Patent ID: 8356470

Claim:
A method of controlling an NOx purification system including, in order from an upstream side of an exhaust gas passage of the system, a first catalyst which is a lean NOx catalyst or a ternary catalyst, and a selective reduction type catalyst, comprising: performing ammonia formation control as follows when a temperature of the first catalyst is less than a prescribed temperature at which ammonia is formed by the first catalyst, performing temperature rise control of the first catalyst; during the first catalyst temperature rise control, calculating an ammonia adsorption amount of the selective type catalyst based on NOx flowing into the selective reduction type catalyst; computing an ammonia adsorption target amount of said selective reduction type catalyst based on the calculated ammonia adsorption amount; and performing said ammonia formation control out only when a cumulative value of an ammonia formation amount formed by said first catalyst is under said ammonia adsorption target amount.