Analysis of Tensioner Induced Coupling in Serpentine Belt Drive Systems

A primary concern in the design of serpentine belt drive systems is resonant strand vibrations induced from engine excitation. Two analysis approaches to investigate the system vibrational response have been reported in the literature. The first, denoted as the "decoupled analysis" approach, employs longitudinal belt stiffness and takes into account only pulley rotation and tensioner displacement as system degrees of freedom. Transverse belt vibration (normal to belt travel) on all belt strands is decoupled from the analysis. The second, denoted as the "coupled analysis" approach, combines transverse tensioner strand belt motion with pulley rotation and tensioner displacement. Transverse belt vibration on strands between fixed pulleys remains decoupled from the system. This paper provides apparently the first cross comparison of these two analysis techniques on three distinct serpentine belt system configurations reported in the literature. Two of the belt drive systems in this study involve numerical models only, and a third published work involves experimental results was used to confirm the accuracy of both analysis techniques. It was observed that the coupled and decoupled analyses did not agree well for low order modes, and only the coupled formulation was able to predict experimentally determined mode shapes. Both analyses indicated that natural frequenices associated with rotational modes were insensitive to crankshaft speed. Natural frequencies associated with transverse belt span modes as computed with the coupled analysis were less sensitive to changes in crankshaft speeds.