Brandl, S., Graf, B., and Rust, A., "NVH Challenges and Solutions for Vehicles with Low CO2 Emission," SAE Int. J. Passeng. Cars - Mech. Syst. 5(3):1084-1090, 2012, doi:10.4271/2012-01-1532.
Driven by worldwide climate change, governments are introducing more stringent emission regulations with particular focus on fuel saving for CO₂ emission reduction. Downsizing and weight reduction are two of the main drivers to achieve these demanding regulations. Both aspects however might have a strong negative effect on the overall vehicle NVH behavior.Weight reduction directly influences NVH due to reduction of absorption and damping material and due to light-weight design affecting the dynamic responses of powertrain and vehicle structures. Engine downsizing however has multiple negative effects on NVH. Beside higher vibrations and speed irregularities due to lower cylinder numbers and displacements also reduction of sound quality is a critical topic that will be handled within this publication.The first part of this publication will focus on excitation of engines with different number of cylinders, an alternative mounting solution for 3-cylinder engines and an overview on the changes of sound quality for downsized engines.In the second part two solutions for vehicles with downsized engines will be presented. The first vehicle is equipped with a 4-cylinder engine and electrical cylinder. By applying appropriate NVH measures the same NVH behavior as for the original 4 cylinder without cylinder deactivation can be achieved. Second example is a vehicle powered by a turbocharged two-cylinder engine. Using active noise generation, the unconventional sound characteristic of that vehicle can be changed to that of a standard 4-cylinder engine in order to increase sound quality and reduce real-life fuel consumption by positive effects on driving behavior.