Weak knock characterization and detection for knock control

Abstract

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 considered from two main aspects: knock detection and knock characterization. The aim of 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 knock traces than the standard model. It is shown that the best-performing knock detector of those investigated is one that supervises changes in signal variance, except for low signal-to-noise ratios where it is advantageous to use also the oscillation frequency. Regarding characterization, an important result is that in a wide range of intensities there is an almost linear dependence between the logarithmic normalized 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; both can in combination with better detection provide possibilities for smoother and more anticipatory control schemes.