# What is Flywheel and How it Works

flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed. Energy is transferred to a flywheel by applying torque to it, thereby increasing its rotational speed, and hence its stored energy. Conversely, a flywheel releases stored energy by applying torque to a mechanical load, thereby decreasing its rotational speed.

Flywheel is a circular wheel (or Disc) made up of steel or cast iron (depends upon the application). It also acts as part of clutch mechanism and fluid drive unit. It has teeth on its outer edge which is meshed with the teeth of the electric cranking motor driven pinion and it used to crank (to rotate crankshaft) the engine during its starting.

Working of Flywheel

To understand that lets take an example of working of single cylinder four stroke engine. In four stroke engine we have four strokes i.e. suction, compression, power and exhaust stoke. Only in the power stroke we get power and in the rest of the strokes, the power is required to perform different process like suction, compression and exhaust process. So we need a device which can stores the power during power stroke and deliver that power to the remaining strokes when required. This could be done with the use of a flywheel. The flywheel stores the power during the expansion or power stroke and then imparts this power to the remaining strokes of the engine for its working.

The Flywheel is made of heavy steel or cast iron and it is attached to the rear end of the crankshaft. The weight of the flywheel depends upon the nature of the variation of the pressure, number of cylinder and design of engine.

The weight of the flywheel decreases with the increase in the number of cylinder. It means a two cylinder engine has lighter flywheel as compared with single cylinder engine.

Main Function of the Flywheel

1. It provides constant power output where there is a fluctuation in the power is observed.
2. It maintains the constant speed of the engine during all the strokes.
3. It stores the mechanical energy (rotational energy) of the engine and deliver it  when required.