Patent ID: 6971343

Claim:
A spark-ignition engine controller for a multi-cylinder spark-ignition engine performing a four cycle consisting of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke at a predetermined phase difference in each cylinder, wherein a gas flow path is formed into a state of two-cylinder connection where, in at least a low-load low-speed range, determined by an operation condition identifier, burned gas discharged from a preceding cylinder, which is a cylinder in the exhaust stroke, of a pair of cylinders having an overlapping exhaust stroke and intake stroke is introduced into a following cylinder, which is a cylinder in the intake stroke, through an intercylinder gas channel, and exhaust gas discharged from the following cylinder is led to an exhaust passage; said spark-ignition engine controller comprising: the operation condition identifier for determining an engine operation condition based on an engine speed and an engine load; an intake air quantity control means for controlling an amount of air to be supplied to the preceding cylinder in such a manner that the air/fuel ratio based on the amount of fuel required to both of said preceding and the following cylinders becomes a stoichiometric air-fuel ratio in said both cylinders in the state of two-cylinder connection; and a combustion controller including: a fuel injection means for injecting fuel at a certain timing in which an amount of fuel injected to both of said preceding and following cylinders is determined in accordance with a required torque in the state of two-cylinder connection; and an ignition controller for controlling an ignition timing; said combustion controller which, during said two-cylinder connection, causes combustion to be performed in said preceding cylinder at an air-fuel ratio which is leaner than the stoichiometric air-fuel ratio by a predetermined amount, and causes combustion in said following cylinder at a predetermined air-fuel ratio by feeding fuel to the lean air-fuel ratio burned gas introduced from said preceding cylinder, said combustion controller performing control such that, in at least a part of an operating range in which said two-cylinder connection is set, combustion is performed in said following cylinder through compression ignition, and said combustion controller controlling, in a low-load region among said operating range in which the two-cylinder connection is set, said injection controller and said ignition controller such that an air-fuel ratio of the preceding cylinder is set such that an excess air ratio of the preceding cylinder becomes at least three and a combustion is performed in the following cylinder by spark ignition at an air-fuel ratio being equal to a stoichiometric air-fuel ratio.