IMPROVEMENTS IN DYNAMO ELECTRICAL MACHINES to be as follows:
Year: 1884

page_text: I MARK HENRY HURRELL of the British Electric Light Company Limited of
Turnmill Street in the City of London Electrical Engineer, do hereby declare the
nature of my invention for "IMPROVEMENTS IN DYNAMO ELECTRICAL MACHINES
to be as follows:-
-
"
In order to construct the armature of that class of dynamo electrical machines
known as Gramme machines, I make the outer circumference of the iron core in
the form of a portion of a sphere. The inner circumference I also make concentric
with the outer circumference.
The insulated conducting coils which are wound transversely around the core lie
closely against the outer convex surface and so make the outer circumference of the
armature into the form of part of a sphere-whilst the part of the coils which
passes across the convex interior of the core will be straight the space so left
between the coils and the core I fill in with insulating material.
The faces of the magnet poles I make of a hollow spherical form conforming to
the spherical form of the exterior of the armature.
By making the armature ring convex instead of in the form of a cylinder as is
usual the transverse coils which are wound around the ring can be drawn with
sufficient tightness against the outer surface of the ring as to prevent their bulging
outwards from the ring whenever it is rotated and so permitting of the armature
being finished without any exterior binding of wire.
To mount the armature upon the axis of the machine I form the hub in two
metallic parts each capable of being slidden endwise along the axis.
The periphery of each part I make somewhat conical and place the smaller ends
of the two cones towards one another. The two parts I connect one to the other
by three or more screws ranged equidistantly around the axis and parallel with it
each screw having a right hand thread at one end and a left hand thread at the
other-the screw thread at one end screwing into one of the conical parts and the
screw thread at the other end into the other conical part. At the centre each
screw is provided with two collars which come one on either side of a collar on
the axis. In this way by turning the screw by keys applied to one of their
ends the two conical parts can be moved towards or away from one another along
the axis..

page_text: The armature is placed over the exterior of the two parts of the hub. Strips of
insulating material laid parallel with the axis being placed between them. The
strips are straight on their outer surface to bear against the inner circumference of
the armature and tapered at each end on their inner surface to conform to the
conical surface of the two parts of the hub. The two parts of the hub are then
drawn towards one another by turning the right and left handed screws thereby
forcing the strips of insulating material outwards against the interior of the ring
armature and so securing it to the axis. This is effected without rubbing the
insulated conductors of the conducting coils of the armature and consequently
without any risk of destroying the insulation of these conductors. Also by
making the insulating material on the inside of the ring armature in several
strips the thickness of the pieces at different points around the circumference can
readily be varied and any eccentricity of the inner circumference of the ring
thereby compensated for. The insulating material interposed between the ring
armature and the hub also allows of the metallic parts of the hub being so far
removed away from the strong part of the magnetic field that little or no current
will be induced in it whilst at the same time they are sufficiently thin as not to be
materially affected by heat. Spaces also are left between the several strips into
which the insulating material is divided to allow of considerable access of air to
the inner circumference of the ring to convey away heat from it.
In small machines where great strength is not required I make the hub in one
piece in the form of a drum of non inductive material and with the circumference
of the drum carried by radial arms from a central hub fixed on the axis. The
outer circumference of the drum I form as a portion of a sphere with a projecting
flange on either side of it whilst the inner circumference of the drum I make
straight and parallel with the axis.
The iron wire core is wound around the outer circumference of the drum so as to
form a layer of even thickness around it and also somewhat to overlap the flanges.
The transverse insulated conducting coils are wound around the iron core and the
periphery of the drum the exterior circumference of the armature so formed is
therefore part of a sphere-and as before winding on these coils the circumference
of the drum is accurately turned so as to be concentric with the axis-the outer
circumference of the armature will be very true with the axis--and also as in
winding on the coils the inner parts of each coil have to lie between the radial
spokes of the drum any rotation of the armature around the drum will be
absolutely prevented. Also as a space is left between the inner parts of the coils
and the central hub there is free access of air to keep them cool. The hub spokes
and circumference of the druin being of a non inductive material such as vulcanite
no waste currents are generated in it.
The commutator or collector of the Gramine or similar machine I form of a
number of metallic segments ranged around the axle and parallel with it-the
several segments being insulated from one another as is usual and to hold the
segments to the axle I make the inner part of each segment of a dovetail form at
its-ends.
The dovetail portions of the several segments at one of their ends lie under a
coned recess in a collar fast on the axis and at the other end under a similar recess
in a coned collar which can be forced along the axis towards the fixed collar by
means of a nut screwed on to a screw thread cut around the axle. When the nut
is screwed up so as to cause the dovetail ends of the segments to be gripped and
held between the two collars the nut itself is locked by a lock nut. In this way
the segments are securely held to the axle and there is no risk of their breaking
away from it when the axle is rapidly rotated. In place of fixing the segments
directly on to the axle they may similarly be secured to a tubular sleeve to be
sipped on to the axle and secured to it. This allows of the commutator or
collector of the machine being rapidly removed and replaced by another. In this
case I do not provide any lock nut to screw on to the sleeve to lock the nut by

