Electro-magnetic Brake for Railways for Reducing High Speeds.
Year: 1890

page_text: Date of Application, 5th June, 1890
Complete Specification Left, 4th Mar., 1891-Accepted, 4th Apr., 1891
PROVISIONAL SPECIFICATION.
Electro-magnetic Brake for Railways for Reducing High Speeds.
1. HENRY EDMOND WALTER, of 31, Westbourne Terrace, in the County of
Middlesex, Electrician, do hereby declare the nature of this invention to be as
follows :-
According to my invention I provide for reducing the speed of trains travelling
at high speeds by means of the reaction produced by causing Foucault currents to
be induced in a stationary line of metal by magnets carried by the train with their
poles in close proximity to the line of metal.
::
There are three principal objects in this:-Firstly to obtain a retarding force on
the train greater than that due to the coefficient of friction given by a brake shoe
on cach wheel at maximum pressure even without "skidding." Secondly (at very
high speeds) the great heat produced does not take place in the carried braking
part but is left behind in the rail or line of metal. Thirdly there is no wear or tear
to either magnets or rails.
I use two or more magnet poles preferably a series alternately of opposite polarity
set in a line parallel with the rail and in close proximity to it so that magnetic
lines of force pass through the rail from one magnet pole to another.
At a high speed say 60 miles an hour there would be an E. M. F. sufficient to
induce very large currents around the rail.
E²
R
The work represented done by these currents is where E is the electro motive
force induced in the part of the rail that the resistance R is taken for as a circuit-
E varies as the speed and the magnetism. Neglecting for the present the reaction
due to the demagnetizing action of the induced current on the magnets and assuming
a constant magnetism then for a given magnetism the work varies as the square of the
speed if the resistance be constant. The resistance at any instant is that due to
the section and length taken by the current induced and this current is induced by
There
the lines of force passing into the top of the rail and not out of the bottom.
must therefore be an E. M. F. in the top and none in the bottom, so a current flows
round the rail. As (assuming no reaction for the present) the lines are in a
constant relative position, independent of the speed, R is constant and we have
work done on rail varying as the square of the speed but force varies inversely as
speed for a given work, so that with this brake the force varies directly as the
speed (remembering that the demagnetizing action of the current on the magnets
is neglected for the present).
In
Such a brake would reduce say from 60 or any amount more miles per hour to 25
or 20 miles and then the air brake or some other form of brake must be used.
case of the necessity of stopping in a given distance the great object is to reduce
the high speed, as from 20 miles an hour a train can be stopped in a very short
distance with the present brakes.
The reaction of the current in the rail produces a retarding force on the magnets
but it also has the effect of weakening the magnets and this requires additional
magnetizing force, so that after a given speed there would only be a given force
and no more. But if a coefficient of say 4, including the brakes which give say
something like 15, is obtained at 60 miles per hour more would hardly be needed
for any speed.
In order that the magnets may be brought very near to the rail but still to have
a definite clearance these magnets could be attached between two pairs of wheels
not far apart as in a bogey either on bearings of their own or attached to the boxes

page_text: but not to the carriages on account of the springs. It would be economical to run
within about of an inch of the rail.
The magnets will take a good deal of energy to charge for this purpose and
although storage batteries on the train could be used it would be less weight to
have a dynaino on 'the engine. The work required of the dynamo-would be only
when it is required to stop so that there would not be any waste of power, except
that to run the dynamo free on open circuit.
Again in the case of an electric railway the magnets might be charged by the
current used for driving.
In place of using magnet poles to set up currents in the rails they might be used
to set up currents in a separate metallic plate which may be of iron or copper or
other good conductor placed say in the middle of the track. With a wide plate
much smaller magnets less energy and a smaller dynamo to charge them will be
required even if the plate be thin.
Dated this 5th day of June 1890.
CARPMAEL & CO.,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Electro-magnetic Brake for Railways for Reducing High Speeds.
I, HENRY EDMOND WALTER, late of 31, Westbourne Terrace, in the County
of Middlesex, and now of 3, Princes Mansions, Victoria Street, in the same County,
Electrician, 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 my invention 1 provide for reducing the speed of trains travelling
at high speeds by means of the reaction produced by causing Foucault currents to
be induced in a stationary line of metal by magnets carried by the train with their
poles in close proximity to the line of metal.
There are three principal objects in this: Firstly to obtain a retarding force on
the train greater than that due to the co-efficient of friction given by a brake shoe
on each wheel at maximum pressure even without skidding." Secondly (at very
high speeds) the great heat produced does not take place in the carried braking
part, but is left behind in the rail or line of metal. Thirdly there is no wear or
tear to either magnets or rails.
I use two or more magnet poles preferably two poles of opposite polarity set in a line
parallel with the rail and in close proximity to it so that magnetic lines of force pass
through the rail from one magnet pole to the other. A magnet so held in proximity
to the head of a rail is shewn in Figure 1 of the drawing annexed. In this
figure A. B. are the magnet poles and the rail.
At a high speed say 60 miles an hour there would be an E. M. F. sufficient to
induce very large currents around an ordinary railway rail.
E
R
The work represented done by these currents is where E is the electro motive
force induced in the part of the rail that the resistance R is taken for as a circuit-
.E varies as the speed and the magnetism. Neglecting for the present the reaction due
to the demagnetizing action of the induced currents "on the magnets and assuming
a constant magnetism then for a given magnetism the work varies as the square of
the speed if the resistance be constant. The resistance at any instant is that due
to the section and length taken by the current induced and this current is induced
by the lines of force passing into the top of the rail and not out of the bottom.
There must therefore be an E. M. F. in the top and none in the bottom, so a
⚫ current flows round the rail. As, assuming no reaction for the present, the lines
. are in a constant relative position, independent of the speed, R is constant and we
have. work done, on rail varying as the square of the speed but force varies
'

