Compared to normal alternators used in conventional FEAD systems the alternator-starters used in BAS systems have higher power requirements and consequently relatively high inertia. BAS systems may experience resonant vibration which causes high loads, noise, discomfort and in some cases requires electrical re-calibration which may offset some of the potential system benefit.
Litens BAS isolator pulley (pending patent application) decouples the alternator rotor inertia from the accessory drive belt by a unique steel torsion spring. Engineered control of the system resonant frequency is achieved by tuning the spring stiffness to the alternator inertia mass. In the case where alternator torsional resonance is the first vibration mode of the system, the BAS isolator pulley completely eliminates the resonance and dramatically reduces the dynamic forces on the belt. Belt induced high speed fluctuations to the alternator are absorbed by the torsion spring and the alternator rotor (inertia mass) is relatively unaffected.
During driving mode the torque is transmitted through the spring. In starting mode the torque is transmitted directly through the pulley by means of solid stops. Boost and Regen modes can be supported.