Dynamic performance analysis of a light van body-in-white structure

Requirement for low emissions and better vehicle performance has led to the demand for lightweight vehicle structures. Lighter gauge panels are being used to construct the body-in-white (BIW) monocoque structure, which is the basic component of the vehicle body. Since lighter gauge panels tend to generate more vibration and interior noise, it is necessary to optimize the dynamic performance of lightweight vehicle structures in order to achieve acceptable levels of vibro-acoustic performance. The design of a light commercial van structure has evolved over the years and through a lightweighting exercise the current BIW is about 10 per cent lighter than the previous BIW even though the volume capacity was increased by 15 per cent and the load-carrying capacity by 18 per cent. In this study, the dynamic performance of the current production light van BIW structure is investigated. Its performance is assessed against the structural dynamic performance standards which have been established for this class of structures. While the input mobility performance was found to exceed the standards easily, the modal mobility performance was found to be unsatisfactory owing to the occurrence of local panel resonant modes in the two side panels. A finite element model of the structure was developed to study the effect of adding stringers to the roof and side panels to eliminate some of the local panel modes and thus to improve the dynamic performance of the structure.