Improvements in Alternating Current Motors.
Year: 1897

page_text: Date of Application, 15th Apr., 1897-Accepted, 5th June, 1897
Improvements in Alternating Current Motors.
We, OTTO TITUS BLÁTHY and KOLOMAN KANDÓ, both of Hauptgasse 73,
Budapest II., Hungary, Engineers, do hereby declare the nature of this invention
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :-
In motors with toothed armatures, the tooth-crowns of the stator and of the rotor
meet opposite each other at certain points of the periphery, dependent on the spacing
of the teeth, while at other points the crown of the tooth of one part covers the
space between the teeth of the other part, which circumstance causes an inequality
in the magnetic resistance of the air space between the stator and rotor, and
consequently also in the distribution of the magnetism.
In consequence of this magnetic inequality the rotor tends to take up certain
positions, or to come to rest at so called dead-points.
This circumstance is very detrimental, more particularly with such motors as
have only a small turning-moment because the starting thereof requires a considerably
greater current supply than if no such dead point existed; it even frequently
prevents the starting of the motor. In order to obviate these dead points, some
makers construct armatures with closed grooves, the crowns of the teeth being made
so broad as to constitute a practically continuous surface covering the whole
periphery. This arrangement however only has the desired effect if the iron surface
covering the groove is of great thickness, and this can only be done at the expense
of other good qualities of the motor, that is to say, the covering the grooves with
a thick layer of iron increases the magnetic dispersion and consequently reduces on
the one hand the torque of the motor and on the other hand increases the phase-shift
of the current.
Our present invention relates to a different method of obviating the said dead
points, and it consists in making the grooves of the stator a, Figure 1 of the
accompanying drawing, or of the rotor b, Figure 2 or of both the stator and the
rotor, obliquely to axial line or to the generatrices c c of the cylindrical surface,
instead of parallel thereto as has heretofore been done.
Various arrangements of such oblique grooves are shewn in the developed
peripheries at Figures 3 to 8 of the drawing.
By this arrangement, at every position of the rotor, there is situated over the
crowns of its teeth the same total amount of surface of the crowns of the stator's
teeth, and consequently the resistance of the air space between the stator and rotor
is uniformly distributed over the entire surface, so that no dead point can be
produced in the motor.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
In single and poly-phase alternating current motors, constructing the grooves of
the stator or of the rotor, or of both, obliquely both as regards each other and as
regards the axis of the machine, substantially as described with reference to the
drawing.
ABEL & IMRAY,
Agents for the Applicants.