IMPROVEMENTS IN COMMUTATORS FOR DYNAMO OR MAGNETO ELECTRIC MACHINES OR ELECTROMOTORS
Year: 1881

page_text: LETTERS PATENT to Edward Griffith Brewer, of 33, Chancery Lane, in the
County of Middlesex, for an Invention of "IMPROVEMENTS IN COMMUTATORS
FOR DYNAMO OR MAGNETO ELECTRIC MACHINES OR ELECTROMOTORS." A com-
munication from abroad by Thomas Alva Edison, of Menlo Park, State of
New Jersey, United States of America.
PROVISIONAL SPECIFICATION left by the said Edward Griffith Brewer
at the Office of the Commissioners of Patents on the 23rd July 1881.
EDWARD GRIFFITH BREWER, of 33, Chancery Lane, in the County of Middlesex.
"IMPROVEMENTS IN COMMUTATORS FOR DYNAMO OR MAGNETO ELECTRIC MACHINES
OR ELECTROMOTORS." (A communication from abroad by Thomas Alva Edison, of
Menlo Park, State of New Jersey, United States of America.)
In the operation of magneto or dynamo electric machines, a heavy spark is
produced at each set of commutator brushes, as they pass from one bar of the
commutator cylinder to another. This spark is caused first by the breaking of a
strong local circuit produced by the brushes bridging the insulation between two
bars, and second, by breaking a portion of the main current at the same time.
Since it is extremely difficult, if not impossible, to adjust the brushes, so that
they will leave a commutator bar exactly together, this spark at each set of brushes
is usually taken principally by one brush, until that is reduced in length by the
heat of the spark, when it is taken by another brush. In large and powerful
dynamo or magneto electric machines the sparks produced in this manner are
exceedingly large, the result being a considerable waste of energy, which is
converted into heat, and injures the face of the commutator and the brushes that
bear thereon.
The object therefore of this Invention is to obtain means for reducing the
sparks at the commutators of these machines to the minimum.
In carrying out this Invention the insulation is widened and the conducting
bars narrowed at one end of the commutator cylinder, and upon this portion of
CC

page_text: said cylinder, on each side thereof, a single commutator brush is arranged to bear,
whose bearing end is noticeably behind the ends of the main brushes beside which
it is placed.
"
This brush, which is termed for the purpose of distinction the "isolated" brush,
is not connected with the main brushes directly, but is connected with a series of
breaking points, resting on a breaking cylinder," which breaking cylinder has
conducting bars and insulating spaces corresponding with those upon which the
"isolated brush" bears.
This cylinder may be a separate cylinder mounted on the end of the shaft of the
machine, or it can be a continuation of the commutator cylinder, its conducting
bars being insulated from those of the commutator cylinder.
"
There may be two or four, or any other desired number of these breaking points
connected with the "isolated brush on each side of the machine, the first point of
each series being connected with the "isolated brush" and the last point with the
main wire. .
In the working of the machine the local circuit, and a portion of the main
current, are continued through each "isolated brush" after the main brushes have
left each commutator bar, so that no spark is produced at the points of the main
brushes.
When each isolated brush" leaves a commutator bar, the current passing
through it is also broken at a number of points on the breaking cylinder,
simultaneously with the breaking of the current on the commutator cylinder by
the "isolated brush."
In this manner the spark is divided up, and the total spark greatly reduced, and
the spark at each point is reduced about as the square of the number of points at
which the current is broken. Hence if two breaking points are connected with
each "isolated brush" the spark at each point will be about one-ninth of what
the entire spark would ordinarily be.
It is evident that this same arrangement could be used for the commutators of
electro motors.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Edward Griffith Brewer in the Great Seal Patent Office on the
23rd January 1882.
EDWARD GRIFFITH BREWER, of 33, Chancery Lane, in the County of Middlesex.
"IMPROVEMENTS IN COMMUTATORS FOR DYNAMO OR MAGNETO ELECTRIC MACHINES.
OR ELECTROMOTORS." A communication from abroad by Thomas Alva Edison, of
Menlo Park, in the State of New Jersey, United States of America.
In the operation of magneto or dynamo electric machines, à spark is produced at
each set of commutator brushes as they pass from one bar of the commutator
cylinder to another. This spark is caused, first, by the breaking of a strong local
circuit produced by the brushes bridging the insulation between two bars; and
second, by breaking a portion of the main current at the same time.
Since it is extremely difficult, if not impossible, to adjust the brushes so that
they will leave the commutator bar exactly together, this spark at each set of
brushes is usually taken principally by one brush until that is reduced in length
by the heat of the spark, when it is taken by another brush. In large and powerful
dynamo or magneto electric machines the sparks produced in this manner are
exceedingly large, the result being a considerable waste of energy which is
converted into heat and injures the face of the commutator and the brushes that
bear thereon.
The object therefore of this Invention is to produce means for reducing the
sparks at the commutators of these machines to the minimum.
In carrying out this Invention the insulation is widened and the conducting
bars narrowed at one end of the commutator cylinder, and upon this portion of
said cylinder on cach side thereof a single commutator brush is arranged to bear,
whose bearing end is noticeably behind the ends of the main brushes beside which
it is placed, that is to say, the end of this brush bears upon the commutator
cylinder at a point which has already passed the main brushes. This brush, which
is termed for purpose of distinction the "isolated brush," is not connected with
the main brushes directly, but is connected with a series of breaking points
resting on a "breaking cylinder," which breaking cylinder has conducting bars
and insulating spaces corresponding with those upon which the "isolated brush "
bears.
This cylinder may be a separate cylinder mounted on the end of the shaft of
the machine, or it can be a continuation of the commutator cylinder, its conducting
bars being insulated from those of the commutator cylinder.
"
There may be two, or four, or any other desired number of these breaking points
connected with the "isolated brush on each side of the machine, the first point
of each series being connected with the isolated brush and the last point with the
main wire.
In the working of the machine the local circuit and a portion of the main
circuit are continued through each "isolated brush" after the main brushes have
left each commutator bar, so that no spark is produced at the points of the main
brushes. When each "isolated brush "leaves a commutator bar the current passing
through it is also broken at a number of points on the breaking cylinder simul-
taneously with the breaking of the current on the commutator cylinder by the.
"isolated brush."
In this manner the spark is divided up and the total spark greatly reduced, it
being a discovery of the communicator that the spark at each point is reduced
about as the square of the number of points at which the circuit is broken.
Hence if two breaking points are connected with each "isolated brush" the
spark at each point will be about one ninth of what the entire spark would
ordinarily be.
It is evident that this same arrangement could be used for the commutators of

