Controller for internal combustion engine

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.