Flywheel: Definition, parts, types, and Function

What is Flywheel?

A flywheel is a mechanical device that uses conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its speed of rotation.

In particular, if we assume that the moment of inertia of the flywheel is constant (i.e. a flywheel with a fixed mass and the second moment of area rotates around a fixed axis), then the (rotational) energy stored is directly related to the square of its rotational speed.

Since a flywheel is used to store mechanical energy for later use, it makes sense to think of it as an analog of the kinetic energy of an electrical inductor. This common principle of energy storage is described in a suitable abstraction in the generalized concept of an accumulator.

As with other types of accumulators, a flywheel inherently smoothes out sufficiently small deviations in a system’s power output, effectively playing the role of a low pass filter on the mechanical velocity (angular or otherwise) of the system.

More precisely, when the power consumption drops, the stored energy of a flywheel will give an increase in the power output and, conversely, absorb any excess power consumption (power generated by the system) in the form of rotational energy.

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Common uses of a flywheel are:

  • Smoothing the power output of an energy source. Flywheels are used in reciprocating engines, for example, because the active torque of the individual pistons is intermittent.
  • Energy storage systems
  • Delivery of energy at rates that are beyond the capabilities of an energy source. It does this by collecting energy in a flywheel over time and then rapidly releasing it at rates that are beyond the capabilities of the energy source.
  • Control the alignment of a mechanical system, gyroscope and reaction wheel

Flywheels are typically made of steel and rotate on conventional bearings; these are usually limited to a maximum speed of a few thousand rpm. High energy density flywheels can be made from carbon fiber composites and use magnetic bearings, which allows them to rotate at speeds of up to 60,000 rpm (1 kHz).

Parts of Flywheel

Following are the parts of a flywheel:

  • Flywheel Housing: The flywheel housing is solid and sits outside the flywheel. The flywheel is the part of the engine that turns and supplies power to the alternator.
  • Springs: The flywheel consists of two-phase springs bent in parallel. The outer arc is adjusted to raise the spring when the engine is running. The soft outer bow spring is only used to improve the unsafe resonance frequency range.
  • Planet Wheel: A planet wheel consists of many planet gears that are attached to a flywheel holder. When the flywheel mount is screw actuated and rotates, engagement with the outer ring gear creates a compound motion made up of each planet gear revolution and rotation.
  • Axial and radial plain bearings: While the axially acting bearing only serves to balance the weight, the imbalances or parasitic radial forces introduced by the motor or generator unit must be compensated by radial bearings.
  • Ring gear: A ring gear is attached to the outside diameter of the flywheel. The fixation on the flywheel is usually done with the help of a interference fit, which is created by heating the ring gear. So the thermal expansion allows it to be placed around the flywheel.
  • Support Disc: As the name suggests, the support disc is placed in the flywheel to support the two-phase bent springs and other components of the flywheel.
  • Flywheel sliding shoe: sliding shoes preferably have a convex, radial outer area which rests against the inner wall of the flywheel. In this area, they are preferably made to be slip-promoting and wear-resistant.
  • Flywheel Cover: The flywheel cover is usually made of chrome. This chrome-plated flywheel cover prevents dust from getting into the internal functions of the flywheel, causing it to run poorly.

Function of Flywheel

Flywheel, heavy wheel attached to a rotating shaft so as to smooth out the delivery of power from a motor to a machine. The inertia of the flywheel opposes and moderates fluctuations in the speed of the engine and stores the excess energy for intermittent use.

Flywheels are found in almost all types of automobiles because they serve a variety of purposes, which are discussed here. The following are the functions of the flywheel in a car engine:

Balancing the engine: because the pistons are offset from the center of the crankshaft oscillation and wobble occurs. This is also because each piston fires at a different angle.

The function of a flywheel in this situation is to suppress the sideways movement. This is achieved by the heavyweight of the flywheel. Flywheels reduce the vibration of the engine as a whole as the engine is stabilized and balanced on the bearings.

Starting the engine: The flywheel plays an additional role in starting the engine. The teeth of the flywheel are attached to a starter motor. This starter is controlled with the car key so that when the vehicle is started, the starter turns the flywheel.

