| Serpentine belt drive systems utilizing a spring-loaded tensioner provide an efficient, low-cost way to power engine accessories, but are subject to adverse dynamic response. Two main responses that may impair performance are transverse and rotational vibration. In transverse vibration, a belt span vibrates transversely to its axis. In rotational vibration, the driven accessories oscillate about their spin axes, the belt spans acting as axial springs.;A theoretical model is derived which includes linear and nonlinear dynamic coupling between these two types of vibration. Belt axial speed effects are included, resulting in a gyroscopic system with continuous (belt spans) and discrete (pulleys and tensioner arm) components. The model is specialized to provide equations governing (1) nonlinear equilibrium, (2) linear vibration, and (3) nonlinear vibration. The equilibrium problem is solved, using an exact numerical solution and a closed-form approximate solution. The approximate solution produces a key parameter, ;Analytical predictions are in very good quantitative agreement with experimental results for the equilibrium and linear free vibration problems. The nonlinear vibration problems leads to good qualitative agreement between analysis and experiment. Results show that tractive span tensions generally drop with increasing belt speed. Linear dynamic coupling between rotational and transverse motions generally produces modeshapes that are neither exclusively rotational or transverse, but include a combination of the two motions. Torque pulses input to the pulleys are shown to be capable of parametrically exciting transverse belt vibration, especially under conditions of internal resonance. As a result, knowledge of both rotational and transverse mode frequencies is critical in avoiding transverse parametric resonance. |
