Method and apparatus for combined levitation and guidance along guideway curvature in electrodynamic magnetically levitated high speed vehicle

An apparatus for guiding and levitating a vehicle. The apparatus comprises a guideway mechanism upon which the vehicle travels. The apparatus is also comprised of a mechanism for actively controlling differential and lateral guidance or differential and vertical levitation strength of the vehicle with respect to the guideway mechanism. The controlling mechanism is electrodynamically reactive with the guideway mechanism. A method for guiding and levitating a vehicle. The method comprises the steps of guiding a vehicle along the guideway with electrodynamic guidance coils. Then, there is the step of actively controlling alternating current through the guidance coils to correspond with guideway curvature so the vehicle is maintained in a stable position relative to the guideway as it moves around a curve in the guideway and experiences roll compensation.

FIELD OF THE INVENTION 
The present invention is related to electrodynamically magnetically 
levitated high speed vehicles. More specifically, the present invention is 
related to electrodynamically magnetically levitated high speed vehicles 
whose lateral guidance is actively controlled. 
BACKGROUND OF THE INVENTION 
In electrodynamically magnetically levitated high speed vehicles, the 
centrifugal force developed along a curved track during travel needs to be 
counteracted for proper operation of the vehicle. Prior art U.S. Pat. Nos. 
4,913,059, 4,779,538 and 4,299,173 disclose such vehicles and their 
operation. Typically, this centrifugal force is dealt with by the value of 
the time constant for a guide conductor being increased either by 
increasing the cross-sectional area of a related conductor loop or by 
providing an additional conductive loop with a desired thickness. In the 
earliest prior art inductive repulsion type magnetic levitation vehicle, 
all the levitation conductors and all the guide conductors have the same 
time constant, and the distance between the levitation superconductive 
magnet and the levitation conductor and between the guide superconductive 
magnet and the guide conductor are the same. 
The present invention provides for lateral guidance combined with 
electrodynamic suspension for both tangent and curved guideway sections 
and includes an electromagnetic turn-out track switch in which the vehicle 
is levitated by an EM force between levitation conductors imbedded in a 
track of two or greater parallel rows and primary superconducting field 
magnets which are preferably vehicle mounted, and arrayed in the direction 
of vehicle motion. The vehicle guidance is from an array of guideway 
mounted secondary coils or conductors have the same inductance and 
resistance and spaced at periodic intervals in the direction of motion and 
separate sets of vehicle mounted SC field magnets. The EM force generated 
by a guidance magnet on one side of vehicle in a curvature, is enhanced 
above the guidance force generated by the other side of the vehicle along 
a curvature, with the differential force being controllable from the 
vehicle and adjustable in magnitude by design used to counteract the 
centrifugal force impinging on the vehicle in high speed turns, thus 
providing a lateral stabilization necessary for high speed controlled 
maneuvers. 
SUMMARY OF THE INVENTION 
The present invention pertains to an apparatus for guiding and levitating a 
vehicle. The apparatus comprises guideway means upon which the vehicle 
travels. The present invention is also comprised of means for actively 
controlling differential and lateral guidance or differential and vertical 
levitation strength of the vehicle with respect to the guideway means. The 
controlling means is electrodynamically reactive with the guideway means. 
The present invention also pertains to a method for guiding and levitating 
a vehicle. The method comprises the steps of guiding a vehicle along the 
guideway with electrodynamic guidance coils. Then, there is the step of 
actively controlling alternating current through the guidance coils to 
correspond with guideway curvature so the vehicle is maintained in a 
stable position relative to the guideway as it moves around a curve in the 
guideway and experiences roll compensation. 
The objective of the invention is to form a high-stiffness, highly stable 
guidance system for electrodynamically operated maglev vehicles wherein a 
large magnetic airgap between vehicle undercarriage and guideway surface 
components is an essential design feature and vehicle field magnets are 
high field superconductors without a mechanism to rapidly adjust 
excitation in response to guideway conditions. Active control is 
preferably made by electrical adjustment of guideway mounted hardware 
which has an electromagnetic time constant typically two or three orders 
of magnitude smaller than the vehicle field magnets. The described 
invention presents a superior method and apparatus for counteracting the 
centrifugal force developed when the vehicle encounters a curved or banked 
track at medium and high speeds.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein like reference numerals refer to 
similar or identical parts throughout the several views, and more 
specifically to FIG. 1 thereof, there is shown an apparatus for guiding 
and levitating a vehicle. The apparatus comprises guideway means upon 
which the vehicle travels. The apparatus is also comprised of means for 
actively controlling differential and lateral guidance or differential and 
vertical levitation strength of the vehicle with respect to the guideway 
means. The controlling means is electrodynamically reactive with the 
guideway means. 
The present invention also pertains to a method for guiding and levitating 
a vehicle. The method comprises the steps of guiding a vehicle along the 
guideway with electrodynamic guidance coils. Then, there is the step of 
actively controlling alternating current through the guidance coils to 
correspond with guideway curvature so the vehicle is maintained in a 
stable position relative to the guideway as it moves around a curve in the 
guideway and experiences roll compensation. 
More specifically, the present invention allows for actively controlling 
the differential in lateral guidance or differential in vertical 
levitation strength by inclusion of electronic high power switches in the 
null-flux loop to regulate the differential current. This scheme is shown 
in FIG. 1 for center positioned vertically oriented guidance coils or the 
"inverted-T" style of guideway with the vehicle mounted superconducting or 
high-field magnets 1 and 1' and interconnected null-flux loop 2 and 2' on 
the vertical guideway center member. The present invention incorporates 
the novel addition of a differential current regulator shown by way of 
example as thyristor pair 3 and 3' which are connected in anti-parallel 
and of identical voltage and current ratings, these two devices being 
externally triggered to modulate currents i.sub.3 and i.sub.3 ' to account 
for differential vehicle loading, guideway curvature, wind loading on 
curves or non-optimum banking of guideway. 
FIG. 2 shows the alternate general scheme where vehicle field magnets are 
positioned in-board and the guideway guidance coils are spatially arranged 
outside of the vehicle magnet array, also in a vertical and longitudinal 
orientation. Current regulators 3 and 3' modulate the differential 
null-flux loop current i.sub.3 and i.sub.3 ' in an active sense to provide 
a strong or light differential flux between the 2 sides to counteract the 
vehicle centrifugal force on high speed curves. 
By way of example, the electronic switching elements are solid-state 
thyristors with ability to modulate current by virtue of phase angle 
chopping of voltage through an external command which signals when to 
trigger the thyristor into conduction and at what phase angle. By having 
two separate units arranged in anti-parallel with separate gating sources, 
it is possible and advantageous to trigger each thyristor to have 
different conduction periods e.g. 30.degree. on device 3 and 90.degree. on 
device 3' to produce a net DC current superimposed on the main AC 
null-flux current. The DC component produces a time offset in the buildup 
of peak guidance force. In the limiting case, when both electronic 
switches are on at full conduction angle (.beta.-180.degree.), then there 
is no differential transfer of energy or power between right and left 
sides, and the effect of self-neutralizing or self-centering action by 
null flux is not active. This situation is to be avoided. However, when 
the switches are fully off, then maximum null-flux centering action is 
present. Alternate types of electronic switches are power transistors, 
MOSFETs, IGBTs, ignitrons and MCTs. 
FIG. 3 shows and equivalent circuit of the present invention noting that 
the thyristor switching loop need not contain separate or discrete 
resistance (R) or inductance (L) as already sufficient L and R are 
contained in each guidance coil. Note that M.sub.1 is the field to stator 
coil mutual inductance of left side, M.sub.2 is field coil to stator coil 
mutual inductance of right side and L.sub.1, L.sub.2 are internal self 
inductances of guidance coils, R.sub.1 & R.sub.2 are internal resistances. 
