Note: Descriptions are shown in the official language in which they were submitted.
S P E C I F I C A T I O N
This invention relates to an infinitely variable
wear-free eddy current and/or hysteresis brake, preferably for
track bound vehicles, which is composed of one or a plurality
of similar elements fastened adjacent to each other in the
direction of motion.
An adjustable hysteresis brake which has already become
known is provided with two ring magnets which are magnetized in
the same direction and are turnable towards each other in order
to completely cancel out the magnetic field used for braking
or to provide a field of maximum value. With such a magnet
arrangement only low braking forces can be achieved. Therefore
these known hysteresis brakes have so far been used for reels in
order to maintain a thread tension during reeling off that is as
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constant as possible. (DAS 1 011 045)
To create a wear-free eddy current or hysteresis brake
for vehicles it is necessary to have available in the air gap
a high density of the magnetic lines of flux e.g. about 10,000 -
14,000 G in order to produce the highest possible braking force.
For the generation of such high air gap inductions it has been
difficult with known adjustable eddy current brakes to accommodate
the required quantity of permanent magnet material in the small
space available and with the lowest leakage possible. For this
reason the known permanent magnetic eddy current brakes have re-
latively large dimensions. For the accommodation of e.g. a track
brake between the running wheels of a bogie only a limited space
is available. Moreover, the magnet material used in the permanent
magnetic eddy current brakes of prior art is utilized badly due to
the great leakage. The foregoing reasons have been essentially
decisive for not introducing e.g. permanent magnetic track brakes
into practice. Therefore electromagnetically energized eddy current
brakes and hysteresis brakes are used although these brakes have
the disadvantage to be dependent on a se~arate current supply,
, 20 e.g. from a battery or a generator provided.
A further disadvantage of the electromagnetic wear-free
brakes is that if the source of current is interrupted, the
brakes will fail. Apart from this dangerous moment in
operation it has to be considered that the total electric
energy for the production of the magnetic field is completely
; converted into heat so that already after a short time of braking
the energizing coils are hested to
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1071282
very high temperatures~ Therefore most of the electromagnetical-
ly energîzed brakes generally provide a full braking effect for
only relatively short periods of time.
To overcome the above-referred problems and others,
it is the object of this invention to provide an infinitely
variable wear-free permanent magnetic eddy current and/or
hysteresis brake, preferably for track bound vehicles, which
has low leakage losses.
In accordance with the invention there is provided
one or a plurality of similar elements fastened adjacent to
each other in the direction of motion, the total permanent
magnet volume of each of said elements being composed of
turnable and stationary permanent magnets, with the turnable
permanent magnet being cylindrical and magnetized in the
direction of its diameter, the cylindrical axis of said
turnable permanent magnet being perpendicular to the surface
to be braked, said stationary permanent magnets being square-
shaped in cross section and elongated and arranged such that
their greatest length is also perpendicular to the surface
to be braked, each of said elements being provided with pole
pieces made from soft iron which on their opposite inner
surfaces are provided with segment-shaped recesses into which -~
said turnable permanent magnet cylinder projects, said ~ :
stationary permanent magnets being positioned with one pole at
said pole pieces and with the other pole facing lateral flux
return plates so that in the switched on position, the same poles
of said stationary permanent magnets and said turnable permanent
magnet cylinder are adjacent to the one same pole piece.
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1071282
Due to the invention it is possible to accommodate
the magnet materlal needed for the generation of a high
air gap induction of e.g. about 12,000 G within a very
small space. The stationary permanent magnets and the
turnable permanent magnet cylinder which are both adjacent
to the pole pieces of each element, serve to increase
the density of the magnetic lines of flux in the pole
pieces and are also part of the magnetic adjusting circuit.
Due to the arrangment according to the invention the
permanent magnet material accommodated in each element is
utilized optimally. The poles of same polarity of the
stationary permanent magnets and the poles of same polarity
of the turnable permanent magnet cylinder are each adjacent
to the same pole piece so that all magnetic lines of flux
are collected by the pole pieces and directed to the
working air gap. By means of the additional permanent
magnets arranged between the pole pieces, the leakage
occuring is minimized.
