Exhaust gas control apparatus and control method for exhaust gas control apparatus

摘要

An exhaust gas control apparatus includes a control device that controls a urea addition valve for adding urea from an upstream side of a NOx reduction catalyst. The control device obtains an ammonia adsorption amount distribution through the NOx reduction catalyst, and when an ammonia adsorption amount in a predetermined part on an exhaust gas flow direction downstream side equals or exceeds a predetermined threshold, the control device controls the urea addition valve to stop the urea supply or reduce the amount of urea supply. The urea addition valve is controlled basis on an adsorption amount distribution obtained from a model on which the catalyst is divided into a plurality of cells such that an ammonia adsorption amount in a first cell positioned furthest upstream equals or exceeds a predetermined threshold close to a saturation adsorption amount and an ammonia adsorption amount in a second cell positioned downstream of the first cell reaches a predetermined target value that is smaller than the threshold.