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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.

This paper presents a study of axle system NVH (noise, vibration and harshness) performance using DFSS (Design for Six Sigma) methods with the focus on the system robustness to typical product variations (tolerances / manufacturing based). Instead of using finite element as the simulation tool, a lumped parameter system dynamics model developed in Matlab/Simulink is used in the study, which provides an efficient way in conducting large size analytical DOE (Design of Experiment) and stochastic studies. The model's capability to predict both nominal and variance performance is validated with vehicle test data using statistical hypothesis test methods. Major driveline system variables that contribute to axle gear noise are identified and their variation distributions in production are obtained through sampling techniques.

Ideally, the calculation of driveline component imbalance sensitivity is a straightforward operation of normalizing the changes in dynamic responses that occur when a known imbalance is added to a rotating component. In practice, however, overlapping driveline component orders (and wheel order harmonics) often prohibit the measurement repeatability required to distinguish these changes. A solution to the measurement repeatability issue is presented for chassis dynamometer testing, based on prescribing minor adjustments to the roll speeds for different wheels in order to separate the orders of various rotating components.

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.