Contrary to the known eddy current brakes, ~here
for the purpose of switching off, the total magnet volume
accommodated must be displaced relative to the pole
pieces, it is only necessary with the device according
to this invention to move about half of the permanent magnet
material provided relative to the pole pieces in order to
adjust the braking torque. Thus switching on and off is
achieved by relatively low forces.
It has been found that the highest braking force
- can be achieved with a length 1 of each element of 70 mm+ 20 mm
and an air gap between the pole face of the brake and the tread
of about 7 mm. A considerable increase of
~71282
this length reduces the number of alternating poles and
consequently the braking force is reduced, too. If this
length is decreased, the leakage occurring will increase
so that a low braking force results as well.
By means of a suitable dimensioning of the magnetic
circuit of each element, i.e. both of the stationary and
the turnable permanent magnets, the magnetic field serving
for braking can be reduced completely or, corresponding to
the addition of both fields, it can be made to reach a
maximum. To achieve a complete reduction when the
movable magnet is turned, the total volume of the turnable
permanent magnet cylinder of each element is up to 10% larger
than the total volume of the stationary magnets, provided
that for both magnets the same magnet material has been
used. If a permanent magnet material of higher quality is
used for the turnable permanent magnet cylinder, the volume
can be correspondingly smaller than that of the stationary
permanent magnets.
It is also possible that only ~art of the turnable
permanent magnets, particularly the part arranged adjacent
to the surface to be braked, is made from a permanent
magnet material that is of higher quality than the material
used for the remaining part of the turnable and stationary
permanent magnets.
To achieve a particularly high air gap induction
with the smallest magnet volume possible, a magnet material
is preferably used for the turnable and stationary permanent
magnets which is made from an alloy of rare earth materials
with cobalt, as e.g. cobalt-samarium. This alloy has been
known for about lO years. As the permanent magnets made
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from rare earths are relatively brittle and tend to crack easily,
the disc-shaped permanent magnets are arranged in layers one upon
the other to form a cylinder. Between the layers of permanent
magnets thin non-magnetic foils are arranged, which are e.g. made
from non-magnetic steel as V2a-steel ~registered trademark) and
have a thickness of less than 0.3 mm. The disc-shaped permanent
magnets which are assembled in this way to form a cylinder and are
magnetized in the direction of their diameter, are arranged in a
tube of non-magnetic material. In the same manner the stationary
magnets may also be arranged in layers with non-magnetic foils
being provided between the individual layers of permanent magnets.
To increase the reliability in operation of the brake, in
particular this means to avoid the freezing of condensates which
may occur between the stationary and turnable parts and to prevent
any damages of the magnets caused by vibrations and shocks due to
the rough nature of most rails for trains, a damping fluid,
preferably silicone oil, is provided in the spaces between the
stationary and turnable permanent magnets.
The principal object of the invention is the provision
of a new and improved eddy current or hysteresis brake, preferably
for track bound vehicles, which is infinitely variable, wear-free
and easily and readily adjusted with a minimum of external force.
Another object of the invention is the provision of a
new and improved track brake of the type described which provides
a maximum braking effort for a given physical size brake.
1071Z8Z
- Another object of the invention is the provision of a
new and improved eddy current or hysteresis track brake wherein
a cylindrical rotatable permanent magnet is arranged between
a pair of pole pieces and magnetized on its diameter, and a
plurality of stationary permanent magnets are provided
polarized so as to magnetize the pole pieces with the opposite
magnetic polarity, the cylindrical magnet being rotatable so as
to change the flux at the ends of the pole pieces from a maximum
to a minimum.
Another object of this invention is to provide an
infinitely variable wear-free permanent magnetic eddy current
and/or hysteresis brake which is easy to operate.
