U.S. patent number 3,768,417 [Application Number 05/165,616] was granted by the patent office on 1973-10-30 for transportation system employing an electromagnetically suspended, guided and propelled vehicle.
This patent grant is currently assigned to Massachusetts Institute of Technology. Invention is credited to Henry H. Kolm, Richard D. Thornton.
United States Patent |
3,768,417 |
Thornton , et al. |
October 30, 1973 |
TRANSPORTATION SYSTEM EMPLOYING AN ELECTROMAGNETICALLY SUSPENDED,
GUIDED AND PROPELLED VEHICLE
Abstract
A system that includes an elongate cylindrical vehicle operable
to travel along a similarly-shaped, trough-like guide-way. At
stations along the guideway, the vehicle is supported by wheels,
but between stations it levitates at about 25 centimeters above the
inside guideway surface. Levitation of the moving vehicle is
effected by interaction between magnetic dipole fields provided by
superconducting coils or permanent magnets disposed over
substantially the whole lower surface area of the vehicle and a
pair of spaced conducting strips located on the guideway inner
surface and oriented parallel to the longitudinal axis of the
guideway throughout its length. The vehicle is free to rotate or
pivot about its longitudinal axis and this, coupled with the very
resilient support over its entire length, permits it to travel at
200 kilometers per hour and beyond with minimum discomfort to
passengers being transported. The magnet dipole fields must be of
the order of 1,000 to 3,000 gauss at a distance of 25 centimeters
from the vehicle to give the support necessary to maintain the 25
centimeter clearance. The necessary propelling force is supplied by
a polyphase winding which is disposed in the lower portion of the
guideway between the conducting strips; the winding produces a
traveling-wave magnetic field that interacts with the magnetic
dipole fields. Between stations synchronous operation is
accomplished by employing a.c. power input with a cycloconverter,
i.e., an a-c to a-c converter, to reduce the input frequency to an
appropriate ratio. Acceleration and deceleration of the vehicle is
accomplished by varying the frequency of the cycloconverter to
provide synchronous interaction between the magnetic field of the
winding and the magnetic dipole fields of the superconducting coils
as the vehicle accelerates. Provision is made for switching
vehicles, and a novel method of guideway fabrication is
disclosed.
Inventors: |
Thornton; Richard D. (Concord,
MA), Kolm; Henry H. (Wayland, MA) |
Assignee: |
Massachusetts Institute of
Technology (Cambridge, MA)
|
Family
ID: |
66818724 |
Appl.
No.: |
05/165,616 |
Filed: |
July 23, 1971 |
Current U.S.
Class: |
104/282; 104/285;
104/286; 104/298; 191/2; 318/135; 335/216; 505/903; 505/906;
104/130.03 |
Current CPC
Class: |
B60L
13/10 (20130101); B61B 15/00 (20130101); B60L
15/005 (20130101); B61B 13/08 (20130101); Y02T
10/64 (20130101); B60L 2200/26 (20130101); Y02T
30/30 (20130101); Y10S 505/903 (20130101); Y02T
10/645 (20130101); Y02T 10/644 (20130101); Y02T
30/00 (20130101); Y10S 505/906 (20130101) |
Current International
Class: |
B60L
13/10 (20060101); B60L 15/00 (20060101); B60L
13/00 (20060101); B61b 013/08 () |
Field of
Search: |
;104/148LM,148MS,148SS,130 ;191/2 ;318/135,227 ;310/12,13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Forlenza; Gerald M.
Assistant Examiner: Libman; George H.
Claims
What is claimed is:
1. An electromagnetic transportation system comprising, in
combination: a vehicle having a cylindrical lower surface and
carrying a plurality of superconducting coils distributed over a
substantial portion of the lower surface, said superconducting
coils being positioned within the vehicle adjacent said lower
surface and having a contour similar to the contour of that
surface, means for maintaining the superconducting coils at a
superconducting temperature, individual coils having sufficient
area and being energized with sufficient peristent supercurrent to
generate a magnetic dipole field having an intensity of 1,000 to
3,000 gauss at a distance of approximately 25 centimeters from the
lower surface of the vehicle, adjacent coils being energized so as
to produce magnetic fields oriented alternately upward and
downward; a trough-like, cylindrically-shaped guideway surrounding
approximately the lower third of the circumference of the vehicle
to support, guide and propel said vehicle, said guideway containing
both active, current-carrying conductors and passive conductors
forming a substantially continuous surface along the length of the
guideway exposed to the magnetic field of the superconducting coils
in the vehicle so as to support the vehicle, when the vehicle is
moving at a speed above a predetermined minimum value, at a
clearance of approximately 25 centimeters by interaction between
the magnetic dipoles of the vehicle coils and the eddy currents
they induce in the passive conductors, the current-carrying, active
conductors being shaped so as to form a series of overlapping
current loops strung axially along the guideway and substantially
conforming to the cylindrical surface of the guideway so as to
generate, when energized, an alternating magnetic field which moves
along the axis of the guideway and propels the vehicle at
synchronous speed by interaction with the magnetic dipoles of the
vehicle coils; a source of multiphase alternating electric current
connected to energize the active conductors in correct sequence;
and control means operable to connect the source of electric
current to any particular active conductor; the moving vehicle
being electromagnetically supported resiliently at a clearance of
about 25 centimeters from the guideway and being free to rotate
about its longitudinal axis so as to establish the correct bank
angle when negotiating turns, the guideway being banked at only
approximately the correct angle in turns, the center of
electromagnetic lift of the vehicle being located above its center
of gravity so as to insure stability.
2. In the electromagnetic transportation system of claim 1 a
cycloconverter connected as part of the source of alternating
electric current, the cycloconverter being operable to generate
frequencies lower than those of the input electric power.
3. In the system of claim 2, speed control means connected to the
cycloconverter to control the frequency output thereof and hence
the speed of the vehicle for cruising and for acceleration and
deceleration of said vehicle.
4. A system as claimed in claim 2 comprising two substantially
parallel-oriented guideways each of which is made up of a plurality
of serial sections of guideway, four sections at each region of the
system constituting a block, the active conductors of each section
being electrically insulated from all other sections, a transformer
associated with each block, a cycloconverter being connected
between the secondary of each transformer and the active conductors
of each section, and speed control means connected to control the
frequency output of each cycloconverter and hence the speed of a
vehicle in any particular section.
