Modeling and Analysis of Powertrain NVH 2012-01-0888
Current modeling techniques of the powertrain noise, vibration and harshness (NVH) involve fully meshed structural components and rely, in general, on predefined excitation loads to evaluate linear transfer or structural attenuation functions. While effective for comparative assessment of various designs, these methods neglect the complex dynamic interactions between the powertrain structure and crankshaft, piston, valve train, timing drive, and accessory drive systems. This paper presents an overview of modeling methods of low and high frequency powertrain NVH with focus on dynamic interaction among structural components. A coupled and fully flexible multi-body dynamics model using AVL/Excite is presented. The model includes the cranktrain, crankcase, cylinder head, covers, oil pan, mounts, and transmission housing represented as finite element meshes. The main bearings are represented using elasto-hydrodynamic joints to account for the effect of oil film stiffness and damping as well as bearing clearance. The structural components are reduced using component mode synthesis and used to determine dynamic loads at various engine speeds and loading conditions. The main excitation sources relevant for both low and high frequency NVH and the influence of cylinder pressure, bottom end design, and crankshaft stiffness are discussed. An overview of piston related noise and modeling techniques to identify the causes and mechanisms leading to excessive impact noise in a floating piston pin design are presented.