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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.

Production variations of a heavy duty truck for its vibrations were measured and then analyzed through an Ishikawa diagram. Noise and Control factors of the truck idle shake were indentified. The major cause was found to be piece to piece variations of its power-train (PT) rubber mounts. To overcome the same, a new nominal level of the mount stiffness was sought based on minimization of a cost function related to vibration transmissibility and fatigue damage of the mounts under dynamic loadings. Physical prototypes of such mounts were proved to minimize the variations of the driver's seat shake at idling among various trucks of the same design. These learning's are useful for design of various subsystems or components to refine the full vehicle-Noise Vibration Harshness (NVH) at the robust design level.