5. A system as claimed in claim 4 in which the transformer and
cycloconverter units which energize each of the four guideway
sections in a block are governed by three control systems: a block
control having its primary input by transmission from the vehicle,
which serves to energize any of the four guideway sections in the
associated block when said section is occupied by a vehicle so as
to provide acceleration, deceleration or synchronous propulsion at
a desired speed; a regional control derived from several
neighboring blocks which serves to over-ride the block control if
this is necessary to maintain a predetermined safe vehicle
separation; and a central control which monitors operation of the
entire system, serves as a backup for the regional control, and
which over-rides the block control if this becomes necessary to
avoid congestion at any point of the system, or in the event of
mechanical failure or accident.
6. An electromagnetic transportation system according to claim 1 in
which the guideway is constructed of bonded aluminum laminations,
suitably interleaved with insulation so as to provide both the
passive and the active current-carrying conductors, and having
sufficient mechanical strength and rigidity to support the vehicle
and to maintain the required dimensional tolerances without the
need for additional re-enforcing structures, and being constructed
in such a manner that all exposed surfaces of the guideway are
smooth and electrically neutral.
7. An electromagnetic transportation system according to claim 1 in
which the vehicle is circular cylindrical and in which the
superconducting coils in the vehicle extend over an appreciable
fraction of the underside of the vehicle to distribute the vehicle
weight more or less uniformly over the entire guideway beneath the
vehicle.
8. An electromagnetic transportation system according to claim 1 in
which wheels are provided on the vehicle to support the vehicle
when its speed falls below the minimum speed required for
electromagnetic levitation, which is approximately 35 kilometers
per hour.
9. An electromagnetic system as claimed in claim 1 in which wheels
are provided on the guideway at station sections thereof to support
the vehicle when its speed falls below the minimum speed required
for electromagnetic levitation.
10. An electromagnetic railway system according to claim 1
characterized by the fact that the guideway trough is covered by an
upper shell so as to provide a sealed tunnel which can be installed
underground and/or partially evacuated to reduce aerodynamic drag
at speeds above 500 kilometers per hour.
11. An electromagnetic transportation system according to claim 1
in which said source is a power supply system comprising
multi-phase transformers located at suitable intervals along the
guideway and in which the control means includes switching elements
controlled in part by signals from the vehicle and operable to
connect the transformer to the active conductors in a determined
sequence, each transformer being capable of energizing any one of
four sections in a block of a two-lane guideway system while the
section in question is occupied by the vehicle.
12. An electromagnetic transportation system according to claim 11
in which the power supply system operates at a fixed frequency in
constant speed cruising sections of the guideway and in which power
supply system utilizes controllable switching elements over
accelerating and/or decelerating sections of the guideway so as to
provide variable speed synchronization at controllable thrust.
13. An electromagnetic transportation system according to claim 1
in which the cross-section of the vehicle and/or of the
superconducting coils adjacent to its surface are slightly
elliptical so that the clearance between the vehicle coils and the
cylindrical guideway trough is slightly smaller at the sides of the
vehicle than its center, thereby to raise the center of lift of the
suspension and increase its lateral stiffness in relation to its
vertical stiffness.
14. An electromagnetic transportation system according to claim 1,
characterized by the fact that the guideway is provided with
vehicle switching sections to permit a vehicle to be routed to one
of several sidings at full cruising speed by elastically deflecting
a sufficiently long section of the guideway to permit a smooth
transition of the vehicle to one of several alternate sidings.
15. An electromagnetic system as claimed in claim 1 in which the
vehicle is provided with a plurality of extendible wheels at each
side thereof and in which the guideway is provided with tracks to
receive the wheels.
16. An electromagnetic system as claimed in claim 15 in which the
wheels are extendible to two positions outward from the vehicle and
in which the guideway has two side-by-side tracks on either side
thereof to receive the wheels at the respective positions, one of
the tracks on each side of the guideway being inclined at an angle
to the other two tracks to allow a vertical change in the direction
of movement of the vehicle along the guideway, thereby to effect
switching thereof.
17. A system as claimed in claim 16 in which means is provided to
extend and retract said wheels and in which means is provided for
raising and lowering said wheels when in the extended position.
18. A system as claimed in claim 16 having means for braking the
vehicle through interaction between the wheels and the track.
19. A system as claimed in claim 1 in which said superconducting
coils are oriented to produce field lines that are primarily normal
to the lower surface of the vehicle at said surface.
20. A system as claimed in claim 1 in which the vehicle is provided
with skids for emergency stops between stations.
21. A transportation system employing magnetic levitation
comprising, in combination, a passive vehicle carrying a series of
superconducting coils capable, when energized, of generating
magnetic fields of the order of 1,000 to 3,000 gauss at a distance
of 25 centimeters from the vehicle lower surface, said coils being
disposed substantially over the whole lower surface area of the
vehicle, an active guideway in the shape of a trough surrounding
about the lower third of the vehicle, said trough containing linear
synchronous motor propulsion coils embedded in the middle section
and capable of providing enough force for acceleration and cruising
of the vehicle, said propulsion coils utilizing the field of the
superconducting coils as part of the linear synchronous motor, the
portions of the trough on either side of the propulsion coils being
constructed of conductive material in which eddy currents are
induced by the passage of the energized superconducting coils over
the trough, which eddy currents produce through interaction with
the field of the superconducting coils a repulsive force that
levitates the vehicle and furnishes lateral guidance, a wayside
power system comprising multiphase transformers located at
approximately 1 to 5 kilometer intervals along the guideway, and
electronically switched electric power means to provide
acceleration and deceleration of the vehicle, said electronically
switched electric power means being connected to effect excitation
of the propulsion coils with a variable frequency electric current,
said frequency being variable so as to allow smooth acceleration
and deceleration of the vehicle, thereby to provide variable speed
synchronization at controllable thrust.
