To reduce interior noise effectively in the vehicle body structure development process, noise and vibration engineers have to first identify the portions of the body that have high sensitivity. Second, the necessary vibration characteristics of each portion must be determined, and third, the appropriate body structure for achieving the target performance of the vehicle must be realized within a short development timeframe.
This paper proposes a new method based on the substructure synthesis method which is effective up to 200Hz. This method primarily utilizes equations expressing the relationship between driving point inertance change at arbitrary body portions and the corresponding sound pressure level (SPL) variation at the occupant's ear positions under external force. A modified system equation was derived from the body transfer functions and equation of motion by adding a virtual dynamic stiffness expression into the dynamic stiffness matrix of the vehicle. It is possible to calculate the sensitivities of hundreds of body portions automatically by incorporating the modified equation into an application program. Thus, a sensitivity table report that enables a comprehensive extraction of high sensitivity body portions, directions, and frequency ranges can be prepared.
The next step is to find feasible solutions of body modifications to achieve the target interior noise SPL. For this, the objective ranges of the desirable driving point inertance levels and phases for each extracted sensitive body portion are calculated at each frequency within the designated range by utilizing a transformed equation based on the modified equation. Once the necessary ranges are determined, body structure modifications can be investigated more efficiently with mechanical engineering knowledge such as resonance frequency shifts and so on.
This method was applied to both a Finite Element trimmed body model and a physical vehicle body for engine booming noise. The results validated the effectiveness of these methods.