1. Field of the Invention
The present invention relates to a rotor employed in a flywheel energy storage device. More specifically, the present invention relates to a rotor wherein the power density and the energy density of the system are optimized while the manufacturing cost is minimized. Methods for manufacturing a rotor according to the present invention are also disclosed.
2. Description of the Prior Art
Flywheel systems currently being designed for mobile energy storage are generally intended to replace batteries in electrically powered vehicles. One specific example of such a system was disclosed in commonly assigned, co-pending application Ser. No. 08/148,361, which is incorporated herein by reference for all purposes. In such applications, multiple units are needed to store the required energy, so that each motor-generator need supply only a small portion of the vehicle's power. In systems where all of the surge power must be supplied by a single flywheel, the relatively large size of the single motor-generator makes it difficult to provide the needed energy density without reducing safety factors, e.g., for radial stresses, to unacceptable low levels or raising manufacturing costs to exorbitantly high levels.
U.S. Pat. No. 3,741,034 discloses rotor designs using high strength-to-weight ratio filament wound composites in relatively thin concentric cylinders, which cylinders are separated by radial springs. While this arrangement limits the radial stresses to tolerable values, it is expensive to manufacture.
U.S. Pat. No. 3,859,868 discloses techniques for varying the elasticity-density ratio of the rotor elements to minimize radial stresses. On the other hand, U.S. Pat. Nos. 4,341,001 and 4,821,599 describe the use of curved metallic hubs to connect the energy storage elements to the axle. Additionally, U.S. Pat. No. 5,124,605 discloses a flywheel system employing counter-rotating flywheels, each of which includes a hub, a rim and a plurality of tubular assemblies disposed parallel to the hub axis for connecting the hub to the rim while allowing for differential radial expansion between the hub and the rim.
None of these references deal with the integration of a large, high power motor-generator into the flywheel energy storage system currently being designed for vehicles.