22. An electromagnetic transportation system comprising, in
combination: a vehicle having a cylindrical lower surface and
carrying a plurality of superconducting coils distributed over a
substantial portion of that lower surface, said superconducting
coils being positioned within the vehicle adjacent said lower
surface and having a contour similar to the contour of that
surface, means for maintaining the superconducting coils at a
superconducting temperature, individual coils having sufficient
area and being adapted, when energized with sufficient persistent
supercurrent, to generate a magnetic dipole field having an
intensity of 1,000 to 3,000 gauss at a distance of approximately 25
centimeters from the lower surface of the vehicle, adjacent coils
being energized so as to produce magnetic fields oriented
alternately upward and downward; a trough-like,
cylindrically-shaped guideway surrounding approximately the lower
third of the circumference of the vehicle to support, guide and
propel said vehicle, said guideway containing both active,
current-carrying conductors and at least one passive conductor
distributed therealong, the passive conductor providing
substantially continuously electrically conductive means along the
length of the guideway exposed to the magnetic field of the
superconducting coils in the vehicle so as to support the vehicle,
when the vehicle is moving at a speed above a predetermined minimum
value, by interaction between the magnetic dipoles of the vehicle
coils and the eddy currents they induce in the passive conductor,
the current-carrying, active conductors being positioned to form a
series of overlapping current loops strung axially along the
guideway and substantially conforming to the cylindrical surface of
the guideway so as to generate, when energized, a traveling
magnetic field which moves along the axis of the guideway and
propels the vehicle at synchronous speed by interaction with the
magnetic dipoles the vehicle coils; a source of multiphase
alternating electric current connected to energize the active
conductors in correct sequence; and control means operable to
connect the source of electric current to any particular active
conductor; the moving vehicle being supported resiliently at a
clearance of about twenty-five centimeters from the guideway and
being free to rotate about its longitudinal axis so as to establish
the correct bank angle when negotiating turns, the guideway being
banked at only approximately the correct angle in turns, the center
of electromagnetic lift of the vehicle being located above its
center of gravity so as to insure stability.
23. An electromagnetic transportation system comprising, in
combination: a vehicle having a cylindrical lower surface and
carrying a plurality of magnetic means for creating a plurality of
radial magnetic dipole fields distributed over a substantial
portion of that lower surface, said magnetic means being positioned
within the vehicle adjacent said lower surface, the magnetic means
having sufficient area to generate a magnetic dipole field having
an intensity adequate to levitate the vehicle ten to fifty
centimeters above the guideway, adjacent dipole fields so created
being oriented alternately upward and downward; a trough-like,
cylindrical-shaped guideway surrounding a portion of the lower
circumference of the vehicle to support, guide and propel said
vehicle, said guideway containing both active, current-carrying
conductors and passive conductive means distributed therealong, the
passive conductive means providing electrically conductive means
along the length of the guideway exposed to the magnetic dipole
fields of the magnetic means in the vehicle so as to support the
vehicle, when the vehicle is moving at a speed above a
predetermined minimum value, by interaction between the magnetic
dipoles of the vehicle magnetic means and the eddy currents they
induce in the passive conductive means, the current-carrying,
active conductors being shaped so as to form a series of
overlapping current loops along the axis of the guideway and
substantially conforming to the cylindrical-shaped surface of the
guideway so as to generate, when energized, a magnetic field which
moves along the axis of the guideway and propels the vehicle at
synchronous speed by interaction with the magnetic dipoles of the
vehicle magnetic means; a source of multiphase alternating electric
current connected to energize the active conductors in correct
sequence; and control means operable to connect the source of
electric current to any particular active conductor; the moving
vehicle being thereby supported resiliently above the guideway and
being free to pivot about its longitudinal axis so as to establish
the correct bank angle when negotiating turns, the guideway being
banked at only approximately the correct angle in turns, the center
of electromagnetic lift of the vehicle being located above its
center of gravity so as to insure stability.
24. A transportation system as claimed in claim 21 in which the
superconducting coils and the conductive material at each side of
the trough-shaped guideway in an operating system act to provide
both levitation and lateral guidance.
25. A transportation system as claimed in claim 24 in which the
electronically switched power means comprises one or more
cycloconverters electrically connected between each multiphase
transformer and the propulsion coils and in which a communication
link is provided between the vehicle and the electronically
switched power means to effect and maintain synchronous
electromagnetic interaction between the superconducting field and
the field of the propulsion coils.
26. A transportation system as claimed in claim 25 in which the
communication link is a short range radio link.
27. A transportation system as claimed in claim 25 in which the
communication link comprises conducting means in the guideway and
electrically coupled to the electronically switched power
means.
28. A transportation system as claimed in claim 21 in which the
conductive material is substantially continuously conductive.
29. A transportation system as claimed in claim 21 in which each of
the superconducting coils with its liquid helium system is
surrounded by a radiation shield, the radiation shields being
cooled by liquified gas which also serves to provide on-board
auxiliary power.
Description
The present invention relates to a transportation system and,
particularly, to a system employing electromagnetic levitation of a
vehicle in a guideway and electromagnetic propulsion of the vehicle
along the guideway; the term "magneplane" is used herein to denote
such a vehicle.
It has become increasingly apparent in the last few years that
railway transportation of some sort, above and beyond that now in
use, will be necessary to replace and/or supplement automobile and
airplane transportation. It is also quite apparent, however, that
existing systems and proposed modifications and replacement of such
systems, heretofore made, do not and will not satisfy needs,
particularly at speeds above about 200 kilometers per hour and into
the supersonic speed range. Thus, for example, conventional wheeled
railway trains are not capable of speeds significantly higher than
those available today. The limitation is imposed by track alignment
tolerances which can be achieved and maintained, by the finite
ratio of sprung-to-unsprung weight of vehicles, by stability, and
by the strength and wear resistance of materials. Furthermore, none
of the alternatives proposed thus far have succeeded in solving all
of the problems involved in achieving train speeds comparable to
those of jet aircraft. Guided air-cushion vehicles are inefficient,
noisy, and difficult to propel without a prohibitive penalty of
weight and pollution. Magnetically suspended vehicles proposed
previously must operate at track clearances which are too small to
permit significantly higher speeds than those speeds now available
and/or leave the propulsion problem unsolved; on board electric
propulsion using wayside power is unlikely because of the problem
of picking up large amounts of electric power at high speeds, while
track-based propulsion systems designed previously are too
expensive and require track clearances too small to permit high
speeds. The present state of the art can be summarized by stating
that even if air cushion or magnetic suspension systems proposed
previously can be refined sufficiently to permit jet aircraft
speeds of the order of a thousand kilometers per hour, propulsion
would have to be accomplished by an on-board combustion engine
burning on-board fuel. This entails a prohibitive penalty of
weight, noise and pollution, and precludes the possibility of
enclosed guideway tunnels and partial evacuation.