According to the convention shown in the FIG. 3, we have 
EQU i.sub.1 +i.sub.3 '-i.sub.3 =i.sub.2 
The three modes of operation are: 
______________________________________ 
a. i.sub.3 ' = 0 Therefore i.sub.1 - i.sub.3 = i.sub.2 
Positive lateral 
compensation 
b. i.sub.3 = 0 Therefore i.sub.1 + i.sub.3 ' = i.sub.2 
Negative lateral 
compensation 
c. i.sub.3 = 0, i.sub.3 ' = 0 Therefore i.sub.1 = i.sub.2 
Max. null-flux mode 
balanced condition. 
______________________________________ 
A further improvement to the present invention and a preferred embodiment 
is the design of the left and right side guidance coils with different 
magnetic reluctance specifically to account for guidance on curvatures and 
counteract vehicle centrifugal forces. The magnet reluctance is defined as 
##EQU1## 
Where l=Length of the magnetic path, typically a lateral path 
A=Cross-section area of magnetic path 
.mu..sub.r =Relative magnetic permeability 
.mu..sub.o =Permeability of free space=4.pi..times.10.sup.-7 H/m 
The present invention hereby pertains to a change in .mu..sub.r between 
left and right side guidance coils by the addition of ferromagnetic 
material with .mu..sub.r &gt;1 on one side (Side 1) and the use of strictly 
non-ferromagnetic material .mu..sub.r =1 on the other side (Side 2). Side 
1 has a combination or hybrid of air-core and iron-core paths, termed 
mixed-mu permeability (MMP) whereas Side 2 is strictly "air-core" path 
with singular-mu magnetic permeability. 
Referring to FIG. 3 the value of inductance L.sub.1 for Side 1 is 
consequently increased significantly (i.e. greater than 50%) above the 
inductance L.sub.2 for Side 2. For example L.sub.l could be .apprxeq.500 
.mu.H, whereas L.sub.2 .apprxeq.50 .mu.H in a full-scale maglev system. 
The values of R.sub.1 and R.sub.2 can be altered to allow either the same 
coil time constants on both sides or different time constants, where time 
constant is defined at T.sub.1 =L.sub.1 /R.sub.1 and T.sub.2 =L.sub.2 
/R.sub.2. The Table 1 presents a summary of the two modes. 
TABLE 1 
______________________________________ 
L.sub.1 L.sub.2 R.sub.1 R.sub.2 
T.sub.1 
T.sub.2 
______________________________________ 
Mode 1: 500 .mu.H 
50 .mu.H 1 m.OMEGA. 
1 m.OMEGA. 
500 ms 
50 ms 
Mode 2: 500 .mu.H 
50 .mu.H 10 m.OMEGA. 
1 m.OMEGA. 
50 ms 50 ms 
______________________________________ 
The preferred embodiment utilized Mode 2 as a standard and thus uniform 
time constant between both sides. This is accomplished physically by 
changing material resistivity e.g. Coil 1 will use high resistance 
aluminum such as Type 7075 and Coil 2 will use low resistance OFHC copper. 
Since the time constants are the same, the two coils will be physically 
similar in cross sectional area and volume. The mechanism of interest in 
controlling guidance force at high speed is the inductance of the total 
null-flux system because as speed increases, so does the induction 
frequency increase linearly with speed and thus above 40-50 m/s linear 
vehicle speed, these systems become "inductance limited" and the effects 
of resistance are negligible. The frequency of induced eddy currents in 
the guideway coils is calculated as 
##EQU2## 
where V.sub.s is the vehicle speed in m/s and T.sub.p is the pole-pitch in 
m of the vehicle magnet field. For a V.sub.s =150 m/s, and Tp=1 m, the 
frequency is thus f=75 Hz by way of example. 
FIG. 4 shows the mechanism by which to decrease the magnetic reluctance 
R.sub.1 of Side 1 by using the mixed-mu pole piece Item 4 inserted in the 
core of the guidance coil Item 2. Side 2 guidance coil Item 2' is an 
air-core stationary coil with reluctance R.sub.2. Vehicle magnets Items 1 
and 1' are identical, closed-loop and preferably superconducting high 
field magnets both of air-core construction. A specific purpose of 
pole-piece Item 4 is to increase the magnitude of lateral flux density 
By.sub.1 over opposing lateral flux density By.sub.2 by virtue of the 
lower magnetic reluctance, 
R.sub.1 or: 
R.sub.1 &lt;R.sub.2 
By.sub.1 &gt;By.sub.2 at the guideway surface 
In general, the magnetomotive force or MMF is related to the product of 
magnetic reluctance "R" and magnetic flux .PHI. for each side as: 
EQU MMF=R.PHI. 
With the superconductive magnets, the total MMF of both sides must be 
identical and consequently the total flux-reluctance product is the same 
for both sides. Side 1 with a low reluctance will have a higher flux and 
vice versa for Side 2. The total flux per side is composed of two 
components: work-producing flux and leakage flux. Leakage flux is higher 
in the single-mu system (Side 2) whereas the Side 1 pole piece Item 4 acts 
as a flux concentrator and lowers the leakage flux. It is important to 
note that FIG. 11 shows an open magnetic circuit for Side 1 in the respect 
the iron magnetic circuit does not form a closed path around its 
excitation source. This is a necessary condition of a mixed-mu system with 
high field superconductors and appropriate when it is necessary to limit 
the peak field induction of the ferromagnetic pole piece to under the 
saturation flux density, a value usually between 1.8 and 2.2 Tesla, 
according to the steel grade selected. The vehicle field SC magnets are 
usually designed between 3.5 and 5.5 Tesla and in combination with 15-30 
cm type airgaps between vehicle and guideway, the field density 
attenuation in space is significant at a factor of usually 3:1 to 4:1 and 
the peak guideway induction is calculated less that 2.0 Tesla, making the 
use of conventional ferromagnetic pole pieces practical in the preferred 
embodiment. 
Item 3 is the shunt-connected current regulator which allows a differential 
to exist in null flux currents i.sub.1 and i.sub.2 by electronic switching 
operation controlled by the programmed lateral vehicle response. There is 
no advantage to altering the vehicle SC magnet array to have either left 
or right differential reluctance because the common vehicle array must 
accommodate both right and left curvatures without modification or active 
control of the vehicle magnet system, which remains uniform in layout and 
MMF distribution. A typical field MMF for a 67 ton vehicle with 7 magnets 
per side in a dual array is in the range of 300-400 kAT/coil for a 
representative 23 cm vertical airgap. The total lift or guidance force is 
calculated on the basis of magnetic moment or the product of field MMF and 
magnet active surface area. 
FIG. 5 shows a further embodiment of the mixed-mu guidance track coil with 
lower magnetic reluctance for Side 1 than FIG. 4 by including magnetic 
side piece Item 4. This also reduces stray magnetic field as well as 
reduce the electrodynamic stress on coil Item 2 conductors by causing 
lateral force to be transmitted directly to the ferromagnetic structures 
Items 5 and 6. Distance .alpha..sub.1 is the lateral spacing between the 
outer plane of the vehicle field magnet and the main ferromagnetic surface 
5, the principal interaction surface. Distance .alpha..sub.2 is the 
spacing from the field magnet plane to the surface of the pole tips Item 6 
on outer coil edges of Coil 2. Note that .alpha..sub.2 &gt;.alpha..sub.1 is a 
necessary requirement for effectively controlling stray field and 
maximizing the lateral component of flux density, By or the vertical 
component, Bz. The optimum differential distance .alpha..sub.2 
-.alpha..sub.1 is a strong function of the absolute airgap, .alpha..sub.1 
i.e. .alpha..sub.2 -.alpha..sub.1 =k(.alpha..sub.1) where k is a constant 
between 0.20 and 0.50 derived from electromagnetic field analysis. 
