Tackle Low Frequency Structural Vibration in AMT Car using Gear Shift Schedule Optimization

The present work focuses on optimization of gear shift pattern of an AMT vehicle to improve its NVH performance without causing any adverse effect on any other vehicle performance attribute. The vehicle which was identified with the structural body resonance at low frequency had discomforting boom noise in a particular engine rpm zone and at corresponding vehicle speed. With the initial shift pattern (will be referred as V1 gear shift schedule), the gear shifts were calibrated such that when vehicle is driven in the city with 20 to 60 kmph speed, the vehicle operated mostly in the best fuel economy zone but it used to pass through structural resonance frequency. This resulted in the presence of continuous boom leading to an unpleasant driving experience. In order to avoid the presence of boom noise during city driving, the gear shift points were optimized (will be referred as V2 gear shift schedule) such that the vehicle did not operate in affected engine speed range. Though, the initial trials resolved the boom noise concern, they imposed severe penalty on fuel economy and drivability performance. This prompted the authors to focus on other variables like gear utilization profile distribution during city driving and % of accelerator pedal utilization during city driving to arrive at an optimized gear shift pattern (will be referred as V3 gear shift schedule). The final gear shift pattern succeeded in reducing the boom noise significantly without causing any adverse effect on other vehicle performance attributes.