Prediction of vibroacoustic excitation due to the timing chains of reciprocating engines

Abstract

Timing drive systems of recent passenger car engines are usually equipped with chain or synchronous belt drives. The comparatively low stiffness of chains and belts, combined with the large moments of inertia, resulting from moving parts of camshafts and valvetrains, lead to natural frequencies in the frequency range between 80 and 250 Hz for the entire timing drive [1]. Obviously, engine orders dominating the noise excitation are in the same frequency range, and resonance effects cannot be avoided. Furthermore, a guarantee is requested that occurring vibration amplitudes do not exceed acceptable limits. Hence, the predicted results of the primary dynamics of the timing drive are key data for the design analysis of a combustion engine. Besides the low frequency range excitation determined by main engine orders, higher-order structure-borne noise excitation is gaining more importance. This is particularly true for chain-driven systems where specific effects lead to considerable excitation of the engine structure in a higher frequency range (typical whine noise). The excitations are caused by the polygon effect, meshing impacts between chain links and sprockets and impacts in the engagement and disengagement between chain, sprockets and guides. This paper presents a comprehensive multi-body dynamics (MBD) model and the relevant simulation environment, which takes into account the entire timing drive as a fully coupled system. While simple MBD models (e.g. longitudinal span representation) are sufficient for the prediction of the primary dynamics of the timing drive, usually the analysis of higher-frequency dynamics and structural excitation requires a high degree of discretization of drive components to ensure a high-quality representation of the physical behaviour. This leads to a discrete model of chains and belts. Each link or tooth is taken into account separately by its mass properties, viscoelastic characteristics and by its contacts to sprockets, pulleys and guides. This paper describes the mathematical modelling of relevant engine components and the relevant interaction of different force elements. In particular, the consideration of the elastic contact between bodies represented by their real surface shapes is outlined. Finally, simulation results and their comparison with experimental data are presented for a chain-driven system, with discussion of low-frequency primary dynamics and higher-frequency structural excitation. Discrete models have also been developed for timing belts, but their verification with measurements is not completely finished. Hence, this paper only gives an overview of modelling issues.