Improvements in Dynamos,
Year: 1899

page_text: Date of Application, 14th July, 1899.
Complete Specification Left, 17th Apr., 1900-Accepted, 2nd June, 1900
Improvements in Dynamos,
I, WILLIAM BROOKS SAYERS, of Glenwood, Bearsden, near Glasgow, in the
County of Dumbarton, Electrical Engineer, do hereby declare the nature of this
invention to be as follows:-
According to this invention in order to enable the brushes of a dynamo electric
generator having an ordinary drum or ring armature to be maintained in a
fixed position without sparking or practically so, for different loads, and to.
obtain an improved regulation of the dynamo, the trailing or rear end of each
field magnet pole, is formed or provided with a polar extension that projects
inward near to the armature like the field magnet pole and is arranged to form
with the main part of the field magnet pole an open cavity or recess opposite
which the sections of the armature winding are successively brought, and each
brush instead of being made of metal, as usual, is made of carbon and so arranged
on the commutator that each section of the armature winding will be short
circuited as it passes opposite the corresponding polar extension of the field
magnet pole and that the forward of the two commutator sections to which the
commutated armature section is connected, will pass onward out of contact with
the brush as the said armature section is brought opposite the said cavity or
recess formed between the field magnet pole and the extension thereof. In this
way practically sparkless commutation with a fixed position of the brushes under
varying loads, and improved regulation of the dynamo, can be obtained in a
very simple manner.
Each polar extension may be made of hook or other shape and project from
the end of the corresponding field magnet pole both in a circumferential direc-
tion and in an inward direction towards the armature so as to form the required
cavity or recess. Or the polar extension and cavity or recess may be formed by
making a deep groove in the face of the field magnet pole near one end thereof.
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page_text: 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:-
According to this invention in order to enable the brushes of a dynamo electric
generator having an ordinary drum or ring armature to be maintained in a
fixed position without sparking, or practically so, for different loads, and to
obtain an improved regulation of the dynamo, the trailing or rear end of each
field magnet pole is formed or provided with a polar extension that projects
inward near to the armature like the field magnet pole and is arranged to form
with the main part of the field magnet pole an open cavity or recess opposite
which the sections of the armature winding are successively brought, and each
brush instead of being made of metal, as usual, is made of carbon and so arranged
on the commutator that each section of the armature winding will be short
circuited as it passes opposite the corresponding polar extension of the field
magnet pole and that the forward of the two commutator sections to which the
commutated armature section is connected, will pass onward out of contact with
the brush as the said armature section is brought opposite the said cavity or
recess formed between the field magnet pole and the extension thereof. In this
way practically sparkless commutation with a fixed position of the brushes under
varying loads, and improved regulation of the dynamo, can be obtained in a
very simple manner.
Each polar extension may be made of hook or other shape and project from
the end of the corresponding field magnet pole both in a circumferential direc-
tion and in an inward direction towards the armature so as to form the required
cavity or recess. Or the polar extension and cavity or recess may be formed by
making a deep groove in the face of the field magnet pole near one end thereof.
The accompanying drawing shows diagrammatically so much of a two pole
dynamo electric machine acting as a generator, as is necessary to illustrate the
manner of carrying out the invention."
a, a, a² etc. are the sections of the armature winding; b, b1, b2 etc. the com-
mutator sections; c and c¹ the carbon brushes bearing upon the commutator:
and d the field magnet poles of which two are shown, each provided at one end
with a polar extension è that projects both in a circumferential direction and
towards the armature f and forms with the main part of the field magnet pole d,
a deep open cavity or recess g opposite which the armature sections are succes-
sively brought.
As will be seen the arrangement is such that whilst each of two opposite arma-
ture sections, say a. a, is passing opposite a polar extension e. each of the two
carbon brushes will bear upon the two commutator sections b, to which the
ends of the armature section in question are connected so that such armature
section will at this time be short circuited, and when each of the two said arma-
ture sections comes opposite the corresponding cavity or recess g, the commu-
tator section b to which one end of the said armature section is connected will
have passed onward out of contact with the corresponding brush.
By arranging the armature sections, commutator sections and brushes in the
manner described and shown, the armature sections will, as they pass in suc-
cession opposite each polar extension e and cavity or recess 9 be subjected alter-
nately to a powerful induced reversing force due to the magnetic field under the
polar extension e and a much weaker induced reversing force due to the weakened
field opposite the cavity g. The result of these conditions is that during the
first part of the period in which each armature section is short-circuited under
the brush, the said armature section will be subjected to a powerful induced
reversing force which dies down to a weak induced reversing force towards the
end of the period of short circuit, so that at the time when the division between
the two commutator sections which are connected by the brush is about to pass
the forward tip of the brush. the reversal of the current in the armature section
will have been approximately accomplished and the current will be changing

page_text: in value at a slow rate. This slow rate of change in the value of the current
in the said armature section at the time when the short circuit is broken under
the brush, is well known to be favourable to sparkless commutation, and, with
the aid of carbon brushes, to favour also a fixed brush position for all loads.
Again in consequence of the fact that the portion of the magnetic field that
enters the armature from the polar extensions e enters it behind the plane of
commutation, the E.M.F. generated by the armature is reduced in value by the
action of this portion of the magnetic field, and as the magnetisation of the
polar extension e is weakened to a greater or less extent by the armature reac-
tion, it follows that the effective E.M.F. generated by the dynamo will tend to
be greater with increase of load so that an improved regulation of the dynamo
will be obtained.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is:
1. A dynamo electric generator having a drum or ring armature wherein the
trailing or rear end of each field magnet pole is provided with an inwardly
extending polar extension and an adjacent cavity or recess opposite which the
sections of the armature winding are successively brought, and each commu-
tator brush is made of material such as carbon and so arranged on the com-
mutator that each armature section will be short circuited as it passes opposite
a polar extension and the forward of the two commutator sections to which the
commutated armature section is connected will pass onward out of contact with
the brush as the said armature section is brought opposite the said cavity or
recess, substantially as herein described for the purposes set forth.
2. The improved dynamo electric generator constructed as herein before
described with reference to and shown in the drawing annexed.
17ated this 17th day of April 1900.
For the Applicant,
W. LLOYD WISE,
4G, Lincoln's Inn Fields, London, W.C.,
Chartered Patent Agent.