Accordingly, it is a principal object of the present invention to
eliminate the above-mentioned shortcomings of all previously
proposed systems by creating a combined electromagnetic vehicle
suspension and propulsion system, one capable of operating
resiliently at guideway clearances of the order of 25 centimeters
and of permitting the vehicle to seek the correct bank angle at a
given speed and guideway curvature.
A further object is to accomplish the foregoing at reasonable
capital and operating costs, at good power efficiency, and without
imposing unrealistic requirements on guideway alignment or
configuration.
The stress concentration involved in supporting and guiding
conventional trains is reasponsible for a large fraction of their
high construction and maintenance costs. Thus, still another object
of the present invention is to provide a train system that offers
an additional and very fundamental advantage over existing and
proposed systems in that the weight and acceleration forces upon
the vehicle are distributed uniformly over the entire guideway
structure occupied by the vehicle.
Still another object is to provide a system having a guideway in
the form of a laminated aluminum shell structure of adequate
rigidity to be set directly in a bed of sand, as is common practice
in laying pipelines, one in which the guideway can be fabricated
continuously in position at the site as a flat lamination of
aluminum sheets and then formed to have a cylindrical cross
dimension bonded to achieve rigidity, as it is laid.
A still further object is to provide a system in which the
propelled vehicle is capable of jet aircraft speeds in open or
enclosed, atmospheric or partially evacuated guideways, and creates
no pollution or noise and yet permits train separations
sufficiently small to handle the passenger density and operating
schedule required for economical operation competitive with air and
train travel.
A still further object is to provide novel acceleration,
deceleration, and speed control in such system by a novel electric
power scheme.
Yet another object is to provide novel means for switching vehicles
from one guideway to another.
These and still further objects are discussed in greater detail
hereinafter and are particularly delineated in the appended
claims.
The foregoing objects are attained in an electromagnetic
transportation system that includes a vehicle having a
substantially cylindrical lower surface and carrying a plurality of
permanent magnet or superconducting coils distributed over a
substantial portion of that lower surface. The magnets or
superconducting coils are positioned within the vehicle adjacent
said lower surface and have a contour similar to the contour of
that surface; in the case of superconducting coils, means is
provided for maintaining the superconducting coils at a
superconducting temperature. Individual magnets or coils have
sufficient area and are operable, when charged, to generate a
magnetic dipole field of 1,000 to 3,000 gauss 25 centimeters from
the lower surface of the vehicle, alternate adjacent magnets or
coils being energized so as to produce magnetic fields oriented
alternately upward and downward. A trough-like cylindrically-shaped
guideway surrounding approximately the lower one-third of the
circumference of the vehicle supports, guides and propels the
vehicle. The guideway contains both active, current-carrying
conductors and passive conductors The passive conductors form two
spaced continuous surfaces along the length of the guideway exposed
to the magnetic field on the vehicle so as to support the vehicle
when the vehicle is moving at a speed above a predetermined minimum
of about 35 kilometers per hour, at a clearance of approximately 25
centimeters, by interaction between the magnetic dipoles of the
vehicle and the eddy currents they induce in the passive
conductors. The current-carrying, active conductors, located in the
space between the passive conductors, are shaped to form a series
of over-lapping current loops or windings longitudinally along the
guideway. The over-lapping loops substantially conform to the
cylindrically-shaped surface of the guideway and generate, when
energized, a traveling magnetic field which moves along the
guideway in the axial or longitudinal direction and propels the
vehicle at synchronous speeds by interaction with the magnetic
dipoles of the vehicle magnets or coils. A source of multiphase
alternating current is connected to energize the active conductors
in correct sequence to produce the traveling wave field. The system
contains control means operable to connect the current source to
any particular active conductor upon the basis of information
transmitted from the vehicle. The moving vehicle is thus supported
resiliently above the inner surface of the guideway at a clearance
of about 25 centimeters from the guideway and is free to rotate or
pivot about the vehicle longitudinal axis so as to establish the
correct bank angle when negotiating turns, the guideway being
banked at only approximately the correct angle in turns. The center
of electromagnetic lift of the vehicle is located above its center
of gravity to insure stability.
The invention is hereinafter described upon reference to the
accompanying drawing, in which:
FIG. 1 is a schematic diagram, partially in block diagram form,
that shows a two-guideway electromagnetic transportation
system;
FIG. 2 shows one of the guideways of FIG. 1 and a vehicle,
partially cut away, adapted to be propelled along the guideway, the
figure being further intended to show one scheme by which vehicles
are switched for loading and unloading;
FIG. 3 is a view, partially cut away and on an enlarged scale,
taken upon the line 3--3 in FIG. 2 looking in the direction of the
arrows, particularly to show active and passive electrical
conductors in the guideway;
FIG. 4 is a view on a reduced scale, taken upon the line 4--4 in
FIG. 3 looking in the direction of the arrows, and is intended to
show an end view of the active and passive electrical conductors of
FIG. 3, the interstices between conductors being exaggerated and
shown as voids in FIG. 4 but being filled with insulating
re-enforcement and bonding material in actual apparatus;
FIG. 5 is an isometric view in schematic form of vehicle like the
vehicle in FIG. 2 and is primarily intended to show a plurality of
superconducting coils positioned along the whole lower portion of
the vehicle, a similar arrangement of permanent magnets also being
possible;
FIG. 6 is a schematic representation of a three-phase guideway
winding;
FIG. 7 is a partial side view showing a vehicle and a guideway like
those shown in FIG. 2 but including a guideway shell over the
vehicle;
FIG. 8 is a view taken upon the line 8--8 in FIG. 7 looking in the
direction of the arrows, slightly enlarged, particularly to show
wheels on the vehicle and two tracks, one on either side of the
guideway, upon which the wheels can run;
FIG. 9 is a partial side view like FIG. 7 and is particularly
intended to show with greater clarity the switching arrangement
shown in FIG. 2;
FIG. 10 is a view taken upon the line 10--10 in FIG. 9 looking in
the direction of the arrows, slightly enalrged, and is like FIG. 8,
except that two tracks for the wheels are shown on each side of the
guideway;
FIG. 11 is an isometric view of a part of the lower portion of the
vehicle shown in FIG. 2 and is intended to show details of
superconducting coils and related apparatus in that portion;
FIG. 12 is a schematic-type representation of a view taken upon the
line 12--12 in FIG. 13 looking in the direction of the arrows and
shows details of the superconducting coils and related cryogenic
apparatus in the vehicle;
FIG. 13 is a view the left-hand part of which is taken upon the
line A--A in FIG. 12 looking in the direction of the arrows and the
right-hand part of which is a view taken upon the line B--B in FIG.
