What Is A Flywheel On A Car? Here’s What To Know
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The first time you see a flywheel you might wonder what the big deal is. After all, to an inexperienced eye, it just looks like a thick wheel with some gear teeth around the edge and bolt holes in the middle.
The truth is that the flywheel in your car is doing a lot of heavy lifting in terms of transferring energy, keeping your vehicle from vibrating too much, and letting the starter do its job.
Sound like a lot of work for one little part? You’re not wrong!
Flywheels are a big part of why manual vehicles work as well as they do, and they’re incredibly important for keeping your vehicle in top working condition.
Let’s talk about what flywheels do, how they do it, and the differences between flywheels and the automatic transmission alternative, a flexplate.
What Is A Flywheel?
On the most basic level, a flywheel is designed to create continuous motion by transferring the movement of the crankshaft into smoother rotation.
To understand how a flywheel works you need to understand 4-stroke engines and how they turn the crankshaft.
A 4-stroke engine has 4 strokes in each cycle of the piston. The strokes are intake, compression, power, and exhaust. The power stroke is the only one that turns the crankshaft, the other three all deal with fuel and exhaust after ignition.
Functionally, both 2-stroke engines and 6-stroke engines work on the same principle, just with a different number of strokes in each cycle.
During the power stroke, the crankshaft will rotate 180 degrees, but it’s still during the other three strokes in the cycle.
In practice, that means that the crankshaft isn’t always in motion and that if we were just relying on the crankshaft we would get a lot of vibration and a jerkier kind of acceleration. This is where the flywheel comes in.
Since the flywheel has a wider outer edge than the crankshaft, it transfers the energy more smoothly and also helps keep the momentum going longer so that there aren’t jerks and stops between movements.
Flywheels also have a few other important purposes, like helping to balance out the engine, and giving your starter something to grip onto so that it can get the engine going.
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What Are Flywheels Made Of?
You might already have realized that flywheels have to be incredibly tough for the job they’re doing. Not only is a flywheel subjected to a lot of torque and internal forces, but it’s also going to have a lot of heat buildup, some from the engine, and some from its own friction as it connects the engine to the transmission.
In general, flywheels are going to be made from a heavy and durable material, like cast iron or steel. Sometimes, though, manufacturers will use hardened aluminum, depending on the size of the vehicle, engine, and flywheel, and what weight they need to balance the engine.
Regardless of the material, flywheels are designed to be incredibly durable and long-lasting. But, just like any part of your vehicle, they can get damaged, and it’s important to replace them as soon as possible if they aren’t working correctly.
Remember, your flywheel works with your engine, transmission, and electric starter. If it’s not working properly, all of those parts, and basically everything else involved in acceleration can be damaged.
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Why Do You Need A Flywheel In Your Vehicle?
There are a lot of reasons flywheels are important in your vehicle, but they aren’t always apparent from the description of how they function.
Let’s take a moment to talk about all the ways having a flywheel changes and improves your vehicle’s function.
One of the biggest impacts of flywheels is that they make electric starters possible. The starter grabs the edge of the flywheel and rotates it to start engine rotation. Without some rotation, to begin with, your engine wouldn’t be able to turn over. The flywheel makes this process both possible without a manual crank, and much more efficient by transferring rotation from a larger surface to a smaller one, the outer edge of the flywheel to the crankshaft.
Your flywheel is also a carefully calculated counterbalance to the engine. It’s designed to keep the crankshaft rotating evenly, reducing vibration, unwanted torque, and any wobble in the shaft.
That might not sound like much, but it has a huge impact on reducing engine vibration.
Your flywheel also provides the rotational inertia needed to keep your engine running when you take your foot off the accelerator. Otherwise, the engine would stall and wouldn’t have enough power to keep rotating. The flywheel’s mass prevents that kind of stalling and keeps your engine going even when you aren’t actively accelerating.
Lastly, and most importantly, a manual flywheel connects the engine to the transmission and transfers power to the wheels via the clutch. You wouldn’t be able to shift properly without a flywheel, and wouldn’t be able to control where power is going.
This works because the clutch is engaged on the flywheel until your foot is on the clutch pedal. When you depress the clutch pedal the clutch disc is disengaged, when the clutch pedal isn’t in use, the transmission input shaft rotates with the engine’s crankshaft.
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What Is The Difference Between A Flywheel And A Flexplate
You might have noticed in the last section we were talking about how the flywheel functions in a manual vehicle. Of course, that might have you wondering how a flywheel works in an automatic vehicle.
The truth is that flywheels are a manual-specific part, automatic vehicles use a slightly different part to accomplish the same things.
Automatic vehicles use a part called a flexplate. The flexplate has the same basic purpose as the flywheel, so there are a lot of similarities in design. However, the flexplate is thinner than a traditional flywheel and may have more holes through the disc, making it a much lighter part.
Part of the reason for the lighter design is that a flexplate doesn’t have to deal with the additional friction and grinding of a clutch.
The holes and shapes cut through a flexplate are also vehicle specific. They’re designed to make sure the flexplate is the exact weight needed for the vehicle while also preserving torque conversion and rotational momentum.
Functionally, these two parts are almost the same. Both work with the starter, engine, and crankshaft, but flywheels have more direct interaction with the transmission compared with an automatic.
It’s also important to know that it’s critical to get both parts fixed as soon as you notice a problem. While possible to drive with a damaged flexplate or flywheel, there are a lot of risks, including damaging other components, losing control of the vehicle, and worse.
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