What Is Flywheel?- Definition, Parts, Types, and Function

Ever wondered how your car can maintain constant power and inertia?

In a manual transmission vehicle, energy is stored within the drivetrain along the transmission and suspension systems. The main source of this stored power is the flywheel that ensures constant rotational inertia from the engine is maintained to keep a car running.

A flywheel that is damaged or needs replacement can cause serious problems for the structural integrity of a car and its occupant’s safety. It is of the utmost importance that a driver picks up the warning signs for a potentially faulty flywheel and gets a replacement flywheel as soon as possible.

What is Flywheel?

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

The flywheel is part of an engine, not a part of a transmission. A flywheel is just a solid wheel mounted on the crankshaft coming out to some extent on the opposite side of the transmission. When an engine is running, a flywheel rotates at the same speed of engine and it stores kinetic energy in it. This energy automatically gets transferred to engine at a time when engine needs it.

What is a flywheel on a car? Technically explained, the flywheel (if manual) or flex plate (if automatic transmission) is defined as a disc that is bolted to the crankshaft at the rear of the engine. It serves many purposes:

There is a toothed ring on its outer edge that the starter turns to start the engine. Because of the large disc (relative to the crankshaft), this allows the starter motor to have more leverage against the engine.

It also serves to perform certain goals of engine operation. Though more massive flywheels require more energy to get spinning, once they are spinning they gain more momentum and help the engine run smoother and shift smoother at higher RPM.

Related Posts: What are automobile engines?

A flywheel’s construction

In a manual transmission, the flywheel is a thick metal disc. It’s typically made of cast iron, steel or, in some cases, aluminum.

It’s extremely rigid to prevent flexing or warpage during use. The edge of the flywheel has a row of gear teeth that engage with the engine’s starter motor.

The flywheel is firmly bolted to a flange on the transmission side of the crankshaft inside the bell housing.

On the side facing the manual transmission, the surface is machined flat for the clutch disc to grab onto.

What does the flywheel do?

But what does the flywheel do? It has a few different purposes:

  • The flywheel provides mass for rotational inertia to keep your car’s engine running. Otherwise, the engine will stall when you let your foot off the accelerator.
  • It balances the engine. A flywheel is specifically weighted to the car’s crankshaft to smooth out the rough feeling caused by a slight imbalance.
  • It allows for an electric starter. The starter motor engages the starter ring on the edge of the flywheel to begin engine rotation.
  • Most importantly for drivers, the flywheel connects the engine with the transmission via a clutch to transfer power to the wheels.

When your foot is on the clutch pedal, the clutch disc is disengaged from the flywheel. This is how a car can sit still at idle with the shifter in gear, or how a car can coast to a stop.

But when the pedal is released, the clutch disc will press firmly against the flywheel. When this happens, the transmission input shaft rotates at the same speed as the engine’s crankshaft.

Parts of Flywheel

The following are the parts of a flywheel:

Parts of 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 an 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.

How Does a Flywheel Work?

A flywheel is essentially a mechanical battery consisting of a mass rotating around an axis. It stores energy in the form of kinetic energy and works by accelerating a rotor to very high speeds and maintaining the energy in the system as rotational energy.

How does a flywheel work for storing energy? Well, you can compare it to the mechanism of a mechanical battery. Whereas the battery stores the energy in a chemical form, a flywheel preserves the power in the form of movement or kinetic energy to be precise.

A flywheel will be able to store more energy if it spins at a higher speed or has a higher moment of inertia, which means bulkier. However, it always works best when you spin it faster rather than increasing its mass.

For example, a wheel will produce twice as much energy as one that weighs half of it, given that both are spun at the same speed. On the other hand, spinning the lighter wheel twice as fast will quadruple the amount of stored energy.

For this reason, it’s always better to use lighter, high-speed wheels rather than the units having a massive weight. Also, compact flywheels make practical sense in racing cars because they need to be as light as possible to run at high speeds.

How does a flywheel work when you keep increasing the speed? It is not possible because there is a point when the wheel material won’t be able to handle the force and smash into fragments.

Function of Flywheel

A flywheel is a 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 heavier flywheels, while sports cars and some commercial vehicles make good use of 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.

Types of Flywheel

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 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.

