Design of a squeak test apparatus based on a modified sprag-slip mechanism

Squeak is an annoying noise generated by a self-excited vibration due to friction. Because of the highly nonlinear nature of the phenomenon, squeak noise is one of the most difficult problems to address for NVH engineers. A modified sprag-slip mechanism is designed that utilizes a geometrically induced instability mechanism to generate squeak noises consistently for most of material pairs. A single-degree-of-freedom system that represents dynamics of the system is developed to refine and guide the design through numerical simulations. Effects of main parameters such as the coefficient of friction and the attack angle are studied to understand their influences on the stability of the system. The equation of motion is numerically solved to obtain transient responses of the system to study characteristics of self-excited instability. Based on the simulation results, a test apparatus that induces squeak noises for a wide range of materials pair was developed. The intended use of the test device is to build a materials database that rank squeaks propensity of various material pairs quantitatively for NVH engineers.