Aspects of engine start/stop comfort
In this paper, the start/stop process of combustion engines is considered as a functional chain from excitation over amplification mechanisms acting on the vehicle body and finally on the passengers. The functional chain is lined up in three fields to display the causality of the different influencing parameters: “Engine Excitation at Start/Stop”, “P/T Body Oscillation System” and “Vehicle Body”. For each field, exemplarily parameters are chosen to improve the start/stop behaviour. In the thematic field “Engine Excitation at Start/Stop” a comparison between a conventional key start to a re-start of a gasoline engine is shown. The excitation mechanisms are depicted and a countermeasure is derived to reduce the excitation in the shown example. In the field “P/T Oscillation System”, the eigenfrequency shift of the most critical P/T body mode as countermeasure has proved effectivity in vibration reduction. Further on, the advantage of a 24V/48V starter regarding vibration reduction is outlined. The last chain element “Vehicle Body” provides an explanation of vehicle sensitivity in different directions of the vehicles´ coordinate system. Finally, the human perception of vibrations is projected on the engine start/stop event. The relevant weighting functions, which take the frequency depending perception into account are outlined. A comparison of two NVH metrics to objectify the sense of vibration is conducted.
KeywordsEngine Speed Vehicle Body Compression Stroke Chain Element Idle Speed
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