Evaluation of Crankshaft Clearance Influence on Specific Roughness Noise Concern 1999-01-1771
Passenger car customer expects both: low interior noise level and a sound quality, adapted to vehicle driving condition. The latter should be based upon a comfortable sound character without outstanding noise effects. One of the very unpleasant noise characteristics is roughness, also called rap noise or rumbling noise.
Beside intake noise and powertrain structure bending, the dynamic crank train behaviour is one of the potential origins of a rough noise pattern. Material properties of the crankshaft and the layout of crankshaft damper can influence roughness as well as the crank train clearances.
Subjects of this study, which was performed on a 4-cylinder spark-ignition (SI) engine, were the identification and objectivation of a specific noise concern which occurred during vehicle acceleration. Aim was to evaluate the noise concern sensitivity to the crank train clearances and to define optimum clearance ranges for noise quality improvement.
The clearance sensitivity analysis revealed optimum radial clearance ranges for conrod and main bearings. The thrust bearing clearance showed no direct influence on the rough noise concern. However, to reduce the influence of radial main bearing clearance tolerance, an optimum clearance range for thrust bearing was defined, too.