Noise Mechanisms in the Inflation of the Automotive Safety Air Bag

Free-field noise from a compressed-gas air bag inflator was recorded and spectrally analyzed. Tests were run with different types of silencing devices inserted in the manifolding, and with and without the bag attached. Comparisons between the noise spectra obtained in these tests permitted the identification of different mechanisms of noise generation. The largest peak in the spectrum was generally below 20 Hz and is due to a monopole-type of source associated with the overall discharge of gas from the inflator system. Other noise sources are associated with the motion of the surface of the bag, “organ-pipe” sources within the manifolding, and broadband jet noise associated with the flow of gas through the diffuser slots into the air bag.