FLYWHEEL : TYPES AND DESIGN

FLYWHEEL, TYPES OF FLYWHEEL AND DESIGN OF FLYWHEEL

A flywheel is a heavy rotating body that acts as a reservoir of energy. The energy is stored in the flywheel in the form of kinetic energy. The flywheel acts as an energy bank between the source of power and the driven machinery. Depending upon the source of power and type of driven machinery, there are two distinct applications of the flywheel.

History of flywheel:

A flywheel is classified among mechanical Energy Storage System that has been endured since thousands of years back. The flywheel works under the effect of maintaining its energy by its inertia. Potter's wheel is an example used as a rotatory object that undergoes the effect. More of it, such as hand mills, lathe, water wheel, and other manually operated rotary objects, performs the flywheel applications.

In IC engines, the power is generated at a variable rate. The flywheel absorbs the excess energy during the expansion stroke, when power developed in the cylinder exceeds the demand. This energy is delivered during suction, compression and exhaust strokes. The flywheel, therefore, enables the engine to supply the power at a practically uniform rate.

The functions of the flywheel are as follows:

1. To store and release energy when needed during the work cycle.
2. To reduce the power capacity of the electric motor or engine. 
3. To reduce the amplitude of speed fluctuations.

Flywheel Materials:

Traditionally, flywheels are made of cast iron. From design considerations, cast iron flywheels offer the following advantages:

1. Cast iron flywheels are the cheapest. 
2. Cast iron flywheel can be given any complex shape without involving machining operations.
3. Cast iron flywheel has excellent ability to damp vibrations.

However, cast iron has poor tensile strength compared to steel. The failure of cast iron flywheel is sudden and total. The machinability of cast iron flywheel is poor compared to steel flywheel. The mass density of materials used for the flywheel is given in Table.

ore recently, flywheels are made of high strength steels and composites in vehicle applications. Graphite-Fibre Reinforced Polymer (GFRP) is considered as an excellent choice for flywheels fitted on modern car engines. 

Material	Mass density (kg/m3 ) (ρ)
Grey cast iron
FG 150	7050
FG 200	7100
FG 220	7150
FG 260	7200
FG 300	7250
Stainless steel
Carbon steel	7800

Types of flywheel: 

1. Solid disc flywheel
2. Rimmed flywheel

1. Solid disc type flywheel:

The Solid disc flywheel is a type of flywheel. It is used in a single flywheel thresher is made of cast iron. The solid disc flywheel is equipped with a flywheel hub and disc. In the design calculation of a solid disk flywheel, various parameters are used as inputs. This includes the dimensions of the solid disk flywheel. Also, resulting functional values are calculated.

2. Rimmed type flywheel:

The rim-type flywheel will explode at a much lower rotary speed than a solid disc-type wheel of equal weight and diameter. For minimal weight and high energy-storage capacity, a flywheel can be formed of high-strength steel and produced as a tapered disk, which is thick in the centre.

Design of flywheel:

A flywheel is mechanical device specifically designed to efficiently store rotational energy(K.E.).

FLYWHEEL, heavy wheel attached to rotating shaft so as t smooth out delivery of power from a motor to a machine. Flywheel used in machines serves as a reservoir which stores energy during the period when the supply of energy is more than the requirement and releases it during the period when the requirement of energy is more than supply.

Parts of flywheel:

1. Arms
2. Shaft
3. Hub
4. Key

STRESSES IN FLYWHEEL ARMS

1. Tensile stresses are induced in the arms.
2. Bending stress due to the torque transmitted from the 
3. rim to the shaft or from the shaft to the rim.
4. Shrinkage stresses due to unequal rate of cooling of casting. These stresses are difficult to determine.

DESIGN OF RIM

Due to the centrifugal force acting on the rim, the arms will be subjected to direct tensile stress.

Tensile stress in the arms,

  centrifugal stress , 

Due to the torque transmitted from the rim to the shaft or from the shaft to the rim, the arms will be subjected to bending, because they are required to carry the full torque load.

T=Maximum torque transmitted

R=Mean radius of the rim

r=Radius of the hub

n=Number of arms

Z=section modulus for arm

We know that the load at the mean radius of the rim

F=T/R

hence, Load on each arm = T/R.n

and maximum bending moment which lies on the arm at the hub,

bending stress in arms,

Total tensile stress in the arms at the hub end,

If flywheel used as a belt pulley

 

where T1-T2 is net tension.