12 looking in the direction of the arrows, the left-hand view being
intended to show a plurality of outer spokes in the cryogenic
apparatus and the right-hand view being intended to show a
plurality of inner spokes in that apparatus;
FIG. 14 is an enlarged side view of one of the spokes in FIGS. 12
and 13;
FIG. 15 is an isometric view, on an enlarged scale, of one of the
superconducting coils shown in other of the figures;
FIG. 16A is the waveform of three-phase 60 Hz electric energy for
powering the active conductor through a cycloconverter and
transformer combination;
FIGS. 16B, 16C and 16D show 20 Hz output waveforms from the
cycloconverter respectively to the X, Y, and Z phases of the active
conductor;
FIG. 17 shows in schematic form a matrix switching arrangement for
the cycloconverter to convert the 60Hz energy of FIG. 16A to the 20
Hz energy of FIGS. 16B-D;
FIG. 18 shows in greater detail an SCR switching arrangement for
the cycloconverter;
FIG. 19 is an isometric view of a proposed scheme for forming the
guideway in situ;
FIG. 20 is a view similar to FIG. 19 showing continuing fabrication
of the guideway and is one fold later than the position of FIG.
19;
FIG. 21 shows a guideway switch adapted to allow vehicle switching
at full cruising speed;
FIG. 22 is a view, on a enlarges scale, taking up the line 22--22
in FIG. 21, looking in the direction of the arrows;
FIG. 23 is a block-diagram representative of apparatus for
providing on-board electric energy for the vehicle; and
FIG. 24 is a block-diagram representative of an alternate way to
cool the superconducting coils to liquid helium temperature.
Turning now to the drawing, an electromagnetic transportation
system is shown schematically at 1 in FIG. 1. The system comprises
vehicles 2 which are supported, guided and propelled by and along
guideways 4 and 4', one such vehicle only and one such guideway are
shown in the remaining figures. The vehicles 2, as shown in FIG. 8,
for example, each has a circular cylindrical lower surface 7 and a
plurality of superconducting coils 5 distributed axially the length
thereof, as shown in FIGS. 2 and 5, the superconducting coils 5
being positioned within the vehicle adjacent the lower surface 7
and having a contour similar to that of said surface, as shown. (It
is recognized that suspension can be effected by use of either
permanent magnets or superconducting coils, but present technology
favors the latter.) The superconducting coils 5 are maintained at a
superconducting temperature in a manner later discussed; individual
ciols 5 have sufficient area and are energized with sufficient
persistent supercurrent to generate a radial magnetic dipole field
having an intensity of 1,000 to 3,000 gauss at a distance outward
of approximately 25 centimeters from the lower surface 7 of the
vehicle 2. Adjacent coils 5', 5" etc., as shown in FIG. 5, are
energized so as to produce magnetic dipole fields, represented by
the arrows numbered 8, 8', etc. respectively oriented alternately
upward and downward. The vehicle 2 can be circular cylindrical
throughout, as shown in a number of the figures, or it can be
flattened at the top, as also shown. At any rate, the lower third
of the vehicle (except for a slight elipticity which may be used
for stability, as later mentioned herein) is circular cylindrical
and the superconducting coils describe an arc through most of that
lower third. The guideway 4, as shown in FIGS. 8 and 10, is
trough-like and is also circular cylindrical in cross-sectional
shape, as shown in FIGS. 8 and 10, (except that a slight elipticity
may be used for stability, as also mentioned later) and surrounds
approximately the lower one-third of the vehicle circumference. The
guideway 4 contains both active, current carrying conductors 10,
further designated X, Y and Z, to represent the phases of a
multi-phase ac system, and spaced passive conductors 9 and 9' which
form a substantially continuous surface along the length of the
guideway 4 exposed to the magnetic field of the superconducting
coils 5 in the vehicle so as to support the vehicle, when the
vehicle is moving at a speed above the predetermined minimum value
of about 35 kilometers per hour, at a clearance of approximately 25
centimeters by interaction between the magnetic dipole fields of
the vehicle ciols and the eddy currents they induce in the passive
conductors 9, 9'. The active conductors 10, as shown schematically
in FIGS. 3 and 6, are positioned in the space between the passive
conductors 9 and 9' and form a series of overlapping current loops
along the axis of the guideway 4 (substantially conforming to the
cylindrically-shaped surface of the guideway) so as to generate,
when energized, an alternating magnetic field which moves along the
axis of the guideway and propels the vehicle 2 in the direction of
the arrow labeled 3 in FIG. 2 at synchronous speed by interaction
with the magnetic dipoles of the vehicle coils 5. A source 11 of
multi-phase electric current in FIG. 1 is connected to energize the
active conductors 10 in correct sequence, as hereinafter discussed.
The system includes control means designated 12 to connect the
source 11 of the electric current to any particular active
conductor 10, signals to the control means being received from
other control means 12, as shown in FIG. 1, or from the vehicles 2,
as represented by the arrows 15, or from a regional control 13 or a
central control 14, depending upon circumstances.
The vehicle 2, as it moves down the guideway 4, is thereby
electromagnetically supported resiliently at a clearance of not
less than about 25 centimeters from the guideway 4 and is free to
rotate or pivot about its longitudinal axis so as to establish the
correct bank angle when negotiating turns. The guideway 4 is banked
at only approximately the correct angle at such turns. The center
of electromagnetic lift of the vehicle is located above its center
of gravity so as to insure stability, and, further electromagnetic
of aerodynamic stabilizing means can be provided to prevent or damp
undesirable oscillations.
The vehicle 2, as shown in FIG. 2, comprises a passenger or cargo
section 20 and, what may be termed, a drive or tractor section 21.
The two sections may be separated at stations for loading and
unloading and the tractor section can be attached to a new load
section, but, for present purposes, they are described as a unit.
The superconducting coils 5 are located within dewars 22 within the
tractor section; the next few paragraphs are devoted to a
discussion of the tractor section 21 with particular attention
being given to the superconducting aspects thereof. The discussion
is made with reference, primarily, to FIGS. 11 to 15. It should be
here-noted that while FIGS. 12 and 13 represent section views, they
are shown nevertheless in single-line form, without any
cross-hatching, a form it is believed most conductive to
understanding. Furthermore, many details of systems, including
means for handling liquid helium and liquid nitrogen, are omitted
since such are known to workers in the cryogenic art.
