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Concern about axle noise/vibration/harshness (NVH) has been increasing with the growing popularity of sport utility vehicles, pick-up trucks, hybrid-vehicles and vans. Consumers want these vehicles to be quieter, with performance more like passenger cars. Traditional controls such as absorber-dampers and isolated/reduced vibration sources can solve some of the noise and vibration problems. An additional approach to enhancing NVH performance, is an active vibration control technique, which deals with the energy at the source. This paper describes an approach which combines an active vibration control technique with signature analysis, operational modal analysis and transfer path analysis to improve NVH performance. A flow chart of this is shown in Figure 1. Using this approach, we can identify and verify noise and/or vibration issues, find the root causes, and determine main contribution paths throughout driveline systems.

The need for improved axle NVH integration has increased significantly in recent years with industry trends toward full-time and automatic four wheel drive (4wd) systems. Along with seamless 4wd operation, quiet performance has become a universal expectation. Axle gear-mesh noise can be transmitted to the vehicle passenger compartment through airborne paths (not discussed in this paper) and structure-borne paths (the focus of this paper.) A variety of mounting configurations are used in an attempt to provide improved axle isolation and reduce structure-borne transmission of gear-mesh noise. The configuration discussed in this paper is a 4-point vertical mount design for an Independent Front Drive Axle (IFDA). A significant benefit of this configuration is improved isolation in the range of drive torques where axle-related NVH issues typically exist.