Optimizing knock thresholds for improved knock control

Abstract

A new method for optimizing the knock threshold is presented and shown to significantly improve the closed loop performance of a standard knock controller. Traditional approaches assume that in order to control potentially damaging knock events, it is necessary to use thresholds set to detect such events. The proposed new method takes a more stochastic view and sets the threshold such that it maximizes the sensitivity to changes in the knock intensity distribution. The behavior of a standard knock controller in response to different threshold and gain values is investigated and illustrated using experimental and simulation data. In particular, it is shown that optimizing the threshold and controller parameters in the manner proposed results in a controller with fast transient response, improved mean spark advance, and reduced cyclic dispersion. With no modifications other than optimizing the parameters of a standard controller, it is therefore possible to operate closer to the knock limit, thereby improving fuel efficiency, emissions, and output torque.