The superconducting vehicle coils, in particular their cryogenic
and structural containment, represent one of the most critical
engineering problems involved in the construction of the
magneplane. It is necessary that these coils be maintained at
liquid helium temperature and that the forces which support and
guide the vehicle be transmitted from these coils to the vehicle
structure without inordinate heat loss, and in such a manner that
the forces are distributed uniformly over the vehicle structure.
This is accomplished in the present apparatus in the following
manner.
A typical vehicle 2 having a length of 40 meters is supported by
approximately 12 coils 5, each having a length of 2.0 meters in the
longitudinal or axial direction and a developed width of 4 meters.
These rectangular coils 5 are wound in the form of "pancakes" on a
curved form (see FIG. 15), so that they conform to the shape or
contour of lower surface 7 of the vehicle, surrounding about
120.degree. of its circular circumference. Each coil conducts a
total of between 100,000 and 300,000 ampere-turns of persistent
current, consisting of 100 to 200 turns of superconductor having a
current carrying capacity of 1,000-1,500 amperes. Suitable
commercially available material is multi-filament niobium-titanium
superconductor imbedded in a copper or aluminum matrix having the
shape of a flat ribbon, as shown at 23 in FIG. 15. The material is
pancake-wound with insulating spacers 24 of a fibrous material
impregnated with stage B epoxy, and subsequently heat-cured to form
a monolithic, bonded structure.
Each coil 5, is rigidly attached (by clamps, not shown) to the
inside of the curved surface of a cylindrical aluminum container 25
having a D-shaped cross section and which also serves to contain a
supply of liquid helium. This helium container 25 is in turn
surrounded by a correspondingly shaped aluminum container 26 which
is maintained at liquid nitrogen temperature by a liquid nitrogen
reservoir 28 which is an integral part of its upper, flat surface,
as best shown in FIG. 12. This nitrogen-cooled container is, in
turn, surrounded by a correspondingly shaped vacuum vessel 32 (the
lower structural member of which is the vehicle skin) that is in
fact a sector of a circular cylinder 40 meters in length and 4
meters in diameter subdivided by structural bulkheads into 12
compartments, each being shaped so as to surround one of the
nitrogen-cooled containers 26. The upper surface of the vessel 32,
which is numbered 27, supports the floor of the cabin 20. The
container 25 is separated from the container 26 by a two centimeter
vacuum space 29 and the container 26 from the vehicle wall by a
similar vacuum space 30.
FIGS. 12 and 13 illustrate the means by which the three nesting
containers are supported with respect to each other by means of
tension spokes which serve to minimize heat conduction. Two sets of
tension spokes are located adjacent each side of each structural
bulkhead: an inner set of spokes 33 connects the helium-cooled
container 25 to its surrounding nitrogen-cooled container 26, and
an outer set of spokes 34 connects said nitrogen-cooled container
to its surrounding vacuum barrier which also represents the vehicle
skin, by being attached to channels surrounding the structural
bulkheads. Each helium-cooled container 25, along with its rigidly
connected superconducting coil, is thus connected mechanically to
its two neighboring bulkheads. The spokes are slightly inclined
with respect to the bulkheads which are perpendicular to the
longitudinal axis of the vehicle. In this manner the spokes provide
rigid constraint in the axial as well as the transverse direction.
The forces which support, guide and propel the vehicle are thus
transmitted from the superconducting coils 5 to all of the
structural bulkheads. Each compartment 22 is also provided with a
sealed service tube or duct 35 through which a mating, coaxial
service nozzle can be inserted from outside the vehicle. This
service nozzle, or umbilical cord, is used to replenish the liquid
helium supply, the liquid nitrogen supply, to evacuate the vacuum
spaces between nesting containers, and to adjust the
superconducting current if required. The service tube also contains
venting lines for the helium and nitrogen reservoirs.
In FIG. 14 there is shown the manner in which each tension spoke 33
or 34 is elastically connected at one of its ends, the other end
being connected rigidly. The purpose of this elastic connection is
to provide the normally required supporting force at a minimum
thermal contact, while providing back-up support at increased
thermal contact to absorb transient mechanical overloads, such as
might occur during severe braking or when passing a badly
mis-aligned section of guideway. As shown, this elastic support is
accomplished by using a stack of Belleville washers, tempered steel
washers 36 of slightly dished or spherical shape. Alternate washers
in this stack are convex upward and downward. Under normal loads,
these washers contact their neighbors only along the inner and
outer periphery. If an abnormal load is applied however, the
washers are flattened elastically and their contact area increases
progressively until the entire stack of washers is compressed to
minimum height. When the abnormal load is removed, the washers
resume their spherical shape.
The vehicle requires auxiliary electrical energy for such things as
lighting, control, hydraulic pumps, air-conditioning, etc. The
energy may be provided for example by an air-driven turbo-generator
on the vehicle or by some conventional electrical generating means
on board. It may, however, be supplied by the scheme shown in FIG.
23 where dewars 22', which may be quite similar to the dewars 22,
are shown. In the arrangement of FIG. 23, the cryogenic radiation
shields, instead of being cooled by liquid nitrogen as before, are
cooled by liquid oxygen and liquid methane. The boil-off gases,
oxygen and methane, are passed through fuel cell 65 to generate
electric power. Alternately these gases could be burned in a heat
engine to generate mechanical and electrical power. The boil-off
gases from the cryogenic reservoirs can also be passed through a
suitable heat exchanger 66 which serves as an air-conditioner for
the cabin 20.
There is contained in this and the next few paragraphs an
explanation of the electrical propulsion system and control which
are mentioned briefly elsewhere herein. The system 1 in FIG. 1 is a
two-lane or dual-guideway system comprising the side-by-side
guideways 4 and 4', each being divided into sections numbered 100,
101, 102, 103, 104, 100', 101', 102', 103', 104', respectively.
Each contiguous group of four guideway sections constitutes one
block, energized by a single power supply unit located at the
center of the associated block. For present explanation purposes
the block consisting of the four contiguous sections numbered 101,
102, 101' and 102' will be discussed.
