A time frequency analysis of the vibration signals was processed by adaptive generalized S transform (AGST) in order to obtain the idling vibration characteristics of a gasoline engine which will be helpful in the targeted NVH optimization. The AGST was proved to own more suitable time frequency resolution, compared with S transform. A vibration measurement was conducted at idling for a four cylinder inline gasoline engine and the valve clearances and the thermal load were adjusted during the experiment. Through the time frequency distribution, the valve mechanism and the piston slap were demonstrated as dominated vibration sources at cold start. At cold idling, the frequencies of these excitations are respectively in the range of 500～2 100 Hz (inlet valve seating), 800～2 200 Hz (exhaust valve seating) and 400～6 000 Hz (piston slap). The overall amplitude slashed and the fuel injector excitation appeared along with the increase of the thermal load while the combustion signal was faint throughout. At hot idling, excitation frequencies respectively change to 2 200～5 800 Hz (inlet valve seating), 3 800～6 000 Hz (exhaust valve seating), 2 500～3 000 Hz and 4 500～5 000 Hz (piston slap). The major variation of vibration characteristics in frequency domain mainly manifest as an obvious decrease in the low frequency band at higher thermal load．
LIU Rui jun, HAO Zhi yong, ZHENG Xu, SU Hang, JIANG Hong feng. Investigation of idling vibration characteristics of gasoline engine based on adaptive generalized S transform. JOURNAL OF ZHEJIANG UNIVERSITY (ENGINEERING SCIENCE), 2016, 50(3): 460-467.
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