Dynamic analysis of a serpentine belt drive with a decoupler/isolator

Belt drives employing a single, flat serpentine belt tensioned by a passive tensioner are found in automotive engine Front End Accessory Drive (FEAD) where the crankshaft supplies power to accessories like alternators, air-conditioning compressors, pumps, etc.. When the FEAD undergoes forced vibration due to crankshaft excitation, dynamic tension fluctuations can cause the belt to slip on the accessory pulleys. The probability of belt slip increases with the peak drop in belt tension over the pulley during steady state operation. In this paper, one possible solution is analyzed, using a decoupler to isolate/separate the accessory inertia (e.g. alternator) from the FEAD system. This is achieved by placing between the pulley and the accessory a combination of a one-way rigid clutch and an isolator spring. In this study, the rotational response of a typical FEAD is extended to include the clutch and isolator. An analytical solution is then obtained by considering it as a piecewise-linearized system moving about an equilibrium angular displacements. The performance of the ordinary FEAD with regard to tension fluctuation is then compared to that of the system equipped with a decoupler/isolator. The results obtained indicate that within the practical working range of engine speeds, use of either an isolator or a decoupler-isolator could significantly lower the dynamic tension drop across the accessory pulley.