New Automotive Study Helps Auto Engineers Reduce Vehicle Weight

Greener, Lighter, Safer Steel Vehicles Can Be Achieved Through New Vehicle Noise, Vibration and Harshness Approach

DETROIT, April 28 -- A study commissioned by WorldAutoSteel shows automotive engineers a new approach to design for noise, vibration and harshness (NVH) called "Hybrid Interior Noise Synthesis (HINS)." The study illustrates how vehicle components can be optimized for NVH performance and weight by applying the new approach and lightweight steel solutions.

"Applying this approach with steel technologies equips automotive engineers with methodology that significantly improves the component design process for fuel-efficient vehicles," said Ed Opbroek, Director, WorldAutoSteel. "Control of the overall vehicle weight is critical."

The study was presented at SAE by Juliette Florentin of LMS International (www.lmsintl.com), who conducted the study on behalf of WorldAutoSteel, and Toyoki Yamamoto, Nippon Steel (WorldAutoSteel member), who provided steel technical expertise to the project. The new HINS approach was applied to a BMW 1-series firewall with integrated cross beam. This HINS method associates a virtual firewall structure with a test-based body model. The vibro-acoustic model includes the firewall structure, trim elements, full vehicle boundary conditions and an acoustic model of the passenger cabin. It is used for predictions of structure-borne engine noise in the 40 Hz to 400 Hz range.

The short calculation time of this set-up allows a wide range optimization, where multiple design iterations can be completed quickly. A significant number of modifications to the firewall and associated transverse beam were modeled to determine impact on weight and NVH.

"We focused on a firewall, as it is a dominant panel for noise and vibration concerning the structure-borne engine noise," said Yamamoto. "And we chose the BMW 1-series firewall because it is already a superior design that would be difficult to improve upon, therefore creating a proper challenge for this new approach."

The results showed that both weight and NVH could be reduced through design changes and use of steel processing technologies, such as tailor-welded blanks (TWB). The TWB allows for greater thicknesses in weaker areas rather than a fully over-designed beam. Bead designs were implemented on the firewall that showed potential to bypass expensive damping sheet treatments, commonly applied to reduce the amplitude of vibrations. The noise contribution of the firewall was improved by 0.9 dB, its mass reduced by 5.1 percent and the structure maintained the same level of crashworthiness.

"This is a good result considering that we only had access to the firewall and were testing a front-end design that is already quite advanced," Florentin noted. "If this approach were applied early on in the design process, we might be able to achieve additional weight reduction."

The study overall demonstrated that complex steel designs are successful at achieving better noise performance while improving mass, yet not compromising crashworthiness. For even more dramatic improvements, the study recommends that NVH be addressed earlier in the design process.

A paper detailing the study and the HINS approach can be purchased from the Society of Automotive Engineers, referenced as follows: "Steel Solution for Firewall using test and CAE Hybrid approach," SAE Document Number: 2009-01-1547, published April 2009.