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Torsional vibrations:
The crankshaft is subjected to two types of loads: bending and torsion. The bending forces occur when a connecting rod is pushed downward by a power stroke. The torsional forces occur because one part of the crankshaft wants to rotate while another part does not (twisting). When these twisting forces are removed, the crankshaft springs back to its original state. In this way, all pistons exert force on the crankshaft. A torsional vibration is not only dangerous at certain high rotational frequencies, but the vibration can also be amplified by one combustion force being stronger than another (for example with a defective ignition coil).
Vibration damper:
The vibration damper attached to the crankshaft is used to damp torsional vibrations as much as possible. This torsional vibration damper is also the multi-rib belt pulley over which the multi-rib belt runs (see image below). The vibration damper consists of two metal parts with a rubber ring in between. One metal part is attached to the crankshaft and the other part acts as a flywheel. Due to the elasticity of the rubber in between, a certain degree of movement is possible. This has a braking effect on the vibration, which therefore becomes damped. The vibration damper is not able to eliminate all vibrations completely, but it can reduce them.
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