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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.

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.

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.

This paper presents the principles of robustness design of axle system dynamics to reduce vehicle system related axle gear whine. Through examining the physics of the axle gear noise, the influence of the system dynamics are identified as two parts, i.e., the dynamics mesh force generated at the gear meshing per unit gear mesh motion variation; and the force transmissibility from mesh to the axle housing, and then further to the bracket attachments. The noise sensitive design parameters are identified and discussed. Component design requirements are proposed to minimize the system resonances in the typical gear mesh frequency range. The use of FEA models for system understanding and further design tuning is illustrated.

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.

The American Axle & Manufacturing Inc. driveline dynamometer provides immense value for experimental validation of product NVH performances. It has been intensively used to evaluate product design robustness in terms of build variations, mileage accumulation, and temperature sensitivity. The current driveline dynamometer input motor system has multiple torsional modes which create strong coupling with test part gear mesh dynamics. Mechanical Engineering seniors at Lawrence Technological University designed, fabricated, and validated a mechanism to decouple the driveline dynamics from the driveline dynamometer dynamics. The student-designed decoupler mechanism is presented with experimental validation of effectiveness in decoupling driveline dynamometer dynamics from the driveline under test.