page_text: which the moveable collar is forced end wise along the sleeve but allow the nut
which screws on to the sleeve to project somewhat beyond the end of the sleeve
and when the sleeve has been placed on to the axle I cause a nut which screws on
to the axle to be screwed up to and against the nut on the sleeve so as to force the
opposite end of the sleeve against a collar on the axle and so grip and hold the
sleeve. The screw thread in the nut on the sleeve I also make of less depth and
width although of the same pitch as the screw thread on the sleeve so that when
the nut on the axle is forced against the nut on the sleeve this latter nut may be
free to move to some extent along the sleeve so that the moveable collar of the
sleeve will then be forced towards the segments by the nut on the axle so that
the strain of bolding down the several segments to the sleeve will be taken by this
nut which may be of large dimensions and which may itself be locked by a lock
nut.

page_text: "
"
Ì MARK HENRY HURRELL of the British Electric Light Company Limited of
Turnmill Street in the City of London Electrical Engineer do hereby declare the
nature of my invention for IMPROVEMENTS IN DYNAMO ELECTRICAL MACHINES
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:-
11. .
The armature of that class of dynamo electrical machines known as Gramme
machines I make with the outer circumference of its iron core in the form of a
portion of the sphere. The inner circumference I also make concentric with the
outer circumference.
L
The insulated conducting coils which are wound transversely around the core lie
closely against the outer convex surface and so make the outer circumference of the
armature into the form of part of a sphere-whilst when first wound the part of
the coils which passes across the convex interior of the core will be straight.
The faces of the magnet poles I make of hollow spherical form conforming to the
spherical form of the exterior of the armature.
By making the armature ring convex instead of in the form of a cylinder as is.
usual the transverse coils which are wound around the ring can be drawn with
sufficient tightness against the outer surface of the ring as to prevent their bulging
outwards from the ring whenever it is rotated and so permitting of the armature
being finished withont any exterior binding of wire.
To mount the armature upon the axis of the machine I form the hub in two
metallic parts each capable of being slidden endwise along the axis.
The periphery of each part I make somewhat conical and place the smaller ends
of the two cones towards one another. The two parts I connect one to the other
by three or more screws ranged equidistantly around the axis and parallel with it
each screw having a right hand thread at one end and a left hand thread at the
other the screw thread at one end screwing into one of the conical parts and the
screw thread at the other end into the other conical part. In this way by turning
the screws by keys applied to one of their ends the two conical parts can be moved
towards or away from one another along the axis.
In smaller machines the right and left handed screw threads might be upon the
axis itself.
Strips of insulating material laid parallel with the axis are placed between the
armature and the two parts of the hub. The outer surfaces of the strips bear
against the inner circumference of the armature and the inner surfaces of the strips
are tapered to conform to the conical surface of the two parts of the hub. When
the two parts of the hub are drawn towards one another by turning the right and
left handed screws the strips of insulating material are thereby forced outwards
against the interior of the ring armature and so secures it to the axis. This is
effected without rubbing the insulated conductors of the conducting coils of the
armature and consequently without any risk of destroying the insulation of these
conductors. The strips of insulating material interposed between the ring armature
and the hub also allow of the metallic parts of the hub being so far removed away
from the strong part of the magnetic field that little or no current will be induced
in it. Spaces are left between the several strips into which the insulating material
is divided to allow of considerable access of air to the inner circumference of the
ring to convey away heat from it.
Figure 1 shews a side elevation one half in section of a Gramme bobbin mounted
upon a shaft in the manner above described. Figure 2 is an end elevation with