Total bending stress in the arms at the hub end ,

DESIGN OF ARM

Let  a1=Major axis and

        b1=Minor axis.

section modulus,

We know that maximum bending moment,

Therefore, Maximum bending stress,

DESIGN OF SHAFT AND KEY

 where, Tmax is maximum given torque.

 

where, d=outer diameter of hub

            d1= inner diameter of shaft.

DESIGN OF HUB

The hub is designed as a hollow shaft, for the maximum torque transmitted. We know that the maximum torque transmitted,

• The diameter of hub=Twice the diameter of shaft.
• Length= 2 to 2.5 times the shaft diameter.

It is generally taken equally to width of the rim.

Difference between flywheel and governance:

The major difference between Flywheel and Governor is explained as follows:

a)Flywheel

• The flywheel is a mechanism that provides equal energy to the engine at all times. 
• The flywheel is constantly in motion. to store during the power stroke and provide during the idle stroke Frictional losses do not occur during the process of transferring energy/supply of energy. 
• This gadget is not appropriate for every engine, such as when there is a minimal amount of output (Low Speed). This is often utilised in stationary engines, punching machines, and other similar machines. 
• The flywheel is a mechanism that provides equal energy to the engine at all times. The flywheel is always spinning, storing energy during the power stroke and supplying it during the idle stroke. 
• Frictional losses do not arise during the transmission of energy or supply of energy. 
• The flywheel is always spinning, storing energy during the power stroke and supplying it during the idle stroke. Frictional losses do not arise during the transmission of energy or supply of energy. This gadget is not appropriate for every engine, such as when there is a minimal amount of output (Low Speed).
• This is often utilised in stationary engines, punching machines, and other similar machines.

b) Governor:

• With the help of the fuel supply, the governor is utilised to control the engine's speed.
• This does not have to run continuously; it only needs to supply fuel as needed by the load. 
• This is a must in every engine.
• Frictional losses arise in this procedure due to the high spinning speed.
• This type of mechanism is commonly found in turbines, engines, and other similar machines.

Applications of flywheel:

1. Flywheel is used to maintain constant angular velocity of the crankshaft in reciprocating Engine.

2. Flywheel is used to provide continuous energy in systems where the energy source not continuous.

3. A flywheel is used to supply intermittent pulses of energy at transfer rate that exceed the ability of its energy source.

4. Flywheel is used in riveting machine to store energy from the motor.

5. Flywheel is used to orient satellite instrument without the use of thruster

rocket.

Reaction Wheel:

A reaction wheel is a spacecraft's version of a flywheel. It is mostly used to regulate the spacecraft's attitude without spending any fuel. Momentum wheels are another name for reaction wheels.

Reaction wheels are electrically propelled wheels that are positioned in three orthogonal axes of a spaceship (or at least three directions such as along x-axis, y-axis, and z-axis).

Reaction wheels are made out of a flywheel with the majority of the mass concentrated at the rim. The reaction wheel is designed in such a way that it assists in maintaining the right attitude of a satellite when it is required.

These wheels are in handy when a spacecraft needs to rotate in extremely small increments. To rotate a vehicle or spacecraft in a specific direction, the wheel must be spun in the opposite direction. The wheel must be slowed in order to rotate the vehicle backwards. Changes in the wheel or vehicle's speed are regulated electronically.

The strength of a reaction wheel's materials determines how much angular momentum it can retain. Reaction wheels make up a very small percentage of the vehicle's total mass (spacecraft). As a result, tiny angular changes are caused by controlled (temporary) adjustments. Over time, a reaction wheel may accumulate stored momentum that must be released.

Any form of failure in one or more reaction wheels can result in a loss of spacecraft's ability to maintain its position which may in turn cause a failure of a mission as a whole.

REFERENCES

[1]http://www.differencebetween.net/technology/difference-between-flywheel-and-governor/#:~:text=The%20main%20difference%20between%20the,run%20at%20its%20mean%20speed.

[2]https://en.wikipedia.org/wiki/Flywheel#:~:text=A%20flywheel%20is%20a%20mechanical,square%20of%20its%20rotational%20speed.&text=Common%20uses%20of%20a%20flywheel,output%20of%20an%20energy%20source.