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This paper discusses approaches to properly design aluminum axles for optimized NVH characteristics. By effectively using well established and validated FEA and other CAE tools, key factors that are particularly associated with aluminum axles are analyzed and discussed. These key factors include carrier geometry optimization, bearing optimization, gear design and development, and driveline system dynamics design and integration. Examples are provided to illustrate the level of contribution from each main factor as well as their design space and limitations. Results show that an aluminum axle can be properly engineered to achieve robust NVH performances in terms of operating temperature and axle loads.

Axle gear whine originates at the hypoid gearset, and can be amplified by the driveline system dynamics as well as the transfer paths into the vehicle. In addition to tremendous efforts in improving the gear quality, it is of some importance that optimized system dynamics be achieved so that the system sensitivity to the gear excitation can be greatly reduced. This methodology has been extensively utilized in American Axle through a combined numerical simulation (FEA) and testing approach. This paper presents the FEA modeling techniques in studying axle system dynamics and the level of accuracy of the model that can be achieved in predicting forced system responses. The use of a driveline system model in the development of a design optimization for total system NVH performance is discussed. Examples are provided to demonstrate the effects of modal alignments and appropriate system tuning.

Today's emerging 4-wheel-drive and all-wheel-drive vehicle architectures have presented new challenges to engineers in achieving low driveline system noise. In the meantime there's also a constant pressure from increasingly stringent noise level requirements. A driveline system's NVH (noise, vibration and harshness) performance is controlled by various noise sources and mechanisms. The common noise issues include the axle gear whine, driveline imbalance/run-out, 2nd order kinematics, engine torque fluctuation, engine idle shake etc. Unfortunately various design alternatives may improve some NVH performance attributes while degrading others. It is important to balance the requirements for these noise sources to achieve an optimized driveline system NVH. However, very little literature is found on this topic. In this paper, discussions on methodologies in balancing these different driveline NVH requirements are presented.