Experimental characterization of engine crankshaft rumble noise signatures

The temporal and spectral characteristics of crankshaft rumble noise and vi bration signatures in vehicles equipped with four-cylinder internal combust ion engines are studied from the viewpoint of source-path-receiver using a series of in-situ, system level operating and stationary experiments. This experimental study reveals new quantitative and qualitative time-frequency characters that have not been discussed previously. The present analysis is applied to two production vehicles of identical design, but with substanti ally opposing rumble quality. Two different operating conditions, neutral n o-load snap and second gear hard acceleration, which are most susceptible t o crankshaft rumble excitations are examined. The measured time-frequency r esults show a direct correlation between the modulation frequency of rumble response and one-half order of the fundamental crankshaft rotational speed , signifying probable sensitivity to only one specific cylinder or main jou rnal bearing. However,some specific response frequencies themselves are spe ed-invariant, suggesting the contribution of structural modes associated wi th certain engine components. Also, data from stationary experiments applyi ng simulated airborne noise and frequency response function techniques indi cate that most of the intermittent burst of vibratory energy responsible fo r rumble sensation is transmitted structurally except for the highest clust er of audible frequencies (Bark 10) in which the air-borne route is predomi nant. (C) 2000 Elsevier Science Ltd. All rights reserved.