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This paper focuses on the diagnostic methodology and troubleshooting process for the coast down noise annoyance for two types of scooters. Both the subjective noise assessment and objective evaluation of the gearbox near field noise and gearbox case vibration were performed in this work. The objective evaluation adopted time analysis, spectrum analysis, order analysis and binaural analysis to identify the acoustic characteristics of the noise annoyance. In addition, the excellent correlation between gearbox case vibration and abnormal coast down noise was confirmed. The diagnostic results show that the noise annoyance is resulted from the improper assembly clearance tolerance between specific parts for Type A scooter, and from the improper clearance between specific parts for Type B scooter.

The study employed the rig test method for the intake/exhaust noise investigation by using shaker. This article describes two case studies including 1.2 liter minivan and a 250 c.c. motorcycle. For the minivan case, it was verified that along with the reduction of 5∼8 dB(A) of intake noise the interior noise was also improved using the rig test optimization result. For the motorcycle case, It was found that there was very good correlation of the exhaust noise measured among the engine dynamometer, road test and rig test after the temperature effect was compensated. Hence, the study chose the rig test as a development tool to get prompt NVH evaluation results on the different exhaust pipe lengths and keep the development time schedule. From the results, it is concluded that the simple and cheap rig test evaluation technique is vital and a very effective tool to achieve the vehicle NVH development goal.