Railways – Magnetically suspended car – Including means to sense or control car position or attitude...
Reexamination Certificate
2002-12-27
2004-12-07
Morano, S. Joseph (Department: 3617)
Railways
Magnetically suspended car
Including means to sense or control car position or attitude...
Reexamination Certificate
active
06827022
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to systems for levitating and propelling a magnetically levitated (MAGLEV) vehicle. More particularly, the present invention pertains to levitation and propulsion systems that are energy efficient over a pre-selected range of vehicle speeds. The present invention is particularly, but not exclusively, useful as an efficient levitation and propulsion system consisting of a linear synchronous motor (LSM) and an Electro-Dynamic (levitation) System (EDS) arranged uniquely into an inherently stable system.
BACKGROUND OF THE INVENTION
Magnetic levitation systems, often called MAGLEV systems, use magnetic fields to levitate a vehicle over a stationary guideway. Because the vehicle does not physically contact the guideway during acceleration and normal high-speed operation, energy losses associated with contact friction are greatly reduced. Still, magnetic drag forces, if not taken into consideration, can offset the benefits of reduced contact friction resulting in an inefficient transportation system.
Heretofore, electromagnetic systems (EMS) and Electro-Dynamic Systems (EDS) have been used to levitate vehicles. The EMS systems use the attraction between electromagnets attached to the vehicle and iron rails on the guideway to produce the required levitation force. Such a system is inherently unstable and active control of the electromagnets is required to maintain the gap between the iron rails and the electromagnets. Specifically, any fluctuation in the gap from irregularities in the track or external forces on the vehicle/guideway must be immediately countered. As one might expect, the required active control system is complicated, expensive and unreliable. With the Electro-Dynamic System (EDS), eddy currents induced in electrically conductive material on the track by a traveling magnetic field from magnets on the vehicle, produce a levitation force by their interaction with the array of magnets in the vehicle. This interaction produces drag forces that must be overcome by the propulsion system.
A linear synchronous motors (LSM), generates forces that can be used to propel a vehicle and additionally, forces that act in a direction orthogonal to the direction of propulsion. One example of a linear synchronous motor includes an armature having an a.c. poly-phase winding on an armature. This armature can be mounted on the stationary guideway for interaction with permanent magnets mounted on the vehicle. By embedding the armature winding in ferromagnetic material, attractive forces generated between the armature and the magnets can be used to levitate the vehicle. These attractive forces are generated without also generating drag forces.
Alone, the LSM is unstable and the LSM gap between the armature and magnets cannot be maintained. Specifically, even slight decreases in the LSM gap cause the attractive force between the armature and magnets to increase, and the increased force acts to further close the LSM gap. In addition to stability considerations, the efficiency of the linear synchronous motor must be considered. In this regard, the efficiency of the LSM is highly dependant on the width of the LSM gap. Specifically, the LSM is most efficient when the LSM gap is maintained relatively small.
In light of the above, it is an object of the present invention to provide systems suitable for the purposes of levitating and propelling a vehicle over a guideway that are stable and energy efficient. It is another object of the present invention to provide MAGLEV levitation and propulsion systems that provide passive levitation control with reduced peak and average magnetic drag forces. It is yet another object of the present invention to provide MAGLEV levitation and propulsion systems that remain stable in spite of unwanted fluctuations in propulsion system currents and/or external forces acting on the vehicle. Still another object of the present invention is to provide MAGLEV levitation and propulsion systems that can be used to provide lateral stability to the MAGLEV vehicle. It is still another object of the present invention to provide MAGLEV levitation and propulsion systems that are efficient during acceleration from low vehicle speeds (i.e. at peak power). It is another object of the present invention to provide MAGLEV levitation and propulsion systems that are efficient at high vehicle speeds (i.e. operating speeds). Yet another object of the present invention is to provide MAGLEV levitation and propulsion systems which are easy to use, relatively simple to implement, and comparatively cost effective.
SUMMARY OF THE INVENTION
The present invention is directed to a system for levitating and propelling a vehicle along a stationary guideway. In functional overview, the system is designed for energy efficiency over a predetermined vehicle speed range. In one embodiment, the system is designed for maximum power and efficiency during vehicle acceleration from zero speed. In another embodiment of the present invention, the system is designed for maximum efficiency at operational speeds. In addition to efficiency considerations, the system is designed to be inherently stable (unlike an EMS system or LSM system acting alone) in spite of increases in LSM armature winding current or external forces acting on the vehicle. This inherent stability of the system also allows the system to be used to provide lateral stability to the vehicle.
In accordance with the present invention, the levitation and propulsion system includes a linear synchronous motor (LSM) having two LSM components. One LSM component is mounted on the vehicle and the other LSM component is mounted on the guideway. When the vehicle is positioned on the guideway, the LSM components of the linear synchronous motor are juxtaposed and define an LSM gap between the LSM components.
For the present invention, one of the LSM components includes either a switched direct-current winding or a poly-phase winding on an iron core, and the other LSM component includes a plurality of magnetic poles mounted on a rail. Functionally, the linear synchronous motor is provided to produce a first electromagnetic force between the LSM components that acts to levitate the vehicle and a second electromagnetic force between the LSM components that acts to propel the vehicle along the guideway. Importantly, the magnitudes of these electromagnetic forces are dependent on the width of the LSM gap, the LSM armature winding current, the size of the iron core and the total vehicle load. As indicated above, a linear synchronous motor, by itself, is unstable and this instability closes the LSM gap prohibiting movement of the vehicle.
For the present invention, the levitation and propulsion system includes an electrodynamic system (EDS) to maintain the LSM gap within a desired width range. More specifically, a small LSM gap is maintained by the EDS over a predetermined range of vehicle speeds because the linear synchronous motor is most efficient when the LSM gap is small. Also, by maintaining the LSM gap within a desired width range, the LSM instabilities described above are eliminated.
Structurally, the electrodynamic system has an EDS component mounted on the vehicle and another EDS component mounted on the stationary guideway. During vehicle movement along the guideway, the EDS components cooperate to create an electromagnetic force that reacts with the levitation forces created by the LSM. Like the LSM, when the vehicle is positioned on the guideway, the EDS components are juxtaposed and define an EDS gap between the EDS components. In the preferred embodiment of the present invention, one of the EDS components is a magnet array and the other EDS component is a plurality of conductive cables, with each cable extending in a direction orthogonal to the direction of vehicle travel and short-circuited at both ends. Importantly, the magnitude of the electromagnetic force generated by the EDS is dependent on the width of the EDS gap and the speed of the vehicle relative to the stationary guideway.
As in
Jeter Philip L.
Kratz Robert
van den Bergh Hugo H.
General Atomics
Nydegger & Associates
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