A block is typically 1 to 5 kilometers long depending on required
vehicle speed, cost considerations, etc. An underground, high
voltage transmission system 106 transmits three-phase power under
the guideway. There is a transformer 11, as before mentioned, in
the center of each block, with four cycloconverters for each
transformer, one for each section. (A two-cycloconverter system can
be used; it would require an additional semiconductor or mechanical
switch so that one cycloconverter could supply either 101', or
102'.) Additionally, each block contains a control system which is
the block control 12 and which can include a small, special purpose
computer. Each control 12 is in constant communication with: (1)
adjacent blocks, (2) all vehicles in its block, and (3) a regional
control 13, as indicated. The pilot of the magneplane in any
particular block can request: (1) constant speed at the synchronous
block speed specified by the regional control 13 (2) acceleration
up to synchronous speed, or (3) deceleration and automatic ejection
from the system. The block control 12 will only allow deceleration
if there is a suitable off-ramp or if emergency conditions exist.
For emergency operation the pilot is placed in direct contact with
a controller who can change the prevailing vehicle speeds in
various parts of the system through the central control 14. The
communication indicated between adjacent blocks is used to control
motion of vehicles from one block to another, and, if an emergency
develops and the link to the regional control 13 should fail, a
block that must shut down can also cause adjacent blocks to shut
down. The communication between the vehicle 2 and block control 12
can either be by short range radio link or by electromagnetic
pickup by wires imbedded in the guideway. Regional control is
necessary in a large system because of the complexity of operation
that would result if a central control had to communicate with
thousands of block controls. The regional control 13 is associated
with a station or terminal and acts as a communication buffer
between blocks and the central control. Also, the regional control
is responsible for acceleration of vehicles and injection into the
system with suitable clearance to leading and trailing vehicles.
The regional control 13 continually monitors vehicles in its
region, and has a communication link to each adjacent region, as
shown. Each regional control may be manned to allow an operator to
make some of the decisions.
As before mentioned, each power unit 11 includes a transformer and,
usually, four cycloconverters. A cycloconverter is a circuit or
device which converts an ac power source into a different frequency
ac source. Today the most common cycloconverter for high power
levels is one which uses SCR's or thyristors to switch the power,
as later discussed in connection with FIG. 18. The output frequency
can be continuously varied up to about half of the supply
frequency. Thus, a multiphase cycloconverter with 60 Hz input power
can produce reasonably good output up to about 30 Hz. For linear
motor applications it is necessary to generate a multiphase output
which, typically, can be six phase. To achieve smooth multiphase
power output at frequencies near one half of the supply frequency
it is desirable to use multiphase input power.
In order to illustrate the operation of a cycloconverter, a
three-phase to three-phase system is discussed in connection with
FIGS. 16 A-D, 17 and 18 for converting 60 Hz to 20Hz. The curves in
FIG. 16A show the waveforms for the three input phases A, B, and C
at 60 Hz (as from the transformers shown at 50 in FIG. 18) and the
curves in FIGS. 16B, 16C, and 16D show respectively three outputs
to phases X, Y and Z at 20 Hz. Each output phase is composed of
segments of each of the input phases as indicated in the figures. A
simplified schematic of a cycloconverter is shown in FIG. 17 with
back-to-back SCR's or triacs represented as the simple switches
labeled 52, 52', etc. The operation of the nine switches in FIG. 17
is synchronized by the control 12 to obtain the required waveforms,
as indicated in FIG. 18 where the switches 52, 52' etc. are shown
as back-to-back SCR's, S.sub.1, S.sub.2, S.sub.3, etc.
A feature of this cycloconverter which makes it particularly simple
and reliable is the fact that there is natural commutation of the
SCR's without any extra commutation circuitry. For the three-phase
to three-phase system shown in FIG. 18 there are 18 SCR's (a
six-phase to six-phase system requires 72) but no other high power
components are required. Moreover, most of the 18 SCR's are in
active use; so the power output can approach 18 times the output
capability of a single SCR. For normal deceleration, the
cycloconverter can pump power back into the ac power line (i.e.,
regenerative braking). For emergency braking, a short-circuit can
be placed across the propulsion coils 10 to provide dynamic braking
at 0.5 g or more.
For variable frequency operation, when the output frequency is not
a sub-multiple of the input frequency, the output waveform is not
perfectly periodic at the output frequency, but it can be made
nearly periodic if the output frequency is less than half the input
frequency and if a sufficient number of input phases (typically
six) are used.
The guideway 4, according to a preferred embodiment of the instant
invention, is constructed of bonded aluminum laminations, as best
shown in FIGS. 19, 20, 3 and 4, suitably interleaved with
insulation so as to provide both the passive and the active
current-carrying conductors and having sufficient rigidity to
maintain the required dimensional tolerances without the need for
additional re-enforcing structures. FIGS. 19 and 20 are intended to
illustrate a method of continuous fabrication of a laminated
guideway from aluminum ribbon; interleaving sheets of insulation
and bonding material are not shown. The method shown employs hand
fabrication but it is adapted to machine fabrication. Turning now
to the figures, the bottom surface of the guideway is formed of a
fibreglass (or aluminum) strip 60 over which is laid the passive
conductors 9 and 9' (only two layers of passive conductors on each
side of the guideway are shown in FIGS. 19 and 20) and the active
conductors 10, comprising phases X, Y and Z. The phases X, Y and Z
are made up of aluminum ribbons from spool pairs 3X -- 3X', 3Y --
3Y', and 3Z -- 3Z', respectively, as shown, each spool of the pair
holding half the amount of ribbon needed for a particular phase.
Each phase, as shown in FIG. 5, has two input terminals. A layer of
fibreglass or the like 61 is laid over the foregoing elements to
provide a smooth surface for the guideway and one that is
electrically neutral or insulated. Induction heated pressure plates
62, of proper contour, shape and curve the laminations. FIG. 20
shows the continuing fabrication of the guideway one fold later
than the condition illustrated in FIG. 19 to illustrate the
procedure for forming the conductors X, Y and Z.
In a system such as that described above it is necessary that the
magneplane leave the high-speed guideway to load and unload
passengers and/or cargo and return to the high-speed guideway to
resume travel. This can be accomplished in the embodiment of FIGS.
1, 9 and 10 by having a guideway 40 that inclines upward from the
guideway 4. In this switching arrangement the vehicle 2 is first
slowed from the 200 kilometers per hour speed to say 100 kilometers
per hour and at this juncture wheels 41 and 42, which are normally
retracted, are extended out to ride on respective outer tracks 43
and 44 at each side of the guideway 4 (and the guideway 40, as
well). In this way the magneplane can be made to run up a ramp onto
the guideway 40 where again it will levitate by electromagnetic
forces until the speed drops to about 35 kilometers per hour. At
that low speed the vehicle will again rest on the wheels 41 and 42.
