Shear force levitator and levitated ring energy storage device

#1. Field of the Invention

#This invention relates generally to magnetic levitation and levitated kinetic energy storage devices.

#2. Related Technology

#FIG. 1a shows the general structure of a conventional flywheel energy storage device.

#FIG. 1b shows a cross-sectional view of the flywheel device of FIG. 1a with a graph showing the spin-induced hoop stress and radial stress as a function of distance from the flywheel axle.

#FIG. 2a shows the primary structural elements of another conventional flywheel system.

#FIG. 4a shows vertically oriented levitator system 60 in which a set of opposed permanent magnet arrays provides a large levitation force per mass unit of magnet, as described in U.S. patent application Ser. No. 10/140,729. A first array 62 is comprised of five magnets arranged to have a rotating magnetization. The polarities of the magnets, shown by arrows in the drawing, are arranged such that the direction of magnetization of each magnet is rotated ninety degrees in a common direction relative to a preceding adjacent magnet. This rotation serves to focus the magnetic field of the array toward the active surface at the expense of the unused surface opposite to the active surface. A second array 64 is comprised of three magnets, the polarities of which are also each rotated by ninety degrees as indicated by the arrows. In a vehicle levitation deployment, the first array 62 is installed on a vehicle or other object to be levitated, and the second array 64 is installed on a track or stationary support structure in opposition to the first array 62. Because a track tends to be much longer than the vehicle that rides on that track, the overall levitator design places more emphasis on minimizing the size and cost of the track array than the vehicle array, hence the difference in the sizes of the arrays. While this example employs arrays having three and five magnets respectively, arrays having larger or smaller numbers of magnets may also be employed. The array configuration of FIG. 4a provides a large improvement in levitation force per mass unit of magnet as compared to other permanent magnet designs. However, while this configuration provides stable forces in the vertical direction, it produces unstable forces in the lateral directions, and if left to itself the vehicle magnet will rapidly slide to one side or the other. Stabilization of the vehicle/track levitation system is therefore required, as described in U.S. patent application Ser. No. 10/140,729.

#FIG. 4b is a graph of the normalized vertical and lateral forces produced by the levitator of FIG. 4a as the vehicle array 62 is offset laterally to the right. This particular graph was produced by finite element analysis of the interaction of two neodymium-iron-boron magnet arrays. If the scale of FIG. 4a is taken such that the width of the vehicle magnet array is 115 millimeters, then the height of that array is 30 millimeters and it is levitated 20 millimeters above a track array having a width of 64 millimeters and a height of 7 millimeters. The graph shows that as the offset increases the vertical force decreases. At just over 20 mm offset, vertical force reaches zero then continues to go negative, i.e. it becomes an attractive rather than a repulsive force. Meanwhile the lateral force is zero at a lateral offset of zero and increases until offset is about 20 mm, at which point it reaches nearly the same value as the zero-offset vertical force, and after which it begins to decrease. From this it is seen that the arrays can be used to generate force in either the vertical direction or the lateral direction, depending on their orientation.

#FIG. 4c shows a sectional view of an arrangement 70 of the magnet arrays of FIG. 4a for levitating an object or vehicle using shear force. Levitator arrays 62a and 62b are mounted on an object or vehicle 66 to be levitated, and levitator arrays 64a and 64b are mounted on a track or guideway 68. Object motion is assumed to be into or out of the paper. The track levitator arrays are offset approximately 30 mm beneath the object levitator arrays. In this orientation the force generated by the interaction of the levitator arrays is applied in the vertical direction with respect to gravity. Force oriented in this manner will be referred to hereinafter as “shear force.” This shear force levitator, like the levitator 60 in FIG. 4a, is laterally unstable and may be stabilized by means of the techniques described in U.S. patent application Ser. No. 10/140,729. Although the embodiment of FIG. 4c shows guideway 68 wrapped around the vehicle or object to be levitated, in other embodiments the vehicle or object to be levitated may wrap around the guideway.