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Flywheel Energy Storage Device for Hybrid and Electric Vehicles

Oak Ridge National Laboratory

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Technology Marketing SummaryThis cost-effective technology stores and reuses what would otherwise be wasted energy inside a hybrid electric vehicle engine. The invention, a mechanical flywheel coupled to a rotor inside the engine, stores rotational energy during engine performance, subsequently feeding it back to assist with acceleration and braking.

The device significantly improves fuel efficiency and does not conflict with other energy storage components, such as batteries. No special container is required, as the flywheel operates at a lower power density. The rotors include a permanent magnet rotor and a magnetic coupling rotor, configured to act with a permanent magnet.

DescriptionWhen the vehicle is in operation, an initial excitation source sets up a magnetic field. When power is applied to drive the permanent magnet rotor, magnetic coupling occurs between the permanent magnet rotor and the flywheel rotor, creating torque between them. Once higher speed is reached, kinetic energy is stored in the flywheel rotor. A secondary excitation source affects the second rotor. The sources are electrically connected for power cycling. In braking mode, power is taken away from the permanent magnet rotor and supplied back through coils to the flywheel rotor. The invention allows the relatively low power density of the second rotor to act as a component for relatively high-frequency energy cycling.Benefits• Rotor kinetic energy storage can be added without extra cost and without any system conflict
• No special housing is required
• Higher fuel efficiency
Applications and Industries• Electrical motors for hybrid and electric vehicles
• Can be applied in both axial gap motors and radial gap motors
• Utilities
• Defense
• Propulsion research
Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 7,936,076
Utilization of rotor kinetic energy storage for hybrid vehicles
A power system for a motor vehicle having an internal combustion engine, the power system comprises an electric machine (12) further comprising a first excitation source (47), a permanent magnet rotor (28) and a magnetic coupling rotor (26) spaced from the permanent magnet rotor and at least one second excitation source (43), the magnetic coupling rotor (26) also including a flywheel having an inertial mass to store kinetic energy during an initial acceleration to an operating speed; and wherein the first excitation source is electrically connected to the second excitation source for power cycling such that the flywheel rotor (26) exerts torque on the permanent magnet rotor (28) to assist braking and acceleration of the permanent magnet rotor (28) and consequently, the vehicle. An axial gap machine and a radial gap machine are disclosed and methods of the invention are also disclosed.
Oak Ridge National Laboratory 05/03/2011
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
UT-B ID 200701859DevelopmentAvailable09/29/201109/29/2011

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To: David L. Sims<>