1 ABSTRACTBelt drives have long been utilized in engine applications to power accessories such as alternators, pumps, compressors and fans. The first belt drives consisted of one or more V-belts powering fixed-centered pulleys and were pre-tensioned by statically adjusting the pulley center separation distances. In recent years, such drives have been replaced by a single, flat, ‘serpentine belt’ tensioned by an ‘automatic tensioner.’ The automatic tensioner consists of a spring-loaded, dry friction damped, tensioner arm that contacts the belt through an idler pulley. The tensioner's major function is to maintain constant belt tension in the presence of changing engine speeds and accessory loads. The engine crankshaft supplies both the requisite power to drive the accessories as well as the (unwanted) dynamic excitation that can adversely affect the accessories and the noise and vibration performance of the belt.The objective of this study is to model the rotational response of each accessory element to harmonic excitation from the crankshaft. This system model includes a nonlinear component model of the tensioner that captures the effect of tensioner arm dry friction. A numerical scheme is created to subsequently integrate the equations of motion and solve for the response of each pulley and the tensioner arm. Computed results illustrate tensioner stick/slip motions, sub- and super-harmonic responses, and secondary resonances; phenomena that cannot be captured in previous linear models of accessory drive dynamics.