Design optimization study of a nonlinear energy absorber for internal combustion engine pistons

Piston impacts against the cylinder liner are the most significant sources of mechanical noise in internal combustion engines. Traditionally, the severity of impacts is reduced through the modification of physical and geometrical characteristics of components in the piston assembly. These methods effectively reduce power losses at certain engine operating conditions. Frictional losses and piston impact noise are inversely proportional. Hence, reduction in power loss leads to louder piston impact noise. An alternative method that is robust to fluctuations in engine operating conditions is anticipated to improve the engine's NVH performance, whilst exacerbation in power loss remains within the limits of conventional methods. The concept of Targeted Energy Transfer (TET) through the use of Nonlinear Energy Sinks (NES) is relatively new and its application in automotive powertrains has not been demonstrated yet. In this paper, a TET device is conceptually designed and optimised through a series of parametric studies. The dynamic response and power loss of a piston model equipped with this nonlinear energy sink is investigated. Numerical studies have shown a potential in reducing the severity of impact dynamics by controlling piston's secondary motion.