page_text: half of the bobbin coils removed from the ring. Figure 3 is a vertical longitudinal
section of the two parts of the conical hub and the right and left handed screws
which draw them together. Figure 4 is an end elevation of one of the parts of the
conical hub.
In these figures A is the shaft B B are the two parts of the hub which can slide
end wise along the axis but cannot turn around it. CC are the right and left
handed screws by which the two parts of the hub can be drawn together. DD are
a series of wooden strips which form a ring around the two conical parts of the hub
and which have their inner surfaces fitting against the two cones. E is the iron
wire ring of the Gramme armature it differs from that of the ordinary Gramme
machine in that its outer surface is made convex and its inner surface concave and
concentric with the outer surface. F F are the insulated conducting coils or
bobbins, when first wound they lie closely against the convex surface of the ring
and are therefore concentric with this surface whilst the other parts of the coils
where they pass across the convex interior of the ring are straight. The wooden
ring which is built up of the wooden strips D has also its outer circumference
turned concentric with the ring E. By preference also I form grooves around the
circumference of the wooden ring into which wooden hoops G divided into com-
paratively short segments may be laid as shown. H H are the pole pieces of the
dynamo electrical machine.
In order to mount the armature ring onto the armature hub the two parts of the
hub are moved away from one another and the strips D are ranged around the
hubs so as to touch one another and form as it were a complete barrel around
the hub with the several strips D touching one another.
The armature ring can then be placed over the exterior of the barrel."
Afterwards by turning the right and left handed screws the two parts of the hub
are made to approach one another and to force the strips D radially outwards away
from one another. The strips D are thereby caused to press against the insulated
wire coils F or bobbins and to bend them froin a straight line into a curve
concentric with the ring. E. In this way the coils F are bent and brought into a
form concentric with the ring E and are at the same time tightened up to such an
extent that partly owing to their exterior form and partly to their being so
tightened up they will not bulge outwards when the axis is rotated so that no
exterior binding of wire is required to keep them in form. Z is a ring having
square holes formed in it to fit over the correspondingly square ends of the right
and left handed screws C and prevent them from turning after they have been
once adjusted-Z₁ are split pins to prevent the ring from slipping end wise off the
ends of the screws.
Figures 5 and 6 show a modification of the above construction in which the
right and left handed screws are upon the axis instead of using three or more
separate screws, in other respects the construction is the same as shewn at
Figures 1. 2. 3 and 4 and the parts are marked with the same letters of reference.
Figure 5 is an end elevation with half of the bobbin coils removed from the ring,
and Figure 6 a longitudinal section.
The commutator or collector of the Gramme or similar machine I form of a'
number of metallic segments ranged around the axle and parallel with it-the
several segments being insulated from one another as is usual and to hold the
segments to the axle I make the inner part of each segment of a dovetail form at
its ends.
The dovetail portions of the several segments at one of their ends lie under a
coned recess in a collar fast on the axis and at the other end under a similar recess
in a coned collar which can be forced along the axis towards the fixed collar by
means of a nut screwed on to a screw thread cut around the axle. When the nut
is screwed up so as to cause the dovetail ends of the segments to be gripped and
held between the two collars the nut itself is locked by a lock nut. In this way
the segments are securely held to the axle and there is no risk of their breaking
away from it when the axle is rapidly rotated.

page_text: This improvement is shewn at Figures 1 and 2 and also partly in end elevation
at Figure 7.
In these figures I. I. are the metallic segments with their ends of a dovetail
form J is a correspondingly coned collar for one end of the segments to rest
against and K a coned collar which can be forced against their opposite end by a
nut L screwed on the axis A-M is insulating material interposed between the
segments and the axis and collars J. K.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is:
First. In dynamo electrical machines in which what is known as a Gramme ring
is employed making the ring of a spherical or convex form on its exterior and the
faces of the magnet pole pieces of a corresponding concave form substantially as
described.
Second. The combination of an iron wire ring E the insulated coils F wound
upon such ring the segments D of wood or insulating material, the two conical
divisions of the hub B and a right and left handed screw or screws for drawing the
two parts of the hub together along the axis upon which they are mounted
substantially as described.
Third. The construction of the commutator or collector of the Gramme or similar
dynamo electrical machines with each of its metallic segments made of a dovetail
form so that its ends may be overlapped and held by correspondingly coned collars
-on the commutator axis substantially as described.