Still another object of this invention is to provide
an infinitely variable wear-free permanent magnetic eddy
current and/or hysteresis brake wherein a large volume of
permanent magnet material can be accommodated in a design
having relatively small dimensions and an optimal succession
of alternating poles so that the necessary air gap induction
for the production of sufficiently high braking forces is
maintained. ;~
In accordance with one broad aspect, the invention
relates to an infinitely variable wear-free permanent magnet
brake, preferably for track-bound vehicles, comprising: one or
a plurality of similar magnetic assemblies fastened adjacent to
each other in the direction of motion, the total permanent
magnet volume of each of said assemblies being composed of a turn-
able magnet and a plurality of stationary permanent magnets, with
the turnable permanent magnet being cylindrical and magnetized
in the direction of its diameter, the cylinder axis of said
turnable permanent magnet being arranged in perpendicular
direction to the surface to be ~raked, said stationary permanent
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magnets being elongated and square-shaped in cross section with
their greatest length also extending in perpendicular direction
to the surface to be braked, each of said assemblies being
provided with pole pieces made from soft iron which on their
opposite inner surfaces are provided with arcuate-shaped
recesses into which said turnable permanent magnet cylinder
projects, said stationary permanent magnets being positioned
with one pole facing said pole pieces and with the other pole
facing lateral flux return plates so that in switched on
position the same poles of said stationary permanent magnets
and said turnable permanent magnet are each adjacent the same
pole piece.
The aforementioned objects and advantages will
become apparent from the following description used to
illustrate a preferred embodiment of the invention when read in
connection with the accompanying drawings in which:
Fig. 1 is a horiæontal section of a braking element
of the brake along the line I-I of Fig. 3;
Fig. 2 is a horizontal section, partly broken away,
through the brake, showing that several elements are arranged
adjacent to each other in the direction of motion or the
rail, respectively;
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107~2~2
Fig. 3 is an enlarged vertical sectional view along
the line II-II of Fig. 2;
Fig. 4 is an enlarged vertical sectional view of
the brake along the line III-III of Fig. 2;
Fig. 5 is a bottom plan view of the brake.
According to Fig. 1 an element of the brake is
composed of six stationary permanent magnets 1-6 and a turnable
permanent magnet 7 which is cylindrical as can be seen from
Fig. 3. Furthermore, two pole pieces 8,9 are provided
(one half of each pole piece is illustrated) which have
arcuate-shaped recesses 10, 11 on their opposite inner surfaces. ~
The cylindrical turnable permanent magnet 7 projects into these -
recesses so as to have a minimum air gap therebetween. One
magnetized pole of the stationary permanent magnets 1,2,3,4 is
adjacent to small lateral faces 12 of the pole pieces 8,9 whereas
the respective counterpole is adjacent to a pair of outside flux
return plates and screen members, respectively 16,17 which
confine the brake. With part of their poles the stationary
permanent magnets 5 and 6 are contiguous to opposite inner
faces 13 of the pole pieces 8, 9 with the same polarity as the
adjacent stationary magnets 1,2,3,4. Non-magnetic intermediate
pieces 14,15 which are preferably made from aluminum, are
provided between the stationary permanent magnets 1,2,3,4 and
between magnets 5,6 and the outside flux return plate and
screen member, respectively,
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16,17. ~s can be seen from the polarities marked with
the letters N and S, poles of same polarity of both the
stationary permanent magnets and the turnable permanent
magnet cylinder are adjacent to the pole pieces 8 and 9,
respectively so that the pole piece 8 forms a north pole
and the pole piece 9 a south pole. In this condition, the
element is switched on. In this position of switching,
' all magnetic lines of flux emanating from the poles are
collected and, within the pole pieces, directed to the
working air gap 18. The stationary permanent magnets 5,6 are
provided for the purpose of minimi~ing the leakage
between the pole pieces 8,9 of opposite polarity.
Operation of the brake will be described subse-
quently.
Fig. 2 clearly shows the complete arrangment of
the brake that is composed of a plurality of elements according
to Fig. 1, which are provided in longitudinal direction
; to the direction of motion or the rail, respectively.
The vertical section of Fig. 3 along the line II-II
of Fig. 1 shows the assembly of the turnable permanent magnet
7 that consists of individual permanent magnet discs 7a, 7b
etc. which are arranged in layers one upon the other and form
a cylinder 19. To avoid the formation of cracks, thin non-
magnetic foils 20 having a thickness of about 0.2 mm are
arranged between the individual permanent magnets. These
foils are made from non-magnetic steel such as e.g. V2a-
steel (registered trademark).
This arrangment will be particularly suitable if the
permanent magnets are made from rare earth alloys
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~07~28Z
which are relativeIy brittle and tend to crack and break
under the influence of shocks.
