What is a flywheel in a car and what is it for

Modern internal combustion engines (ICEs) are made up of many parts and assemblies, each of which plays a specific role. There is such a role for flywheels, which, although quite simple in design, are important components of power units for their purpose.

The flywheels are installed on the end parts of the crankshafts, near the main rear bearings. Many vehicle owners who are not very well versed in the nuances of engine design often have a question: what is a flywheel in a car and why is it needed at all? Let's try to answer this question.

Flywheel: what is it and what is it for

Schematic representation of the flywheel on the crankshaft: 1 - crankshaft; 2 - a flywheel with a toothed rim; 3 - connecting rod neck; 4 - root neck; 5 - counterweight

The flywheel is a disc-like device that attaches to the rear of the crankshaft.

The flywheel has a fairly significant mass and, accordingly, is capable, according to the laws of physics, to accumulate and release kinetic energy. It is due to this property that these units are used in modern internal combustion engines as structures that make it possible to smooth out the uneven rotation of the crankshaft. During the periods of the working stroke of the piston, the flywheels accumulate the energy of the torque, and when the pistons are in the so-called "dead points", they remove these parts from them, giving off energy.

It should be noted that the more cylinders the ICE is equipped with, the more uniform torque it has. Consequently, such internal combustion engines can use lighter flywheels than those with few cylinders.

Another important function of the flywheels of internal combustion engines is the transmission of torque to the crankshaft from the starter. On the outer circumference of this unit, a toothed steel rim is mounted, which is called a crown. It meshes with the shaft from the starter and which has a toothed wheel. When the driver turns on the ignition, the starter turns this shaft, and he, in turn, the flywheel, which drives the crankshaft. It is thanks to this that the engine is started.

In addition, flywheels play an important role in the transmission of modern cars, playing the role of driving clutch discs in them. Thus, it is thanks to them that the torque of the crankshaft of the internal combustion engine is transmitted to the gearbox, and from them is transmitted to the drive wheels.

Varieties of flywheels

What a flywheel looks like on an assembled engine

Modern internal combustion engines use three types of flywheels:

  • Single-mass (solid);
  • Dual-mass;
  • Lightweight.

Each of them has its own characteristics, advantages and disadvantages.

Single mass flywheels

This variety is the most common. The single-mass flywheel of an internal combustion engine has a solid structure and is a rather massive disk with a diameter of 300 to 400 millimeters. Most often, high quality cast iron is used for its manufacture.

On the outer side of a single-mass flywheel, a crown is installed around the entire circumference - a toothed ring made of steel. Its installation is carried out using the press-on technology, and therefore it is fixed very firmly. In order to fix a single-mass flywheel on the crankshaft (or rather, to a special flange installed on it), a hub is made on one side of this part. In this case, the other, opposite plane of the single-mass flywheel, plays the role of the driving clutch disc.

Thus, a single-speed flywheel is quite simple in design, inexpensive to manufacture, which is why it is widely used in modern internal combustion engines. It also has one rather serious drawback, which is that it does not damp torsional vibrations well enough. Dual-mass flywheels are much better at this task. They have been actively used in the design of internal combustion engines since the middle of the 80s of the last century.

Dual-mass flywheels

Example of internal design of a dual-mass flywheel

Structurally, they consist of two discs, which are interconnected by a special spring-damper system. It is designed to relieve the vehicle's transmission from constantly occurring torsional vibrations of the power unit and to make its functioning smooth. The use of a dual-mass flywheel instead of a single-mass flywheel makes it possible to abandon the use of a damping device in the drive clutch disc, thus increasing its reliability and durability.

In addition, the use of such flywheels allows:

  • Significantly reduce vibrations transmitted from the engine to the transmission;
  • Reduce its noise level;
  • Make gear shifting more convenient;
  • Protect the transmission against overloads.

According to some studies, the use of dual-mass flywheels even helps to reduce engine fuel consumption.

It must be recognized, however, that these units also have some disadvantages. The main one is that they are not as reliable as single-mass ones. The fact is that the spring-damper system included in their design experiences considerable loads and therefore wears out rather quickly. Largely for this reason, dual-mass flywheels are not yet widely used.

It should be noted that active development is currently underway to improve the design of these units. They are connected, first of all, with the fact that there is an increasing number of engines operating at low speeds, as well as engines with a sufficiently large power with a relatively modest working volume. Such internal combustion engines require a high degree of vibration damping from the flywheels, and designers are trying to solve this problem. Two-mass flywheels using centrifugal pendulums have already been designed and successfully tested. They create oscillations in antiphase to the main one and, thus, damp them.

Lightweight flywheels

These flywheels are used for tuning powertrains. They are characterized by the fact that their mass is redistributed from the center to the edges. This allows to reduce the weight of structures, as well as the moment of inertia. Cars with lightweight flywheels installed on them have improved acceleration dynamics.

See also :Boxer engine - what is it.

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