FLYWHEEL AND ITS TYPES

 

FLYWHEEL AND ITS TYPES

 

What is a flywheel?

A flywheel as a weighty wheel requires enough forces to rotate on its axis. It resists changes in rotational speed by their moment of inertia. Changing the stored energy on the flywheel, its rotational speed must be increased or decreased. That is, it keeps spinning until lots of force is applied.

A great amount of kinetic energy is preserved when the flywheel rotates. This energy is later used to power up the vehicle when starting the engine or speeding.

 

Construction of a flywheel

Due to the toughness requirement of a flywheel, it is typically made of steel that rotates on conventional bearings. High energy density flywheels are made of carbon fibre composites and use magnetic bearings. Such flywheel revolves at speed up to 60,000 RPM (1 kHz).

 

Functions of Flywheel

Flywheels can be found in almost all types of automobiles as they serve a variety of purposes will be discussed here. Below are the functions of the flywheel in an automobile engine:

Engine Balancing: because the pistons are offset from the centre of the crankshaft vibration and wobbles occur. This is also because of each piston fires at a different angle.

The function of a flywheel in this situation is to suppress the side-to-side motion. This is achieved because of the heavyweight of the flywheel. Flywheels reduce the vibration of the engine as a whole as the engine is stabilized and balance on the mounts.

Engine Start: the flywheel plays another role while starting the engine. The gear teeth on the flywheel are attached to a starter motor. This starter motor is controlled with the car key so when the car is started the starter motor turns the flywheel.

Immediately the engine spins, the combustion effect continues turning the engine. The Bendix gear in the started motor withdraws in order for the flywheel to freely spin.

Drivetrain stress reduction: is another function of a flywheel, achieved by stabilizing the engine’s movement. It also smooths out the engine’s speed and reduce wear and tear on the drivetrain components.

Flywheel also limits the wear between the transmission shaft and the driveshaft. These two are attached with a universal joint.

Engine speed soothing: The crankshaft converts the piston movement into rotary motion which is jerky as the power is generated. the rotational speed of the crankshaft is constant and the engine runs smoothly. This is because the mass of the flywheel applies inertia which kept the engine crankshaft spinning between each piston firings.

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

Heavier flywheels allow the engine to work under loads which may cause the engine to bog down. Big truck or trailer is good with the heavier flywheels while sports car and some commercial cars make good use of the lighter flywheels.

 

Working Principle

The working principle of a flywheel is quite easy and interesting as it stores energy for the vehicle’s usage. Just the way mechanical battery stores energy in a chemical form, flywheels save the power in the form of kinetic energy.

More energy is produced is the flywheel spins at a higher speed. that’s a higher moment of inertia means bulkier. It is better to spin faster than to increase its mass. This is because lighter flywheels produce twice the energy than flywheels that weighs more or double. That’s, the lighter the flywheel the more the energy stored.

It is advisable to use lighter, highspeed wheels rather than the ones with massive weight. But for a heavier vehicle like trailers, truck, van etc. heavier ones will be suitable. This is because they carry extra load and not important to run at higher speeds.

So, knowing how a flywheel work is that the higher the speed the higher the energy stored. However, if the speed kept increasing, the wheel material might not be able to handle the force. This may lead to breaking up.

 

Types of flywheel depending on velocity:-

 

1.     High-Velocity Flywheel

The angular velocity of these type of Flywheels comes between 30000 rpm to 60000 rpm which may even be adjusted up to 1,00,000 rpm. They contain magnetic levitation bearings and need less maintenance. They are lighter in weight if compared size/capacity wise to low-velocity flywheels. They are costly in comparison to Low-velocity Flywheels.

2.     Low-Velocity Flywheel

The angular velocity of these type of Flywheels comes up to 10000 rpm. They are bulky and heavy if compared to high-velocity Flywheels. They need periodic maintenance and do not use magnetic levitation bearings. Their installation needs special concrete construction to support its weight. They are cheaper in comparison to high-velocity Flywheels.

