents--such as
pulsating or undulating currents generally--Mr. Tesla found it desirable
and even necessary to give due consideration to this phenomenon and to
make special provisions in order to obviate its consequences. With the
specific object of taking advantage of this action or effect, and to
render it more pronounced, he constructs a field magnet in which the
parts of the core or cores that exhibit at different intervals of time
the magnetic effect imparted to them by alternating or equivalent
currents in an energizing coil or coils, are so placed with relation to
a rotating armature as to exert thereon their attractive effect
successively in the order of their magnetization. By this means he
secures a result similar to that which he had previously attained in
other forms or types of motor in which by means of one or more
alternating currents he has produced the rotation or progression of the
magnetic poles.
This new mode of operation will now be described. Fig. 72 is a side
elevation of such motor. Fig. 73 is a side elevation of a more
practicable and efficient embodiment of the invention. Fig. 74 is a
central vertical section of the same in the plane of the axis of
rotation.
[Illustration: FIGS. 72 and 73.]
Referring to Fig. 72, let X represent a large iron core, which may be
composed of a number of sheets or laminae of soft iron or steel.
Surrounding this core is a coil Y, which is connected with a source E of
rapidly varying currents. Let us consider now the magnetic conditions
existing in this core at any point, as _b_, at or near the centre, and
any other point, as _a_, nearer the surface. When a current impulse is
started in the magnetizing coil Y, the section or part at _a_, being
close to the coil, is immediately energized, while the section or part
at _b_, which, to use a convenient expression, is "protected" by the
intervening sections or layers between _a_ and _b_, does not at once
exhibit its magnetism. However, as the magnetization of _a_ increases,
_b_ becomes also affected, reaching finally its maximum strength some
time later than _a_. Upon the weakening of the current the magnetization
of _a_ first diminishes, while _b_ still exhibits its maximum strength;
but the continued weakening of _a_ is attended by a subsequent weakening
of _b_. Assuming the current to be an alternating one, _a_ will now be
reversed, while _b_ still continues of the first imparted polarity. This
action continues the magnetic condition of _b_, following that of _a_ in
the manner above described. If an armature--for instance, a simple disc
F, mounted to rotate freely on an axis--be brought into proximity to the
core, a movement of rotation will be imparted to the disc, the direction
depending upon its position relatively to the core, the tendency being
to turn the portion of the disc nearest to the core from _a_ to _b_, as
indicated in Fig. 72.
[Illustration: FIG. 74.]
This action or principle of operation has been embodied in a practicable
form of motor, which is illustrated in Fig. 73. Let A in that figure
represent a circular frame of iron, from diametrically opposite points
of the interior of which the cores project. Each core is composed of
three main parts B, B and C, and they are similarly formed with a
straight portion or body _e_, around which the energizing coil is wound,
a curved arm or extension _c_, and an inwardly projecting pole or end
_d_. Each core is made up of two parts B B, with their polar extensions
reaching in one direction, and a part C between the other two, and with
its polar extension reaching in the opposite direction. In order to
lessen in the cores the circulation of currents induced therein, the
several sections are insulated from one another in the manner usually
followed in such cases. These cores are wound with coils D, which are
connected in the same circuit, either in parallel or series, and
supplied with an alternating or a pulsating current, preferably the
former, by a generator E, represented diagrammatically. Between the
cores or their polar extensions is mounted a cylindrical or similar
armature F, wound with magnetizing coils G, closed upon themselves.
The operation of this motor is as follows: When a current impulse or
alternation is directed through the coils D, the sections B B of the
cores, being on the surface and in close proximity to the coils, are
immediately energized. The sections C, on the other hand, are protected
from the magnetizing influence of the coil by the interposed layers of
iron B B. As the magnetism of B B increases, however, the sections C are
also energized; but they do not attain their maximum strength until a
certain time subsequent to the exhibition by the sections B B of their
maximum. Upon the weakening of the current the magnetic strength of B B
first diminishes, while the sections C have still their maximum
strength; but as B B continue to weaken the interior sections are
similarly weakened. B B may then begin to exhibit an opposite polarity,
which is followed later by a similar change on C, and this action
continues. B B and C may therefore be considered as separate
field-magnets, being extended so as to act on the armature in the most
efficient positions, and the effect is similar to that in the other
forms of Tesla motor--viz., a rotation or progression of the maximum
points of the field of force. Any armature--such, for instance, as a
disc--mounted in this field would rotate from the pole first to exhibit
its magnetism to that which exhibits it later.
It is evident that the principle here described may be carried out in
conjunction with other means for securing a more favorable or efficient
action of the motor. For example, the polar extensions of the sections C
may be wound or surrounded by closed coils. The effect of these coils
will be to still more effectively retard the magnetization of the polar
extensions of C.