Some Effects of Gear Eccentricities on Automotive Rattle Noise

This study deals with the problem of automotive gear rattle noise, primary caused by the engine torque fluctuations. Even if the rattling phenomenon has no consequence on reliability, it may be particularly annoying for vehicle interior sound quality and acoustic comfort. Gear rattle noise results from vibro-impacts that may occur on unloaded gears under excessive fluctuations of the engine torque and driveline dynamic responses. It is reasonable to assume very short time duration for impacts between teeth due to rattle. Then, the main parameters which govern this kind of vibrations are the restitution coefficient introduced for impact modeling, the drag torque acting on the free running wheel during its free flight motion, its inertia and the excitation source which can be modeled by an imposed displacement. This excitation source is often modeled as a harmonic or, sometimes, periodic excitation related to the acyclism behavior of the engine torque fluctuation, at twice the rotation frequency of the primary input shaft. The aim of this study is to deal on several effects of the gear eccentricities considered first as a superimposed periodic excitation source and second as a time varying backlash source. For this end, a simple non-linear oscillator is introduced, based on restitution coefficient for impact modeling. The parameters studied are the operating rotation speed of the input shaft, the inertia of the free running wheel, the drag torque, and the eccentricities compared to the acyclism source. Results are presented through dimensionless parameters.