The vibration of an automotive serpentine belt drive system greatly af
fects the perceived quality and the reliability of the system. Accesso
ry drives with unfavorable vibration characteristics transmit excessiv
e noise and vibration to other vehicle structures, to the vehicle occu
pants, and may also promote the fatigue and failure of system componen
ts. Moreover, these characteristics are a consequence of decisions mad
e early on in the design and arrangement of the accessory drive system
. The present paper focuses on fundamental modeling issues that are ce
ntral to predicting accessory drive vibration. To this end, a prototyp
ical drive is evaluated, which is composed of a driven pulley, a drivi
ng pulley, and a dynamic tensioner. The coupled equations of free resp
onse governing the discrete and continuous elements are presented here
in. A closed-form(1) solution method is used to evaluate the natural f
requencies and modeshapes. Attention focuses on a key linear mechanism
that couples tensioner arm rotation and transverse vibration of the a
djacent belt spans. Modal tests on an experimental drive confirm the t
heoretical predictions.