Control system for multi-cylinder internal combustion engine

Claim 1

A control system for a multi-cylinder internal combustion engine (E) in which switching between full cylinder operation with all cylinders in operation and part cylinder operation with some of the cylinders kept out of operation is performed at least in the course of idling, the internal combustion engine having an associated engine speed sensor and engine load sensor, comprising: a microcomputer receiving an engine speed signal from the engine speed sensor and an engine load signal from the engine load sensor. wherein said microcomputer is programmed to perform the steps of: calculating a basic ignition timing on the basis of load on and an engine speed of said internal combustion engine (E); calculating a difference between a smoothed engine speed, which has been obtained by smoothing engine speeds of said internal combustion engine, and the engine speed of said internal combustion engine; calculating an ignition timing correction amount corresponding to the difference and a correction gain at least in the course of the idling; performing ignition timing correction control by changing the correction gain to a value different from that for the full cylinder operation upon at least one of the switching between the full cylinder operation and the part cylinder operation and the part time operation; calculating a target ignition timing on the basis of the basic ignition timing and the ignition timing correction amount; and providing an output driving signal; wherein the control system further comprises means for driving the ignition of the respective cylinders in the internal combustion engine, wherein said output driving signal from said microcomputer is provided to said ignition driving means to drive the ignition of the respective cylinders at said target ignition timing.