For providing a better stability and avoiding cracks,
the breaking out of edges and the like, the permanent
magnet discs 7a of the cylinder 19 which are arranged in
layers one upon the other, including the intermediate non-
magnetic foils, are arranged in a tube 21 of non-magnetic
material. The upper front face 22 of the tube is provided
with a toothed wheel or gear 23 in which opposite toothed
10 racks 24 engage for the purpose of turning the magnet
cylinder 7. The bottom side of the magnet cylinder 7
is pivoted by means of shafts 26,27. These shafts are
fastened toa cover plate 28 and a non-magnetic base plate
29.
Fig. 3 further shows the stationary magnets 5,6,
the non-magnetic intermedi^ate pieces 14,15 and the flux
return plates and screen members, respectively, 16, 17
which confine the longitudinal sides of the brake. For
increasing the reliability in operation, particularly at
20 low temperatures and under the influence of shocks, a
damping fluid, e.g. silicone oil, is provided in the air -
gap 30 between the turnable magnet cylinder 19 and the
stationary permanent magnets.
As may be seen in Fig. 4, showing the vertical
section along the line III-III of Fig. 2, the stationary
magnets 1,3 are adjacent to the pole piece 8. At its lower
part this pole piece is broadened towards the pole head 31.
The working air gap 18 of about 7 mm is provided between
the pole face 34 of the pole head 31 and the tread 32 of
30 the rail (shown partly broken away). The pole head
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10712~2
projects into the non-magnetîc base plate 29 and is flush with
the bottom side of this plate.
The bottom plan view of the brake according to Fig. 5
shows the pole faces 34 of the pole heads which are arranged
in corresponding recesses of the non-magnetic base plate 29.
In~Fig. 2 the brake is shown in switched-on position.
The poles of both the stationary and the turnable permanent
magnets are marked with the letters N and S. As may be seen
in the drawing. The south poles of both the stationary and
the turnable permanent magnets are adjacent to the pole
piece 8, whereas the north poles of the stationary and turnable
permanent magnets are contiguous to the pole piece 9. In
this matter a north pole results in the pole piece 8 and a south
pole in the pole piece 9. Thus two magnetic circuits are
formed, both contributing to the excitation of the pole pieces
and the adjustment of the braking torque. In this position
of switching the lines of magnetic flux of the magnetic circuit
emanate from the pole piece 8, cross the air gap 18, pass through
the rail 33 and enter into the pole piece 9 of opposite
polarity. If for the purpose of switching off the permanent
magnets 7 are turned by 180 by opposite displacement of the
racks 24, poles of alternate polarity are adjacent to the pole
pieces so that the lines of magnetic flux short-circuit within
the magnet arrangement of each element and the resulting magnetic
field in the air gap is cancelled out.
Depending on the desired value, the braking torque
can be infinitely varied by turning the turnable permanent
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~71219Z
magnets by more or less degrees.
In order to switch off the brake completeIy, the
magnet volume of the turnable permanent magnets must be
about 10% larger than the total volume of the stationary
permanent magnets, provided that the same magnet material
is used for both the turnable and the stationary permanent
magnets.
In order to obtain the highest possible air gap
induction and consequently particularly effective braking
forces, the permanent magnet material preferably used for
the stationary and turnable magnets may be an alloy of
rare earths with cobalt. Of course, the invention is not
limited to this magnet material. Any other magnet material
having the highest possible ~BH) max-value may be used as
well.
The invention is not restricted to the aforedescribed
embodiment. Instead of a plurality of stationary permanent
magnets it is also possible to provide only one stationary
permanent magnet adjacent to the turnable permanent magnet.
It is further possible to form the pole pieces, which
are provided with segment-shaped recesses, as a whole body or
subdivide them centrally.
Often it is desired that the brake acts on ring- or
disc-shaped surfaces. In this case, the brake is formed
as a ring-segment-shaped body.
For braking a track-bound vehicle the ring-segment-
shaped brake may be arranged on one or both sides of the running
wheels or on one or both sides of a brake disc arranged on
the wheel axle such that the pole faces of the brake are
opposite to the front faces of the wheel rim or brake disc.
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