Improvements in Dynamo Electric Machinery.
Year: 1897

page_text: Improvements in Dynamo Electric Machinery.
We, JOSEPH SLATER LEWIS, and FELIX JOHN HOWITT, both of the Salford Rolling
Mills, Manchester, in the County of Lancaster, Engineers, do hereby declare the
nature of this invention to be as follows:-
"
This invention relates to dynamo electric machines, and has for its object to
improve the construction of that kind or class of generator in which additional
coils or bars are provided on the armature for the purpose of reversing the current
in the armature coils at the instant of commutation. Our invention further com-
prises an improved construction of pole piece for a purpose hereinafter mentioned.
Armatures constructed in the manner above described are now well known
under the name of "Sayers" armatures and the additional coils are called "Sayers
coils. With pole pieces of the ordinary construction, only one side of the loop.
of wire forming. a Sayers coil is utilized, such loop being provided in order. to
render the direction of rotation of the armature reversible; therefore, in order to
utilize both sides of the loop and thus increase the load of the machine, auxiliary
poles were provided in the air space between the ordinary pole pieces. These
auxiliary poles were either extensions of the ordinary poles or provided with an
independent magnetic circuit, with and without magnetising coils, there being
in either case gaps or air spaces between the ordinary poles and the auxiliary
poles. The ordinary armature coils at the time of commutation were situated
in one of these gaps, so that they were unaffected by the magnetic field. This
construction is costly, and has other disadvantages.
According to our present invention, we dispense with auxiliary poles and utilize
in lieu thereof the horns of the ordinary pole pieces, which we design in such a
manner that electromotive forces are induced in the Sayers coils during the period
of commutation which effect the complete reversal of the current in each armature
coil to which they are connected. Under these circumstances the machine will
run sparklessly as a generator, or as a motor, with fixed brushes of copper, or
other suitable conductive material, for all variations of load, and, with suitable
brushes, the direction of rotation may be reversed without altering the position
of the said brushes, or making any other structural alterations. The machine
can also be overloaded without sparking or altering the position of the brushes,
provided that the temperature of the armature is maintained below a suitable limit.
In carrying out our invention, we diminish the distance between the horns of
the poles by increasing the angular breadth of the said poles until the circum-
ferential distance through the air between the pole horns is, in consequence of a
slight allowance having to be made for the magnetic fringes, slightly greater
than the angular breadth of one Sayers coil on the armature. The length or ex-
tent of each of the said fringes of each horn may be regarded as approximately.
equal to the clearance between the armature and pole pieces. By this arrange-
ment we ensure that as soon as one side of a Sayers coil has quitted the magnetic
field of one pole piece the other side of the said coil will have entered the mag-

page_text: netic field of the other pole piece. When this said Sayers coil and the Sayers
coil following are symmetrically disposed about the pole horns, and consequently
in active operation, the armature coil to which the said Sayers coils is appro-
priated is approximately midway between the said pole horns, and consequently
outside the magnetic field of either of them.
The span of each said Sayers coil is so arranged that a minimum amount of
magnetic leakage from the poles passes into the armature at the region traversed
by 'the said main coil during reversal, consistent with a maximum angular breadth
of pole piece. In designing the pole horns we arrange that. the section shall be
sufficient across the direction of the magnetic flux, to carry the necessary flux
into the regions of the armature immediately under the pole tips, traversed by
the Sayers coils during commutation, in order that the reversal of the current
in the main coils may be completed; and at the same time, the magnetic parts
behind the said pole horns are as far as possible kept away from the spaces be-
tween opposite pole horns to avoid more leakage into the armature in those spaces
than is necessary to reducé sensitiveness at. the brushes... Similar considerations
in respect to these two last. conditions are well understood with Sayers machines
already built with and without auxiliary-poles..
517
Our improved construction of pole piece, which is a second feature of our in-
vention, is more especially intended for use in experimental machines though it
may be employed in ordinary machines if desired. In this construction we form
the curved portions of each nole piece opposite the armature of two or more plates
of a suitable thickness, the division line or lines between the said plates being
parallel to the armature shaft. The said plates can be adjusted upon the poles
so as to vary the angular breadth of the pole piece, the small gap which is formed
when the plates are moved apart having little if any effect upon the working of
the machine.
.
With a dynamo furnished with this construction of pole piece we can very
readily determining experimentally the most suitable angular breadth of the pole
pieces; for example in the case of a machine with a-Sayers armature as above
described, we can determine the angular breadth of pole piece which gives the
best results as regards regulation and diminution of sparking, without taking into.
account the fringing or spreading of the magnetic field (which always occurs at
the horns of the pole pieces) or determining its extent.
We provide in connection with our said improved pole pieces removable or
adjustable pole tips so arranged that by suitable slots. and locking nuts; the tips
of the said pole pieces may be thickened up to the required extent, and the sec-
tion in this way controlled in the manner herebefore described.
Dated this 15th day of September 1897.:
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Machinery.
We, JOSEPH SLATER LEWIS, and FELIX JOHN HOWITT, both of the Salford Rolling
Mills, Manchester, in the County of Lancaster, 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:
This invention relates to dynamo electric machines of that kind or class in which
additional coils or bars are provided on the armature for the purpose of reversing
the current in the armature coils at the time of commutation. The object of our

