A New or Improved Method of Regulating or Varying the Speed and or Twisting Moment of Electro-motors, and Apparatus therefor.
Year: 1894

page_text: Date of Application, 14th Mar., 1894
Complete Specification Left, 14th Dec., 1894-Accepted, 9th Mar., 1895
PROVISIONAL SPECIFICATION.
A New or Improved Method of Regulating or Varying the Speed
and or
Twisting Moment of Electro-motors, and Apparatus
therefor.
I, JOHN GRICE STATTER, of 68 Victoria Street, Westminster, in the County
of Middlesex, Electrical Engineer, do hereby declare the nature of this invention
to be as follows:-
:
My invention has reference to electro motors designed for use with direct
currents having approximately constant electromotive force and its objects are
to enable the motor to be run at two speeds and to give out for short periods about
twice the twisting moment on the shaft at the lower speed that is given out at the
higher. My invention is specially applicable in the propulsion of vehicles and in
the lifting or hauling of loads.
In order to attain these objects I take a frame-work of a machine, that of any
of the ordinary types of direct current machines will answer my purpose, and I
provide its armature core with two distinct windings (as for example in the
manner set forth in the Complete Specification filed in pursuance of my application
for Letters Patent No. 6528 of the year 1893) each having the same number of
active turns, and which windings can be placed at will either in series or in
parallel. I wind the field magnets as in an ordinary shunt wound machine; but,
in addition to the ordinary shunt winding suitable for the motor when used with
the armature windings in parallel, I employ upon the field an extra winding
(either series or shunt) to be switched into circuit as required, and to be used in
the manner hereafter to be described.
A motor wound as above described and put to work on a circuit of constant
electromotive force will run at two speeds one being about half that of the other
according as the armature windings are in series or parallel.
Under existing conditions the work given out by the motor at the lower speed
would be about half that given out at the higher speed (with the same field
excitation) since in order to keep within sparking limits the current with the
arinature windings in series must not exceed half that which is passed when the
armature windings are in parallel.
Now I usually require to increase my twisting moment when running at the
lower to nearly double that required at the higher speed; and I require therefore
to pass at the lower speed the full current that passes through. the motor at the
higher speed. In order therefore that I may not exceed the sparking limit when
the motor is working at the slower speed I switch into circuit during the time that
the armature windings are in series the extra winding on the field magnets; and
this provides extra excitation which prevents sparking during the lower speed,
that is to say, during the time that the armature windings are pressed with twice
their normal current.
When the extra winding on the field is not in circuit the magnetic density should
be kept low.

page_text: A New or Improved Method of Regulating or Varying the Speed
and or Twisting Moment of Electro-motors, and Apparatus
therefor.
I, JOHN GRICE STATTER, of 68 Victoria Street, Westminster, in the County
of Middlesex, Electrical Engineer, 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 :-
My invention consists of a new or improved method of regulating or varying
the speed and or twisting moment of electro-motors designed for use with direct
currents having approximately constant electromotive force. It also has reference
to the apparatus employed for such purposes. My invention is specially applicable
in the propulsion of vehicles and in the lifting or hauling of loads.
In order to attain these objects I take a frame-work of a machine, that of any
of the ordinary types of direct current machines will answer my purpose, and I
provide its armature core with two distinct windings (as for example in the manner set
forth in the Complete Specification accompanying my Letters Patent No. 6,528 of
the year 1893), each having the same, or approximately the same, number of
active turns, and which windings can be placed at will either in series or in
parallel. I wind the field magnets as in an ordinary shunt wound machine; but,
in addition to the ordinary shunt winding suitable for the motor when used with
the armature windings in parallel, I employ upon the field an extra winding
(either series or shunt) to be switched into circuit as required, and to be used in the
manner hereinafter to be described.
A motor wound as above described, and put to work on a circuit of constant
electromotive force, will run at varying speeds according as the armature windings
are in series or in parallel.
Under existing conditions the work given out by the motor at the lower speed
would be about half that given out at the higher speed (with the same field
excitation) since, in order to keep within sparking limits, the current with the
armature windings in series must not exceed say half that which is passed when
the armature windings are in parallel.
Now I usually require to increase my twisting moment when running at the
lower to nearly double that required at the higher speed; and I require therefore
to pass, at the lower speed, the full current that passes through the motor at
the higher speed. In order therefore that I may not exceed the sparking limit
when the motor is working at the slower speed, I switch into circuit, during the
time that the armature windings are in series, the extra winding on the field
magnets; and this provides extra excitation which prevents sparking during the
lower speed, that is to say, during the time that the armature windings are pressed
with twice their normal current.
When the extra winding on the field is not in circuit the magnetic density should
be kept low.
In order that my invention may be more readily understood I have appended
hereto a drawing showing, in schematic diagrammatic manner, the best way known
to me at present of carrying my invention into effect: and for purposes of
description I shall now refer to the said drawing.
For such purposes of description, I shall assume the case of a motor whose
armature core has two windings, one of the drum type, and one of the ring type,
as described in the Specification accompanying my above mentioned prior Patent.
In the diagram I have shown, for purposes of clearness, the two commutators,
to which the said windings are connected, as entirely separate; whereas in actual

