Flywheel

A flywheel is a heavy wheel that is rigidly attached to a shaft. Because of its rotary inertia, the flywheel resists changes in the speed of rotation of the shaft; it also can be used to store and deliver mechanical energy on demand.

In a piston engine, a flywheel is used to moderate fluctuations in the speed of rotation of the crankshaft; these fluctuations result from the fact that the impulses transmitted from the piston to the crankshaft through the connection rods are intermittent. On machines for punching or forming sheet metal, the large forces that are periodically required are delivered by a flywheel, whose kinetic (rotary) energy is built up by a comparatively low-powered motor while the machines is idling.

Current concern for dwindling sources of energy has stimulated renewed interest in applications of flywheels. A promising recent application is regenerative braking system in automobiles. When a car is braked by an ordinary braking system, its kinetic energy (energy of motion) must be dissipated as heat in the brakes. To accelerate the car again, the engine must supply additional energy, in generative braking, most of the energy stored in a flywheel, instead of being dissipated as heat in the brakes. This flywheel energy is then used to assist the engine in accelerating the car. Flywheel for energy storage systems must be capable of high speeds because the energy stored increase as the square of the rotational speed. Hence, there is a continuing search of improved materials for such applications.