Car Talk

Understanding FlyWheel: Functionality and Applications

Avatar Adie Tinkle -

A flywheel is a mechanical battery that reserves rotational energy by resisting changes in rotational speed. It consists of a mass rotating around its axis that stores kinetic energy. It accelerates the rotor to a high speed while ensuring the energy in the system is maintained as rotational energy. Flywheel energy storage is a promising technology that can replace conventional lead acid batteries as energy storage systems. 

A flywheel uses abundant force to rotate on its axis. While rotating at high speed, the wheel keeps spinning unless stopped by an external force. During rotation, it preserves a significant amount of kinetic energy that it uses to power up the vehicle when starting or accelerating the engine. 

What is a Flywheel on a Car?

A flywheel or flex plate is a disc bolted to an engine’s crankshaft. It offers various purposes. For example, it provides friction surfaces for the clutch on a car with a manual transmission. The clutch pressure plate is bolted to the flywheel, and the clutch disk is sandwiched between them.

To start the engine, the starter turns a ring gear located on its outer side. The starting motor has more impact on the engine since the pulley is larger than the crankshaft.

Larger flywheels take more energy to spin, but once they do, they have greater momentum, which improves engine performance and smoothens faster speed shifting.

How Does a Flywheel Work?

You must be wondering how a flywheel works. Well, in simple words, you can think of it as a working mechanical battery. The difference is that a battery stores energy in a chemical form while a flywheel preserves power in the form of kinetic energy. 

The higher the spinning speed of the flywheel, the higher will be the moment of inertia, and the flywheel will store more energy. However, it works better if we spin it at a higher speed rather than increasing its mass. Therefore, it is preferable to use lightweight and high-speed wheels than those with massive weights. 

Compact flywheels can be the practical choice in racing cars as they need to be as lightweight as possible and run at high speeds simultaneously. 

So, does the efficiency keep increasing as you keep increasing the speed? It is not possible because, at one point, the wheel will not be able to handle more force and will break into fragments. 

What are the Functions of a Flywheel?

Flywheels are used in almost all types of automobiles, including trains, buses, and race cars. Previously, the vehicles used to have bully metal rims and large diameters with spokes. However, modern units are made with carbon fiber materials and composite, making them more compact. 

The functions served by them include:

Engine Start

The teeth cut into the flywheel’s outer rim support the engine’s start. When you turn the key in an engine starter, a tiny gear known as a Bendix gear slides into the flywheel.

The engine flywheel is rotated by the Bendix gearbox and starter, which also turns the crankshaft and initiates the compression cycle required to start the engine. The Bendix gear retracts as the engine begins, enabling the flywheel to spin freely.

Engine Speed Smoothing 

After being started, the crankshaft converts the up-and-down movement of the piston into rotary motion. 

The power is generated twice in a four-cylinder engine, while in an eight-cylinder engine, it is generated four times during one engine revolution. The mass of the flywheel applies inertia to keep the crankshaft turning between each of these piston firings. This way, the rotational speed of the crankshaft stays consistent, and the engine runs smoothly. 

Stress Reduction 

The flywheel limits wear and tear on other drivetrain components by stabilizing the engine’s movement and balancing the speed. Although the engine and transmission shaft are parallel, the connection between the axle and the gearbox is not parallel to the motor and transmission shafts.

A universal joint, included in the driving shaft, spins at a constant angle. These joints see less wear thanks to a flywheel.

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