The guideway 4 can, in fact, be provided with two side-by-side
tracks on either side thereof, i.e., the outer tracks 43 and 44 and
inner tracks 45 and 46, to receive the wheels at one of two
outwardly extended positions. The inner tracks 45 and 46, as shown,
provide for horizontal movement and/or landing of the magneplane
and the tracks 43 and 44 provide for vertical changes in the
direction of the movement of the vehicle along the guideway to
effect switching thereof. The wheels 41 and 42 can be raised or
lowered hydraulically and can be braked. A substantial number of
wheels may be used on each vehicle to minimize local mechanical
stresses, for example one pair built into every second structural
bulkhead. Also, a horizontal switching arrangement can be employed,
as shown in FIGS. 21 and 22, where the guideway 4 is shown in two
alternate positions to align with a guideway 4" or a guideway 4"',
as the case may be. A long flexible portion of the guideway 4 (up
to 5 kilometers for high-speed switching), which is supported on a
plurality of cradles 47, is made to move from one or the other of
the two positions shown by a hydraulic or other force. The cradles
47 each slide on a Teflon surface 48 of a slide 49.
There is in this paragraph a number of statistics and comments,
some of which appear elsewhere herein. The vehicle 2 is a passive
cylindrical structure carrying a series of super-conducting
solenoids of large dipole moment, energized (by known means) and
refrigerated for 8 to 10 hours of operation. Its weight is
distributed uniformly over the guideway 4 at a clearance of about
25 centimeters. The vehicle is self-banking (free to rotate or
pivot about its longitudinal axis) and does not require secondary
articulation (the unsprung weight is zero). The guideway is a
trough of laminated aluminum surrounding one third of the vehicle
circumference, and provides all the mechanical strength and
electrical conduction needed. Propulsion coils form an integral
part of the laminated structure. It can be set directly in a bed of
sand, requiring no additional structural support. At speeds up to
about 500 kilometers per hour it can be operated open; at higher
speeds it is expedient to add an upper shell 70 so as to form a
partially evacuated tunnel or the shell 70 can act merely as a
cover to exclude rain, snow, thrown objects, etc. from the
guideway. Alignment tolerance is of the order of 5 centimeters.
Propulsion is guideway-based and synchronous. It requires one
multiphase transformer and one or more cycloconverters to feed two
guideways for both synchronous cruising speed and for acceleration
and deceleration. Some estimated specifications follow.
Vehicle
length: 40 m (wt of superconductor--5,000 kg)
diameter: 4 m (total wt of cryogenic units--10,000 kg)
gross wt: 50,000 kg
payload: 30,000 kg (200 passengers)
Guideway
clearance: 25 cm
material: laminated aluminum
weight 100-150 kg/m (100 lb/ft single track)
electrical power: 1 transformer/km
Power
60 Hz, 3.phi. at available transmission line voltage, 5-15 MW
input, depending on speed (electrical efficiency 67%)
Performance
lift/drag of suspension: 20 (excluding windage loss)
acceleration and deceleration: 0.1 - 0.2g
emergency deceleration: 0.5g by shorting propulsion coils, field in
passenger cabin 100 gauss max
The foregoing discussion is primarily concerned with vehicles
intended to operate at long distances and speeds at least the order
of 200 kilometers per hour. The apparatus described, however, is
useful at lower speeds and shorter distances where smaller
magneplanes can be used. In such smaller vehicle recent
developments in permanent magnets (e.g. samarium-cobalt alloys)
indicate the possibility of creating the necessary magnetic flux at
required distance from the vehicle, which can be less than 25
centimeters for smaller, slower vehicles, and less favorable but
still permissible lift-to-weight ratios. In such apparatus, the
dipoles 8, 8' etc. in FIG. 5 would be created by permanent
magnets.
A few more details, of some interest, are contained in this
paragraph. The system described above employs retractable wheels on
the vehicle for landing at stations or in emergency situations. An
alternate or complementary system might employ wheels 67 at the
station (which can be represented by the portion of the guideway
shown in FIG. 5) and the vehicle 2 can be supplied with retractable
skids 68 in addition, or as an alternate, to the wheels 41 and 42.
The cabin floor 7 can be provided with a plurality of
superconducting and ferromagnetic sheets arranged so as to reduce
the magnetic field in the passenger or cargo cabin 20 to an
intensity of less than 100 gauss. In the system described above,
the vehicle and the guideway are circular in cross-section. A
system may employ vehicles in which the cross-section of each
vehicle and/or of the superconducting coils adjacent to its surface
7 and/or the guideway 4 are slightly elliptical so that the
clearance between the vehicle coils 5 and the guideway 4 is
slightly smaller at the sides of the vehicle than at the center,
thereby to raise the center of lift of the suspension. When the
vehicle is slightly elliptical its lateral stiffness is increased
over its vertical stiffness. The cryogenic apparatus may be
modified to employ a closed loop liquid-helium apparatus as shown
schematically in FIG. 24 and as more particularly described in
letters U.S. Pat. No. 3,364,687 granted to Kolm, one of the present
inventors, on Jan. 23, 1968. The liquid helium at a pressure above
its critical point, or "supercritical helium," is cooled by a heat
exchanger 81 immersed in a central dewar reservoir 82 containing
helium at ordinary pressure. The supercritical helium is then
circulated by a pump 80 through all the superconducting coils
labeled 5A, which may be made of hollow conductors or thermally
connected to suitable tubing, ultimately returning to the central
helium reservoir, where it is re-cooled by the heat exchanger 81.
The use of a closed circulation loop of this type has several
advantages, the most notable being that the individual
superconducting coils are not immersed in liquid helium reservoirs,
but are merely surrounded by a vacuum barrier and a suitable
radiation shield. This radiation shield, designated 22", can be
cooled by liquid nitrogen which is also circulated from a central
reservoir 83 through the same connecting lines which conduct the
liquid helium, thereby serving to provide radiation shielding for
the helium conductors. This arrangement makes it possible to
service the vehicle from one single connection.
Further modifications will occur to persons skilled in the art and
all are considered to be within the spirit and scope of the
invention.
* * * * *