SYSTEM AND METHOD FOR CONTROLLING THE EMISSIONS OF A SPARK-IGNITION INTERNAL COMBUSTION ENGINE OF A MOTOR-VEHICLE

A system for controlling emissions of a motor-vehicle spark-ignition internal combustion engine includes first and second exhaust gas treatment devices and a secondary air feeding system for feeding secondary air into an exhaust gas conduit, between the first and second exhaust gas treatment devices. The secondary air feeding system is activated only when engine load is greater than a predetermined load value and/or when engine rotational speed is greater than a predetermined speed value. In this condition, an air/fuel ratio of the engine is kept at a value lower than the stoichiometric value, so as to feed the engine with a rich mixture. In one example, an electronic controller is configured for controlling activation of the secondary air feeding system on the basis of a map, as a function of values of the engine load and rotational speed. The map is predetermined depending upon specific characteristics of the engine.