page_text: inversely as speed for a given work, so that with this brake the force varies
directly as the speed (remembering that the demagnetising action of the current on
the magnets is neglected for the present).
The reaction of the current in the rail produces a retarding force on the magnets
which constitutes the braking force, but it also has the effect of weakening the
magnets, and now to overcome this a great deal of additional magnetizing force is
used, but at the limit of magnetizing force or current available for the magnets,
there would after a given speed be a given force and no more.
But if a co-efficient
of say 4, including the brakes which give say something like 1 or 15, is obtained
at 60 miles per hour, more would hardly be needed for any speed.
Such a brake would reduce say from 60 or any amount.more miles per hour to 25
or. 20 miles or perhaps less than the air brake or some other form of brake must be
used. In case of the necessity of stopping in a given distance the great object is to
reduce the high speed, as from 20 miles an hour a train can be stopped in a very
short distance with the present brakes.
In ordinary railway rails a great portion of the energy developed occurs in the
uppert part or head of the rail. In order to utilize this without having to magnetize
the web and lower part with every magnet, a brake can be constructed as in
Figures 2 or 3. Where the outer magnet after developing currents in the upper
part magnetizes as fully as possible the web and lower part and the intermediate
one, two or more magnets only develop enough magnetism to about fill the head.
This arrangement also tends to reduce the leakage as two similar poles occur
together.
In order that the magnets may be brought very near to the rail but still to have
a definite clearance these magnets could be attached between two pairs of wheels
not far apart either on bearings of their own or attached to the boxes but not to the
scarriages on account of the springs. It would be economical to run within about of
an inch of the rail.
In fastening to axle boxes &c. a piece of india rubber at ii in Figure 4 could be
used to be compressed down to a stop, when the magnetic brake is used, by the
attraction of the magnets to the rail thus giving the magnet with its winding &c. a
spring except just when being used and at the same time saving the strain of extra
mass (of material) directly on the wheels.
The magnets-will-take a good deal
although storage batteries on the car of energy to charge for this purpose and
could be used it would be less weight to
have a dynamo in the guard's van or on the engine. The work required of the
dynamo would be only when it is required to stop, so that there would not be any
waste of power, except that to run the dynamo free on open circuit.
Again in the case of an electric railway the magnets might be charged by the
current used for driving.
In place of using magnet poles to set up currents in the rails they might be used
to set up currents in a separate metallic plate which may be of copper or other
good conductor placed, say in the middle of the track as illustrated in Figures 5
and 6. In these figures A B are the magnet poles and C the metallic plate. With
a suitable plate of copper, much less total weight of magnets, less energy, and a
smaller dynamo to charge them will be required, even if the plate be very thin, or
else a breaking force at much lower speeds could be obtained. In some cases it may
be advantageous to form the magnets with laminated pole pieces.
If the magnets are arranged to act on the rails a magnet or magnets should be
used to act on each rail. Preferably also the magnets are applied to every vehicle
in a train and their coils supplied with current from one dynamo, on one or other
of the vehicles.
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
claun is:-
1. An electro magnetic brake for railways composed of electro magnets carried

page_text: by the vehicles with the magnet poles in close proximity to the rail or rails or to a
fixed conducting bar parallel therewith but retained by stops from coming into
contact with them and a dynamo or other suitable means for supplying the coils of
such magnet or magnets with electrical current when the speed at which the
vehicle is travelling has to be diminished.
2. An electro magnetic brake for railways composed of electro magnets carried
by the vehicles with both poles of, each magnet in close proximity to and in a line
parallel with the rails but retained by stops from coming into contact with them
and means for supplying the coils of such magnet or magnets with electrical current
when the speed at which the vehicle is travelling has to be diminished.
3. An electro magnetic brake for railways composed of electro magnets carried
by the vehicles with the poles of each magnet on two opposite sides of a fixed
metallic conductor which is parallel with the rails the poles being kept in close
proximity to the bar but restrained from coming into contact therewith and means
for supplying the coils of such magnet or magnets with electrical current when the
speed at which the vehicle is travelling has to be diminished.
4. An electro magnetic brake for railways composed of one or more electro
magnets carried by the vehicles with both poles in proximity to one of the rails but
retained from coming into contact with it and with both poles situated between the
poles of another electro magnet all the poles being in one line parallel with the rail
substantially as described.
5. An electro magnetic brake for railways composed of electro magnets carried
from the axles or axle boxes of the vehicles in such manner that both magnet poles
are in a line with the rails and in close contiguity to them substantially as described.
6. An electro magnetic brake for railways composed of electro magnets carried
from the axles or axle boxes of the vehicles in close contiguity to the rails and
with springs interposed between the magnets and the axles or boxes which allow
the magnets to move nearer to the rails when current is passed through the magnet
coils substantially as described.
Dated this 4th day of March 1891.
CARPMAEL & Co.,
Agents for the Applicant.