Ignition timing controller for internal combustion engine

An ignition timing controller for an internal combustion engine, the controller comprising:

• a basic knock-limit ignition timing calculation means for calculating a basic knock-limit ignition timing on the basis of an operating state of the internal combustion engine, the basic knock-limit ignition timing being a knock-limit ignition timing when a predetermined basic octane number fuel is used and an ambient humidity is at a predetermined basic ambient humidity;
• a learning-region variation calculation means for learning the knock-limit ignition timing of the internal combustion engine in two predetermined operating regions and calculates a learning-region variation due to octane number and a learning-region variation due to humidity on the basis of learning values of the knock-limit ignition timing in the two operating regions, the learning-region variation due to octane number being an amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of an octane number of a fuel used in one of the two operating regions, the learning-region variation due to humidity being an amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of the ambient humidity in the one of the two operating regions;
• an estimated variation calculation means for estimating a variation due to octane number and a variation due to humidity on the basis of the learning-region variation due to octane number and the learning-region variation due to humidity, the variation due to octane number being the amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of the octane number of the fuel used in a present operating state, the variation due to humidity being the amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of the ambient humidity in the present operating state;
• and
• a knock-limit ignition timing calculation means for calculating the knock-limit ignition timing in the present operating state on the basis of the basic knock-limit ignition timing, the variation due to octane number, and the variation due to humidity.

An ignition timing control method for an internal combustion engine, the method comprising:

• calculating a basic knock-limit ignition timing on the basis of an operating state of the internal combustion engine, the basic knock-limit ignition timing being a knock-limit ignition timing when a predetermined basic octane number fuel is used and an ambient humidity is at a predetermined basic ambient humidity;
• learning the knock-limit ignition timing of the internal combustion engine in two predetermined operating regions and calculating a learning-region variation due to octane number and a learning-region variation due to humidity on the basis of learning values of the knock-limit ignition timing in the two operating regions, the learning-region variation due to octane number being an amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of an octane number of a fuel used in one of the two operating regions, the learning-region variation due to humidity being an amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of the ambient humidity in the one of the two operating regions;
• estimating a variation due to octane number and a variation due to humidity on the basis of the learning-region variation due to octane number and the learning-region variation due to humidity, the variation due to octane number being the amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of the octane number of the fuel used in a present operating state, the variation due to humidity being the amount of change in the knock-limit ignition timing from the basic knock-limit ignition timing due to an influence of the ambient humidity in the present operating state;
• and
• calculating the knock-limit ignition timing in the present operating state on the basis of the basic knock-limit ignition timing, the variation due to octane number, and the variation due to humidity.