FIG. 6 shows a secondary embodiment of the ferromagnetic flux concentrator 
Item 4 on Side 1 surrounding guidance coil Item 2 but with increased 
magnetic reluctance in comparison with FIG. 11 baseline design. The inner 
core of the pole-piece Item 6 has a graded reluctance versus vertical 
distance which has a beneficial influence on the dynamic characteristics 
of the vehicle in both vertical and lateral perturbations at medium or 
high speed. Distance .alpha..sub.1 is the furthest lateral separation from 
inner side wall of pole piece Item 4 to plane of vehicle field magnet Item 
1 and .alpha..sub.2 is lateral distance from vehicle field magnet plane to 
inward parallel surface of guidance pole piece Item 4 closest to vehicle. 
The distance d.sub.2 is preferably larger than distance d.sub.1 to enhance 
vertical oscillation damping. The differential .alpha..sub.1 
-.alpha..sub.2 represents the amount of change in airgap magnetic path for 
the lateral component of magnetic flux entering the pole-pieces normal to 
its surface. The general effect of the graded pole piece Item 4 is to 
cause the flux to concentrate at the surface Item 7 or surrounding the 
guidance coil Item 2 to increase the magnetic flux in the d.sub.2 area and 
focus the field more intensely than in a 100% air-core system. The 
dimension .alpha..sub.2 must be sized to insure that the maximum flux 
density does not exceed the saturation flux density of the ferromagnetic 
material, which has a limit of about 2.2 Tesla typical value. The FIG. 6 
system also incorporates a shunt loop electronic-switch Item 3 which 
regulates the null-flux currents i.sub.1 and i.sub.2 to insure 
differential adjustment of Coil i/Coil 2 MMF in high speed curves. Item 3 
may be comprised of semiconductor or gaseous conduction high power 
switches with response times in the range of 1 .mu.s to 80 .mu.s for use 
in 150 m/s linear speed systems. In FIG. 6, gap 1 corresponding to Side 1 
is shown larger than gap 2 corresponding to Side 2 representing a vehicle 
on a high-speed curve where curvature of the guideway is to the left. 
Clearly, for curvature in the opposite direction, the gap 2 becomes larger 
than gap 1 to counteract centrifugal force developed by the vehicle. 
FIG. 7 shows a plot of current in the null-flux loop versus vehicle speed 
noting that at speed V.sub.0 and above the current is substantially 
constant due to "inductance limited" nature of the Coils 1 and 2 at medium 
and high frequencies. In typical maglev systems, the V.sub.0 point occurs 
prior to the 50% speed point i.e. V.sub.0 &lt;0.5 V.sub.s where V.sub.s is 
the final synchronous linear speed at the nominal rating point. Curve 1 
pertains to the case where i.sub.3 =0, that is prior-art and no shunt 
regulation or active control. Curve 2 corresponds to the case where 
i.sub.3 &gt;0 and specifically the magnitude of i.sub.1 &lt;i.sub.2 i.e. the 
higher inductance coil results in less null-flux current than the air-core 
coil, and i.sub.1 =i.sub.2 -i.sub.3. Since Coil 1 has the higher 
inductance, its system becomes inductance limited at a lower vehicle speed 
V.sub.2 and has the response show by Curve 2. The Coil 1 current loop has 
the Curve 1 response. Curve 3 describes the regulator current which peaks 
at or below speed point V.sub.2. The preferred embodiment has the design 
speed V.sub.2 variable by coil and pole piece design including the ability 
to shift V.sub.2 beyond V.sub.0 as shown in FIG. 8. The technology is 
intended to be used at speeds in excess of 150 m/s, which is a convenience 
sample speed for calculation. 
FIG. 9 shows an automatic electronic measurement and control system for the 
guideway--located current regulator connected to Item 3 as shown in FIGS. 
4, 5 or 6. The lateral airgap on both sides of the vehicle is detected by 
guideway mounted sensors spaced at periodic intervals and these airgap 
signals and its differential are entered as data to the master control 
scheme. By way of example, the control scheme may be a Type II 
proportional and integral servo control with zero feedback error. The 
controller has the following data input ports: 
Side 1 lateral airgap 
Side 2 lateral airgap 
Side 1 vehicle induced voltage 
Side 2 vehicle induced voltage 
Vehicle velocity 
Monitor signal from adjacent null-flux loop regulator 
The servo controller then computes the following intermediate parameters: 
Side 1--Side 2 differential lateral airgap 
Side 1 guidance magnet magnetic field 
Side 2 guidance magnet magnetic field 
Angle of inclination 
Prospective Side 1 null-flux current 
Prospective Side 2 null-flux current 
The controller outputs three quantities 
Forward thyristor or switching device gate turn-on/turn-off pulse. 
Reverse thyristor or switching device gate turn-on/turn-off pulse. 
Monitor signal to central system controller and subsequent (adjacent) local 
controller for diagnostics function. 
Table 2 provides an example of the design parameters for a vehicle of the 
present invention; although a multitude of alternative design parameters 
are available depending on the constraints of the system. 
TABLE 2 
______________________________________ 
Specification of Electrical/Mechanical Design Parameters for 
Full-scale High-speed Maglev Guideway and Vehicle 
______________________________________ 
Operational Characteristics of a Representative Maglev Vehicle 
Capacity Range 200 passengers 
Overall Length 39 m 
Width (nominal) 3.65 m 
Height (nominal) 3.2 m 
Aerodynamic Drag Coefficient 
0.26 
Nominal Laden Weight (200 passengers) 
67 tons 
Acceleration 1.0 m/sec.sup.2 (0.1 g) 
Deceleration - Normal 2.5 m/sec.sup.2 (0.25 g) 
Deceleration - Emergency 
10 m/sec.sup.2 (1.0 g) 
Propulsion Linear Synchronous 
Motor 
Upper Speed 500 km/hr. 
Propulsion Magnet Refrigeration Load 
41-50 kW 
Characteristics at Cruising Speed of 500 km/hr. 
Maximum Continuous Thrust 
60 kN 
Ground Clearance 0.10-0.12 m 
Magnetic Drag 12-15 kN 
Aerodynamic Drag 35-37 kN 
Side Wind Loading 70 kN 
(100 km/hr. cross wind) 
Noise, at 15 m Sideline 
89 d BA 
Guideway Aluminum for Levitation 
42 metric tons/km 
Strips 
Superelevation limit 15.degree. 
Maximum Roll Ram-rate 12.sup.0 per second 
Minimum Radius at Maximum Speed 
1.6 km 
Suspension Stiffness - 3 .times. 10.sup.6 N/m 
Nominal-Vertical 
Levitation System - Natural Frequency 
2 Hz 
Levitation Lift Off Speed Range 
48-60 km/hr. 
Substation Electrical Output 
12.9 MVA at 
122 Hz 
Guidance System - Typical Values 
Vehicle SC Magnet Strength 
385 kAT 
Magnet Width 0.40 m 
Magnet Length 1.50 m 
Vertical Airgap 23 cm 
Guidance Natural Frequency 
0.85-1.0 Hz 
Guidance Stiffness - Nominal-Lateral 
4.2 .times. 10.sup.6 N/m 
Total Superconducting Magnets 
7 per side vehicle 
Magnetic Moment (MMF .times. Surface Area) 
1617 kAT - sq. m./ 
side 
______________________________________ 
In regard to FIG. 10, this is an electrodynamically suspended vehicle with 
dual propulsion motors, dual guidance and dual suspension systems along a 
non-conducting, non-ferromagnetic guideway structure Item 16. Item 1 (item 
3) is a high frequency inductive power pickup mounted on the vehicle left 
(right) outrigger item 17. Item 2 (item 4) is the corresponding high 
frequency stator section mounted underneath guideway which transfers 
electrical power to the vehicle by induction action. Items 5, 7 are the 
left and right side electrodynamic lateral guidance coils mounted on the 
vehicle outrigger and driving magnetic flux in principally a lateral 
direction with respect to vehicle motion and interacting with the guideway 
mounted longitudinally-meaning conductive strips items 6, 8 respectively. 
