Knock control device for internal combustion engine

Abstract

Disclosed is a knock control device for an internal combustion engine wherein, when performing knock control based on an ion current detected using a configuration containing an ignition coil secondary in an ion current path, a knock detection gate period is controlled appropriately in accordance with variation of a mask period in order to ensure complete removal of residual magnetic noise. An ion current output detected through an ion current detection circuit and an inverting amplifier circuit is masked by a mask circuit until a prescribed time elapses after the end of spark discharge, thereby accomplishing complete removal of noise occurring after the end of the discharge. A band-pass filter (BPF) extracts a knock frequency component from the output of the mask circuit, and an integrator circuit integrates the output of the BPF during the gate period. A CPU learns the initiation timing of the gate period in accordance with variation of the end timing of the mask period so that the initiation timing of the gate period occurs later than the end timing of the mask period. As a result, the effects of the noise caused by a signal discontinuity associated with mask removal are eliminated.