| 摘要 |
To accurately estimate the concentration of a reducing agent in system including a reduction catalyst reducing nitrogen oxide by absorbing the reducing agent. A control apparatus 60 according to the present invention includes a measured NOx purification ratio calculation unit 72 calculating a measured NOx purification ratio of a reduction catalyst 20 based on outputs of NOx sensors 14 and 16 provided upstream and downstream of the reduction catalyst 20 reducing nitrogen oxide in an exhaust gas, an estimated NOx purification ratio calculation unit 70 calculating an estimated NOx purification ratio of the reduction catalyst based on a temperature of the reduction catalyst 20, a flow rate of the exhaust gas, and an absorption amount of the reducing agent 20 by the reduction catalyst 20, and a reducing agent concentration estimation unit 76 estimating a concentration of the reducing agent injected from a reducing agent injection valve 34 based on the measured NOx purification ratio and the estimated NOx purification ratio. |