Symptoms of a Bad Flywheel

Unfortunately, flywheels do not last forever. They gradually become worn as they are consistently used in the vehicle. If your flywheel becomes too worn out or damaged, there will be some noticeable symptoms that you won’t be able to ignore.

Do not let these symptoms carry on for too long or else it will impact the overall drivability of the vehicle. Here are some of the most common signs of a bad flywheel.

1. Gears Slipping

Slipping gears more commonly occurs when you increase your gears. For example, you may go to put your car from second gear into third gear. As you shift gears, your engine revs and you can tell that it did not shift gears. Your car likely has slipped back to the gear you tried to advance from, or in this case, slipped back to second gear.

Unfortunately, slipping gears is also a tell-tale sign of clutch trouble. As such, if you experience slipping gears, you need to look for other signs so you can determine if the clutch or flywheel is going bad.

Related: What is Gear?

2. Burning Smell

If there is a burning smell that consumes your passenger cabin, this could be attributed to many possible causes. A bad flywheel could be one of those causes because of all the heat generated from the friction in the clutch.

If you have used the clutch at times when you weren’t supposed to, this could cause problems with the flywheel.

3. Clutch Chatter

If your clutch pedal is experiencing lots of vibrations, then your flywheel is likely going bad. The vibrations will eventually get so bad that you will be able to feel them on the floor rather than just from the clutch pedal.

As you drive your vehicle, the flywheel could end up with excessive runout over time, which leaves the surface feeling warped as you engage the clutch.

If you’ve ever overheated your flywheel or driven too long with a clutch that was on its last legs, it is very likely that you have damaged the flywheel due to excessive heat or metal-on-metal wear. Clutches that are worn down to the rivets will damage the flywheel.

Related: What is Clutch?

A damaged flywheel may have a bluish color as the metal is heated far past its operating temperature. You’ll likely see some hairline cracks on the surface as well. There may even be smears of metal on the surface as the flywheel has heated and cooled.

Some flywheels contain springs, such as dual-mass flywheels. If your car is equipped with one of these, the flywheel’s springs may be causing these vibrations. Dual mass flywheels will likely need replacement, as they cannot be resurfaced like a standard flywheel.

4. Unable to Start, or Inconsistent Starts

If the teeth on the flywheel are damaged, the flywheel may have trouble engaging with the starter motor. This could make it difficult or impossible to start the vehicle.

If you are having issues starting your vehicle, you may want to take a look at your starter as well.

5. Engine Stalling

An aftermarket flywheel that is too light for the vehicle (or the driver) will make it much easier to stall the vehicle and could give you a rough idle.

On very light flywheels, you may even stall the vehicle simply by pushing the clutch in, just because the engine speed drops too fast for the ECU to add additional air and fuel to compensate.

6. Engine Vibrations with Clutch Engaged

If a flywheel is unbalanced, it may vibrate the whole powertrain even while the clutch is engaged.

If you recently replaced the clutch, flywheel, or pressure plate, make sure you torqued all bolts to spec and applied thread locker if it was called for in the factory service manual. A flywheel that comes loose or disintegrates while driving is incredibly dangerous, as there is a considerable amount of energy stored in the flywheel.

The flywheel is very heavy and has the potential to shake the vehicle considerably if everything isn’t balanced and lined up properly.

Flywheel Replacement Cost

On average, flywheel replacement cost is anywhere between $600 to $1,100. You can save yourself a lot of coins if you did the replacement by yourself but only attempt that if you’re an experienced mechanic.

The replacement cost of a flywheel can range considerably. There are some flywheels that cost under $50 while others cost as much as $400 or more. It all depends on what type of car you drive, how durable the flywheel is, and whether the part is an exact OEM replacement or aftermarket. In addition, clutch and/or release bearing replacement may also be necessary.

Then, of course, you have to consider the labor costs of doing the replacement job. Since most auto mechanics charge about $90 to $110 per hour, you could be looking at paying close to $500 just for labor.

The reason for this is that the flywheel is attached to the crankshaft in an engine and it is harder for the mechanics to take out and replace. This requires more time which means you’ll be paying more money.

In total, you could be looking at anywhere between $550 and $1,000 on average. If you’re an experienced mechanic who knows how to replace a flywheel or clutch or you have a friend who is, then it would be better to use this option rather than paying for the labor. It will save you a lot of money this way.

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 the 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