Powertrain Optimization Strategy for Downsizing and NVH Refinement

The prime target of IEA (international energy association) to reduce global average emission by 50% in 2030 has prompted focused R&D on automotive emission reduction as well as NEV (new energy vehicles). Of these strategies, engine downsizing constitutes the group of strategies employed to meet lower emission and fuel consumption targets in IC engines. Downsizing strategies have been proved successful in reducing emissions. There is widespread trend of downsizing existing engines with a goal to produce lower emissions along with equal or better performance. To achieve the stated goals downsized engines are usually charged or employ higher compression ratios. This raises NVH as well as structural issues that need further analysis. While the concept of downsizing has been studied in deep, its structural effects and NVH related issues are of concern. This paper throws light into different engine downsizing strategies and their effect on NVH. The variations in unbalanced forces, increase in higher frequency excitations due to use of higher compression ratios, noise and vibration challenges related to turbocharging are discussed with respect to its NVH and structural aspects. A prevalent approach of reducing number of cylinders adds to concern of NVH engineers as unbalanced forces increases with odd number of cylinders. The effect of gas pressure and inertial forces on overall vibration levels are discussed in detail. An analytical approach to calculation of unbalanced forces, various testing and CAE methodologies for optimization of vibration and noise responses is discussed. Finally, comparison of a downsized single cylinder diesel engine with its base engine and strategies adopted is presented