page_text: invention is to construct a machine in which the position of the brushes is prac
tically fixed and into which no sparking at the brushes occurs. A further object
is to reduce the cost of manufacture of the machine. Our invention also com-
prises improved constructions of pole piece for these machines as hereinafter
described.
!
Armatures constructed in the manner above described are now well known
under the name of "Sayers" armatures and the additional coils are called "Sayers" i
coils. With pole-pieces of the ordinary construction, only one side of the loop
of wire forming a Sayers coil is utilized, such loop being provided in order to
reuder the direction of rotation of the armature reversible, therefore, in order to
utilize both sides of. the loop and thus increase the power of the machine, auxiliary,
poles were provided. in the air space between the ordinary pole pieces. These
auxiliary poles were either extensions of the ordinary poles or provided with an
independent magnetic circuit, with or without magnetising coils, there being
in either case gaps or air spaces between the ordinary poles and the auxiliary.
poles. The ordinary armature.coils at the time of commutation were situated
in one of these gaps, so that they were uneffected by the magnetic field. This
construction is costly, and has other disadvantages.
"
According to our present invention, we dispense with auxiliary poles and utilize
iu lieu thereof the horns of the ordinary pole pieces, which we design in such a
manner that electro-motive forces are induced in the Sayers coils during the period:
of commutation which effect the complete reversal of the current in each armature
coil to which they are connected. Under these circumstances the machine "will
run, sparklessly as a generator, or as a motor, with fixed brushes of copper, or
other suitable conductive material, for all variations of load, and, with suitable
brushes the direction of rotation. may be reversed without altering the position
of the said brushes, or making any other structural alterations. The machine
can also be loaded beyond the ordinary.load without sparking or altering the
position of the brushes, provided that the temperature of the armature is main-
tained below a suitable limit.
In carrying out our invention, we diminish the distance between the horns of.
the poles by increasing the angular breadth of the said poles until the circum-;
ferential distance through the air between the pole horns is, in consequence of a
slight allowance having to be made for the magnetic fringes, slightly greater.
than the angular breadth of one Savers coil on the armature. The length or ex-:
tent of each of the said fringes of each horn may be regarded as approximately:
equal to the clearance between the armature and the pole-pieces.
By this arrangement we ensure, that as soon as one side of a Sayers coil has
quitted the magnetic field of one pole-piece the other side of the said coil will
have entered the magnetic field of the next pole-piece.
Our invention further comprises an improved construction of pole piece the
angular breadth of which can be readily varied as will be hereinafter fully. set
forth.
In order that our invention may be clearly understood we will proceed to-de-
scribe the same with reference to the accompanying drawings in which,..
Figure 1 is an end view somewhat diagrammatic of a dynamo constructed in
accordance with our invention:
Figures 2 and 3 are diagrams hereinafter explained...
Figure 4 is an end view of our improved construction of pole-pieces..
Figure 5 is a section on line
Figure 4.
Figure 6 is an end view shewing an improved form of pole piece hereinafter
explained.
Similar letters of reference denote like parts throughout the drawings.
A is the field-magnet, B the armature core, C. the commutator, D the ordinary
armature conductors, E the conductors of the Sayers coils,, F. one of the brushes,
Referring now to Figure 1 a Sayers coil E is shewn starting from the, commu-
tator sector C¹ and through a slot B in the armature core B returning up through
47

