State of the art review on rattle index formulations for geartrain applications

Gear rattle is a major source of noise, vibration, and harshness in automotive transmissions, arising from vibro-impact excitations of unloaded gear pairs caused by engine torque fluctuations and functional backlash. Several rattle indices have been proposed to provide an objective and quantitative characterization based on physical or signal-processing formulations. However, their interpretation and comparative applicability are often limited by heterogeneous modeling assumptions and simplified transmission layouts. This survey classifies rattle indices according to their underlying physical quantities and diagnostic objectives and evaluates their performance through numerical simulations under identical excitation conditions. The analysis distinguishes between indices aimed at detecting rattle onset and those capable of tracking the evolution of tooth contact dynamics. A progressive validation framework is adopted, ranging from a single gear pair to a multi-stage transmission with multiple loose and idle gears. The results clarify the applicability of existing rattle indices and support informed metric selection for vibration and signal analysis in complex transmission systems.