Patent attributes
An ECU converts a cylinder pressure P and a cylinder volume V corresponding to a crank angle θ at least from a compression stroke to a combustion and expansion stroke to a logarithmic value log P and a logarithmic value log V, respectively, to find a logarithmic conversion waveform and estimates a motoring waveform which is obtained by subtracting a pressure rise developed by combustion in a cylinder from the logarithmic conversion waveform, that is, corresponds to a non-combustion state. Further, the ECU computes a determination line Y of an ignition timing Tburn on the basis of the base line X of the estimated motoring waveform and determines the ignition timing Tburn on the basis of this determination line Y and the logarithmic conversion waveform.