page_text: electro-motors and for other machines where the bad effect of a large spark is to be
obviated.
In the annexed Drawing
Figure 1 represents a commutator in which a separate breaking cylinder is used.
Figure 2, one in which only one cylinder is used, and
Figure 3 shows the manner of connecting a large number of breaking points.
In Figures 1 and 3, A is the commutator cylinder; a, a, a, being insulating
and b, 6, 62, conducting bars of its surface. The conducting bars are narrowed
and the insulating spaces widened at the outer end of the cylinder; B is the
breaking cylinder whose conducting bars c, c', correspond to those at the outer end
of the commutator cylinder.
d, d, are the main commutator brushes which take off the current and convey it
to the wire 1. e is the "isolated brush" connected by the wire 2 to the brushes
h, h, (Fig. 1) on the breaking cylinder.
The conducting bars of the breaking cylinder are of such width that the brushes
h, h, break circuit simultaneously with the brush e.
In Figure 3 four brushes m, m, n, n, are used, all making and breaking circuit
simultaneously with e, the last brush m being connected by wire 3 to the first
brush n, and the last brush n to the main wire 1.
In Figure 2 only one cylinder C is used, divided by an insulating section f into
two parts, one part forming the commutator cylinder, and the other the breaking
cylinder. The arrangement and connection of the brushes are similar to tho
construction shown in Figure 1.
In all these cases similar brushes or sets of brushes are of course placed at the
opposite side of the commutator to correspond with the other pole of the machine.
What is claimed is,―
First. The method of reducing the spark at the commutators, of dynamo or
magneto electric machines, which consists in breaking the circuit at a number of
points simultaneously, substantially as set forth.
Second. A series of commutator brushes, one of which is set noticeably behind
the other, substantially as and for the purposes described.
Third. The combination with the commutator brush or brushes of a magneto or
dynamo electric machine of two or more circuit breaking points arranged in series,
and breaking circuit simultaneously with the breaking of the circuit at the com-
mutator, substantially as set forth.
Fourth. A commutator cylinder, at one end-of-which the conducting spaces are
--narrowed and the insulating spaces widened, substantially as and for the purposes
described.
Fifth. The combination with the commutator cylinder and its brushes of a
breaking cylinder mounted on the same shaft and provided with means for breaking
the circuit at several points simultaneously with the breaking of the circuit at the
commutator, substantially as set forth.
Sixth. The breaking cylinder whose surface is composed of alternate metal and
insulation provided with a number of brushes which make and break circuit
simultaneously during the revolution of the cylinder, substantially as set forth.
Seventh. The combination with the "isolated brush of the commutator of two
or more brushes on the breaking cylinder which break circuit simultaneously with
the "isolated brush," substantially as set forth.
:"
In witness whereof, I, the said Edward Griffith Brewer, have hereunto set
my hand and seal, this Twenty third day of January, in the year of our Lord
One thousand eight hundred and eighty two.
E. G. BREWER.
(L.S.)