Weak knock characterisation and detection for knock control
Knock is a fundamental phenomenon in combustion engines, and knock
control is central in any engine management system. Better
understanding of knock, and weak knock in particular, is searched in
two main directions, knock detection and knock characterisation. The
aim of the knock detectors is both to detect knock and to estimate the
crank angle at knock onset. Focusing on weaker knock than before, it
is shown that knock detectors and algorithms have to take into account
other characteristics of the knock traces than the standard model. It
is shown that the best performing of the investigated knock detectors
is one that supervises changes in signal variance, except for low
signal to noise ratios where it is advantageous to use also
oscillation frequency. Regarding characterisation, an important result
is that in a wide range of intensities there is an almost linear
dependence between the logarithmic normalised knock energy and the
rate of cycles with knock. This means for example that a knock
controller can use feedback on the rate of cycles with knock instead
of knock intensity and vice versa, and both can in combination with
better detection provide possibilities for smoother and more
anticipatory control schemes.
Ylva Nilsson, Erik Frisk and Lars Nielsen
Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering,
2009
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