CAE-Driven Design for NVH Optimization of an Independent Rear Suspension Subframe

The way a subframe for an independent rear suspension attaches to a unibody vehicle is critical for its NVH performance. The force path from the control arms to the body may, in some cases, pass through spots where some body vibration modes with relatively high acoustic radiation efficiency are excited, generating undesired peaks at some frequencies for point and transfer mobilities, as well as for acoustic transfer functions from the subframe to the driver's and passenger's ears. This paper describes a case study of an initial design for a subframe, where a vibration mode of the vehicle's rear underfloor panel was particularly strongly excited causing unacceptable both acoustic and vibrational behaviours, is modified through the evaluation of point mobility curves, as well as acoustic transfer functions, both obtained via finite elements method. Both the vehicle's body and acoustic normal modes are obtained by using Lanczos method, with the fluid-structure coupling being done by imposing a normal velocity compatibility at the solid-fluid interface. After a few design iterations, a significant shift in the critical frequency was achieved and a significant reduction in point mobility and acoustic transfer function levels in most of the frequency range of interest was achieved