The small dual-mass flywheel in the auxiliary drive

The PYD decouples the belt drive from the rotational irregularities of the internal combustion engine, with a specifically designed arc spring isolating the belt pulley from the crankshaft. The PYD is mounted directly on the crankshaft. It usually also contains a torsional vibration damper, which is needed to limit the natural vibrations of the crankshaft in the upper speed range to a level permissible for durability and acoustic comfort.

The crankshaft pulley is decoupled from the vibrations of the crankshaft. Arc springs, such as those in a dual mass flywheel, are used for this, placed in a steel channel. From the crankshaft, the torque is transferred via a flange to the arc springs, which are supported on stops on the belt pulley. The torsion characteristics of the belt pulley decoupler can be flexibly influenced by the selection and combination of the springs used.
In comparison to the system without a belt pulley decoupler, there is an additional reduction of the dynamics in the belt drive throughout the entire operating range. In comparison with decouplers with elastomer springs, which use a rubber layer for resiliency, the mechanical arc springs have a significantly larger spring capacity and thus allow for the transmission of higher torques and power outputs. Thus, the increased power requirements for mild hybrid applications with belt start-stop can be covered. The characteristic curve can be flexibly adjusted by using multiple spring stages. This helps avoid resonances during engine start and driving operation.