Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-02-09
2002-05-14
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090500, C310S266000, C310S083000, C074S572200
Reexamination Certificate
active
06388347
ABSTRACT:
FIELD OF TECHNOLOGY
The present invention is directed to electromechanical battery flywheel systems for energy storage and power delivery. More particularly, the present invention is directed toward flywheel energy storage systems having a variable speed, counter-rotating containment vessel for mechanical containment of high speed rotors and managing net momentum and net external gyroscopic forces.
BACKGROUND OF THE INVENTION
Generally, battery flywheel systems comprise a single high-speed rotor which is mounted on a central shaft and which is supported by bearings attached to each end of the shaft. The flywheel and shaft are often enveloped within a heavy stationary containment vessel which is generally evacuated to minimize energy losses. In such arrangements, the shaft bearings are attached to the end plates of the flywheel containment vessel and the rotor is driven by one or more motor/generators mounted to the end plate. It has been proposed that flywheel energy storage systems be used in terrestrial (e.g. electrical) and extra-terrestrial (e.g. satellite) vehicles. However, management of momentum together with substantial gyroscopic forces associated with many prior flywheel storage system designs has impeded development in this area. In a flywheel system, gyroscopic forces arise from prescribed angular rotation of the flywheel about directions not coincident with the flywheel spin axis. Such forces result when the motion of the vehicle in which the flywheel is mounted are imposed on the flywheel rotor. Thus, when a vehicle having a flywheel situated therein undergoes a change in direction, gyroscopic forces may result which are orthogonal to the imposed movement. The gyroscopic forces grow larger with the size of the flywheel, with the rate of change and direction of the imposed motion, and with the speed at which the flywheel rotates about its spin axis.
Several methods have been suggested to compensate for the external gyroscopic forces associated with flywheels. A first method involves gimbal mounting the flywheel containment vessel so as to avoid or minimize the external gyroscopic moments that would result if the containment cylinder were rigidly attached to the vehicle. Rigid attachment of a single flywheel to the flywheel containment cylinder results in direct transfer of the external gyroscopic forces to the vehicle. Although the gimbal mount is effective in preventing transfer of vehicle motion to the flywheel, the gimbal mount provides a relatively weak mechanical connection between the flywheel containment cylinder and the vehicle. In the event of flywheel failure, large forces and moments may be applied to the gimbal which could well exceed the strength of the mechanical connection of the gimbal. Further, some gimbal designs compensate for limited degrees of motion. If the motion of the vehicle exceeds the limited degree of motion for which the gimbal is designed to compensate, the gyroscopic forces are transferred to the vehicle. Thus, the mechanical limitations of the gimbal may preclude it in some applications from being a satisfactory solution to the problem of gyroscopic forces.
Another method for preventing external gyroscopic forces from being exerted on a vehicle having a flywheel therein involves utilizing two coaxial, counter-rotating flywheels or rotors as disclosed in U.S. Pat. No. 5,124,605, entitled, “A Flywheel-Based Energy Storage Methods and Apparatus” rather than a single flywheel. The application of two rotors also provides momentum management which is particularly useful in satellite operation when charging or discharging a flywheel system. The object of the multiple flywheel design is to counter-rotate two flywheels so as to control momentum and produce a net zero external gyroscopic force. In most such embodiments, two identical flywheels are mounted onto a single or separate shaft with each flywheel being driven by (and driving) a separate motor. The success of this method of preventing gyroscopic forces and managing momentum depends upon synchronizing the operating frequencies of the counter-rotating flywheels. Such systems still require heavy stationary containment vessels in addition to the multiple rotors in order to insure safe operation. Indeed, a shortcoming of prior flywheel systems in general is the need for heavy stationary containment vessels which offer protection during flywheel failure. In the event of a sudden failure of a flywheel rotor, the large angular momentum of the high-speed flywheel rotor can be rapidly transferred to a containment cylinder. In conventional flywheel systems, the containment cylinder does not rotate and is rigidly attached to the vehicle. Strong and heavy attachments are required to prevent angular motion of the containment cylinder during (and immediately after) a flywheel burst. Some prior systems have a second stationary inner containment vessel which is free, although not driven, to rotate inside the outer containment cylinder. Such prior art systems operate by imparting some of the energy dispersed during a flywheel failure onto the inner containment cylinder which is free to rotate and dissipate energy. Under a burst rotor scenario the flywheel angular momentum is transferred first to the inner cylinder and then to the outer cylinder and ultimately to the vehicle. Thus despite the use of multiple containment cylinders, the prior art does not adequately isolate the vehicle from reaction forces resulting during flywheel failure. Further, the use of multiple large cylinders for containment generally produces an overweight and impractical design for mobile deployment.
A farther shortcoming of prior flywheel systems is the inability to simultaneously provide adequate torque and power. Typically, in prior systems, a motor/generator is directly coupled to the high-speed energy storage rotor and is the only source of torque and power. Because currently available high-speed motor/generators are limited in torque and power capacity, the flywheel battery is likewise limited.
In general, the maximum torque and horsepower which a motor/generator an produce depends primarily on the physical size of the motor. The high-speed motors which are typically used in flywheel systems are necessarily small in size because the rotating elements of the motor must withstand the high rotational stresses produced by the very high rotational frequency of the flywheel. In contrast, more powerful motors are large in size and operate at lower rotational frequencies than current state-of-the-art flywheel rotors. The maximum torque which a high-speed motor/generator is capable of producing is limited by the interacting magnetic fields located within the motor. In other words, the maximum torque for a given motor is determined by the number of magnetic poles located on the motor as well as the strength, volume and mean diameter of the permanent magnets. A motor/generator with a large diameter has sufficient room for a greater number of magnetic poles than a motor/generator with a small diameter; therefore a motor/generator with a large diameter can be designed with a higher maximum torque capacity. Thus, for configurations where the high speed rotor and motor are directly coupled, the diameter of the motor/generator limits the torque capacity of the system.
The torque limitation of the prior art is important to applications which require large power transfer during charge and discharge from a single energy storage unit. One such application is a hybrid electric vehicle where the primary function of the flywheel is to provide peak power to the vehicle drive train when vehicle power demand exceeds the horsepower capacity of the internal combustion engine. Another such application where the torque limitation is important, is satellite control systems which use motor reaction torques for altitude control. Thus, there is a need in the art for a flywheel battery system which can provide broader torque and power characteristics.
Still another shortcoming of prior art flywheel systems is the suspension/drive systems. Prior flywheel
Blake H. Wayland
Zorzi Edward S.
Tamai Karl
Trinity Flywheel Power
Woodcock & Washburn LLP
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