Patent ID: 8899024

Claim:
An engine exhaust purification device which reduces NOx discharged from an engine by use of ammonia as a reducing agent to purify an exhaust gas, comprising: a selective reduction type NOx catalyst disposed in an exhaust passage of the engine; a reducing agent adding device which adds ammonia or a precursor thereof to the exhaust gas of the engine on an upstream side of the NOx catalyst; and a control device which calculates an amount of the ammonia to be supplied to the NOx catalyst, to control the reducing agent adding device in accordance with the calculated amount of the ammonia to be supplied, wherein the control device includes: a first storage section in which there is stored a first catalytic reaction model where a chemical reaction concerned with the reduction of the NOx by use of the ammonia adsorbed on a catalyst layer of the NOx catalyst as an effective reducing agent is numerically formulated; an ammonia adsorption amount calculating section which acquires the first catalytic reaction model from the first storage section, and calculates ammonia adsorption amounts of a plurality of cells by the acquired first catalytic reaction model, the respective cells being obtained by dividing the inside of the NOx catalyst so that the cells are continuously aligned in an axial direction of the catalyst; and an ammonia supply amount calculating section which calculates the amount of the ammonia to be supplied based on the ammonia adsorption amount of the predetermined cell corresponding to an operation state of the engine, among the ammonia adsorption amounts of the respective cells which are calculated by the ammonia adsorption amount calculating section.