Noise Generation Through Movement of the Crankshaft in the Main Bearings of a Gasoline Engine

The statically indeterminate supported crankshaft system (with several degrees of redundancy) in multi-cylinder combustion engines moves in the main bearings due to the gas and inertia forces acting on it. The sometimes very rapid changes in movement of the individual main bearing journals lead to impulsive force excitations, which act via the lubrication film on the main bearings, generating vibration in the main bearing lane. In order to clarify these relationships, experiments have been carried out on a gasoline engine, whereby, in addition to combustion chamber pressure, recordings are also made of the movements (journal orbits) of all main bearing journals and of the vibration excitation at the main bearing caps. The analysis of the results has been carried out both with regard to time (represented as a function of crank angle) and with regard to frequency, so that interesting relationships between the displacement of the crankshaft main bearing journals and the resulting vibration excitation can be shown dependent of load and speed.