1999-01-13

Ancillary Noise Development: A Practical Engineering Approach towards Identifying and Solving Ancillary Noise Quality Problems 990037

Improved levels of powertrain refinement in vehicles have led to an increased occurrence of engine ancillary noise quality issues, including power-assisted steering, air-conditioning and other hydraulic pumps, in addition to alternators. Traditionally the development and target setting of these systems has been supported by a combination of both rig and vehicle based development. However, objective and subjective analysis of ancillary in-vehicle noise can be complex and difficult due to interactions with engine harmonics and broadband masking from other noise sources. Rig-based ancillary development exercises often fail to directly correlate with vehicle based measurements.To address these issues MIRA has developed a hybrid rig and synchronous sampling system, which has been applied successfully to both the Noise Vibration and Harshness (NVH) development of ancillary systems and their in-vehicle installation. The system provides a controlled repeatable in-vehicle environment for ancillary testing with precise angle domain analysis.With such a system, accurate, incisive indices can be developed for the objective noise quality parameters that correlate with subjective ratings for ancillary noise. These not only account for inter-harmonic effects but also masking of the ancillary system noise: a critical aspect. By providing an accurate measurement of the noise quality issues, this practical experimental technique can be used to identify the key paths and sources that directly influence the noise quality parameters, thus avoiding over engineering and ensuring an optimised solution.

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