page_text: a slot B in said core there being five teeth between slots. B and B between two,
of which the armature bar Doonnected to said Sayers, coil is located. The figure
shews that the distance between the pole tips A A is a little greater than the
span of the coil E, because the lines of magnetic force as shewn by the dotted
lines G spread out from the pole tips. The spreading of the field will in general
depend upon the degree of magnetic saturation of the armature teeth under the
pole tips. Hence taking into account this "fringing" of the fields one side of the
loop practically leaves the field of one pole tip at the same time as the other
side of the loop enters the field of the other pole tip and as one side of the loop
becomes practically inactive the other side in advance becomes active. In order
to render this. construction more clear we have shewn in Figure 2 a diagram of
the development of an armature the commutator sectors CC being joined through
the Sayers, loops E¹ E to the armature bars, D1 Ds. The pole pieces are shewn,
at A³ in dotted lines the distance from the tip A to the tip As being a little greater
than the span of the Sayers. loop. E. Referring now to Figure 3 which shews
two Sayers coils E and E symmetrically disposed about the pole horns, and
consequently in active operation, the armature coil D to which the said Sayers
coils are connected is approximately midway between the said pole horns, and
consequently outside the magnetic field or either of them.
The span of each said Sayers coil is so arranged that a minimum amount of
magnetic leakage from the poles passes into the armature at the region traversed
by the said main coil during reversal, consistent with a maximum angular
breadth of pole-pieces. In designing the pole horns we arrange that the section
shall be sufficient, across the direction of the magnetic flux, to carry the neces-
sary flux into the regions of the armature immediately under the pole tips tra-
versed by the Sayers coils during commutation, in order that the reversal of the
current in the main coils may be completed, and, at the same time, the magnetic
parts behind the said pole horns are as far as possible kept, away from the space be-
tween opposite pole-horns so that there will be as little leakage into the armature in
those spaces as possible consistent with the necessary shading or gradual
diminution of the field required to prevent undue sensitiveness of the brushes.
Similar considerations in respect to these two last conditions are well understood
with Sayers machines already built with and without auxiliary poles.
"
Our improved construction of pole-pieces, which is a second feature of our in-
vention, is more especially intended for use in experimental machines though
it may be employed in ordinary machines if desired. In this construction as
illustrated in Figures 4 and 5 we form the curved portions of each pole-piece
opposite the armature, of two plates H of a suitable thickness, the division line
or lines between the said plates being parallel to the armature shaft. The plates
embrace the poles being secured by means of studs and nuts passing through.
circular slots H. The said plates can therefore be adjusted upon the poles so
as to vary the angular breadth of the pole-pieces the small gap which is formed
when the plates are moved apart having little if any effect upon the working of
the machine.
With a dynamo or motor furnished with this construction of pole-pieces we
can very readily determine experimentally the angular breadth of pole-piece
which gives the best results without calculating the amount of the fringing or
spreading of the magnetic field.
We may further provide in connection with our said improved pole pieces, re-
movable or adjustable pole tips, so arranged that by suitable slots and locking
nuts the tips of the said pole-pieces may be thickened up to the required extent,
and the section in this way controlled in the manner here before described.
In Figure 6 we shew an improved construction of pole pieces by means of which
the difference in the total magnetic flux when the dynamo is running at full load
and at a very small or no load is considerably lessened. The armature B being
rotated in the direction of the arrow it is well known, that if the machine running
as a generator is loaded considerably the magnetic flux will be small at the part A
10+7

page_text: even if the air gap at that place were not increased. We can therefore increase
the air gap as shewn without substantially altering the magnetic flux at full load.
When however the machine is running with a very small load the increase in the
air gap at the place A* causes the field to diminish at that point to a considerable
extent and consequently reduces the total magnetic flux through the armature.
Hence the total flux at a small load is rendered more nearly equal to the total
flux at full load and the rise of the voltage at the brushes when the load is taken
off the machine is reduced.
The improvements hereinabove set forth are applicable both to motors and
generators and we use the term dynamo electric machine to include both classes
of machine. Although we have shewn in the drawings a two pole machine we
do not restrict ourselves in this respect as our invention is equally applicable
to four pole or multipolar machines.
Having now particularly described and ascertained the nature of our said in-
vention and in what manner the same is to be performed we declare that what we
claim is:-
1. For a dynamo electric machine having an armature provided with "Sayers"
coils, a field magnet in which the angular breadth of the poles is such that the
distance between 'the forward horn or tip of one pole and the back horn of the next
pole is approximately equal to the span of a Sayers" coil, and the leading side
of the coil reaches the magnetic field of one pole at the same time that the trailing
side of the coil leaves the field of the other pole.
"
"
2. In a dynamo electric machine having an armature provided with "Sayers"
coils, the provision of a field magnet having pole pieces the angular breadth of
which can be varied substantially as described.
3. Dynamo electric machines constructed and operating substantially as
described.
CHIDCU
Dated this 18th day of November 1897.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham,
Patent Agents for the Applicants.