Experimental characterization of engine crankshaft rumble noise signatures

The temporal and spectral characteristics of crankshaft rumble noise and vibration signatures in vehicles equipped with four-cylinder internal combustion 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 substantially opposing rumble quality. Two different operating conditions, neutral no-load snap and second gear hard acceleration, which are most susceptible to crankshaft rumble excitations are examined. The measured time-frequency results 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 journal bearing. However, some specific response frequencies themselves are speed-invariant, suggesting the contribution of structural modes associated with certain engine components. Also, data from stationary experiments applying simulated airborne noise and frequency response function techniques indicate that most of the intermittent burst of vibratory energy responsible for rumble sensation is transmitted structurally except for the highest cluster of audible frequencies (Bark 10) in which the air-borne route is predominant.