Powertrain Torsional Vibration System Model Development in Modelica for NVH Studies

Abstract

For developing high-quality and cost-efficient products, it is important to evaluate and compare system level performance for different configura-tions early in the development process. This paper will present the development of a vehicle system model in Modelica that is used to study the overall vehicle power-train torsional vibrations that impact Noise, Vibration & Harshness (NVH) characteristics of the vehicle. In this study, a detailed crank-angle resolved, multi-cylinder engine model is constructed, which includes intake/exhaust dynamics, combus-tion, heat transfer, engine friction and rotational dy-namics of piston-crank mechanism. The engine model accurately reproduced real-world engine torque and acceleration fluctuations. The lumped parameter powertrain system model which includes clutch (and associated vibration isolation compon-ents), transmission, driveline and chassis is de-veloped and used with the engine model to predict torsional vibrations. This system model is used to understand the powertrain torsional vibration charac-teristics in different operating regions such as idling, driving and coasting conditions. To demonstrate the applicability of the developed models, results of unit tests for independent compon-ents, especially the engine torque variation and the clutch torsion characteristic, and the system-level quantitative validation with test data are presented. A special model that does fast Fourier transform of the signal on the fly is presented and its role in the ana-lysis discussed. We present a comparison of rattle noise between two compliant clutch (isolator) designs and discuss the rattle metrics used in the ana-lysis. Generic considerations for the deployment of such system level models are also discussed in this paper.