These coils 5, 7 may or may not be superconducting coils depending on the 
magnitude of the lateral guidance force desired. Items 9, 11 are the left 
and right side combination suspension magnets and linear propulsion motors 
mounted on vehicle undercarriage; they are powered by corresponding 
variable frequency power supplies 13, 14. Items 9, 11 interact with 
guideway-mounted horizontal levitation/propulsion strips items 10, 12 
which are composed of a sandwich arrangement of ferromagnetic strip 
material closest to the guideway surface and conductive, non-ferromagnetic 
strip material closest to the vehicle undercarriage. Items 10, 12 may be 
composed of continuous material in the longitudinal direction (i.e. 
direction of vehicle motion) or may be composed of discrete loops or a 
ladder configuration depending on overall performance requirements. In the 
preferred embodiment, items 10, 12 are composed of aluminum strip on the 
upper surface and steel plate for the lower material; depending on the 
relative thicknesses of these two materials the vertical force developed 
between items 9 and 10 and between items 11 and 12 can be either 
attractive or repulsive. For example, when the amount of aluminum exceeds 
the amount of steel material then the overall vertical force on item 9 or 
11 will be repulsive. Items 18, 19 are the left and right side coolant 
supplies for items 9, 11 respectively which in the preferred embodiment 
items 18, 19 are refrigerator/liquifiers for liquid nitrogen or liquid 
helium cryogens. Items 18, 19 also feeds either cold gas or liquid cryogen 
to items 5, 7 if the system uses cryogenic lateral guidance coils. Item 15 
is the centrally located power supply consisting of either a fuel cell or 
an electrical frequency changer such as cycloconverter which takes as 
input the power brought on-board by items 1, 5 at high frequency and 
reduces this to either low frequency AC (e.g. 0-200 Hz) or direct current 
to feed into items 13, 14. The passenger compartment floor preferably 
contains a sandwich combination of ferromagnetic and conductive shielding 
in the form of horizontal plates spanning the entire vehicle width and 
length to attenuate the magnetic fields generated by the propulsion and 
suspension coils. 
As shown in FIG. 11, the secondary coils or conductors 6 and 8 have the 
same inductance and resistance and are spaced apart at periodic, 
reoccurring intervals in the direction of motion to interact with the 
separate set of vehicle mounted SC field magnets. The vehicle lateral 
guidance means is composed of an array of guideway mounted secondary coils 
6 and 8 or conductors having the same inductance and resistance and spaced 
at periodic intervals in the direction of motion and separate sets of 
vehicle mounted SC field magnets 5 and 7. The EM force generated by a 
guidance magnet on one side of the vehicle in a horizontal orientated 
curvature, is enhanced above the guidance electrodynamic force generated 
by the other side of the vehicle along a guideway curvature C shown in 
FIG. 11, with the differential force being controllable from the vehicle 
and adjustable in magnitude in accordance with radial acceleration limits 
for passenger comfort used to counteract the centrifugal force impinging 
on the vehicle in high speed turns, thus providing a lateral stabilization 
necessary for high speed controlled maneuvers. Also shown in FIG. 11 is a 
straight guideway section S adjoining the section of guideway identified 
as guideway curvature C. 
FIG. 12 shows maglev vehicle 62 situated above guideway 66 having top 
surface 64 and with a T-shaped guideway cross section composed on 
non-ferromagnetic, non-conducting structural material suitable for heavy 
loadings. Vehicle 62 has outrigger arms 54, 52 and passenger compartment 
floor 60 with magnetic shielding 58 and conductive shielding 56 also used 
for structural support and vehicle cross member. The vehicle is propelled 
by propulsion motor primary 66 interacting with guideway mounted secondary 
electrical member 68 if a linear induction motor is specified. 
Alternately, if a linear synchronous motor is chosen, unit 66 is the field 
magnet or secondary electrical member and the guideway mounted member 68 
is the stator or primary electrical member being fed electrical power from 
the wayside power substation. Vehicle main levitation magnets 10 and 10' 
interact with corresponding secondary electrical members 20, 20' over 
vertical airgaps G.sub.1, G.sub.2 and magnets 10,10' are mounted to the 
bottom of the vehicle undercarriage 50. Magnets 10, 10' also interact with 
null-flux coils 30, 32 respectively whereby a current regulator 34 is 
interposed between coils 30, 32 and can develop currents of differing 
magnitudes in connecting lines 36, 38 to assist with roll compensation. 
Secondary electrical member 20 is mounted on guideway upper surface 64 
without ferromagnetic backing and may be composed of discrete 
electrically-conductive coils, a conducting ladder arrangement or a flat 
conductive strip according to the speed and force characteristics of the 
systems. Secondary electrical member 20' has a different time constant 
than 20 and is shown attached to ferromagnetic backing plate 24 which is 
on the opposite side of 20' from the side facing the airgap G.sub.2. In 
the particular case shown whereby G.sub.1 &gt;G.sub.2, then levitation force 
developed by the components 10 and 20 will exceed that developed by 
components 10' and 20'. Members 20 and 20' are normally passive and 
members 10, 10' are normally active and excited electrically for the same 
magnetomotive force by power supply 44 mounted on support 56. 
Auxiliary levitation magnets 1, 1' are mounted on the vehicle outrigger 54, 
52 and interact with guideway mounted tertiary electrical members 2, 2' 
which are arranged with their plane in a horizontal orientation and 
vertically positioned with airgaps G.sub.1, G.sub.2 which are different 
when the vehicle experiences a roll moment. It is an important feature of 
this invention that member 2 be mounted underneath tertiary ferromagnetic 
member 28 to either lower the repulsive levitation force on the left side 
below that produced by members 1', 2' or to create an electromagnetic 
attractive force between members 1, 2 while members 1', 2' remain in 
repulsive force mode. This creates a controllable roll moment M or 
electromagnetic banking even in the case of a level guideway 66. It is 
intended during roll maneuver that member 1 will have a different 
magnitude of magnetomotive force (MMF) from member 1' and in the specific 
embodiment shown in FIG. 12, the member 1' will require a larger MMF than 
that for member 1. Corresponding to this condition, a power supply 40' 
feeding auxiliary levitation magnet 1 must produce a higher power output 
or higher current that the power supply 40 which operatively feeds 
auxiliary levitation magnet 1. For the specific embodiment shown, tertiary 
electrical member 2 has a lower magnetic reluctance than member 2' to the 
pressure of tertiary ferromagnetic member 28 due to the presence of 
tertiary ferromagnetic member 28 and consequently the terminal impedance 
of member 1 will be higher than the terminal impedance of member 1 for the 
condition G.sub.7 &gt;G.sub.6. Power supplies 40 and 40' are separately 
controlled and may be a DC supply, or AC supply, or a hybrid DC/AC power 
supply. The command signals for 40 and 40' are derived from either a 
vehicle-mounted or wayside mounted master control system which determines 
the proper amount of electromagnetic banking for speed conditions, 
passenger comfort levels or response to abnormal conditions such as 
side-wind loading or weight differential across the vehicle width. 
Lateral control magnets 5, 7 are spring-mounted with their major plane in a 
vertical direction on the vehicle outrigger 54, 52 and are operatively 
connected to power supplies 42, 42 which are in the preferred embodiment 
variable frequency, variable voltage AC power supplies. Lateral control 
magnets 5, 7 interact with guideway mounted lateral control member 6, 8 
which are passive, electrically conductive coils or strip conductor 
without use of ferromagnetic inserts in the members 6, 8. If it is 
desirous to have an asymmetrical lateral force developed between pair 5-6 
and pair 7-8, then it is a necessary aspect of this invention to have 
member 6 of a different time constant than member 8 while retaining 
identical construction and materials for magnets 5, 7. For example, if 
dynamic vehicle conditions or perturbations from outside the vehicle 
demand, in the interests of vehicle stability, that airgap G.sub.5 should 
be greater than airgap G.sub.4 as shown in FIG. 12 then it is advantageous 
to have lateral control strip 78 with a larger electrical time constant 
than lateral control strip 6. In practice, member 8 would have a greater 
volume of conductor per unit of guideway length manifest as either an 
increase in vertical height or transverse width (thickness) of the member 
or both in contrast to the dimensioning wire with either AC or DC 
excitation or alternately can be wound of normal conducting wire on a 
ferromagnetic core. These members are designed to maximize their repulsive 
force characteristic which is achieved by having a pole-pitch to airgap 
ration exceed 3.1. 
