A Hybrid Method for Characterization and Improvement of NVH Performance of Axle System

The axle system is a major contributor for road induced vehicle interior noise. However, it is challenging to characterize the NVH performance of the axle system because it is coupled with both the tire/wheel and the body structure. In this article, we introduce a global approach to control the NVH performance of the axle system. The force transmissibility based on the blocked force concept was defined as the indicator of NVH performance of the axle system. A hybrid method combining test and simulation was developed to assess the intrinsic NVH performance of the axle system.The force transmissibility of the axle system is the blocked force generated by the axle system at the body mounting points with a unit of input force on the wheel. It can be simulated easily by FEM with rigid boundary conditions. However, measuring the blocked forces of the axle system is much more complex because it requires very stiff boundary conditions, which are difficult to realize on a realistic test rig. Our approach involves measuring the forces at the train-body interfaces on a standard test bench with realistic boundary conditions and simulating the interface forces with models that include not only the axle parts but also the rig and mounting parts. The simulation results can be compared directly with those of measurement, making it possible to recalibrate the simulation models. Once the model of the axle system is recalibrated, it can be used to simulate the blocked forces by setting infinitely rigid boundary conditions. This hybrid method allows obtaining the blocked forces from the axle system using a standard test rig without the need to build expensive new rigs.Using this method, different axle systems can be measured and NVH performance compared. In general, the axle system has worse NVH behavior in the transverse direction than in the vertical and longitudinal directions. Consequently, to improve the NVH performance of the axle system, the priority is to treat the weakness and make improvements in the transverse direction. The definition of the force transmissibility of the axle system, together with the hybrid characterization method, allows us to control the axle NVH performance more efficiently and carry out the necessary improvements in the design at the early stage of vehicle development.