A Design Optimization Process of Improving the Automotive Subframe Dynamic Stiffness Using Tuned Rubber Mass Damper

Automotive subframe is a critical chassis component as it connects with the suspension, drive units, and vehicle body. All the vibration from the uneven road profile and drive units are passed through the subframe to the vehicle body. OEMs usually have specific component-level drive point dynamic stiffness (DPDS) requirements for subframe suppliers to achieve their full vehicle NVH goals. Traditionally, the DPDS improvement for subframes welded with multiple stamping pieces is done by thickness and shape optimization. The thickness optimization usually ends up with a huge mass penalty since the stamping panel thickness has to be changed uniformly not locally. Structure shape and section changes normally only work for small improvements due to the layout limitations. Tuned rubber mass damper (TRMD) has been widely used in the automotive industry to improve the vehicle NVH performance thanks to the minimum mass it adds to the original structure. Therefore, this article establishes a design optimization process utilizing the TRMD to improve the vehicle subframes DPDS more efficiently. First, the subframe critical normal modes for the DPDS issue are identified through modal participation factor analysis with the finite element (FE) model of the subframe. A lumped mass–stiffness–damper mathematical model is established by the TRMD and the identified critical modes. The parameter correlation analysis is conducted through the simple math model. Thereafter, parameter tuning is done based on the DOE study with an integrated FE model composed of the subframe and the TRMD. Furthermore, a rubber steel-type TRMD is built and verified virtually for demonstration. The proposed framework could solve the component-level DPDS problems efficiently with minimum mass and cost penalty compared to traditional methods. And it could be introduced into the subframe early design stage to ensure a lightweight final design, which meets all the component-level DPDS requirements.