Members 1, 1', 5', 7, 10, 10' may be cryogenically cooled if 
superconducting excitation is used or alternately these members may be 
air-cooled, water-cooled or other suitable fluid coolant used. The 
preferred embodiment in FIG. 12 shows members 10, 10' as superconducting 
magnets with associated refrigerator/liquifier 46 feeding the two members 
whereas members 1, 1', 5, 7 are shown as non-superconducting and use a 
combination of conduction cooling to the vehicle outrigger 52, 54 and 
convection cooling from the ambient air in the airgaps G.sub.4, G.sub.5, 
G.sub.6, G.sub.7. 
It should be apparent to anyone skilled in the art that the arrangement 
shown in FIG. 12 can be readily adapted to impart a vehicle roll moment in 
the direction opposite as shown by relocating tertiary ferromagnetic 
member 28 to be on top of member 2' instead of 2, and secondly by 
relocating member 24 to be underneath member 20 instead of 20' accompanied 
by corresponding changes in excitation level for members 10, 10', 1 and 
1'. 
FIG. 13 shows maglev vehicle 62 situated above semi-circular guideway 66 
having top-surface 64 with the contour of this surface matched to the 
contour of the vehicle undercarriage 50 to yield a nearly constant 
vertical airgap between vehicle and guideway in both steady-state and sway 
conditions. The guideway structural material 66 is composed of 
nonferromagnetic, non-conducting structural beams or concrete with 
fiberglass reinforcing. Vehicle 62 contains 4 arrays of superconducting 
magnets, labeled 10, 84, 86, 10' whereby each array is longitudinally 
disposed in sets of magnet subassemblies with alternating polarities. 
Looking transversely, the 4 arrays are polarized in an alternating 
sequence such as N-S-N-S which is also effective in attenuating stray 
magnetic field s in the passenger compartment, 98. The vehicle is 
propelled by a linear synchronous motor (LSM) in a dual array with the 
vehicle carrying the dual field excitation magnets 84, 86 which establish 
the primary magnetic field in the airgap G.sub.3. Magnets 84, 86 interact 
with guideway mounted armature windings for the lawyer synchronous motor 
80, 82 which are composed of multiple linear synchronous motor 80, 82 
which are composed of multiple layer air-core windings and generally 
without ferromagnetic material core. The windings 80, 82 are encased in an 
armature tray 96 held by a non-conductive potting agent such as epoxy 
resin and on top of the windings 80, 82 is embedded a null-flux lateral 
guidance ladder 88 of conductive material. The advantage of the dual 
field/dual armature LSM is that each side has independent repulsion force 
characteristics independent of propulsive thrust output. LSM windings 80, 
82 are actively fed from stationary power conditioning unit 92, 92' 
providing variable-voltage, variable-frequency power for speed/thrust 
control of vehicle. Three-phase power cables 93, 93' operatively connect 
windings 80, 82 with power conditioning units 92, 92'. 
Vehicle main levitation magnets 10, 10' interact with corresponding 
secondary electrical members 20, 20' through airgaps G.sub.1, G.sub.2 
respectively and magnets 10, 10' are mounted in the vehicle undercarriage 
compartment 99 facing the guideway. Magnets 10, 10' also interact with and 
induce current in guideway-mounted null-flux loops 30, 32 and can develop 
alternating current of differing magnitudes in connecting lines 36, 38 
responsive to lateral perturbations of the vehicle from the centerline 
position, sway or roll motions. The current induced on null-flux loops 30, 
32 acts in a fashion to restore the vehicle to a centerline or stable 
lateral position due to the direction of the electromagnetic forces 
created by the interaction of the magnetic field originating from magnets 
10, 10' and the induced current in null-flux loops 30, 32. Current 
regulator 34 is interposed between loops 30 and 32 and allows for loop 30 
to have a greater current than loop 32 or vice versa for the purpose of 
creating a differential in lateral restoring force between the two sides 
of the guideway albeit both 30, 32 act in the same direction to restore 
the vehicle's lateral centerline when a lateral perturbation occurs. 
Secondary electrical member 20 is mounted on the guideway in a tray 21 and 
designed with a contour to be flush with upper surface of the guideway 64. 
In FIG. 13, member 20 is composed of an electrically conductive ladder, 
loop or short-circuited (closed-path) loop without ferromagnetic backing 
or ferromagnetic core, whereas secondary electrical member 20' has a 
ferromagnetic back-iron plate or ferromagnetic core. This arrangement 
causes member 20 to have a lower self inductance than member 20' due to 
the smaller magnetic reluctance of the magnetic path surrounding 20 versus 
the path surrounding 20'. Additionally member 20 will, as shown in FIG. 
13, have a smaller time constant than 20'. This differential in time 
constant is advantageous for producing a differential in leviation force 
between left and right sides assuming that the vehicle magnets 10, 10' are 
excited at identical MMF. For the specific arrangement of FIG. 13, the 
levitation force produced by the pair 10-20 will exceed that produced by 
pair 10'-20' resulting in a net roll moment or torque direction as 
indicated by "M." This will tend to decrease airgap G.sub.2 and increase 
airgap G.sub.1 about the steady state or straight guideway condition and 
thus create electromagnetic banking without need for active control. The 
rate at which the airgaps G.sub.1, G.sub.2 change in response to the 
differential in levitation force is dependent on the rotational inertia of 
the vehicle and the electromagnetic damping provided. The system provided 
results in an inherently stable operating mode in that the vehicle roll 
moment is damped by the electromagnetic induction action occurring in the 
secondary electrical members. 
For the embodiment shown in FIG. 13, there is provided 3 mechanisms of 
lateral restoring force production: 
1. Null-flux ladder 88 (passive) 
2. Null-flux loop 30-32 (passive) with induced current regulator (34) 
3. Lateral force developed by levitation magnets 10, 10' interacting with 
guideway levitation conductor 20, 20'. 
Prior art describes the use of a centrally-mounted surface ladder for the 
null-flux conductor when used in conjunction with 2 vehicle mounted field 
magnets comprising a dual linear synchronous motor. There is no active 
regulation with this scheme but because of the low inductance of the 
ladder conductor, high currents and high forces are developed for lateral 
restoring. It is important that magnets 84 and 86 must be excited in a 
North-South fashion to permit a null-flux condition to exist in the center 
zone of the guideway being enclosed by ladder 88. This mechanism can 
typically provide 40-50% of the vehicle's need for lateral restoring 
force. In addition, the controlled null-flux loops 30, 32 act as an 
independent system from 88 and in general 30 or 32 has a smaller time 
constant than 88. The system is arranged in FIG. 13 so that when the 
vehicle experiences a positive roll (clockwise direction), loop 30 is 
mostly effective, has the highest induced current and results in a 
restoring force to center the vehicle. Conversely, when the vehicle 
experiences a negative roll (counterclockwise), loop 32 has high induced 
current which flows through cables 34 and into the shunt current regulator 
34 for current limiting (phase-back thyristor modulation) or 
full-conduction, maximum loop current. 
Power supply 70, 72 feeds either single-phase alternating current or direct 
current to levitation magnets 10, 10' respectively; the magnitude of this 
supply cannot be adjusted for fast change of current due to limitations on 
internal heating in the superconductor in 10, 10'. 
