Stoichiometric and enrichment mixture control during different split engine modes

Claim 1

A control system for an internal combustion engine having first and second cylinders, comprising: split engine control means for operating said engine on full cylinders in which said first and second cylinders are activated to give higher engine power when the magnitude of engine load is above a predetermined value or operating said engine on partial cylinder in which only said second cylinder is activated to give lower engine power when the engine load magnitude is below said predetermined value and said first cylinder is deactivated to allow air to be pumped therethrough; first and second upstream exhaust conduits for gases from said first and second cylinders when the engine is operated on full cylinders, respectively, to a common junction and for passing the pumped air from said first cylinder and the exhaust gases from said second cylinder to said common junction when the engine is operated on partial cylinder; a common downstream exhaust conduit connected to said common junction for passing said gases therethrough to the atmosphere; a first catalytic converter disposed in said second upstream exhaust conduit; an exhaust gas sensor and a second catalytic converter disposed in said common downstream exhaust conduit; feedback control means responsive to a signal from said exhaust gas sensor during the full cylinder engine operation for correcting the air-fuel ratio of mixture supplied to said first and second cylinders to the stoichiometric point; and means for disabling said feedback control means during the partial cylinder engine operation and controlling the air-fuel ratio of mixture supplied to said second cylinder to a point which lies to the rich side of the stoichiometric point, whereby during said full cylinder engine operation the NOx, HC and CO components of the gases from said first and second cylinders are purified simultaneously in said second and first catalytic converters, respectively, and during said partial cylinder engine operation the NOx component of the gases from said second cylinder is purified in said first catalytic converter and the HC and CO components thereof are mixed with said pumped air in said common exhaust conduit and purified in said second catalytic converter.