Flywheel Trivia Questions & FAQ

A flywheel is a heavy body rotating about its axis. It acts as a reservoir of energy which is storedin the form of kinetic energy. The extra energy is stored during the idle stroke of the drivenmachinery and released during the working stroke. Thus flywheel controls the fluctuations of speed during each cycle of the driven machinery.

The primary function of a flywheel is to absorb energy when demand of energy is less than the supply. The other function is to give out energy when demand of energy is more than the supply.

Stresses are set up in the flywheel rims are:
Tensile stress due to the centrifugal force.
Tensile bending stress due to restraint of the arms.
Shrinkage stresses due to the unequal rate of cooling of casting.

Solid disc type and Rimmed type with either arms or solid web. Solid disc type flywheel is rarely used because they have less capacity of storing energy. Rimmed type flywheels with arms are preferred because they can store more energy. Small rimmed type flywheels are manufactured with solid web or holes drilled in the web.

Use of flywheel in punching machine is due to the following reasons:
It decreases the variation of speed during each cycle of punching machine.
It decreases the fluctuation of speed due to difference in output and input.

Flywheels can be used to store energy and used to produce very high electric power pulses for experiments, where drawing the power from the public electric network would produce unacceptable spikes. A small motor can accelerate the flywheel between the pulses.
The phenomenon of precession has to be considered when using flywheels in moving vehicles. However in one modern application, a momentum wheel is a type of flywheel useful in satellite pointing operations, in which the flywheels are used to point the satellite's instruments in the correct directions without the use of thrusters rockets.
Flywheels are used in punching machines and riveting machines. For internal combustion engine applications, the flywheel is a heavy wheel mounted on the crankshaft. The main function of a flywheel is to maintain a near constant angular velocity of the crankshaft.

MOI stands for moment of inertia. It is a quantity expressing body?s tendency to resists angular acceleration.

The expression for the MOI of Flywheel is: mgh = 1/2 mv² + 1/2 I?² + n₁E

In a flywheel, most of the mass is concentrated at its rim. So it has a large moment of inertia. Any change of angular momentum imparted to the wheel by the piston results in a lesser change of angular velocity(L=I? or ?=L/I ). Moreover, a flywheel stores a large amount of rotational energy(1/2 I?²). This helps the wheel c fly off the dead point.

This bending moment lies in the plane of rotation of the flywheel. The arm axis also lies in the plane of rotation. Thus the axis should be as large as possible. In a circular section it is equal to the radius. But in case of an elliptical section, the arm major axis can be as large as twice the minor axis. Flywheel arm with elliptical section having major axis twice the minor axis can resist twice the bending moment. It is not obtainable with any other shape of the arm cross section. Thus only elliptical section for the flywheel arm is selected.

It is based on the type of stresses produced. Due to centrifugal force arm comes in tension. There is a tensile stress due bending of arm which is due to torque. There is a reversal of stress due to reverse motion of the flywheel which causes fatigue. Thus the main considerations in the selection of the material are
(i) High tensile strength
(ii) High fatigue strength

The difference between maximum and minimum speed during a cycle is called the fluctuation of speed. Recall the speed of the engine is not the same during suction, compression, power and exhaust strokes. This fluctuation of speed can be reduced by having a large mass moment of inertia ?I? of the flywheel.

It is the ratio of maximum speed to mean speed.
C_s = (N_max ?N_min)/N_mean
Where N is RPM