Power supply 74, 76 is a direct-current power supply for example with a 
1500 Amp terminal rating for energization of each propulsion magnet 84 or 
86 separately. The propulsion magnets are excited to a level of 
500,000-600,000 amp-turns and may use commercially available 
superconducting wire such as Nb-Ti or Nb.sub.3 Sn. 
In the embodiment shown in FIG. 13, all 4 vehicle magnet arrays are cooled 
by a common refrigerator/liquifier 78 which has cryogenic fluid reservoir 
79 and feed/extraction coldlines 77 to each vehicle magnet. The 
refrigerator/liquifier 78 would in the most general embodiment include 
provisions for a compressor, controls, pressure regulator and valving. 
It should be apparent that a minimal amount of electric power is required 
on board the vehicle due to the low losses of the superconductor; this 
power may be provided by a better, air turbine-generator or fuel cell and 
typically 125-185 kW for a full-scale 100 passenger vehicle. By contrast, 
the guideway inverter units 92, 92' must impart between 7 MW and 15 MW to 
the linear synchronous motor armature windings to propel said vehicle. 
FIG. 13 shows a preferred location of the AC or DC power bus duct 90, 90' 
in the open space compartment 100 below the upper guideway components. 
Ducts 90, 90' contain a system of DC or poly-phase AC solid conductors 
with current in the range of 2,000-6,000 amps and a voltage rating of 1500 
to 4160 volts rms. 
Table 1 gives dimensions and characteristics for principal components shown 
in FIG. 13 specific to a 300 mph system with a 67 ton vehicle. 
FIG. 14 shows a top view of the guideway corresponding to section Y--Y of 
FIG. 13 and superimposing the vehicle field magnets 84, 86 and levitation 
magnets 10, 10' on top of the guideway components. It should be clear that 
although the FIG. 14 only shows 2 magnets 10, 10' per side that the 
invention covers a multiplicity of levitation magnets arranged in tandem 
per side, the exact number dependent on the levitated mass and MMF 
strength/magnet. Similarly, while FIG. 14 only shows two LSM field magnets 
per side, the invention is applicable to a multiplicity of field magnets 
arranged in tandem along the direction of travel of the vehicle denoted 
"V." In the preferred embodiment, the levitation magnets are 
longitudinally space, periodically at a pitch labeled .tau..sub.1 as 
shown. The LSM field magnets 84, 86 are longitudinally spaced at periodic 
intervals labeled .tau..sub.2 and also referred to as the pole-pitch. The 
null flux loops 30, 32 are shown spaced at a longitudinal pitch 
.tau..sub.3. The loops 30, 32 are shown connected through electrical power 
cables 36, 38 to the current regulator 34 which in the preferred 
embodiment contains a bilateral thyristor pair for the switching device. 
Two such current regulators 34 are shown in FIG. 14 for simplicity but it 
is intended that each null-flux loop pair 30, 32 have an independent 
current regulator that links each set. Optical means or electrical means 
are provided to gate the bilateral thyristor pair into the conduction mode 
or partial conduction mode responsive to a wayside vehicle motion control 
system 37 which is in communication with motion sensor units originating 
from the vehicle. The optical or electrical input signal line 35 is the 
preferred means to gate or control current regulator which does not 
require power from an outside source. 
FIG. 14 shows LSM windings 80, 82 and in a preferred embodiment each 
winding is composed of 6 phases as indicated OC1, OC2, OB1, OB2, OA1, OA2. 
It is clear that windings 80, 82 are interposed between null-flux loops 
30, 32 and the null-flux ladder 88 with small transverse clearances on the 
order of 25-100 mm. Null-flux ladder 88 as shown is specific to the use of 
a dual LSM propulsion motor with requisite dual field coil arrays as 
shown. The ladder may be a continuous preformed metallic, conductive strip 
for example a punched aluminum strip or as shown in FIG. 14, a series of 
overlapping rectangular conducting loops is sufficient and constitutes the 
preferred embodiment. The amount of longitudinal overlap of loops or the 
spacing pitch is an important factor and established by the operating 
speed of the vehicle and the pitch of the propulsion field magnets 84, 86. 
In the example shown, the null flux loops have a 2/3 or approximately 67% 
pitch overlap and are composed of aluminum or copper without ferromagnetic 
cores or ferromagnetic structural supports. 
The secondary electrical member 20, 20' constituting the leviation 
component is composed of longitudinal conductive members 2 which are 
electrically joined to rungs 23 which are conductive but not necessarily 
of the same conductivity as 21. In the preferred embodiment, 21 and 23 are 
stamped as a ladder assembly out of high conductivity aluminum Type 
6101-T64 plate; thus avoiding major welding of parts. FIG. 14 shows 
guideway section denoted "S" for straight section and denoted "C" for 
curved section, which in a maglev system is a gently curve with typically 
a radius of horizontal curvature of 1.6-2.0 km. In section "S" both 
members 20 and 20' are without ferromagnetic inserts, back-iron or other 
apparatus to cause a differential in the self inductance or time constant 
between 20 and 20'. The major radius is designated R.sub.o and the minor 
radius is denoted R.sub.1. If the intended minor radius occurs along 
member 20' (as shown in FIG. 14) when the vehicle enters a curved section 
"C," the first and subsequent leviation magnets 10' on this side of 
vehicle will experience a drop in leviation force, an increase in lateral 
stabilizing force and a change in the electrical time constant of the 
secondary electrical member 20' which is coupled by induction to the 
primary or vehicle-based levitation magnets. By contrast, the levitation 
magnet 10 on the major radius at the edge of member 20 will not have any 
change in levitation force, time constant or lateral stabilizing force 
upon entering the curved section. 
It should be clear from FIG. 14 that the inclusion of the flat, monolithic 
secondary ferromagnetic plate 25 underneath secondary electrical member 
20' constitutes the means by which to change the electrical time constant, 
the reflected impedance into the vehicle levitation magnets and to 
increase the lateral restoring force/lateral stability of this one side of 
the vehicle. The plate 25 in the preferred embodiment is dimensioned to 
have at least the transverse width of the corresponding levitation magnet 
but designed to be smaller in width (denoted D11) than the width D1 of the 
member 20'. The thickness of plate 25 is determined by the total magnetic 
flux generated by the vehicle magnet 10', the vertical airgap, pitch 
.tau..sub.1 and saturation characteristics of the steel. Other physical 
arrangements of member 25 other than a flat plate are possible such as a 
plate with side ears to enclose the pieces 21 or to laminate the plate to 
reduce eddy current losses. In an alternate embodiment, instead of a 
ferromagnetic plate, a solid high-conductivity plate underneath the member 
20 in the curved zone "C" would increase the levitation force and also 
change the electrical time constant by reducing the self inductance of the 
secondary member and reducing the dynamic impedance as reflected into the 
primary 10. The invention includes both means by fitting of a conductive 
plate and a ferromagnetic plate to provide for a transverse differential 
in levitation force to either correct for a roll moment imparted by 
outside forces or to purposely provide electromagnetic banking to maintain 
better dynamic stability and passenger comfort levels around high speed 
curvature. 
Table 2 is a specification for electrical members 20, 20', 30, 32, 36, 38 
constituting the null flux loops, secondary member, cables and current 
regulator, specific to the preferred embodiment shown in FIG. 14. The 
preferred embodiment uses an array of 50 vehicle magnets per side with a 
pitch of 0.65 m and excited to an MMF level of 600 KAT using niobium-tin 
(Nb.sub.3 Sn) superconducting wire in the magnet windings which are cooled 
to 8 K and operated at a current density of 12,500 A/sq. cm. 
