Acoustic Analysis of Isolated Engine Valve Covers

Abstract

The powertrain engine is a major source of vibration and noise in automotive vehicles. Among the powertrain components, the valve cover has been identified as one of the main noise contributors due to its large radiating surface and thin shell-like structure. There has been an increasing demand for rapid assessment of the valve cover noise level in the early product design stages. The present study analyzes the radiated sound pressure level (SPL) of a valve cover assembly using the finite element method (FEM). The analysis is first performed using a fully coupled structural-acoustic approach. In this case the solid structure is directly coupled to the enclosed and surrounding air in a single analysis, and the structural and acoustic fields are solved simultaneously. In the next approach, the analysis is performed in a sequential manner, using a submodeling technique. First, the structural vibration of the cover is analyzed in the absence of the surrounding air. In the next analysis, the structural motion of the cover is used to drive the acoustic motion of the surrounding air. A comparison of the results between these two approaches shows them to be consistent. In addition to mechanically induced noise, the air-flow induced noise is also explored in the present study by applying flow pressure fluctuations in the interior air. The overall sound level is determined by superposition of both air-flow and mechanical excitations. In particular, this paper addresses the structural acoustics of an isolated engine valve cover where elastomer isolators and gaskets are used to isolate the cover through viscous damping. The frequency-dependent damping and dynamic modulus used are based on experimental measurements. The results obtained show that the radiated sound level of an isolated cover is noticeably lower than that of a hard-mount one.