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Passenger comfort has become one of the key areas to achieve success in the passenger car market segment. New upcoming products are rejected by customers not because of durability, but more by irritants like noise and vibrations. Hiss noise is one of the major irritants in passenger cars employing hydraulic power steering. This paper describes an attempt to evolve a structured methodology to identify and characterize power steering hiss noise from a rack and pinion type hydraulic power steering system. Extensive testing and detailed analysis of noise data was performed for characterization of power steering hiss noise, from which frequencies responsible for hiss noise were identified at vehicle level and component level. Subsequently several solutions were tried to reduce the hiss noise to an acceptable level considering the limitations of manufacturing and cost. Test results show the effectiveness of approach and methodology towards arriving at a solution for hiss noise.

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.