FIG. 15 shows a U-channel guideway 65 supporting maglev vehicle 62 and 
forming three principal airgaps G.sub.V, G.sub.L, G.sub.R. The vehicle 
contains an array of left-side levitation magnets 11, right-side 
levitation magnets 15 in communication with and acting on a combined 
system of levitation, propulsion and lateral stabilizing coils mounted in 
the guideway sidewall 67. On the left side, the linear synchronous motor 
armature 80, the null flux loop 81 and short-circuited levitation 
conductor 83 are mounted in the same stator tray 69 and without 
ferromagnetic pieces or ferromagnetic supports. In a curved section of 
guideway, assuming to be curving to the right, in the stator tray 71 on 
the right side, there are four components: linear synchronous motor 
armature 82, null flux loop 85, short-circuited levitation conductors 87 
and ferromagnetic pole piece 89 which is specific to the invention. Pole 
piece 89 changes the inductance of all three windings or coils 82, 85, 87 
in the tray 71 but reduced the lateral repulsive force between the vehicle 
magnet 15 and the stator tray 71 or sidewall as compared to the level of 
repulsive lateral force generated by magnet 11 n the left sidewall 
members. The net result is an increase in coil inductance for coils 82, 
85, 87, an increase in their electrical time constant and an increase in 
the reflected impedance as seen by the vehicle magnet 15. Since the LSM 
has a series connected stator for typically 205 km, the increase in coil 
inductance over a 500 m long curvature for one side of the stator has 
little consequence on the overall LSM performance except an increase in 
terminal voltage. 
FIG. 15 shows null-flux loops 81 and 85 being operatively connected via 
electrical power cables 36, 38 to separate, dedicated current regulators 
34, 33 respectively, which has control signal input lines 35 for either 
optical or electrical gating of the semiconductor switches 37, which are 
shown as thyristor devices. 
In this system, levitation, lateral guidance and propulsion functions all 
use a common vehicle superconducting magnet 11, 15 and placement of the 
guideway components for these systems in a vertically orientated tray 
common to all 3 systems. 
There is no need for electrical components to be mounted on the vehicle 
undercarriage outer surface 50. Vehicle shielding for the passenger 
compartment 98 is accomplished by a four-layer shield separating the 
equipment compartment 99 from passenger compartment. Layer 61 is a 
ferromagnetic plate acting also as a floor; layer 60 is a conductive 
shielding plate; layer 58 is a ferromagnetic shield plate; layer 56 is a 
conductive shield and structural support for mounting of undercarriage 
equipment. Power supplies 74, 76 feed magnets 11 and 15 which in turn is 
feed from power source 77 which may be a fuel cell or battery. Supplies 
74, 76 being variable-voltage, variable frequency power conditioning 
units. Each magnet is fed a cryogen such as liquid helium or nitrogen from 
refrigerator/liquifier/compressor unit 78 which includes a temperature 
control system and cold-head. Each magnet has a separate reservoir 79 for 
the cryogen and independent pressure and flow regulators. 
The current regulators 34 for the null-flux loops are intended to be spaced 
at periodic intervals along or underneath the guideway. For example, if 
the pitch of the null-flux loops is 0.57 m, then it is appropriate to have 
one current regulator every 0.57 m for as long as a curved section exists. 
When in a straight section, there is no need for the differential 
current/force control subject of this invention unless for special 
operating feature, the system needs to have electromagnetic banking on a 
straight guideway. 
Reference sectional lines Z--Z in FIG. 15 for the view shown in FIGS. 16a 
and 16b. FIGS. 16a and 16b show a side view of the guideway looking in the 
longitudinal-vertical plane to show the layout of members 82, 85, 87 as 
each component has a specific layout which is not fully shown by the 
vertical-transverse drawing of FIG. 15. Vehicle magnet 15 is shown 
superimposed on top of the three principal guideway electrical members, 
magnet 15 may be either a single magnet or a multiplicity of magnets 
spaced at a pitch of .tau..sub.p as indicated in the figure. Levitation 
conductors 87 are arranged on guideway in an array with longitudinal pitch 
.tau..sub.p in the preferred embodiment. 
It is an important feature of this system that in straight sections "S" the 
null-flux loops 101 are included on each sidewall but without any current 
regulator or insertion of ferromagnetic pieces or other apparatus to alter 
the electrical time constant, impedance or current versus repulsive force 
characteristics. Loops 101 comprise two rectangular loops of approximately 
full pole-pitch .tau..sub.p in length but each loop has upper 102 and 
lower 103 conductors which have a vertical height of approximately 45% of 
the vehicle magnet 15 vertical height H.sub.1. The loop conductors 102 and 
103 are connected in series null-flux i.e., with electrically opposing 
polarities such that there is no net induced voltage around the loop until 
magnetic fluxes .PHI..sub.1 and .PHI..sub.2 are different due to vertical 
perturbations of magnet 15. 
In curved section "C" subject of the invention, null-flux loops 81 again 
comprise upper 102 and lower 103 conductors which add tap points 104 and 
105 to connect outgoing power cable 36 to the external current regulator 
34. Thus when a differential exits between magnetic fluxes .PHI..sub.1 and 
.PHI..sub.2, the amount of current build-up in the loop 81 can be 
increased on one side and simultaneously reducing the current on the other 
side of the loop. For example, magnet 15 is shown in a vertical position 
lower than steady-state condition and thus when passing over loop 81 in 
the curved zone will produce flux .PHI..sub.2 &gt;.PHI..sub.1 and 
consequently the voltage induced around the loop with conductors 103 will 
exceed the voltage for conductors 102. In the case when it is desirable to 
purposely develop roll moment M (reference FIG. 15) for electromagnetic 
banking, then it is essential that the thyristors 37 in current regulator 
34 be switched on so as to cause current to flow in line 36. This will 
insure that the induced current in conductors 103 exceeds that in 
conductors 102. In the preferred embodiment, the means of control is by 
shunting current away from the guideway null-flux conductors which 
experience the lower vehicle induced voltage. 
FIGS. 16a and 16b also show the addition of a ferromagnetic pole piece 89' 
in the lower portion of the null-flux loops, surrounding conductors 102 
for the purpose of creating an additional differential in the magnetic 
flux conditions. It is understood that piece 89 is underneath the entire 
group of 3 electrical components 85, 82, 87 in the stator tray 71 and may 
or may not extend more than one-half of the height H.sub.2 of the 
null-flux loops. FIGS. 16a and 16b is applicable with a clockwise roll 
moment; otherwise, if a counterclockwise roll moment is desired, then the 
locations of pole pieces 89, 89' are reversed i.e. pole-piece 89' is 
placed in the top portion of stator tray 71 and pole-piece 89 is located 
in the lower portion of stator tray 69. 
FIG. 17b shows the simplified electrical schematic for one null flux loop 
corresponding to the elementary drawing shown in FIG. 17a appropriate to 
FIGS. 16a, 16b and 15. The regulator current is defined as i.sub.r, loop A 
(upper) current is defined as i.sub.a, loop B (lower conductors) current 
is defined as i.sub.b. By Kirchoff's Law, we have i.sub.r +i.sub.b 
=i.sub.a where i.sub.r can be a controllable current from zero up to a 
value, when in full conduction of the greater of i.sub.a or i.sub.b. For 
example, if i.sub.a is marginally greater than i.sub.b with thyristors 37 
in partial conduction, then if 37 is put into full conduction mode, 
i.sub.r =i.sub.a and i.sub.b =zero. The force developed by each loop is 
proportional to the rms value of current since the field coil 15 or 11 is 
at constant excitation. By creating a differential in current from lower 
to upper loops, the roll moment of the vehicle is compensated or a 
deliberate roll is imposed which is controllable by the phasing of 
thyristors 37 in the current regulator. Resistor R is the critical 
resistance of the cabling from the guideway sidewall to the regulator 
according to type and length of cable used. 
The magnitude of repulsive force developed by a short-circuited loop or 
strip conductor is a function of 4 main design variables. 
a. excitation strength (MMF) and pole-pitch of the primary magnet 
b. the airgap to pole-pitch ratio 
c. the magnetic Reynolds number, G 
d. the electromagnetic slip s, for induction action. 
