Characterization of Rubber Mounts Through Virtual Point Transformation Using Different Boundary Conditions in the Context of Dynamic Substructuring

Nowadays, especially in the electric mobility field, noise and vibrations is becoming day by day a more important topic that requires accurate prediction. In the context of dynamic substructuring applied to the automotive field, a crucial aspect for determining the noise property of a vehicle is the evaluation of the transfer behavior of the rubber elements connecting the different components of a car. The goal of this research is to extract the frequency-dependent dynamic stiffness for different models of rubber bushings presenting a similar architecture and belonging to the rear drivetrain of a BMW i4 and iX. In particular, we will compare two different methods for characterizing the dynamic behavior of nonlinear elements. Firstly, for each type of bushings, a free-free measurement procedure will be considered. In comparison to literature, this approach will be adapted with a third metal bracket to account for the current bushing’s architecture. In this procedure, the dynamic properties are determined from triaxial accelerometers measurements with impact hammer excitation. The output results in terms of dynamic stiffness will be compared with dedicated measurements conducted on a Hydropulse machine inside a test bench of the BMW Group. Secondly, on the same bushings, an experiment will be performed by clamping the rubber mounts to the ground and creating fixed boundary conditions. This second approach should allow to directly extract dynamic stiffness properties, without first performing a system inversion. Since this approach is suitable both for hammer impacts or shaker excitations, both approaches will be explored and further analyzed. Both the free-free and the fixed boundary condition experiment implement the technique of virtual point transformation. Therefore, further attention will be given to error evaluations coming from such technique and how to improve the transformation in terms of accuracy and numerical stability. Future research will focus on how the extracted dynamic stiffness models can be integrated into a system-level simulation framework for electrical vehicle noise generation.