Patent ID: 7117082

Claim:
A controller for an internal combustion engine comprising: a cylinder pressure sensor for sensing a cylinder pressure representing a pressure in a cylinder of the internal combustion engine; a crank angle sensor for sensing a crank angle representing a crank position of the internal combustion engine; and an ignition timing sensing means for sensing an ignition timing of the internal combustion engine on the basis of information obtained from the cylinder pressure sensor and the crank angle sensor, wherein the ignition timing sensing means includes: a cylinder pressure converting means that has a conversion map P for logarithmically converting a previously set pressure and converts such a cylinder pressure at least from a compression stroke to a combustion and expansion stroke that is sensed by the cylinder pressure sensor to a logarithmic value log P by the conversion map P; a cylinder volume converting means that has a conversion map V for logarithmically converting a cylinder volume corresponding to a previously set crank angle and converts such a cylinder volume at least from a compression stroke to a combustion and expansion stroke that is sensed by the crank angle sensor to a logarithmic value log V by the conversion map V; a cylinder pressure waveform logarithm display means that has a logarithm map having coordinate axes of a logarithmic value log V of the cylinder volume corresponding to the crank angle and a logarithmic value log P of the cylinder pressure, reads the logarithmic value log P and the logarithmic value log V in the logarithm map to display a change in the cylinder pressure at least from a compression stroke to a combustion and expansion stroke as a logarithmically converted cylinder pressure waveform on the logarithm map; a motoring waveform estimating means for estimating a motoring waveform representing a non-combustion cylinder pressure waveform which is obtained by subtracting a pressure rise developed by combustion in the cylinder of the internal combustion engine from the logarithmically converted cylinder pressure waveform, that is, corresponds to a state of non-combustion; a determination line computing means for computing a determination line of an ignition timing on the basis of a base line of the estimated motoring waveform; and an ignition timing determining means for determining the ignition timing on the basis of the computed determination line and the logarithmically converted cylinder pressure waveform.