Patent ID: 8006483

Claim:
An exhaust emission purifying apparatus for an engine, comprising: a reduction catalytic converter that reductively purifies nitrogen oxides in the exhaust emission by using a reducing agent; a reducing agent tank that stores a liquid reducing agent or its precursor; a reducing agent dosing device that doses the liquid reducing agent or its precursor stored in the reducing agent tank to the exhaust emission upstream side of the reduction catalytic converter; a level measuring device that measures a level of the liquid reducing agent or its precursor stored in the reducing agent tank; and a control unit, including a computer, to execute: a dosing flow rate computing process of computing a dosing flow rate of the liquid reducing agent or its precursor according to engine operating conditions, a reducing agent dosing process of controlling the reducing agent dosing device, based on the dosing flow rate computed in the dosing flow rate computing process, an integrated amount computing process of computing an integrated amount obtained by sequentially integrating the dosing flow rate computed in the dosing flow rate computing process, a consumed amount computing process of computing a consumed amount of the liquid reducing agent or its precursor, based on the level measured by the level measuring device, and a failure judging process of judging whether or not a supply system of the liquid reducing agent or its precursor is failed, based on a ratio between the integrated amount computed in the integrated amount computing process and the consumed amount computed in the consumed amount computing process.