Long-life vacuum system for energy storage flywheels
View Patent ↗The invention, intended primarily for use in a steel flywheel power source ( 30 ), provides a vacuum system and a method of maintaining a vacuum inside a flywheel chamber ( 32 ) for the life of the power source ( 30 ). The vacuum system combines the use of cleaning and de-gassing treatments in the chamber ( 32 ) and vacuum tempering of the steel flywheel ( 31 ) with the use of a chemical type metal alloy nonevaporable getter, such as zirconium-vanadium-iron, that cooperatively matches the outgassing of the flywheel ( 31 ) and chamber ( 32 ) by sorbing those gases that are released. The getter may be reactivated throughout the life of the flywheel system by reheating it with an integral heater that is triggered by a timer instead of a vacuum gauge to increase the system reliability, using power taken directly from the energy stored in the flywheel. The electronics ( 45 ) of the flywheel power source are used to signal an alarm or prevent achieving or maintaining full speed of the flywheel when the vacuum in the chamber degrades.
1. A vacuum system for a flywheel power source comprising:
a metal chamber having walls with a thickness sufficient to resist atmospheric pressure when said chamber is evacuated;
an energy storage flywheel constructed of steel and supported on a bearing system mounted in said chamber for rotation about an axis;
a motor/generator coupled to said flywheel for accelerating and decelerating said flywheel for storing and retrieving energy;
said chamber being maintained at low pressure for the life of the flywheel power source by the use of a nonevaporable metal alloy chemical type getter;
an electric heater in heat conducting relationship to said getter and connected in a circuit to a source of electrical energy for energizing said electric heater when required to activate and reactive said getter material.
2. A vacuum system for a flywheel power source as described in claim 1 , further comprising:
a timer in said circuit for connecting said source of electrical energy to said electric heater when reactivation of said getter is required.
3. A method for establishing and maintaining a vacuum in a flywheel power source that employs a steel flywheel coupled to a motor/generator and housed in a metal chamber, comprising:
assembling said flywheel inside said chamber and sealing said chamber;
heating said entire chamber to at least about 120 degrees F. while pulling a vacuum on said chamber for removal of internal gasses, contaminants and water vapor using a connection to an external vacuum pump;
establishing communication between a separate vacuum pump and said chamber, said separate vacuum pump having a chemical type metal alloy nonevaporable getter material that can be activated by heating said getter material; and
closing said vacuum connection between said chamber and said external vacuum pump and sealing said chamber completely.
4. A method for establishing and maintaining vacuum as describe in claim 3 wherein:
reheating said getter during the life of said flywheel power source to reactivate said getter material through the use of a heater that is integral with the flywheel power source.
5. A method for establishing and maintaining vacuum as described in claim 4 wherein:
the reactivation of the getter is triggered by a timer.
6. A method for establishing and maintaining vacuum as described in claim 4 wherein:
energizing said heater using energy produced in said generator from said spinning flywheel.
7. A flywheel power source comprising:
an energy storage steel flywheel supported on a bearing system for rotating about an axis;
a motor/generator coupled to said flywheel for accelerating and decelerating the flywheel for storing and retrieving energy;
a metal chamber surrounding said flywheel and adapted to be evacuated and maintained at a low pressure;
electronics are connected to said motor for charging said flywheel by energizing said motor of said motor/generator, said electronics having detectors for detecting when the drag on said flywheel is normal, and thereafter preventing maintaining or achieving full speed.
8. A flywheel power source as described in claim 7 wherein:
said prevention of maintaining or achieving full speed is achieved by current limiting to said motor.
9. A flywheel power source comprising:
an energy storage flywheel constructed of steel and supported on a bearing system for rotation about an axis,
a motor/generator is coupled to said flywheel for accelerating and decelerating the flywheel for storing and retrieving energy,
a metal chamber enclosing said flywheel and maintained at a low pressure,
electronics for controlling the charging and discharging of said flywheel power source, said electronics having a detector that activates a signal when aerodynamic drag on said flywheel is detected to be above normal.
10. A flywheel power source as described in claim 9 wherein:
said detector detects above normal drag on said flywheel at a speed lower than full operating speed of said flywheel by the electronics calculation using the motor power, rotational speed and the flywheel acceleration.
11. A flywheel power source as described in claim 9 , wherein:
said flywheel includes a rotor having a principal rotating mass of steel, and said signal triggers reactivation of a chemical type metal alloy nonevaporable getter material by activating a heater in thermal contact with said getter material for heating said getter material to reduce said pressure and reduce said aerodynamic drag.
12. A method for maintaining vacuum in a flywheel power source having an energy storage flywheel coupled to a motor/generator for accelerating and decelerating the flywheel for storing and retrieving energy and supported on a bearing system for rotation inside a vacuum chamber enclosing said flywheel and maintained at a low pressure, comprising:
determining an occurrence of increased pressure above a predetermined threshold inside said vacuum chamber with use of said flywheel motor power, flywheel speed and flywheel acceleration; and
triggering the vacuum to be reestablished upon said determination of increased pressure.
13. A method as described in claim 12 , wherein:
said vacuum is reestablished by reactivating a chemical type metal alloy nonevaporable getter through use of a heater.
14. A method as described in claim 12 wherein:
said flywheel has a steel rotor and said increased pressure inside said vacuum chamber is less than 10 −3 Torr.
15. A method as described in claim 12 wherein:
said steel flywheel has a steel rotor that has been tempered by heating said solid steel rotor to a temperature of between 800° F. and 1200° F. and holding it at that temperature for more than one hour.
16. A method as described in claim 12 wherein:
said electronics of said flywheel power source prevent said motor from maintaining full speed of said flywheel when the pressure in the vacuum chamber exceeds a predetermined minimum pressure, as determined by increased aerodynamic drag on said flywheel.
17. A method as described in claim 16 wherein:
said electronics limit current to the motor when said pressure in said vacuum chamber exceeds said predetermined minimum pressure.
18. A method for reducing outgassing from elements of an energy storage flywheel system having a forged and quenched steel flywheel and a metal container for holding said flywheel and adapted to be evacuated to provide an evacuated space in which said flywheel can spin at high speed with little aerodynamic drag, comprising:
tempering said flywheel material in a vacuum.
19. A method as described in claim 18 , further comprising:
tempering said metal container in a vacuum.
20. A method as described in claim 18 wherein:
said forged steel flywheel is heat treated at above about 1500° F. and then is tempered in said tempering step; and
said tempering step includes heating said steel flywheel to a temperature of between 800° F. and 1200° F. and holding it at that temperature for more than one hour at a pressure of no greater than about 10 −4 Torr.