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In this paper, a methodology is discussed to achieve cost-effective solutions for improving vehicle Noise, Vibration and Harshness (NVH) performance of a body-on-frame Multi-Utility Vehicle (MUV). The subject vehicle had objectionable levels of in-cab boom and gear rattle while accelerating in higher gears due to power-train and driveline excitations. Potential transfer paths which might be responsible for amplifying these phenomena were tracked using contemporary noise and vibration measurement techniques. Various modifications were evaluated to improve NVH performance under constraints of vehicle-packaging. An optimized combination of these modifications resulted in improvements in the NVH performance over a wide range of operating speeds with reductions of up to 10 dB achieved in firing frequency excitation, thus eliminating the objectionable boom and gear rattle from the vehicle.

This paper is an outcome of development work done in improving Noise Vibration Harshness (NVH) performance of a bus. A concern from built-up prototypes was high floor vibration levels at higher speeds when Air-Conditioner (AC) was switched on. Running mode analysis of bus-vibrations was performed to visualize exact behavior of its frame. It was revealed that a 4th order vibrations of the AC compressor was matching with a structural resonance of the bus frame on which the AC compressor was mounted. The frame suffered from high amplitudes of torsional vibrations especially near a power-train mount. And these excitations were transferred to the bus-floor. With a change in drive-ratio of the AC compressor, decoupling of its vibrations from the Bus-frame mode was made. This led to a significant reduction of the floor vibrations and increased comfort to the passengers at higher speeds.