Gear Whine Noise Investigation of a Bus Rear Axle - Todays Possibilities and Outlook

This paper presents a simulation environment and methodology for noise and vibration analyses of a driven rear axle in a bus application, with particular focus on medium to high frequency range (400 Hz to 3 kHz). The workflow demonstrates structure borne noise and sound radiation analyses. The fully flexible Multi-Body Dynamics (MBD) model - serving to cover the actual mechanical excitation mechanisms and the structural domain - includes geometrical contacts of hypoid gear in the central gear and planetary gear integrated at hubs, considering non-linear meshing stiffness. Contribution of aforementioned gear stages, as well as the propeller shaft universal joint at the pinion axle, on overall axle noise levels is investigated by means of sensitivity analysis. Based on the surface velocities computed at the vibrating axle-housing structure the Wave Based Technique (WBT) is employed to solve the airborne noise problem and predict the radiated sound. Actual capabilities and limitations of the applied hypoid gear contact model are identified by comparing simulated and measured housing surface acceleration as well as sound pressure levels. Finally, a superior hypoid gear contact model based on preceding Loaded Tooth Contact Analysis (LTCA) is suggested for future extension of the methodology.