Measurement and Analysis of Cam Chain Noise for Source Identification and Mitigation

This paper investigates the source of noise from the rejected cam chains used in motorcycles for valve timing control. The client seems to be rejecting mainly the cam chains that have run for few thousands of kilometers.

An ingenious hybrid approach of noise source localization is formulated for the purpose of chain noise analysis, where in the sound quality/jury testing is used as a diagnosis tool. Noise measurements were conducted on chosen sets of cam chain/sprockets on a motorcycle to characterize the noise in terms of amplitude and frequency. Various techniques like narrowband frequency analysis, order analysis & modal testing were used to identify the major frequencies contributing to the chain noise and their sources. The reported chain noise assessment and subsequent rejections were purely based on the perception. Therefore the measured noise (objective data) was correlated with the subjective perception using sound quality tools and jury testing to arrive at the frequency/ies attributable to the perceived chain noise.

From present study, it is concluded that the distinguishable source of the perceived chain noise is attributable to the second flexural mode of the larger sprocket. The results of the study also lead to hypothesize that the second flexural mode is more likely to participate under the time-induced adverse combination of axial clearance and chain slackening. Further, the study also indicated that the structural (free/extensional or constrained layer) damping treatment has good potential to reduce the amplitude of noise associated with the sprocket's flexural modes.