As soon as the engine turns, the combustion effect keeps turning the engine. The Bendix gearbox in the started motor will retract to allow the flywheel to rotate freely.

Reducing the load on the drive train: is another function of a flywheel, which is achieved by stabilizing the movement of the engine. It also smoothes the engine speed and reduces wear on the drive components.

The flywheel also limits wear between the transmission shaft and the drive shaft. These two are attached with a universal joint.

Speed-reducing: The crankshaft converts the piston movement into a jerky rotary movement when the force is generated. the speed of the crankshaft is constant and the engine runs smoothly. This is because the mass of the flywheel creates inertia that kept the engine crankshaft rotating between each piston firing.

Weight manipulation: The weight of a flywheel determines the performance of an engine. The weight depends on the performance of the vehicles.

Heavier flywheels allow the engine to work under loads, which can cause the engine to stall. Large trucks or trailers work well with the heavier flywheels, while sports cars and some commercial vehicles make good use of the lighter flywheels.

Types of Flywheel

Following are the types of flywheels used in vehicles:

  • Solid disc flywheel
  • Rimmed flywheel
  • High-velocity flywheel
  • Low-velocity flywheel

1. Solid Disc Flywheel

The solid disc flywheel is a type of flywheel. It is used in a single flywheel threshing machine that is made of cast iron. The full disc flywheel is equipped with a flywheel hub and disc.

When calculating the design of a full-disc flywheel, various parameters are used as inputs. This includes the dimensions of the full-disc flywheel. The resulting function values are also calculated.

2. Rimmed Flywheel

The rim-type flywheel explodes at a much slower speed than a full disc wheel of the same weight and diameter. For minimal weight and high energy storage capacity, a flywheel can be formed from high-strength steel and manufactured as a centrally thick conical disk.

3. High-Velocity Flywheel

In these types of flywheels, the high-speed flywheel has a speed between 30,000 rpm to 80,000 rpm. This can also be set up to 100,000 rpm.

They have magnetic levitation bearings and are low-maintenance. Compared to a slow-running flywheel, these are light depending on size/capacity. They are more expensive than a low-velocity flywheel.

4. Low-Velocity Flywheel

In these types of flywheels, the low-velocity flywheel has a speed of 10,000 rpm. They are heavier and bulkier than the high-velocity flywheels.

They require maintenance from time to time and do not use magnetic levitation bearings. Their installation requires a special concrete structure to support their weight. They are cheaper than high-speed flywheels.

Material selection

Flywheels are made from many different materials; the application determines the choice of material. Small lead flywheels can be found in children’s toys. Cast iron flywheels are used in old steam engines.

Flywheels in car engines are made of cast or nodular cast iron, steel or aluminum. High-strength steel or composite flywheels have been proposed for use in vehicle energy storage and braking systems.

The efficiency of a flywheel is determined by the maximum amount of energy it can store per unit of weight. As the speed of rotation or angular speed of the flywheel is increased, the stored energy increases; however, stress is also mounting.

If the hoop stress exceeds the tensile strength of the material, the flywheel breaks apart. Thus, tensile strength limits the amount of energy a flywheel can store.

In this context, the use of lead for a flywheel in a children’s toy is not efficient; however, the flywheel velocity never approaches its burst velocity since the limit in this case is the child’s pulling force.

In other applications, such as an automobile, the flywheel operates at a certain angular velocity and is limited by the space it must fit, so the goal is to maximize the stored energy per unit volume. The choice of material, therefore, depends on the application.

Applications of Flywheels

  • Use In wind turbines
  • Along with motor driven generator to store energy
  • In Automobile Engines
  • In Electric Cars To Boost Speed (In Experimental Stage)
  • In Advanced Locomotive Propulsion Systems
  • In Advanced Technology Transit Buses
  • In Satellites To Control Direction
  • In Big Electricity Grids For Protection Against Interruptions

Advantages of flywheel

  • Less overall cost
  • High energy storage capacity
  • High power output
  • They are safe, reliable, energy efficient, durable
  • It is independent of working temperatures
  • Low and inexpensive maintenance
  • High energy density           

Limitations of flywheel

  • They can take a lot of space
  • They are expensive to manufacture
  • Building material is always a limitation for it