EXHAUST GAS CONTROL APPARATUS AND EXHAUST GAS CONTROL METHOD FOR INTERNAL-COMBUSTION ENGINE

摘要

An exhaust gas control apparatus for an internal-combustion engine includes a catalyst, an adding valve, an exhaust gas recirculation device, and a controller. The catalyst reduces NOx in exhaust gas by addition of a reductant. The adding valve adds the reductant to the exhaust gas. The exhaust gas recirculation device performs an exhaust gas recirculation process of introducing a part of the exhaust gas into intake air. The controller is configured to: (a) perform an equivalent ratio control of adjusting an amount of reductant to be added depending on an amount of NOx in the exhaust gas; (b) perform a decreasing process of decreasing the amount of reductant added when the performing of the exhaust gas recirculation process is inhibited so as to be less than the amount of reductant set in the equivalent ratio control; and (c) set a decrement of the amount of reductant by the decreasing process to be smaller as an exhaust gas temperature is higher.