When the secondary magnetic circuit contains only conductive components, 
the direction of force is singular and repulsive. When the secondary 
circuit contains ferromagnetic inserts or ferromagnetic backing, it is 
then possible to obtain bidirectional force control when special 
conditions are met. In the most general case, the vehicle magnet 11 or 15 
has AC low-frequency excitation which enables use of the scheme at low 
vehicle speeds including down to zero speed. 
FIG. 18 shows an inherent levitation force and attractive force versus 
parametric values of Reynolds number electromagnetic-slip product "s.G". 
The family of curves are plotted for variations in the parameter K=.pi.x 
airgap/pole-pitch. The curve shows both attractive and repulsive operation 
of a representative curved-zone, sidewall-mounted, null flux loop A 
(reference FIGS. 16a, 16b, 17a and 17b) with a degree of ferromagnetic 
backing. In the normal operating mode for the 6.7 ton vehicle, for example 
with s.G=2 and K=0.20, the optimum slip is 4% and the repulsive pressure 
developed is -10,600 N/sq.m. surface area. If the slip is increased by 
inverter action to s=16%, the parameter s.G=8 and the net force changes to 
be attractive with a pressure loading of 1,820 N/sq.m. The change from 
attractive mode to repulsive mode is accomplished by a minor retardation 
in inverter frequency; this change is affected in a period of typically 4 
ms. 
In one embodiment such as FIG. 15, the null flux loop for lateral 
stabilizing control operates with a 28 mm levitation gap, a 780 mm 
pole-pitch and K=0.113 which FIG. 18 shows a cross-over point at s.G=8.85. 
In general, the cross-over from levitation to attraction occurs in an 
electrodynamic system at: K.s.G=1.0 
With a larger excitation magnet in longitudinal dimension or pole-pitch, 
with a design speed up to 134 m/s (480 km/hr), the levitation cross-over 
occurs at s.G=1.0/K=5.0; this has a pole-pitch of 2.79 m which indicates 
an upper inverter frequency of 25 Hz for a 4% operating slip. This 25 Hz 
excitation to the vehicle main field magnet array is within 
state-of-the-art specifications for a multi-filament, twisted 
superconductor. 
FIG. 18 shows that if the design can yield K=0.045 or less, then the entire 
operation will be repulsive independent of the slip-Reynolds number 
product. FIG. 18 is specific to an excitation loading of 100,000 Amps per 
meter longitudinal with alternate loadings being proportional to the 
square root of the repulsive/attractive force produced. 
The electrodynamic levitation force is strongly dependent on the slip times 
Reynolds number product. The magnetic Reynolds number is calculated as: 
G=2 T.sup.2 .mu..sub.o ft' 
p g RF .pi. 
where 
T=stator pole pitch (m) 
f=excitation frequency (Hz) 
p=resistivity of secondary conductor (ohm-m) 
g=airgap between stator pole to secondary Fe plate (m) 
t'=effective thickness of secondary plate (m) 
RF=Russell & Norsworthy Factor for overhang dimension 
(applicable to ladder or strip type secondaries only) 
Substituting values of T=2.79 m, f=24 Hz, p=2.17.times.10.sup.-8, g=0.069, 
RF=1.43, t'=0.019 the resultant factor is G=120. From inspection of FIG. 
18 it is seen that for the parametric curve .pi.g/T=0.08 (which is 
appropriate to the 6.7 ton vehicle), a high resultant repulsive density 
would require a slip x Reynolds number product of s.G=7.0 or less to 
produce a force density of at least 10,000 N/sq.m. The operating slip is 
then established at s=7.0/G=0.058 per unit. 
TABLE 1 
______________________________________ 
Operational Characteristics and Dimensions of the Reference 
Maglev Vehicle (shown in FIG. 13) 
______________________________________ 
Capacity range 76, 118 or 200 
passengers 
Overall length 15, 23 or 39 m 
Width (nominal) 3.12 m 
Height (nominal) 3.2 
Aerodynamic drag coefficient 
0.26 
Nominal laden weight (200 pass.) 
67 tons 
Acceleration 1.0 m/sec.sup.2 
Deceleration - normal 2.5 m/sec.sup.2 
Deceleration - emergency 
10 m/sec.sup.2 
Propulsion LSM - Dual Stator 
Upper speed range 400-500 km/hr. 
Propulsion magnet refrigeration load 
41-50 kW 
At Cruising Speed of 500 km/hr. 
Max. Continuous thrust 60 kN 
Ground clearance 0.10-0.12 m 
Magnetic drag (est.) 12-15 kN 
Aerodynamic drag (est.) 
35-37 kN 
Side wind loading (100 km/hr. cross wind) 
70 kN 
Guideway aluminum for levitation strips 
42 metric tons/km 
Minimum radius at max. speed 
1.6 km 
Guidance stiffness - nominal-lateral 
4.2 .times. 10.sup.6 N/m 
Suspension stiffness - nominal-vertical 
3 .times. 10.sup.6 N/m 
Levitation system - natural frequency 
2 Hz 
Guidance natural frequency 
0.85-1.0 Hz 
Levitation Magnet MMF 385 kAT 
Substation Electrical Output 
12.9 MVA at 
122 Hz 
LSM Mechanical Output 8.33 MW 
Linear Power Generator Output 
475 KW 
LSM Field Magnet MMF 600 kAT 
Dimensions 
D.sub.1 = 550 mm 
D.sub.5 = 550 mm 
D.sub.9 = 100 mm 
D.sub.2 = 1600 mm 
D.sub.6 = 250 mm 
D.sub.10 = 480 mm 
D.sub.3 = 650 mm 
D.sub.7 = 1525 mm 
D.sub.4 = 230 mm 
D.sub.8 = 3120 mm 
______________________________________ 
TABLE 2 
______________________________________ 
Specification for Guideway Components for Null-Flux Loops, 
Null-Flux Ladders and Levitation Strips 
Reference FIGS. 13 & 14 
Semi-circular Guideway 
Vehicle: 67,000 kG mass Baseline Lateral Restoring Force: 
210 kN 
______________________________________ 
a) Null-flux loops (30, 32) 
Transverse width 0.25 m 
Longitudinal pitch, .tau..sub.p 
0.57 m 
Conductor cross section 
11 mm .times. 25 mm 
Overlap 0% 
Inductance 0.98 micro-Henry 
Material Aluminum 6101-T64 
Frequency of Induced Current 
117 Hz 
Reactance at 117 Hz 114.7 micro-ohm 
X/R ratio at high speed 
1.10 
Resistance at 117 Hz 104 micro-ohm 
b) Null-flux ladder (88) 
Transverse width 0.32 m 
Longitudinal pitch 0.50 m 
Conductor cross section 
12 mm .times. 15 mm 
Overlap 67% 
Inductance 0.92 micro-Henry 
Resistance 111 micro-ohm 
c) Secondary electrical member/levitation strips (20, 20') 
in straight or curved section 
Width (D.sub.1) .times. depth 
550 mm .times. 12.5 mm 
Sidebar conductor width 
5.0 cm 
Rung longitudinal dimension 
5.0 cm 
Rung pitch 51 cm 
Material Aluminum 6101-T64 
Peak induced current in rung @ 134 mls 
290,000 Amp 
d) Secondary ferromagnetic plate (25) underneath levitation 
strip (20') 
Material Carpenter Steel Type 
430FR plate 
Thickness 15 mm 
Width, D.sub.11 480 mm 
Peak magnetic field 1.3 Tesla 
Electrical resistivity 
760 micro-ohm-mm 
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Although the invention has been described in detail in the foregoing 
embodiments for the purpose of illustration, it is to be understood that 
such detail is solely for that purpose and that variations can be made 
therein by those skilled in the art without departing from the spirit and 
scope of the invention except as it may be described by the following 
claims.