 

Types of flywheel depending on design:-

 

1.      Rimmed

A rimmed flywheel has a rim, a hub, and spokes. Calculation of the flywheel's moment of inertia can be more easily analyzed by applying various simplifications. For example:

• Assume the spokes, shaft and hub have zero moments of inertia, and the flywheel's moment of inertia is from the rim alone.
• The lumped moments of inertia of spokes, hub and shaft may be estimated as a percentage of the flywheel's moment of inertia, with the majority from the rim, so that 

I_rim =KI_flywheel

For example, if the moments of inertia of hub, spokes and the shaft is deemed negligible, and the rim's thickness is very small compared to its mean radius the radius of rotation of the rim is equal to its mean radius and thus: I_rim=M_rimR²

2.     Shaftless

A shaftless flywheel eliminates the annulus holes, shaft or hub. It has a higher energy density than conventional design but requires a specialized magnetic bearing and control system.^[2

The specific energy of a flywheel is determined by

·        E/M=K(σ / ρ)

In which K is the shape factor, σ the material's tensile strength and ρ  the density. A typical flywheel has a shape factor of 0.3. Better designs, such as the shaftless flywheel, have a shape factor close to 0.6, the theoretical limit is about 1

3.     Super flywheel

The first super flywheel was patented in 1964 by the Soviet-Russian scientist Nurbei Guilia.

A super flywheel consists of a solid core (hub) and multiple thin layers of high-strength flexible materials, such as special steels, carbon fibre composites, glass fibre, or graphene, wound around it. Compared to conventional flywheels, super flywheels can store more energy and are safer to operate

In case of failure, the super flywheel does not explode or burst into large shards, like a regular flywheel, but instead splits into layers. The separated layers then slow a super flywheel down by sliding against the inner walls of the enclosure, thus preventing any further destruction.

Although the exact value of energy density of a super flywheel would depend on the material used, it could theoretically be as high as 1200 Wh (4.4 MJ) per kg of mass for graphene superflywheels.

 

Types of flywheel depending on mass:-

 

1.      Dual Mass Flywheel

The demands of modern engines have put a lot of strain on conventional flywheels. High torque, fast spinning motors have proven to be much less refined in terms of vibrations they produce. Managing these vibrations has reached the practical limits of simple flywheels. Adding more mass could eventually solve the problem, but it would only cause a different one. The more mass you add at the end of the crankshaft, the more energy you’ll have to expend to spin that mass up to speed.

Since that’s not feasible, automotive engineers have come up with the dual-mass flywheel. Just like its name implies, there are two masses inside one of these. These two separate pieces of the flywheel are connected by a pair of springs. Each spring usually features progressive tension, making it softer at the beginning of the compression and harder as it reaches maximum travel.

The idea behind dual-mass flywheels is to dampen the excess vibrations from the engine using this spring setup. As it turns out, this system works reasonably well.

 

The Downsides to Dual Mass Flywheels

Although highly efficient, DMFs aren’t without flaws. The increase in complexity means that you’re looking at compromised durability compared to an average solid flywheel. On top of that, when a DMF decides to go, it’s gone. There’s no refurbishing it as it’s effectively impossible to machine its surface with any measure of precision.

2.     Single Mass Flywheel

Single mass flywheels are designed to replace DMFs by meeting the same or similar dimensions without internal complexity. Instead of having two masses moving independently, you now have a solid metal slab connecting your clutch with your crank. Installing a conversion kit isn’t necessarily hard either, which is another plus. However, it’s essential to understand the pros and cons of such a decision before you commit.

Pros:

• Price – It’s no secret that single mass flywheels are cheaper than their dual-mass counterparts. The sheer fact that there are no complex springs inside make them easier to manufacture and hence less expensive to sell.
• Increased Durability – Durability is always an important aspect when you’re discussing anything drivetrain-related. Single mass units are generally much more durable than DMFs due to their simplicity. If they eventually fail, there’s no risk of them falling apart, which can’t be said for the dual mass design.
• Can be Machined – Another significant benefit of a single mass design is the ability to machine it when servicing the clutch. DMFs can’t be machined due to the way they’ve been engineered.

Cons:

• Vibrations and Noise – Single mass flywheels fail at everything a DMF was designed to do. No matter which conversion kit you get, you’ll experience a considerable increase in vibrations and noise during your daily commute. So much so that you might find going to work a gruelling experience.
• Potential Damage to Transmission and Engine – DMFs aren’t there only to improve your quality of life. A part of their mission is to protect the transmission and the engine from excessive vibrations. Once you go to a single mass unit, you’ll lose all of that protection, leaving your transmission and other parts of the drivetrain exposed to higher stresses.

BY:

Students of Vishwakarma Institute of Technology

Archit Khewle

Shubhada Khoraskar

Shivani Kinnake

Vedant Kodgirwar

Giriraj Kokare