Active vibration control system for reducing gear whine noise

Gear whine noise of rear axles is a well-known acoustical issue in passenger cars with rearwheel or four-wheel drive. Due to its annoying character, this narrow band noise is well perceptible inside the passenger compartment. The acoustical optimization of gear whine needs a detailed analysis of the noise excitation mechanism and transfer paths. As a result, individual primary or secondary optimization measures are developed which often influence other functionalities and properties of a gear box (e.g. fatigue, mass, construction space). The Fraunhofer Institute for Machine Tools and Forming Technology (IWU) has developed innovative solutions for this issue applying active vibration control systems (AVC) on the transfer path from the rear axle to the driver's ear. The paper describes two approaches for the AVC system using an electrodynamic exciter and a piezoelectric actuator which can be integrated in the mechanical structure. Based on FEM simulation, optimal actuator positions on the structure-borne transfer paths have been identified. In a next step, a rear axle test bench and full vehicle measurements have been used to implement a feedforward FxLMS control algorithm and to evaluate the noise reduction potential of the AVC system based on both actuator types.