04.14.08
The diagram of Fig
The diagram of Fig. 68 is merely intended to illustrate the principle
involved. In the practical construction of magneto generators more
than one bar magnet is used, and, in addition, the conductors in the
armature are so arranged as to include a great many loops of wire.
Furthermore, the conductors in the armature are wound around an iron
core so that the path through the armature loops or turns, may present
such low reluctance to the passage of lines of force as to greatly
increase the number of such lines and also to cause practically all of
them to go through the loops in the armature conductor.
Armature. The iron upon which the armature conductors are wound is
called the _core_. The core of an ordinary armature is shown in Fig.
69. This is usually made of soft gray cast iron, turned so as to form
bearing surfaces at _1_ and _2_, upon which the entire armature may
rotate, and also turned so that the surfaces _3_ will be truly
cylindrical with respect to the axis through the center of the shaft.
The armature conductors are put on by winding the space between the
two parallel faces _4_ as full of insulated wire as space will admit.
One end of the armature winding is soldered to the pin _5_ and,
therefore, makes contact with the frame of the generator, while the
other end of the winding is soldered to the pin _6_, which engages the
stud _7_, carried in an insulating bushing in a longitudinal hole in
the end of the armature shaft. It is thus seen that the frame of the
machine will form one terminal of the armature winding, while the
insulated stud _7_ will form the other terminal.
[Illustration: Fig. 69. Generator Armature]
Another form of armature largely employed in recent magneto
generators is illustrated in Fig. 70. In this the shaft on which the
armature revolves does not form an integral part of the armature core
but consists of two cylindrical studs _2_ and _3_ projecting from the
centers of disks _4_ and _5_, which are screwed to the ends of the
core _1_. This =H= type of armature core, as it is called, while
containing somewhat more parts than the simpler type shown in Fig. 69,
possesses distinct advantages in the matter of winding. By virtue of
its simpler form of winding space, it is easier to insulate and easier
to wind, and furthermore, since the shaft does not run through the
winding space, it is capable of holding a considerably greater number
of turns of wire. The ends of the armature winding are connected, one
directly to the frame and the other to an insulated pin, as is shown
in the illustration.
[Illustration: Fig. 70. Generator Armature]
[Illustration: Fig. 71. Generator Field and Armature]
The method commonly employed of associating the pole pieces with each
other and with the permanent magnets is shown in Fig. 71. It is very
important that the space in which the armature revolves shall be truly
cylindrical, and that the bearings for the armature shall be so
aligned as to make the axis of rotation of the armature coincide with
the axis of the cylindrical surface of the pole pieces. A rigid
structure is, therefore, required and this is frequently secured, as
shown in Fig. 71, by joining the two pole pieces _1_ and _2_ together
by means of heavy brass rods _3_ and _4_, the rods being shouldered
and their reduced ends passed through holes in flanges extending from
the pole pieces, and riveted. The bearing plates in which the armature
is journaled are then secured to the ends of these pole pieces, as
will be shown in subsequent illustrations. This assures proper
rigidity between the pole pieces and also between the pole pieces and
the armature bearings.
The reason why this degree of rigidity is required is that it is
necessary to work with very small air gaps between the armature core
and its pole pieces and unless these generators are mechanically well
made they are likely to alter their adjustment and thus allow the
armature faces to scrape or rub against the pole pieces. In Fig. 71
one of the permanent horseshoe magnets is shown, its ends resting in
grooves on the outer faces of the pole pieces and usually clamped
thereto by means of heavy iron machine screws.
With this structure in mind, the theory of the magneto generator
developed in connection with Fig. 68 may be carried a little further.
When the armature lies in the position shown at the left of Fig. 71,
so that the center position of the core is horizontal, a good path is
afforded for the lines of force passing from one pole to the other.