page_text: [
Iractice the said commutators would preferably be mounted as shown in the
drawings accompanying my said prior Specification. Referring, then, to the
ccompanying drawing, A is the commutator to which the ring winding is
Ennected, and B the commutator to which the drum winding is connected.
Sand S¹ represent the shunt coils on the field magnets, whilst M and M' represent
the coils which I provide to supply the extra excitation required by my invention,
and which in this case are shown as series coils. T is a terminal board which I
generally find it convenient to attach to the motor. On this board are mounted the
terminals 1, 2, 3, 4, 5, 6, 7, 8 which are in electrical connection as shown with
the brushes of the two distinct armature windings, the ends of the shunt coils and
the ends of the extra excitation coils. These terminals are in electrical connection
also with the segments or contact plates of the switch K; which segments or
contact plates are, in the diagram, marked with numbers corresponding with those
on the terminals of the board T. It will be seen that the switch K has two
concentric sets of segments constituting the fixed contacts. E is the switch bar,
in this case of non-conducting material, and C and D are bridge pieces attached
to bar E, and which serve to connect the segments of one circle with those of the
other when desired. This bar E, which is pivoted at its centre, when in the
position shown in full lines connects, by means of the bridge picce C, the segment
marked 4 with that marked 2 and 7; whilst the bridge piece D connects the
segment marked 1 with that marked 3. Segment 4 is connected with the positive
line wire X and segment with the negative line wire Y. Segments 3 and 311 are
permanently and electrically connected.
It will be seen from the diagram that the current enters the switch by segment 4,
whence it passes by terminal 4, drum winding B, terminal 3, segments 3 and 31,
bridge piece D and segment 1 to the negative line wire Y. From segment 4 it
also passes by bridge piece C, segment 2 and 7, terminal 2, ring winding A,
terminal 1, and segment 1 to negative line wire Y. None of the current can pass
from segment 2 and 7 by terminal 7, as segment 8 is unconnected to any other part
of the switch whilst bar E is in the position shown in full lines in the drawing.
Terminals 5 and 6, between which the shunt coils S and S¹ are connected, are
directly connected in any convenient way with the line wires X and Y, so that
they receive the full potential of the circuit. It will be seen that the shunt coils
are fully excited, and that both armature windings are in parallel. The motor
therefore runs at its full speed; and this speed remains practically constant for all
variations of load, provided that the maximum current for which the motor has
been designed is not exceeded.
If, now, the bar E be turned into the position shown in dotted lines, bridge
piece C will connect segments 3 and 8 and the course of the current will be as
follows. Entering at segment 4 as before, it will pass by terminal 4, drum
winding B, terminal 3, segment 3, bridge piece C, segment 8, terminal 8, extra
excitation coils M and M¹, terminal 7, segment 7 and 2, terminal 2, ring winding A,
terminal 1, segment 1, to negative line wire Y. Thus it will be seen that the
current traverses the two armature windings in series as well as the extra excitation
coils so that the field is thereby increased in strength. The motor now runs at
somewhat less than half the speed at which it did when the armature windings
were in parallel. In practice I find it convenient to so proportion the parts of the
machine that the increase of torque, with the same current as formerly employed,
amounts to sixty per cent. 1 do not however bind myself to such ratio of increased
torque.
I have hereinbefore spoken of my invention as embracing the use of two distinct
windings, and as enabling two variations of speed and of twisting moment to be
obtained. It is obvious, however, that such windings may be subdivided: and
that the result of such subdivision would be the securing of an increased number of
variations of speed and of twisting inoment. It will be obvious that my invention
lends itself to use with multi-polar motors. Thus for example if the frame of a
four-pole machine be employed the windings under one pair of poles may be led to

page_text: one commutator and those under the other pair to the second commutator. Or,
with an eight-pole machine, either two or four commutators, with their accom-
panying windings, or sets of windings, may be employed; and two or four different
speeds may thus be obtained.
Heretofore I have spoken of each winding having the same number of active
turns; but I desire it to be understood that this, whilst desirable, is not absolutely
necessary; for I have found that a slight deviation, say to the extent of five or
even ten per cent., may be admitted without serious detriment. To put this matter
more clearly, and in another way, 1 would state that it is not essential that the
windings should generate the same counter electromotive force at a given speed.
One winding may produce a slightly greater counter electromotive force per
revolution of the armature than the other, provided that the difference is not so
great that one winding would work sensibly as a dynamo or generator winding,
with regard to the other, when the two are in parallel. The effect of such an
inequality would be to enhance the difference in torque between parallel and series
working, as well as the difference in speed. If, however, the switch K be modified
so that one or other winding or both in series are in circuit at one time, three
different speeds, and three different torques, can be obtained from a two-pole
motor.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :—
1. The new or improved method of regulating or varying the speed and or
twisting moment of electro-motors, substantially as set forth.
2. In an electro-motor, the employment of an extra excitation coil, substantially
as, and for the purpose, set forth.
3. In an electro-motor the combination of a combined ring and drun wound
armature, a shunt coil or coils and a super exciting coil or coils, substantially as,
and for the purpose, set forth.
Dated this 14th day of December 1894.
Dated this 14th day of December 1894.
For the Applicant,
J. G. LORRAIN, M. Inst. E.E., M. Inst. M.E.,
Norfolk House, Norfolk Street, Strand, London, W.C.,
Chartered Patent Agent.