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This paper discusses combined experimental and simulation approach used for NVH refinement of Passenger Vehicle for in-cab Boom Noise. On initial testing of Proto Vehicles a boom was identified in the speed range of 1300-1600 rpm in all the gear conditions. Investigations through measured Vibrations and Operational Deflection Analysis (ODS) identified that the rear axle had a vibration mode of the axle on the trailing arm bushes at around 43 Hz excited by the engine combustion forces. This finding was concurred by predicted full vehicle level modal and acoustic response analysis results. Based on simulation findings, conceptual change of rigid attachment between rear axle and trailing arm suppressed the vehicle boom. Using simulation approach a realistic design solution was worked out in terms of optimization of trailing arm rear bush stiffness values. Benefits of same were confirmed on the vehicle.

Noise Vibration and Harshness (NVH) refinement is one of the important parameters in modern vehicle development. In city traffic conditions, idling is an engine operating condition where a driver focuses attention more to his/her vehicle. Tactile vibration & noise levels inside the cab play an important role in all vehicles, especially those powered by diesel engines where combustion pressures are higher. They lead to discomfort & fatigue of passengers of even a low cost vehicle. Now its idle NVH is influenced mainly by vibration-isolation provided by power-train (PT) mounting design, This paper describes steps taken to improve the idle vibrations at a driver seat of a small commercial vehicle (SCV) with a 2-cylinder diesel engine of 800 cc through redesign of PT-mounting along with fine tuning of idle speed of the engine. A resonance was avoided between the first firing order at idling and PT rigid-body mode in pitching.